The Effects of Some External Factors upon the Metabolism of the Rat

Abstract

The oxygen consumption of two adult female and two young male rats in the first 20 hours after food (2 a.m. to 10 p.m.) was high at the start and reached a minimum slightly above the basal level at midday. After 4 p.m. the metabolism increased again and in the last hours of measurement was from 13 to 50 per cent higher than during the middle of the day. The rats were restless before 6 a.m., quiet during the middle of the day, and active after 4 p.m. The 24-hour heat production of the three rats per 200 gm. of body weight, calculated from the oxygen consumption measured between 2 a.m. and 10 p.m., was from 13 to 31 per cent above the basal heat production calculated from the oxygen consumption measured under conditions of repose between 10 a.m. and 4 p.m. Hence, for comparative purposes, the basal metabolism of the rat should be measured only between 10 a.m. and 4 p.m. The metabolism of four adult male rats and four young females did not vary with changes from daylight to complete darkness between 10 a.m. and 4 p.m. The metabolism of adult male rats increased, on the average, 7.3 per cent per degree decrease in environmental temperature below 30°C. That of young, growing male rats increased only 3.8 per cent. The rectal temperatures of adult males averaged 37.7° at an environmental temperature of 17° and 37.3° at 30°C. The rectal temperatures of young, growing male rats were essentially the same (38.0°C.) at 20°, 25°, and 30°C. At thermic neutrality the metabolism of female rats was lower than that of males, both at young and adult ages, and with both sexes the metabolism decreased with age.