In vivo diuretic actions of renal vasopressin V₁ receptor stimulation in rats

The specific vasopressin V₁ receptor agonist (V₁AG; [Phe²,Ile³,Orn⁸]vasopressin) was infused (2.0 ng · kg^-1 · mi^-1) into the renal medullary interstitial space to determine the effects of selective medullary V₁ receptor stimulation on sodium and water excretion in normal rats. Responses were compared with those of arginine vasopressin (AVP) and vasopressin V₂ receptor stimulation resulting from infusion of a V₁ receptor antagonist with AVP. Medullary infusion of V₁AG or AVP in euvolemic rats produced no changes in hemodynamics or glomerular filtration rate. V₁AG increased urine flow > 60% in euvolemic rats, whereas no change was observed with AVP. This response could not be explained by a rise of arterial pressure or by volume retention. With V₂ stimulation in euvolemic rats, urine flow was decreased. In water diuretic rats, V₁AG produced no change, whereas AVP infusion decreased urine flow. The results provide in vivo evidence that tubular V₁ vasopressin receptor activity results in increased urine flow and thereby modulates the antidiuretic actions of vasopressin in the euvolemic state.