Journal of steroid biochemistry最新文献

The binding of progestin and glucocorticoid hormones was examined in the cytosol of rat adipose precursor cells. Progestin binding sites of high affinity and limited capacity were present in the cytosol of adipose precursor cells from female rats, but not from male rats, by using [³H]R5020 as radioligand. Glucocorticoid binding sites of high affinity and limited capacity were present in the cytosol of these cells from both male and female rats by using [³H]dexamethasone and [³H]triamcinolone acetonide as radioligands. The dissociation constants were in the physiological concentration range. Studies of competitive binding showed that progestin could compete with glucocorticoids at glucocorticoid binding sites. In a serum free medium glucocorticoid effect on cellular differentiation, monitored by glycerophosphate dehydrogenase (GPDH), was effectively counteracted by progesterone which by itself had no effect.

These results demonstrate that progestin receptor exists only in rat adipose precursor cells from female rats, while glucocorticoid receptor exists in rat adipose precursor cells of both sexes. Glucocorticoid effects on cellular differentiation in these cells are mediated by the glucocorticoid receptor. Progestin binds to the glucocorticoid receptor and antagonizes glucocorticoid effect on cellular differentiation in these cells.

Selective association of germ-free (GF) rats with dehydroepiandrosterone sulfate (DHEAS) desulfating bacteria allowed us to assess the exact impact of intestinal bacterial desulfation on the excretion and enterohepatic circulation of orally administered DHEAS. Germ-free rats selectively associated with the DHEAS-desulfating strain Peptococcus niger H4 (H4 rats) excreted 50% of the total label recovered within 17 h vs 21 h in GF rats and 13 h 23 min in conventional (CV) rats. Germ-free rats excreted 30% of the total label recovered via their urine. However, association of GF rats with the desulfating microorganism increased urinary excretion to 46%, comparable to the 45.5% found in CV rats. Fractionation of fecal label yielded 70% sulfoconjugated DHEAS and 2% unconjugated dehydroepiandrosterone in GF rats vs 5 and 77% in CV rats, and 55 and 14% in H4 rats, respectively. Our results demonstrate that the intestinal bacterial desulfation of DHEAS stimulated the enterohepatic circulation of DHEAS. This in turn increased the urinary excretion of label resulting in an accelerated elimination of labeled DHEAS from the body.

Treatment of ZR-75-1 human breast cancer cells with oestrogen has no direct effect on the expression of a transfected MMTV-LTR but enhances its inducibility in response to glucocorticoid treatment. This effect which can be produced with both oestradiol and diethylstilbestrol is specific to induction of the MMTV-LTR, no effect of the treatment on expression driven by the RSV-LTR being observed. The effect can be observed in cells pre-treated with oestrogen prior to removal of DNA and glucocorticoid addition but not in cells where oestrogen is added after removal of the DNA. The possible mechanisms of these effects and their relationship to the induction of oestrogen-responsive genes by this hormone are discussed.

Gas chromatography-mass spectrometry has revealed the existence of a novel lanosterol-like sterol which is produced by fungi in response to treatment with azole drugs. The significance of this finding may be related to the changes in fungal sterol synthesis as a consequence to prolonged exposure to azoles and consequent development of resistance to these agents.

We have recently demonstrated that 7,12-dimethylbenz(a)anthracene (DMBA), a potent inducer of mammary tumors in rodents, can in vitro decrease the number of membrane dopamine D₂ receptors and stimulate prolactin (PRL) release, by direct estrogen-like actions on anterior pituitary. In the present study, we tested the ability of DMBA to mimic the in vivo estradiol (17βE₂) effects on pituitary D₂ receptors and on PRL as well as LH release. We have found that DMBA, like 17βE₂, when injected to ovariectomized rats, induced a decrease in the number of anterior pituitary D₂ receptors, a release of PRL and exerted a biphasic (acute negative and longer term positive) action on LH secretion. We thus examined the ability of DMBA to interact with 17βE₂ receptors in the hypothalamo-pituitary axis: DMBA binds to the pituitary cytosolic estrogen receptors with an affinity 0.001% that of 17βE₂. Finally [³H]DMBA binds to hypothalamus-containing brain sections. This binding was displaced partially by RU 2858 a pure estrogen agonist and totally by tamoxifen, a purported estrogen antagonist. No competition for [³H]DMBA binding was observed with an androgen (RU 1881) or a glucocorticoid (RU 26988) agonist.

From these data, it may be concluded that DMBA can act as a partial estrogen in pituitary and hypothalamic tissues.

A direct urinary ELISA for estrone-3-glucuronide has been produced following cloning and characterisation of a monoclonal antibody to the above estrogen metabolite. The ELISA follows our established pattern of absorbing a thyroglobulin conjugate, to which estrone-3-glucuronide has been coupled, to the wells of a microtitre plate using guanidine hydrochloride. A competition reaction between either standards/samples and the adsorbed hormone compete for antibody combining sites. The assay is completed by addition of an antimouse Ig-peroxidase complex and read at 492 nm following additions of O -phenylenediamine substrate in under 4 h. The correlation between urinary “total estradiol” and “total estrone and estradiol” is very good and, in conjunction with our ELISA for pregnanediol glucuronide, has allowed for the improved clinical management of infertile and subfertile women.

We have previously reported that treatment of cultured mouse adrenal tumor cells with 0.6-1.2 μ M monensin, a monovalent carboxylic ionophore, results in disruption of the organized structure of the Golgi complex. This is associated with an inhibition of adrenocorticotropic hormone (ACTH) or dibutyryl cAMP-stimulated steroidogenesis and impairment of mitochondrial cholesterol side-chain cleavage activity. The present report describes further investigations regarding possible mechanisms for the inhibition. Monensin inhibits both synthesis of fluorogenic steroids and incorporation of [¹⁴C]acetate into the end-product steroid 11β,20α-dihydroxy-4-pregnen-3-one. Supplementation of monensin-treated cells with 25-hydroxycholesterol, a readily available substrate for steroidogenesis, does not reverse the inhibitory effect on the reaction. The incorporation of l-[³⁵S]methionine into trichloroacetic acid precipitable proteins in the isolated mitochondria of monensin-treated cells is inhibited approximately by 40%, whereas the inhibitory effect on the proteins in the cell homogenate is marginal. These findings suggest that a deficiency of newly synthesized proteins in mitochondria, rather than the availability of the substrate cholesterol, may be the primary factor causing impairment of steroidogenesis.

Addition of concentrated rat Sertoli cell conditioned medium (rSCCM) to isolated Leydig cells from immature rats stimulated steroid production more than 13-fold within 4h. LH-stimulated steroidogenesis was not enhanced by addition of rSCCM. The biological activity of the concentrated rSCCM was higher after incubation of Sertoli cells with FSH, whereas FSH alone did not stimulate steroid production. This effect of rSCCM was not due to inhibin, since highly purified 32 kDa rat inhibin, in doses equivalent to those present in rSCCM, had no effect on steroidogenesis during the 4 h incubation period. Furthermore, inhibin could be separated from the Leydig cell stimulating factor by anion-exchange chromatography. These results indicate a short-term paracrine control of Leydig cell steroidogenesis by Sertoli cell derived factors, which differ from inhibin.