Comparative Studies on the Metabolism of Oestradiol in the Brain, the Pituitary and the Liver of the Rat

Abstract

Radioactive oestradiol was incubated with homogenates of hypothalamus, pituitary and liver and slices of cortex, hippocampus, hypothalamus, pituitary and liver of ovariectomized rats. 2-and 4-substituted oestrogens were the main metabolites in the brain and were found in the same proportions.In the liver only the 2-substituted oestrogens were the main metabolites, while the 4-substituted ones were of minor quantitative importance. On the basis of wet weight the 2-hydroxylating capacity of the liver was approximately 50 fold greater than that of the brain and the 4-hydroxylating capacity about the same as that of the brain. Only slight differences in the 2-and 4-hydroxylating capacity of various brain areas were observed, although apparently the hypothalamus and the pituitary were more active in the formation of catecholoestrogens than the cortex and the hippocampus.The importance of oestradiol in the control of the hypothalamic-pituitary function is well established (Vande Wiele et al. 1970; Young 8c Jaffe 1976).A recent report concerning the participation of catecholamines in this process (Kamberi 1974) and our findings dealing with the competitive interaction of catecholamines and catecholoestrogens via the catechol O-methyltransferase

Sexual patterns of monooxygenase function in the liver of marine teleosts and the regulation of activity by estradiol

“…With rat hepatic microsomes, 4-0 H-E 2 is such a minor metabolite relative to 2-0H-E, (Ball and Knuppen, 1978) that release of 3H from the 4-0H-E 2 would not significantly influence accurate measurement of E 2 2-hydroxylase activity. Since the bulk of radiolabeled material co-migrated with 2-0H-E 2 on a TLC plate developed in a system that cleanly separated 2-0H-E 2 and 4-0H-E 2 (Fig.…”

“…The dominant hydroxylated products were the catechol estrogens 2-0H-E 2 and 4-0H-E 2 , principally the former (Ball et al, 1978). Hepatic microsomes also hydroxylated E 2 at positions C-6a, -68, -7a, and -16a, and oxidized it at C-17 to estrone (Ball et al, 1978;Gustafsson, 1978).…”

“…Hepatic microsomes also hydroxylated E 2 at positions C-6a, -68, -7a, and -16a, and oxidized it at C-17 to estrone (Ball et al, 1978;Gustafsson, 1978).…”

“…The physiologial role of the catecho1estrogens is uncl ear. 2-0H-E 2 is synthesi zed by mi crosoma 1 cytochrome P-450 in many tissues, but activity is dominant in the liver, followed by the brain (Ball et al, 1978;Hoffman et al, 1980). Activity in male liver and brain microsomes was greater than in female tissues and was maintained at the higher levels by testosterone (Barbieri et al, 1978;Hoffman et al, 1980).…”

Immunocytochemical localization of catechol estrogen in the rat pituitary gland. I Posterior lobe.

“…The possible significance of catechol estrogens as potential mediators of estrogen action and a direct biochemical link between estrogen and catecholaminergic function has been considered (1, 4, 12, 17-20, 27, 28, 32). Biochemical studies have shown that catechol estrogen is widely distributed in animal tissue including the pituitary gland (1,3,5,9, 12, 17, 21, 28,32,33). However, the physiological roles of catechol estrogen in the pituitary gland have not been determined, although they may be the links connecting primary estrogens and catechol amines in the regulation of gonadotropin and prolactin secretion (16, 30).…”