Serotonin-induced vasoconstriction in rabbit femoral artery: mediation by both 5-HT2 serotonergic and alpha 1-adrenoceptors.

We determined the receptors mediating the contractile response of the rabbit femoral artery to serotonin in isolated vascular rings mounted in tissue baths for the measurement of isometric contraction. Serotonin elicited a biphasic concentration-response curve (CRC). The threshold and maximal concentrations of the first phase were 0.03 and 3 microM, respectively. The respective values for the second phase were 10 and 1,000 microM. Benextramine, a selective, irreversible alpha-adrenoceptor antagonist, eliminated the second phase. Similar results were obtained with benextramine in femoral arteries acutely denervated with 6-hydroxydopamine (6-OHDA). In contrast, the reversible, competitive 5-HT2 antagonist ketanserin shifted the first phase of the serotonin CRC to the right ina concentration-dependent manner but had little or no effect on the second phase. No evidence for functional alpha 2-adrenoceptors was found. We conclude that the first phase of the serotonin CRC in rabbit femoral artery was mediated predominantly by 5-HT2 receptors and that the second phase was mediated by alpha 1-adrenoceptors.