[Changes in water metabolism in rats under the influence of naloxone: role of vasopressin].

The effect of naloxone (0.6 mg; 1.2 mg; 2.4 mg X kg-1) were compared in normal Long Evans (N) and Brattleboro (D.I.) conscious rats. Naloxone did not change the values of drinking, diuresis, food intake, blood pressure, Na+ and K+ urinary excretion measured during 24 hours. During the two hours following drug injection, naloxone (1.2 and 2.4 mg X kg-1) reduced diuresis in normal as well as in D.I. rats. Water drinking was only modified in D.I. rats: this effect was shown to be a consequence of antidiuresis. These results suggest that the antidiuretic properties of naloxone are independent of vasopressin secretion. They do not support in a role of opiate receptors on vasopressin secretion in normal hydrated animals.