Factors modifying water metabolism in rats fed dry diets

Abstract

To determine dietary factors which govern water turnover in rats, water intake and output were studied during 24-hour intervals. Rats given water ad libitum and Purina laboratory chow or a synthetic diet voluntarily maintained an antidiuretic state, restricting water intake and excreting urine of nearly maximum concentration. Dietary modifications which have been studied include: addition of large amounts of NaCl or urea; a protein-free diet with or without urea added; and diets containing various levels of Na, K and Cl. Conclusions drawn from these studies are as follows: under most conditions water intake was determined by the minimum urine water for solute excretion or by changes in fecal volume; the degree of antidiuresis maintained by the rats may depend on the electrolyte content of the diet. Nitrogen turnover has an additional influence on water metabolism through the effect of urea excretion on the renal concentrating mechanism. Evidence also presented indicates that Pitressin may act to ‘reset’ the threshold of drinking, with a resulting concentration of body fluids.