A Seasonal Occurrence of Ketonuria in Fasting Rats Accompanied by Changes in Carbohydrate Metabolism.

Abstract

It was found that in the summer months, from the 24th to the 48th hour of fasting, an average of 6.1 mg. of total acetone bodies was excreted per 100 gm. of body weight per 24 hours. The determinations were made by Van Slyke's method. Beginning with late September, the excretion diminished to 1.9 mg. per 100 gm. of body weight per 24 hours. Non-fasting rats excreted 0.4 mg. per 100 gm. per 24 hours. Metabolism experiments, made more or less continuously for a whole year, showed that from October until May the fasting respiratory quotient was in most instances above 0.700, while the opposite was true in the summer months. Since the housing, food and care of the rats was the same throughout the year, the appearance of ketonuria in the summer months was attributed to a seasonal change in fat metabolism. Apparently, in the winter months the fasting rat can oxidize its body fat completely without the simultaneous oxidation of carbohydrates, while this is no longer possible in the summer months. The appearance of ketonuria in fasting rats in the summer months offered a possibility of studying various phases of carbohydrate metabolism during that period.

In the winter months the intravenous glucose tolerance of nonfasting and of fasting rats was found to be close to 2.5 gm. per kilo per hour. 1 , 2 In the summer months the tolerance of non-fasting rats remained unchanged, while the tolerance of fasting rats was diminished to 1.6 gm. per kilo per hour or by 36 per cent. In order to decide, whether a decrease in sugar oxidation or in glycogen formation was responsible, recovery experiments were undertaken. In the winter months, from 750 mg. of glucose absorbed from the intestine per 100 gm. of body weight per 4 hours, 281 mg. were oxidized and 388 mg. were converted into glycogen.