Postnatal changes in carbamylphosphate synthetase-I and ornithine transcarbamylase activities after normal birth, premature delivery and prolonged gestation in rat liver: effects of actinomycin D and glucose.
The development of two urea cycle enzymes, carbamylphosphate synthetase-I and ornithine transcarbamylase was examined in neonatal rat liver. Normal birth on day 21.5 caused a marked increase of both activities as early as 4 h of extrauterine life. That increase occurred later in newborns delivered by cesarian section on day 21.5, but they exhibited a greater hepatic urea level. Premature delivery on day 20.5 caused a marked increase of both activities and hepatic urea level while prolonged gestation abolished these increases. The postnatal increase in both activities and in hepatic urea level was therefore dependent on a factor associated with birth. The in vivo administration of actinomycin D (2 microgram) at birth did not abolish the postnatal increase of both activities. Moreover, the administration of glucose (25 mg every 2 h) to newborns delivered by cesarian section on day 21.5 abolished the postnatal increase of ornithine transcarbamylase activity and hepatic urea level 23 h later. It seems that the transient hypoglycemia and appearance of gluconeogenesis at birth were the physiological mechanisms involved in the postnatal induction of ornithine transcarbamylase activity.
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002585:Cesarean Section; D003609:Dactinomycin / Q000494:pharmacology*; D005865:Gestational Age; D005947:Glucose / Q000494:pharmacology*; D008099:Liver / Q000201:enzymology*; D009954:Ornithine Carbamoyltransferase / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D051381:Rats
D003609:Dactinomycin; D009954:Ornithine Carbamoyltransferase; D010770:Phosphotransferases; D005947:Glucose