THERMOGENESIS OF BAT (MYOTIS MYOTIS BORKH) DURING AROUSAL FROM HIBERNATION

The arousal from hibernation of the bat Myotis myotis was investigated in order to estimate the contribution of nonshivering thermogenesis and the thermogenic capacity of brown adipose tissue. 1. The arousal of M. myotis (body weight 25 g) at room temperature takes place in about 40 minutes. The increase in skin temperature is more rapid at the neck than at the side of the body; so that a temperature difference of 10° C developped between these two sites of the body. 2. In the first 20 minutes of arousal the rate of the in vivo protein synthesis (incorporation of 1-histidine-2,5-3H into tissue protein within 20 minutes) is reduced to about 1/30 of normal rate, except for the brain cortex in which protein synthesis is reduced to 1/120 of normal rate. With increasing body temperature during arousal the rate of the in vivo protein synthesis increases equally in all tissues and reaches the normal rate at the end of arousal. Brown fat and muscle tissues which have a high thermogenic activity do not show a greater in vivo protein synthesis than the other tissues. 3. The speed of the arousal process depends upon body weight within the species investigated. A Myotis myotis with a body weight of 29 g and large depots of brown fat, increases body temperature about three times faster than an animal which has a body weight of 17 g and only traces of brown fat. 4. During the normal arousal process the concentration of free glycerol in the blood increases from 1,3 mg-% to 25 mg-% (normal concentration 3,8 mg-%). This increase may be caused by the lipid mobilization of nonshivering thermogenesis. After blocking the nonshivering thermogenesis by means of the β-adrenergic blocking agent Propranolol (Dociton, ICI) the following changes occur during arousal: the complete arousal process takes twice the time of normal arousal, the temperature difference between the neck and the side of the body is reduced for about 80 per cent and the remarkable increase in free glycerol in the blood is almost totally depressed (95%). 5. On the basis of the delayed increase in body temperature due to the blocking agent, nonshivering thermogenesis was calculated to account for 55 per cent of total heat production during the normal arousal process. Since brown fat is not the only site of nonshivering thermogenesis this value is too high in order to represent the thermogenic capacity of brown fat. 6. This percentage of nonshivering thermogenesis is not constant in all individuals, but it depends on the relative weight of brown fat. Since small Myotis myotis have less brown fat than bigger individuals there are differences in the contribution of brown fat and nonshivering thermogenesis during arousal, and these differences can also account for individual differences in the speed of rewarming. © 1969 Springer-Verlag.