RECEPTOR SUBTYPES INVOLVED IN RELAXATION AND CONTRACTION BY ARGININE-VASOPRESSIN IN CANINE ISOLATED SHORT POSTERIOR CILIARY ARTERIES

Arginine vasopressin (AVP) produced relaxations at low concentrations( 10(-11) and 10(-10) M) and contractions at higher concentrations in ca nine ciliary arterial strips with endothelium, partially contracted wi th prostglandin F-2 alpha. The AVP-induced relaxation was abolished or reversed to a contraction by removal of the endothelium or treatment with N-G-nitro-L-arginine. The effect of this antagonist was reversed by L-arginine. The relaxant response was inhibited dose-dependently by SR49059 (10(-10)-10(-9) M), [Pump(1),Tyr(Me)(2)]Arg(8)-vasopressin (P MP-AVP) (10(-10)-10(-9) M), V-1 receptor antagonists, and OPC31260 (3 x 10(-8) M), a reported V-2 receptor antagonist, but not by OPC21268 ( 10(-7)-10(-6) M), a reported V-1 antagonist. In the endothelium-denude d strips, the AVP-induced contraction was attenuated by SR49059, PMP-A VP and OPC31260, but not by OPC21268. It is concluded that AVP in low concentrations elicits intense relaxation of canine ciliary arteries, possibly due to nitric oxide synthesized in association with activatio n of the endothelial V-1 receptor subtype. AVP-induced contractions ap pear to be mediated also by the V-1 receptor in smooth muscle. Antagon istic selectivities of the OPC compounds to vasopressin receptor subty pes could not be seen in this particular material.