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PubMed1981

A comparison of cytoplasmic and nuclear estradiol and progesterone receptors in human fallopian tube and endometrial tissue.

Quantitative and qualitative aspects of the in vitro binding of 3H-estradiol and 3H-progesterone to receptor components from human endometrium and fallopian tube cytoplasmic and nuclear fractions were studied. The steroid binding macromolecules formed in vitro could be extracted from nuclei by 0.4 M KCl and detected by glycerol gradient centrifugation. Both estradiol- and progesterone-binding compounds formed only one peak (under high ionic strength conditions) with a sedimentation coefficient of about 4-5 S. The number of cytoplasmic and nuclear binding sites for both estradiol and R5020 varied dramatically throughout the menstrual cycle: the estradiol and progesterone receptor concentrations were highest during the proliferative phase and were very significantly lower in the second half of the menstrual cycle. Furthermore, measurement of both receptors in the cytosol revealed differences among the anatomic segments of the fallopian tube. The highest estradiol and progesterone binding could be detected in the ampullary region; significantly lower levels of estradiol and progesterone receptors were seen in the infundibulum and the isthmus.

Cell Nucleus↗
PubMed1986

Characterization and assay of the nuclear and cytosolic progesterone (P) receptors in Premarin-primed human endometrium and myometrium after single-dose P administration.

Progesterone receptors (RP) were characterized and measured in the 0.4 M KCl nuclear extract and in the cytosol of 7 to 11 days Premarin (Premarin, Ayerst Laboratories, New York, NY) primed human endometrium and myometrium with [3H]R5020 as the ligand. The test group comprised 12 women who received progesterone injection 1 to 3 hours before tissue collection; the control group numbered 10 women. Receptor characteristics in both the endometrium and the myometrium, in the nuclear extract and cytosol in the test group and in the cytosol in the control group, were similar and were demonstrated by (1) high specificity, (2) sedimentation constant of 4.7 to 6.5S in the cytosols and 2.8 to 3.9S in the nuclear extract, (3) saturable affinity with Kd of 2.2 to 3.5 nM and 1.9 to 3.3 nM, respectively. Total RP levels (nuclear extract and cytosol) ranged from 1030 to 13,270 and 1280 to 17,300 fmol/mg DNA, respectively, in the endometria of women in the test and control groups. In 13 of 14 women myometrial total RP levels were higher than in the endometrium. There was a significant difference in the distribution of the RP between the test and the control groups: 50% and 48% of the receptor were measured in the nuclear extract in the endometrium and myometrium, respectively, in the test group, compared with 25% and 21% in the control group (P less than 0.001).

Adult↗
PubMed1984

Hormone receptor in renal cell carcinoma and correlation with clinical response to endocrine therapy.

Analyses of hormone receptors in cytosols from 41 renal cell carcinoma specimens were performed by the dextran-coated charcoal technique, using estradiol, synthetic progestin R5020 and synthetic androgen R1881. Binding data were calculated according to the method of Scatchard. Of 41 renal cell carcinomas estradiol receptor was detected in 11, R5020 receptor in 11 and R1881 receptor in 13. No significant correlation between histopathological findings and hormone receptors was observed. Patients were classified into those positive and negative for receptors. The clinical response of endocrine therapy for 17 with advanced residual or metastatic lesions after nephrectomy was studied in regard to the survival rates. Although there was no complete or partial regression in tumor size, the survival rate of patients with 1 or more receptors was significantly higher than that of patients negative for receptors (p less than 0.01). In conclusion, hormonal manipulation in patients with renal cell carcinoma cannot induce an antitumor effect but seems to increase survival in patients with receptors.

Adenocarcinoma↗
PubMed1997

Inhibition of 17 beta-estradiol and progesterone activity in human breast and endometrial cancer cells by carbamate insecticides.

Using a combination of in vitro assays we have examined the capacities of contemporary-exposure chemicals to modulate human estrogen and human progesterone receptor (hER and hPR) activity in human breast and endometrial cancer cells. The carbamate insecticides aldicarb, Baygon (propoxur), bendiocarb, carbaryl, methomyl, and oxamyl were used in this study. The carbamates alone weakly activated estrogen- or progesterone-responsive reporter genes in breast and endometrial cancer cells. All of the carbamates decreased estradiol- or progesterone-induced reporter gene activity in the breast and endometrial cancer cells. In whole cell competition binding assays, the carbamates demonstrated a limited capacity to displace radiolabeled estrogen or progesterone from ER or PR. Based on the results presented here, the carbamate insecticides may represent a class of chemicals which function through a mechanism separate from ligand-binding and, therefore, may act as general endocrine modulators in mammalian cells.

Binding, Competitive↗
PubMed1999

Hormone replacement therapy and plasma homocysteine levels.

OBJECTIVE: To compare the effects of 4 and 12 weeks of combined estradiol-progestogen replacement with unopposed estradiol therapy on fasting plasma total homocysteine concentrations in healthy postmenopausal women. METHODS: In this prospective, 12-week study in healthy postmenopausal women, we randomly assigned 59 women to sequentially combined daily 2 mg estradiol (E2) plus either trimegestone 0.5 mg daily or dydrogesterone 10 mg daily (n = 28), or to unopposed daily 2 mg estradiol (n = 16), or to placebo (n = 15). RESULTS: Fasting plasma total homocysteine concentrations decreased by 9.4% in the combined estradiol-progestogen group and by 5.1% in the estradiol-only group, and they increased by 2.4% in the placebo group (analysis of covariance: combined hormone replacement therapy compared with placebo (P = .02); combined therapy compared with estradiol (P = .23); and estradiol compared with placebo (P = .26). Reductions were detectable after 4 weeks of combined estradiol-progestogen treatment. The data suggest an additional progestogen-related reduction in homocysteine levels of 0.7 micromol/L and 0.4 micromol/L after 4 and 12 weeks, respectively. Women with a baseline homocysteine concentration in the highest quartile had significantly greater reductions in homocysteine compared with women with an initial homocysteine value in the lowest quartile. CONCLUSION: Fasting total homocysteine concentrations were significantly reduced by combined estradiol-progestogen replacement. Women with high homocysteine levels at baseline benefit the most. The progestogens used in this study did not have an unfavorable effect on homocysteine metabolism.

Dydrogesterone↗
PubMedDate not supplied

In vitro characterization of trimegestone: a new potent and selective progestin.

Trimegestone (TMG) is a novel 19-norpregnane progestin under development for hormone replacement therapy and oral contraception. The objective of the current study was to characterize the potency and steroid receptor selectivity of TMG in several in vitro assays and to compare its activity to that of medroxyprogesterone acetate (MPA). TMG and MPA had a similar competitive binding affinity for human and rabbit progesterone receptor (PR). However, TMG had a significantly higher affinity for rat PR (IC(50) = 3.3 nM) than MPA (IC(50) = 53.3 nM). In T47D cells, both compounds increased alkaline phosphatase activity and cell proliferation with comparable potencies (EC(50s) of 0.1 nM and of 0.02 nM, respectively). To further characterize the progestational activity and steroid receptor selectivity, we established an immortalized human endometrial stromal cell line (HESC-T). This cell line lacks endogenous estrogen receptor (ER) and PR but does have functional glucocorticoid receptors (GR). When ER is transiently expressed in the cells, 17beta-estradiol (E(2)) induces PR, allowing the study of PR-regulated genes. In HESC-T cells expressing exogenous ER, and therefore PR, both TMG and MPA increased HRE-tk-luciferase activity tenfold with an EC(50) of 0.2 nM. In HESC-T cells without exogenous ER, and therefore no PR, TMG did not induce HRE-tk-luciferase activity, whereas MPA induced the reporter activity with an EC(50) of about 10 nM. This MPA-induced reporter activity is believed to be mediated through GR. The steroid receptor selectivity of TMG was further evaluated using the HRE-tk-luciferase assay in the human lung carcinoma cell line A549, which contains GR but no PR. In these cells TMG had no effect on luciferase activity, whereas MPA increased the reporter activity in a dose-dependent manner with an EC(50) of approximately 30 nM. Furthermore, HRE-tk-luciferase assay in mouse fibroblast cell line L929, which expresses androgen receptor (AR) but no PR, showed that TMG had weak antiandrogenic activity whereas MPA had androgenic activity. In summary, data from several in vitro assays demonstrate that TMG is a potent progestin with a better receptor selectivity profile than MPA.

Adult↗
PubMed2003

The preclinical biology of a new potent and selective progestin: trimegestone.

Trimegestone (TMG) is a 19-norpregnane progestin being developed, in combination with an estrogen, for the treatment of postmenopausal symptoms. TMG binds to the human progesterone receptor with an affinity greater than medroxyprogesterone acetate (MPA), norethindrone (NET), and levonorgestrel (LNG). In contrast, TMG binds with low affinity to the androgen, glucocorticoid and mineralocorticoid receptor and has no measurable affinity for the estrogen receptor. Compared to other progestins, TMG demonstrates an improved separation of its PR affinity from its affinity to other classical steroid hormone receptors. In vivo, TMG has potent progestin activity. For example, TMG produces glandular differentiation of the uterine endometrium in rabbits and is about 30 and 60 times more potent than MPA and NET, respectively. In the rat, TMG maintains pregnancy, induces deciduoma formation, inhibits ovulation and has uterine anti-estrogenic activity. With respect to these endpoints, TMG appears to be more potent and selective on uterine epithelial responses than other classical progestin responses. In vivo, TMG does not have significant androgenic, glucocorticoid, anti-glucocorticoid or mineralocorticoid activity but does have anti-mineralocorticoid activity and modest anti-androgenic effects. This overall profile is qualitatively similar to progesterone. When TMG is administered chronically, it antagonizes the effect of estradiol on the uterus but does not antagonize the beneficial bone sparing activity of estradiol. In rat studies evaluating CNS GABAA receptor modulatory activity, TMG is less active on this likely undesirable endpoint than progesterone and norethindrone acetate, which may translate into fewer mood-related side effects. The results indicate that TMG is a potent and selective progestin with a preclinical profile well suited for hormone replacement therapy.

Animals↗
PubMed1985

Progestin regulation of progesterone biosynthetic enzymes in cultured rat granulosa cells.

Progestins have recently been shown to augment gonadotropin-stimulated progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) biosynthesis in cultured rat granulosa cells. The mechanism by which progestins autoregulate ovarian progestin biosynthesis was investigated by studying the modulation of pregnenolone biosynthesis as well as the activities of the enzymes 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD). Granulosa cells obtained from immature hypophysectomized, estrogen-treated rats were cultured with FSH and/or progestins. Pregnenolone production was measured in the presence of cyanoketone (10(-6) M) to inhibit 3 beta-HSD activity. Enzymatic activities of 3 beta-HSD and 20 alpha-HSD were determined in cell homogenates by direct enzyme assays. FSH stimulated pregnenolone production, while treatment with progesterone or R5020 alone was ineffective. Concomitant treatment with the progestins further enhanced FSH-stimulated pregnenolone production in a dose-dependent manner with minimal effective doses of 10(-8) and 10(-7) M for R5020 and progesterone, respectively. In FSH-primed cells, LH increased pregnenolone accumulation, and concomitant treatment with R5020 also enhanced the LH action. Furthermore, the gonadotropins stimulated the activity of 3 beta-HSD, and this effect was further enhanced by concomitant treatment with either R5020 or progesterone in a dose-dependent manner. In addition, the 20 alpha-HSD activities were enhanced by progestins in cells treated with FSH but not with LH. Thus, both natural and synthetic progestins stimulate the gonadotropin-induced progesterone production in cultured granulosa cells via enhancing the 3 beta-HSD enzyme as well as pregnenolone biosynthesis.

20-Hydroxysteroid Dehydrogenases↗
PubMed1999

Expression and hormonal regulation of rat ovarian interleukin-1beta converting enzyme, a putative apoptotic marker: endocrine- and paracrine-dependence.

It is the purpose of this paper to assess the expression, cellular localization, and hormonal regulation of rat ovarian interleukin (IL)-1beta converting enzyme (ICE), a putative apoptotic marker. In agreement with previous observations ICE transcripts were noted in relatively increased abundance in the thymus, lung, spleen and small intestine. Although ICE transcripts were barely expressed in the untreated, immature rat ovary, they were apparent throughout a simulated estrous cycle. The in vivo expression of ovarian ICE rose gradually from 6 h after ovulation triggering to a peak (1.74-fold increase versus control, P < 0.05) 24 h after human chorionic gonadotropin administration, a marked and significant decrease to baseline being noted 24 h later. To examine the effect of in vitro culture on ovarian ICE gene expression, whole ovarian dispersates from immature rats were cultured without treatment for 72 h. ICE gene expression significantly (P < 0.01) increased to a maximum 24 h post plating (2.55-fold increase as compared with time zero). Treatment with IL-1beta was associated with a small but statistically insignificant increase in ovarian ICE gene expression. Similarly, provision of IL-RA resulted in a modest, albeit statistically insignificant, decrease in ovarian ICE gene expression. Treatment with GnRH (but not FSH, LH or PMSG) significantly (P < 0.05) increased ovarian ICE gene expression (41.5% increase versus control). Treatment with dexamethasone (but not diethylstilbestrol, R5020 or R1881) produced a significant (P < 0.05) 42.3% decrease in ovarian ICE gene expression as compared with untreated controls. Treatment with TNF alpha (but not ET-1, TGF alpha, TGF beta, IGF-I or bFGF) produced a significant (P < 0.01) 2.5-fold increase in ovarian ICE gene expression as compared with untreated controls. Taken together, our present findings: (1) reaffirm the ovarian expression of the ICE gene, (2) document a periovulatory increase in ovarian ICE gene expression, (3) show the inhibitory effect of glucocorticoids in this regard, and (4) establish TNF alpha as an upregulator. Taken together, these findings suggest a role for ovarian ICE either in the context of apoptosis/atresia or in the context of the ovulatory process.

Animals↗
PubMed1997

o,p'-DDT and its metabolites inhibit progesterone-dependent responses in yeast and human cells.

Using a combination of in vitro assays we have evaluated whether DDT metabolites can interact with the progesterone receptor pathway in yeast expressing human progesterone receptor (hPR) and in T47D human breast cancer cells which express endogenous hPR. In transactivation assays using both yeast and T47D cells, o,p'-DDT and the metabolites p,p'-DDT, o,p'-DDD, p,p'-DDD, o,p'-DDE, p,p'-DDE, p,p'-DDA, and DDOH inhibited progesterone-induced reporter gene activity in a dose-dependent manner. None of the DDT metabolites functioned as hPR agonists. Whole cell competition binding assays using T47D cells indicated that the inhibitory effects of DDT metabolites on progesterone-dependent activites may occur through both hPR-dependent and hPR-independent pathways. Our results and previous reports of DDT metabolites interacting with estrogen and androgen receptors suggests that this class of environmental chemicals may interact with numerous hormone receptor signaling pathways.

Binding, Competitive↗
PubMed1997

A 361 base pair region of the rat FSH-beta promoter contains multiple progesterone receptor-binding sequences and confers progesterone responsiveness.

The rat is frequently used as a model to study the role of progesterone (P) in regulating FSH secretion and synthesis. The ability of P to modulate rat FSH-beta mRNA levels suggests the presence of a functional hormone response element. We have found three PRE-like sequences upstream of the transcription start site in the rat FSH-beta gene. These sequences are herein referred to as PRE-like sequence #1, #2 and #3 with #1 being most distal from the start site. The current studies determined whether these PRE-like sequences bound P receptor (PR) and were functional in regulating the induction of expression by P. Electrophoretic mobility shift assays (EMSA) demonstrated that a single 289 base pair (bp) DNA fragment encompassing all three PRE-like sequences specifically bound PR. Further, PR bound with high affinity to double-stranded oligonucleotides representing individual PRE-like sequences #1, #2 and, with lower affinity to a double-stranded oligonucleotide representing PRE-like sequence, #3. We have cloned a 361 bp sequence from the promoter region of the rat FSH-beta gene encompassing all three PRE-like sequences into a luciferase reporter vector (pGL3-promoter) yielding pFSHbeta361-luc+ which when transiently transfected into primary rat pituitary cell cultures, conferred P-responsiveness to a heterologous promoter. P-responsiveness was dependent upon the presence of PR and was blocked by the PR antagonist RU-486. These data strongly suggest the presence of functional PRE's in the rat FSH-beta gene promoter.

Animals↗
PubMed2000

Progestin receptors mediate progesterone suppression of epileptiform activity in tetanized hippocampal slices in vitro.

Clinical and laboratory studies suggest that progesterone reduces epileptic seizure activity. The mechanisms underlying this effect are not known. The present study determined the effects of progesterone on extracellular evoked responses recorded in the CA1 field of hippocampal slices, as well as epileptiform responses recorded from tetanized slices. Slices were prepared from ovariectomized rats, with or without estrogen replacement. Hippocampal slices were superfused in vitro with one of the following treatments: progesterone with or without RU486 (a progesterone receptor antagonist); allopregnanolone (a progesterone metabolite that potentiates GABA action at GABA(A) receptors); RU5020 (a high-affinity progesterone receptor agonist); or cholesterol (control). In non-tetanized slices, a twofold increase in the excitatory postsynaptic field potential and population spike amplitude occurred during both cholesterol and progesterone superfusion. In contrast, under the same conditions, exposure to allopreganolone caused a 25% reduction in both field potential and population spike amplitude of evoked responses within 30min of treatment. In tetanized slices, progesterone and RU5020, but not allopregnanolone or cholesterol, caused significant reductions in the field potential and population spike amplitude of evoked responses. Progesterone and RU5020 also significantly reduced the duration of tetanic stimulus-induced afterdischarges and the frequency of spontaneous interictal discharges. The effects of allopregnanolone were restricted to a reduction in the primary afterdischarge duration. Estrogen replacement slightly attenuated progesterone's suppression of spontaneous discharges and depression of evoked responses. All responses to progesterone were blocked by prior or concurrent exposure to RU486. These data indicate that allopregnanolone suppresses evoked potentials in non-tetanized hippocampal slices, consistent with previous reports that this neurosteroid has marked anxiolytic and anticonvulsant effects. After tetanization, however, progesterone receptor-mediated responses become quantitatively more important as a mechanism for suppressing hippocampal electrical activity.

Animals↗
PubMed1997

Endometrial effects of three doses of trimegestone, a new orally active progestogen, on the postmenopausal endometrium.

OBJECTIVE: To study the effects of oral trimegestone on endometrial histology and vaginal bleeding when given in combination with oral 17-beta-oestradiol. METHODS: This was a prospective, randomised, double-blind, parallel groups, pilot comparative study. Thirty-eight healthy postmenopausal women with normal endometrial histology were given oral 17-beta-oestradiol, 2 mg/day for three continuous cycles of 28 days, plus oral trimegestone, 0.10, 0.25 or 0.50 mg/day from day 15 to day 28 of each cycle. A Vabra biopsy was performed late in the oestradiol/trimegestone phase of cycle 3 and examined for histological evidence of secretory transformation of the endometrium. Characteristics of vaginal bleeding were recorded on a daily basis. RESULTS: Thirty-seven women completed the study, of whom 31 yielded adequate tissue for histological assessment. All showed secretory transformation of the endometrium. Bleeding was of earlier onset and longer duration with the lowest dose of trimegestone. CONCLUSIONS: Trimegestone is a highly effective oral progestogen for endometrial protection, all doses inducing secretory endometrial transformation. Although bleeding patterns suggest a weaker effect of the lowest dose used, the minimum effective dose for endometrial protection has still to be determined and may be lower than those used in this study.

Administration, Oral↗
PubMed2000

Physical evaluation of a new patch made of a progestomimetic in a silicone matrix.

The adhesion of a new Transdermal Therapeutic System (TTS) made of silicone and loaded with a progestomimetic drug was characterised. The goal of this study was to use well-known methods or to adapt them to collect representative data. Individually, methods such as surface tension, peel test and rheology are already widely used. Results show that the choice of a substrate for peel tests can be made in the light of surface tension data and that polymers like poly(tetrafluoroethylene) (PTFE) are good alternatives to skin. Peeling characterisations are made a function of thickness of films, drug content in active, conditions of preparation and conditions of use such as pressure. Dynamic rheology is more difficult to link to other methods as it mainly reflects internal phenomena and properties that arise in the bulk, as opposed on its surface. Master curves enable results to be used more easily, but the theories to interpret the data are still not powerful enough to replace peel testing.

Adhesiveness↗
PubMed2000

A study of the adhesive-skin interface: correlation between adhesion and passage of a drug.

The phenomena taking place at the patch-skin interface, in particular the adhesion of a pressure sensitive adhesive (PSA) film loaded with drug and the partition of the drug between the patch and the skin were correlated. The kinetics of adhesion as well as those of drug passage were studied in detail. Adhesion data were collected from peel test either on skin or on a polymer model. Passage of the drug was studied in a simple system composed of PSA film stuck on skin. In some experiments the film was left on the skin throughout the experiment; in others, it was periodically removed and stuck on again to keep the adhesion force constant during the whole of the experiment. We observed a rapid increase of the drug content in the skin until a plateau was reached. One adhesion for the whole experiment or several adhesions gave a similar curve. The main difference was the rate of increase of skin drug content and the value of the plateau. Different hypotheses concerning the relationship between the adhesion of this PSA and changes in the flux of drug have been put forward. However, it is difficult to extrapolate from this model to the in vivo situation because of variation both between individuals and with time.

Adhesiveness↗
PubMed2000

Progesterone effect on cell growth, ultrastructural aspect and estradiol receptors of normal human breast epithelial (HBE) cells in culture.

The stimulating effect of estradiol (E2) on breast cell growth is well documented. However, the actions of progesterone (P) and its derivatives remain controversial. Additional information is therefore necessary. On a culture system of normal human breast epithelial (HBE) cells, we observed an inhibitory effect on cell growth of a long-term P treatment (7 days) in the presence or absence of E2, using two methods: a daily cell count providing a histometric growth index, and [3H]-thymidine incorporation during the exponential phase of cell growth. A scanning electron microscopy study confirmed these results. Cells exhibited a proliferative appearance after E2 treatment, and returned to a quiescent appearance when P was added to E2. In both studies, P proved to be as efficient as the synthetic progestin R5020. Moreover, the immunocytochemical study of E2 receptors indicated that E2 increases its own receptor level whereas P and R5020 have the opposite effect, thus limiting the stimulatory effect of E2 on cell growth. In the HBE cell culture system and in long-term treatment, P and R5020 appear predominantly to inhibit cell growth, both in the presence and absence of E2.

Adolescent↗
PubMed2001

Differential regulation of retinoblastoma protein by hormonal and antihormonal agents in T47D breast cancer cells.

Phosphorylation of the tumor suppressor protein, retinoblastoma (pRb), regulates the progression of the cell cycle. Previous work from this laboratory had shown that estradiol (E(2)) regulates tumor suppressor proteins, p53 and retinoblastoma in breast cancer cells. In the present study, we have examined the phosphorylation of pRB in T47D breast cancer cells following treatments with R5020 and antiprogestins. In growth medium containing serum depleted of endogenous steroids by charcoal treatment, pRb appeared mainly in its hypophosphorylated form. Addition of 10 nM R5020 to the culture medium caused hyperphosphorylation of pRb within 24 h, but the hypophosphorylated form of pRb began to accumulate after 72 h. Upon prolonged R5020 treatment (72-96 h), pRb was detected exclusively in its hypophosphorylated form. While treatment of cells with R5020 caused a transient increase in the level of cyclin D1, E(2) addition caused a sustained increase in the level of cyclin D1 consistent with its role in stimulating pRb phosphorylation. Antagonists of both estrogen receptor (ER) and progesterone receptor (PR) blocked the E(2) and R5020-induced pRb phosphorylation, respectively. These results suggest that R5020 induces pRb phosphorylation via a transient increased expression of cyclin D1, whereas E(2) treatment results in sustained expression of cyclin D1 and increased pRb phosphorylation. Furthermore, R5020 effects on pRb phosphorylation appear PR-mediated as no cross-antagonism of pRb phosphorylation was observed: the R5020 effects were blocked by RU486 and ZK98299, but not by the pure ER antagonist, ICI 182, 780 (ICI).

Breast Neoplasms↗
PubMed2001

Rat uterine complement C3 expression as a model for progesterone receptor modulators: characterization of the new progestin trimegestone.

Progestins have a wide variety of activities in female reproduction. There are also pharmacological applications for progestins, including hormone replacement therapy and contraception. Here we report the development and characterization of the rat uterine complement component C3 mRNA as a molecular target for the evaluation of the antiestrogenic activity of progestins in the uterus. In this assay, ethinyl estradiol (EE) is used to stimulate C3 expression and progestins are then evaluated for their ability to inhibit this expression. The three reference progestins, progesterone (P4), levonorgestrel (LNG), and medroxyprogesterone acetate (MPA) blocked the increase in C3 mRNA levels induced by EE. Dexamethasone (DEX) and 17alpha-methyl testosterone did not inhibit the estrogen induced C3 mRNA levels; in fact, DEX caused a further increase in C3 mRNA levels. Finally, the antiprogestin RU486 was able to block the MPA inhibition of C3 message. RU486, like DEX, caused an increase in C3 mRNA levels above that of estrogen treatment alone. The model was also used to evaluate trimegestone (TMG), a new steroidal progestin, that has been shown to be a potent and selective progesterone receptor agonist. The activity of TMG in the rat uterine decidualization and ovulation inhibition assays was similar to MPA. However, in the C3 model, TMG caused a dose-dependent inhibition of the EE induced C3 message and was approximately five-fold more potent in this model than MPA (EC(50) of 4.7 microg/kg and 26.5 microg/kg, respectively). Therefore, TMG was a more potent antagonist of estrogenic activity in the uterine endometrium than any of the reference progestins tested and therefore may be more effective in protecting the endometrium in hormone replacement therapy.

Animals↗