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 renal medullary interstitial space to determine the effects of selective medullary V-1 receptor stimulation on sodium and water excretion in normal rats. Responses were compared with those of arginine vasopressin (AVP) and vasopressin V-2 receptor stimulation resulting from infusion of a V-1 receptor antagonist with AW. Medullary infusion of V(1)AG or AVP in euvolemic rats produced no changes in hemodynamics or glomerular filtration rate. V(1)AG increased urine flow >60% in euvolemic rats, 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 decreased urine flow. The results provide in vivo evidence that tubular V-1 vasopressin receptor activity results in increased urine flow and thereby modulates the antidiuretic actions of vasopressin in the euvolemic state.