VASOPRESSIN RECEPTORS INVOLVED IN ADRENERGIC NEUROTRANSMISSION IN THECIRCULAR MUSCLE OF THE HUMAN VAS-DEFERENS

We studied the effects of vasopressin on the adrenergic responses of i n vitro preparations of circular muscle from the vas deferens obtained from 28 men undergoing elective vasectomy. Vasopressin (3 X 10(-9)-3 X 10(-8) M) enhanced the phasic contractions elicited by electrical fi eld stimulation and noradrenaline. This potentiation was blocked by th e vasopressin V-1 receptor antagonist d(CH2)(5)Tyr(Me)vasopressin (10( -6) M) but not by the vasopressin V-2 receptor antagonist [d(CH2)(5), D-Ile(2),Ile(4),Arg(8)]vasopressin (10(-6) M). The Ca2+ antagonist nif edipine (10(-6) M) did not affect the potentiation of electrical field stimulation induced by vasopressin and noradrenaline but reduced KCl- induced contractions and abolished the induction of phasic activity by vasopressin in the presence of KCl. The results demonstrate that vaso pressin, in addition to its direct contractile effects, strongly poten tiates contractions of human vas deferens elicited by adrenergic stimu lation. Both the direct and indirect effects of vasopressin appear to be mediated by vasopressin V-1 receptor stimulation and are independen t of Ca2+ entry through dihydropyridine Ca2+ channels. (C) 1998 Elsevi er Science B.V. All rights reserved.