[Effects of clonidine on diuresis and water intake in normal and Brattleboro rats. (author's transl)].

1. The effects of clonidine on water balance were compared in normal (N.) and diabetes insipidus (Brattleboro D.I.) conscious rats. Animals were housed in individual cages and feed food and water ad libitum. The dose of clonidine was 100 microgram . kg-1 by subcutaneous route during consecutive 9 days. A control period of 12 days without drug treatment (only saline as a sham injection) separated the different period treatments. Under these experimental conditions the values of diuresis, water and food intakes, blood pressure were measured every morning before clonidine-treatment. 2. In normal rats, clonidine induced a diuretic and dipsogenic action (fig. 1). In contrast, the drug elicited an antidipsogenic and antidiuretic response in D.I. rats (fig 2). 3. In another series of experiments, the short term responses to clonidine treatment were studied in the two groups of animals. During the two first hours of treatment, clonidine elicited a rapid and marked reduction in water intake in the two groups of animals (table I). In normal rats, the drug also elicited an increase in urine flow. In contrast, in D.I. (Brattleboro) rats, an antidiuretic effect was observed during the first 30 minutes after clonidine- injection but not during the following 30 minutes periods (fig 3). 4. Clonidine increased both the natriuretic and kaliuretic excretion in normal rats, but failed to modify these values in D.I. rats (fig 4). 5. Clonidine decreased blood pressure in the two groups of animals (table II) but failed to modify the values of food intake (table III). 6. These results suggest that clonidine-induced diuresis is related to inhibition of vasopressin (ADH) secretion. Since the early observation of water balance revealed a clonidine antidipsogenic-induced effect in the two groups of animals, it is suggested that vasopressin was not involved in the clonidine induced water intake and that the daily antidiuretic response in Brattleboro (D.I.) rats was only related to the antidipsogenic property of clonidine.