Effects of Pancreatic Hormones and Glucocorticosteroids on Argininosuccinate Synthetase and Argininosuccinase Activities of Rat Liver during the Perinatal Period:In Vivoandin VitroStudies*

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Abstract
The activity changes of two urea cycle enzymes, argininosuccinate synthetase (ASS) and argininosuccinase (ASL), were followed after corticosteroid and pancreatic hormone treatments in utero and in primary cultured fetal hepatocytes. The ASL activity which was induced by glucagon or by (Bu)2cAMP administration was enhanced by cortisol administration in utero only in streptozotocin-treated fetuses, suggesting an inhibitory effect of insulin. In cultured fetal hepatocytes, dexamethasone produced a marked increase of the two enzyme activities, which was abolished by the simultaneous addition of insulin. The parallel results obtained with these two experimental models allow one to conclude that the high plasma insulin level in late gestation might repress the development of ASS and ASL activities in utero and antagonize the effect of corticosteroids on these enzyme activities.