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Published in final edited form as: Pharmacol Res. 2023 Dec 28;199:107047. doi: 10.1016/j.phrs.2023.107047

β-arrestin biased signaling is not involved in the hypotensive actions of 5-HT7 receptor stimulation: use of Serodolin

Stephanie W Watts 1, Hannah Garver 1, Severine Morisset-Lopez 2, Franck Suzenet 3, Gregory D Fink 1
PMCID: PMC11416702  NIHMSID: NIHMS2020520  PMID: 38157998

Abstract

The 5-hydroxytryptamine 7 receptor (5-HT7) is necessary for 5-HT to cause a concentration-dependent vascular relaxation and hypotension. 5-HT7 is recognized as having biased signaling, transduced through either Gs or β -arrestin. It is unknown whether 5-HT7 signals in a biased manner to cause vasorelaxation/hypotension. We used the recently described β-arrestin selective 5-HT7 receptor agonist serodolin to test the hypothesis that 5-HT7 activation does not cause vascular relaxation or hypotension via the β -arrestin pathway. Isolated abdominal aorta (no functional 5-HT7) and vena cava (functional 5-HT7) from male Sprague Dawley rats were used in isometric contractility studies. Serodolin (1 nM – 10 μM) did not change baseline tone of isolated tissues and did not relax the endothelin-1 (ET-1)-contracted vena cava or aorta. In the aorta, serodolin acted as a 5-HT2A receptor antagonist, evidenced by a rightward shift in 5-HT-induced concentration response curve [pEC50 5-HT [M]: Veh = 5.2α0.15; Ser (100 nM) = 4.49α0.08; p<0.05]. In the vena cava, serodolin acted as a 5-HT7 receptor antagonist, shifting the concentration response curve to 5-HT left and upward (%10 μM NE contraction; Veh = 3.2α1.7; Ser (10 nM) = 58α11; p< 0.05) and blocking relaxation of pre-contracted tissue to the 5-HT1A/7 agonist 5-carboxamidotryptamine. In anesthetized rats, 5-HT or serodolin was infused at 5, 25 and 75 μg/kg/min, iv. Though 5-HT caused concentration-dependent depressor responses, serodolin caused an insignificant small depressor responses at all three infusion rates. With the final dose of serodolin on board, 5-HT was unable to reduce blood pressure. Collectively the data indicate that serodolin functions as a 5-HT7 antagonist with additional 5-HT2A blocking properties. 5-HT7 activation does not cause vascular relaxation or hypotension via the β -arrestin pathway.

Keywords: 5-HT, 5-HT7 receptor, hypotension, biased agonist, cardiovascular disease

Graphical Abstract

graphic file with name nihms-2020520-f0001.jpg

1.0. INTRODUCTION

Serotonin (5-hydroxytryptamine or 5-HT) was discovered as a vasoconstrictor, a substance that could change blood pressure in animal and human (Page and McCubbin 1953). It is without question that 5-HT is a vasoconstrictor primarily through activation of 5-HT2A receptor. However, with the discovery of other classes of 5-HT receptors, the (cardio)vascular actions of 5-HT expanded (Watts et al, 2012). Of specific interest in this study is the 5-HT7 receptor, cloned in 1993 (Ruat et al, 1993; Shen et al, 1993).

The 5-HT7 receptor is best known to play a role in circadian rhythm and photic response (Gardani and Biello, 2008; Sprouse et al, 2005); sleep and wakefulness (Monti and Jantos, 2014); temperature regulation (Hedlund et al, 2003); learning and memory (Roberts and Hedlund, 2012) and inflammation (Guseva et al, 2014). Relative to its function in the cardiovascular system, the 5-HT7 receptor mRNA was first localized to the blood vessels, both arteries and veins, by Ullmer et al (1995).

The functions of this receptor in control of vascular tone and blood pressure are of interest for several reasons. 5-HT possesses low nanomolar affinity for the 5-HT7 receptor such that free circulating 5-HT has the potential to activate this receptor (Watts et al, 2012). The 5-HT7 receptor also possesses interesting properties. It can be allosterically modified (Alberts et al, 2001); has constitutive activity (Andressen et al, 2018; Gellynck et al 2013; Hobson et al, 2003, Krobert et al, 2002; Kvachnina et al, 2009; Mahe et al, 2004; Purohit et al, 2005; Romero et al, 2006); has natural variants that change receptor pharmacology (Bruss et al, 2005; Kiel et al, 2003); can heterodimerize (Renner et al, 2012); and, discussed below, can be biased in its signal transduction.

Independent groups have consistently shown that infusion of 5-HT or its pathway limited precursor 5-hydroxytryptophan can lower blood pressure in animals, primarily the rat, that have either normal or elevated blood pressure (Balasubramaniam 1993, 1995; Baron et al, 1991; Cade and Fregly, 1992; Centurion et al, 2004; Dalton et al, 1986; DeVries et al, 1999; Ding et al, 1989; Echizen and Freed, 1981; Fregly et al, 1987; Itskovitz et al, 1989). Our group has focused on the mechanisms of long term hypotension caused by infusion of 5-HT over the course of a week (Diaz et al 2008). 5-HT, given as such, reduces total peripheral resistance (TPR), invoking involvement of the vasculature (Davis et al, 2012). We now know that 5-HT can relax skeletal muscle arterioles and reduce hindquarter vascular resistance (Jackson et al, 2023; Seitz et al, 2021), and relax veins in vitro and in vivo (Seitz et al, 2016; 2017; Watts et al, 2015). These events are predominantly mediated by activation of the 5-HT7 receptor, validated by a loss of many of these effects in the 5-HT7 KO rat we created (Demireva et al, 2019; Seitz et al, 2019) or antagonism by SB269970 (Hagan et al, 2000). Our findings follow important work by Terron et al whom first suggested the 5-HT7 receptor could be involved in a hypotensive response to 5-HT (Terron 1997; Terron et al, 2007). As such, the 5-HT7 receptor is an attractive target for developing new therapeutics for combating diseases of elevated total peripheral resistance, such as hypertension.

Only recently has the 5-HT7 receptor, a G protein coupled receptor, been observed to show biased agonism, with activation of Gs and β-arrestin pathways those towards which agonist may be differently biased (El Khamlichi et al, 2022). Our goal is to determine the ideal way of activating the 5-HT7 receptor to effect a fall in TPR/blood pressure with minimal side effects. Thus, we test here the hypothesis that the 5-HT7 receptor is not β-arrestin biased in its actions on blood pressure/vascular function. We use a vascular model – the isolated abdominal aorta and vena cava – that we’ve well established as being a vessel with a non-functional (aorta) and functional 5-HT7 receptor (vena cava) (Gonzalez-Pons et al, 2021; Seitz et al, 2019; Watts et al, 2015). We take advantage of the newly created drug serodolin as a β-arrestin biased agonist at the 5-HT7 receptor (El Khamlichi et al, 2022). Using a combination of in vitro and in vivo methods, our findings strongly support that activation of the 5-HT7 receptor unlikely utilizes β-arrestin pathways to effect the fall in vascular resistance/blood pressure.

2.0. MATERIALS AND METHODS

2.1. Animal approval, use and dissection

Male Sprague Dawley rats were purchased from Charles River Laboratories (Matawan, MI, USA). Previous studies indicate no difference in the cardiovascular functioning of the 5-HT7 receptor between male and female (Seitz et al, 2019). Thus, in the interest of reducing animal use, only males were used. Animals were on a normal diet [Teklad 22/5 Rodent diet (Madison WI, USA)]. Food and drinking water were available ad libitum. Procedures using animals complied with National Institutes of Health Guide for the Care and Use of Laboratory Animals (2011). Procedures used in this study were approved by the MSU Institutional Animal Care and Use Committee (PROTO202000009). Finally, this study was conducted with Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines (essential 10 and recommended) in mind.

For in vitro work and before tissue removal, rats were given pentobarbital as a deep anesthetic (80 mg kg−1, ip). A bilateral pneumothorax was created prior to vessel dissection. The abdominal vessels [vena cava (AbIVC) and aorta (AbA)] were removed in toto and separated from one another under a stereomicroscope and in a Silastic®-coated dish filled with physiological salt solution [PSS in mM: NaCl 130; KCl 4.7; KH2PO4 1.18; MgSO4 • 7H2O 1.17; NaHCO3 14.8; dextrose 5.5; CaNa2EDTA 0.03, CaCl2 1.6 (pH 7.2).].

2.2. Isometric Contractility

Rings of tissues (3–5 mm wide) were placed onto two L-shaped stainless-steel rings. Rings were mounted in warmed (37°C) and aerated (95% O2, 5% CO2) tissue baths (10 ml or 30 ml volume) on Grass isometric transducers (FT03; Grass instruments, Quincy, MA, USA) connected to an 8 channel PowerLab C through an Octet Bridge (ADInstruments, Colorado Springs, CO, USA) or a 4 channel PowerLab connected to a Quad Bridge. Sample type (aortic or vena cava ring) and exposure to vehicle or inhibitor were randomized daily into different tissue baths. Tissues were placed under optimum resting tension (determined in previous experiments: AbA 4 grams; AbIVC: 1 gram) and allowed to equilibrate for one hour with frequent exchange of buffer. At this time, tissues were challenged with a maximum concentration of norepinephrine (10 μM). Tissues were washed to baseline, and one of the following protocols commenced. Tissues were used in only one of the following protocols.

  • Test of vehicle or serodolin from baseline: Vehicle (increasing % of DMSO to 0.1% or serodolin) were added in a cumulative fashion (1 nM - 10 μM), waiting at least three minutes before adding the next concentration. If an effect was observed, a plateau was allowed to be achieved before addition of next concentration.

  • Test of serodolin as a relaxant (vena cava only): AbIVC were contracted with a half maximal concentration of the thromboxane A2 mimetic U46619 (1 μM) or endothelin-1 (ET-1; 1 nM). Once contraction plateaued, either vehicle or serodolin (1 μM) were added to observe whether relaxation ensued.

  • Test of serodolin vs 5-carboxamidotryptamine (5-CT) (vena cava only): AbIVC were incubated with vehicle (0.01% DMSO) or serodolin (100 nM) for 45 minutes. Tissues were then contracted to a half-maximal concentration of U46619, and 5-CT (1 μM) added to stimulate relaxation.

  • Test of serodolin vs 5-HT: AbA and AbIVC were incubated with either vehicle (up to 0.1% DMSO) or one concentration of serodolin (10 nM, 100 nM, 1 μM) for one hour without washing. A cumulative concentration response curve to 5-HT (10−9 – 3×10−4 M) was then constructed.

2.4. In vivo administration of 5-HT, serodolin

The catheter of a telemeter probe (Data Sciences International, Minneapolis, MN, USA) was inserted into a femoral artery to measure blood pressure throughout the experiment. An open catheter was inserted via a femoral vein for drug infusion. A 30-minute baseline period was followed by a 20-minute infusion of 5-HT or serodolin at progressive rates of 5, 25 and 75 μg/min by means of an infusion pump. A 30-minute recovery period was allowed between 5-HT and serodolin infusion.

2.5. Data/Statistical analyses and presentation.

All quantitative data are reported as means α SEM for number of animals in parentheses. N represents the number of biological replicates (e.g. individual animals). For isometric contractile studies, contraction is reported as milligrams (tracing) or as a percentage of initial contraction to a maximum concentration of NE (10 μM). Relaxation is reported as a percentage of a half-maximal contraction to the thromboxane A2 mimetic U46619 or endothelin −1 (ET-1). Agonist potencies were calculated using a non-linear regression (curve fit) within GraphPad Prism 9.0 (La Jolla, CA, USA) and are reported as –log EC50 values [M]. Maximums are reported as the maximal effect achieved. Where a maximal response was not achieved, the actual potency (EC50 value) was considered equal or greater than the reported value. The pKB value or the apparent antagonist dissociation constant for an serodolin at the 5-HT2A receptors was calculated using the equation:

Log(DR-1)=log[B]-logKB

where DR is the EC50 value of agonist in the presence of antagonist/EC50 value in the absence of antagonist; [B] is the molar concentration of the antagonist.

Repeated measures two-way ANOVA followed by the Bonferroni post hoc test was used to compare concentration-response curves. In all cases, p < 0.05 was considered significant.

2.6. Materials

5-HT hydrochloride, norepinephrine hydrochloride and dimethylsulfoxide were obtained from Sigma Chemical Company (St. Louis, MO USA). 5-CT and SB269970 were purchased from Tocris (R & D systems, Minneapolis, MN, USA). ET-1 was purchased from Echelon Biosciences (Salt Lake City, UT, USA). U46619 was purchased from Cayman Chemical Co (Ann Arbor, MI USA). Serodolin was provided through a Materials Transfer Agreement with Dr. Morisset-Lopez, the CNRS and Orléans University.

3.0. Results

3.1. Serodolin did not change baseline tone of isolated aorta or vena cava

These two tissues – the AbA and AbIVC – were tested for their ability to respond to serodolin given in a cumulative fashion. When compared to a vehicle that carried an equivalent percentage of DMSO, serodolin neither increased nor decreased the baseline tone of either vessel (figure 1). Tissues were alive given their contraction to NE (in figure legend 1).

Figure 1.

Figure 1.

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Effect of vehicle (graded DMSO) and serodolin in the abdominal aorta (red) and Vena Cava of the male Sprague Dawley rat. Points are meansαSEM for number of animals stated in parentheses. Contraction to NE (10−5 M; in milligrams): Aorta Vehicle = 2249α196; Aorta Serodolin = 1739α115; AbIVC Vehicle = 383α111; AbIVC Serodolin = 461α88.

3.2. Serodolin did not cause relaxation of contracted vena cava

The lack of response from baseline is not surprising given that this would not be expected unless tone had been established. However, when the AbIVC was contracted with half-maximal ET-1 or U46619, serodolin (1 μM) did not cause relaxation (figure 2A). Collectively, these data support serodolin is likely not an agonist that causes relaxation.

Figure 2.

Figure 2.

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A. Effect of vehicle or serodolin on the contracted Vena Cava of the male Sprague Dawley rat. ET-1 contraction in milligrams: Vehicle = 447α163; Serodolin = 658α125. B. Ability of serodolin (100 nM) to reduce the relaxation caused by 5-CT (1 μM) in the contracted vena cava. ET-1/U46619 contraction in milligrams Vehicle = 294α78; Serodolin = 518α88. *signifies statistically significant differences as determined by an unpaired Students t test. Bars are means+SEM for number of animals stated in parentheses.

3.3. Serodolin antagonized 5-CT-induced relaxation in contracted vena cava.

In the next experiment, serodolin (100 nM) was tested for its ability to antagonize a response recognized as being 5-HT7 receptor dependent, 5-CT-induced relaxation. 5-CT caused a relaxation to 30% of U46619-induced contraction (figure 2B; open bar) that was reduced significantly in the presence of serodolin (figure 2B; shaded bar). This finding supports serodolin acting as a 5-HT7 receptor antagonist in this model.

3.4. Serodolin acted as a 5-HT2A and 5-HT7 receptor antagonist

In final in vitro experiments, increasing concentrations of serodolin (10 nM, 100 nM or 1 μM) were tested for the ability to modify 5-HT-indcued contraction. Figure 3 depicts effects in the AbA (figure 3A) and AbIVC (figure 3B), as well as pharmacological parameters calculated for Table 1. In the aorta, Serodolin caused a concentration dependent rightward shift of 5-HT induced contraction. The antagonist dissociation constant (pKB) calculated for 5-HT in the Ab Awa was 7.57. Contraction in the AbA is largely mediated by the 5-HT2A receptor; serodolin is most likely antagonizing the 5-HT2A receptor.

Figure 3.

Figure 3.

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Effect of vehicle (graded DMSO) or increasing concentrations of serodolin in modifying 5-HT-induced contraction in the Abdominal Aorta (A) and Vena Cava (B) of the male Sprague Dawley rat. Points are meansαSEM for number of animals stated in parentheses. (NE maxes in milligrams for aorta were ( Vehicle = 2261α235; 10 nM Ser = 1867α220; 100 nM Ser = 2065α163; 1 μM Ser = 1849α85; p>0.05 by one way ANOVA. NE maxes for vena cava were: Vehicle = 393α96; 10 nM Ser = 606α117; 100 nM Ser = 509α106; 1 μM Ser = 260α109; p0.05 by one way ANOVA).

Table 1.

Potencies and Maximal contraction of 5-HT in vessels incubated with vehicle or serodolin. Potency is reported as −log EC50 [M] and maximums as a percentage of initial NE (10 μM) induced contraction. Reported as means±SEM.

Tissue Vehicle 10 nM Ser 100 nM Ser 1 μM Ser
Abdominal Aorta
(−log EC50)		 5.17±0.15
0/13 unstable		 5.27±0.04
(0/3 unstable)		 4.49±0.07*
(1/6 unstable)		 3.86±0.06*
(0/5 unstable)
Abdominal Vena Cava
(−log EC50)		 5.36+0.48
(7/10 unstable)		 5.73+0.17
(0/4 unstable)		 4.93+0.13
(1/7 unstable)		 3.99
(2/4 unstable)
Abdominal Aorta
Maximum (%)		 89.0±7.2 103.1±8.5 101.8±20.4 71.8±11.1
Abdominal Vena Cava
Maximum (%0		 3.2±1.7 58.3±11.4* 81.2±19.2* 36.6±7.7
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*

signifies statistically significant differences (p<0.05) from vehicle as determined by a one way ANOVA followed by Tukey’s multiple comparisons.

•

Unstable means Graphpad Prism could not calculate a value. The frequency of this occurrence is reported in the table with the denominator equivalent to the number of tissues tested.

The actions of serodolin were different in the AbIVC. Consistent with past results, 5-HT did not cause a concentration-dependent contraction in the AbIVC. Whereas serodolin alone did not modify contraction in the AbIVC (see Figure 2), it potentiated the effect of 5-HT in stimulating contraction at all tested concentrations. The potency of 5-HT to induce contraction was greatest in the presence of 10 nM serodolin, and progressively decreased as increasing concentrations were used. Table 1 shares the pharmacological parameters of these curves in figure 3. In the AbIVC, the increased potency of 5-HT can be explained by serodolin acting as a 5-HT7 receptor antagonist at a low concentration. With increasing serodolin concentration, 5-HT2A receptor antagonism was observed.

3.5. Serodolin alone did not decrease blood pressure and antagonized 5-HT-induced hypotension

Figures 4 and 5 share data on the effects of serodolin when given in vivo to anesthetized male Sprague Dawley rats. Serodolin, infused independently, did not modify blood pressure. By contrast, 5-HT caused the expected hypotension, best observed at the 25 μg/kg dose (figure 4). If this same dose response curve is constructed after the final addition of serodolin (75 μg/kg on board), 5-HT no longer caused a reduction in blood pressure (figure 5). Here, the ability of serodolin to antagonize a 5-HT7 receptor mediated event in vivo is consistent with 5-HT7 receptor antagonism exerted in vitro.

Figure 4.

Figure 4.

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Comparison of change in mean arterial blood pressure (MAP) caused by infusion of 5-HT and serodolin when given iv in a dose-dependent fashion to anesthetized Sprague Dawley male rat. Points represent meansαSEM for number of animals in parentheses. * signifies statistical differences calculated through two way ANOVA.

Figure 5.

Figure 5.

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Antagonism of 5-HT-induced hypotension by serodolin (75 μg/kg) when 5-HT was administered iv in a dose-dependent fashion to anesthetized Sprague Dawley male rat. Points represent meansαSEM for number of animals in parentheses. * signifies statistical differences calculated through two way ANOVA.

4.0. Discussion

Blood pressure control is regressing in the US and groups of resistant (3 meds do not decrease blood pressure) and refractory (5 meds do not decrease blood pressure) hypertension exist (Acelajado et al, 2019; Egan et al, 2021; Muntner et al, 2022). These daunting facts raise the idea that we do not fully understand how both normal and elevated blood pressures are regulated. As such, we and others have invested in the idea that agonism at the 5-HT7 receptor could provide a new therapeutic. The present study supports that 5-HT7 receptor agonists that are not β-arrestin biased are likely the drugs with the best potential of therapeutic efficacy.

4.1. Serodolin shows no agonism but acts as an antagonist

Whether serodolin was tested from baseline or in a contracted tissue, serodolin did not stimulate either direct contraction or relaxation in either the isolated abdominal vena cava or aorta. Importantly, this is not because tissues were not viable. All data are reported as a percentage of an initial contraction (NE) or half-maximal contraction (ET-1/U46619). All tissues contracted to an acceptable magnitude to these agonists such that response allowed their continuance in the protocol. We conclude that serodolin does not have the ability to activate a receptor that would directly influence vascular contraction. This was validated by in vivo studies which support little to no direct effect of serodolin on mean arterial pressure.

Rather, our data support that serodolin, in these blood vessels, functions as a 5-HT7 receptor antagonist at low nM concentrations and at higher concentrations as a 5-HT2A receptor antagonist. The ability to antagonize the 5-HT7 receptor was particularly evident in the profound enhancement of 5-HT-induced contraction in the AbIVC. This finding is consistent with previous work which discovered that the 5-HT7 receptor restrained the contractile function of the 5-HT2A receptor in the vena cava (Gonzalez-Pons et al, 2021; Seitz et al, 2019). In these two studies either pharmacological blockade by the antagonist SB269970 (Gonzales-Pons et al, 2021; Hagan et al, 2000) or genetic removal (Seitz et al, 2019) of the 5-HT7 receptor unveiled a 5-HT contraction conducted through the 5-HT2A receptor in the rat abdominal vena cava. The mechanism of how this occurs, such as a physical association of the two 5-HT receptors that is modified with antagonism/loss, is not known. The 5-HT7 receptor can heterodimerize with the 5-HT1A receptor (Renner et al, 2012); we were unable to find reports of the 5-HT7 receptor heterodimerizing with the 5-HT2A receptor.

The ability of serodolin to act as a 5-HT7 receptor antagonist is consistent with its known pharmacology (El Khamlichi et al, 2022). Occupancy of the orthosteric site of the 5-HT7 receptor with no measurable efficacy would permit antagonism of 5-HT-stimulated events.

4.2. 5-HT7 biased ligands

Serodolin is among the first described β -arrestin biased ligands. Kim et al published a series of tetrahydroazepine derivatives with β-arrestin bias (Kim et al, 2018). In parallel with El Khamlichi et al, Onyameh published on β -arrestin biased 5-HT7 receptor agonists (2022).

The intent of production of these molecules was largely focused on effects in the central nervous system, including endpoints such as sleep time, grooming and pain. Here, we use (one of) them in a different way: to examine whether the 5-HT7 receptor, through the β-arrestin pathway, was sufficient to cause vascular relaxation or hypotension. Serodolin caused neither of these events, leading to the conclusion that activation of the β -arrestin pathway through the 5-HT7 receptor is not necessary for producing hypotension. As such, it is most likely activation of Gs through the 5-HT7 receptor that leads to vascular relaxation and hypotension.

There is a small amount of information about the Gs/β-arrestin bias of agonists used to interrogate the 5-HT7 receptor. While important, such information comes with the caveat of bias measures being done in artificial, constructed cells, typically human embryonic kidney or HEK cells, that allow for measure of cAMP (Gs) or β-arrestin trafficking. This makes it impossible to be fully confidentthat the observations made in these artificial systems could be translated to, in our case, the venous smooth muscle cell. In such systems, 5-CT activates cAMP production through activation of the Gs pathway through the 5-HT7 receptor, but may also minimally activate β-arrestin through protein kinase A (El Khamlichi et al 2022). 5-CT is significantly more potent than 5-HT in reducing blood pressure in the rat, in part because it lacks the affinity for the 5-HT2A receptor possessed by 5-HT. Lee et al (2021) calculated the bias factor for 5-HT and the 5-HT7 receptor agonist E-55888, finding that 5-HT was equivalently biased towards Gs and β-arrestin (bias factor 1:1), while E-55888 was more biased towards β-arrestin (bias of 0.34:1). Onyameh et al confirmed that 5-HT is equally biased to Gs and β-arrestin (2022). If these findings translate to the naïve 5-HT7 receptor, then the 5-HT-induced vascular relaxation and hypotension is likely mediated predominantly by Gs stimulation. It will be interesting to compare a 5-HT7 receptor agonist that has pure Gs bias to serodolin.

4.4. Limitations

We did not carry out assays that would demonstrate the ability of serodolin to recruit β-arrestin in any of the cell types of the blood vessel. This was not considered necessary given the significant proof of principle done by El-Khamlichi et al (2022). We have also not compared it to other β-arrestin biased ligands. Again, the present studies are proof of principle for us to now understand the β-arrestin arm of 5-HT7 receptor activation is not necessary for the hypotensive actions of 5-HT. Finally, our conclusions can only be made relative to the rat given that this is the only species tested.

5.0. Conclusions

We conclude that activation of the β-arrestin pathway through the 5-HT7 receptor is not necessary for the relaxant/hypotensive effects of 5-HT (Graphical Abstract). This knowledge allows focus on 5-HT7 receptor ligands that are biased towards Gs for development of cardiovascular therapeutics.

Highlights.

  • 5-HT7 receptor stimulation mediates the hypotension when 5-HT is infused, but the ability of this receptor to function in a biased manner calls to question how 5-HT effects a hypotension: through Gs or β-arrestin?

  • Serodolin as a β -arrestin biased agonist at the 5-HT7 receptor was unable to relax isolated vessels nor did it cause a dose-dependent hypotension.

  • These findings point to the actions that proceed from 5-HT stimulation of the 5-HT7 receptor to be dependent on Gs signaling.

6.0. Acknowledgements, Conflicts, Funding and Author Contributions

Graphical abstract created using Biorender.com.

No AI tools were used in the writing of this manuscript.

Funding Sources

This work was funded by the National Heart Lung and Blood Institute through HL151413 and the Region Centre Val de Loire (project APR-IR TheraSEP).

Abbreviations

5-HT

5-hydroxytryptamine, serotonin

5-CT

5-carboxamidotryptamine

ET-1

endothelin-1

SB269970

(2R)-1-[(3-Hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine

Footnotes

Conflict of Interest

The authors have conflicts as noted below.

Greg D Fink: MSU Faculty; Funded by HL151413

Hannah Garver: MSU Employee

Severine Morisset-Lopez: CNRS

Franck Suzenet: Orléans University

Stephanie W Watts: MSU Faculty; funded by NIH HL151413; Keystone Scientific Advisory Board.

Author Contributions (CreDiT roles)

Greg D Fink : Conceptualization; Data Curation; Formal Analysis; Investigation; Methodology; Writing-review & Editing; Funding acquisition

Hannah Garver: Data Curation; Formal Analysis; Investigation; Methodology; Writing-review & Editing

Severine Morisset-Lopez: Conceptualization; Investigation; Resources; Funding acquisition Writing-review & Editing

Franck Suzenet: Supply of Serodolin; Funding acquisition

Stephanie W Watts: Conceptualization; Data Curation; Formal Analysis; Investigation; Methodology; Writing: Original Draft; Writing-review & Editing; Funding acquisition; Visualization.

Data Availability

All data generated during this study are included in this article.

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