Enzymatic conversion of heme to bilirubin in normal and starved fetuses and newborn rats

Abstract

Heme oxygenase (HO), the enzyme system responsible for the conversion of heme to bilirubin, has an average activity of 0.143 ± 0.036 m^moles bilirubin/10 mg protein/ min in fetal rat liver between 15 and 21 days of gestation, compared with 0.070 ± 0.020 in mature liver. Heme oxygenase activity increases rapidly during the first postnatal day (0.237 ± 0.078) and reaches 4 times adult rates at 1 week of age. Thereafter, activity declines to basal adult rates at weaning. Splenic HO activity is relatively low during the fetal and immediate postnatal period compared with its activity in mature animals (0.206 versus 0.790), and rises to nearly 11 times the hepatic activity in mature animals. Fasting of pregnant rats for 3 days before delivery caused a 20% average increase in hepatic HO of fetuses and newborns. In newborn rats fasted for 3 hr and 6 hr, HO activity increased two- and threefold, respectively, compared with fed controls. Refeeding after 3 hr resulted in a decline to basal values at 6 hr of age. Splenic activity was not affected by fasting or refeeding. These results show that the capacity of the liver for bilirubin production is greater in fetuses compared with adults, and increases further at birth. Starvation in mother or offspring stimulates the hepatic enzymic process for conversion of heme to bilirubin. These studies should provide a basis for investigating nutritional and hormonal factors which influence the conversion of heme to bilirubin in fetuses and newborns. © 1972 International Pediatric Research Foundation, Inc.