Effect of Insulin on FFA Mobilization and Ketosis in Fasting Pregnant Rats

Abstract

The concentrations of FFA and ketone bodies in plasma increased more in rats pregnant for eighteen days than in nonpregnant rats when both groups were fasted for two days. The immunoreactive insulin content of plasma was the same in fasted nonpregnant and pregnant rats whether the latter were ketotic or not. Hence, decreased circulating insulin, per se, did not appear to be the primary cause of ketosis in fasting pregnant rats. FFA mobilization was not suppressed completely by insulin in ketotic pregnant rats. The adipose tissue of pregnant rats showed impaired metabolism of glucose and increased FFA release in vitro. Lipolysis, in the presence or absence of insulin, was greater in adipose tissue of pregnant than in that of nonpregnant rats. Ketogenesis by liver slices of pregnant rats was greater than that of nonpregnant control rats and was not reduced thirty minutes after insulin injection despite a 50 per cent lowering of the concentration of plasma FFA and ketone bodies during this time. It is suggested that the ketosis of fasting in pregnant rats is caused by increased lipolysis in their adipose tissues and that increased FFA release is due to the absence of sufficient glucose to support re-esterification in the adipose tissues. The small effect of insulin (0.2 and 1.0 U., subcutaneously) on the plasma FFA may be due to the very low plasma glucose in fasting pregnant rats.