GnRH Response Research Articles

Luteinizing hormone response to clomiphene citrate in central precocious puberty.

The aim of the present study was to determine the LH response to clomiphene citrate administration in children with central precocious puberty and different bone ages to gain insight into the hypothalamic maturation mechanism. Twelve children with untreated central precocious puberty were studied. Five had central nervous system lesions and seven had idiopathic central precocious puberty. Their chronological and bone ages ranged from 1.7 to 8.8 years and 3.5 to 13.5 years, respectively. Clomiphene citrate (3 mg/kg/day) was administered orally for 7 days. Blood samples were collected on days 0, 6 and 8. LH and FSH were determined by RIA. The results were compared with GnRH responses or with bone age. No increase over basal LH levels was detected in four patients, but increased LH levels were detected in the remaining eight during clomiphene administration. The shift from negative to positive responses was around 8-9 years bone age. The sum of LH responses (days 6 and 8) to clomiphene citrate, and particularly the 8th-day LH levels, were significantly correlated with their respective bone age (r = 0.83). However, the LH responses to GnRH were not significantly correlated with bone age or with LH responses to clomiphene. This study shows that the LH responsiveness to clomiphene citrate in central precocious puberty increases with skeletal maturation, indicating that the activation of the hypothalamic pubertal mechanism in central precocious puberty may progress in a gradual sequence. These changes in LH response to clomiphene in central precocious puberty mimic those observed with the development of normal puberty, but occur at a much earlier age.

Effects of Steroid Administration on Pituitary Luteinizing Hormone and Follicle-Stimulating Hormone in Ovariectomized Pony Mares in the Early Spring: Pituitary Responsiveness to Gonadotropin-Releasing Hormone and Pituitary Gonadotropin Content1

These experiments tested the hypothesis that administration of steroid hormones to ovariectomized (OVX) mares during the vernal transition to the breeding season would influence LH and FSH secretion. Circulating gonadotropin concentrations, response to exogenous GnRH, and pituitary gonadotropin content were monitored. Experiments 1 and 2 were conducted, beginning 10 March, and 3 February, respectively, utilizing a total of 30 long-term OVX pony mares. In experiment 1, mares were administered vehicle (n = 5) or estradiol-17 beta (E2, n = 5, 5 mg/3 ml sesame oil), twice daily for 16 days. Blood samples were collected daily for assessment of circulating LH and FSH concentrations. On Day 10 of treatment, 400 micrograms GnRH were administered to all mares. LH increased significantly over days of treatment in the estradiol-treated group, but pituitary response to GnRH tended to be less than in control mares. Circulating FSH tended to decline over days of treatment in estradiol-treated mares, and the pituitary response to GnRH was significantly reduced. Pituitary LH, but not FSH, was increased on Day 16 of treatment with estradiol. In experiment 2, 20 OVX mares received, twice daily, vehicle (n = 5), E2, n = 5; 5 mg), progesterone (P4, n = 5; 100 mg), or progesterone plus estradiol (P4/E2, n = 5; 100 + 5 mg). Treatment continued for 14 days. GnRH (100 micrograms) challenges were administered on Days 6 and 13 of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of Pituitary Gonadotropin Secretion by the Gonadotropin-Releasing Hormone Antagonist Antide. I. In Vitro Studies on Mechanism of Action*

The GnRH antagonist antide is among the most promising "third generation" compounds available for clinical evaluation. In primates, antide manifests prolonged (several weeks) and reversible inhibition of pituitary gonadotropin secretion after a single high dose injection. In the present study, we have examined the effects of antide on pituitary gonadotropin secretion in vitro. Dispersed anterior pituitary cells from adult female rats were plated (48 h; 5 x 10(5) cells/well), washed, and exposed to increasing concentrations of antide for up to 48 h. Media were removed, and cells were washed twice and then incubated with GnRH (1 x 10(-8) M) plus antide for 4 h. Media and cell lysates were assayed for LH/FSH by RIA. Antide had no effect on basal LH/FSH secretion at any dose tested (10(-6)-10(-12) M). In contrast, GnRH-stimulated LH/FSH secretion was inhibited by this GnRH antagonist in a dose- and time-dependent manner. When incubated simultaneously, antide blocked GnRH-stimulated gonadotropin secretion, with a maximal effect at 10(-6) M (ED50, 10(-7) M). Preincubation of pituitary cells with antide for 6-48 h before GnRH exposure shifted the dose-response curve to the left; the maximally effective dose was 10(-8) M; the ED50 was 10(-10) M antide after 48-h preincubation. Intracellular LH/FSH levels increased concomitant with the decrease in secreted gonadotropins. Total LH/FSH levels (secreted plus cell content) remained unchanged. The inhibition of LH secretion by antide was specific for GnRH-stimulated gonadotropin secretion; antide had no effect on K(+)-stimulated LH secretion. Moreover, antide had little or no residual effect on LH secretion; full recovery of GnRH responsiveness in vitro occurred within 4 h after removal of antide. Lineweaver-Burke analysis of antide inhibition of GnRH-stimulated LH secretion indicated that antide is a direct competitor of GnRH at the level of the pituitary GnRH receptor. In summary, antide is a pure antagonist of GnRH stimulation of gonadotropin secretion; no agonistic actions of antide were manifest in vitro. Moreover, antide has no apparent noxious or toxic effect on pituitary cells in culture; the actions of antide are immediately reversible upon removal of antide from pituitary gonadotropes. We conclude that the long term inhibition of gonadotropin secretion by antide in vivo is not due to deleterious effects of this compound at the level of the pituitary gonadotrope.

Intracellular responses to gonadotropin-releasing hormone in a clonal cell line of the gonadotrope lineage.

We recently derived a GnRH-responsive pituitary cell line of the gonadotrope lineage (alpha T3-1) by targeted oncogenesis in transgenic mice. Here, we report studies characterizing the GnRH receptors present in these cells and the intracellular responses to GnRH treatment. The receptors in alpha T3-1 cells show specificity for different GnRH analogs, with dissociation constants very similar to those found in normal rat and mouse pituitary. The concentration of receptors is within the range found in normal pituitary. The addition of GnRH or GnRH agonists increases phosphoinositide turnover and protein kinase-C translocation to membranes, and enhances activation of voltage-sensitive calcium channels. However, GnRH does not affect cAMP levels. Analysis of alpha-subunit mRNA levels demonstrated induction by GnRH and phorbol esters. Our results indicate that GnRH initiates a cascade of intracellular events that generate a set of second messengers, one or more of which is involved in the regulation of gene expression. The responses of alpha T3-1 cells to GnRH appear to have characteristics equivalent to those of primary pituitary gonadotropes, indicating the utility of this cell line as a model system for the study of GnRH responses.

Human Fetal Adenohypophysis: Morphologic and Functional Analysis in vitro

Pituitaries from 24 human fetuses at 7-20 weeks of gestation were studied in culture to assess hormone release, response to adenohypophysiotropic hormones and cytodifferentiation by electron microscopy in cultures lasting 4-8 days and in some cases up to 28 days. At 7 weeks of gestation, ACTH was released by cultured cells which included recognizable corticotrophs. GH was released by cells cultured from 8- to 9-week fetuses and densely granulated somatotrophs were present in the cultures. alpha-Subunit of glycoprotein hormones was present in cultures from 10-week fetuses and TSH and LH were released from 12-week fetuses. FSH was found in cultures of a 13-week female fetus but not before 14 weeks in cultures from males. The levels of FSH and LH were higher in media from cultures of females than from those of males at all ages from detection to 20 weeks, whereas alpha-subunit was slightly higher in media from males. While cells with features of the glycoprotein hormone cell line were found in cultures from 10-week fetuses, no characteristic thyrotrophs or gonadotrophs were recognized. PRL was not measured in basal incubations before 14 weeks. The amounts of all hormones released were proportional to fetal age and decreased with duration of culture. Cortisol suppressed ACTH release in cultures from 7- to 8-week fetuses. Responsiveness of GH release to GRH/SRIH, of ACTH to CRH, and of FSH to GnRH, was found at 12 weeks; LH stimulation by GnRH and TSH response to TRH were documented at 14 weeks. Increments of gonadotropin release during incubation with GnRH were greater in cultures from females than in those from males. PRL release responded to GRH stimulation and to SRIH inhibition in parallel with GH; this behavior is consistent with production of both hormones by mammosomatotrophs. The onset of hormone release by cultured human fetal pituitaries correlates with the detection of hormones biochemically and immunohistochemically. Responsiveness of fetal adenohypophysial cells to hormonal influences indicates functional maturity early in gestation.

Neither exogenous nor endogenous GnRH stimulation alters the bio/immuno ratio of serum LH in healthy women and in polycystic ovarian disease

The purpose of this study was to re-evaluate the quantitative and qualitative responses of LH to exogenous and endogenous GnRH stimulation in normally cycling women and in polycystic ovarian disease (PCOD). Responses of serum LH to GnRH (100 micrograms i.v.) and the opioid antagonist naloxone (10 mg i.v.) were determined in healthy women in the early (n = 5) and late (n = 4) follicular phase, and in patients with PCOD (n = 20). Serum bioactive (B) LH was determined by a mouse interstitial cell in vitro bioassay, and immunoreactive LH by a conventional RIA (I-LH) and a novel sensitive (0.05 IU/l) and specific immunofluorimetric assay (F-LH). The B/I (2.4 +/- 0.1) and B/F (2.7 +/- 0.6) ratios in basal serum samples of the PCOD patients were significantly higher (p less than 0.05) than the corresponding ratios (1.6-1.8 and 1.8-2.0) of the control women. GnRH stimulated the secretion of I-LH (2-4-fold), F-LH and B-LH (3-5-fold each) in all groups studied. There were no apparent changes of the B/I and B/F ratios in normal women during early follicular phase or in patients with PCOD. However, the normal women during late follicular phase displayed a significant (p less than 0.05) increase in the B/I ratio, albeit no change was found in the B/F ratio. During naloxone-induced endogenous GnRH responses, the control women during late follicular phase showed a 3-6-fold increase in B-LH, I-LH and F-LH, with unchanged B/I and B/F ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypogonadotropic hypogonadism in idiopathic hemochromatosis: evidence for combined hypothalamic and pituitary involvement

Hypogonadism is a common finding in idiopathic hemochromatosis. Most studies have localized the defect to either the pituitary gland or the testes. We describe a case with evidence that favors the likely concomitant involvement of the hypothalamus as a factor in the observed hypogonadism. A clinically hypogonadal male with hemochromatosis had a low testosterone concentration with inappropriately normal serum LH levels. Leydig cell function was intact, as demonstrated by a normal increase in serum testosterone following HCG administration. However, although the pituitary secretion of LH was normal in response to GnRH stimulation, clomiphene administration did not produce an increase in LH and FSH, suggesting that there was a defect in the hypothalamic GnRH response. Since the FSH and prolactin responses to stimulatory testing were inadequate, coexisting pituitary dysfunction was likely also present. We conclude that this man had hypogonadism with laboratory evidence for a combined defect in hypothalamic and pituitary function.

Gonadotropin-Releasing Hormone Receptor Expression inXenopusOocytes

The rodent GnRH receptor was characterized in Xenopus oocytes injected with RNA isolated from rat pituitary and from a gonadotrope cell line, alpha T3, derived from a transgenic mouse. Three to 4 days after 150-200 ng RNA injection, 93% of the oocytes, which were recorded by voltage clamp, responded to 10(-7) M GnRH. The mean inward currents obtained after RNA injection were 620 +/- 88 nA (n = 22) with pituitary RNA and 1415 +/- 598 (n = 4) with alpha T3 RNA. The threshold GnRH concentration able to evoke the dose dependent current after pituitary RNA injection was 3 x 10(-9) M GnRH. The GnRH receptor response of the oocyte was antagonized by [D-Phe2,6,Pro3] GnRH and [N-Ac-D-Na](2)1, D-alpha D-Me, pCl-Phe2, D-Arg6, D-Ala10-NH2]GnRH and could be elicited by D-Ser(But)6,Pro9-N-ethylamide GnRH (buserelin). The reversal potential of the GnRH generated current as determined by voltage-ramp was -22.5 +/- 1.0 mV (n = 7) and -25.6 +/- 3.3 mV (n = 3) in pituitary and cell line RNA-injected oocytes respectively, consistent with the chloride reversal potential. The GnRH receptor response was virtually eliminated by intracellular EGTA injection but was unaffected by ligand application in calcium-free perfusate. The GnRH-evoked response is mimicked by intracellular injection of inositol 1,4,5-trisphosphate. To determine the size of the GnRH receptor mRNA, alpha T3 RNA was size fractionated through a sucrose gradient. The maximal GnRH response was induced by a fraction larger than the 28S ribosomal peak. Thus we find that oocytes injected with RNA from an appropriate source develop an electrophysiological response to GnRH which is dependent on intracellular calcium mobilization, is independent of extracellular calcium, and may be mediated by inositol 1,4,5-trisphosphate.

Peripubertal Changes in the Nature of the GnRH Response to Alpha-Adrenoceptor Stimulation in vitro and their Modulation by Testosterone

Adrenergic mechanisms have been widely implicated in the regulation of GnRH secretion in adult rats but their role in young animals, in which the activity of the GnRH neurones is minimal, is unclear. These experiments were done to examine the effects of alpha-adrenoceptor stimulation on the secretion in vitro of GnRH by hypothalami from immature and adult male rats. The alpha 1-adrenoceptor agonist, phenylephrine (10(-9) - 10(-7) M), stimulated release of GnRH from hypothalami from adult (200 g) and peripubertal (150 g) rats but inhibited markedly the secretion of the releasing factor from the limited stores available in hypothalami from immature (50 or 100 g) rats. The stimulatory and inhibitory responses to phenylephrine, evident in adult and younger rats respectively, were concentration-dependent and antagonized readily by the selective alpha 1-adrenoceptor antagonist, alfuzosin (10(-6) M), but not by the beta-adrenoceptor antagonist, propranolol (10(-6) M). Hypothalami from 14-day castrated adult rats, in which the serum LH was elevated and hypothalamic GnRH content reduced, responded to alpha 1-adrenoceptor stimulation in vitro, like those from immature rats, with a marked reduction in GnRH release. In contrast, hypothalami from corresponding castrates bearing testosterone implants, which maintained the hypothalamic GnRH content and serum LH and testosterone concentrations at levels similar to those of intact controls, exhibited the normal 'adult' response to phenylephrine. Studies utilizing 3H-prazosin indicated that the number (Bmax) of hypothalamic alpha 1-adrenoceptor binding sites increases at puberty but that receptor affinity (KD) is unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on gonadal dysgenesis: variable expressivity of the XY testicular dysgenesis syndrome; two case reports

Two adult unrelated XY phenotypically female individuals with sexual infantilism and genital ambiguity were studied. Mosaicism was ruled out by the assessment of a normal 46,XY karyotype in four different cell lines. Persistently elevated LH and FSH serum levels with concomitant normal pituitary Gn-RH responsiveness were found. Baseline serum testosterone concentrations were low, but they exhibited a slight though significant rise following HCG stimulation. Surgical and histological findings included the presence of Mullerian and Wolffian derivatives and small bilateral dysgenetic testes with absence of germ cell epithelium, scarce Sertoli cells, and hyperplastic Leydig cells. The overall data indicated an anatomofunctional testicular impairment particularly confined to the tubular compartment. By comparing the clinical and endocrine features of this incomplete form of the XY testicular dysgenesis with the complete and other unusual forms, further evidence is provided of a wide heterogeneity of the syndrome, and a more detailed classification is proposed.

Eftects of Gonadectomy and Steroids on Pituitary Gonadotropin Secretion in a Frog, Rana Pipiens1

Secretory dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured at various times following gonadectomy in adult male grass frogs, Rana pipiens. Plasma levels and in vitro initial secretory rates of both LH and FSH increased significantly within 1 wk and remained elevated for 3-4 wk of castration. Pituitary FSH and LH content were unchanged. However, dissociation between the two gonadotropins (Gth) occurred thereafter: Secretion of FSH remained elevated for 70 days, but those of LH declined to control levels after 30 days. In vitro secretion of Gth from gonadectomized (gonadx) frogs declined progressively over time reaching control levels after 24 h incubation. The results indicate that elevated pituitary secretion contributes to the observed circulating LH and FSH levels in gonadx frogs, and that FSH and LH may be controlled independently. Replacement therapy with 17 beta-estradiol (E2) suppressed post-gonadectomy increases in plasma Gth and in vitro responses to GnRH, whereas 5 alpha-dihydrotestosterone (DHT) had little effect in vivo and augmented GnRH responses in long-term castrates. In vitro, E2 also inhibited, while 48 h of DHT treatment had no effect on GnRH responsiveness of pituitaries from gonadx frogs. The actions of these steroids were opposite to those typically observed in mammals (and birds), and support the hypothesis that E2 may contribute to seasonal testicular regression in ranid frogs.

Gonadotropin-Releasing Hormone- Induced Rise in Cytosolic Free Ca2+Levels: Mobilization of Cellular and Extracellular Ca2+Pools and Relationship to Gonadotropin Secretion

Addition of GnRH to pituitary gonadotrophs preloaded with Quin 2 resulted in a rapid (approximately 8 s) mobilization of an ionomycin-sensitive intracellular Ca2+ pool. A second component of Ca2+ entry via voltage dependent channels contributed about 45% of the peak cytosolic free Ca2+ concentration ([Ca2+]i). Thereafter, influx of Ca2+ via voltage-sensitive and -insensitive channels is responsible for maintenance of elevated [Ca2+]i during the second phase of GnRH action. Addition of inositol 1,4,5-trisphosphate (IP3) to permeabilized pituitary cells resulted in a Ca2+ transient, released from a nonmitochondrial pool, which maintained ambient free Ca2+ concentration around 170 nM in an ATP-dependent mechanism. Successive stimulations of the cells with IP3 produced an attenuated response. Elevation of the gonadotroph [Ca2+]i by ionomycin, to levels equivalent to that induced by GnRH, resulted in LH release amounting to only 45% of the response to the neurohormone. Activation of the voltage-dependent Ca2+ channels by the dihydropyridine Ca2+-agonist [methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine- 5-carboxylate (BAYK8644)] stimulated LH release, 36% of the GnRH (100 nM) response being reached by 10(-8) M of the drug, both [Ca2+]i elevation and GnRH-induced LH release were inhibited similarly (40-50%) by the dihydropyridine Ca2+-antagonist nifedipine. The results indicate that peak [Ca2+]i induced by GnRH in pituitary gonadotrophs is derived mainly from ionomycin-sensitive cellular stores most likely via IP3 formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of hypothalamic neuropeptide Y and effects of exogenous NPY on the release of hypothalamic GnRH and pituitary gonadotropins in intact and ovariectomized does in vitro

The effect of NPY on the hypothalamic release of GnRH and pituitary release of gonadotropins was examined in intact and ovariectomized (OVEX) rabbits in a superfusion system. Exposure of mediobasal hypothalami (MBH) from intact rabbits to NPY (8×10 −8 M) resulted in a sustained stimulation of GnRH secretion into the medium. The same dose of NPY had no effect on MBH-GnRH release from OVEX rabbits. NPY also produced a sustained stimulation of LH and FSH release by pituitary fragments from intact rabbits, but NPY caused only a transient release of these hormones by pituitaries from OVEX does. Media samples from MBH superfusions were also measured for NPY concentrations. NPY was released episodically into the medium. The amplitude and frequency of NPY pulses in intact and OVEX rabbits did not differ; nor were mean levels of NPY significantly affected by castration. These results suggest that NPY has direct effects on both the hypothalamus and pituitary to modulate the activities of GnRH neurons and gonadotropes. The pattern of GnRH and gonadotropin response to NPY exposure is determined by ovarian factors.

Estradiol Sensitization of Cultured Human Fetal Pituitary Cells to Gonadotropin-Releasing Hormone*

In adult women, estradiol (E2) sensitizes the pituitary to GnRH. To assess whether this effect develops during intrauterine life, dispersed pituitary cells from second trimester male and female fetuses were cultured on extracellular matrix-coated plates. E2 (10(-8) mol/L) exposure for 72 h resulted in a significant increase in LH release when cells were stimulated with GnRH and caused a significant shift to the left of the dose-response curve for GnRH-stimulated LH release [relative potency ratio, 0.33 +/- 0.05 (+/- SE)]. E2-enhanced LH release was not associated with an increase in cell number, total LH content, or percentage of LH-containing cells (immunocytochemistry). The EC50 of GnRH-stimulated LH release and the degree of E2 sensitization were not sex dependent, although female fetal pituitary cells in the absence of E2 had significantly greater LH content and released more LH under basal and GnRH-stimulated conditions than cells from male fetuses. Therefore, E2 sensitization of second trimester human fetal gonadotrophs to GnRH does occur, is not influenced by sex, and may involve an acutely releasable LH pool. At these gestational ages, basal and maximal GnRH-stimulated LH release as well as total LH content are greater in the female than the male. Thus, E2 sensitization of GnRH responsiveness appears to have its origins during intrauterine fetal life.

Subcutaneous administration of gonadotropin-releasing hormone: absorption kinetics and gonadotropin responses.

To evaluate the suitability of the sc route for the pulsatile delivery of GnRH, plasma GnRH, LH, and FSH levels were measured by RIA in five women with hypothalamic amenorrhea after sc injection of single doses of 2.5, 5, and 10 micrograms GnRH. The results were compared with those obtained after bolus iv injection of 10 micrograms GnRH. After sc injection, plasma GnRH levels rose to a dose-related maximum after 5-10 min and fell to less than 10% of the peak value by 90 min. The mean plasma disappearance half-time was 24 min (range, 18-30 min). After bolus iv injection, an initial rapid phase of disappearance (t1/2, 2.8 min) was followed by a slower phase (t1/2, 33 min), falling within the 95% confidence intervals for the disappearance half-time after sc administration (12-36 min). The patterns of LH response to sc and iv GnRH were similar, with maximum levels reached between 20 and 30 min after injection, then declining to 50-69% of the peak value by 90 min after sc injection and 61% of the peak value 90 min after iv injection. There was no significant difference between peak LH responses to 10 micrograms iv and sc doses of GnRH [15.2 +/- 2.5 (+/- SEM) vs. 13.2 +/- 2.2 IU/L]. Subcutaneous administration of three consecutive GnRH pulses at 90-min intervals to four women resulted in gonadotropin responses to each GnRH pulse. We conclude that sc GnRH administration results in pulsatile plasma GnRH and gonadotropin responses, the latter resembling those seen after iv GnRH. These results confirm the suitability of the sc route for pulsatile GnRH delivery.

NEUROENDOCRINE CHANGES WITH D His GnRH ANALOGUE (D-His-A)

To correlate neuroendocrine changes with clinical response, 4 girls (4-7 yrs) and 1 boy age 6 with central precocious puberty were treated with D-His-A subcutaneously. D-His-A was given at a dose of 4 μg/kg/day for 4 mos; then, the dose was increased to 8 μg/kg/day. The children were serially studied at 0, 3, and 6 mos. Blood was analyzed for GH, LH, FSH q 20 min (1800-0600). GnRH (2.5 μg/kg IV) tests and response to D-His-A (usual treatment dose sc) were followed. Gonadal steroids fell to prepubertal range in the first 3 mos. Results of mean growth velocity (GV), GH, Somatomedin C, LH and FSH, GnRH and D-His-A Tests are shown: Bone age advanced 6 mos/6 mos therapy. We conclude D-His-A at 4 μg/kg/day for 3 mos did not decrease growth velocities despite decreases in mean overnight GH, Somatomedin C and gonadal steroids. Mean overnight LH and FSH values showed stepwise decrease with higher doses of D-His-A. We suggest that children with D-His-A need a minimum of 8 μg/kg/day and that D-His-A response should be used to evaluate therapy rather than GnRH tests.

ABORTED PUBERTY: A NEW CLINICAL ENTITY

Previous studies have shown that gonadotropin response to I/V bolus injection of GnRH differs in prepubertal (PPP) and pubertal patients (PP). In the PPP patients GnRH response is minimal, with the LH/FSH ratio being less than one. In contrast, the PP patient demonstrates a marked response in LH secretion with the LH/FSH ratio being greater than one. We studied a group of 12 girls, aged 6 to 8 years, designated as Aborted Puberty (AB). They all presented with signs of precocious puberty (breast & pubic hair development) but differed from true precocious puberty in that their early pubertal development spontaneously regressed. These AB patients responded differently to GnRH than expected, as seen in the table below. They demonstrated a greater rise in both FSH and LH than the PPP patients. In contrast to the PP patients their LH/FSH ratio is less than one. We submit to have discovered a new variant of normal pubertal development, termed “Aborted Puberty”, which is different from all other pubertal states based on its gonadotropin response to GnRH stimulation.

Effects of phytoestrogens on GnRH-induced luteinizinghormone secretion in ovariectomized rats

Ovariectomized rats were pretreated with intravenous estradiol-17β (E 2), coumestrol or genisteinand were challenged 2 h later with GnRH (50 ng/kg BW, i.v.). Blood samples, drawn at the time of GnRH administration and 15 min afterwards, were assayed for luteinizing hormone (LH). While low-dose E 2 pretreatment (10 ng/kg BW) significantly enhanced GnRH-induced LH release, high dose E 2 pretreatment (1000 ng/kg BW) blocked the GnRH-induced rise. Intermediate-dose E 2 pretreatment (100 ng/kg BW) yielded a GnRH response that did not differ from that in the vehicle pretreatment group. At all doses studied, coumestrol pretreatment (10 ng/kg BW, 100 ng/kg BW, and 1000 ng/kg BW) appeared to diminish but not abrogate GnRH-induced LH release. While intermediate-dose genistein pretreatment (100 ng/kg BW) significantly enhanced GnRH-induced LH release, high-dose genistein pretreatment (1000 ng/kg BW) yielded a GnRH response that did not differ from that in the vehicle pretreatment group. Both low-dose (10 ng/kg BW) and very high-dose (10,000 ng/kg BW) genistein pretreatment appeared to inhibit GnRH-induced LH release. The results demonstrate that acute exposure to phytoestrogens alters GnRH-induced LH release in ovariectomized rats. The dose-response pattern of enhanced GnRH-induced LH release at lower pretreatment doses but inhibited GnRH-induced LH release at higher pretreatment doses was observed for E 2 and genistein. The potency of genistein appears to be approximately 1/10 that of E 2 in this system. Phytoestrogens acutely perturb reproductive neuroendocrine function.

Prolactin-releasing action of gonadotropin-releasing hormone in hypogonadal women.

To gain insight into the PRL-releasing effect of GnRH, serum PRL and gonadotropin responses to a 10-microgram iv bolus dose of exogenous GnRH were studied in hypergonadotropic hypogonadal women (HHW) and patients with functional hypothalamic amenorrhea (FHA). The results were compared with those obtained in normal cycling women during the early follicular phase of the cycle. GnRH induced a significant increase in PRL levels (P less than 0.001) in HHW compared to early follicular phase women, in whom no significant response occurred. In HHW, the maximal PRL percent increment was positively correlated with the ratio of the maximal percent increments of FSH and LH (r = 0.93). GnRH induced a significant increase in PRL levels in every FHA patient, but in four of them (high PRL responders), the PRL response was at least 5-fold greater than in the other six (low PRL responders). The clinical profiles, basal hormone concentrations, and LH responses to GnRH were similar in these two groups of FHA patients, but the FSH response to GnRH was greater (P less than 0.05) in the high PRL responders. The maximal percent increment of PRL was also positively correlated with the maximal percent increment of FSH (r = 0.76; P = 0.01). These data demonstrate that in these two hypogonadal models, the PRL response to exogenous GnRH corresponds to the FSH response and suggests that GnRH-stimulated PRL release may be mediated by a paracrine effect between FSH-enriched gonadotrophs and lactotrophs.

Gonadotropin-releasing hormone induces classical meiotic maturation in subpopulations of atretic preantral follicles.

GnRH has been shown to induce premature meiotic maturation in preantral follicles of the immature estrogen-primed hypophysectomized rat. As these animals are free of circulating gonadotropins and contain large numbers of full-grown oocytes in preantral follicles, we have investigated this model to determine its usefulness in studying meiotic maturation. We show that a maximum dose of the agonist D-Trp6,Pro9,Net-LRF (GnRH-a) induces approximately 25% of full grown oocytes to resume meiosis within a 12-h period. This response is dose dependent (ED50 = 0.24 microgram/rat) and specific for GnRH-a. GnRH-a stimulates germinal vesicle breakdown and first polar body formation within 2 and 8 h, respectively. More than 75% of those oocytes that initiate meiotic maturation reach metaphase II by 15 h. This effect of GnRH parallels the time course of physiological meiotic maturation triggered by LH as well as that of oocytes maturing spontaneously in vitro. Oocytes in primordial and primary follicles do not respond to GnRH. The majority of affected follicles are small tertiary follicles (200-400 micron in diameter) and show signs of atresia. This atresia is not caused by GnRH-a and does not, in itself, result in meiotic maturation, but appears to confer susceptibility to GnRH-a-induced meiotic maturation. Our studies indicate that this animal model will be useful to elucidate further the mechanisms and requirements for meiotic maturation. It will also facilitate investigation of the role of atresia in the GnRH response of tertiary follicles and the issue of follicle heterogeneity within these animals.