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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The metabolism of dihydrotestosterone (DHT) and 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-Adiol) was assessed in full homogenates of rat prostate and epididymis. The major degradational route of DHT was catalysed by the enzyme(s) 3 alpha-hydroxysteroid oxidoreductase (HSOR). Enzyme kinetic characteristics Vmax, Km and Vmax/Km ratio, were obtained for the NADP(H)- and NAD(H)-dependent interconversion of DHT and 3 alpha-Adiol at pH 7.0 and at saturated co-factor concentration. For both the reduction of DHT and the oxidation of 3 alpha-Adiol, NAD(H) was the preferred co-factor when activities were rated by their Vmax and Vmax/Km ratio. Combining the data with the earlier established Vmax/Km ratios for the 5 alpha-reductase isozyme type I and II activities in rat prostate and epididymis indicated that DHT, at saturated co-factor concentrations, would not be sustained in either tissue considering the reported enzyme characteristics. The reported exclusive bioavailability of the co-factors NADPH and NAD+ in vivo, however, will direct the metabolic pathways in these tissues to sustain the formation of DHT.
J Steroid Biochem Mol Biol 1996 Jun
PMID:3 Alpha-hydroxysteroid oxidoreductase activities in dihydrotestosterone degradation and back-formation in rat prostate and epididymis. 883 71

It has previously been described that the growth hormone (GH) releasing effect of clonidine (CLO), an agonist of alpha2-adrenoreceptors, disappears after orchidectomy and is restored by testosterone replacement when started immediately after orchidectomy. In the present experiments, the effects of CLO on GH release was analysed in long-term (LTO; 12 weeks) and short-term (STO; 2 weeks) orchidectomized rats. In the first experiment, LTO males were implanted with silastic capsules containing testosterone 10 weeks after orchidectomy and killed 2 weeks later, 15 min after injection of CLO (150 microg/kg) or vehicle. In the second experiment, adult males were implanted with testosterone at the moment of orchidectomy and decapitated 2 or 12 weeks later, 15 min after vehicle or CLO administration. In addition, in order to evaluate the effects of orchidectomy and androgen replacement on alpha2 agonists GH release further, prepubertal males (21-days-old) implanted with testosterone or 5-alpha-androstane-3-alpha,17beta diol (alpha-diol) at the moment of orchidectomy were killed 2 weeks later, 15 min after ketamine-xylazine (an alpha2 agonist) administration. Finally, 10-day-old males (orchidectomized 72 h before) were decapitated 15 min after CLO or vehicle administration. Our results show that: (a) LTO and STO abolished the stimulatory effect of clonidine on GH secretion; (b) orchidectomy also abolished the stimulatory effect of clonidine in neonatal rats and that of xylazine in prepubertal males; (c) testosterone implanted at the moment of orchidectomy prevented the loss of the CLO effect in LTO and STO, but testosterone-delayed administration in LTO was unable to restore the effectiveness of CLO inducing GH release. We conclude that orchidectomy at all ages tested abolishes GH secretion induced by alpha2 agonists, which suggests that the functionality of alpha-adrenergic receptors involved in the control of GH secretion is critically dependent on a permanent exposure to testosterone in males.
J Steroid Biochem Mol Biol 1996 Aug
PMID:The pattern of testosterone replacement influences the recovery of the stimulatory effect of clonidine on growth hormone (GH) secretion in orchidectomized rats. 891 79

Neuroactive steroids have been postulated to cause anesthesia by binding to unique steroid recognition sites on gamma-aminobutyric acid (GABA) receptors and modulating GABA receptor function. Steroids interact with these sites diastereoselectively, but it is unknown whether steroid sites show enantioselectivity. To address this issue, we synthesized enantiomers to (+)-3alpha-hydroxy-5alpha-androstane-17beta-carbonitrile and (+)-3alpha-hydroxy-5alpha-pregnan-20-one. In this study, we show that potentiation of GABA-mediated currents and gating of the GABA(A) channel by steroids, as well as steroid-induced anesthesia in tadpoles and mice, is enantioselective, with the (+)-enantiomers exhibiting significantly greater potency in all assays. The correlation between the effects of steroid enantiomers on channel behavior and their effects as anesthetics provides strong evidence that GABA(A) receptors play a predominant role in steroid-induced anesthesia. The enantiomers also provide a tool to probe the relative contributions of direct chloride channel activation versus potentiation of GABA-elicited currents to the induction of anesthesia. Studies examining the effects of combinations of (+)- and (-)-3alpha-hydroxy-5alpha-androstane-17beta-carbonitrile were consistent with the hypothesis that potentiation of GABA-activated currents contributes to steroid-induced anesthesia but indicated that direct steroid activation of GABA(A) receptors is not mechanistically important in producing anesthesia.
Mol Pharmacol 1996 Dec
PMID:Enantioselectivity of steroid-induced gamma-aminobutyric acidA receptor modulation and anesthesia. 896 80

The present study examines the effects of acidic (FGF-1) and basic (FGF-2) fibroblast growth factors on Leydig cell steroidogenesis by cells from 5-, 21- and 90-day-old rats. These ages represent three distinct time points in Leydig cell development: fetal Leydig cells (day 5), immature Leydig cells (day 21) and adult Leydig cells (day 90). The results demonstrate that the actions of the two growth factors on steroidogenesis are developmentally regulated, and require the presence of heparan sulphate proteoglycans (HSPG). FGF-1 and FGF-2 both had stimulatory effects on basal, but not maximally LH-stimulated, testosterone production by fetal Leydig cells, and both growth factors stimulated basal 5 alpha-androstane-3 alpha, 17 beta-diol production by immature Leydig cells. These effects were mediated by heparan sulphate-proteoglycans (HSPG), as they were blocked by the addition of protamine sulphate and sodium chlorate. FGF-1 and FGF-2 had no effect on basal testosterone production by adult Leydig cells, however, FGF-1 alone inhibited LH-stimulated testosterone production by adult Leydig cells in a dose-dependent manner. These data demonstrate that the effects of FGF-1 and FGF-2 are dependent on the specific stage of Leydig cell differentiation and development and may vary accordingly. Furthermore, although FGF-1 and FGF-2 are closely related structurally, a different effect of these two growth factors can be observed on the same type of Leydig cells. The data therefore suggest that these growth factors may have different but specific roles in the regulation of Leydig cell steroidogenesis, at different stages of development.
J Steroid Biochem Mol Biol 1997 Feb
PMID:Developmental response by Leydig cells to acidic and basic fibroblast growth factor. 919 74

Although follicle-stimulating hormone (FSH) and estrogens are known to be the main physiological stimuli for the development of the ovarian follicle in mammals, their growth-promoting activity has not been clearly established "in vitro". Furthermore, experimental evidence indicates that FSH and estradiol can independently inhibit granulosa cell proliferation. The present study was aimed at examining the effect of sex steroids in combination with FSH, on DNA synthesis in rat granulosa cells cultured in completely defined medium. Estradiol and FSH, when added separately, produced a significant inhibition of [3H] thymidine incorporation. In contrast, a combination of a low dose of FSH (20 ng/ml) with estradiol (100 ng/ml) produced a shift in the period of maximal DNA synthesis from 96 to 48 h after plating. Dose response studies showed that estradiol effects were produced at physiological intraovarian concentrations (1-100 ng/ml), whereas the effects of FSH were biphasic, with high doses (200 ng/ml) being inhibitory. A similar biphasic dose response curve was observed with increasing concentrations of a cAMP derivative in the presence of maximally effective doses of either an aromatizable steroid (androstenedione), insulin or insulin-like growth factor I. Non-aromatizable androgens (5alpha-dihydrotestosterone, 5alpha-androstane 3alpha-17beta diol and androsterone) showed a potency comparable to that of estradiol. The effect of 5alpha-dihydrotestosterone was completely blocked by a specific antiandrogen (hydroxy-flutamide), indicating that it was mediated by the androgen receptor. The effects of estradiol and androgens were not additive. The interaction between estradiol and FSH was further amplified in the presence of a maximally effective dose of insulin. Data presented herein indicate that both estrogens and androgens are able to elicit a mitogenic response in purified granulosa cells, cultured in a completely defined medium, provided the cells are stimulated by a physiological dose of FSH. These results suggest that, during follicular development, the stimulus for granulosa cell proliferation is given by the concerted action of steroid and peptide hormones acting through different signalling pathways.
J Steroid Biochem Mol Biol 1997 May
PMID:Concerted stimulation of rat granulosa cell deoxyribonucleic acid synthesis by sex steroids and follicle-stimulating hormone. 936 94

A monkey cDNA, UGT2B18, encoding a UDP-glucuronosyltransferase (UGT) active on 3-hydroxyandrogens, has been isolated and characterized. Previous results suggested that the monkey represents the most appropriate animal model for studying the physiologic relevance of steroid UGTs. UGT2B18 was isolated from a cynomolgus monkey prostate cDNA library using human UGT2B7, UGT2B10 and UGT2B15 cDNA as probes. The cDNA is 1748 bp in length and contains an open reading frame of 1587 bp encoding a protein of 529 residues. The UGT2B18 cDNA clone was transfected into HK293 cells and a stable cell line expressing UGT2B18 protein was established. Western blot analysis of the UGT2B18-HK293 cell line using a human UGT2B17 polyclonal antibody (EL-93) revealed high expression of a 53 kDa UGT2B protein. The transferase activity of UGT2B18 was tested with over 60 compounds and was demonstrated to be principally active on C19 steroids having an hydroxyl group at position 3alpha of the steroid molecule. UGT2B18 was also active on planar phenols and bile acids. Kinetic analysis revealed that UGT2B18 glucuronidates 3-hydroxyandrogens with high velocity and affinity. Using cell homogenates, Km values of 5.1, 7.8 and 23 microM for androsterone (ADT), etiocholanolone and androstane-3alpha, 17beta diol (3alpha-diol) were obtained, respectively. Specific RT-PCR analysis demonstrated the expression of UGT2B18 transcripts in several tissues including liver, prostate, kidney, testis, adrenal, bile duct, bladder, colon, small intestine, cerebellum and pancreas suggesting a contribution of this isoenzyme to the high plasma levels of glucuronidated ADT and 3alpha-diol found in the cynomolgus monkey.
J Mol Biol 1998 Feb 06
PMID:Isolation and characterization of a simian UDP-glucuronosyltransferase UGT2B18 active on 3-hydroxyandrogens. 948 Jul 69

In the last years there has been an extraordinary development in the synthesis of new progestins. These compounds are classified, in agreement with their structure, in various groups which include progesterone, retroprogesterones, 17alpha-hydroxyprogesterones, 19-norprogesterones, 17alpha-hydroxyprogesterone derivatives, androstane and estrane derivatives. The action of progestins is a function of many factors: its structure, affinity to the progesterone receptor or to other steroid receptors, the target tissue considered, the biological response, the experimental conditions, dose, and metabolic transformation. The information on the action of progestins in breast cancer patients is very limited. Positive response with the progestins: medroxyprogesterone acetate and megestrol acetate was obtained in post-menopausal patients with advanced breast cancer. However, extensive information on the effect of progestins was obtained in in vitro studies using hormone-dependent and hormone-independent human mammary cancer cell lines. It was demonstrated that in the hormone-dependent breast cancer cells, various progestins (nomegestrol acetate, tibolone, medrogestone, promegestone) are potent sulfatase inhibitory agents. The progestins can also involve the inhibition of mRNA of this enzyme. In another series of studies it was also demonstrated that various progestins are very active in inhibiting the 17beta-hydroxysteroid dehydrogenase for the conversion of estrone to estradiol. More recently it was observed that the progestins promegestone or medrogestone stimulate the sulfotransferase for the formation of estrogen sulfates. Consequently, the blockage in the formation of estradiol via sulfatase, or the stimulatory effect on sulfotransferase activity, by progestins can open interesting and new possibilities in clinical applications in breast cancer.
J Steroid Biochem Mol Biol 1998 Apr
PMID:Progestins and breast cancer. 969 77

Conjugation of compounds by glucuronidation is a pathway found in all vertebrates studied to date. Although, it is widely recognized that the liver is a major site of glucuronidation, it is now clear that extrahepatic tissues are also involved in the conjugation of compounds to which these tissues are exposed. High levels of androsterone glucuronide and androstane-3alpha,17beta-diol glucuronide found in the human prostate, breast cyst fluid and ovary follicular fluid suggest that glucuronidation of 5alpha-reduced C19 steroids occurs in these tissues. Recently, we have reported the tissue distribution of UGT2B15, which can conjugate steroids in several human extrahepatic steroid target tissues including the skin, breast and prostate. We have also isolated a new UGT2B cDNA encoding UGT2B17, that conjugates ADT which is the major 5alpha-reduced C19 steroid glucuronide in the circulation of humans. UGT2B17 is also widely distributed in several human steroid target tissues. This gene was mapped to human chromosome 4q13 and has an exon/intron structure similar to that of rat UGT2B1 and UGT2B2. Both UGT2B15 and UGT2B17, which are able to catalyze the glucuronidation of DHT, are expressed in LNCaP cells. Interestingly, glucuronidation of steroids is markedly regulated by several factors including androgens and growth factors. Treatment of LNCaP cells with dihydrotestosterone (DHT) and epidermal growth factor (EGF) caused a decrease of DHT glucuronidation and UGT2B mRNA levels. RNase protection assays showed a specific decrease of UGT2B17 transcript in LNCaP cells treated with DHT and EGF however, the level of UGT2B15 mRNA was not affected. As well, Western blot analysis demonstrated a diminution of UGT2B17 protein level in response to DHT and EGF. These results demonstrate a differential regulation of different isoforms of steroid conjugating UGTs present in human prostate LNCaP cells. In addition, UGT2B17 was shown to be more labile than UGT2B15 indicating that regulation of UGT2B17 expression would lead to a more rapid change in the level of glucuronidated steroids. Expression of exogenous UGT2B17 in LNCaP cells by gene transfer led to a significant decrease in the androgen response. This result indicates the ability of UGT enzymes to regulate the androgen response by conjugating androgens which abolishes their interaction with their receptor and facilitates their clearance from the cell. The glucuronidation of steroids by UGT enzymes is an important mechanism by which the levels of steroids is regulated in steroid target tissues.
J Steroid Biochem Mol Biol 1998 Apr
PMID:Characterization and regulation of UDP-glucuronosyltransferases in steroid target tissues. 969 84

High voltage-activated (HVA) Ca2+ current (ICa) was recorded from neonatal rat hippocampal and adult rat dorsal root ganglion neurons. In both cell types, (+)-3alpha-hydroxy-5alpha-androstane-17beta-carbonitrile [(+)-ACN], a neuroactive steroid, had no effect on nifedipine- (L-type) or omega-agatoxin IVA- (P-type) sensitive ICa. Selective blockade of N-type current with omega-conotoxin GVIA and of Q-type current with omega-conotoxin MVIIC indicated that (+)-ACN inhibits both N- and Q-type current components in both cell types. Current persisting after blockade of all other current components (R-type) was also sensitive to (+)-ACN. Half-blockade of (+)-ACN-sensitive HVA current occurred in the range of 3-25 microM, with N-type current somewhat more sensitive than Q- or R-type. The (+)-ACN enantiomer, (-)-ACN, and pregnanolone were somewhat less effective at inhibiting total HVA current than (+)-ACN, whereas several steroid analogs, including alfaxalone, were relatively ineffective at inhibiting total HVA current. Neither guanosine-5'-O-(2-thio)diphosphate nor guanosine-5'-O-(3-thio)triphosphate altered the ability of (+)-ACN to inhibit HVA current in dorsal root ganglion neurons, indicating that (+)-ACN acts directly on Ca2+ channels. The partial selectivity exhibited by (+)-ACN among different HVA current components suggests that manipulations of steroid analogues may be a useful strategy in the generation of more selective, more potent, small-molecular-weight HVA channel blockers.
Mol Pharmacol 1998 Sep
PMID:The anesthetic steroid (+)-3alpha-hydroxy-5alpha-androstane-17beta-carbonitrile blocks N-, Q-, and R-type, but not L- and P-type, high voltage-activated Ca2+ current in hippocampal and dorsal root ganglion neurons of the rat. 973 Sep 15

HEK293 cells were stably transfected with rat neuronal nicotinic alpha4 and beta2 subunits. Binding of tritiated cytisine and nicotine to cell homogenates revealed the presence of a single class of high-affinity sites (dissociation constants 0.1 nM and 0.4 nM, respectively). Activation of nicotinic receptors was studied using whole-cell patch clamp methods, and acetylcholine, nicotine, dimethylphenylpiperazinium, and cytisine all produced a conductance increase. Responses desensitized to prolonged applications, at both positive and negative membrane potentials. The conductance was strongly rectifying, and outward currents were essentially absent. Responses were maximal at about 2 mM external calcium ion concentration and were reduced by about one-half at either nominally 0 or 10 mM external calcium. Di-hydro-beta-erythroidine blocked physiological responses to acetylcholine and nicotine (IC50, 2.5 nM), and reduced cytisine binding in a competitive manner (Ki 20 nM). Physostigmine enhanced the response to low concentrations of acetylcholine or nicotine. The anesthetic steroid (+)-3alpha-hydroxy-5alpha-androstane-17beta-carbonitrile blocked responses to acetylcholine (IC50, 1.3 microM), but had no effect on cytisine binding at a concentration of 30 microM. The binding properties of the receptors are those expected for rat neuronal nicotinic receptors composed of alpha4 and beta2 subunits. The pharmacological properties indicate that the responsiveness of the receptors may be allosterically enhanced or inhibited.
Mol Pharmacol 1999 Jan
PMID:Ligand binding and activation of rat nicotinic alpha4beta2 receptors stably expressed in HEK293 cells. 988 98


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