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The Metabolism of the Albino Rat During Prolonged Fasting at Two Different Environmental Temperatures

(From the Laboratory of the Connecticut Agricultural Experiment Station and the Laboratory of Physiological Chemistry, Yale University, New Haven, and the Nutrition Laboratory of the Carnegie Institution of Washington, Boston.)

The metabolism of female albino rats (average age about 200 days) was studied during fasting prolonged until the occurrence of death. Four rats were maintained at an environmental temperature of 26°C. and four other rats at a temperature of 16°C. A multiple-chamber, closed-circuit respiration apparatus was employed, and the oxygen consumption was directly measured in periods of from one to four hours in length.

The rats fasting at 26°C. lived on the average for 161/2 days and lost 49 percent of their initial body weight. The animals fasting at 16°C. survived on the average a shorter time, 11 days, and lost somewhat less weight, 44 per cent. The longest fast was at 26°C. and lasted 25 days.

The total metabolism of the rats fasting at 26°C. (but measured at 28°C.) was at a lower level than was that of the group fasting and measured at 16°C., but the decrease in the total metabolism as the fast progressed was greater, amounting on the average to 36 per cent at the end of the seventh day as compared with a decrease of 19 per cent noted with the rats at 16°C., fasting the same length of time. The metabolism per unit of weight decreased much less markedly than the total metabolism, in the case of both groups, and tended to become fairly constant. Per square meter of body surface the heat production of the group at 26°C. decreased distinctly as the fast progressed, from an initial average of 700 calories to a level at the end of the fast as low as 400 or 450 calories per 24 hours. With the group at 16°C. the heat production on this basis averaged 1260 calories at the 22nd hour and fell only imperceptibly in 7 days.

The basal metabolism of these adult female rats fasting at 26°C. (but measured at 28°C.) and about 24 hours after food was from 600 to 700 calories per square meter of body surface per 24 hours.

The length of survival of these fasting rats refutes the supposition that small animals succumb quickly to fasting.