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This study was designed to evaluate the capacity of vitrified-warmed porcine immature oocytes to mature and to be fertilized using in vitro fertilization or intracytoplasmic sperm injection, and to determine the subsequent embryo development. Immature oocytes were vitrified using ethylene glycol and dimethylsulphoxide as cryoprotectants and the Cryolock method. After warming oocytes were cultured 44 h for maturation. Oocytes were randomly distributed in three treatment groups and subjected to in vitro fertilization (Experiment 1) or intracytoplasmic sperm injection (Experiment 2) procedures. The results indicate that the embryo development was higher in denuded oocytes co-cultured with granulosa cells (NkO-CC group) fertilized by in vitro fertilization or intracytoplasmic sperm injection compared to cumulus-cell oocyte complexes (COCs group), showing no significant differences with control. Vitrified denuded oocytes matured with a co-culture system NkO-CC group, displayed higher cleavage rate and blastocyst production than vitrified COCs group. Blastocysts were successfully obtained after IVF and ICSI procedures; however, the development to the blastocyst stage was better after IVF. These results show that the vitrification-warming media, the employment of a granulosa cell co-culture system and the Cryolock method during vitrification, increased the nuclear and cytoplasmic maturation of vitrified porcine immature oocytes. Further experiments are required to enhance porcine embryo production after vitrification., (Copyright © 2015 Elsevier Inc. All rights reserved.)

17β-amino-1,3,5(10)estratrien-3-ol (17βAE2), is the 17β-aminoestrogens prototype possessing anticoagulant activity, contrasting with the procoagulant effects of 17β-estradiol (17βE2). Its estrogenicity profile has not been reported, and it was evaluated by uterotrophic assay, estrogen receptor binding affinity and its ability to induce gene transcription of the human estrogen receptor (hER)α mediated in a Saccharomyces cerevisiae yeast expression system. Additionally, 17βAE2 and 17αAE2 were compared with 17βE2 in HeLa cells co-transfected with expression vectors for hERα or hERβ subtypes and for an estrogen-responsive reporter gene. Immature female CD1 mice and Wistar rats (21 days old) were treated for three days with 17βAE2 (10-5000 μg/kg), 17βE2 (0.001-1000 μg/kg) or vehicle (propylenglycol 10 ml/kg) and uterine weights were estimated. 17βAE2 increased uterine weight in a dose-dependent manner. The effective dose (ED)50 uterine weight values: 17βAE2=552 and 764 μg/kg (17βE2=4.8 and 16 μg/kg) and their relative uterotrophic potency were 0.86 and 2.1 (17βE2=100) in mice and rats, respectively. 17βAE2 competed with [(3)H]E2 for the estrogen receptor. The 17βAE2 relative binding affinities (RBAs) were: 0.074; Ki=2.2×10(-6)M (17βE2=100; Ki=1.6×10(-9)M); 0.029 and Ki=3.8×10(-6)M (17βE2=100; Ki=1.1×10(-9)M) for mice and rats uteri respectively. 17βAE2 activated hERα-mediated β-galactosidase transcription activity in the yeast system co-transfected with hERα gene. 17βAE2 effective concentration (EC)50=1.82 μM (17βE2=2.14 nM) with a relative potency of 0.12 (17βE2=100). These transactivation effects were abolished by the antagonist fulvestrant (ICI 182,780), similarly to 17βE2. 17βAE2 and 17αAE2 bind with low relative affinity to hERα and hERβ. Both induced hER-mediated reporter gene transactivation in a dose-response manner. The overall results provide evidence that 17βAE2 has a weak agonist estrogenic action greatly mediated through the hERβ and to a lesser extent the hERα at genomic level., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This study was designed to evaluate the efficiency of two oocyte vitrification-warming procedures using two different devices: Superfine Open Pulled Straws (SOPS) and Cryolock, as well as the effect of the co-culture of vitrified immature oocytes with fresh granulosa cells to improve in vitro maturation (IVM). Immature oocytes were vitrified with two procedures: A) Oocytes were exposed to an increasing concentration of ethylene glycol (EG) from 4% to 35% with 0.5 M trehalose. They then, were loaded in SOPS or Cryolock. For warming, oocytes were exposed to decreasing concentrations of trehalose 0.3, 0.2 and 0.1 M for IVM. B) Oocytes were exposed to two mixtures of EG and dimethylsulfoxide (Me2SO), at 7.5% and 16%, both with 0.4 M of sucrose and then loaded in SOPS or Cryolock and stored in liquid nitrogen. For warming, oocytes were exposed to a single concentration of sucrose 0.5M. After warming, viability was determined; and after 44 h of IVM both viability and meiotic stages were evaluated. The results indicate no significant differences between procedures A and B with SOPS in all maturation stages, reaching a maximum maturation rate of 21%. As to Cryolock, significant differences were observed between both procedures, being procedure B, more efficient with a yield of 38% in MII stage and increased to 49% due to the co-culture with fresh granulosa cells. In conclusion, viability and maturation rates were improved with Cryolock and procedure B with the co-culture system in vitrified immature oocytes., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Testosterone (T) restores bone mass loss in postmenopausal women and osteoporotic men mainly through its bioconversion to estradiol (E2). In target tissues, T is also biotransformed to the A-ring-reduced metabolites 3α,5α-androstanediol (3α,5α-diol) and 3β,5α-androstanediol (3β,5α-diol), which are potent estrogen receptor (ER) agonists; however, their biological role in bone has not been completely elucidated. To assess if osteoblasts bioconvert T to 3α,5α-diol and to 3β,5α-diol, we studied in cultured neonatal rat osteoblasts the metabolism of [14C]-labeled T. In addition, the intrinsic estrogenic potency of diols on cell proliferation and differentiation in neonatal calvarial rat osteoblasts was also investigated. Osteoblast function was assessed by determining cell DNA, cell-associated osteocalcin, and calcium content, as well as alkaline phosphatase activity and Alp1 gene expression. The results demonstrated that diols were the major bioconversion products of T, with dihydrotestosterone being an obligatory intermediary, thus demonstrating in the rat osteoblasts the activities of 5α-steroid reductase and 3α- and 3β-hydroxysteroid dehydrogenases. The most important finding was that 3β,5α- and 3α,5α-diols induced osteoblast proliferation and differentiation, mimicking the effect of E2. The observation that osteoblast differentiation induced by diols was abolished by the presence of the antiestrogen ICI 182,780, but not by the antiandrogen 2-hydroxyflutamide, suggests that diols effects are mediated through an ER mechanism. The osteoblast capability to bioconvert T into diols with intrinsic estrogen-like potency offers new insights to understand the mechanism of action of T on bone cells and provides new avenues for hormone replacement therapy to maintain bone mass density.

The anticoagulant activity of 17ß-amino-1,3,5(10)estratrien-3-ol (AE(2)) was established for the first time. Experiment 1: mice groups were treated with a single subcutaneous (s.c.) AE(2) injection (0.5, 1, 2, 4, and 8 mg/100 g BW) or vehicle (propylenglycol; 0.5 ml/100 g). After 24 h, AE(2) produced dose-dependent blood clotting time increases related to control, Emax=+121% (P<0.01) finishing the sixth day. Experiment 2: four groups received a single s.c. administration of AE(2) (4 or 8 mg/100g BW) or 17ß-estradiol (E(2); 3mg/100g BW) or vehicle. After 24 and 48 h post-administration, the times of blood clotting, prothrombin, thrombin, and activated partial thromboplastin and fibrinogen concentrations were assessed. Both AE(2) doses increased blood clotting and fibrinogen similarly, blood clotting time: 64, 94%; fibrinogen: 71, 107% (P<0.01). Prothrombin, activated partial thromboplastin and thrombin times, increased 13-15%, 27-55%, and 15-29%, respectively (P<0.01). Meanwhile E(2) decreased blood clotting 20% (P<0.01) and thrombin 23% (P<0.01) after 48 h. Experiment 3: for five consecutive days, mice received AE(2) or E(2) (0.1, 1, 10, 100, and 1000 μg/kg/day), or vehicle. Blood clotting time was assessed at 1, 2, 3, 4, 5, 8, and 11 days after treatment. AE(2) at all doses were anticoagulant for 2-3 days after administration whereas E(2) was procoagulant for 8-11 days. These opposite effects were: AE(2) Emax=+29%; E(2) Emax=-30%; (P<0.01). AE(2) is the parent compound of the 17ß-aminoestrogens, with the largest and longest anticoagulant effect until now reported., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Background: Buame [17β-(butylamino)-1,3,5(10)-estratrien-3-ol] possesses anticoagulant and antiplatelet activities that are potentially antithrombotic. Since its estrogenicity is unknown, it was evaluated by established methods., Methods: Buame (10, 100, 500, and 1,000 μg/kg), 17β-estradiol (E(2)) (100 μg/kg), or propylene glycol (10 ml/kg) were subcutaneously (sc) administered for three days to immature Wistar female rats (21 days old). The relative uterotrophic effect to E(2) was 78 (E(2) = 100) with a relative uterotrophic potency of 1.48 (E(2) = 100). Adult ovariectomized Wistar rats received an sc injection at 8:00 h (reversed cycle) of: 7.5 μg of E(2) (≈ 30 μg/kg), buame (≈ 750, 1,500, 3,000 μg/kg), or corn oil (≈ 1.2 ml/kg). After 24 h, progesterone (4-5 mg/kg) was administered. Sexual receptivity was assessed 5 to 7 h later, and the lordosis quotient (LQ; number lordosis/number mounts x 100) was evaluated., Results: Buame induced lordosis (LQmax 85 ± 9; ED50 952 ± 19 μg/kg) and E(2) LQmax 56 ± 8; ED50 10 ± 2 μg/kg; the relative LQ-potency was 0.51 (E(2) = 100). Buame competed with [(3)H]E(2) for the estrogen receptor (Buame RBA= 0.15 and Ki = 5.9 x 10(-7) M; E(2) RBA= 100;Ki = 6.6 x 10(-9) M). Buame increased MCF-7 cells proliferation, from 10(-11) to 10(-)9 M, its proliferative effect was 1.73-1.79 (E(2) = 3.0-3.9); its relative proliferative effect to E(2) was 33-40% (E(2) = 100%) and relative potency 10.4-10.7 (E(2) = 100). Tamoxifen and fulvestrant (ICI 182,780) inhibited buame's proliferation indicating mediation through estrogen receptors in this response., Conclusion: Buame is therefore an estrogen partial agonist with a weak estrogenic activity.

A number of clinical studies have demonstrated that norethisterone (NET), a potent synthetic progestin, restores postmenopausal bone loss, although its mode of action on bone cells is not fully understood, while the effect of naturally occurring progesterone in bone has remained controversial. A recent report claims that the potent effects of NET on osteoblastic cell proliferation and differentiation, mimicking the action of estrogens, are mediated by non-phenolic NET derivatives. To determine whether osteoblasts possess the enzymes required to bioconvert a progesterone receptor (PR) agonist into A-ring reduced metabolites with affinity to bind estrogen receptor (ER), we studied the in vitro metabolism of [(3)H]-labeled NET in cultured neonatal rat osteoblasts and the interaction of its metabolic conversion products with cytosolic -osteoblast ER, employing a competition analysis. Results indicated that NET was extensively bioconverted (36.4%) to 5 alpha-reduced metabolites, including 5 alpha-dihydro NET, 3 alpha,5 alpha-tetrahydro NET (3 alpha,5 alpha-NET) and 3beta,5 alpha-tetrahydro NET (3beta,5 alpha-NET), demonstrating the activities of 5 alpha-steroid reductase and two enzymes of the aldo-keto reductases family. Expression of Srd5a1 in neonatal osteoblast was well demonstrated, whereas Srd5a2 expression was not detected. The most striking finding was that 3beta,5 alpha-NET and 3 alpha,5 alpha-NET were efficient competitors of [(3)H]-estradiol for osteoblast ER binding sites, exhibiting affinities similar to that of estradiol. The results support the concept that the interplay of 5 alpha-steroid reductase and aldo-keto reductases in osteoblastic cells, acting as an intracrine modulator system is capable to bioconvert a PR agonist into ER agonists, offering an explanation of the molecular mechanisms NET uses to enhance osteoblastic cell activities.

The key role of estrogens on osteoblastic cell function is well documented; however, the role of progesterone (P) and synthetic progestins remains controversial. While several reports indicate that P has no significant effects on bone cells, a number of clinical studies have shown that 19-norprogestins restore postmenopausal bone loss. The mechanisms by which 19-norprogestins induce estrogen-like effects on bone cells are not fully understood. To assess whether the actions of 19-norprogestins on osteoblasts are mediated by their non-phenolic metabolites, we studied the effects of norethisterone (NET), levonorgestrel (LNG), and two of their A-ring reduced derivatives upon cell proliferation and differentiation in neonatal rat osteoblasts. Osteoblast function was assessed by determining cell DNA, cell-associated osteocalcin and calcium content, alkaline phosphatase activity, and mineral deposition. P failed to induce changes on osteoblasts, while NET and LNG exerted a number of actions. The most striking finding was that the 3beta,5alpha- and 3alpha,5alpha-tetrahydro derivatives of NET and LNG induced osteoblast proliferation and differentiation with higher potency than those exerted by their parent compounds, mimicking the effects of estradiol. Interestingly, osteoblast differentiation and mineral deposition induced by NET and LNG were abolished by finasteride, a 5alpha-reductases inhibitor, while the potent effect on osteoblast proliferation induced by progestin derivatives was abolished by a steroidal antiestrogen. Results demonstrate that A-ring reduced derivatives of NET and LNG exhibit intrinsic estrogen-like potency on rat osteoblasts, offering a plausible explanation for the mechanism of action of 19-norprogestins in bone restoration in postmenopausal women and providing new insights for hormone replacement therapy research.

Estrogen receptor alpha (ERalpha) participates in the neuroendocrine regulation of male sexual behavior, primarily in brain areas located in the limbic system. Males of many species present a long-term inhibition of sexual behavior after several ejaculations, known as sexual satiety. It has been shown that androgen receptor density is reduced 24 h after a single ejaculation or mating to satiety, in the medial preoptic area, nucleus accumbens and ventromedial hypothalamus. The aim of this study was to analyze if the density of ERalpha was also modified 24 h after a single ejaculation or mating to satiety. Sexual satiety was associated with an increased ERalpha density in the anteromedial bed nucleus of the stria terminalis (BSTMA), ventrolateral septum (LSV), posterodorsal medial amygdala (MePD), medial preoptic area (MPA) and nucleus accumbens core (NAc). A single ejaculation was related to an increase in ERalpha density in the BSTMA and MePD. ERalpha density in the arcuate (Arc) and ventromedial hypothalamic nuclei (VMN), and serum estradiol levels remained unchanged 24 h after one ejaculation or mating to satiety. These data suggest a relationship between sexual activity and an increase in the expression of ERalpha in specific brain areas, independently of estradiol levels in systemic circulation.

Breast cancer is a sex steroid hormone-dependent malignant neoplasia. The role of oestradiol in this malignancy has been well documented; however, the involvement of androgens has remained controversial. To determine the role of non-phenolic androgen metabolites in human breast cancer, we studied the metabolism of [(14)C] testosterone and [(14)C] androstenedione in oestrogen-dependent MCF-7 cells and non-oestrogen-dependent MDA-MB 231 cells, at different substrate concentrations (1-10 muM) and time periods (30 min-48 h). Cultured non-oestrogen-dependent HeLa and yeast cells served as controls. Metabolites were identified and quantified by reverse isotope dilution. A distinctive pattern of androgen metabolism was identified in MCF-7 cells, being the 5alpha-androstane-3alpha,17beta-diol (3alpha,5alpha-diol) and its 3beta epimer (3beta,5alpha-diol), the major conversion products of testosterone (48.3%), with 5alpha-dihydrotestosterone as intermediary. The formation of 3alpha,5alpha-diol and 3beta,5alpha-diol (diols) was substrate concentration- and time-dependent, and abolished by finasteride. In contrast, very little of any diol formation was observed in MDA-MB 231, HeLa and yeast cell incubations. Additional enzyme gene expression studies revealed an overexpression of 5alpha-steroid reductase type-1 in MCF-7 cells, as compared with MDA-MB 231 cells. The oestrogen-like activities of diols were assessed in HeLa cells co-transfected with expression vectors for alpha or beta subtypes of the human oestrogen receptor (hER) genes and for an oestrogen-responsive reporter gene. The results show that 3beta, 5alpha-diol and to a lesser extent 3alpha,5alpha-diol bind with high relative affinity to hERalpha and hERbeta. Both diols induced hER-mediated reporter gene transactivation in a dose-response manner, similar to that induced by oestradiol, though with lower potency, an effect that was abolished by ICI-182 780. Furthermore, 3beta,5alpha-diol and to lesser extent 3alpha,5alpha-diol induced MCF-7 cell proliferation. The overall results demonstrated that MCF-7 cells exhibit enhanced expression and activity of androgen-metabolising enzymes, leading to rapid and large diol formation, and provide evidence that these androgen metabolites exert a potent oestrogen-agonistic effect, at genomic level, in oestrogen-dependent breast cancer cells. The data suggest that diols may act as in situ intracrine factors in breast cancer and that its formation can be pharmacologically inhibited.

The binding of estradiol (E(2)) to estrogen receptors (ER) is followed by conformational changes resulting in coactivator or corepressor recruitment that influences gene transcription. A series of synthetic A-ring reduced 19-nortestosterone-derived progestins has the capacity to selectively bind and activate transcription through the ERalpha. Herein, the molecular mechanisms involved in ER subtype-selective interactions of these compounds as assessed by their effects upon both ERalpha and ERbeta structural conformation and their ability to induce recruitment of steroid receptor coactivator-1 (SRC-1) to ERalpha were investigated. The results demonstrated that all synthetic A-ring 3beta,5alpha-tetrahydro-reduced derivatives of 19-nortestosterone induced an ERalpha trypsin digestion pattern similar to that seen with E(2), without effects upon ERbeta. In addition, these compounds had the ability to recruit SRC-1 to the ligand-binding domain of ERalpha similar to E(2). Our data indicate that A-ring 3beta,5alpha-tetrahydro-reduced 19-nortestosterone-derived progestins behave as selective ERalpha agonists with ligand-receptor structural and functional responses similar to those induced with natural E(2).

Synthetic 19-nortestosterone-derived progestins show affinity for the androgen receptor (AR) and retain varying degrees of androgenic activity. In this study, AR- and progesterone receptor (PR)-dependent transcriptional activation induced by norethisterone (NET), levonorgestrel (LNG) and gestodene (GSD), and their 5alpha-reduced derivatives, including limited trypsin digestion of AR in the presence of natural and synthetic progestins were investigated. The results confirmed the progestogenic activity of the three 19-nortestosterone derivatives, which decreases after reduction of the 4-ene-double bound. These compounds were able to activate AR-dependent reporter gene expression, LNG and GSD being the stronger activators. 5alpha-Reduction of LNG and GSD did not change their androgenic transcriptional activity; however, the activation of AR by 5alpha-NET was four-fold higher than NET. The highest selectivity transcriptional index, as a measure of progestogenicity versus androgenicity, was obtained for NET. The 5alpha-reduced derivatives had values significantly lower than those of their parent compounds. Non-reduced and 5alpha-reduced 19-nortestosterone progestins induced virtually identical proteolysis fragmentation patterns of the AR to those observed with DHT.

Estrogens are generally administered in hormone replacement therapy in combination with synthetic progestins. Studies of cardiovascular risk factors in postmenopausal women have shown a variety of responses according to the molecular structure of the progestin used in hormone replacement therapy schemes. The present study sets out to determine the vasoactive effects of norethisterone and its 5alpha-dihydro (5alpha-norethisterone) and -tetrahydro (3alpha,5alpha-norethisterone and 3beta,5alpha-norethisterone) metabolites in isolated precontracted rat thoracic aorta. The addition of norethisterone and 3alpha,5alpha-norethisterone in rat aorta exhibited a potent, concentration-response inhibition of noradrenaline-induced contraction, while 5alpha- and 3beta,5alpha-norethisterone had very little, if any, vasorelaxing effect. Relaxation to norethisterone and 3alpha,5alpha-norethisterone had very rapid time-courses and it was neither affected by the absence of endothelium nor by the inhibitor of nitric oxide synthase, Nomega-nitro-L-arginine methyl ester (L-NAME). The addition of specific anti-androgen, anti-progestin and anti-estrogen compounds and protein synthesis inhibitors did not preclude the vasorelaxing effect of norethisterone and its 3alpha,5alpha-reduced metabolite. The results strongly suggest that these effects are not mediated by nuclear sex steroid hormone receptors. The overall data document a novel nongenomic endothelium-independent vasorelaxing action of a 19-nor synthetic progestin and one of its A-ring-reduced derivatives.

The alkyl esters of p-hydroxybenzoic acid known as parabens (Pbens) are used as preservatives in food, pharmaceutical and cosmetic formulations. They have been reported as estrogenic. Here, we present evidence for the in vivo and in vitro bioactivities and receptor binding affinities of methylparaben (MePben), ethylparaben (EtPben), propylparaben (PrPben), and butylparaben (BuPben) compared with those of estradiol (E2). Estrogenicity was studied using the uterotrophic assay in immature (Im) and adult ovariectomized (Ovx) CD1 mice, and in immature female Wistar rats (IW). Animals were subcutaneously (sc) treated for three consecutive days with different molar equivalent doses ranging from 3.62 to 1086 micromol/kg body weight of Pbens, E2 (0.036 micromol/kg), or vehicle. Pbens increased uterine weight in Im and Ovx animals and their relative uterotrophic effect to E2 (100) (RUEE2) were from 34 to 91. The relative uterotrophic potencies related to E2 (100) (RUPE2) of these compounds were from 0.003 to 0.007. The E2 ED50 for CD1 animals able to increase the uterine weight was 7 microg/kg (0.9-55 confidence limits); and that of Pbens ranged from 18 to 74 mg/kg. In IW rats, the ED50 were from 33 to 338 mg/kg. All Pbens, except MePb, competed with [3H]E2 for the estrogen receptor binding sites. The uterotrophic effects of Pbens in Im mice have a positive correlation with the side-chain length of the ester group of these compounds. The E2 and Pbens relative binding affinities (RBA) and Ki values correlated to their estrogenic activity. The NOELs values for Pbens uterotrophic activity in Im were from 0.6 to 6.5 mg/kg per day; and Ovx from 6 to 55 mg/kg. The NOELs IW ranged from 16.5 to 70 mg/kg indicating that Im were more susceptible than Ovx and IW to these effects. The data shown here confirm the estrogenicity of Pbens.

Levonorgestrel (LNG), a contraceptive progestin, exhibits, besides its progestational activity, other hormone-like effects at the peripheral level. To assess whether LNG and its metabolites exert androgenic and/or estrogenic actions at the central nervous system (CNS), their effects on male sexual behavior in castrated rats were examined. LNG, 5alpha-dihydro LNG (5alphaLNG), and the 3alpha,5alpha- and 3beta,5alpha-tetrahydro derivatives of LNG (3alphaLNG and 3betaLNG, respectively) were administered for 3 weeks either alone (1000 microg/day) or in combination (300 microg/day) with 5alpha-dihydrotestosterone (DHT, 300 microg/day) or with estradiol-17beta (E(2), 5 microg/day). Copulatory behavior was assessed twice per week and sex accessory organs weights recorded at the end of treatments. LNG restored full copulatory behavior comparable to that of testosterone treated animals, although with a slight delay, whereas 5alphaLNG induced male sexual behavior in a significantly lower number of subjects. 3betaLNG and 3alphaLNG induced mounting but failed to restore intromission and ejaculation. Combined LNG+E(2) treatment fully activated mounting and intromission, but ejaculation was only partially restored. Combined 5alphaLNG+E(2) treatment and the combinations of 3alphaLNG or 3betaLNG with E(2) were significantly less effective, activating fewer intromissions and ejaculations. 3alphaLNG and 5alphaLNG, in combination with DHT, restored male sexual behavior. LNG, but not its metabolites, induced a significant increase on the weight of sex accessory organs. The overall results demonstrated that high doses of LNG induce a potent androgen agonistic behavioral effect and that its A-ring reduction diminishes this potency and enables a shift towards a weak estrogen-like effect.

Levonorgestrel (LNG), a 19-nor-testosterone derivative, is widely used in contraceptive formulations. This compound does not bind to the estrogen receptor (ER), but it shows estrogen-like effects under in vivo and in vitro conditions. The estrogenicity of LNG may be attributed to its bio-transformation into non-phenolic metabolites. In this study, the ability of A-ring reduced LNG metabolites to activate transcription via an estrogenic mechanism of action, including differences between ER alpha and ER beta subtypes, were investigated. Transactivation assays were performed in HeLa cells transfected with expression vectors for ER alpha and ER beta and an estrogen-responsive reporter gene. Cells were also transfected with expression vectors for both progesterone receptor (PR) isoforms (A or B). As expected, the tetrahydro derivatives of LNG (3 alpha,5 alpha- and 3 beta,5 alpha-LNG) showed significantly lower PR-mediated transcriptional activities through both isoforms when compared with progesterone (P(4)) and LNG. In contrast, the 3 beta,5 alpha-tetrahydro derivative resulted in a significant activation of estrogen-dependent gene transcription. This effect was selectively confined to the ER alpha, since little if any activity could be observed with the ER beta and no antagonistic activities were demonstrated. This study provides structural and molecular clues for the well documented in vitro and in vivo intrinsic estrogenicity of 19-nor-testosterone-derived progestins and ligand requirements for ER alpha recognition.

Levonorgestrel (13beta-ethyl-17alpha-ethynyl-17beta-hydroxy-4-gonen-3-one), a potent contraceptive progestin stimulates growth and proliferation of cultured breast cancer cells through a receptor-mediated mechanism, even though levonorgestrel does not bind to the oestrogen receptor (ER). To assess whether the oestrogen-like effects induced by this synthetic progestin are exerted via its metabolic conversion products, we studied the binding affinity of three A-ring levonorgestrel derivatives to the ER and their capability to transactivate an oestrogen-dependent yeast system co-transfected with the human ER gene and oestrogen responsive elements fused to a beta-galactosidase reporter vector. The results demonstrated that the 3beta,5alpha reduced levonorgestrel derivative and to a lesser extent its 3alpha isomer interact with the oestrogen receptor, with a significantly lower relative binding affinity (2.4% and 0.4%, respectively) than that of oestradiol (100%), while levonorgestrel does not. Both levonorgestrel metabolites were able to activate, in a dose-dependent manner, the beta-galactosidase reporter gene in the yeast expression system, an effect that was precluded by a steroidal antioestrogen. The oestrogenic potency of levonorgestrel metabolites was significantly lower (750-fold) than that of oestradiol. Furthermore, high doses of 3beta,5alpha levonorgestrel (2.5 mg/day/6 days) induced an increase of oestrogen-dependent progestin receptor in the anterior pituitary of castrated rats. The overall data offer a plausible explanation for the weak oestrogenic effects induced by high, non-pharmacological doses of levonorgestrel.

It has previously been demonstrated that 19-nor contraceptive progestins undergo in vivo and in vitro enzyme-mediated A-ring double bond hydrogenation. Bioconversion of 19-nor progestins to their corresponding tetrahydro derivatives results in the loss of progestational activity and acquisition of estrogenic activities and binding to the ER. Herein, we report subtype-selective differences in ligand binding and transcriptional potency of nonphenolic synthetic 19-nor derivatives between ER alpha and ER beta. In this study, we have examined both ER- and PR-mediated transcriptional activity of a number of A-ring chemically reduced derivatives of norethisterone and Gestodene. Double bond hydrogenation decreased the transcriptional potency of norethisterone and Gestodene through both PR isoforms with a 100- to 1,000-fold difference, respectively. In terms of the effects of norethisterone and Gestodene and their corresponding 5 alpha-dihydro (5 alpha-norethisterone and 5 alpha-Gestodene), or 3 alpha,5 alpha-tetrahydro or 3 beta,5 alpha-tetrahydro derivatives (3 alpha,5 alpha-norethisterone/3 alpha,5 alpha-Gestodene and 3 beta,5 alpha-norethisterone/3beta,5 alpha-Gestodene, respectively) on estrogen-mediated transcriptional regulation, the 3 beta,5 alpha-tetrahydro derivatives of both norethisterone and Gestodene showed the highest induction when HeLa cells were transiently transfected with an expression vector for ER alpha. This activity could be inhibited with tamoxifen. These compounds did not activate gene transcription via ER beta, and none of them showed antagonistic activities through either ER subtype. The 3 beta,5 alpha-tetrahydro derivatives of both norethisterone and Gestodene were active in other cells in addition to HeLa cells and activated reporter expression through the oxytocin promoter. In summary, two ER alpha selective agonists have been identified. These compounds, with ER alpha vs. ER beta selective agonist activity, may be useful in evaluating the distinct role of these receptors as well as in providing useful insights into ER action.

Gestodene (13beta-ethyl-17alpha-ethynyl-17beta-hydroxy-4,5-gonadien-3-one), the most potent progestin ever synthesized, stimulates breast cancer cell growth through an oestrogen receptor-mediated mechanism, and its use in hormonal contraception has been associated with side effects attributable to oestrogenic actions. These observations have remained controversial, since gestodene does not bind to the oestrogen receptor or exert oestrogen-like activities. Recently, we have demonstrated that non-phenolic gestodene derivatives interact with oestrogen receptors and induce oestrogenic effects in cell expression systems. To assess whether gestodene is biotransformed to metabolites with intrinsic oestrogenic potency, [3H]- and [14C]-labelled gestodene were incubated in vitro with rat anterior pituitary, hypothalamus and ventral prostate homogenates under different experimental conditions. The most remarkable finding was the isolation and identification of 3beta,5alpha-tetrahydrogestodene and 3alpha,5alpha-tetrahydrogestodene as metabolic conversion products of gestodene, presumably with 5alpha-dihydrogestodene as intermediate. The overall results seem to indicate that the weak oestrogenic effects attributable to gestodene could be mediated by its tetrahydro metabolites.

Gestodene (17 alpha-ethynyl-13 beta-ethyl-17 beta-hydroxy-4, 15-gonadien-3-one) is the most potent synthetic progestin currently available and it is widely used as a fertility regulating agent in a number of contraceptive formulations because of its high effectiveness, safety and acceptability. The observation that contraceptive synthetic progestins exert hormone-like effects other than their progestational activities, prompted us to investigate whether gestodene (GSD) administration may induce oestrogenic effects, even though the GSD molecule does not interact with intracellular oestrogen receptors (ER). To assess whether GSD may exert oestrogenic effects through some of its neutral metabolites, a series of experimental studies were undertaken using GSD and three of its A-ring reduced metabolites. Receptor binding studies by displacement analysis confirmed that indeed GSD does not bind to the ER, whereas its 3 beta,5 alpha-tetrahydro reduced derivative (3 beta GSD) interacts with a relative high affinity with the ER. The 3 alpha,5 alpha GSD isomer (3 alpha GSD) also binds to the ER, though to a lesser extent. The ability of the A-ring reduced GSD derivatives to induce oestrogenic actions was evaluated by the use of two different molecular bioassays: (a) transactivation of a yeast system co-transfected with the human ER alpha (hER alpha) gene and oestrogen responsive elements fused to the beta-galactosidase reporter vector and (b) transactivation of the hER alpha-mediated transcription of the chloramphenicol acetyl transferase (CAT) reporter gene in a HeLa cells expression system. The oestrogenic potency of 3 beta GSD was also assessed by its capability to induce oestrogen-dependent progestin receptors (PR) in the anterior pituitary of castrated female rats. The results demonstrated that 3 beta GSD and 3 alpha GSD were able to activate, in a dose-dependent manner, the hER alpha-mediated transcription of both the beta-galactosidase and the CAT reporter genes in the yeast and HeLa cells expression systems respectively. In both assays the 3 beta derivative of GSD exhibited a significantly greater oestrogenic effect than its 3 alpha isomer, while unchanged GSD and 5 alpha GSD were completely ineffective. Neither 3 beta GSD nor 3 alpha GSD exhibited oestrogen synergistic actions. Interestingly, the pure steroidal anti-oestrogen ICI-182,780 diminished the transactivation induced by 3 beta GSD and 3 alpha GSD in the yeast expression system. Furthermore, administration of 3 beta GSD resulted in a significant increase of oestrogen-dependent PR in the anterior pituitaries of castrated rats in comparison with vehicle-treated animals. The characteristics of the 3 beta GSD-induced PR were identical to those induced by oestradio benzoate. The overall results demonstrate that 3 beta GSD and its 3 alpha isomeric alcohol specifically bind to the ER and possess a weak intrinsic oestrogenic activity, whereas unmodified GSD does not. The data contribute to a better understanding of the GSD mechanism of action and allow the hypothesis to be advanced that the slight oestrogenlike effects attributable to GSD are mediated by its non-phenolic, tetrahydro reduced metabolites.

Estrogenic activities of the two 17beta-aminoestrogen (AE) derivatives, prolame and butolame, were studied upon coagulation, serum luteinizing hormone (LH) and uterine weight, including endometrial morphology in castrated female rats. We have also investigated the ability of these two compounds, as well as another AE pentolame, to activate transcription through the estrogen receptor alpha (ERalpha) and the estrogen receptor beta (ERbeta). Administration of prolame and butolame to castrated animals increased significantly (P < 0.01) the mean clotting time when compared with that obtained in the group of control animals. Butolame was a more potent anticoagulant than prolame (P < 0.01), as judged by their corresponding IC(50) (5.4 +/- 0.65 and 66.6 +/- 2.57 micro;g/animal, respectively). In contrast, estradiol significantly shortened blood clotting times (P < 0.005). Both prolame and butolame caused a significant inhibition of serum LH levels (EC(50) 8.10 +/- 0.79 and 17 +/- 64 microg/animal, respectively), and restored castration-induced reduction in uterine weight of ovariectomized rats (EC(50) 4.14 +/- 1.57 and 17.0 +/- 1.78 microg/animal, respectively). In terms of the effects of prolame, butolame and pentolame in transient transfection assays, all the three AE activated ER dependent reporter gene expression, however, only at high concentrations. Prolame had the highest activity followed by butolame and pentolame. Induction of transcription by these compounds was preferentially mediated through the ERalpha, especially in the case of pentolame where little, if any, activation occurred through the ERbeta. None of the compounds showed antagonistic activities through either ER subtype. The overall data suggest that modifications in the structure and length of the amino-alcohol side-chain at C-17 might have an impact on the affinity and estrogenic intrinsic properties of AE at the level of diverse target tissues.

Norethisterone (NET) and its metabolite 5alpha-norethisterone (5alpha-NET) are competitors for the androgen receptor. The sensitivity of the rat vas deferens to the contractile action of methoxamine and serotonin is regulated by hormonal and anatomical factors. The aim of this study was to evaluate the ability of NET and 5alpha-NET to induce the androgen-regulated contractile response to methoxamine and serotonin in the epididymal and prostatic portions of rat vas deferens. Adult male rats either intact, castrated or steroid-treated castrated were used. The contractility was recorded isometrically, and non-cumulative concentration-response curves to either methoxamine or serotonin were obtained. NET and 5alpha-NET partially restored the sensitivity to methoxamine and serotonin in the epididymal portion of castrated rats. The maximal responses to both agonists were significantly higher than those observed in castrated rats, and significantly lower than the responses observed in either intact or androgen-treated castrated rats. The prostatic portion was less responsive to both agonists than the epididymal portion, in all groups but castrated rats, as castration induced sensitivity to both agonists. NET and 5alpha-NET displayed a partial though similar androgenic activity in the rat vas deferens. These results contrast with previous reports where a decrease of androgenic effect due to the 5alpha-reduction of NET has been found.

In this study, we investigated the effects of pentolame, a 17 beta-aminoestrogen derivative, upon coagulation, serum LH, pituitary progestin receptors, uterine weight, and endometrium morphological changes in the castrated female rat. Groups of animals were subcutaneously (s.c.) injected with either estradiol (E2) (0.1 up to 1000 micrograms/animal), pentolame (1 up to 1000 micrograms/animal), or the vehicle alone daily for 5 consecutive days starting 2 weeks following ovariectomy. Administration of pentolame (10 to 1000 micrograms/animal) increased significantly (p < 0.05) the blood clotting time when compared with that obtained in the group of control animals (EC50 582 micrograms). Pentolame (500 and 1000 micrograms/rat for 5 days) caused a significant inhibition (p < 0.01) of serum LH levels (IC50 860 micrograms), which remained suppressed until Day 5 post last injection. In addition, treatment with pentolame was able to restore in the castrated female rat the presence of specific estrogen-dependent progestin binding sites at the anterior pituitary level. The affinity constants and the number of binding sites of pentolame-induced progestin receptors were similar to those obtained with estradiol at equipotent doses (860 micrograms vs. 1 microgram/animal, respectively). Administration of the 17 beta-aminoestrogen derivative resulted in a significant increase in uterine weight (EC50 420 micrograms) and endometrial characteristics were indistinguishable from those observed in the group of rats treated with E2.

The putative anxiolytic action of the synthetic progestins, norethisterone (NET), levonorgestrel (LNG) and their respective 5 alpha-reduced metabolites, (5 alpha-NET), (3 alpha,5 alpha-NET), (3 beta,5 alpha-NET), (5 alpha-LNG), (3 alpha,5 alpha-LNG) and (3 beta,5 alpha-LNG), were studied in the burying behavior paradigm. From these compounds only 3 alpha,5 alpha-NET and 3 beta,5 alpha-LNG reduced burying behavior without modifying other parameters. Burying behavior latency was prolonged after administration of the highest dose (1.0 mg/rat) of NET and 5 alpha-NET. As a positive control 3 alpha,5 alpha-pregnanolone (allopregnanolone) was included at the same doses used for synthetic steroids. This steroid produced a clear dose-dependent reduction in burying behavior without affecting latency. No steroid with anxiolytic properties affected the general ambulatory behavior. All synthetic steroids with anxiolytic activity proved to be less potent than allopregnanolone. Results are discussed on the basis of the chemical structure requirements necessary to induce tranquilizing effects.

Norethisterone (NET), a 19-nor synthetic progestin, undergoes enzyme-mediated 5alpha-reduction and exerts potent androgenic effects in target organs. To investigate its mode of androgenic action we examined, in a comparative manner, the in vitro metabolism of NET and testosterone (T), as well as the binding affinities to androgen receptors (AR) and the androgenic potency of NET, T, and their 5alpha-reduced derivatives. Bioconversion of [3H]-NET and [3H]-T was studied in rat prostate homogenates, AR binding affinity was assessed in rat ventral prostates using [3H]-mibolerone as the radioligand, and the androgenic potency was evaluated by the increase of beta-glucuronidase activity in the mouse kidney, and by the growth of accessory sex organs in castrated male rats. The results demonstrated that 5alpha-NET displayed a higher AR binding affinity but a significantly lower androgenic potency than unchanged NET. The bioconversion studies indicated that the metabolism of NET was similar to that of T, although to a lesser extent, thus ruling out the possibility that the synthetic progestin metabolizes rapidly into less active derivatives. To investigate the nature of the paradoxical effect of 5alpha-reduction upon the NET molecule, the interaction with AR and the androgenic potency of T, 19-nortestosterone (19norT), 17alpha-ethynyl testosterone (ET) and their 5alpha-reduced derivatives were examined. The results of AR binding studies revealed that 5alpha-reduction of T and ET significantly enhanced their affinities, and that the 5alpha-derivative of 19norT displayed a similar binding affinity to that exhibited by 19norT. In terms of biological activity, the results showed that 5alpha-reduction of T and 19norT significantly increased their androgenic potency, whereas 5alpha-reduction of ET resulted in a significant diminution of its androgenicity in a manner similar to that observed with the 5alpha-reduction of NET. When NET and 19norT were simultaneously administered with 5alpha-dihydrotestosterone they exhibited a potent synandrogenic activity, an effect that was cancelled by their 5alpha-reduction. Interestingly, ET displayed an antiandrogenic activity, an effect that was also suppressed by its 5alpha-reduction. The overall results demonstrated a distinctive, paradoxical effect of 5alpha-reduction upon the NET molecule, which was different from that seen in naturally occurring androgens, and which suggests that the presence of the 17alpha-ethynyl group plays a key role in this phenomenon. The data provided further evidence that the metabolism of synthetic contraceptive progestins modulates the expression of their hormone-like actions.

The 5 alpha-reduction of levonorgestrel (LNG) as well as its binding capacity to the androgen receptors of the hamster flank organ were investigated. Furthermore, the effects of LNG and its 5 alpha-reduced metabolite in the flank organ test and on [U-14C]glucose incorporation into lipids by this tissue were determined. Homogenates from female hamster flank organs were incubated in the presence of [3H]LNG at pH 7.4. The radioactive 5 alpha-LNG metabolite was isolated and its purity was assessed. Competition experiments for androgen binding receptors were carried out with 1.38 nM [3H-7 alpha-17 alpha]dimethyl-19- nortestosterone (DMNT), Kd, plus a range of increasing concentrations of the different unlabeled steroid hormones. The flank organ test was performed in vivo, and [U-14C]glucose incorporation into lipids was determined under organ culture conditions. The 5 alpha-LNG had the same binding capacity to androgen receptors (AR) as LNG in male flank organs. The flank organ test demonstrated that 5 alpha-LNG activity was similar to that observed for levonorgestrel and testosterone (T) on gonadectomized male hamster flank organs. Topical applications of LNG or 5 alpha-LNG increased [U-14C]glucose incorporation into lipids in a way similar to that of T. The overall data indicate that LNG and 5 alpha-LNG produced androgenic activity in the lipid pathway of male flank organs, and that 5 alpha-reduction is not essential for the LNG effect on this tissue.

The estrogen-like effects of norethisterone (NET) seem to be mediated by the interaction of 3 beta 5 alpha- and 3 alpha 5 alpha-tetrahydronorethisterone (3 beta 5 alpha- and 3 alpha 5 alpha-NET, respectively) with the estrogen receptor. Considering that the in vitro uterine contractile response to serotonin (5-HT) is specifically dependent on estrogen, the aim of the present study was to investigate whether NET and its A-ring reduced metabolites administered in vivo to ovariectomized rats induce uterine sensitivity to 5-HT in vitro. The administration of 3 beta NET in vivo, which is the NET metabolite with the highest affinity for the estrogen receptor, induced a maximal contractile response to serotonin similar to that of 17 beta-estradiol treatment. The other metabolites induced less uterine activity. According to the effective dose 50, the order of estrogenic potency was 17 beta-estradiol > 3 beta 5 alpha NET > 3 alpha 5 alpha NET > NET > 5 alpha NET. The estrogenic effect of 3 beta 5 alpha- and 3 alpha 5 alpha NET may be exerted through their interaction with the estrogen receptor, whereas NET and 5 alpha NET, which do not bind to the estrogen receptor and display a minor estrogenic activity, require prior bioconversion to 3 beta 5 alpha NET and perhaps to 3 alpha 5 alpha NET. The A-ring reduced metabolites of NET, mainly the 3 beta 5 alpha NET, may be exerting estrogenic responses and modulating uterine activity when administered in vivo.

To assess whether naturally occurring 5 alpha-androstanediols (5 alpha-androstane-3 alpha, 17 beta-diol and 5 alpha-androstane-3 beta, 17 beta-diol) play a role in the regulation of male sexual behavior in the rat, their capability to restore copulatory behavior in castrated animals was evaluated. Androstanediols were chronically administered either alone or in combination with 5 alpha-dihydrotestosterone (DHT) or with estradiol-17 beta (E2). Animals treated with testosterone (T), DHT, E2, and vehicle, either alone or in different combinations, served as controls. The occurrence of mounting, intromission, and ejaculation as well as detailed parameters of copulatory behavior were recorded twice per week for 3 weeks. At the end of treatments, the weights of sex accessory organs were also recorded. When 3 beta, 5 alpha-androstanediol (3 beta-diol; 500 micrograms/day) was administered in combination with DHT (300 micrograms/day), full copulatory behavior was restored in all subjects in a manner similar to that obtained with E2 plus DHT or T plus DHT combinations, thus indicating an estrogen-like behavioral effect of 3 beta-diol. Administration of 3 alpha, 5 alpha-androstanediol (3 alpha-diol; 500 micrograms/day) combined with DHT also restored sexual behavior, though to a lesser extent. When 3 alpha-diol (500 micrograms/day) was simultaneously administered with E2 (5 micrograms/day), the copulatory behavior of castrated animals was fully restored in a fashion similar to that observed after administration of DHT plus E2 and T plus E2 combinations, indicating a potent androgen-like effect of 3 alpha-diol.(ABSTRACT TRUNCATED AT 250 WORDS)

The synthetic steroid 7 alpha-methyl-19-nortestosterone (MENT) binds with high affinity to the androgen receptor and exerts biological effects at some peripheral target tissues with a potency greater than that of naturally occurring androgens. In vivo, MENT does not undergo enzymatic 5 alpha-reduction and as a consequence, its biologic action on prostate and other organs of the male reproductive tract is not amplified as is that of testosterone (T). Thus, in castrated rats, a dose of MENT that will maintain normal muscle mass and gonadotropin levels will not maintain normal prostate and seminal vesicle weights. To investigate the ability of MENT to restore male sexual behavior in castrated rats, varying doses of MENT acetate were administered for 4 wk by use of s.c. mini-osmotic pumps. Animals treated with T acetate (200 micrograms/day) and nontreated intact animals served as positive controls, while a group of animals receiving vehicle alone were the negative controls. Steroid acetates are rapidly converted to T and MENT in blood. Appropriate steroid delivery was assessed by measurement of serum androgen concentrations. Male behavioral parameters were recorded twice per week. At the end of treatment, the weights of sex accessory organs were also recorded. The administration of MENT acetate at daily doses of 100 micrograms and 10 micrograms induced full copulatory behavior in a manner similar to that observed with doses of 200 micrograms T acetate.(ABSTRACT TRUNCATED AT 250 WORDS)

19-Nor synthetic progestins undergo extensive metabolism at the target cells. The resulting metabolic conversion products interact with putative steroid receptors within the cells, and through those interactions, they may exert either agonistic, synergistic and antagonistic hormonal effects. Studies conducted in our laboratories have disclosed that norethisterone (NET) and D-(1) norgestrel (LNG), two widely used contraceptive progestins, are biotransformed to several A-ring reduced (dihydro and tetrahydro) derivatives. The resulting metabolites 5 alpha-dihydro NET (5 alpha-NET) and 5 alpha-dihydro LNG bind with relative high affinity to the progesterone and androgen receptors. To gain insight into the underlying molecular events mediating the mode of action of NET and its neutral metabolites, we have examined the expression of their biological effects at target organs by using the rabbit uteroglobin gene model and the beta-glucuronidase activity of the mouse kidney. The results of a series of experiments seem to indicate that the enzyme-mediated formation of the 5 alpha (trans A/B ring junction) NET derivative results in a significant diminution of its progestational and androgenic potencies. Furthermore, 5 alpha-NET acquire a potent anti-progestational/contragestational effect as assessed in the female rabbit. These results demonstrated that 5 alpha-reduction of 19-nor progestins exerts a paradoxical effect, at least in terms of their hormone-like effects. The overall data are in line with the concept that metabolism of synthetic progestins at hormone-sensitive organs modulates their mechanisms of action.

Levonorgestrel (LNG) is a synthetic steroid that displays potent progestational and androgenic effects but it lacks estrogen-like activity. To examine the mode of action of this progestin, we studied its metabolism in vitro in target organs and the specific interactions of LNG and its metabolites with putative steroid receptors. The results demonstrated that [3H]LNG was efficiently converted to A-ring reduced derivatives when incubated with rat hypothalamus and pituitary. Under optimal incubation conditions, [3H]5 alpha-dihydro LNG (5 alpha-LNG) and [3H]3 alpha,5 alpha-tetrahydro LNG (3 alpha,5 alpha-LNG) were identified as the major metabolic conversion products, while [3H]3 beta,5 alpha-LNG formation occurred to a lesser extent. A-ring reduction of LNG was NADPH-dependent. Assessment of the relative binding affinities of LNG and its derivatives to progesterone (PR), androgen (AR) and estrogen (ER) receptors by displacement analysis revealed that unchanged LNG binds with high affinity to PR and AR but not to ER. 5 alpha-LNG exhibited a diminished though significant interaction with PR and an enhanced binding affinity for AR as compared with LNG, indicating that 5 alpha-reduction of LNG increases its affinity for AR. The most striking finding was that further reduction of the 5 alpha-LNG molecule at C-3 abolished its binding activity to PR, AR, and even to ER. The overall data provides a plausible explanation for the lack of estrogen agonistic action of LNG and for its potent progestational and androgenic effects.

The estrogenic and androgenic potencies of norethisterone (NET), a synthetic nonaromatizable progestin, and three of its reduced metabolites (5 alpha-NET; 3 alpha, 5 alpha-NET; 3 beta, 5 alpha-NET) were assessed by their ability to restore male sexual behavior in castrated male rats following their chronic administration in combination with either 5 alpha-dihydrotestosterone (DHT) or estradiol (E2), or when given alone. Full restoration of mating was achieved when 3 beta, 5 alpha-NET was administered with DHT, indicating an estrogenic effect of this compound. Lower estrogenic effects were noticed with 3 alpha, 5 alpha-NET and 5 alpha-NET, while NET had very little estrogenic potency. The only effective compound to restore ejaculation, when administered with E2, was NET, indicating its androgen-like intrinsic potency. When administered alone, NET exerted the most potent effect on male behavior, followed by 5 alpha-NET, while the tetrahydro derivatives were ineffective. The observation that NET alone restored male sexual activity at a level identical to that induced by testosterone demonstrated an androgenic-estrogenic activity of this progestin exerted through its intrinsic androgenic effect, and the estrogenic effect of its tetrahydro derivatives. Overall results indicated that the metabolism of NET modulates its mode of action at the brain, and support the concept that both estrogenic and androgenic effects are required for mating activation.