EFFECTS ON RENAL SODIUM AND POTASSIUM EXCRETION OF VASOPRESSIN AND OXYTOCIN IN CONSCIOUS DOGS

Renal effects of arginine vasopressin and oxytocin were studied in conscious dogs, made water-diuretic by a waterload equivalent to 2% of body weight. Body water and content of sodium were maintained by separate servo-controlled infusions. Peptides were infused for 60 min at rates of 50 pg kg-1 min-1 (arginine vasopressin) or 1 ng kg-1 min-1 (oxytocin), either separately or combined. Infusions increased plasma arginine vasopressin to 1.9 +/- 0.2 (arginine vasopressin alone) and 1.8 +/- 0.3 pg kg-1 (arginine vasopressin plus oxytocin and plasma oxytocin to 72 +/- 5 (oxytocin alone) and 77 +/- 8 pg ml-1 (oxytocin plus arginine vasopressin). Arginine vasopressin or arginine vasopressin plus oxytocin increased urine osmolality similarly by a factor of 13, decreased urine flow to between 5 and 7 % of control and decreased free water clearance. Oxytocin reduced urine flow and free water clearance and increased urine osmolality by a factor of 2. Oxytocin and arginine vasopressin separately increased excretion of sodium from 4 +/- 2 to 15 +/- 6-mu-mol min-1 and from 7 +/- 4 to 25 +/- 13-mu-mol min-1, respectively. Arginine vasopressin plus oxytocin led to a pronounced natriuresis (13 +/- 4 to 101 +/- 27-mu-mol min-1). Arginine vasopressin and arginine vasopressin plus oxytocin increased the excretion of potassium by a factor of 2.5. Oxytocin and arginine vasopressin plus oxytocin increased urinary Na+/K+ ratio by a factor of 3.7. It is concluded, that oxytocin at plasma concentrations of 70-80 pg ml-1 has modest antidiuretic and natriuretic effects and that the combined action of arginine vasopressin oxytocin may elicit supra-additive natriuretic effects.