Various bilirubin conjugates in pregnant and nonpregnant rats with and without phenobarbital treatment.

The relative participation of bilirubin conjugating systems other than uridine diphosphate glucuronic acid-dependent bilirubin glucuronyl transferase in 21-day pregnant (P) and nonpregnant (NP) rats with and without prior phenobarbital (PB) administration was studied. Relative enzyme activities of 74.5%, 17.6%, and 7.9% were observed for glucuronic acid, xylose, and glucose conjugates, respectively, in untreated NP rats. Pregnancy itself did not alter the relative activities. In response to PB administration, P rats increased activity less than NP animals for all three enzymes. The ratios of the three conjugates remained unchanged in both P and NP groups after PB stimulation.