Body Water Content and Turnover in Several Species of Rodents as Evaluated by the Tritiated Water Method

Abstract

Listen

Translate article

Body water content and turnover were determined on 80 rodents, representing 12 species, using the tritiated water method. All experimental rodents were maintained under similar laboratory conditions. Measurements of body water content indicated wide variability in the degree of body fatness. Mean values of body fat as a percentage of body weight ranged from 3.0 to 38.8 per cent for the 12 species. The equation, WTR = n (LBM)b, was used to relate water transfer rate (WTR) to lean body mass (LBM). The overall exponent (b) for 12 species of rodents equaled 0.78 ? 0.044 (standard deviation) and represents the interspecies esti- mate. The exponent computed for three species of the genus Microtus equaled 0.69 ? 0.093. Specific water transfer rates ranged from 0.34 to 1.76 (ml/g'69)/d. In general, water transfer rates were correlated with water availability in the natural habitat of each species. Species inhabiting moist areas had high specific water transfer rates while species inhabiting arid regions had lower specific water transfer rates. Water content of fat-free body tissue is essentially constant among homeo- therms (Reid, 1967). However, the kinetics of body water are variable (Rich- mond et al., 1962). Within the order Rodentia rates of body water turnover are diversified. Rapid rates of water turnover may be found in semiaquatic species such as the muskrat, whereas slower rates of water turnover would be expected for the desert adapted kangaroo rat. Factors influencing body water turnover in rodents include metabolic rate, body size, environment, and species. The introduction of tracers of water has provided a sophisticated tool for determining water content and turnover in biological systems without drasti- cally disturbing the system. Several tracers have been used and compared (Reid et al., 1958). However, tritiated water possesses several advantages over other tracers. It was used in this study. The primary objective of this study was to determine the body water con- tent and turnover in several species of rodents maintained under similar labo- ratory conditions. An ancillary objective was to consider factors contributing to variability in body water turnover in rodents.