Effects of Water Deprivation in Rats with Polydipsia and Polyuria Due to Long‐term Administration of Lithium

Wistar rats with Li‐induced polydipsia and polyuria (group 3) were deprived of water in order to examine their maximal urinary concentrating ability. For comparison, water deprivation was also achieved in rats with “polydipsia” induced by replacing the drinking water with 5 % glucose (group 1) and in rats with hereditary hypothalamic diabetes insipidus (group 2). The animals were totally deprived of water either for 72 hours or until 20 % loss of body weight had been obtained. Body weight, urine flow and urine osmolality were recorded every 6 hour, and serum osmolality at maximal dehydration. The urine osmolality was initially less than 250 mosm/kg in all groups. Maximal urine osmolality recorded during water deprivation was (1) 2732±100, (2) 1067±84, and (3) 1200±216 (S.D.) mosm/kg. Under the same conditions normal Wistar rats concentrated the urine to 3529±170mosm/kg. Terminal serum osmolality was (1) 310±1, (2) 346±9, and (3) 390 ±31 mosm/kg as compared to 307±2 mosm/kg in normal Wistar rats. During water deprivation, the urine flow was diminished more rapidly and to a lower level in group (1) than in groups (2) and (3). The results indicate that rats with Li‐induced polydipsia and polyuria exhibit marked impairment of the renal concentrating ability. Nothing in the results suggests Li‐polyuria to be secondary to a primary polydipsic action of the lithium ion.