Vasopressin V1-antagonist increases the hydroosmotic response to arginine vasopressin in frog urinary bladder.

V1-antagonist, [Mca1, D-Phe2, Sar7] arginine vasopressin, at a concentration 0.5 nM to 5 nM increased hydroosmotic effect of 5 nM arginine vasopressin in frog urinary bladder. 1 nM V1-antagonist [Mca1, O-Me-Tyr2] arginine vasopressin does not changed hydroosmotic effect of 0.1 nM dibutyryl cAMP. We suggest that-both V1- and V2-receptors are present on epithelial cells of frog urinary bladder and that V1-receptors are involved in the modulation of the hydroosmotic effect of arginine vasopressin-mediated by V2-receptors. by V2-receptors.