Water uptake by Rana temporaria: effects of diuretics and the renin--angiotensin system, and nephrectomy

Adult Rana temporaria, acclimated to tap water or hyperosmotic (0.9% NaCl saline) media, were injected with Acetazolamide, Frusemide, or Captopril, or were nephrectomized and injected with captopril. Saline-injected animals served as controls. Total water flux and drinking rates were determined by body weight changes and by the rate of accumulation of an environmental marker (phenol red) in the gut, respectively. Changes in plasma corticosteroids and ion concentrations were also assessed. Acetazolamide and frusemide produced hyponatraemia in tap water-acclimated animals, but induced increased aldosterone levels in frogs in both environments. Captopril reduced body weight and aldosterone levels of tap water frogs, but had no effect on plasma ion composition. Animals treated with captopril on immersion in saline had plasma hypoosmotic to their environment. Saline-acclimated frogs drank less environmental water than did those in tap water. Captopril, acetazolamide, and frusemide all stimulated drinking rates of saline-acclimated frogs; captopril, however, had no effect on the drinking rates of nephrectomized animals, indicating that the dipsogenic actions of this drug are probably reflected by inhibition of the renin-angiotensin system. In tap water animals, acetazolamide stimulated drinking, while frusemide stimulated integumental water uptake. No correlation was apparent between plasma aldosterone and corticosterone concentrations, or between changes in body weight and drinking rates. This suggests that there are independent mechanisms controlling aldosterone and corticosterone secretion, as well as integumentary and buccal uptake of water in R. temporaria.