Acute effects of antidiuretic hormone on urinary prostaglandin excretion

Although it is well established that chronic treatment with antidiuretic hormone increases renal prostaglandin (PG) excretion, the effects of short-term infusions are controversial. Therefore, in the present study the effect of acute administration of arginine vasopressin on urinary PG excretion was investigated in conscious Brattleboro rats and in water-diuresing Long-Evans rats. Water balance was kept constant during arginine vasopressin infusion. Arginine vasopressin caused a significant, dose-related and reversible increase in urinary PG excretion within 20 min in both models. Similar results were obtained during the infusion of 1-deamino-8-D-arginine vasopressin in the Brattleboro rat. Normalization of the hydropenia of Brattleboro rats by infusion of large amounts of hypotonic fluid failed to elevate urinary PG excretion. These results give no support to the hypothesis that the acute enhancement of urinary PG excretion by vasopressin is mediated through either vasoconstriction or volume retention or induction of cyclooxygenase, but rather they indicate that antidiuretic hormone can increase renal PG synthesis through a more direct mechanism in vivo.