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Published in final edited form as: Hypertension. 2012 May 14;60(1):114–122. doi: 10.1161/HYPERTENSIONAHA.112.192955

OXIDATIVE STRESS CONTRIBUTES TO SEX DIFFERENCES IN BLOOD PRESSURE IN ADULT GROWTH RESTRICTED OFFSPRING

Norma B Ojeda 1,2,3, Bettye Sue Hennington 3,4, Danielle T Williamson 4, Melanie L Hill 4, Nicole EE Betson 4, Julio C Sartori-Valinotti 2, Jane F Reckelhoff 2,3, Thomas P Royals 2, Barbara T Alexander 2,3
PMCID: PMC3655434  NIHMSID: NIHMS452504  PMID: 22585945

Abstract

Numerous experimental studies suggest that oxidative stress contributes to the pathophysiology of hypertension and importantly, that oxidative stress plays a more definitive role in mediating hypertension in males than in females. Intrauterine growth-restriction induced by reduced uterine perfusion initiated at day 14 of gestation in the rat programs hypertension in adult male growth-restricted offspring; yet, female growth-restricted offspring are normotensive. The mechanisms mediating sex differences in blood pressure in adult growth-restricted offspring are not clear. Thus, this study tested the hypothesis that sex specific differences in renal oxidative stress contribute to the regulation of blood pressure in adult growth-restricted offspring. A significant increase in blood pressure measured by telemetry in male growth-restricted offspring (P<0.05) was associated with a marked increase in renal markers of oxidative stress (P<0.05). Chronic treatment with the antioxidant tempol had no effect on blood pressure in male control offspring, but it normalized blood pressure (P<0.05) and renal markers of oxidative stress (P<0.05) in male growth-restricted relative to male control. Renal markers of oxidative stress were not elevated in female growth-restricted offspring; however, renal activity of the antioxidant catalase was significantly elevated relative to female control (P<0.05). Chronic treatment with tempol did not significantly alter oxidative stress or blood pressure measured by telemetry in female offspring. Thus, these data suggest that sex differences in renal oxidative stress and antioxidant activity are present in adult growth-restricted offspring, and that oxidative stress may play a more important role in modulating blood pressure in male, but not female growth-restricted offspring.

Keywords: Intrauterine growth restriction, blood pressure, antioxidant

Intrauterine growth restriction (IUGR) is a marker of impaired fetal growth and can result from a wide range of etiological factors including maternal conditions, placental insufficiency, and fetal genomic pathology 1. Numerous studies indicate that growth restriction during late gestation is associated with the developmental programming of adult health and disease 2, 3. Dr. David Barker was the first to correlate adverse influences during fetal life with later cardiovascular risk such as hypertension 4. Although numerous human and experimental studies address the theory of developmental programming of hypertension 3, 5, the exact mechanism(s) remain unclear. However, insight from experimental studies indicates that hypertension programmed in response to adverse influences during critical periods of early life may involve activation of the renal nerves 6, 7, the renin angiotensin system (RAS) 8, 9, and oxidative stress 10, 11. Thus, developmental programming of adult cardiovascular risk may involve multiple regulatory system interactions on target organs.

Men have higher blood pressure and exhibit greater cardiovascular (CV) and renal risk than age-matched women prior to menopause 12. Studies addressing sex differences in programmed CV and renal risk are limited, but many indicate an inverse association between birth weight and blood pressure is present in both men and women 13, 14. However, whether men and women differ in response to programmed CV and renal risk, and whether age augments or attenuates this sex difference is not completely clear. Jones et al., report that smaller size at birth is associated with higher blood pressure in boys, but not girls during childhood 15. Hallan et al., report that the effect of IUGR on renal function in young adulthood is weaker and less consistent in women compared to men 16. Jarvelin et al. report an inverse association between birth weight and systolic blood pressure for young adult men regardless of adjustment for body mass index (BMI); however, this inverse association is significant only in young adult women when adjusted for current BMI 14. Andersson et al., report that size at birth, as a predictor of CV risk is present in women at greater than 60 years of age, but not at 50 years of age 17. Thus, these studies indicate that human males exhibit greater programmed CV and renal risk compared to age-matched females, but the mechanisms responsible remain unknown.

Our laboratory utilizes a rat model of placental insufficiency that results in IUGR and sex differences in adult blood pressure 18. Adult male growth-restricted offspring are hypertensive, whereas adult female growth-restricted offspring are normotensive 18. Previous studies indicate that the renal nerves 7, 19and the RAS 9 play a critical role in the etiology and maintenance of hypertension in male growth-restricted offspring. However, the exact mechanisms that mediate sex differences in adult blood pressure in this model of IUGR are not clear.

Numerous studies implicate oxidative stress in the development and maintenance of hypertension 20-22. However, in many experimental models of hypertension oxidative stress plays a more important role in the regulation of blood pressure in males than in females 23. Several studies indicate that oxidative stress contributes to hypertension programmed by prenatal undernutrition 10, 11 indicating a role for oxidative stress in the etiology of hypertension programmed by in utero insult. Many models of prenatally programmed hypertension exhibit sex differences in adult blood pressure 11, 24-27; however, the exact mechanisms that mediate the sex difference in adult blood pressure in response to prenatal insult are not known. Thus, the goal of this study was to test the hypothesis sex specific differences in renal oxidative stress contribute to the regulation of blood pressure in adult growth-restricted offspring.

METHODS

Animals

All experimental procedures were conducted in accordance with National Institutes of Health guidelines for the Care and Use of Laboratory Animals with approval by the Animal Care and Use Committee at the University of Mississippi Medical Center. Timed pregnant Sprague Dawley rats were purchased from Harlan Laboratories, Inc. (Indianapolis, IN) and housed in a temperature-controlled room (23°C) with a 12:12-hour light/dark cycle with food and water available ad libitum. At day 14 of gestation rats destined for reduced uterine perfusion underwent either a sham or reduced uterine perfusion procedure as described below. All dams delivered at term (21-22 days of gestation) with birth weight recorded within 12 hours of delivery. Forty-eight hours after birth offspring in each litter were culled to 8 pups per dam to ensure equal nutrient access for all offspring. Animal weights were recorded twice per week; pups were weaned at 3 weeks of age. Male and female offspring from 9 control pregnant and 9 reduced uterine perfusion pregnant litters were randomly assigned into eight groups: male control untreated (vehicle or tap water) n=8; male IUGR untreated, n=8; male control treated (superoxide dismutase mimetic, tempol), n=8; and male IUGR treated, n=8; female control untreated, n=5; female IUGR untreated, n=5; female control treated, n=5; and female IUGR treated, n=5. To ensure diversity and that study of sex differences in oxidant status are the result of IUGR and not representative of a litter effect, only one male and one female offspring were selected per litter for study. All animals undergoing surgical procedures were anesthetized using 2-5% isoflurane by inhalation. All experimental endpoints were measured at 16 weeks of age to allowing complete passage through puberty and into adulthood.

Reduced uterine perfusion in the pregnant rat

IUGR was induced by a reduction in uterine perfusion initiated at day 14 of gestation as previously described 18. Pregnant rats for production of control offspring underwent a sham procedure. For more detail, see online supplement. Chronic administration of the superoxide dismutase (SOD) mimetic, tempol. Tempol was administered by drinking water (1mMol/L) for 2 weeks starting at 14 weeks of age utilizing a dose reported as effective to reduce oxidative status 28. Untreated animals received vehicle (tap water ad libitum). Drinking water was measured daily during the treatment period in all animals. Mean arterial pressure in conscious offspring. Mean arterial pressure (MAP) was measured continuously in conscious, free moving offspring using radio telemetry (Data Sciences International, Minneapolis, MN) as previously described 9. For more detail, see online supplement.

Superoxide anion production measurement

To determine basal and NADPH-stimulated renal and superoxide production in male and female rats, basal and NADPH-stimulated renal and superoxide production was measured using lucigenin chemiluminescence in the presence (NADPH stimulated) or absence (basal) of 0.1 mmol/L NADPH. Briefly, renal basal superoxide anion production was measured via the lucigenin chemiluminescence method as previously described by Schiffrin et. al 21. For more detail, see online supplemental files.

F2-Isoprostanes

24 hour urinary excretion of F2-isoprostanes were measured according to a modified version of Dobrain and colleagues 22 by a competitive enzyme-linked immunoassay (ELISA) (Oxford Biomedical Research) as previously described 29 with values normalized to urinary creatinine levels (CR 01 Oxford Biomedical Research).

Renal antioxidants enzymes protein expression

Kidneys were flash frozen and stored at −80°C until use. Frozen tissue was homogenized in RIPA buffer containing a protease inhibitor cocktail (Roche Pharmaceuticals). Protein concentration was determined using Pierce BCA Protein Assay (Pierce). Protein lysates were subjected to SDS-PAGE, transferred onto PVDF membranes, and blocked with Odyssey Brand blocking buffer. Membranes were incubated with antibodies overnight: anti-catalase, anti-Mn SOD, anti-Cu/Zn SOD, anti-Glutathione Peroxidase (Meridian Life Science) and anti-alpha tubulin (Neomarkers). Membranes were probed with the appropriate Infrared Dye secondary antibodies with bands visualized with Odyssey infrared imaging system and quantification performed using the QuantOne software. All samples were run in triplicate. Renal Catalase, Glutathione Peroxidase, and Superoxide Dismutase Activity Assays. Renal Catalase, Glutathione Peroxidase, and Superoxide Dismutase activities in whole kidney tissue were analyzed according to manufacturer directions (Cayman Chemical Company). Activity data was normalized to protein concentration (Protein assay kit, Pierce Product). For more detail, see online supplemental files.

Statistics

Graphpad PRISM version 5 and IBMR SPSS Statistics version 19 were utilized for all statistical analysis. Comparisons made between groups utilized ANOVA with adjustment for multiple comparisons. Bonferroni’s post hoc test was utilized for multiple comparisons. The General Linear Model (GLM-SPSS) univariate with 3 way interactions (3way ANOVA) was used to calculate interactions related to birth weight, gender and treatment. Statistical significance of interaction was set with P<0.05 and F values greater than 5. The sample size for all experiments were calculated to attain a statistical power of at least 0.85.

RESULTS

Body weight and water consumption

Birth weight was significantly reduced (P<0.05) in growth-restricted offspring from reduced uterine perfusion dams as compared to control offspring from control or sham dams (Table 1). At 16 weeks of age body weight did not differ upon comparison of same-sex growth-restricted offspring to same-sex control offspring (Table 1). However, male offspring were heavier relative to counterpart female offspring within control and growth-restricted groups (Table 1). Water consumption did not differ between animals receiving vehicle (tap water) relative to animals receiving tempol (Table 1).

Table 1.

Body Weight and Water Consumption

Experimental
groups		 Body Weight
(g)
at birth		 Body Weight
(g)
16 weeks of
age		 Water consumption
(ml/day)
16 weeks of age
Control Male
Untreated		 6.27±0.13 446.5±8.64 41.93±0.30
IUGR Male
Untreated		 5.32±0.16 * 442.9±19.18 41.75±0.11
Control Female
Untreated		 5.92±0.10 266.4±5.92 † 26.68±0.38 †
IUGR Female
Untreated		 5.13±0.14 * 268.4±13.43 † 27.48±0.39 †
Control Male
Treated		 6.31±0.23 443.9±11.64 41.11±0.21
IUGR Male
Treated		 5.27±0.07 * 439.4±11.39 41.81±0.33
Control Female
Treated		 5.97±0.13 274.2±8.69 † 26.58±0.36 †
IUGR Female
Treated		 4.88±0.20 * 273.4±6.98 † 27.40±0.22 †
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in male and female control and growth-restricted (IUGR) offspring

*

P < 0.05 vs. control counterpart;

†

P <0.05 vs. male counterpart. Data values represent mean±SEM

Mean arterial pressure

As previously reported, IUGR leads to a marked in increase in MAP at 16 weeks of age in adult male growth-restricted offspring (P<0.05) relative to control offspring, that is not observed in adult female growth-restricted offspring (Data Supplement, Figure S1). Chronic treatment with the antioxidant tempol had no effect on MAP in male control offspring (Figure 1). However, chronic treatment with tempol significantly reduced MAP in male growth-restricted offspring (P<0.05) normalizing blood pressure in tempol treated male growth-restricted offspring to levels comparable to untreated male control offspring (Figure 1). MAP was not significantly different between adult female control and adult female growth-restricted offspring in the untreated group; moreover, chronic treatment with the antioxidant tempol did not significantly alter blood pressure in female offspring, control or growth-restricted (Figure 2). Renal markers of oxidative stress. 24-hour urinary excretion of F2-isoprostanes were significantly elevated in untreated male growth-restricted offspring compared to untreated male control (P<0.05) (Figure 3a). Chronic treatment with tempol significantly reduced urinary F2-isoprostanes in male growth-restricted offspring (P<0.05); but had no significant effect in male control (Figure 3a). Urinary excretion of F2-isoprostanes did not differ upon comparison of untreated female control and untreated female growth-restricted offspring; chronic treatment with tempol did not alter F2-isoprostanes levels in female control or female growth-restricted offspring (Figure 3a). However, urinary excretion of F2-isoprostanes was significantly elevated in untreated male growth-restricted offspring relative to untreated female growth-restricted (P<0.05) (Figure 3a).

Figure 1. Mean arterial pressure in male control and growth-restricted (IUGR) offspring measured by radio telemetry in conscious, free moving animals from 12 weeks of age until 16 weeks of age.

Figure 1

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Animals received the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) for 2 weeks (14 weeks to 16 weeks of age). *P<0.05 versus Control treated and untreated offspring. †P<0.05 versus untreated counterpart. Data values represent mean±SE.

Figure 2. Mean arterial pressure in female control and growth-restricted (IUGR) offspring measured by radio telemetry in conscious, free moving animals from 12 weeks of age until 16 weeks of age.

Figure 2

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Animals received the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) for 2 weeks (14 weeks to 16 weeks of age). Data values represent mean±SE.

Figure 3. Renal superoxide production and urinary excretion of F2-isoprostanes in male and female control and growth-restricted (IUGR) offspring treated with the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) from 14 weeks to 16 weeks of age.

Figure 3

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4a) 24-hour urinary excretion of F2-isoprostane; 4b) Renal basal superoxide anion production; and 4c) Renal NADPH-oxidase dependent superoxide anion production. *P<0.05 versus untreated male counterpart, #P<0.05 versus untreated male IUGR †P<0.05 versus untreated male IUGR. Data values represent mean±SE.

Renal basal superoxide anion production was significantly elevated in untreated male growth-restricted offspring as compared to untreated male control (P<0.05) (Figure 3b). Chronic treatment with tempol significantly decreased renal basal superoxide anion production in male growth-restricted offspring (P<0.05) with no effect in male control (Figure 3b). Renal basal superoxide anion production did not differ upon comparison of female control and female growth-restricted offspring in the untreated group or following chronic treatment with tempol (Figure 3b). However, basal superoxide anion production within the kidney was significantly elevated in male growth-restricted offspring compared to female growth-restricted offspring (P<0.05) (Figure 3b).

Renal NADPH-oxidase dependent superoxide anion production was significantly elevated in untreated male growth-restricted compared to untreated male control (P<0.05); no difference was observed in untreated female growth restricted relative to untreated female control; yet, it was significantly elevated in untreated male growth-restricted offspring compared to untreated female growth-restricted offspring (P<0.05) (Figure 3c). Chronic treatment with tempol significantly decreased renal NADPH-oxidase dependent superoxide production in male growth-restricted offspring relative to its untreated counterpart (P<0.05); however, it had no effect in male control, female control or female growth-restricted offspring relative to their untreated counterparts (Figure 3c).

Renal anti-oxidant enzymes protein expression

Renal protein expression of antioxidant enzymes catalase (CAT), glutathione peroxidase (GPX), manganese superoxide dismutase (Mn-SOD) and copper/zinc superoxide dismutase (Cu-Zn-SOD) did not differ upon comparison of male growth-restricted offspring relative to male control in the untreated group (Figure 5). Tempol significantly increased renal CAT and GPX protein expression in male growth-restricted offspring relative to untreated counterparts (P<0.05) (Figure 4). In female offspring renal expression of the antioxidants enzymes CAT and GPX were significantly elevated in untreated growth-restricted offspring relative to untreated control (P<0.05) (Figure 5). Chronic treatment with tempol significantly reduced renal CAT and GPX protein expression in female growth restricted offspring compared to their untreated counterparts (P<0.05) (Figure 5). Renal expression of Cu-Zn-SOD and Mn-SOD did not differ upon comparison of female control or growth-restricted offspring, treated or untreated.

Figure 5. Protein expression of renal antioxidant enzymes catalase (CAT), glutathione peroxidase (GPX), manganese SOD (Mn-SOD), and copper-zinc SOD (Cu-Zn SOD) in adult female control and growth-restricted (IUGR) offspring treated with the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) from 14 weeks to 16 weeks of age.

Figure 5

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Visualization of the protein of interest and tubulin are from the same blot. Results are expressed in arbitrary units for the protein normalized to tubulin. *P<0.05 versus female control. †P<0.05 versus untreated female counterpart. Data values represent mean±SE.

Figure 4. Protein expression of renal antioxidant enzymes catalase (CAT), glutathione peroxidase (GPX), manganese SOD (Mn-SOD), and copper-zinc SOD (Cu-Zn SOD) in adult male control and growth-restricted (IUGR) offspring treated with the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) for 2 weeks from 14 weeks to 16 weeks of age.

Figure 4

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Visualization of the protein of interest and tubulin are from the same blot. Results are expressed in arbitrary units for the relative optical density of the protein bands factored for the density of the tubulin bands. *P<0.05 versus male control; †P<0.05 versus untreated male counterpart. Data values represent mean±SE.

Renal anti-oxidant enzyme activity

Activity of renal antioxidant enzymes catalase CAT, GPX, and Cu-Zn-SOD did not differ upon comparison of male growth-restricted offspring relative to male control in the untreated group (Figure 6). Chronic treatment with the antioxidant tempol significantly increased activity of renal CAT enzyme in male growth-restricted offspring relative to its untreated counterpart (P<0.05) (Figure 6). Activity of renal Mn-SOD enzyme was not measured due to technical difficulties with the assay. In female offspring activity of renal CAT activity was significantly elevated in untreated growth-restricted relative to untreated control (P<0.05) (Figure 6). Chronic treatment with tempol significantly reduced activity of the renal CAT enzyme in female growth restricted offspring relative to treated female control and untreated female growth restricted (P<0.05) (Figure 6). Activity of renal GPX and Cu-Zn-SOD did not differ upon comparison of female control or female growth-restricted offspring, treated or untreated. The General Linear Model (GLM. IBMR SPSS) with 3 way interaction showed statistically significant effects of treatment (P<0.03 F=5.17) and gender (P<0.02 F=5.88) for CAT enzyme activity, and an effect of gender (P<0.000 F= 41.00) for GPX enzyme activity in growth restricted offspring. No effects were observed for Cu-Zn-SOD enzyme activity.

Figure 6. Activity of renal antioxidant enzymes catalase (CAT), copper-zinc SOD (Cu-Zn SOD), and glutathione peroxidase (GPX) in adult male and female control and growth-restricted (IUGR) offspring treated with the SOD mimetic, tempol (1mMol/L), or vehicle (tap water ad libitum) from 14 weeks to 16 weeks of age.

Figure 6

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*P<0.05 versus control. †P<0.05 versus untreated counterpart. §P<0.05 versus male growth-restricted tempol treated. Data values represent mean±SE

Heart Rate

Heart rate (HR) averaged for a 24 hour period at 16 weeks of age was significantly elevated in adult male growth-restricted compared to adult male control offspring (P<0.05) (Figure 7). Heart rate was significant elevated in adult female compared to age-matched male control and growth-restricted offspring (P<0.05) (Figure 7). Chronic treatment with the antioxidant, tempol, significantly reduced HR in adult male growth-restricted offspring (P< 0.05) normalizing it relative to untreated male control offspring; chronic tempol had no effect on HR in control male, female control, or female growth-restricted offspring (Figure 7).

Figure 7. Heart rate in male and female control and growth-restricted (IUGR) offspring at 16 weeks of age measured by radio telemetry in conscious, free moving animals untreated and treated with tempol.

Figure 7

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*P<0.05 versus untreated male control offspring; †P<0.05 versus untreated male growth-restricted offspring; ‡ P<0.05 versus all male offspring. Data values represent mean±SE.

DISCUSSION

The major findings from this study are 1) hypertensive male growth-restricted offspring exhibited a marked increase in renal markers of oxidative stress compared to normotensive male control offspring. 2) Chronic treatment with the SOD mimetic, tempol, normalized blood pressure in male growth-restricted offspring relative to male control, and 3) renal markers of oxidative stress in male growth-restricted offspring relative to untreated male animals. 4) Hypertensive male growth-restricted offspring exhibited a marked increase in renal markers of oxidative stress compared to normotensive female control and growth-restricted offspring. 5) Renal markers of oxidative stress did not differ upon comparison of normotensive female growth-restricted offspring to normotensive female control offspring. Importantly, 6) a significant increase in renal catalase protein expression and activity, were observed in female growth-restricted offspring compared to female control. Thus, these findings suggest that sex differences in renal markers of oxidative stress are present in adult growth-restricted offspring, and that oxidative stress may play a more important role in modulating blood pressure in male, but not female growth-restricted offspring. Furthermore, up-regulation of renal catalase in female growth-restricted offspring may serve as a counter-regulatory mechanism against the increase in renal superoxide production and hypertension programmed by in utero insult.

Experimental models of hypertension such as obesity-induced, deoxycorticosterone acetate-salt, and the SHR indicate a link between increased oxidative stress and hypertension 20-22, 30, 31. However, recent studies indicate that oxidative stress may have differential effects on blood pressure in males versus females in experimental models of hypertension 23. Sex differences in adult cardiovascular risk are observed in models of developmental programming of hypertension induced via prenatal protein restriction, uteroplacental insufficiency, and fetal glucocorticoid exposure 11, 24-27. Furthermore, marked increases in markers of oxidative stress are observed in experimental models of hypertension programmed by in utero insult10, 11. However, whether sex differences in oxidative stress and antioxidant capacity contribute to the sex-specific programming of hypertension in these models of in utero insult is not clear. Previously, we noted a key role for testosterone in mediating hypertension in adult male growth-restricted offspring 9. Plasma levels of testosterone are elevated two-fold in adult male growth-restricted offspring relative to control offspring and, castration abolishes hypertension in adult male growth-restricted offspring 9. Testosterone induces oxidative stress in the male SHR 32, 33. Furthermore, male SHR exhibit higher levels of oxidative stress in microvessels as compared to female SHR 34. In the current study, only male growth-restricted offspring exhibited an increase in renal production of superoxide and urinary excretion of F2-isoprostanes. Thus, the increase in renal superoxide production and urinary excretion of F2-isoprostanes in adult, male growth-restricted offspring may be mediated via increased plasma levels of testosterone programmed by IUGR.

We previously reported that male and female growth-restricted offspring develop hypertension as early as 4-6 weeks of age 18, and that female growth-restricted offspring become normotensive after puberty 18. Ovariectomy induces hypertension in adult female growth-restricted offspring, whereas estrogen replacement reverses this effect indicating that estrogen is protective against hypertension programmed by IUGR in adult female growth-restricted offspring 35. Numerous studies indicate that estrogen exhibits antioxidant properties 36-38. Activity of the antioxidant enzyme, CAT, is strongly regulated by estrogen in female rats; furthermore, total SOD activity is greater in females rats compared to males 39. GPX is increased by estrogen treatment in female rats 40 and in humans; serum GPX levels and activity are higher in women compared to men 41. In the current study renal protein expression of CAT and GPX were significantly increased in female growth-restricted offspring relative to female control. Importantly, female growth-restricted offspring exhibited a significant increase in renal CAT activity relative to female control. Increased ROS production and hypertension in angiotensinogen transgenic mice is prevented by overexpression of catalase 42. Therefore, compensatory up-regulation of antioxidant capacity may contribute to normalization of blood pressure in adult female growth-restricted offspring and contribute to sex differences in hypertension programmed in response to IUGR. Furthermore, up-regulation of antioxidant capacity by estrogen may be one mechanism by which estrogen is protective against hypertension induced by IUGR in adult female growth-restricted rats.

The exact mechanisms by which ROS contribute to elevations in blood pressure are not clear. Experimental studies indicate that ROS may increase blood pressure via activation of the sympathetic nervous system (SNS) 43-46. Whether ROS activates peripheral SNS activity 46 or peripheral and central SNS activity is not clear 43. Moreover, the acute actions of systemic tempol to reduce blood pressure in several experimental models of hypertension are associated with a reduction in renal sympathetic nerve activity (RSNA) 43-46 that occurs in the absence of a reduction in vascular superoxide production 44. Thus, the mechanism by which tempol reduces blood pressure acutely may involve different sites and mechanisms of action that may be specific to the experimental model. The marked increase in blood pressure and heart rate in male growth-restricted offspring was normalized relative to male control offspring by chronic treatment with tempol. In addition, the reduction in blood pressure following chronic treatment with tempol was associated with a marked reduction in renal superoxide production suggesting that the drop in blood pressure in male growth-restricted offspring is associated with a decrease in ROS within the kidney. However, the antihypertensive effect of tempol on male growth-restricted offspring in this study may also be due to influences mediated via the SNS. The renal nerves play a key role in hypertension induced by IUGR in male growth-restricted offspring 7, 19. Thus, further studies will determine whether the reduction in MAP in male growth-restricted offspring following chronic treatment with tempol involves direct inhibition of sympathetic nerve activity. In addition, further studies may be needed to determine if the mechanism by which chronic treatment with tempol leads to a reduction in MAP in male growth-restricted offspring involves down-regulation of inflammation 47, 48. Adult male growth-restricted offspring exhibit a marked increase in circulating inflammatory cytokines indicative of chronic inflammation 49. Thus, the mechanisms by which the antioxidant tempol acts to reduce blood pressure may be complex and multi-factorial.

In conclusion, hypertension in adult male growth-restricted offspring was associated with a marked increase in renal markers of oxidative stress. Female growth-restricted offspring did not demonstrate an increase in renal markers of oxidative stress. Chronic treatment with the antioxidant tempol abolished hypertension and reduced renal markers of oxidative stress in adult male growth-restricted offspring. Female growth-restricted offspring showed elevated renal CAT activity. Thus, data from this study suggest that IUGR induced by placental insufficiency programs an increase in renal oxidative stress that contributes to the etiology of hypertension in male growth-restricted offspring. Testosterone may exacerbate renal superoxide production while estrogen may counteract the increase in renal superoxide production via up-regulation of key antioxidant enzymes. Therefore, sex-specific programming of renal superoxide production and antioxidant capacity may contribute to sex differences in hypertension programmed by IUGR

Perspectives

Hypertension is a major risk factor for cardiovascular disease and is the primary cause of death in men and women worldwide. Although, the efforts to prevent and/or find a cure for hypertension are great, the number of patients with hypertension is increasing. New paradigms suggest an association between the pathophysiology of hypertension and birth weight. Insight into the mechanisms linking birth weight with blood pressure in later life may help or prevent cardiovascular disease by targeting populations at risk. Whether sex differences in cardiovascular risk exist in low birth weight individuals is not yet clear. However, experimental studies indicate that sex hormones may be an important determinant of oxidative status and cardiovascular risk in models of IUGR. CV risk increases with age. Thus, further studies are need to clarify whether sex hormones, in particular when impacted by aging, alters CV risk in low birth weight individuals.

Supplementary Material

1

NOVELTY AND SIGNIFICANCE.

  1. What is new: Investigation into mechanisms that mediate sex differences in models of hypertension programmed by fetal insult are very limited. We previously reported that female growth restricted offspring are protected against marked increases in blood pressure in adulthood whereas male growth restricted offspring are hypertensive.

  2. What is relevant? Numerous experimental models of hypertension report that oxidative stress plays a more important role in blood pressure regulation in males compared to females. Thus, oxidative stress may be one mechanism that contributes to sex differences in adult blood pressure in models of prenatal programmed hypertension.

  3. Summary: Thus, this study indicates that sex-specific programming of renal oxidative stress contributes to sex differences in the developmental programming of adult blood pressure in growth restricted offspring. Insight from this study highlights the sex-specific programming of oxidant status in male growth restricted offspring relative to female growth restricted offspring.

Acknowledgments

SOURCES OF FUNDING Dr. Alexander is supported by NIH grants HL074927 and HL51971. Dr. Hennington is supported by NIH grants P20MD002725, P20RR016476, and P20GM103476; and NSF grants DBI-0957421 and HBCU-UP

Footnotes

Disclosures: None

References

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