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Biomedical subjects

F Petraglia

Publications and source records attributed to F Petraglia.

At least 127 records · Page 7Linked to original sources
PubMed1998

Hypothalamic amenorrhea and cardiovascular hormones: changes of plasma calcitonin gene-related peptide and atrial natriuretic peptide levels.

Typical modifications of cardiovascular activity and water and salt homeostasis throughout female reproductive life are well known. Differences in plasma levels of calcitonin gene-related peptide (CGRP) and atrial natriuretic peptide (ANP) have been observed in conditions characterized by different estrogenic levels, suggesting a correlation between female reproductive function and these cardiovascular hormones. The aim of our study was to investigate in hypothalamic amenorrhea the relationship between estrogen deficiency and plasma ANP and CGRP response to adaptive tests (saline infusion test and upright posture test, respectively). Women with hypothalamic amenorrhea (aged 18-28 years) (n = 6) and age-matched healthy controls (n = 6) underwent both functional tests. Plasma CGRP and ANP levels were measured by specific radioimmunoassays before and in course of the tests. Basal plasma CGRP levels of amenorrheic patients did not significantly differ from those of normal women, while basal plasma ANP levels were significantly higher compared to controls (p < 0.01). In amenorrheic women, plasma CGRP levels showed a significant increase in response to upright posture test, though lower than the increase observed in normal women. In contrast, saline infusion test determined a significant increase in plasma ANP levels only in control subjects. In women with hypothalamic amenorrhea, the altered response of CGRP and ANP to adaptive stimuli indicates a partial derangement in the control of the secretion of these cardiovascular hormones. Nevertheless, the differences between such modifications and those observed in other conditions of altered estrogenic levels, suggest that in amenorrheic women hypogonadism is not the major factor influencing CGRP and ANP response to adaptive stimuli.

Adolescent↗
PubMed1998

Estrogen replacement therapy modulates spontaneous GH secretion but does not affect GH-RH-induced GH response and low T3 syndrome in women with hypothalamic amenorrhea associated to weight-loss.

Severe dieting and negative energy balance usually lead to the occurrence of amenorrhea together with several endocrine disturbances such as the "low T3 syndrome" and an abnormal GH secretion. To evaluate whether estrogen replacement therapy (ERT) affects thyroid hormones and GH secretion, two groups of patients affected by weight-loss-related amenorrhea and with low plasma T3 levels were treated with two different schedules of ERT using 50 or 100 micrograms estradiol transdermal patches twice a week (Dermestril, Rottapharm, Monza, Italy). Before and after 5 weeks of therapy in each patient thyroid hormones, spontaneous GH secretion and GH-RH-induced GH release were evaluated. After ERT, plasma GH and IGF-1 levels increased in both groups and a consistent change in GH spontaneous release was observed. Conversely the low T3 plasma levels and GH-RH-induced GH response were not modified by ERT. Our present data suggest that in amenorrhea related to weight-loss, hormonal abnormalities are only in part dependent from the hypoestrogenic condition.

Administration, Cutaneous↗
PubMed1998

Low levels of serum inhibin A and inhibin B in women with hypergonadotropic amenorrhea and evidence of high levels of activin A in women with hypothalamic amenorrhea.

OBJECTIVE: To examine serum levels of inhibin A, inhibin B, and activin A in women with secondary hypergonadotropic or hypothalamic amenorrhea. DESIGN: Retrospective study. SETTING: Universities of Udine, Pisa, and Modena in Italy, and of Wien in Austria. PATIENT(S): Forty women with idiopathic premature ovarian failure (POF), 23 women with hypogonadotropic hypothalamic amenorrhea, 40 healthy postmenopausal women, and 40 age-matched women with normal ovarian function (controls). INTERVENTION(S): Blood samples were collected between 8 and 9 AM. MAIN OUTCOME MEASURE(S): Serum levels of inhibin A, inhibin B, and activin A. RESULT(S): Women with POF had lower concentrations of serum inhibin A and inhibin B than women with hypothalamic amenorrhea and fertile controls, and the difference between these concentrations was statistically significant. Levels of inhibin A and inhibin B were low in postmenopausal women and were no different than in women with POF. Serum levels of activin A were not significantly different among women with POF, fertile controls, and postmenopausal women. Women with hypogonadotropic hypothalamic amenorrhea had higher activin A values than did controls. No significant correlation was found between the level of inhibin A or inhibin B and the length of amenorrhea or the level of FSH. CONCLUSION(S): Low levels of circulating inhibins A and B, but not activin A, reflect ovarian failure in women with POF, whereas women with hypogonadotropic hypothalamic amenorrhea have normal levels of inhibins A and B and high levels of activin A.

Activins↗
PubMed1998

Acute infusion of naloxone, an opioid receptor antagonist, does not modify serum leptin concentrations in amenorrheic and healthy women.

OBJECTIVE: To determine whether the opioidergic system is involved in the modulation of leptin secretion in healthy and amenorrheic subjects. DESIGN: Prospective study. SETTING: Department of Obstetrics and Gynecology, University of Modena, Modena, Italy. PATIENT(S): Healthy subjects (n = 8) and patients with hypothalamic amenorrhea (n = 17) or hyperandrogenism (n = 7) and low body mass index (BMI). INTERVENTION(S): Acute infusion of naloxone (4-mg bolus) and blood sampling 15 minutes before infusion; at time of infusion; and 15, 30, 45, 60, 75, 90, and 120 minutes after infusion. MAIN OUTCOME MEASURE(S): Plasma leptin, LH, FSH, E2, and cortisol concentrations. RESULT(S): Plasma leptin concentrations were lower (P <.01) in both hypothalamic and hyperandrogenic amenorrheic subjects than in healthy controls. In all groups of subjects, no significant changes in leptin levels were observed after infusion of naloxone. A significant correlation was found between leptin concentrations and BMI when all subjects were considered together (P <.05) but was not found in the single groups. CONCLUSION(S): The present data do not support the hypothesis that opioidergic receptors are involved acutely in the modulation of leptin release in healthy and amenorrheic women.

Amenorrhea↗
PubMed1998

Paracrine regulation of human placenta: control of hormonogenesis.

There is much evidence indicating that the human placenta plays a very important role in modulating the endocrinology of pregnancy. Placental tissue produces cytokines, hormones and growth factors that are essential in the regulation of the feto-maternal unit. The production of these substances is regulated by a network of interactions within and between intra-uterine through paracrine and/or autocrine mechanisms. Communication between the gestational intra-uterine tissues is critical for successful pregnancy, from the earliest stage of implantation until the expulsive phase of delivery. This is confirmed by the demonstration that the human placenta directly controls the release of substances such as hCG, hPL, steroid hormones and prostaglandins. Furthermore, there is evidence that intra-uterine tissues also can regulate ACTH release and have effects on the hypothalamus-pituitary-gonadal axis and the hypothalamus-pituitary-adrenal axis. The set of data reported in this article confirms that the placenta must be considered an organ that is essential for the initiation, maintenance and successful conclusion of pregnancy and that an imbalance between the complex network of placental regulating systems may cause serious gestational disorders.

Adrenocorticotropic Hormone↗
PubMed1998

Ultrasonographic patterns of polycystic ovaries: color Doppler and hormonal correlations.

Ultrasound has been used in the identification of two different morphological patterns of polycystic ovaries, namely a peripheral cystic pattern and a general cystic pattern. The aim of this study was to evaluate whether patients with the peripheral form of polycystic ovaries showed different ovarian and uterine blood flow from those with the general form, and to investigate whether there was a correlation between the forms and different hormonal parameters. Eighteen patients with the general form and 16 patients with the peripheral form of polycystic ovary underwent clinical, biochemical, gray-scale and color Doppler ultrasonographic evaluation. The parameters analyzed confirmed polycystic ovarian syndrome (PCOS) in all patients. Individual levels of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone, androstenedione and estradiol did not differ between the groups. However, there was a significantly higher LH/FSH ratio and a greater stromal echodensity in the peripheral cystic group than in the general cystic group. Doppler ultrasonography demonstrated significantly lower pulsatility index values in the intraovarian arteries of the peripheral cystic group and a higher rate of visualization of these arteries than in the general cystic group. These findings suggest that, apart from the LH/FSH ratio, the different morphological types of polycystic ovary do not reflect differences in endocrine profile. The differences in blood flow demonstrated by Doppler assessment in each case, however, showed that PCOS does not predetermine a single intraovarian blood flow pattern.

Adolescent↗
PubMed1998

Somatotropic axis and body weight in pre-menopausal and post-menopausal women: evidence for a neuroendocrine derangement, in absence of changes of insulin-like growth factor binding protein concentrations.

The altered function of the somatotropic axis observed in perimenopause may underlie the changes in body weight and fat distribution. The aim of the present study was to evaluate, in pre-menopausal and post-menopausal women with body mass index (BMI) > or = or <25, the basal plasma levels of growth hormone (GH), insulin-like growth factor (IGF)-I and -II, IGF binding protein (IGFBP)-1 and -3, and the response of GH and IGFBP-1 and -3 to GH releasing hormone (GHRH) and GHRH plus arginine tests. GH and IGF-I basal concentrations were significantly higher in pre-menopausal than in post-menopausal women, while IGF-II, IGFBP-1 and IGFBP-3 concentrations did not vary significantly. IGFBP-1, but not IGFBP-3, concentrations were higher in lean than in obese patients. Insulin concentrations were significantly higher in obese patients, while no differences were observed between pre-menopausal and post-menopausal women. In all subjects, GH concentrations increased significantly during GHRH test; pre-menopausal and lean women showed a higher response compared to post-menopausal and obese women. The GHRH plus arginine test stimulated GH response in all women, irrespective of age and BMI. IGFBP-1 and -3 concentrations did not vary in response to GHRH or GHRH plus arginine tests. The somatotropic axis undergoes modifications in post-menopausal women, apparently not involving IGFBP-1 and -3. Arginine infusion restores the response of GH to GHRH, in both post-menopausal and obese subjects. A somatostatinergic hyperactivity at the climateric period may underlie the changes both in body weight and somatotropic axis.

Arginine↗
PubMed1998

Healthy women and patients with endometriosis show high concentrations of inhibin A, inhibin B, and activin A in peritoneal fluid throughout the menstrual cycle.

Inhibin A, inhibin B, and activin A are growth factors which play local autocrine/paracrine roles in reproductive tissues. Since peritoneal fluid hormone content may reflect in part ovarian and endometrial secretory activities, the present study aimed to evaluate: (i) whether inhibin alpha-, activin betaA- and betaB-subunits, and activin receptor type II and type IIB mRNA are expressed in peritoneal tissues; (ii) expression and secretion of inhibin A and B, and activin A in cultured endometriotic cells; and (iii) concentrations of inhibin A and B, and activin A in serum and in peritoneal fluid in healthy women and in patients with endometriosis throughout the menstrual cycle. A group of women (n = 72) was recruited at laparoscopy for infertility investigation and divided into two groups: (i) control healthy women (n = 35), (ii) women with endometriosis (n = 37). Both groups were subdivided according to the follicular and luteal phase of the menstrual cycle. At the time of laparoscopy, specimens of peritoneal tissues were collected from three healthy women, while endometriotic tissue samples were collected and cultured from three women with endometriosis. Peritoneal tissues and cultured endometriotic cells expressed inhibin alpha-, activin betaA-, and betaB-subunits, and activin receptors mRNAs; in addition, inhibin-related proteins were measurable in culture medium. In healthy women, inhibin A and B, and activin A concentrations in peritoneal fluid were significantly higher than in serum (P < 0.001), at both phases of the menstrual cycle. Peritoneal inhibin A and B, and activin A concentrations were not significantly different between healthy women and patients with endometriosis, either when evaluated according to the degree of the disease and/or to the phase of the menstrual cycle. In conclusion, the findings that high concentrations are present in peritoneal fluid and that menstrual cycle-related changes occur suggest that reproductive organs may contribute to inhibin-related proteins in peritoneal fluid.

Activins↗
PubMed1998

Acute estradiol and progesterone administration reduced cardiovascular and catecholamine responses to mental stress in menopausal women.

Steroid hormones are involved in the regulation of sympathoadrenal activity. Since the effect of sex steroids on the cardiovascular system and catecholamine secretion could also be exerted through an acute, nongenomic mechanism, we have studied the response to mental stress (color word test, CWT) in a group of 15 menopausal women during estrogen (100 microg of estradiol by patch), progesterone (100 mg i.m.) or placebo administration. Systolic blood pressure (SBP) increased during CWT in the three sessions (F = 11.0, p < 0.001) but the area under the curve of SBP was higher during placebo (2,855 +/- 131 mm Hg x min) than during estradiol (2,585 +/- 139 mm Hg x min) and progesterone (2,553 +/- 179 mm Hg x min, p < 0.05 for both). Plasma epinephrine increased during CWT in the three sessions (F = 31.1, p < 0.001) and the plasma epinephrine response to mental stress was higher during placebo than during estradiol administration (F = 4.3, p < 0.01). The area under the curve of epinephrine was 10,342 +/- 1,348 pmol/min x 1 during placebo and 7,280 +/- 818 pmol/min x 1 during estradiol (p < 0.03). The plasma glycerol levels at the end of CWT were higher during placebo (0.26 +/- 0.04 nmol/l) than during estradiol (0.19 +/- 0.03 mmol/l) and progesterone (0.17 +/- 0.04 mmol/l) administration (p < 0.05 for both). No significant differences were found in the responses of diastolic blood pressure, heart rate, norepinephrine and cortisol to mental stress during placebo and estradiol or progesterone administration. This study demonstrates that acute steroid administration is able to modify the cardiovascular and catecholamine response to mental stress in menopausal women.

Adrenal Glands↗
PubMed1998

Inhibin B is the major form of inhibin/activin family secreted by granulosa cell tumors.

Both experimental and clinical studies suggest that inhibin plays a critical role in the development of granulosa cell tumors (GCT), a subgroup of malignant ovarian tumors. Inhibin has been proposed as a biological marker for the follow-up of patients bearing these particular tumors. Hitherto, there is no general agreement on the molecular form(s) of the inhibin family that are secreted by malignant granulosa cells. Using specific and sensitive immunoassays for activin A and for inhibins A and B, we investigated the production of these molecules in patients with either an adult GCT (n=13) or an epithelial ovarian cancer (n=11). Results showed that serum activin A level was increased in all patients, independently of their clinical status (progressive disease or remission) in comparison to that observed in the healthy pre- and postmenopausal women. Most of the patients also presented a moderate increase in serum inhibin A level compared to that in controls. Only one of eight patients with a progressive granulosa cell tumor had a high value of serum inhibin A. In contrast, serum inhibin B was dramatically increased in eight of nine patients with a granulosa cell tumor and its level correlated with the clinical status of the patients. No correlation was found between the level of serum inhibin B and that of serum antimüllerian hormone, a recently described specific and reliable marker for GCT. None of the patients with an epithelial ovarian cancer presented an increase of serum inhibin B. These observations demonstrate that inhibin B is the major molecular form of the inhibin family proteins produced by malignant granulosa cells.

Activins↗
PubMed1998

Expression and secretion of inhibin and activin in normal and neoplastic uterine tissues. High levels of serum activin A in women with endometrial and cervical carcinoma.

Inhibins and activins are growth factors belonging to the transforming growth factor-beta) family and are known to influence cell proliferation and differentiation. Because transforming growth factor-beta is involved in physiological and tumoral changes of uterine tissues, the present study aimed to evaluate whether human normal and neoplastic endometrial and cervical epithelial cells express and secrete inhibin A, inhibin B, and activin A. To test this hypothesis, different approaches were used. By RT-PCR, the expression of specific messenger RNAs (mRNAs) for the inhibin alpha, activin betaA and betaB subunits, and activin receptor type II and type IIB was investigated: 1) in primary cultures of endometrial (stroma and epithelium) or cervical (epithelium) cells from healthy women; and 2) in specimens of endometrial or cervical carcinoma. To demonstrate a possible secretion of the proteins, dimeric inhibin A, inhibin B, and activin A were measured in culture medium of normal epithelial or stromal endometrial cells and in uterine washing fluid of healthy women or patients with endometrial adenocarcinoma. Levels of the proteins were also measured in serum of women with endometrial or cervical carcinoma. Cultured endometrial stromal or epithelial cells and epithelial cervical cells expressed inhibin alpha, activin betaA and betaB, and activin receptor type II and type IIB mRNAs. The same finding was obtained in specimens of endometrial or cervical carcinomas. Dimeric inhibin A, inhibin B, and activin A were measured in culture medium of both endometrial and cervical cells. In particular, resulting activin A levels were significantly higher in epithelial than in stromal cultured endometrial cells (P < 0.01). Dimeric proteins were also detected in the washing fluid of the uterine cavities of healthy women (controls) and with endometrial adenocarcinoma, in which higher activin A levels were found (P < 0.01 vs. controls). Women with endometrial carcinoma showed serum activin A levels significantly higher than healthy controls (P < 0.01), which significantly decreased after surgical removal of endometrial or cervical tumors (P < 0.01). The present study, for the first time, showed that inhibin A, inhibin B, and activin A, as well as activin receptors, are expressed in normal and neoplastic human uterine tissues. A secretion of activin A from tumoral cells into systemic circulation is suggested by the observation that the high levels in serum of patients with endometrial or cervical carcinoma decreased after the surgical removal of the tumor.

Activin Receptors↗
PubMed1998

Circulating levels of allopregnanolone in humans: gender, age, and endocrine influences.

Allopregnanolone is a neuroactive steroid involved in modulating behavioral functions, stress, and neuroendocrine axes in rats. Changes in plasma allopregnanolone levels throughout the menstrual cycle have been reported in healthy women, but there exists no information on the possible gender or age-related changes or on the source(s) of circulating allopregnanolone. The aim of the present study was to assess serum allopregnanolone concentrations according to gender, menstrual cycle, age, and menopause in normal men and women; serum progesterone (P) and dehydroepiandrosterone (DHEA) levels were evaluated in the same specimens. In addition, the possible source of circulating allopregnanolone in fertile women was investigated by using stimulatory and inhibitory endocrine tests acting on the ovary and/or adrenal cortex. The present study included 189 fertile women, 112 postmenopausal women, and 46 men. Serum steroid levels were determined after extraction, using specific RIAs. Allopregnanolone levels in fertile women in the follicular phase were similar to those in age-matched men; no significant difference was found between fertile women in the follicular phase and postmenopausal women. The highest levels were found in fertile women during the luteal phase (P < 0.01). An age-related decrease was observed in men (P < 0.01), but not in women. P and DHEA levels were significantly higher in women than in men and were higher in fertile women than in postmenopausal women (P < 0.01). Both P and DHEA showed an age-related decrease in men and women (P < 0.01). Serum allopregnanolone and P, but not DHEA, significantly increased in response to a GnRH test, whereas corticotropin-releasing factor and ACTH tests elicited a significant increase in allopregnanolone, P, and DHEA levels (P < 0.01). The suppression of adrenal steroidogenesis by dexamethasone markedly reduced both allopregnanolone and DHEA serum levels (P < 0.01). In conclusion, the present study demonstrated that although men show an age-related decrease, serum allopregnanolone levels in women do not change with age and correlate with P levels during the menstrual cycle and in response to endocrine tests. Ovary and adrenal cortex may be major sources of circulating allopregnanolone in fertile women.

Adrenal Cortex↗
PubMed1998

Aging is associated with changes in allopregnanolone concentrations in brain, endocrine glands and serum in male rats.

OBJECTIVE: Allopregnanolone is a potent neuroactive steroid hormone produced in the brain and in peripheral endocrine glands. The present study investigated possible age-related variations in allopregnanolone content in brain areas, endocrine glands and serum of male rats. DESIGN: Wistar male rats were categorized into 5 groups (6 rats in each) according to age: 6, 12, 16, 18 and 20 months respectively. METHODS: Allopregnanolone content in acidic homogenates of brain cortex, hypothalamus, pituitary, adrenals and gonads was measured by a specific radioimmunoassay. Serum allopregnanolone, corticosterone and testosterone were also assayed by radioimmunoassay. RESULTS: Brain cortex allopregnanolone content decreased significantly with age, while hypothalamic allopregnanolone content remained constant until 18 months and increased significantly at 20 months. Pituitary content showed a significant age-related reduction. Adrenal allopregnanolone content remained constant until 18 months, and was significantly higher at 20 months. Testis and serum allopregnanolone contents showed significant age-related increases. Serum testosterone levels showed an age-related decrease, while no age-related variation in serum corticosterone was found. CONCLUSIONS: The present study showed a significant impact of aging on allopregnanolone contents in brain, endocrine glands and serum, showing an age-related decrease in brain cortex and pituitary, and an age-related increase in testes, adrenals and serum.

Adrenal Glands↗
PubMed1998

Second trimester levels of maternal serum total activin A and placental inhibin/activin alpha and betaA subunit messenger ribonucleic acids in Down syndrome pregnancy.

OBJECTIVES: Previous data have shown that inhibin A (alpha/betaA) is increased about twofold in maternal serum samples from Down syndrome pregnancy. Our objectives were to determine whether activin A (betaA/betaA) was similarly increased in maternal serum from pregnancies affected with fetal Down syndrome, and to investigate whether increased expression of each inhibin/activin subunit occurred in placental tissue from cases of fetal Down syndrome. DESIGN AND METHODS: Maternal serum total activin A levels were measured in 20 cases of fetal Down syndrome and 100 unaffected pregnancy samples. In addition, analysis of inhibin/activin alpha and betaA subunit mRNA levels was performed in placental tissue extracts from six cases of fetal Down syndrome and six tissues with a normal karyotype. RESULTS: The median total activin A level in the Down syndrome cases was 0.82 MoM (multiples of the median); values did not differ significantly (P = 0.36, Mann-Whitney U analysis) from those in unaffected pregnancies. The inhibin alpha subunit/GAPDH mRNA ratio, but not that of betaA subunit/GAPDH mRNA, was significantly greater (P < 0.01, ANOVA) in placental tissue from Down syndrome than in control placental tissue. CONCLUSIONS: Unlike inhibin A, activin A is not significantly increased in Down syndrome relative to unaffected pregnancy. Furthermore, increased amounts of maternal serum inhibin A in Down syndrome pregnancy probably result from increased placental expression of inhibin alpha, but not betaA, subunit.

Activins↗
PubMed1998

Influence of age and sex on serum concentrations of total dimeric activin A.

Several studies have shown that activin A is secreted in substantial amounts into the systemic circulation. The changes that occur during menstrual cycle and pregnancy suggest a correlation with reproductive function. At present, however, no definitive evidence has confirmed this pattern throughout adult life; moreover, neither the origin nor the physiological implications of this circulating growth factor have been clearly defined. The aim of the present study was to evaluate whether circulating concentrations of activin A change in adult men and women according to age and sex, and to examine the possible correlation with serum concentrations of FSH. Total dimeric activin A was measured using a specific two-site enzyme immunoassay in serum specimens collected from a cohort of normal individuals enrolled in an epidemiological survey. A group of men (n = 106) and one of women (n=151) were subdivided into six age groups (20-30, 30-40, 40-50, 50-60, 60-70 and 70-90 years). In a small group of 8 men and 11 women, serum concentrations of activin A were evaluated twice, in specimens collected at an interval of 10 years. Serum FSH concentrations were also measured in all specimens. Serum concentrations of activin A were not significantly different in men and women and showed an age-related progressive increase between 20 and 50 years of age (P<0.01, those aged 40-50 compared with those aged 20-30 years). After the age of 50 years, activin A concentrations remained in the same range of values in women, whereas they increased significantly in men, reaching peak values between 70 and 90 years (P<0.01 compared with the group aged between 20 and 50 years). From the age of 50 years, activin A concentrations were significantly greater in men compared with those in women in the corresponding age groups (P<0.001). Activin A concentrations correlated with age in men, but not in women. No significant correlation between concentrations of activin A and FSH was found in either sex. Activin A concentrations in specimens collected 10 years apart showed an increase in seven of eight men, but not in women. Finally, no significant variations of activin A concentrations were observed when fertile and postmenopausal women were compared. The present data indicate that circulating concentrations of activin A vary according to age; furthermore, men older than 50 years have greater concentrations than women. These changes, which occur irrespectively of FSH concentrations, indicate that circulating activin A is not a hormone of the reproductive axis.

Activins↗
PubMed1998

The neuroactive steroid allopregnanolone suppresses hypothalamic gonadotropin-releasing hormone release through a mechanism mediated by the gamma-aminobutyric acidA receptor.

The central nervous system (CNS) is able to synthesize and/or metabolize steroid hormones. These neuroactive steroids are capable of modulating several brain functions and, among these, they seem to regulate the hypothalamic-pituitary-gonadal (HPG) axis. Indeed, recent observations have shown that 5 alpha-pregnane-3 alpha-ol-20-one (allopregnanolone), one of the most abundant naturally occurring neuroactive steroids, suppresses ovulation and sexual behaviour when administered within the CNS. The present study was undertaken to evaluate the effects of allopregnanolone and its inactive stereoisomer, 5 alpha-pregnane-3 beta-ol-20-one, upon the release of gonadotropin-releasing hormone (GnRH) from individually-incubated hemihypothalami. Allopregnanolone suppressed GnRH release in a concentration-dependent manner with maximal activity in the nanomolar range, a range at which this neurosteroid is capable of playing a biological action. The specificity of allopregnanolone suppression of GnRH release was provided by the lack of effect of its known inactive stereoisomer. To evaluate the involvement of gamma-aminobutyric acidA (GABAA) receptor, we examined the effects of two neurosteroids with GABA-antagonistic properties, pregnanolone sulfate (PREG-S) and dehydroepiandrosterone sulfate (DHEAS), and of bicuculline, a selective antagonist of the GABA binding site on the GABAA receptor, on allopregnanolone (10 nM)-suppressed GnRH release. Both PREG-S and bicuculline overcame the inhibitory effects of allopregnanolone on GnRH release, whereas DHEAS did not. To substantiate the involvement of the GABAA receptor further, we tested the effects of muscimol, a selective agonist for this receptor, which suppressed GnRH release. In conclusion, allopregnanolone suppressed hypothalamic GnRH release in vitro and this effect appeared to be mediated by an interaction with the GABAA receptor. We speculate that the inhibitory effect of allopregnanolone on the HPG axis may also be caused by its ability to suppress hypothalamic GnRH release.

Animals↗