Vascular smooth muscle serotonin and alpha-adrenoceptors

Rat isolated perfused tail arteries were used to investigate interactions between serotonin receptors and alpha-adrenoceptors. Ketanserin was shown to be a potent serotonin antagonist (pA2 = 9.17, s.e.m. = 0.06, n = 6) which also antagonized phenylephrine (pA2 = 7.47, s.e.m. = 0.10, n = 4) and noradrenaline (pA2 = 7.55, s.e.m. = 0.14, n = 6). Ketanserin reduced the maximal response to serotonin but not to phenylephrine or noradrenaline. Prazosin antagonized phenylephrine (pA2 = 9.60, s.e.m. = 0.12, n = 5) and noradrenaline (pA2 = 9.14, s.e.m. = 0.11, n = 6) and had no effect on maximal responses. Prazosin reduced the maximal response to serotonin but did not displace the dose-response curve. These results are interpreted to indicate the existence of separate, but overlapping, serotonin and alpha-adrenoceptors.