Phenylephrine precontraction increases the sensitivity of rabbit femoral artery to serotonin by enabling 5-HT1-like receptors

Overview of the Microenvironment of Vasculature in Vascular Tone Regulation

Hypertension is asymptomatic and a well-known “silent killer”, which can cause various concomitant diseases in human population after years of adherence. Although there are varieties of synthetic antihypertensive drugs available in current market, their relatively low efficacies and major application in only single drug therapy, as well as the undesired chronic adverse effects associated, has drawn the attention of worldwide scientists. According to the trend of antihypertensive drug evolution, the antihypertensive drugs used as primary treatment often change from time-to-time with the purpose of achieving the targeted blood pressure range. One of the major concerns that need to be accounted for here is that the signaling mechanism pathways involved in the vasculature during the vascular tone regulation should be clearly understood during the pharmacological research of antihypertensive drugs, either in vitro or in vivo. There are plenty of articles that discussed the signaling mechanism pathways mediated in vascular tone in isolated fragments instead of a whole comprehensive image. Therefore, the present review aims to summarize previous published vasculature-related studies and provide an overall depiction of each pathway including endothelium-derived relaxing factors, G-protein-coupled, enzyme-linked, and channel-linked receptors that occurred in the microenvironment of vasculature with a full schematic diagram on the ways their signals interact. Furthermore, the crucial vasodilative receptors that should be included in the mechanisms of actions study on vasodilatory effects of test compounds were suggested in the present review as well.

Overview of Antagonists Used for Determining the Mechanisms of Action Employed by Potential Vasodilators with Their Suggested Signaling Pathways

This paper is a review on the types of antagonists and the signaling mechanism pathways that have been used to determine the mechanisms of action employed for vasodilation by test compounds. Thus, we exhaustively reviewed and analyzed reports related to this topic published in PubMed between the years of 2010 till 2015. The aim of this paperis to suggest the most appropriate type of antagonists that correspond to receptors that would be involved during the mechanistic studies, as well as the latest signaling pathways trends that are being studied in order to determine the route(s) that atest compound employs for inducing vasodilation. The methods to perform the mechanism studies were included. Fundamentally, the affinity, specificity and selectivity of the antagonists to their receptors or enzymes were clearly elaborated as well as the solubility and reversibility. All the signaling pathways on the mechanisms of action involved in the vascular tone regulation have been well described in previous review articles. However, the most appropriate antagonists that should be utilized have never been suggested and elaborated before, hence the reason for this review.

Inversion of the response to serotonin in rats with traumatic shock

Normally serotonin reduced blood pressure. It was shown that in rats with traumatic shock its hypotensive effect was transformed into hypertensive one. In vitro serotonin exhibited a slight vasoconstrictor effect on isolated rat aorta, while 24 h after injury, the strength of aortic contractions in response to serotonin increased 2.2 times. Desensitization of glucocorticoid receptors caused by injection of high doses of dexamethasone (3 mg/kg) to rats for 5 days led to similar changes in serotonin effect. We hypothesized that inversion of the response to serotonin in shock was caused by increased activity and/or expression of vasoconstrictor serotonin receptors in blood vessels.

Amplification of sumatriptan-induced contraction in rabbit saphenous vein but not in basilar artery

The modulation of serotonin (5-HT(1B/1D)) receptor-induced vascular contractility by histamine and U-46619 was compared in the rabbit basilar artery and saphenous vein. In the saphenous vein, histamine (5 x 10(-7) M) significantly increased the potency (from pEC(50) of 6.0 to 6.8) and efficacy (from 52.3% to 88.2%) of sumatriptan. Likewise, U-46619 (5 x 10(-9) M) also increased the potency (from pEC(50) of 5.9 to 6.6) and efficacy (from 51.8% to 92.1%) of sumatriptan in the saphenous vein. In contrast, equieffective concentrations of histamine (10(-7) M) and U-46619 (3 x 10(-9) M) failed to amplify contraction to sumatriptan in the basilar artery. Contraction to sumatriptan was inhibited by nitrendipine (10(-7) M) in the basilar artery but not in the saphenous vein, suggesting that different contractile signaling mechanisms are operating in these tissues. Furthermore, U-46619- and thrombin-induced contractility in the basilar artery were also not amplified by histamine, suggesting that lack of amplification of contraction in the basilar artery was not restricted to sumatriptan but was rather a characteristic of this cerebral vessel. These data suggest that in the in vivo plasma milieu sumatriptan will more markedly contract the peripheral saphenous vein than the basilar artery, a cerebral blood vessel.

Pharmacologic characterization of contractile serotonergic receptors in human isolated mesenteric artery

The 5-hydroxytryptamine (5-HT) receptors mediating contraction in human isolated mesenteric arteries were characterized. Endothelium-denuded human isolated mesenteric arteries were used. 5-HT induced concentration-dependent contractions in mesenteric arteries (Emax, 127.37 +/- 7.61% of 80 mM KCl maximal contraction; pD2, 6.73 +/- 0.09 [-logEC50]). Sumatriptan, a selective 5-HT1B/1D receptor agonist, induced concentration-dependent contractions in some of the arteries (Emax, 61.82 +/- 10.04%; pD2, 6.56 +/- 0.21, n = 9) but not in the others (Emax < 5%, n = 13), suggesting that functional 5-HT1B/1D receptors exist in some but not in all mesenteric arteries. GR127935 (a selective 5-HT1B/1D receptor antagonist, 3 nM) inhibited sumatriptan-induced contractions in arteries in which sumatriptan responses were strong in an insurmountable manner. GR127935 (10 nM) also inhibited 5-HT responses and shifted the concentration-response curve of 5-HT to the right significantly (p < 0.05; pD2s were 6.54 +/- 0.18 and 5.93 +/- 0.11 in the presence of vehicle and GR127935, respectively). Ketanserin (0.01-1 microM) competitively antagonized 5-HT responses in human mesenteric arteries: pA2 value was 8.40 +/- 0.25 (slope of Schild regression, 1.43 +/- 0.18; r2, 0.98). Tropisetron (5-HT3 receptor antagonist) and prazosin (alpha1-adrenoceptor antagonist) did not affect the contractions induced by 5-HT. These results suggest that 5-HT2A and 5-HT1B/1D receptors, but not 5-HT3 and alpha1-adrenoceptors, are involved in the 5-HT-induced contractions in human isolated mesenteric arteries. Sumatriptan-induced and 5-HT1B/1D receptor-mediated responses vary greatly among patients.

Evidence that the hypotensive effect of WAY 100635, a 5-HT1A receptor antagonist, is related to vascular alpha 1-adrenoceptor blockade in the adult rat

1. The effect of WAY100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride), a 5-HT1A receptor antagonist, on cardiovascular function was studied. 2. The i.v. injection of WAY100635 dose-dependently decreased blood pressure in anaesthetized rats; while in pithed rats WAY100635 (1 mg kg(-1)) displaced the phenylephrine pressor effect. 3. WAY100635 antagonized phenylephrine-induced contraction in rabbit and rat aorta (pA2 of 6.88 and 7.93 and Schild slopes of -0.83 and -1.21, respectively); while in rat caudal artery pK(B) was 7.45 and the Schild slope of -0.56, suggesting a complex interaction in this vessel. 4. The results show that WAY100635 induced hypotension in the anaesthetized rat and suggest that this effect could be partially explained by antagonism of vascular alpha1-adrenoceptors.

Functional characterization of serotonin receptors in rat isolated aorta

Interactions of serotonin (5-HT) with different specific 5-HT receptors that can coexist in the same blood vessel sometimes generate opposite effects. The aim of this study was to characterize the functional role of previously described mRNAs for 5-HT receptors in the rat aorta (5-HT(2A), 5-HT(2B), 5-HT(1B), 5-HT(7)) as well as to study the known 5-HT(2A) receptor-mediated constrictor response and investigate the influences of endothelium and preconstriction on the tissue in that response. A slight endothelium- and concentration-dependent relaxant effect was observed for 5-HT in aorta precontracted with either 5 microM phenylephrine (PE) or 1 microM prostaglandin F2alpha (PGF2alpha) in the presence of 0.3 microM ketanserin. EC50 values for 5-HT and alpha-methyl-5-HT relaxant responses after PE were 43.10 +/- 4.00 and 57.11 +/- 8.01 nM, respectively. pK(B) values for antagonists cyproheptadine and rauwolscine were 8.92 +/- 0.22 and 7.15 +/- 0.12, respectively. In nonprecontracted tissues, the contractile potency of 5-HT was higher in the absence of endothelium (EC50, degreesM): 2.60 +/- 0.28 and 4.12 +/- 0.21 in the absence and in the presence of endothelium, respectively. The differences were statistically significant (p<0.05). In precontracted tissues, the differences in EC50 values (2.22 +/- 0.40 and 4.65 +/- 0.60 microM without and with endothelium, respectively) were also statistically significant (p<0.05). pK(B) values for the 5-HT(2A) antagonist ketanserin were similar under all conditions tested. In conclusion, under our experimental conditions there are two functional 5-HT receptors in rat aorta: 5-HT(2A) contractile receptor in smooth muscle and a high-affinity relaxant receptor that mediates a very slight response and the pharmacology of which could be compatible with an endothelial 5-HT(2B) receptor.

Activation of Erk mitogen-activated protein kinase proteins by vascular serotonin receptors

We previously demonstrated that 5-hydroxytryptamine 2A (5-HT 2A ) receptor-mediated rat arterial contraction was dependent on activation of tyrosine kinases, including mitogen-activated protein kinase (MAPK) kinase. In the current study, we examined arterial smooth muscle for the presence of serotonin (5-hydroxytryptamine, 5-HT) 5-HT 1B, 5-HT 1D, 5-HT 1F, 5-HT 2A, 5-HT 2B, and 5-HT 7 receptor mRNA and hypothesized that, if present, activation of these receptors would stimulate the extracellular signal-regulated kinase (Erk) MAPK pathway and an Erk MAPK-dependent contraction. RT-PCR analyses of rat aortic smooth muscle cells, cultured and fresh, indicated the presence of 5-HT 1B, 5-HT 1D, 5-HT 1F, 5-HT 2A, 5-HT 2B, and 5-HT 7 receptor mRNA. The 5-HT 1B agonists RU24969 and CGS12066B, 5-HT 1B/1D/1F receptor agonist sumatriptan, and 5-HT 2B receptor agonist BW723C86 (10(-9) - 10(-4) M ) did not contract the aorta, nor did the 5-HT 7 receptor antagonist LY215840 leftward shift 5-HT-induced contraction. The 5-HT 1E/1F receptor agonist BRL54443 induced contraction, but this was abolished by the 5-HT 2A/2C receptor antagonist ketanserin (10 nM ); contraction was not observed with a different 5-HT 1F receptor agonist, LY344864. 5-HT and alpha-methyl-5-HT produced a concentration-dependent increase in Erk MAPK activity in cultured aortic smooth muscle cells and in aorta contracted with these agonists. All other agonists were inactive; a high concentration of BRL54443 (10 microM ) stimulated Erk MAPK activation (150% basal). Thus, while mRNA and possibly protein for multiple 5-HT receptors are present in aortic smooth muscle, only the 5-HT 2A receptor plays a significant role in directly modulating contractility and activating the Erk MAPK pathway.