Effect of pregnenolone-16 alpha-carbonitrile on bilirubin-and sulfobromophthalein-binding to hepatic Y and Z proteins in the rat.

Pregnenolone-16 alpha-carbonitrile (PCN), administered twice daily p.o. for 3 days at a dose level of 20 mumol/100 g body weight, significantly enhances in vivo binding of 14C-bilirubin and sulfobromophthalein (BSP) to hepatic Y and Z proteins in female Charles River CD rats. 14C-bilirubin-binding to Y protein showed a 61% increase, while binding of the same moiety to the Z protein fraction was augmented by 59%. BSP-binding in vivo demonstrated rises of 114 and 71% in relation to Y and Z proteins, respectively. These data correlate well with previous investigations in which PCN was found to have a beneficial influence on experimentally induced hyperbilirubinemias and, furthermore, there is an indication that phenobarbital, another potent microsomal enzyme inducer, acts via a similar mechanism.