Sexual Variation in the Carbohydrate Metabolism of Rats

Abstract

A distinct variation exists in the rate of development and the extent to which ketosis occurs in normal men and women during the early days of fasting. 1 The present investigation was undertaken to determine whether such a difference can be ascribed to a more rapid depletion of the carbohydrate supply of the female.

Rats were used as experimental animals. In order to insure a uniform content of carbohydrate at the beginning of the test, the animals were first fasted for 48 hours after having been previously fed on an adequate normal diet. Glucose was then administered by stomach tube in 50% solution, 0.500 gm. per 100 sq. cm. of body surface. The animals were again fasted for 24, 36, 48 or 72 hours, then anesthetized with amytal and the whole liver, a sample of muscle and the heart were quickly removed and frozen in a mixture of CO₂ snow and ether. Glycogen was determined by a combination of the Pfluger method and the Shaffer-Hartmann procedure.

The glycogen content of the livers of mature female rats was invariably lower than that of mature males. However, no significant difference in the glycogen store in the liver, muscle or heart of sexually immature male and female rats was found. In castrated female animals as high or higher values were found as in males. In a series of 50 castrated female rats, half of which received sufficient theelin several times daily over a period of a week to keep them continuously in active oestrus, it was found that the injected animals behaved as normal females in respect to their glycogen stores. It is concluded that a sexual difference exists in the rate at which the carbohydrate stores are depleted in fasting.