Hepatic microsomal glucuronidation of clofibric acid in the adult and neonate albino rat.

Hepatic microsomal UDP glucuronyltransferase activity towards the acid substrate clofibric acid has been described in the adult and neonate albino rat. The enzyme was maximally activated, approximately 2-fold, in the presence of 0.1-0.4% (w/v) digitonin. Induction of the digitonin activated clofibric acid glucuronyltransferase was observed following phenobarbitone treatment in vivo (2.2-fold), and to a lesser extent, following beta-naphthoflavone treatment (1.3-fold). Clofibrate treatment in vivo (of which clofibric acid is the ester hydrolysis product) had no effect on clofibric acid glucuronidation in vitro. The activity of clofibric acid glucuronyltransferase in the liver of rat before and at birth was low (approx. 0.08 nmoles glucuronide formed/min/mg microsomal protein). The activity increased 5-fold during the first three post-natal days. After this time, the activity increased linearly reaching adult levels by four weeks after birth. The data indicated that clofibric acid glucuronyltransferase belongs to the neonatal cluster of enzymes and clofibric acid is a group 2 substrate. Clofibric acid, a common therapeutic agent, is a useful, acid substrate for the estimation of mammalian hepatic microsomal glucuronyltransferase activity.