[Control of argininosuccinate synthetase, argininosuccinase and arginase activities in the newborn rat].

Some factors influencing the postnatal development of three urea cycle enzyme activities, argininosuccinate synthetase, argininosuccinase, and arginase, in the liver of newborn rats, are studied. Premature and postmature birth change the developmental pattern of these enzyme activities, suggesting that the increase in enzyme activity after birth is initiated by the birth process. Starvation of newborn animals after birth has no effect on the postnatal development of the three enzyme activities. Bilateral adrenalectomy at birth causes a partial inhibition of the postnatal increase of argininosuccinase and arginase activities while injection of cortisol prevents the effects of adrenalectomy. It is suggested that presence of adrenal secretion is one condition necessary for the increased activity of the prematures.