1227 UREA CYCLE ENZYMES DURING FASTING IN THE OVINE FETUS

Abstract

Activities of five urea cycle enzymes were measured in maternal and fetal sheep liver during the normal fed state and following five days of fasting. Six ewes and 10 fetuses were studied in both the fed and fasted periods at 132 days gestation (term = 147 days) for liver protein, DNA and enzyme levels. Results indicated that protein and DNA contents remained unchanged during fasting in both the maternal and fetal liver. Fetal liver weight was decreased during fasting from 108 ± 23 to 71 ± 21 gm (mean ± SD). Fed state fetal enzyme levels were at 25-50% of maternal values per mg DNA and 50-125% of maternal levels per gm liver. After fasting, four of the five enzymes increased by 2.3 to sixfold (per mg DNA) in fetal liver; only one enzyme (AS) increased significantly in maternal liver. Activities of each enzyme per whole fetal liver'gave similar results.These data indicate that the in vivo studies which demonstrate a doubling in fetal urea production in the fasted sheep in latter gestation are associated with parallel increases in the fetal hepatic activities of several enzymes responsible for urea synthesis.