Induction of drinking by insulin in the rat

Unanesthetized rats were injected i.v. either with commercial regular insulin, or the diluting fluid of the commercial insulin solution used, or with 0.9 percent NaCl, and placed in individual cages containing no food. Water intake was measured for 2 hr. Injection of the hyposmolar diluting fluid containing glycerol and phenol slightly, but significantly, enhanced the water intake. Insulin in doses from 0.05 to 43.0 U/kg induced an additional drinking response, while 0.02 U/kg had no effect. A linear log dose--response for insulin-induced drinking was obtained between 0.05 and 21.0 U/kg. Small doses of insulin, thus, undoubtly, enhance water intake. Insulin could play a minor role in body water honeostasis in mammals.