Tritiated water turnover in free-living desert rodents

Abstract

1. 1. Tritiated water (HTO) turnover and urine osmolarity were followed in free-living and laboratory maintained desert rodents as indices of the state of their water economy. 2. 2. HTO turnover rates in free-living Peromyscus maniculatus (0.32 of HTO per day) were three times those of the heteromyid rodents ( Dipodomys merriami and Perognathus penicillatus) in the community. 3. 3. HTO turnover varied seasonally in the free-living heteromyids and the magnitude of the seasonal change suggested that the Perognathus made use of torpor in colder months. 4. 4. In laboratory work on Perognathus, HTO turnover was inversely related to body weight and ambient temperature but independent of the protein content of the diet. Urine osmolarity was directly related to ambient temperature and to dietary protein. 5. 5. HTO turnover behaved as would be expected of a water tracer but in all laboratory trials, HTO turnover exceeded actual water turnover as determined by food consumption. 6. 6. The use of HTO turnover as an index of water turnover, with emphasis upon the implications of isotope effects and multi-compartment kinetics, is discussed in light of these findings.