Receptor mechanisms for 5-hydroxytryptamine (5-HT) in isolated ovine umbilical vein

Effects of congeners of amphetamine on the human heart

Central stimulatory and hallucinogenic drugs of abuse like amphetamine and most congeners of amphetamine can have cardiac harmful effects. These cardiac side effects can lead to morbidities and death. In this paper, we review current knowledge on the direct and indirect effects of these amphetamine congeners on the mammalian heart-more specifically, the isolated human heart muscle preparation. In detail, we address the question of whether and how these drugs affect cardiac contractility and their mechanisms of action. Based on this information, further research areas are defined, and further research efforts are proposed.

Mediation by 5-HT2 receptors of 5-hydroxytryptamine-induced contractions of human placental vein

1. In isolated human placental chorionic vein segments, 5-hydroxytryptamine (5-HT; 10(-8) to 5 x 10(-5) M) elicited concentration-dependent contractions with EC50 = 5.5 (5.2-5.7) x 10(-8) M) and Emax = 93.1 +/- 7.3% of 75 mM KCl-induced contraction. 2. The agonist of 5-HT2 receptors, alpha-methyl-5-hydroxytryptamine, and the selective agonist of 5-HT1 receptors, N,N-dipropyl-5-carboxamidotryptamine and 5-carboxamidotryptamine, induced pronounced concentration-related contractions, which reached 71.1 +/- 6.0%, 53.0 +/- 5.0% and 75.0 +/- 7.8% at the highest dose tested, respectively. The agonist of 5-HT3 receptor, 2-methyl-5-hydroxytryptamine, reached a maximum averaging 36.7 +/- 5.1% of the maximal response to KCl. 3. The 5-HT1 and 5-HT3 receptor antagonists, methiothepin and metoclopramide (10(-7) to 10(-6) M) did not alter the response to 5-HT. However, ketanserin (10(-7) to 10(-6) M), a 5-HT2 receptor antagonist, induced significant inhibition of the concentration-response curve to 5-HT. 4. Contractile responses to 5-carboxamidotryptamine and 2-methyl-5-hydroxytryptamine were not affected by methiothepin and metoclopramide, respectively, whereas ketanserin significantly attenuated the contractile response to these agonists. 5. In conclusions, our study shows that 5-HT2 receptors mediate contraction of the human placental vein with no obvious role for 5-HT1-like, or 5-HT3 receptors.

Pharmacological characterization of alpha-adrenoceptors in the bovine median caudal artery

This study was initiated to characterize alpha-adrenoceptors in the isolated bovine median caudal (tail) artery preparation for use as a model of blood vessels in the extremities of cattle. Prazosin shifted the concentration-response relationship for noradrenaline and phenylephrine to the right with pA2 values of 8.74 and 9.04, respectively. Against noradrenaline, phentolamine yielded a pA2 of 7.36. The concentration-response relationship for medetomidine was not inhibited by rauwolscine or idazoxan. The noradrenaline KA was 3.11 microM. These results suggest that catecholamines elicit alpha-adrenoceptor-mediated contractions primarily through alpha1-adrenoceptors and not alpha2-adrenoceptors.

5-Hydroxytryptamine induces endothelium-independent relaxations of sheep pulmonary vein: role of cyclic nucleotide

5-Hydroxytryptamine produced concentration-dependent relaxations in isolated sheep pulmonary vein, which were insensitive to removal of the endothelium. 5-Hydroxytryptamine stimulated concentration-dependent increases of cyclic AMP levels in the pulmonary vein, and there was a significant linear correlation between relaxations elicited by 5-hydroxytryptamine and tissue cyclic AMP formations. The soluble guanylate cyclase inhibitor methylene blue (10 microM) failed to block 5-hydroxytryptamine-induced relaxations. The results suggest that 5-hydroxytryptamine-induced relaxations of sheep pulmonary vein are mediated, at least in part, by increases of tissue cyclic AMP levels.

Effect of R(-)2,5-dimethoxy-4-methylamphetamine on uterine and umbilical blood flow in conscious pregnant sheep

Pregnant sheep and their fetuses were instrumented between 110 to 120 days of gestation (term, 145 days) for monitoring maternal and fetal arterial blood pressure, heart rate and blood flow in the maternal uterine and fetal intra-abdominal umbilical arteries. The administration of 2,5-dimethoxy-4-methylamphetamine (DOM, a 5-HT2 agonist) i.v. to the ewe in doses ranging from 1 to 20 micrograms/kg of ewe body weight produced dose-dependent decreases in the blood flow of the uterine and umbilical arteries. This was accompanied by an increase in the arterial blood pressure of the mother and fetus and a decrease in the fetal heart rate. DOM significantly increased the vascular resistance to blood flow in the uterine and umbilical arteries. The maximal increase in the vascular resistance of the uterine and umbilical arteries was 19.6- and 2.6-fold, respectively. Ketanserin, a 5-HT2 antagonist (1 mg/kg), administrated 30 min prior to DOM significantly inhibited the reduction in blood flow in the uterine and umbilical arteries to DOM and blocked the increased vascular resistance in these vessels. The inhibitory effects of ketanserin on the responses to DOM in the uterine and umbilical arteries were surmountable. Our results indicate that DOM is a potent constrictor of the uterine and umbilical vasculature which may lead to fetal distress as evidenced by a decrease in fetal heart rate and arterial blood PO2. 5-HT2 receptor stimulation by DOM may be involved in these effects since they were blocked by ketanserin.

Characterization of alpha-adrenoceptors mediating contraction in isolated ovine umbilical vein

Responses to alpha-adrenoceptor agonists were studied in isolated umbilical vessels obtained from fetal lambs within 2 weeks of term (term = 145 days). Norepinephrine produced concentration-dependent contractions of the umbilical vein, but not in the umbilical artery. The contraction elicited by norepinephrine in the umbilical vein was not potentiated by cocaine (10(-5) M). Epinephrine also produced contractions of the umbilical vein with a potency similar to that of norepinephrine. Phenylephrine was less potent than norepinephrine while clonidine and xylazine were inactive in producing contractions of the umbilical vein. The dissociation constant (KA) of norepinephrine in the umbilical vein was 172 +/- 41 nM. There was little, if any, alpha-adrenoceptor reserve in the umbilical vein. Contraction produced to norepinephrine in the umbilical vein was effectively blocked by prazosin and phentolamine. Yohimbine was 500 times less potent than prazosin in blocking norepinephrine-induced contraction in the umbilical vein. Idazoxan only minimally antagonized the contractions elicited to norepinephrine. We conclude that alpha 1-adrenoceptors are present and mediate vasoconstriction in the ovine umbilical vein and that alpha 2-adrenoceptors are not present in this tissue.