IN-VIVO DIURETIC ACTIONS OF RENAL VASOPRESSIN V-1 RECEPTOR STIMULATION IN RATS

The specific vasopressin V-1 receptor agonist (V(1)AG; [Phe(2),Ile(3), Orn(8)]vasopressin) was infused (2.0 ng . kg(-1). min(-1)) into the re nal medullary interstitial space to determine the effects of selective medullary V-1 receptor stimulation on sodium and water excretion in n ormal rats. Responses were compared with those of arginine vasopressin (AVP) and vasopressin V-2 receptor stimulation resulting from infusio n of a V-1 receptor antagonist with AW. Medullary infusion of V(1)AG o r AVP in euvolemic rats produced no changes in hemodynamics or glomeru lar filtration rate. V(1)AG increased urine flow >60% in euvolemic rat s, whereas no change was observed with AW. This response could not be explained by a rise of arterial pressure or by volume retention. With V-2 stimulation in euvolemic rats, urine flow was decreased. In water diuretic rats, V(1)AG produced no change, whereas AVP infusion decreas ed urine flow. The results provide in vivo evidence that tubular V-1 v asopressin receptor activity results in increased urine flow and there by modulates the antidiuretic actions of vasopressin in the euvolemic state.