Ontogeny of guinea pig liver cholesterol 7α-hydroxylase: Unexpected inverse correlation of enzyme activity with expanding bile acid pool

Changes in the activity of guinea pig liver cholesterol 7α-hydroxylase (rate limiting enzyme of cholesterol catabolism) from birth to adult life was investigated using a microsomal acetone extraction method (to remove endogenous cholesterol). Contrary to the previously held notion, it was noted that while the total bile acid pool increased progressively with age after birth, hepatic cholesterol 7α-hydroxylase specific activity declined. Neonatal hepatic cholesterol 7α-hydroxylase showed an increase in enzyme activity in response to cell supernatant factors (100,000 xg supernatant) from neonatal livers, but not from adult livers.