Mechanism of diuretic action of U-62,066E, a kappa opioid receptor agonist.

The mechanism of the diuretic action of U-62,066E, a highly selective kappa opioid agonist, was examined in unanesthetized rats and in isolated perfused inner medullary collecting ducts (IMCD). In Long-Evans rats, U-62,066E caused a dose-dependent increase in urine flow and a decrease in urine osmolality without affecting urinary excretion of Na+. The diuretic effect of U-62,066E was blocked by MR-2266, a kappa opioid receptor antagonist. U-62,066E showed no diuretic effect in homozygous hereditary diabetes insipidus rats (Brattleboro strain). In water-deprived rats, U-62,066E markedly inhibited plasma arginine vasopressin (AVP) levels through a kappa receptor-mediated mechanism. In rat IMCD perfused in vitro, 10(-5) M U-62,066E did not inhibit either the baseline or the AVP-stimulated osmotic water permeability. We conclude that the inhibition of the release of AVP is the major if not the entire mechanism of the diuretic action of U-62,066E in rats. Although we ruled out the effect of this drug on the water permeability of IMCD, possible direct effects on other nephron structures remain to be established.