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G Emons

Publications and source records attributed to G Emons.

At least 55 records · Page 3Linked to original sources
PubMed2000

The effect of long-term, non-suppressive levothyroxine treatment on quantitative ultrasonometry of bone in women.

OBJECTIVE: To evaluate the impact of long-term, non-suppressive levothyroxine (L-T(4)) treatment on quantitative ultrasonometry in women. DESIGN: This was a case-control study. SUBJECTS AND METHODS: Altogether 667 women (mean age+/-s.d., 49.5+/-13.1 years) were studied. Of these, 156 (23%) had non-toxic goitre or hypothyroidism and had been taking L-T(4) (75-100 microg/day) for at least 5 years (mean+/-s.d., 12.5+/-7.5 years); the remaining 511 (77%) women were not receiving L-T(4). All women had completed a questionnaire on risk factors for thyroid dysfunction and osteoporosis, and those with diseases or treatments known to effect bone metabolism - other than thyroxine or hormone replacement therapy (HRT) - were excluded. Women underwent quantitative ultrasonometry (QUS) at the heel. Speed of sound (SOS), broadband ultrasound attenuation (BUA) and the stiffness index (SI) were compared, first, in all women taking L-T(4) and controls and, secondly, in women taking L-T(4) and controls pair-matched for age, weight, body mass index (BMI), menopausal status and HRT use. RESULTS: Even after matching for age, weight, BMI, menopausal and HRT status, women taking L-T(4) had significantly lower values for SOS and SI (P<0.05), but not for BUA. However, absolute T- and Z-scores for SI were not low in either the study or control groups. Lower values were associated, but not significantly so, with years since the menopause and duration of L-T(4) treatment. CONCLUSIONS: Long-term, non-suppressive L-T(4) treatment in women with goitre or hypothyroidism was associated with a slight reduction in QUS values, which was more pronounced in postmenopausal women. This group could be at higher risk for osteoporotic fracture.

Adult↗
PubMed2000

LHRH might act as a negative autocrine regulator of proliferation of human ovarian cancer.

OBJECTIVE: More than 80% of human ovarian cancers express LHRH and its receptor. The proliferation of human ovarian cancer cell lines is reduced by both LHRH agonists and antagonists. This study was designed to further clarify the possible biological function of this LHRH system. DESIGN: As LHRH agonists and antagonists uniformly reduce proliferation of human ovarian cancer in a dose-dependent way, the effect of low concentrations of authentic LHRH was studied. In addition, longer periods of treatment (up to 9 days) were analyzed. To assess the physiological role of LHRH produced by ovarian cancer cells it was neutralized by adequate concentrations of a specific LHRH antiserum. METHODS: Human ovarian cancer cells EFO-21 and EFO-27, which express LHRH and its receptor, were incubated for 1-9 days with increasing concentrations (1pmol/l to 10 micromol/l) of authentic LHRH or with concentrations of LHRH antiserum capable of neutralizing at least 1nmol/l LHRH. Proliferation was assessed by counting cells. RESULTS AND CONCLUSIONS: Authentic LHRH reduced time- and dose-dependently proliferation (by maximally mean+/-s.e.m. 32.7 +/- 4.4%, Newman-Keuls, P < 0.001) of both ovarian cancer cell lines. At very low concentrations (1pmol/l) a marginal reduction of proliferation or no effect was observed. A mitogenic effect of authentic LHRH was never detected. Treatment of ovarian cancer cell cultures with antiserum to LHRH significantly increased (up to mean+/-s.e.m. 121.0 +/- 2.8% of controls, Newman-Keuls P <0.001) proliferation of EFO-21 and EFO-27 cells. These findings suggest that LHRH produced by human ovarian cancer cells might act as a negative autocrine regulator of proliferation.

Adenocarcinoma, Mucinous↗
PubMed2000

The influence of menopause and body mass index on serum leptin concentrations.

OBJECTIVE: The aim of this study was to evaluate the influence of menopausal status, serum estradiol and body mass index (BMI) on serum leptin concentration in a large sample of pre- and postmenopausal women. DESIGN: 434 healthy women (mean age +/-s.d., 52.2 +/- 10.3 years) were recruited at the University of Marburg on the occasion of a routine gynecological visit. Two hundred and eighteen (50.2%) women were premenopausal (mean age, 36.5 +/- 10.4 years) and not on oral contraceptives or hormone replacement therapy (HRT) and 216 (49.8%) women were postmenopausal (mean age 61.8 +/- 8.9 years) not on HRT. To evaluate the influence of menopausal status, estradiol level and BMI on serum leptin concentrations, women were allocated to one of the four groups: (a) premenopausal women BMI <25 kg/m(2) (n=137), (b) premenopausal women BMI >25 kg/m(2) (n=81), (c) postmenopausal women BMI <25 kg/m(2) (n=94) and (d) postmenopausal women BMI >25 kg/m(2) (n=122). RESULTS: Irrespective of the menopausal status, women with a BMI >25 kg/m(2) had significantly higher leptin concentrations in all age groups compared with women with a BMI <25 kg/m(2) (P<0.001). The multiple linear regression analyses showed that BMI was the only statistically significant independent predictor for leptin. In comparison to postmenopausal women, premenopausal women showed a significantly lower mean age, weight, BMI and FSH concentration (P<0. 001), a higher mean height and serum estradiol (P<0.01 and P<0.001 respectively) but significantly lower serum leptin concentration (P<0.01). The multiple linear regression model showed no significant influence of menopausal status or serum estradiol on serum leptin concentration, even after controlling for BMI. CONCLUSIONS: Serum leptin concentrations are significantly higher in pre- and postmenopausal obese women, compared with normal weight controls. Serum leptin concentrations are not influenced by menopausal status or serum estradiol level.

Adult↗
PubMed2000

Hormonal interactions in endometrial cancer.

Endometrial cancer (EC) is the most frequent malignant tumor of the female genital tract. Increasing evidence suggests that at least two different types of EC exist. Type I is associated with an endocrine milieu of estrogen predominance. These tumors are of endometrioid histology and develop from endometrial hyperplasia. They have a good prognosis and are sensitive to endocrine manipulation. Type II EC is not associated with a history of unopposed estrogens and develops from the atrophic endometrium of elderly women. They are of serous histology, have a poor prognosis, and do not react to endocrine manipulation. Both types of EC probably differ markedly with regard to the molecular mechanisms of malignant transformation. This article reviews reproductive and lifestyle factors modifying the risk of developing type I EC, including the use of hormonal contraceptives, hormone replacement therapy and tamoxifen. The roles of established and novel therapies for precancerous lesions and for invasive EC in the adjuvant and palliative settings are discussed.

Contraceptives, Oral, Hormonal↗
PubMed2000

Receptor mediated antiproliferative effects of the cytotoxic LHRH agonist AN-152 in human ovarian and endometrial cancer cell lines.

Eighty percent of human ovarian and endometrial cancers express receptors for luteinizing hormone-releasing hormone (LHRH). These receptors might be used for targeted chemotherapy with cytotoxic LHRH analogs such as AN-152, in which doxorubicin is linked to agonist carrier [D-Lys6]LHRH. The antiproliferative effects of doxorubicin and AN-152 were assessed in LHRH receptor-positive ovarian (EFO-21, EFO-27) and endometrial (HEC-1A, Ishikawa) cancer cell lines as well as in LHRH receptor negative ovarian SKOV-3 and endometrial MFE-296 lines. The mechanism of action of AN-152 was investigated by a blockage of receptors using an excess of the LHRH agonist [D-Trp6]LHRH. In some cases, confocal laser-scanning microscopy was used to visualize the accumulation of AN-152 or doxorubicin within the cells. In 3 of 4 LHRH receptor-positive cell lines (EFO-21, HEC-1A, Ishikawa) AN-152 was more effective than doxorubicin in inhibiting cell proliferation. The effect of AN-152 was shown to be receptor-mediated because it could be reduced by competitive blockade of the LHRH receptors with [D-Trp6]LHRH. In contrast, AN-152 was less active than doxorubicin in LHRH receptor-negative lines. Confocal laser-scanning microscopy showed an intranuclear accumulation of AN-152 and competitive inhibition thereof by [D-Trp6]LHRH in LHRH receptor-positive cell lines, but no intracellular accumulation of AN-152 could be detected in the receptor-negative SKOV-3 line. These results suggest a selective receptor-mediated action of AN-152 in receptor-positive cell lines.

Adenocarcinoma↗
PubMed1999

Stiffness index identifies patients with osteoporotic fractures better than ultrasound velocity or attenuation alone.

OBJECTIVES: To compare a composite ultrasonometry variable, the stiffness index (SI), with its two component variables of speed of sound (SOS) and broadband ultrasound attenuation (BUA), in identifying post-menopausal women with low bone mineral density (BMD) and/or osteoporotic fracture. METHODS: A cross sectional sample of 1217 women (mean (S.D.) age 53.9 (9.7) years) was studied. Risk factors for osteoporosis were assessed by detailed questionnaire and women with diseases, or those taking treatments known to affect bone metabolism were excluded. Women were allocated to one of four groups: pre-menopausal women (n = 476), healthy post-menopausal women (n = 583), post-menopausal women with low BMD (n = 101), and post-menopausal women with osteoporotic fracture (n = 57). An Achilles ultrasonometer was used to perform quantitative ultrasonometry (QUS) at the os calcis. The SI. calculated mathematically from SOS and BUA, was computed. RESULTS: Analysis of receiver operating curves (ROC) between healthy post-menopausal women and post-menopausal women with low BMD but no fracture, showed that the area under the curve (AUC) for SI was significantly greater than that for BUA (P < 0.001) or SOS (P < 0.05). For healthy post-menopausal women compared to women with fracture, the area AUC for SI was significantly greater than that for BUA (P < 0.05) or SOS (P < 0.001). No significant difference was found for AUC between BUA and SOS. CONCLUSION: QUS variables discriminated women with low density or fracture from healthy postmenopausal controls. The SI was a significantly better indicator than BUA or SOS in this retrospective study.

Bone Density↗
PubMed1999

Age changes of calcaneal ultrasonometry in healthy German women.

This study assessed age changes in quantitative ultrasound sonometry (QUS) in a large sample of healthy German women. Speed of sound (SOS), broadband ultrasound attenuation (BUA), and stiffness index (SI) of the calcaneus were measured in 1333 women (mean age 50.5 +/- 11.5 years) using the Achilles ultrasonometer (Lunar Corp., Madison, WI, USA). The short-term precision in 31 adults was 0.2% for SOS, 1. 2% for BUA, and 1.3% for SI. There was an overall decline of 15% for BUA, 4% for SOS, and 31% for SI between late adolescence and old age. In premenopausal women, BUA decreased only slightly (-3%), whereas postmenopausal women showed a significantly increased decline (-12%). In contrast, SOS continuously decreased from the age of 15; there was a decline of 2% from adolescence to the menopause; postmenopausal women showed a slightly larger decline (-2.5%). The SI of premenopausal women decreased by 10%, but the postmenopausal decline of almost 22% was significantly greater. SI values for premenopausal German women were comparable to those observed in the American Achilles reference population, but postmenopausal German women had significantly higher SI values of 7% due to a lower rate of aging loss.

Adolescent↗
PubMed1999

Hormonal interactions in ovarian cancer.

According to the epidemiologic literature and the laboratory characterization of receptor content and molecular interactions, there is a relationship between the microenvironment of ovarian cancer and steroid hormones. Advances in our knowledge of the molecular-hormonal nature of ovarian cancer will help in designing a rationale for clinical trials in appropriate subsets of patients. However, currently, development of successful therapies and prevention strategies for women at risk remains a true challenge.

Female↗
PubMed1999

Serum leptin and gonadotropin levels in patients with anorexia nervosa during weight gain.

Leptin plays an important role in reproductive function. In patients with acute anorexia nervosa, serum leptin levels have repeatedly been shown to be lower than in age-matched controls. We have previously hypothesized that the amenorrhea characteristic of anorexia nervosa is related to this low leptin secretion. In an attempt to address this hypothesis, serum levels of leptin and follicle stimulating hormone (FSH) and luteinizing hormone (LH) of 16 female inpatients with anorexia nervosa or an eating disorder not otherwise specified (atypical anorexia nervosa) were measured on a biweekly basis during weight gain. We hypothesized that a serum leptin level of 1.85 microg L(-1) would be associated with gonadotropin levels at or above the minimal level observed during the menstrual cycle in healthy adult fertile females. Our results revealed that increments of LH levels generally tracked increments of leptin levels during the first weeks of treatment. Similarly, in those patients with low referral leptin levels, FSH initially also tracked leptin levels. In contrast, a relationship between gonadotropin levels and leptin secretion was no longer discernible after LH and FSH levels had peaked. Those patients with exceedingly low leptin levels upon admission revealed a slow increase of gonadotropin levels. Our hypothesis of a threshold leptin level of 1.85 microg L(-1) was supported for LH only.

Adolescent↗
PubMed1999

Interactions of ovarian steroids with pituitary adenylate cyclase-activating polypeptide and GnRH in anterior pituitary cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) releases LH and FSH from anterior pituitary cells. Although this effect is relatively weak, it has a strong sensitizing action on GnRH-induced gonadotropin secretion. Here we investigated the possibility that ovarian steroids, which are well-known modulators of LH secretion, interact with PACAP and GnRH in pituitary gonadotrophs. Rat pituitary cells were treated for 48 h with vehicle, 1 nmol/l estradiol, 1 nmol/l estradiol + 100 nmol/l progesterone or 48 h with 1 nmol/l estradiol and 4 h with 100 nmol/l progesterone. The cells were stimulated for 3 h with 1 nmol/l GnRH or 100 nmol/l PACAP. Estradiol treatment alone enhanced basal as well as GnRH- or PACAP-stimulated LH secretion. LH release was facilitated by additional short-term progesterone treatment. Long-term treatment with estradiol and progesterone led to reduced LH responses to GnRH and PACAP. Neither treatment paradigms affected cAMP production. However, estradiol treatment led to enhanced cAMP accumulation in quiescent or GnRH-stimulated cells. PACAP-induced increases of cAMP production were inhibited by estradiol treatment. After 7-h preincubation with 10 nmol/l PACAP, cells responded with enhanced LH secretion to GnRH stimulation. When steroid pretreatment was performed the responsiveness of gonadotrophs to low concentrations of GnRH was still increased. In contrast, at high concentrations of GnRH the sensitizing action of PACAP on agonist-induced LH secretion was lost in steroid-treated cells. There were no significant differences between the steroid treatment paradigms. It is concluded that estradiol but not progesterone acts as a modulator of adenylyl cyclase in gonadotrophs. The stimulatory effect of estradiol is thought to be involved in its sensitizing action on agonist-induced LH secretion. The inhibitory effect of estradiol on PACAP-stimulated adenylyl cyclase activities seems to be responsible for the loss of its action to sensitize LH secretory responses to GnRH.

Adenylyl Cyclases↗
PubMed1998

Effects of LHRH-analogues on mitogenic signal transduction in cancer cells.

The expression of luteinizing hormone-releasing hormone (LHRH) and its receptors has been demonstrated in a number of human malignant tumors, including cancers of the breast, ovary, endometrium and prostate. These findings suggest the presence of an autocrine regulatory system based on LHRH. Recent studies in our laboratory have demonstrated that the function of LHRH produced by ovarian cancer cells is the inhibition of their proliferation. Dose-dependent antiproliferative effects of LHRH-agonists have been observed by several laboratories in cell lines derived from the above cancers. Interestingly, also LHRH-antagonists have marked antiproliferative activity in most of the ovarian, breast and endometrial cancer cell lines tested so far, indicating that the dichotomy of LHRH-agonists/LHRH-antagonists is not valid for the LHRH-system in cancer cells. In addition, our data suggest that the classical LHRH receptor signal transduction mechanisms known from the pituitary (phospholipase-C, protein kinase C, adenylyl cyclase) are not involved in the mediation of LHRH effects in cancer cells. Data obtained by several groups, including ours, rather suggest that LHRH analogs interfere with the signal transduction of growth-factor receptors and related oncogene products associated with tyrosine-kinase activity. The mechanism of action is probably an LHRH-induced activation of a phosphotyrosine phosphatase, counteracting the effects of receptor associated tyrosine kinase. In our hands, LHRH analogs virtually blocked the EGF-induced MAP-kinase activity of ovarian and endometrial cancer cells. The pharmacological exploitation of this mechanism might provide promising new therapies for these cancers.

Cell Transformation, Neoplastic↗
PubMed1997

Low leptin levels predict amenorrhea in underweight and eating disordered females.

Evidence that leptin plays an important role in reproductive function is accumulating rapidly. We hypothesized that low leptin synthesis is associated with amenorrhea. We therefore determined serum leptin levels in 43 underweight female students, who were screened for lifetime occurrence of amenorrhea. We assessed the predictive value of leptin, body mass index (BMI), fat mass and percent body fat, respectively, for lifetime occurrence of amenorrea. Factors predicting amenorrhea were tested for their capability to predict current amenorrhea in a second cohort of 63 inpatients with anorexia nervosa (AN) or bulimia nervosa (BN). Furthermore, the relationships between serum leptin levels and of follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol and progesterone, respectively, were evaluated. Only leptin predicted lifetime occurrence of amenorrhea in the student cohort. The critical leptin level was in the range of 1.85 micrograms L-1. This level served to largely separate anorectic from bulimic patients. In patients with AN mean serum log10 leptin levels over the first 4 weeks of inpatient treatment were correlated with mean FSH, LH and estradiol levels, respectively. Evidently, a critical leptin level is needed to maintain menstruation. In affluent populations eating disorders are likely to be a major cause of a low leptin synthesis.

Adolescent↗
PubMed1996

Luteinizing hormone-releasing hormone agonist triptorelin in combination with cytotoxic chemotherapy in patients with advanced ovarian carcinoma. A prospective double blind randomized trial. Decapeptyl Ovarian Cancer Study Group.

BACKGROUND: Several lines of evidence suggest that the proliferation of ovarian carcinoma might be stimulated by gonadotrophins. A number of Phase I/Phase II clinical trials have reported that the suppression of endogenous luteinizing hormone and follicle-stimulating hormone secretion by luteinizing hormone-releasing hormone (LHRH) analogs induced objective remissions and/or disease stabilization in 10-30% of patients with advanced refractory ovarian carcinoma. The current study was performed to evaluate whether the addition of LHRH agonist treatment to standard platinum-based chemotherapy could prolong survival of patients with surgically treated Stage III or IV epithelial ovarian carcinoma. METHODS: One hundred and thirty-five patients with Stage III or IV epithelial ovarian carcinoma participated in this prospective randomized double blind trial. After cytoreductive surgery, 69 patients received monthly injections of a depot preparation of the LHRH agonist [D-Trp6] LHRH (triptorelin, 3.75 mg) and 66 patients received placebo until their deaths or termination of trial, respectively. All patients were treated with a standard platinum-based chemotherapy, and, if necessary, with second- or third-line cytotoxic regimens. RESULTS: Endogenous gonadotrophins were reliably suppressed in patients treated with triptorelin. However, their progression free and overall survival were not significantly different from that of patients receiving placebo injections (statistical power > 80% for a difference between both groups of > or = 20%). CONCLUSIONS: The results of this trial suggest that the suppression of endogenous gonadotrophins by conventional doses of an LHRH agonist produces no relevant beneficial effects in patients with advanced ovarian carcinoma who receive standard surgical cytoreduction and cytotoxic chemotherapy.

Adult↗
PubMed1996

Modulatory actions of progesterone on gonadotropin-releasing hormone-induced arachidonic acid liberation from perifused rat pituitary cells.

The stimulatory action of gonadotropin-releasing hormone (GnRH) on gonadotropin secretion from cultured rat pituitary cells is modulated by estradiol and progesterone. Recent studies provided evidence that both steroids exert effects on different pathways of GnRH signal transduction, which might be responsible for their actions on luteinizing hormone (LH) release. Here we investigated whether the steroids are able to modulate GnRH-induced liberation of arachidonic acid, which is thought to be involved in GnRH signal transduction. Pituitary cells obtained from female rats were treated for 48 h with vehicle, 1 nmol/l estradiol or 1 nmol/l estradiol + 100 nmol/l progesterone, 48 h with 1 nmol/l estradiol and 2 h with 100 nmol/l progesterone. In addition, these cells were prelabeled with [3H]arachidonic acid. Then the cells were transferred to a perifusion system and challenged with a 6-min pulse of 100 nmol/l GnRH. Estradiol treatment enhanced the LH secretory response while GnRH-induced [3H]arachidonic acid liberation remained unaffected. However, progesterone modulated both LH secretion and [3H]arachidonic acid release in response to the GnRH stimulus. The short-term progesterone treatment paradigm enhanced the LH and arachidonic acid responses by up to 160 +/- 13 and 204 +/- 18%, respectively, while long-term treatment was inhibitory (59 +/- 9 and 63 +/- 4% vs control). Because arachidonic acid has been shown to be involved in GnRH signal transduction, it seems reasonable to speculate that the actions of progesterone described in the present study are related to its modulatory effect on GnRH-induced LH secretion.

Animals↗
PubMed1995

Expression of the messenger RNAs for luteinizing hormone-releasing hormone (LHRH) and its receptor in human ovarian epithelial carcinoma.

Recently we reported the presence of specific high affinity binding sites for luteinizing hormone-releasing hormone (LHRH) and its analogues (Kd = 1.5 or 1.7 nM) in the human epithelial ovarian cancer cell lines EFO-21 and EFO-27. The proliferation of these cell lines was inhibited by nM concentrations of a LHRH agonist. This study was performed to ascertain whether these ovarian cancer cell lines produce LHRH and whether the high affinity LHRH binding site found previously was identical to the pituitary LHRH receptor. Significant amounts of immunoreactive LHRH were found in the extracts of both the EFO-21 cell line (449 +/- 56 fmol/10(6) cells) and the EFO-27 line (409 +/- 76 fmol/10(6) cells). LHRH bioactivity of these extracts, assessed in terms of release of luteinizing hormone by rat pituitary cells, was comparable to that of authentic LHRH. EFO-21 and EFO-27 cells expressed the mRNAs for both human LHRH and human LHRH receptor as assessed by reverse transcriptase-PCR using oligonucleotide primers according to published sequences. In addition, in eight of eight biopsy samples of human epithelial ovarian cancers we detected mRNA for LHRH, six of these specimens expressed the mRNA representing the LHRH receptor. These data support the concept that human epithelial ovarian cancers might have a local system based on LHRH to regulate cell proliferation. It is still obscure at present whether LHRH produced locally has a stimulatory, inhibitory, or no impact on the proliferation of ovarian cancer cells. However, exogenous LHRH agonists seem to have clear antiproliferative activity, probably mediated through LHRH receptors. This finding might provide the base for novel approaches in the therapy of epithelial ovarian cancer.

Animals↗
PubMed1995

Ovarian steroids modulate gonadotropin-releasing hormone-induced biphasic luteinizing hormone secretory responses and inositol phosphate accumulation in rat anterior pituitary cells and alpha T3-1 gonadotrophs.

The ovarian steroids estradiol and progesterone act as important modulators of GnRH-induced luteinizing hormone (LH) secretion from anterior pituitary cells. Recently, we demonstrated that the steroids are able to influence GnRH-stimulated Ca2+ mobilization from extra- and intracellular sources. Here we investigated the actions of estradiol and progesterone on GnRH-induced biphasic LH secretory responses in the model of perifused female rat pituitary cells. A 20 min GnRH stimulus elicited biphasic LH responses composed of an initial peak followed by a prolonged plateau phase. Both phases were equally enhanced by long-term (48 h) estradiol treatment. This action was facilitated by subsequent short-term progesterone treatment. In contrast, combined treatment with estradiol and progesterone for 48 h led to inhibited LH secretory profiles. To determine the steroid actions on the extracellular Ca2+ independent component of LH secretion we performed experiments using cells that were perifused with Ca2+ deficient medium. Under these conditions the cells responded exclusively with a single peak phase of LH secretion, which was augmented or inhibited by estradiol and progesterone treatment as described above. To test the hypothesis that an effect of estradiol and progesterone on GnRH-induced polyphophoinositide hydrolysis is responsible for their modulatory actions on Ca2+ signals and LH secretion we measured inositol phosphate (IP) accumulation after different steroid treatment paradigms in rat pituitary cells and alpha T3-1 immortalized gonadotrophs. GnRH-induced IP production was enhanced by long-term estradiol treatment. Short-term exposure of estradiol-primed cells to progesterone did not lead to significant changes of IP production. The long-term progesterone treatment paradigm enhanced GnRH-induced IP formation, while it decreased Ca2+ signals and LH secretion. Alpha T3-1 cells were used to perform more detailed analysis of IP formation. The actions of estradiol and progesterone on the production of inositol mono-, bis-, and trisphosphates were similar to those observed in the mixed cell population. It is concluded that estradiol and progesterone modulate both peak and plateau phases of GnRH-stimulated LH secretory responses, effects which are associated with their impact on Ca2+ signals. Our findings argue against a role of IP modulation in the mechanism of progesterone actions on Ca2+ signaling and LH secretion in gonadotrophs. Such a mechanism might be involved in the positive effects of estradiol in these cells.

Animals↗
PubMed1994

Modulation of calcium signaling and LH secretion by progesterone in pituitary gonadotrophs and clonal pituitary cells.

In estradiol-treated pituitary cells, progesterone enhances gonadotropin-releasing hormone (GnRH)-induced LH secretion from cultured rat pituitary cells during short-term treatment but attenuates this response during prolonged treatment. In the present study, the effects of gonadal steroids on GnRH-induced cytoplasmic calcium ([Ca2+]i) responses in gonadotrophs were analyzed in rat pituitary cells and immortalized (alpha T3-1) murine gonadotrophs. Ca2+ responses were measured in cell suspensions and single gonadotrophs, loaded with Fura-2 or Indo-1, respectively, and pretreated for 48 h with 1 nM estradiol with or without 100 nM progesterone, or for 48 h with 1 nM estradiol and then for 3 h with 100 nM progesterone. In cells of the alpha T3-1 gonadotroph lineage, GnRH elicited biphasic Ca2+ signals composed of an initial peak response followed by a prolonged plateau phase. The amplitudes of both the extracellular Ca(2+)-independent spike phase and the extracellular Ca(2+)-dependent plateau phase were enhanced or inhibited by short- or long-term progesterone treatment, respectively. In single pituitary gonadotrophs, GnRH (0.5 nM) elicited oscillatory responses due to intermittent release and uptake of Ca2+ from intracellular stores. Treatment with progesterone shifted the oscillatory signal toward biphasic (3 h) or subthreshold (48 h) response profiles, revealing a steroid-induced change in the pattern of Ca2+ mobilization. In addition to these agonist-induced responses, the transient [Ca2+]i responses of pituitary cells and individual gonadotrophs to high K+ were enhanced or inhibited after short- or long-term progesterone treatment, respectively. These actions were correlated with the effects of progesterone on K(+)-induced LH secretion. The [Ca2+]i and LH secretory responses to phorbol ester treatment were also enhanced by short-term exposure of the cells to progesterone. The results demonstrate that the stimulatory and inhibitory effects of progesterone on agonist-induced Ca2+ signaling result from changes in Ca2+ mobilization and entry, and contribute to the modulatory actions of the steroid on GnRH-induced LH secretion.

Animals↗