The time course of the effect of hypophysectomy and oestrogen treatment on the hepatic metabolism of androst-4-ene-3,17-dione in male and female rats

Sex and the Liver – A Journey Through Five Decades

Metabolism of steroids and drugs in rodents is sexually differentiated. The reason for this turned out to be the sexually differentiated growth hormone (GH) secretory pattern regulating the expression of a number of hepatic cytochrome P-450 genes. Although not fully resolved, it is clear that several signaling pathways and transcription factors are involved in mediating the effects of GH. It may be argued that such a well-controlled physiological system should have an important biological role and we speculate that the demands of a robust hepatic steroid metabolism during pregnancy has led to the development of this sexually differentiated hypothalamo-pituitary-liver axis.

Effect of age, gonadectomy and hypophysectomy on mitochondrial hydroxylation of vitamin D3 (cholecalciferol) and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol in female and male rat liver

In a previous study we found that liver mitochondrial side-chain hydroxylation of vitamin D3 (cholecalciferol) and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol was higher in female than in male rats [Saarem & Pedersen (1987) Biochem. J. 247, 73-78]. The present paper describes the effects of age, gonadectomy and hypophysectomy on these activities. The sex difference became manifest above the age of 7 weeks. Ovariectomy and/or injection of oestradiol valerate had no effect on the hydroxylase activities in adult females. Castration increased, and subsequent testosterone treatment decreased, the hydroxylase activities in adult males. Hypophysectomy had no effect in females, but increased the hydroxylase activities in males. Testosterone treatment had no effect in hypophysectomized females or males. Injection of oestradiol valerate had no effect on the hydroxylase activities in hypophysectomized females. In hypophysectomized males this treatment had no effect on the vitamin D3 25-hydroxylase activity, but decreased the C27-steroid 27-hydroxylase activity in males. Microsomal 1 alpha-hydroxyvitamin D3 25-hydroxylase activity was lower in females than in males in all age groups. Castration or hypophysectomy decreased the activity in male rats. It is concluded that, in adult female rats, the mitochondrial side-chain hydroxylation of vitamin D3 and of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol is independent of sex hormones. In males these activities are regulated by influence of sex hormones on the hypophysis, probably by the presence of androgens in the neonatal period. Different effects on the two hydroxylases indicate the presence of at least two different cytochromes P-450 in rat liver mitochondria.

The effects of glucagon and TH-glucagon on steroid metabolism in isolated rat hepatocytes

Glucagon decreases the activity of steroid-metabolising enzymes in isolated rat liver cells at physiological concentrations. Higher concentrations are less effective. TH-glucagon (1-N-alpha-trinitrophenylhistidine-12-homoarginine-glucagon) also reduces enzyme activity but does not lose activity at higher concentrations. The effects of the two hormones mimic closely their reported effects on phosphatidylinositol-4,5-bisphosphate breakdown. It is, thus, likely that the effect of glucagon on steroid metabolism is mediated via breakdown of this phospholipid. The calcium ionophore, A23187, had no effect on steroid metabolism whereas the phorbol ester 4 beta-phorbol-12-myristate-13-acetate (PMA) mimicked the effect of glucagon, showing that activation of protein kinase C but not Ca2+ mobilization may be involved in glucagon's action on hepatic steroid metabolism.

Regulation of bile salt sulfotransferase isoenzymes by gonadal hormones

We studied the regulation of hepatic bile salt sulfotransferase activity by gonadal hormones and the effect of gonadal hormones on two bile salt sulfotransferase isoenzymes. Bile salt sulfotransferase enzyme activity was three times greater in the female than in the male rats. Oophorectomy significantly decreased bile salt sulfotransferase activity in the female, but orchidectomy had no effect on bile salt sulfotransferase activity in the male. Estrogen treatment of intact as well as orchidectomized males markedly stimulated the enzyme activity, while testosterone treatment of intact or oophorectomized females did not effect bile salt sulfotransferase activity. We concluded that the 3-fold greater activity in female rats is due to the striking stimulatory effect of estrogen on bile salt sulfotransferase activity, and the testosterone has little or no role in the sexually related differences in bile salt sulfotransferase activity in mature rats. These sex-related differences in bile salt sulfotransferase activity were investigated further using DEAE-Sephadex A50 ion-exchange chromatography of rat hepatic cytosol. Two bile salt sulfotransferase isoenzymes were identified both with an approximate molecular weight of 130,000. Bile salt sulfotransferase I eluted with 0.05 M NaCl, had an isoelectric point at pH 6.8, was stimulated by estrogen, and was responsible for 90% of total bile salt sulfotransferase activity in the mature female. Bile salt sulfotransferase II eluted with 0.14 M NaCl, had an isoelectric point at pH 5.3, was unresponsive to estrogen, and accounted for 75 to 80% of bile salt sulfotransferase activity in the mature male.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of sexually dimorphic hepatic steroid metabolism by the somatostatin-growth hormone axis

Lesions in the periventricular hypothalamic area in male rats results in a "feminization" of steroid metabolizing enzymes in the liver. These lesions also resulted in a decrease of somatostatin levels in the median eminence. Since blockade of somatostatin by in vivo administration of an antiserum also caused "feminization" of the liver, it is possible that at least one hypothalmic factor responsible for "feminization" is related to somatostatin. Also extrahypothalmic areas seem to influence sexually differentiated functions in the liver. The neuroendocrine control of the "feminizing factor" secretion from the pituitary bears several resemblances to the central control of GH. The hypothesis that the plasma pattern of GH regulates hepatic steroid metabolism in the rat was studied in two different animal models: (1) Different plasma patterns of GH were achieved by administration of human GH (hGH) at different frequencies or by infusing the hormone continuously by means of Alzet osmotic minipumps to hypophysectomized female rats. (2) The plasma pattern of GH in animals with an intact pituitary gland was investigated under conditions which lead to "feminization" of hepatic steroid metabolism. The results demonstrate that the plasma pattern of GH influences hepatic steroid metabolism. Increased trough plasma GH values or absence of time periods with undetectable plasma levels of GH appears to be a major determinant for "feminization" of hepatic steroid metabolism. Since sex steroids were found to influence the plasma pattern of GH it seems as if differences in the plasma pattern of GH between male and female rats explain the sex-differentiated hepatic steroid metabolism.