Progestin target cell distribution in forebrain and midbrain regions of the 8-day postnatal mouse brain

The present study investigated the anatomical distribution of progestin target cells throughout the forebrain and midbrain regions of the 8-day postnatal female mouse. Female ICR mice were sc injected with 100 micrograms/100 g BW estradiol valerate on postnatal day 5 (birth = day 0). On postnatal day 8, treated mice were sc injected with 0.32 micrograms/100 g BW (Z)-17 beta-hydroxy-17 alpha-(2-[125I]iodovinyl)4-estren-3-one ([125I] progestin). For competition, additional estrogen-treated mice were each injected with 320 micrograms R5020 (17,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione; a potent synthetic progestin), 320 micrograms dihydrotestosterone, or 32, 160, or 320 micrograms corticosterone 1 h before [125I]progestin to show the specificity of [125I]progestin for the progestin receptor. Two hours after injection of [125I]progestin, the brains were removed, frozen, and processed for high resolution thaw-mount autoradiography. After 8-60 days of exposure, nuclear uptake and retention of [125I]progestin were detected in many brain regions, including the septum; bed nucleus of the stria terminalis; and preoptic area, periventricular nucleus, ventromedial nucleus, arcuate nucleus, and dorsomedial nucleus of the hypothalamus. In addition, labeling was seen in the cerebral cortex, caudate putamen, hippocampus, amygdala, and substantia nigra. Competition studies showed that excess R5020 prevented nuclear concentration of ligand, while dihydrotestosterone and corticosterone did not. The results indicate that the distribution of progestin target cells in extrahypothalamic regions of the developing brain is more extensive than that in the adult, while a similar topography was seen in the preoptic area and hypothalamus. The results further suggest that progestin action during brain development may influence the growth and development of target cells not only in the hypothalamus but also in regions of the brain previously not considered to be sites of hormone action.

A pathway for luteinizing hormone releasing-hormone self-potentiation: cross-talk with the progesterone receptor

This study investigates the signaling pathways that lead to acute augmentation of secretagogue-induced LH secretion, the physiologically relevant manifestation of which is LHRH self-potentiation. The consequence of LHRH self-potentiation is an augmented LH secretory response to subsequent exposure to the peptide. Although the mechanism for LHRH self-potentiation remains obscure, the second messenger cAMP and the steroid hormone progesterone share common characteristics in their acute augmentation of secretagogue-induced pituitary LH secretion, suggesting that cross-talk between the peptide and steroid hormone pathways may occur. The progesterone receptor would represent a point of convergence of several effectors known to augment secretagogue-induced LH secretion. In rat anterior pituitary cells cultured in the absence of progesterone, it was found that the progesterone receptor antagonist RU486 (2 nM) inhibits LHRH self-potentiation induced by hourly pulses of 1 nM LHRH. In the absence of added progesterone, RU486 also suppresses the augmentation of LHRH-stimulated LH secretion which is a consequence of increasing [cAMP]i with either 8-bromo-cAMP (1 mM) or forskolin (1 microM) treatment. The extent of the suppression of the cAMP action in the presence of RU486 is similar to that found with the RNA synthesis inhibitor, actinomycin D. The data are consistent with the hypothesis that a LHRH-stimulated protein kinase A cascade acts, in part, through transcriptional activation of the progesterone receptor. It is concluded that the mechanism of LHRH self-potentiation requires cross-talk with the progesterone receptor.

Growth factor-like activity of phenol red preparations in the MCF-7 breast cancer cell line

Hormonal responsiveness of the estrogen-sensitive MCF-7 human breast cancer cell line is known to vary between laboratories although the causes and implications of these variations remain unclear. Our findings lead us to conclude that the pH indicator phenol red (PHR) has growth factor-like effects in addition to its well known estrogen-like effects. To demonstrate this hypothesis, we have assessed the importance of PHR either in the absence or in the presence of the estrogens contained in the serum added to the culture medium. The basal growth rate of MCF-7 cells was significantly reduced by short-term or long-term withdrawal of PHR. The stimulatory effects of estradiol and the inhibitory effects of the antiestrogen 2-CH3,4-OH-tamoxifen (MHT) were not significantly affected by long-term withdrawal of the dye. Moreover, long-term cell maintenance without PHR alone or in complete estrogen-depleted medium did not change their basal steroid receptor content. The molecular structure of the estrogen receptor which is usually modified under estrogenic stimulation remained identical whether or not the cells were maintained in the presence of the dye. Maintaining cells without the dye in the presence of serum estrogens led to the death of the cell line after 50 transfers. Lastly, addition of PHR had clearcut growth stimulatory effects on the hormono-independent cell line Evsa-T.

A single amino acid that determines the sensitivity of progesterone receptors to RU486

The progesterone analog RU486, an abortifacient, inhibits the action of progestins in humans but not in chickens or hamsters. Substitution of cysteine at position 575 by glycine in the hormone binding domain (HBD) of the chicken progesterone receptor (cPR) generated a cPR that binds RU486 and whose activity is antagonized by that compound. In fact, all receptors that bind RU486 have a glycine at the corresponding position. The hamster PR, like cPR, has a cysteine. Only glycine--not methionine or leucine--at position 575 allowed binding of RU486 to cPR. Substitution of this glycine by cysteine in the human PR (hPR) abrogated binding of RU486 but not that of an agonist. The corresponding mutation in the human glucocorticoid receptor resulted in a loss of binding of both dexamethasone and RU486. Examination of a series of 11 beta-substituted steroids showed that antagonism is not an intrinsic property of an antihormone, because one hPR antagonist acted as an agonist for a mutated hPR. The positioning of an aromatic 11 beta-substitution in the PR HBD appears to be critical for generating agonistic or antagonistic activity.

Effects of hormone and cellular modulators of protein phosphorylation on transcriptional activity, DNA binding, and phosphorylation of human progesterone receptors

Human progesterone receptors (PR) in T47D breast cancer cells are synthesized as two different sized proteins, PR-A [94 kilodaltons (kDa)] and PR-B (120 kDa). Progestin addition to cells (in vivo) causes a 2-fold increase in total phosphorylation of PR and an increase in the apparent mol wt of both PR-A and PR-B on sodium dodecyl sulfate (SDS)-gels. Time-course experiments showed that increased PR phosphorylation that results from hormone addition is a multistep process and involves a rapid increase into total 32P labeling that takes place before the more slowly occurring phosphorylation(s) responsible for the change in electrophoretic mobility of PR on SDS-gels. As an approach to test whether phosphorylation is involved in regulating PR activity, we have examined the effects of cellular modulators of protein phosphorylation on PR-mediated target gene transcription in vivo using a T47D cloned cell line containing a stably transfected mouse mammary tumor virus-chloramphenicol acetyltransferase construct. Treatment with 8-bromo-cAMP (activator of cAMP-dependent protein kinases) or okadaic acid (protein phosphatase-1 and -2A inhibitor) did not stimulate target gene expression in the absence of progestin. When added together with progestin, either compound augmented PR-mediated target gene transcription by 3- to 4-fold. The cyclic nucleotide-dependent protein kinase inhibitor H8 completely blocked target gene responsiveness to hormone. Neither 8-bromo-cAMP, okadaic acid, nor H8 altered the hormone- or DNA-binding activities of PR, as measured in vitro or affected cellular concentrations of PR. These agents, therefore, appeared to selectively modulate PR transcriptional activity. Moreover, none of these compounds altered expression from a control reporter gene, pSV2CAT, indicating that these agents affect PR-mediated processes directly and are not acting through a general effect on transcription. Effects on PR phosphorylation were assessed by measuring 32P labeling of PR in vivo. None of these treatments had a substantial effect on the extent of total 32P labeling of immune isolated PR or on the phosphorylation(s) responsible for PR up-shifts on SDS-gels. This suggests that these agents modulate PR transcriptional activity either through phosphorylation of another protein intimately involved in PR-mediated transcription or through modification of a key site(s) not measurable as a change in total PR phosphorylation or electrophoretic mobility on SDS gels.

Immunocytochemical determination of estrogen and progesterone receptors in human endometrial adenocarcinoma cells (Ishikawa cells)

The regulation of both estrogen and progesterone receptor levels in human endometrial adenocarcinoma cells of the Ishikawa line was investigated immunocytochemically by using monoclonal antibodies. Positive staining for estrogen and progesterone receptors was observed in the nuclei of Ishikawa cells. Intercellular heterogeneity in receptor content was evident from the presence of receptor-positive or -negative cells and from differences in staining intensity of positive cells. Quantitative analysis was performed by scoring the staining intensity and the proportion of positively stained cells. The time and dose-dependent stimulatory effect of estradiol added to culture media on progesterone receptor levels was studied by applying both immunocytochemical and biochemical methods. Estradiol at 10 nM (optimal concentration) increased the intensity score for PR from an initial value of 10.1 to 78.3 after 72 h incubation, and the proportion of the positive staining cells from 6.7 to 42.7%. Promegestone (R5020) was effective at 1 microM concentration in decreasing the intensity score for ER from 31.1 to 14.6 after 72 h exposure and the proportion of positive cells from 19.0 to 11.4%.

Estradiol pulses induce progestin receptors selectively in substance P-immunoreactive neurons in the ventrolateral hypothalamus of female guinea pigs

Low doses of estradiol, administered as pulses, are as effective as higher doses for priming ovariectomized (OVX) guinea pigs to display progesterone-facilitated lordosis. High doses of estradiol, administered by constant-release implants, induce progestin receptors in many substance P-immunoreactive (SP-IR) neurons in the ventrolateral hypothalamus (VLH), a site at which estradiol primes OVX guinea pigs to respond behaviorally to progesterone. To test the hypothesis that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P-containing neurons in the VLH, OVX females received estradiol implants 1 week prior to perfusion, or two pulses of estradiol-17 beta, injected 39 and 11 h before perfusion. Colchicine was administered intracerebroventricularly prior to perfusion. No significant differences were observed in the total number of progestin receptor-immunoreactive (PR-IR) or substance P-immunoreactive cells in the VLH and VLH/ventromedial hypothalamus (VMH), respectively, of females receiving the two estradiol treatments. However, the percentage of PR-IR cells in the VLH also immunoreactive for SP was significantly higher in the estradiol pulse-treated (53%), than in the estradiol capsule-implanted animals (36%). These data suggest that behaviorally effective estradiol pulses induce progestin receptors selectively in substance P-containing neurons in the VLH and are consistent with the hypothesis that substance P is involved in progesterone-facilitated lordosis in guinea pigs.

Recombinant interferon-alpha 2b affects proliferation, steroid receptors and sensitivity to tamoxifen of cultured breast cancer cells (CG-5)

Exposure of CG-5 human breast cancer cells to recombinant interferon (IFN)-alpha 2b results in a significative inhibition of cell proliferation; this is observed when cells are cultured in their standard conditions and is not modified if serum concentration present in the culture medium is lowered. Estrogen receptors are increased in CG-5 cells following a 5 day treatment with concentrations of IFN-alpha 2b ranging from 10 to 1000 IU/ml of culture medium. Progesterone receptors seem to be more influenced by a longer treatment with the drug (7 days). The Kd of both receptors is not modified by the exposure of cells to IFN-alpha 2b. Finally, the antiproliferative effect of tamoxifen on CG-5 cells is amplified by the simultaneous addition to culture medium of IFN-alpha 2b even at very low concentrations.

Mechanisms of hormonal and antihormonal action of contraceptive progestins at the molecular level

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.

Effects of a normal, human-concentration, phytoestrogen diet on rat uterine growth

The estrogenic action of the prototype natural phytoestrogen coumestrol was examined in rats in in vitro and in vivo tests. To establish the binding specificity of coumestrol and its relation to biological activities, saturation analyses and uterine weight assays were performed. These assays indicated that coumestrol competitively inhibited binding to the estrogen receptor and induced increases in uterine weight in keeping with its estrogen receptor affinity constant. Most importantly, coumestrol was uterotrophic when incorporated in a semipurified diet at natural dietary concentrations. Significant increases occurred in both uterine wet weight and dry weight, indicating that coumestrol produces true uterine growth. Effects appeared to be cumulative, raising questions of time-related interactions with other estrogen-sensitive mechanisms and clearance of isoflavonoids. Coumestrol induced uterine growth over a 90-hour period at dietary concentrations of 0.01 to 0.1%. Lower doses not active over this period were active when provided over a longer period of time: a 0.005% concentration was not active over a 90-hour period, but was active when provided over a 180-hour period. Coumestrol-induced uterine growth was accompanied by the induction of cytosolic progestin receptors and increases in nuclear estrogen binding. Scatchard analyses verified that these changes were due to changes in receptor number. These studies show that the naturally occurring phytoestrogens have dramatic estrogenic effects at natural dietary levels. These actions may be expressed via traditional receptor-mediated actions and therefore may have the same implications for development, health, and disease as do the steroidal estrogens produced by the body. Because rats have no sex hormone-binding globulin, further studies must be conducted in humans. However, these findings suggest that the natural dietary phytoestrogen coumestrol is a potent estrogen that must be considered in calculating the total estrogenic load to which humans are exposed during normal life.

Accumulation of a non-binding form of estrogen receptor in MCF-7 cells under hydroxytamoxifen treatment

It is well known that MCF-7 cells, when incubated with hydroxytamoxifen (OH-Tam) loose their capacity to bind [3H]estradiol. By using Western blotting and [3H]tamoxifen aziridine labeling of KCl extracts from these cells we found that this loss in binding capacity was not associated with a disappearance of the estrogen receptor (ER) protein, an event known to occur after incubation with estradiol. Attempts to label under exchange conditions these ER molecules, which, on the basis of enzyme immunoassays appear to accumulate under OH-Tam treatment, were unsuccessful. Cell fractionation suggested that their origin is nuclear. Assessment of a few triphenylethylenic antiestrogens, as far as their inhibitory potency towards the in vitro MCF-7 cell growth is concerned, indicated a correlation between accumulation of these non-binding ER molecules and the antiestrogen antiproliferative action. However, we were unable to demonstrate absence of such an ER accumulation in two tamoxifen-resistant variants. Impaired folding of the ER protein or impaired phosphorylation of its hormone-binding domain are attractive hypotheses to account for these non-binding ER molecules. Whether these ER molecules have any physiological role, such as competition with the "normal" receptor molecules for the estrogen responsive elements on the DNA is unknown and deserves further study.

Demonstration of steroid hormone receptors and steroid action in primary cultures of rat glial cells

Primary cultures of rat glial cells were established from newborn rat forebrains. A mixed population of oligodendrocytes and astrocytes was obtained, as confirmed by indirect immunofluorescence staining with specific markers for each cell type. Receptors were measured 3 weeks after primary culture in glial cells cultured in the presence or not of 50 nM estradiol and we have identified progesterone, glucocorticoid, estrogen, and androgen receptors (PR, GR, ER and AR), but only PR was inducible by the estrogen treatment. This estrogen-induction of PR was more dramatic in glial cells derived from female offsprings than from males, as measured by binding studies and by immunohistochemical techniques with the KC 146 anti-PR monoclonal antibody. The antiestrogen tamoxifen inhibited the estrogen induction, but had no effect by itself on PR concentration. Specific binding sites for PR, GR, ER and AR were measured by whole cell assays after labeling cells with, respectively, [3H]R5020, [3H]dexamethasone, [3H]OH-tamoxifen or [3H]R1881. PR and GR were also analyzed by ultracentrifugation and after exposure of cells to agonists, both receptors were recovered from cytosol as a 9S form, and from the nuclear high-salt, tungstate ions-containing fraction as a 4-6S form. In contrast, when the antiprogestin- and antiglucocorticosteroid RU486 was used as a ligand, a non-activated 8.5S receptor complex was found for both receptors in this nuclear fraction. The 8.5S complex of the GR was further analyzed in the presence of specific antibodies and, in addition to GR, the presence of the heat shock protein hsp90 and of a 59 kDa protein was found. During primary culture, the effects of progesterone (P) and estradiol (E2) were tested on glial cell multiplication, morphology and differentiation. Cell growth was inhibited by P and stimulated by E2. Both hormones induced dramatic morphologic changes in oligodendrocytes and astrocytes and increased synthesis of the myelin basic protein in oligodendrocytes and of the glial fibrillary acidic protein in astrocytes.

Mechanisms of antihormone action

The mechanisms of action of two types of anti-hormones is discussed. Type I anti-hormones comprise the antiestrogen hydroxy-tamoxifen and the antiprogestin RU486, both of which promote DNA binding of the cognate receptors and, due to the activity of one of the two transcription activation functions of the estrogen and progesterone receptors, act as mixed agonist/antagonists. Evidence supporting that ICI 164,384 is also a member of the same group is presented. Type II antagonists impair DNA binding of the corresponding receptor in vitro and, in some cases, also in vivo. Ligand-mapping, an approach to identify the site of interaction of a steroid substitution within the hormone-binding domain of the receptor has been used to identify the 11 beta-pocket of the progesterone receptor and revealed that a single amino acid is responsible for the differential antagonistic effect of RU486 in man, chicken and hamster.

Mechanisms of nuclear localization of the progesterone receptor

Deletion mutants of the rabbit progesterone receptor were used to identify two major mechanisms of its nuclear localization. A putative signal sequence, homologous to that of the SV40 large T antigen, was localized around amino acids 638-642 and was shown to be constitutively active. When amino acids 638-642 were deleted, the receptor became cytoplasmic but could be shifted into the nucleus by the addition of hormone (or anti-hormone), it was almost fully active. A second putative nuclear localization signal is located in the DNA binding domain activated either through ligand binding or through production of constitutive receptor. By deleting epitopes recognized by monoclonal antibodies, it was possible to follow different receptor mutants inside the same cells. In the absence of ligand the receptor was transferred into the nucleus as a monomer. After administration of hormone (or anti-hormone) a "cytoplasmic" monomer was transferred into the nucleus through interaction with a "nuclear" monomer. These interactions occurred through the steroid binding domains of both monomers.

The effect of 6-nitro-1,3,8-trichlorodibenzofuran as a partial estrogen in the female rat uterus

Administration of 6-nitro-1,3,8-trichlorodibenzofuran (6-NCDF) caused a dose- and time-dependent increase in uterine wet weight and cytosolic and nuclear estrogen receptor (ER) and progesterone receptor (PR) levels in immature female Sprague-Dawley rats. These estrogenic effects persisted for up to 96 or 144 hr after initial administration of 6-NCDF and could be observed at a dose as low as 2 mumol/kg. In contrast, 6-NCDF (25 mumol/kg) did not increase rat uterine peroxidase activity or epidermal growth factor (EGF) receptor binding activity. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), which exhibits a broad spectrum of antiestrogenic effects in the female rat uterus, inhibited the 17 beta-estradiol-induced increase in uterine wet weights, cytosolic and nuclear ER and PR levels, peroxidase activity, and EGF receptor binding activity. In contrast, 2,3,7,8-TCDD inhibited the uterotropic effects caused by 6-NCDF but did not affect the 6-NCDF-induced uterine ER and PR levels. 6-NCDF is a weak inducer of hepatic microsomal ethoxyresorufin O-deethylase activity and competitively binds to the aryl hydrocarbon (Ah) receptor but not the PR or ER. Thus both 6-NCDF and 2,3,7,8-TCDD, two ligands which bind to the Ah receptor, exhibit both partial estrogenic and antiestrogenic properties and serve as useful models for delineating the complex biochemical interactions between the ER and Ah receptor signal transduction pathways.

Effects of estradiol treatment on responses of rat preoptic warm sensitive neurons to progesterone in vitro

Single unit activity was recorded extracellularly in preoptic slice preparations from ovariectomized female rats. The rats were pretreated daily with (1) estradiol benzoate (20 micrograms/0.1 ml sesame oil) for 3 consecutive days just prior to the experiment (OVX+E72h), (2) sesame oil (OVX+Oil), or (3) untreated (OVX). In the preparations from OVX rats, 12 (50%) of 24 warm-sensitive neurons were inhibited and 2 (8%) were excited by the application of progesterone (P) in perfusion medium (30 ng/ml). In OVX+Oil preparations, 4 (40%) of 10 warm-sensitive neurons were inhibited and none was excited by P. In OVX+E72h preparations, however, only 4 (10%) were inhibited by P and 16 (38%) of 42 warm-sensitive neurons were excited. When Ru38486, a P-receptor antagonist, was applied together with P, no excitation was observed in warm-sensitive neurons in OVX+E72h preparations. These findings suggest that the P-induced excitation of preoptic warm sensitive neurons is mediated through the estrogen-induced P-receptors.

Immunocytochemical localization of progestin receptors in monkey hypothalamus: effect of estrogen and progestin

The increase in PRL secretion which follows progesterone (P) administration to estradiol (E)-primed women and monkeys cannot be due to an action of P at the pituitary level because lactotropes do not contain progestin receptors (PR). To further the hypothesis that P increases PRL secretion by an action in the hypothalamus, PR-expressing neurons were studied in free-ranging and steroid-manipulated monkeys using immunocytochemistry with a monoclonal antibody to human PR. Specific PR immunoreactivity is localized in the nucleus of individual hypothalamic neurons. Male and female adult and juvenile macaque hypothalami contain significant populations of PR-positive neurons throughout the anterior and medial basal hypothalamus. Ovariectomy decreases, but does not abolish, the number of neurons expressing PR. PR expression was not altered in the supraoptic nucleus (SON) by ovariectomy. Estrogen treatment for 28 days caused a significant increase in the number of PR-positive neurons in the medial preoptic area, the ventro-medial nucleus, the arcuate nucleus, and the median eminence, but not in the SON. P treatment added to the E treatment from day 14 to day 28 did not alter the number of PR-positive neurons in any area. These data suggest that PR may be constitutively expressed in the magnocellular neurons of the SON and in certain other cells throughout the hypothalamus. E induces PR in a large proportion of neurons in the medial basal hypothalamus and this action is not blocked by subsequent P treatment. The inability of P to down-regulate PR in the hypothalamus differs from the reproductive tract and pituitary. Indeed, this observation is consistent with the fact that PRL secretion remains elevated during chronic P administration.

Heterogeneity of progesterone receptor content and remodeling by tamoxifen characterize subpopulations of cultured human breast cancer cells: analysis by quantitative dual parameter flow cytometry

Breast cancers treated with the antiestrogen tamoxifen invariably become resistant. To analyze the behavior of cell subpopulations within a tumor following tamoxifen treatment, we have used a new flow cytometry-based immunoassay and software that simultaneously quantitate PR levels and the DNA indices of ploidy and cell cycle stage in total cell populations or any subset thereof. The human breast cancer cell line T47D and its clonal derivatives were used as models of stage IV breast cancer, and growth and PR were measured as markers of antiestrogen responsiveness. We demonstrate and quantitate a remarkable heterogeneity in PR content and show the existence of distinct subpopulations with large differences in their PR levels and DNA indices, even among T47D sublines that are clonally derived. Following chronic tamoxifen treatment, an overall decrease in PR levels and growth masks an extensive heterogeneity in the response of cell subpopulations. PR levels decrease in some cells but increase in others; populations having a growth advantage expand while others contract. We find little evidence that cells, unaffected by the hormone, gain a growth advantage. Rather than exhibiting autonomy, we propose that under the influence of tamoxifen, tumors become remodeled as selected subpopulations emerge that are stimulated by the hormone, explaining the paradoxical recurrence of disease in patients undergoing endocrine therapy.

Enhancement of progesterone receptor bindings by estradiol in pituitary cells of the hen

Isolated cells from pituitaries of nonlaying hens were incubated in vitro with and without estradiol-17 beta (E2), and the amount of progesterone receptor binding in the cytosolic fraction of the cells was measured by an exchange assay. When the cells were incubated with 1.0 ng E2 for 1, 2, or 4 h, the progesterone receptor bindings were increased. The bindings were not increased when incubated together with cycloheximide, actinomycin-D, or alpha-amanitin. The results suggested that the cytosolic progesterone receptor binding of pituitary cells was enhanced by the action of estrogen through a protein-synthesizing pathway.

[The content of sex steroid receptors and the activity of marker enzymes of estrogenic action in the uterus of androgen-sterile rats]

In rats with preserved ovaries, both in normal and in neonatally androgenized, the activity of enzymes kreatinphosphokinase and peroxidase cannot serve as the marker of the estradiol effect upon the uterus. In ovariectomised animals, the dynamics of activity of these enzymes corresponds to uterotropic responses to estradiol. but not to the dynamics of hormone receptor complexes. The data obtained makes doubtful the participation of the hormone receptor complexes in realisation of the estrogens effect upon the uterus.

Selectivity and minimal androgenicity of norgestimate in monophasic and triphasic oral contraceptives

The contraceptive progestin norgestimate (NGM) has a high affinity for uterine progestin receptors and a lack of affinity for androgen receptors similar to that of natural progesterone. NGM's selectivity results in excellent efficacy, cycle control, and minimal androgenicity when it is combined with ethinyl estradiol (EE). Clinical studies of a monophasic regimen of NGM/EE indicate a positive impact on lipid metabolism, revealing an increase in serum levels of high-density lipoprotein cholesterol with a concomitant and significant decrease in the low-density lipoprotein/high-density lipoprotein cholesterol ratio. Little impact on carbohydrate metabolism was noted. Serum levels of sex hormone binding globulin, an indicator of androgen-estrogen balance, also increased significantly with NGM/EE in accordance with its low androgenic activity. A significant between-regimen difference in SHBG was seen in a comparison study of NGM/EE and LNG/EE triphasic formulations (a mean rise of 68.6% with NGM/EE vs a decrease of 6.1% with LNG/EE). NGM's lack of estrogenicity was evidenced by unchanged prolactin levels and absence of effect on the coagulation system. In a large study of the monophasic formulation in 59,701 women, some improvement in acne was reported as well as minimal weight gain. An overview of clinical data is provided from United States and European trials as well as some preclinical data relevant to NGM's selectivity.

[The role of progesterone and its receptors in the development of the uterotropic reaction in ovariectomized rats]

In intact rats, the progesterone level in cytosolic fractions of various organs did not correspond to the level of the progesterone receptors. In ovariectomised animals receiving progesterone, the hormone accumulation in the uterus was fulfilled without participation of progesterone receptors. Over half of the progesterone in the rat uterine tissues exists in receptor-unbound "free" form or, possibly, in the form of complexes with small molecular weight. The uterotropic effect of progesterone in ovariectomised animals seems to be determined by the presence of the hormone in the "free" form in the uterus cells or, possibly, in the form of low-molecular complexes.

Treatment effects of GnRH agonist on the binding of estrogen and progesterone, and the histological findings of uterine leiomyomas

The changes in the histology and steroid hormone binding capacity of the uterine leiomyomas treated with; GnRH agonists (GnRHa buserelin acetate in, 900 micrograms/day for 16 weeks) were investigated. The occurrence of hyaline degeneration in the myometrium was significantly higher in the GnRHa-treated group than in the control group, and the grade of hyaline degeneration was more advanced in the GnRHa group. After the GnRHa treatment, the Bmax of the estrogen receptor increased significantly in the leiomyomas and myometrium. The Bmax of progesterone receptors in the myometrium decreased significantly and the reduction rates of leiomyomas (% of the initial volumes) measured by MRI correlated (r = 0.775) with the Bmax of progesterone receptors. In summary, GnRHa caused hyaline degeneration of the uterine leiomyomas which were responsible for the shrinkage. The shrunk leiomyomas have the potential for regrowth in response to estrogen as they still have high concentrations of the estrogen receptors.

[Cell adhesion in neoplastic cells and syngeneic fibroblasts of the rat: effect of progesterone and estradiol]

Recent advances in the study on the importance of steroid receptors in the treatment of hormone-responsive tumors established the relationship between plasma membrane and the first steps of the cellular response to the endocrine stimulus. We have therefore found interesting to study the influence of estrogen and progesterone on cell adhesion of neoplastic (SGS/3A) and normal syngeneic (FG) cells. We demonstrated the presence of a nuclear estrogenic and a cytosolic progestin receptor in the SGS/3A cells. In syngeneic fibroblasts both receptors are absent. Cell adhesion kinetics obtained determining the percent of single labeled cells with 3H-leucine adhering to confluent monolayer (cell-cell adhesion) showed that the physiological concentrations of estradiol and progesterone induce an inhibition of cell-substratum adhesion (25-30%) in neoplastic cells, but do not influence cell-cell adhesion. In FG cells the two hormones cause an increase of cell-substratum adhesion (35-40%), but do not influence cell-cell adhesion. Results suggest that FG cells, although lacking cytoplasmic or nuclear receptors for estradiol and progesterone, probably have other steroid-receptive molecules involved in adhesive processes on their cell-surface.