Antagonistic Action of Estrogens, Flutamide, and Human Growth Hormone on Androgen-Induced Changes in the Activities of Some Enzymes of Hepatic Steroid Metabolism in the Rat*

Abstract

The dose-dependent effects of daily estrogen (estradiol, ethinyl estradiol, diethylstilbestrol) administration on the activities of three hepatic androgen-dependent microsomal enzymes (3 alpha- and 3 beta-hydroxysteroid dehydrogenase and 5 alpha-reductase) in male rats were examined. Antiestrogens were then tested for their ability to block the feminizing action of 10 micrograms estradiol/day on these enzyme activities; nafoxidine and monohydroxytamoxifen were the most effective. The prevention of 5 alpha-dihydrotestosterone-induced changes in these activities in ovariectomized females was investigated. All three estrogens at a dose of 1 microgram blocked the action of 500 micrograms androgen. A similar androgenic blockade was achieved by daily administration of 5 mg flutamide or constant infusion of human GH (5 micrograms/h). Simultaneous administration of 200 micrograms monohydroxytamoxifen prevented the androgen-antagonizing action of estrogens, but not of flutamide nor of GH. Large doses of estrogens have the same repressive effect as androgens on 5 alpha-reductase activity in female castrates. Using the diethylstilbestrol-treated rat as a model, it is demonstrated that this effect can be prevented by antiestrogen, but not by GH. It is concluded that androgens and low doses of estrogens affect these enzyme activities by acting at different levels of central regulation, whereas large doses of estrogens act directly on the liver via hepatic estrogen receptors. These conclusions are corroborated by studies of hepatic estrogen receptor concentrations.

Sex change in cytochrome P-450 phenotype by growth hormone treatment of adult rat hepatocytes maintained in a culture system on matrigel.

“…Possibly, we have not yet identified the precise growth hormone concentration and duration of hepatocyte exposure that sufficiently mimics in culture the pulsatile pattern of growth hormone release observed in male rats in vivo (2). It is also possible that induction of P-450h in female cells may require other hormonal factors (46) acting in concert with growth hormone or IGF-I.…”

Effect of Gonadectomy and Exogenous Sex Hormone Administration on the Concentrations of Hepatic Oestrogen Receptors and Hepatic Atypical Sex Hormone Binding Protein (HASP) in the Rat

“…This mode of regulation has been demonstrated for hepatic microsomal 5a-reductase (Lax et al 1983). The different effects of the same estrogen dose on male and female gonadectomized animals might be explained in terms of differential oestrogen inactivation, which is higher in males than females.…”

“…Hepatic oestrogen receptor concentrations were determined using a single point assay as described by Lax, Rumstadt, Plasczyk, Peetz and Schriefers (1983). In order to measure unoccupied binding sites 0.25 ml cytosol containing 100 mg liver tissue equivalents/ml TED buffer (10 mmol/1 tris -15 mmol/1 EDTA -10 mmol/1 dithiothreitol, pH 7.4 at 0°C) was incubated for 3 h at 0° with 0.1 ml 52.5 nmol/1 tritiated oestradiol (3.1-4.1 TBq/mmol).…”

“…Non-specific binding was determined in parallel incubations containing 1 x 10 -5 mol/15a-dihydrotestosterone. The only difference to the previously described method (Lax et al 1983) was the addition of dextran-coated charcoal as a suspension instead of as a pellet when separating bound ligand from free.…”

Ligand-protein inverse docking and its potential use in the computer search of protein targets of a small molecule

“…These include estrogen receptor, 36 protein kinase C, 37 collagenase, 38 17␤-hydroxysteroid dehydrogenase, 39 alcohol dehydrogenase, 40 and prostaglandin synthetase. 41 It has been observed that two other INVDOCK identified proteins, glutathione transferase and 3␣-hydroxysteroid dehydrogenase, exhibited altered activity by tamoxifen, 42,43 which may be indicative of direct binding of tamoxifen to these proteins. Experiments showed that the level of another two identified proteins, dihydrofolate reductase and immunoglobulin, is changed by tamoxifen.…”