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American Journal of Physiology - Heart and Circulatory Physiology logoLink to American Journal of Physiology - Heart and Circulatory Physiology
. 2015 Jun 8;309(3):H499–H511. doi: 10.1152/ajpheart.00765.2014

Analysis of erectile responses to bradykinin in the anesthetized rat

Justin A Edward 1, Edward A Pankey 1, Ryan C Jupiter 1, George F Lasker 1, Daniel Yoo 1, Vishwaradh G Reddy 1, Taylor C Peak 1, Insun Chong 1, Mark R Jones 1, Samuel V Feintech 1, Sarah H Lindsey 1, Philip J Kadowitz 1,✉
PMCID: PMC4525086  PMID: 26055796

These results indicate that bradykinin (BK) has erectile activity in the rat, mediated by kinin B2 receptors and cyclooxygenase products. Responses to BK are modulated by changes in driving pressure, angiotensin-converting enzyme activity, and angiotensin-(1–7). Erectile responses to cavernosal nerve stimulation are not modulated by BK or B2 receptors under physiologic conditions.

Keywords: bradykinin, erectile responses, cavernosal nerve stimulation, angiotensin-converting enzyme, angiotensin-(1–7)

Abstract

The kallikrein-kinin system is expressed in the corpus cavernosa, and bradykinin (BK) relaxes isolated corpora cavernosal strips. However, erectile responses to BK in the rat have not been investigated in vivo. In the present study, responses to intracorporal (ic) injections of BK were investigated in the anesthetized rat. BK, in doses of 1–100 μg/kg ic, produced dose-related increases in intracavernosal pressure (ICP) and dose-related deceases in mean arterial pressure (MAP). When decreases in MAP were prevented by intravenous injections of angiotensin II (Ang II), increases in ICP, in response to BK, were enhanced. Increases in ICP, ICP/MAP ratio, and area under the curve and decreases in MAP in response to BK were inhibited by the kinin B2 receptor antagonist HOE-140 and enhanced by the angiotensin-converting enzyme (ACE) inhibitor captopril and by Ang-(1–7). Increases in ICP, in response to BK, were not attenuated by the nitric oxide (NO) synthase inhibitor (Nω-nitro-l-arginine methyl ester) or the soluble guanylate cyclase inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) but were attenuated by the cyclooxygenase inhibitor, sodium meclofenamate. Decreases in MAP were not attenuated by either inhibitor. These data suggest that erectile responses are mediated by kinin B2 receptors and modulated by decreases in MAP. These data indicate that ACE is important in the inactivation of BK and that erectile and hypotensive responses are independent of NO in the penis or the systemic vascular bed. Erectile responses to cavernosal nerve stimulation are not altered by BK or HOE-140, suggesting that BK and B2 receptors do not modulate nerve-mediated erectile responses under physiologic conditions. These data suggest that erectile responses to BK are mediated, in part, by the release of cyclooxygenase products.

NEW & NOTEWORTHY

These results indicate that bradykinin (BK) has erectile activity in the rat, mediated by kinin B2 receptors and cyclooxygenase products. Responses to BK are modulated by changes in driving pressure, angiotensin-converting enzyme activity, and angiotensin-(1–7). Erectile responses to cavernosal nerve stimulation are not modulated by BK or B2 receptors under physiologic conditions.

the biologically active peptide, bradykinin (BK), is formed in many organ systems, including the corpora cavernosa, from the substrate kininogen by the enzyme kallikrein (2, 5, 34, 39, 52). BK interacts with kinin B1 and B2 G protein-coupled receptors to produce a physiologic response (10, 30, 46). Kinin B2 receptors are constitutively expressed in most tissues, whereas kinin B1 receptor expression is upregulated by inflammatory stimuli (10, 30, 40). BK has been shown to relax vascular smooth muscle and produce hypotension in the rat and other laboratory species (7, 12, 26, 31, 37, 46). It has been reported that responses to BK are mediated by the release of nitric oxide (NO) and cyclooxygenase products or an endothelial-derived hyperpolarizing factor (2, 12, 39).

The tissue kallikrein-kinin system is expressed in the corpora cavernosa of the rat and is changed with aging (52). BK, the major product of the kallikrein-kinin system, relaxes isolated smooth muscle of the corpora cavernosa from a variety of species, including man (24, 25, 48). In the majority of studies in the literature, relaxant responses to BK have been reported to be dependent on the release of NO from the endothelium of the corpora and are attenuated by NO synthase (NOS) inhibitors (2, 39). Although it has been demonstrated in many studies that BK has relaxant properties in isolated smooth-muscle preparations from the corpora cavernosa, responses to BK have not been investigated in the intact rat, where factors, in addition to the release of NO from the endothelium, may influence the response to the vasoactive peptide. Responses to BK may be mediated differently in isolated tissue preparations and in the intact animal (12, 19).

In the present study, erectile responses to intracorporal (ic) injections of BK; the role of BK B2 receptors, soluble guanylate cyclase (sGC), NOS, and products of the cyclooxygenase pathway; the effects of a kininase inhibitor and angiotensin-(1–7) [Ang-(1–7)], which have been reported to enhance responses to BK; as well as changes in mean arterial pressure (MAP) in mediating or modulating responses to BK were investigated (1, 15, 19, 28, 29, 38, 50). The results of these studies show that BK has significant erectile activity in the rat mediated by the activation of kinin B2 receptors and the release of products in the cyclooxygenase pathway. Erectile responses to BK are enhanced by the angiotensin-converting enzyme (ACE) inhibitor captopril and Ang-(1–7). In contrast to many reports in the literature, our data suggest that erectile and vasodilator responses to BK are independent of NO production in the rat. These data also indicate that erectile responses to BK can be modulated by changing driving pressure, the ACE inhibitor, and Ang-(1–7).

MATERIALS AND METHODS

The Institutional Animal Care and Use Committee of the Tulane University School of Medicine approved the experimental protocol to be used in these studies, and all procedures were conducted in accordance with institutional guidelines. For these experiments, adult, 9- to 14-wk-old male Sprague-Dawley rats, weighing 290–410 g, were anesthetized with a 100-mg/kg ip injection of Inactin (thiobutabarbital; Sigma-Aldrich, St. Louis, MO). Supplemental doses of Inactin were given intraperitoneally as needed to maintain a uniform level of anesthesia. Body temperature was maintained with the help of a heating lamp. The trachea was cannulated with a short segment of polyethylene (PE)-240 tubing to maintain a patent airway, and the left carotid artery was catheterized with PE-50 tubing for the measurement of systemic arterial pressure. Intracavernosal pressure (ICP) was measured with a 25-gauge needle inserted into the left crura of the penis connected to PE-50 tubing filled with heparinized saline. MAP and ICP were measured with Namic Perceptor DT pressure transducers and a data acquisition system (MP100A-CE; Biopac Systems, Santa Barbara, CA). ICP, systolic pressure, and diastolic pressure were measured, and MAP was calculated by electronic averaging, continuously recorded, displayed, and stored on a Dell personal computer. The left jugular vein was catheterized with PE-50 tubing for the systemic administration of drugs and fluids. A 25-gauge needle was placed in the right crura of the penis for administration of pharmacologic agents. Maximal ICP, in response to ic injection of drugs, was measured at the peak of the erectile response. The increase in ICP, ICP/MAP ratio (ICP/MAP), and area under the curve (AUC) were used to characterize the total erectile response. For experiments in which changes in MAP, in response to intravenous (iv) injections, were investigated, BK, Ang II, and Ang-(1–7) were injected into the jugular-vein catheter. In experiments in which multiple agents were injected close together, the agents were mixed together and injected or injected separately using a stopcock manifold system.

For cavernosal nerve-stimulation experiments, the bladder and prostate were exposed through a midline abdominal incision, and the major pelvic ganglia and cavernosal nerve were identified posterolateral to the prostate on one side. A stainless-steel-stimulating electrode (Harvard Apparatus, Holliston, MA) was placed around the nerve, and the cavernosal nerve was stimulated at 5 V with 5 ms pulses at frequencies of 2, 4, and 8 Hz for 60 s using an SD9 square wave stimulator (Grass Technologies, Warrick, MA). A rest period of 10 min was allowed between cavernosal nerve-stimulation trials.

Drugs.

BK (Phoenix Pharmaceuticals, Burlingame, CA); Nω-nitro-l-arginine methyl ester (l-NAME), captopril, sodium meclofenamate, HOE-140, Ang II, and sodium nitroprusside (Sigma-Aldrich); and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (Cayman Chemical, Ann Arbor, MI), dissolved in 10/10/80 (cremophor/transcutol/saline), Ang-(1-7), and A-779 (Bachem, Torrance, CA), were dissolved in 0.9% NaCl, and solutions were made on a frequent basis. For ic injections, all drug doses were prepared in a total volume of 50 μl and were injected through the 26-gauge needle into the right crura. BK, Ang II, Ang-(1–7), and combinations of these agents were iv injected into the jugular vein catheter using a single or double stopcock system. The doses of BK were reduced in experiments with captopril because of the marked potentiation of the decrease in MAP after treatment with the ACE inhibitor, which reduced the breakdown of BK by the kininase II (ACE). The doses of agonists and antagonists used in these studies and the relative selectivity of antagonists were determined from studies in the literature and from pilot studies in our laboratory (12, 13, 22, 35, 36, 43, 44, 47).

Statistics.

The data were expressed as means ± SE and were analyzed using a one-way ANOVA and a Student's t-test for paired and unpaired data. P < 0.05 was used as the criterion for statistical significance.

RESULTS

Responses to BK.

In the present study, the effect of BK on erectile function was investigated in the rat, and ic injections of BK in doses of 1–100 μg/kg produced dose-related increases in ICP, ICP/MAP, AUC, duration of response, and dose-related decreases in MAP (Fig. 1A). These data show that ic injections of BK produce dose-dependent erectile and hypotensive responses in the rat. The time course of the changes in ICP and MAP, in response to BK (30 μg/kg ic), is shown in the record from an experiment in Fig. 1B. The influence of the decrease in MAP on the increase in ICP, in response to ic injection of BK, was investigated further. In these experiments, Ang II (0.1 μg/kg iv) and BK (30 μg/kg ic) were injected at the same time or close together, within seconds, to investigate the effect of the decrease in MAP on the erectile response to BK. In these experiments, iv injections of Ang II reduced or reversed the BK-induced decrease in MAP and enhanced the increase in ICP, ICP/MAP, and AUC in response to ic injection of BK (Fig. 2). Ang II (0.1 μg/kg), when injected ic, had no consistent effect on the increase in ICP in response to BK (30 μg/kg ic) when injections were made close together or at the same time. The iv injections of Ang II increased ICP 9–12 mmHg when injected alone in the absence of an ic injection of BK. These data suggest that the decrease in MAP modulates the increase in ICP, in response to ic injection of BK, by decreasing driving pressure.

Fig. 1.

Fig. 1.

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A: bar graphs showing changes in intracavernosal pressure (ICP), mean arterial pressure (MAP), ICP/MAP ratio (ICP/MAP), area under the curve (AUC), and duration in response to intracavernosal (ic) injections of bradykinin (BK; 1–100 μg/kg) in the anesthetized rat. n, number of animals. *P < 0.05, ANOVA. Bars indicate means ± SE. B: records from an experiment showing the time course of the decrease in MAP and the increase in ICP, in response to ic injection of BK (30 μg/kg). Average values are 103 ± 3 and 8 ± 1 mmHg MAP and ICP, respectively, in this group of rats.

Fig. 2.

Fig. 2.

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Bar graphs showing the effect of ic injection of BK (30 μg/kg) on changes in ICP, MAP, ICP/MAP, and AUC, before and at the same time as an intravenous (iv) injection of angiotensin II (Ang II), to prevent or reverse the decrease in MAP in response to ic injection of BK. *P < 0.05, paired comparison. Bars indicate means ± SE.

Role of BK B2 receptors, NOS, sGC, and the cyclooxygenase pathway.

To investigate the role of kinin B2 receptors, the effects of HOE-140 were investigated. In these experiments, HOE-140 (50 μg/kg iv) significantly attenuated the increase in ICP and the decrease in MAP in response to ic injection of BK (Fig. 3A). These data indicate that erectile and systemic hypotensive responses to BK are mediated by kinin B2 receptor activation in the penis and in the systemic vascular bed of the rat.

Fig. 3.

Fig. 3.

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A: bar graphs comparing decreases in MAP and increases in ICP, ICP/MAP, and AUC, in response to ic injections of BK, before and after treatment with the kinin B2 receptor antagonist HOE-140 (50 μg/kg iv). B: bar graphs showing the effect of ic injections of BK (3–30 μg/kg) on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME; 50 mg/kg iv). *P < 0.05, paired comparison. Bars indicate means ± SE.

The role of NO release in mediating responses to BK was investigated in experiments with the NOS inhibitor l-NAME. The iv injection of l-NAME produced a significant (30–40 mmHg) increase in MAP. Following the injection of l-NAME in a dose of 50 mg/kg iv, the increase in ICP and the decrease in MAP, in response to ic injection of BK, were not attenuated, and responses to BK were increased significantly (Fig. 3B). These data suggest that the increase in ICP and the decrease in MAP, in response to ic injection of BK, are not mediated by the release of NO in the corpora cavernosa or in the systemic vascular bed of the rat.

The role of cyclooxygenase product release in mediating responses to BK was investigated in experiments with the cyclooxygenase inhibitor sodium meclofenamate. After administration of sodium meclofenamate (5 mg/kg iv), the increases in ICP, ICP/MAP, and AUC, but not the decrease in MAP in response to ic injection of BK, were significantly attenuated (Fig. 4A). These data suggest that release of products in the cyclooxygenase pathway plays a significant role in mediating erectile responses to BK but is not involved in mediating the systemic, hypotensive response to the peptide.

Fig. 4.

Fig. 4.

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A: bar graphs showing the effect of ic injection of BK (100 μg/kg) on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with the cyclooxygenase inhibitor, sodium meclofenamate (5 mg/kg iv). *P < 0.05, paired comparison. Bars indicate means ± SE. B: bar graphs comparing the increases in ICP, ICP/MAP, and AUC, in response to ic injection of BK (100 μg/kg), before and after treatment with the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 2 mg/kg ic).

The role of sGC activation in mediating responses to BK was investigated in experiments with the sGC inhibitor ODQ. After administration of ODQ (2 mg/kg ic), the increases in ICP, ICP/MAP, and AUC, in response to ic injection of BK, were not altered significantly (Fig. 4B). These data suggest that sGC activation and increased cGMP formation do not play a significant role in mediating erectile responses to BK.

Role of ACE and Ang-(1–7) in modulating BK response.

The effect of ACE, an enzyme that degrades BK, in modulating responses to BK was investigated in experiments with the ACE inhibitor captopril. Following administration of captopril (2 mg/kg iv), the increases in ICP and the decreases in MAP, in response to ic injection of BK (3 μg/kg), were enhanced significantly (Fig. 5A). The effect of a lower dose of captopril was investigated in another series of experiments, and following administration of captopril (200 μg/kg iv), the increases in ICP and decreases in MAP, in response to subthreshold doses of BK (0.03–1 μg/kg), were enhanced significantly (Fig. 5B). The doses of BK used in experiments with captopril were reduced because of the marked enhancement of the fall in MAP in response to the peptide.

Fig. 5.

Fig. 5.

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A: bar graphs showing the effect of ic injection of BK on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with the angiotensin-converting enzyme (ACE) inhibitor captopril (2 mg/kg iv). B: bar graphs showing the effect of ic injections of subthreshold and threshold doses of BK on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with a lower dose of captopril (200 μg/kg iv). The lower doses of BK were used because of the marked enhancement of BK hypotensive responses after treatment with the ACE inhibitor. *P < 0.05, paired comparison. Bars indicate means ± SE.

The effect of a very low dose of captopril was investigated further in an experiment designed to dissociate the erectile and hypotensive responses to BK. Following an injection of captopril (5 μg/kg ic), the ic injection of BK in a dose of 0.1 μg/kg produced a significant increase in ICP without a large decrease in MAP (Fig. 6). These data provide support for the hypothesis that the erectile response to BK can occur in the absence of a large change in MAP and may be elicited without a large change in driving pressure (Fig. 6).

Fig. 6.

Fig. 6.

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Bar graphs showing the effect of ic injection of a threshold dose of BK (0.1 μg/kg ic) on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with captopril (5 μg/kg ic). *P < 0.05 compared with control. Bars indicate means ± SE.

It has been reported in a number of studies that Ang-(1–7) enhances vasodepressor responses to BK (1, 15, 19, 28, 29, 38, 50). However, the effect of Ang-(1–7) on the erectile response to BK has not been investigated. In the present study, the effect of Ang-(1–7) on the erectile response to BK was investigated. In these experiments, Ang-(1–7) was injected in doses of 1–30 μg/kg ic, which produced small, inconsistent changes in ICP and no significant change in MAP (Fig. 7A). However, when injected in a dose of 3 μg/kg ic, Ang-(1–7) significantly enhanced the increase in ICP, ICP/MAP, and AUC in response to ic injection of BK (3 μg/kg; Fig. 7B).

Fig. 7.

Fig. 7.

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A: bar graph showing the effect of ic injection of Ang-(1–7) (1.0–30 μg/kg ic) on changes in ICP. B: bar graphs showing the effect of ic injections of BK (3.0 μg/kg ic) on changes in ICP, MAP, ICP/MAP, and AUC, before and after treatment with Ang-(1–7) (3 μg/kg ic) and combined treatment with Ang-(1–7) (3 μg/kg ic) and the Ang-(1–7)-Mas receptor antagonist A-779 (200 μg/kg ic). *P < 0.05, paired comparison. Bars indicate means ± SE.

Role of the Ang-(1–7)-Mas receptor axis in modulating Ang-(1–7)-potentiated BK responses.

To investigate the role of the Ang-(1–7)-Mas receptor axis in modulating the Ang-(1–7)-potentiated BK response, the effects of Ang-(1–7)-Mas receptor antagonist A-779 were investigated. In these experiments, following control ic injections of BK (3 μg/kg ic) and combined ic injections of both Ang-(1–7) (10 μg/kg ic) and BK (3 μg/kg ic), the animals were pretreated with A-779 (200 μg/kg ic) before repeating the combined ic injections of both Ang-(1–7) (10 μg/kg ic) and BK (3 μg/kg ic) to study the effects of the Ang-(1–7)-Mas receptor axis in modulating the Ang-(1–7)-potentiated BK response. Following the injection of A-779 (200 μg/kg ic), the increases in ICP, ICP/MAP, and AUC and the decreases in MAP, in response to combined ic injection of Ang-(1–7) (10 μg/kg ic) and BK (3 μg/kg ic), were not altered significantly (Fig. 7B). These data suggest that the enhanced erectile response to BK- and Ang-(1–7)-combined ic injection is not mediated by the Ang-(1–7)-Mas receptor in the rat.

Role of Ang II and Ang-(1–7) in modulating systemic BK responses.

The effect of Ang-(1–7) on changes in MAP, in response to BK, was investigated in experiments in which both peptides were iv injected. In these experiments, when injected in doses of 3–30 μg/kg iv, Ang-(1–7) had no consistent effect on MAP (Fig. 8A). However, the iv injection of Ang-(1–7) (1–10 μg/kg), when administered along with and at the same time as BK (1 μg/kg iv), enhanced the decrease in MAP in response to iv injection of BK in a dose-dependent manner (Fig. 8C). The iv injections of BK, in doses of 1–30 μg/kg, decreased MAP significantly (Fig. 8B). These data provide additional support for the observation that Ang-(1–7) potentiates the decrease in MAP in response to iv injections of BK.

Fig. 8.

Fig. 8.

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A: bar graph showing the effects of iv injections of Ang-(1–7) (0.1–30 μg/kg iv) on MAP. B: bar graph showing the effects of iv injections of BK (1.0–30 μg/kg iv) on MAP. C: bar graph showing effects of iv injections of BK (1.0 μg/kg iv) on changes in MAP with treatments using Ang-(1–7) (0–10.0 μg/kg iv). D: bar graph showing the effects of iv injections of Ang II (0.3 μg/kg iv) on changes in MAP, before and after treatment with Ang-(1–7) (0–9.0 μg/kg iv). E: bar graph showing the effects of iv injections of Ang II (0.3 μg/kg iv) on changes in MAP with treatments using BK (3.0 μg/kg iv) and BK (3.0 μg/kg iv) + Ang-(1–7) (3.0 μg/kg iv). *P < 0.05, ANOVA and group comparison. Bars indicate means ± SE. F: diagram showing the potential interactions among Ang II, BK, and Ang-(1–7), suggesting that BK, along with Ang-(1–7), can act in a counter-regulatory manner to the pressor effect of Ang II on MAP.

When administered at the same time as Ang II (0.3 μg/kg iv), Ang-(1–7), in doses of 0–9.0 μg/kg iv, which represents ratios of Ang II:Ang-(1–7) between 1:1 and 1:30, did not significantly attenuate or blunt the increase in MAP in response to the iv injection of Ang II (Fig. 8D). Although the iv injection of Ang-(1–7) did not alter the increase in MAP, in response to Ang II, the iv injection of BK and BK plus Ang-(1–7) attenuated the increase in MAP in response to Ang II (0.3 μg/kg iv; Fig. 8E). These data do not provide support for the concept that Ang II and Ang-(1–7) have counter-regulatory effects in the regulation of MAP (Fig. 8F). However, these data do provide support for the alternate hypothesis that BK alone and BK along with Ang-(1–7) can act in a counter-regulatory manner to modulate or attenuate the pressor effect of Ang II on MAP in the normotensive male rat (Fig. 8F).

Effects of BK, HOE-140, and Ang-(1–7) on responses to cavernosal nerve stimulation.

The effect of BK, HOE-140, and Ang-(1–7) on responses to cavernosal nerve stimulation was investigated by injecting BK ic, Ang-(1–7) ic, and HOE-140 iv and electrically stimulating the cavernosal nerve. The ic injection BK (3–100 μg/kg), Ang-(1–7) (3–100 μg/kg ic), or HOE-140 (50 μg/kg iv) had no significant effect on the increase in ICP, ICP/MAP, and AUC in response to cavernosal nerve stimulation (Fig. 9).

Fig. 9.

Fig. 9.

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Bar graphs showing effect of BK (3–100 μg/kg ic), Ang-(1–7) (3–100 μg/kg ic), and HOE-140 (50 μg/kg iv) on the change in ICP, ICP/MAP, and AUC in response to cavernosal nerve stimulation at 2, 4, and 8 Hz at 5 V with 5 ms pulses for 60 s. n = 4–9 for each group; total number of animals (n = 36). Bars indicate means ± SE.

DISCUSSION

The results of the present investigation show that BK has significant erectile activity in the anesthetized rat, confirming and extending the results of prior studies in isolated smooth-muscle preparations from the corpora cavernosa (24, 25, 48). The ic injections of BK produce dose-related increases in ICP, ICP/MAP, and AUC and dose-related decreases in MAP. Erectile and hypotensive responses to BK were rapid in onset (3–6 s), as seen in the record from an experiment in Fig. 1B, and the response duration was dose dependent. The erectile and hypotensive responses to BK were attenuated by the potent kinin B2 receptor antagonist HOE-140, indicating that the responses are mediated by the activation of kinin B2 receptors. This observation is consistent with the findings of blood-pressure studies and studies in isolated corpora cavernosal strips from the rat (3, 27, 35, 44, 47, 51). Additionally, the erectile and hypotensive responses to BK were enhanced by the ACE inhibitor captopril. The iv injection of captopril, in a dose as low as 200 μg/kg, greatly enhanced erectile and hypotensive responses to subthreshold and to very low doses of BK, indicating the importance of ACE or kininase II in the regulation of responses to BK in both the corpora cavernosa and in the systemic vascular bed. ACE inhibitors enhance the formation of Ang-(1–7), and it is possible that endogenously produced Ang-(1–7) could play a role in the enhanced response to BK after treatment with captopril (49).

BK has been reported in many studies to be an endothelium-dependent vasodilator, which has been shown to relax vascular smooth-muscle preparations by releasing NO, vasodilator PGs, or an endothelial-derived hyperpolarizing factor (2, 12, 14, 30, 36, 39). The decrease in MAP and the increase in ICP are both the result of smooth-muscle relaxation. The relaxation of corpus cavernosa smooth muscle results in an increase in pressure in the corpus cavernosa, whereas relaxation of vascular smooth muscle in the systemic vascular bed results in a decrease in MAP.

It has been reported that relaxant responses to BK are attenuated by NOS inhibitors in isolated corpora cavernosal smooth preparations from a variety of species, including man (24, 25, 48). In the present study, the role of NO in mediating erectile and hypotensive responses to BK was investigated in the rat. Following iv injection of the NOS inhibitor, l-NAME, erectile, and hypotensive responses to BK were not attenuated and, in fact, were enhanced. In the dose used in the present study, l-NAME had previously been shown to increase systemic arterial pressure and inhibit erectile responses to ic injection of ACh and to cavernosal nerve stimulation in the rat (16, 20). The present results with the NOS inhibitor suggest that the erectile and systemic hypotensive responses to BK are not mediated by the release of NO and, in fact, can be enhanced, which may, in part, be related to the increase in baseline MAP in the rat. The mechanism behind this difference in the effect of l-NAME on erectile responses to BK in the rat and in isolated corpora cavernosal smooth-muscle preparations is uncertain. These findings are similar to observations in isolated vascular smooth-muscle preparations and in the anesthetized rat, in which responses to BK are not inhibited by l-NAME (13, 17, 20, 37). The effect of ODQ on erectile responses to BK was investigated, and the results of these studies show that erectile responses are not inhibited and provide additional support for the hypothesis that the NO-sGC-cGMP pathway is not involved in mediating erectile responses to the peptide in the rat.

The role of the cyclooxygenase pathway in mediating responses to BK was investigated, and following administration of the cyclooxygenase inhibitor sodium meclofenamate, increases in ICP were significantly attenuated, whereas the decreases in MAP were not altered. These data suggest that the erectile response to BK is mediated, at least in part, by the released products in the cyclooxygenase pathway, which have not yet been identified. However, it has been reported that PGI2, PGE1, and PGE2 have erectile activity in the rat (32). The observation that decreases in MAP, in response to BK, are not inhibited by l-NAME, ODQ, or sodium meclofenamate suggests that a mechanism other than the release of NO or vasodilator PGs is mediating the systemic vasodepressor response to the peptide. It has been reported that vasodilator responses to BK are mediated by the release of an endothelial-derived hyperpolarizing factor that has not yet been identified, and it is possible that the decrease in MAP, in response to the peptide in the present study, is mediated by this mechanism (2, 12–14, 33, 39).

BK has potent vasodepressor activity in the rat, and the decrease in MAP, in response to the peptide, reduces driving pressure and as shown in the present study, can modulate the erectile response. In an experiment designed to study the opposing vascular responses to Ang II and BK, an iv injection of Ang II was administered at the same time as an ic injection of BK. Ang II reduced or reversed the decrease in MAP in response to BK and also enhanced the increases in ICP, ICP/MAP, and AUC produced by BK. The enhanced increase in ICP, ICP/MAP, and AUC, in response to ic injection of BK produced by the iv injection of Ang II, suggests that the decrease in MAP or driving pressure modulates the erectile response to BK, and under baseline conditions, the iv injection of Ang II can increase ICP.

In an experiment designed to dissociate the erectile and hypotensive responses to BK, a low dose of both the ACE inhibitor captopril and BK was injected ic at the same time. The results of this experiment showed that BK could increase ICP while only producing a small increase in MAP, indicating that erectile and hypotensive responses can be partially separated. BK itself does not appear to increase the ICP/MAP to the generally accepted, so-called ratio of 0.6, indicating a full erection even when combined with iv injection of Ang II. These data suggest that BK induces a partial erection under physiologic conditions.

The discovery of ACE2 and the vasodilator properties of Ang-(1–7), an Ang II ACE2 metabolite, has led to the hypothesis that Ang-(1–7) and Ang II have counter-regulatory effects in the regulation of MAP (4, 8, 21, 41, 45). Although it has been reported that Ang-(1–7) has vasodilator properties, the failure of Ang-(1–7) to produce vasodilation has also been reported (34). Our data suggest that, by itself, Ang-(1–7) has no apparent effect on ICP or MAP in the rat. The absence of an effect of Ang-(1–7) on MAP has been explained by the observation that Ang-(1–7) produces increases in cardiac output and decreases in total peripheral resistance, which can result in no net change in MAP (6, 42, 45). However, the present results confirm the observation that Ang-(1–7) enhances hypotensive and erectile responses to BK when both peptides were iv injected together (1, 15, 19, 28, 29, 38, 50). Contrary to previous studies, Ang-(1–7) did not antagonize increases in MAP in response to iv injections of Ang II (4, 21, 41, 45). These results suggest that when administered acutely in male normotensive rats, Ang-(1–7) does not possess significant vasodilator activity or the ability to counter balance pressor responses to Ang II. These data are in agreement with the studies from Collister and Nahey (9), who report that the simultaneous administration of Ang-(1–7) or A-779 does not affect the chronic hypertensive effects of Ang II in normal rats. However, when given along with BK, Ang-(1–7) does enhance the hypotensive response to BK, which is able to counteract pressor responses to Ang II. The ability of Ang-(1–7) to enhance BK-induced decreases in blood pressure was not NO dependent in the present study. The differences between these results and others showing NO dependence may be a result of a whole animal vs. an ex vivo approach (28). In an in vivo setting, cyclooxygenase products may mediate the effects of Ang-(1–7) on BK-induced decreases in MAP (38).

The effect of BK, HOE-140, and Ang-(1–7) on the erectile response to cavernosal nerve stimulation was investigated, and following ic injection of BK in a wide range of doses, the erectile response to nerve stimulation was not altered. In addition, the iv injection of HOE-140, in a dose that attenuated responses to BK in the rat, was without effect on the increase in ICP, ICP/MAP, and AUC in response to cavernosal nerve stimulation at 2, 4, and 8 Hz. These data suggest that BK and kinin B2 receptors have no significant role in modulating the response to cavernosal nerve stimulation in normotensive male Sprague-Dawley rats. It is, however, possible that BK and B2 receptor activation could play a role in modulating responses to cavernosal nerve stimulation in pathophysiological conditions. It has been reported that the expression of the kallikrein-kinin system and B2 receptors in the corpora cavernosa is downregulated in the aged rat (52).

The effect of Ang-(1–7) on the response to cavernosal nerve stimulation was investigated, and the ic injections of Ang-(1–7), in doses of 3–100 μg/kg, had no significant effect on the increase in ICP, ICP/MAP, and AUC in response to cavernosal nerve stimulation. The results of the present study are not in agreement with a previous study (11). The reason for the difference in results is uncertain but may involve differences in experimental design (11). In the experiments of da Costa Goncalves et al. (11), Ang-(1–7) was infused into the corpora cavernosa, whereas in our study, the peptide was injected ic. It has, however, been reported that Ang-(1–7) can improve responses to cavernosal nerve stimulation in diabetic rats and hypercholesterolemic mice (18, 23, 53). It is therefore possible that Ang-(1–7) could enhance erectile function in pathologic conditions.

In summary, the results of the present study show that BK has significant erectile activity in the anesthetized rat. The erectile response to BK was attenuated by sodium meclofenamate and was not inhibited by l-NAME or ODQ. These data suggest that the erectile response to BK is NO independent and mediated, at least in part, by the release of products in the cyclooxygenase pathway in the corpora cavernosa of the rat. Responses to BK are inhibited by HOE-140 and enhanced by captopril, suggesting that they are mediated by kinin B2 receptors and modulated by ACE activity in penile tissue and the systemic vascular bed. The increase in ICP and the total erectile response to BK were enhanced when the fall in MAP in response to BK was decreased, suggesting that the fall in driving pressure in response to BK modulates the erectile response to the peptide. The explanation for the difference in the effect of the NOS inhibitor l-NAME on erectile responses to BK in the intact rat and in isolated corpora cavernosa smooth-muscle strips is uncertain. The erectile and hypotensive responses to BK are enhanced by Ang-(1–7), but Ang-(1–7) had no consistent effect on ICP or MAP when injected alone. In addition, Ang-(1–7) had no effect on increases in MAP in response to Ang II. However, when injected together, Ang-(1–7) and BK were able to counteract increases in MAP in response to Ang II. These data provide support for the hypothesis that BK and BK along with Ang-(1–7) can act in a counter-regulatory manner to Ang II in the control of MAP in normotensive male rats. These data can be interpreted to suggest that an increase in both BK and Ang-(1–7) levels, after treatment with an ACE inhibitor, may contribute to the beneficial effect of ACE inhibitor therapy in patients with cardiovascular disease. The erectile response to cavernosal nerve stimulation was not altered by BK or HOE-140, suggesting that BK or B2 receptors are not involved in the modulation of erectile function in normotensive rats. It is, however, possible that the kallikrein-kinin system and BK B2 receptors may be involved in the modulation of erectile function in pathologic conditions.

GRANTS

Support for this work was provided, in part, by the National Heart, Lung, and Blood Institute (Grants HL 77421 and HL 103974).

DISCLOSURES

No conflicts of interest, financial or otherwise, are declared by the authors.

AUTHOR CONTRIBUTIONS

Author contributions: J.A.E., E.A.P., G.F.L., and P.J.K. conception and design of research; J.A.E., E.A.P., R.C.J., G.F.L., D.Y., and T.C.P. performed experiments; J.A.E., R.C.J., D.Y., V.G.R., T.C.P., I.C., M.R.J., S.V.F., and P.J.K. analyzed data; J.A.E., R.C.J., D.Y., V.G.R., T.C.P., I.C., M.R.J., S.V.F., and P.J.K. interpreted results of experiments; J.A.E., R.C.J., D.Y., V.G.R., T.C.P., and P.J.K. prepared figures; J.A.E., E.A.P., R.C.J., D.Y., V.G.R., and P.J.K. drafted manuscript; J.A.E., E.A.P., R.C.J., D.Y., V.G.R., T.C.P., S.V.F., S.H.L., and P.J.K. edited and revised manuscript; J.A.E., E.A.P., R.C.J., G.F.L., D.Y., V.G.R., T.C.P., I.C., M.R.J., S.V.F., S.H.L., and P.J.K. approved final version of manuscript.

REFERENCES

  • 1.Almeida AP, Frabregas BC, Madureira MM, Santos RJ, Campagnole-Santos MJ, Santos RA. Angiotensin-(1–7) potentiates the coronary vasodilatatory effect of bradykinin in the isolated rat heart. Braz J Med Biol Res 33: 709–713, 2000. [DOI] [PubMed] [Google Scholar]
  • 2.Azadzoi KM, Kim N, Brown ML, Goldstein I, Cohen RA, Saenz de Tejada I. Endothelium-derived nitric oxide and cyclooxygenase products modulate corpus cavernosum smooth muscle tone. J Urol 147: 220–225, 1992. [DOI] [PubMed] [Google Scholar]
  • 3.Becker AJ, Uckert S, Stief CG, Truss MC, Machtens S, Scheller F, Knapp WH, Hartmann U, Jonas U. Possible role of bradykinin and angiotensin II in the regulation of penile erection and detumescence. Urology 57: 193–198, 2001. [DOI] [PubMed] [Google Scholar]
  • 4.Benter IF, Ferrario CM, Morris M, Diz DI. Antihypertensive actions of angiotensin-(1–7) in spontaneously hypertensive rats. Am J Physiol 269: H313–H319, 1995. [DOI] [PubMed] [Google Scholar]
  • 5.Bhoola KD, Figueroa CD, Worthy K. Bioregulation of kinins: kallikreins, kininogens, and kininases. Pharmacol Rev 44: 1–80, 1992. [PubMed] [Google Scholar]
  • 6.Botelho-Santos GA, Bader M, Alenina N, Santos RA. Altered regional blood flow distribution in Mas-deficient mice. Ther Adv Cardiovasc Dis 6: 201–211, 2012. [DOI] [PubMed] [Google Scholar]
  • 7.Chand N, Altura BM. Acetylcholine and bradykinin relax intrapulmonary arteries by acting on endothelial cells: role in lung vascular diseases. Science 213: 1376–1379, 1981. [DOI] [PubMed] [Google Scholar]
  • 8.Chappell MC, Iyer SN, Diz DI, Ferrario CM. Antihypertensive effects of angiotensin-(1–7). Braz J Med Biol Res 31: 1205–1212, 1998. [DOI] [PubMed] [Google Scholar]
  • 9.Collister JP, Nahey DB. Simultaneous administration of Ang(1–7) or A-779 does not affect the chronic hypertensive effects of angiotensin II in normal rats. J Renin Angiotensin Aldosterone Syst 11: 99–102, 2010. [DOI] [PubMed] [Google Scholar]
  • 10.D'Orleans-Juste P, de Nucci G, Vane JR. Kinins act on B1 or B2 receptors to release conjointly endothelium-derived relaxing factor and prostacyclin from bovine aortic endothelial cells. Br J Pharmacol 96: 920–926, 1989. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.da Costa Goncalves AC, Leite R, Fraga-Silva RA, Pinheiro SV, Reis AB, Reis FM, Touyz RM, Webb RC, Alenina N, Bader M, Santos RA. Evidence that the vasodilator angiotensin-(1–7)-Mas axis plays an important role in erectile function. Am J Physiol Heart Circ Physiol 293: H2588–H2596, 2007. [DOI] [PubMed] [Google Scholar]
  • 12.Dabisch PA, Kerut EK, Liles JT, Wien G, Smith M, Patterson M, McCoul ED, Sears BW, Saenz R, Kadowitz PJ. Responses to bradykinin are mediated by NO-independent mechanisms in the rat hindlimb vascular bed. Pharmacol Res 50: 575–584, 2004. [DOI] [PubMed] [Google Scholar]
  • 13.Dabisch PA, Liles JT, Baber SR, Golwala NH, Murthy SN, Kadowitz PJ. Analysis of l-NAME-dependent and -resistant responses to acetylcholine in the rat. Am J Physiol Heart Circ Physiol 294: H688–H698, 2008. [DOI] [PubMed] [Google Scholar]
  • 14.Danser AH, Tom B, de Vries R, Saxena PR. l-NAME-resistant bradykinin-induced relaxation in porcine coronary arteries is NO-dependent: effect of ACE inhibition. Br J Pharmacol 131: 195–202, 2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 15.Fernandes L, Fortes ZB, Nigro D, Tostes RC, Santos RA, Catelli De Carvalho MH. Potentiation of bradykinin by angiotensin-(1–7) on arterioles of spontaneously hypertensive rats studied in vivo. Hypertension 37: 703–709, 2001. [DOI] [PubMed] [Google Scholar]
  • 16.Finberg JP, Levy S, Vardi Y. Inhibition of nerve stimulation-induced vasodilatation in corpora cavernosa of the pithed rat by blockade of nitric oxide synthase. Br J Pharmacol 108: 1038–1042, 1993. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Fischer LG, Horstman DJ, Hahnenkamp K, Kechner NE, Rich GF. Selective iNOS inhibition attenuates acetylcholine- and bradykinin-induced vasoconstriction in lipopolysaccharide-exposed rat lungs. Anesthesiology 91: 1724–1732, 1999. [DOI] [PubMed] [Google Scholar]
  • 18.Fraga-Silva RA, Costa-Fraga FP, Savergnini SQ, De Sousa FB, Montecucco F, da Silva D, Sinisterra RD, Mach F, Stergiopulos N, da Silva RF, Santos RA. An oral formulation of angiotensin-(1–7) reverses corpus cavernosum damages induced by hypercholesterolemia. J Sex Med 10: 2430–2442, 2013. [DOI] [PubMed] [Google Scholar]
  • 19.Greco AJ, Master RG, Fokin A Jr, Baber SR, Kadowitz PJ. Angiotensin-(1–7) potentiates responses to bradykinin but does not change responses to angiotensin I. Can J Physiol Pharmacol 84: 1163–1175, 2006. [DOI] [PubMed] [Google Scholar]
  • 20.Hurt KJ, Sezen SF, Lagoda GF, Musicki B, Rameau GA, Snyder SH, Burnett AL. Cyclic AMP-dependent phosphorylation of neuronal nitric oxide synthase mediates penile erection. Proc Natl Acad Sci USA 109: 16624–16629, 2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.Iyer SN, Chappell MC, Averill DB, Diz DI, Ferrario CM. Vasodepressor actions of angiotensin-(1–7) unmasked during combined treatment with lisinopril and losartan. Hypertension 31: 699–705, 1998. [DOI] [PubMed] [Google Scholar]
  • 22.Kadowitz PJ, Chapnick BM, Joiner PD, Hyman AL. Influence of inhibitors of prostaglandin synthesis on the canine pulmonary vascular bed. Am J Physiol 229: 941–946, 1975. [DOI] [PubMed] [Google Scholar]
  • 23.Kilarkaje N, Yousif MH, El-Hashim AZ, Makki B, Akhtar S, Benter IF. Role of angiotensin II and angiotensin-(1–7) in diabetes-induced oxidative DNA damage in the corpus cavernosum. Fertil Steril 100: 226–233, 2013. [DOI] [PubMed] [Google Scholar]
  • 24.Kim SC, Ahn SY, Park SH, Lee MY, Uhm DY. A comparison of the relaxation responses of isolated cavernosal smooth muscles by endothelium-independent and endothelium-dependent vasodilators in diabetic men with impotence. J Korean Med Sci 10: 1–6, 1995. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Kimoto Y, Kessler R, Constantinou CE. Endothelium dependent relaxation of human corpus cavernosum by bradykinin. J Urol 144: 1015–1017, 1990. [DOI] [PubMed] [Google Scholar]
  • 26.Klinge E, Sjostrand NO. Comparative study of some isolated mammalian smooth muscle effectors of penile erection. Acta Physiol Scand 100: 354–367, 1977. [DOI] [PubMed] [Google Scholar]
  • 27.Lasker GF, Pankey EA, Allain AV, Dhaliwal JS, Stasch JP, Murthy SN, Kadowitz PJ. Analysis of erectile responses to BAY 41–8543 and muscarinic receptor stimulation in the rat. J Sex Med 10: 704–718, 2013. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Li P, Chappell MC, Ferrario CM, Brosnihan KB. Angiotensin-(1–7) augments bradykinin-induced vasodilation by competing with ACE and releasing nitric oxide. Hypertension 29: 394–400, 1997. [DOI] [PubMed] [Google Scholar]
  • 29.Lima CV, Paula RD, Resende FL, Khosla MC, Santos RA. Potentiation of the hypotensive effect of bradykinin by short-term infusion of angiotensin-(1–7) in normotensive and hypertensive rats. Hypertension 30: 542–548, 1997. [DOI] [PubMed] [Google Scholar]
  • 30.Loiola RA, Reis FC, Kawamoto EM, Scavone C, Abdalla DS, Fernandes L, Pesquero JB. Role of vascular kinin B1 and B2 receptors in endothelial nitric oxide metabolism. Peptides 32: 1700–1705, 2011. [DOI] [PubMed] [Google Scholar]
  • 31.Lopes-Martins RA, Antunes E, Oliva ML, Sampaio CA, Burton J, de Nucci G. Pharmacological characterization of rabbit corpus cavernosum relaxation mediated by the tissue kallikrein-kinin system. Br J Pharmacol 113: 81–86, 1994. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Matsudaira T, Kogo H, Aizawa Y, Satoh T. Significance of gonad and renal prostaglandin E2 in the antihypertensive effect of pindolol in spontaneously hypertensive rats. J Pharmacobiodyn 8: 539–548, 1985. [DOI] [PubMed] [Google Scholar]
  • 33.Mishra RC, Wulff H, Cole WC, Braun AP. A pharmacologic activator of endothelial KCa channels enhances coronary flow in the hearts of type 2 diabetic rats. J Mol Cell Cardiol 72: 364–373, 2014. [DOI] [PubMed] [Google Scholar]
  • 34.Moreau ME, Garbacki N, Molinaro G, Brown NJ, Marceau F, Adam A. The kallikrein-kinin system: current and future pharmacological targets. J Pharmacol Sci 99: 6–38, 2005. [DOI] [PubMed] [Google Scholar]
  • 35.Nossaman BD, Feng CJ, Kadowitz PJ. Analysis of responses to bradykinin and influence of HOE 140 in the isolated perfused rat lung. Am J Physiol 266: H2452–H2461, 1994. [DOI] [PubMed] [Google Scholar]
  • 36.Nossaman BD, Kaye AD, Feng CJ, Kang B, Kadowitz PJ. Analysis of responses to bradykinin in the rat hindquarters vascular bed. Am J Physiol 272: R631–R639, 1997. [DOI] [PubMed] [Google Scholar]
  • 37.Pankey EA, Kassan M, Choi SK, Matrougui K, Nossaman BD, Hyman AL, Kadowitz PJ. Vasodilator responses to acetylcholine are not mediated by the activation of soluble guanylate cyclase or TRPV4 channels in the rat. Am J Physiol Heart Circ Physiol 306: H1495–H1506, 2014. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 38.Paula RD, Lima CV, Khosla MC, Santos RA. Angiotensin-(1–7) potentiates the hypotensive effect of bradykinin in conscious rats. Hypertension 26: 1154–1159, 1995. [DOI] [PubMed] [Google Scholar]
  • 39.Pelc LR, Gross GJ, Warltier DC. Mechanism of coronary vasodilation produced by bradykinin. Circulation 83: 2048–2056, 1991. [DOI] [PubMed] [Google Scholar]
  • 40.Pesquero JB, Bader M. Molecular biology of the kallikrein-kinin system: from structure to function. Braz J Med Biol Res 31: 1197–1203, 1998. [DOI] [PubMed] [Google Scholar]
  • 41.Roks AJ, van Geel PP, Pinto YM, Buikema H, Henning RH, de Zeeuw D, van Gilst WH. Angiotensin-(1–7) is a modulator of the human renin-angiotensin system. Hypertension 34: 296–301, 1999. [DOI] [PubMed] [Google Scholar]
  • 42.Sampaio WO, Nascimento AA, Santos RA. Systemic and regional hemodynamic effects of angiotensin-(1–7) in rats. Am J Physiol Heart Circ Physiol 284: H1985–H1994, 2003. [DOI] [PubMed] [Google Scholar]
  • 43.Santiago JA, Garrison EA, Champion HC, Smith RE, Del Rio O, Kadowitz PJ. Analysis of responses to kallidin, DABK, and DAK in feline hindlimb vascular bed. Am J Physiol 269: H2057–H2064, 1995. [DOI] [PubMed] [Google Scholar]
  • 44.Santiago JA, Osei SY, Kadowitz PJ. Inhibitory effects of Hoe 140 on vasodilator responses to bradykinin in the mesenteric vascular bed of the cat. Eur J Pharmacol 236: 315–318, 1993. [DOI] [PubMed] [Google Scholar]
  • 45.Santos RA. Angiotensin-(1–7). Hypertension 63: 1138–1147, 2014. [DOI] [PubMed] [Google Scholar]
  • 46.Sharma JN, Stewart JM, Mohsin SS, Katori M, Vavrek R. Influence of a kinin antagonist on acute hypotensive responses induced by bradykinin and captopril in spontaneously hypertensive rats. Agents Actions Suppl 38: 258–269, 1992. [PubMed] [Google Scholar]
  • 47.Smith DE, Kaye AD, Kang B, Feng CJ, DeWitt BJ, Kadowitz PJ, Nossaman BD. Influence of HOE 140, a bradykinin receptor antagonist, in the isolated mesenteric vascular bed of the rat. Am J Ther 3: 479–483, 1996. [DOI] [PubMed] [Google Scholar]
  • 48.Teixeira CE, Moreno RA, Ferreira U, Rodrigues Netto N Jr, Fregonesi A, Antunes E, De Nucci G. Pharmacological characterization of kinin-induced relaxation of human corpus cavernosum. Br J Urol 81: 432–436, 1998. [DOI] [PubMed] [Google Scholar]
  • 49.Tom B, Dendorfer A, Danser AH. Bradykinin, angiotensin-(1–7), and ACE inhibitors: how do they interact? Int J Biochem Cell Biol 35: 792–801, 2003. [DOI] [PubMed] [Google Scholar]
  • 50.Ueda S, Masumori-Maemoto S, Wada A, Ishii M, Brosnihan KB, Umemura S. Angiotensin(1–7) potentiates bradykinin-induced vasodilatation in man. J Hypertens 19: 2001–2009, 2001. [DOI] [PubMed] [Google Scholar]
  • 51.Wang T, Liu JH, Chen J, Xiao HJ, Li Y, Ye ZQ. [Expression of the kallikreins-kinins system in the corpus cavernosum of rats]. Zhonghua Nan Ke Xue 11: 278–280, 2005. [PubMed] [Google Scholar]
  • 52.Wang T, Wan ZH, Liu JH, Chen MY, Chen RB, Yang WM, Ye ZQ. Age-related changes in kallikreins-kinins system in rat corpus cavernosum. Int J Androl 34: 33–40, 2011. [DOI] [PubMed] [Google Scholar]
  • 53.Yousif MH, Makki B, El-Hashim AZ, Akhtar S, Benter IF. Chronic treatment with Ang-(1–7) reverses abnormal reactivity in the corpus cavernosum and normalizes diabetes-induced changes in the protein levels of ACE, ACE2, ROCK1, ROCK2 and omega-hydroxylase in a rat model of type 1 diabetes. J Diabetes Res 2014: 142154, 2014. [DOI] [PMC free article] [PubMed] [Google Scholar]

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