SELECTIVE CHANGES IN OXIDATIVE XENOBIOTIC METABOLISM IN-VIVO AND IN-VITRO AFTER PARENTERAL ADMINISTRATION OF RECOMBINANT BOVINE SOMATOTROPIN TO RATS

Effects of recombinant bovine somatotrophin (rBST) on in vivo and in v itro oxidative drug metabolism were studied in male rats. rBST was giv en subcutaneously at a dose of 250 or 500 mug 100 g-1 bodyweight 24 h- 1 in different dosage patterns. Sulphadimidine (SDD) plasma clearance, urinary excretion of 6-hydroxy-SDD and the in vitro microsomal SDD-hy droxylations were only inhibited when rBST was given in three injectio ns per 24 hours. The hepatic microsomal ethylmorphine N-demethylation rate and the testosterone hydroxylation rate at the 6beta position wer e significantly reduced after one rBST injection per 24 hours. Microso mal testosterone hydroxylation rates at the 16alpha and 2alpha-positio ns were reduced depending on the frequency of rBST administration. It is concluded that the inhibition of in vivo and in vitro drug oxidatio n in rats by rBST is associated with selective changes in activity of cytochrome P450 enzymes in the liver.