Potentiation by quipazine of adrenergic transmission in mesenteric arteries of spontaneously hypertensive rats

Hemodynamic and renin responses to (+-)-DOI, a selective 5-HT2 receptor agonist, in conscious rats

The effect of the selective 5-HT2 agonist (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI) on arterial pressure (AP), heart rate (HR), renal blood flow (RBF) and plasma renin activity (PRA) was determined in conscious rats. DOI increased AP and PRA, but decreased HR and RBF. All responses to DOI were abolished by central (LY 53857) or peripheral (xylamidine) 5-HT2 antagonists. Prazosin did not alter the AP or HR response to DOI. Chlorisondamine abolished the bradycardia but slightly increased the hypertension produced by DOI, while enalapril attenuated the pressor response. No further reduction was produced by the combination of enalapril and prazosin. Propranolol attenuated but did not eliminate the renin response, and blocked the bradycardia elicited by DOI. The data suggest that DOI activates 5-HT2 receptors located on vascular smooth muscle and/or the circumventricular organs of the brain to: (1) increase AP and reflexly decrease HR, (2) decrease RBF and (3) increase PRA. The hypertension is mediated by angiotensin II and direct vascular effects whereas the increase in PRA is mediated by an interaction of increased sympathetic nerve activity and decreased renal perfusion pressure.

Effects of perfusion flow rate, prostaglandin F2 alpha, phenylephrine, and serotonin on isolated, perfused brains of spontaneously hypertensive rats

Effects of perfusion flow rate and three vasoconstrictors, phenylephrine, prostaglandin F2 alpha (PGF2 alpha) and serotonin, on isolated, perfused brain preparations of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY) were investigated. The basal perfusion pressure of the cerebral vascular beds at a flow rate of 2.5 ml/min was 48 +/- 3 mm Hg (n = 11) in SHR and 32 +/- 2 mm Hg (n = 12) in WKY (P less than 0.005). The perfusion pressures at all flow rates tested (2.5-6.5 ml/min) in SHR were significantly greater than those in WKY. Concentration-perfusion pressure curves for the vasoconstrictors showed that the brain vascular bed was much more reactive to serotonin compared with phenylephrine and PGF2 alpha. EC50 values (-logM) for serotonin in the perfused brains of SHR and WKY were 7.0 +/- 0.06 (n = 10) and 6.5 +/- 0.06 (n = 11), respectively (P less than 0.01). There were no differences in EC50 values for phenylephrine or PGF2 alpha between SHR and WKY. Exogenous serotonin and phenylephrine caused significantly greater maximal vasoconstrictor responses in SHR compared with WKY, while the pressor response to PGF2 alpha was very weak and no significant difference between SHR and WKY preparations was observed. These results indicate that cerebral vascular beds in SHR exhibit higher cerebrovascular resistance than those in WKY. and that reactivity and sensitivity to serotonin and reactivity to phenylephrine in SHR rats are enhanced to a greater extent compared to WKY.

Excitatory and inhibitory effects of 5-hydroxytryptamine in mesenteric arteries of spontaneously hypertensive rats

Some of the presynaptic and postsynaptic excitatory and inhibitory actions of 5-hydroxytryptamine (5-HT) in the rat mesenteric arteries were reexamined with particular reference to the genetic hypertensive rat model. Mesenteric arteries were perfused and the perfusion pressure monitored in the presence or absence of 5-HT, norepinephrine or periarterial sympathetic nerve stimulation. The vasoconstrictor response to 5-HT was resistant to prazosin but effectively inhibited by cyproheptadine and ketanserin. The vasoconstrictor responses to norepinephrine and nerve stimulation were markedly potentiated by 5-HT, and this potentiation was blocked by ketanserin at concentrations which inhibited the 5-HT-induced vasoconstriction, while much higher concentrations were required for cyproheptadine. No significant difference was found in these regards between mesenteric arteries from the spontaneously hypertensive rats (SHR) and those from the normotensive Kyoto Wistar rats (WKY). 5-HT significantly increased the nerve stimulation-evoked 3H overflow in [3H]norepinephrine-treated mesenteric arteries of SHR, but reduced the 3H overflow in the WKY preparations. These results suggest that ketanserin-sensitive 5-HT2 receptors are involved in the potentiating effect of 5-HT in the rat mesenteric arteries, and that an increase in transmitter release by 5-HT may contribute to its potentiation of nerve stimulation-induced vasoconstriction in SHR.