The effects of pituitary hormones on hepatic drug metabolism in the rat.

Sex differences exist in the hepatic microsomal metabolism of drugs in the rat. These differences have been shown to be related to the presence of androgen in the male and the pituitary gland in the female. The present study was designed to identify the pituitary 'feminizing factor' by continuously infusing hormones via an osmotic mini-pump. Rat somatotropin and prolactin mimicked somewhat the 'feminizing' effect of pituitary extract infused into male animals while human somatotropin, which binds to both lactogenic and somatogenic receptors in rat liver, completely reversed the effect of hypophysectomy of female rats with respect to most of the parameters studied. It thus appears that the somatogenic/lactogenic receptors in the rat liver are involved in the maintenance of the sex differences in drug metabolism but the identity of the hormone that normally acts on these receptors in the rat is still uncertain.