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.min-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.