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 mM 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 or the hydroosmotic effect of arginine vasopressin — mediated by V₂-receptors.