Hibernation and marmot physiology [Hibernation et physiologie de la marmotte].

Résumé

A metabolic survey of the marmot or woodchuck (Arctomys monax) was made to contribute information regarding the physiology of the animal itself and for comparison with other warm-blooded animals that do not hibernate and with cold-blooded animals. As the marmot may be living on one day as a normal warm-blooded animal and on another day more nearly as a cold-blooded animal, it bridges the gap, so to speak, between these two great animal classes. Forty-eight marmots, of both sexes, ranging in weight from 1 to 5 kg, were studied in the non-hibernating and hibernating states, and in the transitional stages of entering and awakening from hibernation. The measurements made included those of body weight changes, insensible perspiration, heart and respiration rates, rectal temperature, respiratory exchange, and water-vapor ouput. The effects of different environmental temperatures upon the various physiological functions were also studied, as well as the body composition after prolonged fasting. Observations were made on several marmots that were under nembutal and subsequently exposed to a cold environment and upon others that were subjected to carbon-dioxide narcosis and cold. The metabolism of the marmot under nembutal was measured and compared with that of the normal marmot in deep hibernation. Analyses were made of the urine of several marmots while fasting and hibernating, including determinations of the total nitrogen and the percentages of nitrogen in the form of ammonia nitrogen, amino-acid nitrogen, urea nitrogen, and preformed creatinine. The study of the respiratory quotients was materially aided by the measurements made on marmots under the influence of nembutal. Contrary to the commonly assumed changes in metabolism due to hibernation, there was not a marked change in the character of the respiratory exchange, the respiratory quotient was not lowered, there was no evidence of a retention of oxygen, and there was no hint of a perturbed oxidation of body material. The protein metabolism underwent no qualitative alteration in hibernation. These two purely chemical findings support the belief that there are no profound anatomical or functional changes associated with hibernation, and all theories involving such an assumption are, therefore, invalided. The marmot, when non-hibernating, has an extremely labile basal heat production average about 400 calories per 10w2/3 per 24 hours. This is much lower than that other warm-blooded animal of similar size at a cell temperature of 37° C. The hibernating marmot simulates the cold-blooded animal to some extent in that when exposed to low environmental temperature it assumes a very low rectal temperature and a very low respiration rate, but its heat production per 10w2/3, even at the lowest level, is at least two or three times that of the cold-blooded animal of approximately equal size having the same lox cell temperature. The monograph concludes with a digest of the main findings and a consideration of the possible causes of hibernation. On fit une étude de la marmotte (Arctomys monax), afin d’obtenir des données portant sur la physiologie de l’animal même, ainsi que pour faire des comparaisons avec d’autres animaux à sang chaud qui n’hibernent pas et aussi avec des animaux à sang froid. Vu qu’un jour la marmotte peut vivre comme un animal à sang chaud tandis qu’un autre elle se rapproche plutôt d’un animal à sang-froid, elle sert de trait d’union, pour ainsi dire, entre ces deux grandes classes animales. On étudia 48 marmottes des deux sexes, dont le poids variait d’un à 5 kg, aussi bien lorsqu’elles n’hibernaient pas que durant l’état d’hibernation, ainsi que dans les phases intermédiaires de l’entrée et de la sortie de l’hibernation. On mesura les changements dans le poids corporel, la transpiration imperceptible, les fréquences cardiaques et respiratoires, la temp