Regulation of water intake by rats deprived of food

Abstract

Rats deprived of food drink water in excess of apparent requirement. To investigate the reason for this apparently excessive intake, work loads were coupled to drinking, by requiring the rats to press a lever for water. In fed and re-alimented states, rats maintained their water intake up to a high work rate for water and accepted a high total work load, but at the highest work rate water intake decreased and the general metabolic pattern was distorted. For 2 days of food deprivation rats reduced their water intake with increasing work rate and accepted only a low total work load until urine concentration lay within the normal (fed) range. Further increase in coupled work rate distorted general metabolic patterns and the span of constant water intake was short. It is suggested that water intake is regulated to minimize energy expenditure subject to constraints imposed by limiting processes such as maximum ability to concentrate urine.