Influence of Temperature Stress on Uptake of P³² in the Rat

¹ From the Zoology Department, University of Arkansas, Fayetteville, Arkansas

Different groups of rats were individually exposed to cold (2° ± 1.5°C) and hot (35° ± 1.5°C) environments for periods of 10, 23 and 29 or 30 days. After each period of exposure to either heat or cold a group of rats was dosed with tracer phosphorus, each rat receiving an intraperitoneal injection of about 20 µc P³². The rats were returned to the hot or cold environments and were killed after 48 hours. Five control rats were treated similarly but were kept at ordinary room temperatures. Measurements of P³² and total P on liver, bone, paired adrenals, brown fat and body fat showed that the percentage of the injected dose was significantly higher in heat-stressed as compared with cold-stressed rats in liver, bone and adrenal tissue. The percentage of injected dose in brown fat was significantly higher in cold-stressed rats than in heat-stressed rats. No significant differences were apparent for body fat. Observed differences in relative specific activity in different tissues from heat- and cold-stressed rats were interpreted primarily on a dilution basis. Evidence of acclimation to heat and cold after exposure periods of 29–30 days was provided by the reappearance of visible fat depots, recovery of body weight and adrenal weight changes. These findings suggest that the thermal environment of the animal must be carefully considered in any interpretation of tracer isotope studies concerned with metabolic processes.