Liver microsomal monooxygenase activities with several drugs and model substrates were determined for male rats, that had been given a pituitary implant or which had been hypophysectomized and injected with 3-methylcholanthrene. The effect of implanting a male or female rat pituitary into an immature male rat was to cause a change to a more typically female pattern of monooxygenase activities, i.e. ethylmorphine and aminopyrine N-demethylases and ethoxycoumarin O-deethylase, which are less active in adult female than male rats, were suppressed and ethoxyresorufin O-deethylase, which is more active in females, was induced. The effects of pituitary implantation on the biphenyl and benzo(a)pyrene hydroxylases were apparently unrelated to sex-differences in the activities of these enzymes. The inducibility by 3-methylcholanthrene of cytochrome P448-catalysed reactions was decreased 2-3-fold by prior hypophysectomy of adult male rats.
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