The effects of long-term oral treatment with chlorothiazide or furosemide on hereditary diabetes insipidus in rats.

The polyuria of homozygous Brattleboro (BB) female rats is halved when they are given chlorothiazide (about 250 mg/day) or furosemide (about 60 mg/day) orally for one day. The effect of chlorothiazide is still found after 16 days of treatment, whereas the effect of furosemide entirely disappears within 5 days. Both diuretics induce chronically increased plasma renin activity (PRA) and decreased natriuresis as long as they are added to the diet; the effect on Na is more evident during furosemide treatment. Urinary urea content as well as urinary osmolality are increased by chlorothiazide and "free water" output is normalized. Furosemide does not affect urea content and decreases urinary osmolality from the start, as compared to untreated BB homozygotes; it raises "free water" output above BB values.