Effects of lithium on circadian cycles in food and water intake, urinary concentration and body weight in rats.

Circadian cycles in food and water intake, urinary concentration and body weight were studied in normal rats, lithium-polyuric rats, rats with hereditary diabetes insipidus and rats infused continuously with arginine vasopressin (ADH) 10 mU/hr IV. Normal rats showed characteristic cycles in body weight and urine flow and osmolality with diuresis in the dark (eating and drinking period) and antidiuresis in the light (resting) period. ADH-infusion eliminated the circadian cycle in urine osmolality, but not in urine flow, suggesting that factors besides. ADH mediate the antidiuresis during the resting period. Rats with ADH-deficient diabetes insipidus showed obliteration of all circadian cycles studied, indicating the importance of the renal concentrating mechanism for the amplitude of the circadian-cycles, observed in normal rats. In rats treated with lithium, circadian cycles in body weight and urine osmolality were absent. However, there was a significant circadian variation in urine flow and food and water consumption with peak values during the light period, when normal rats showed minimal values. It is concluded that in rats lithium causes marked changes in circadian cycles, which probably cannot be explained by its effect on the renal concentrating mechanisms alone.