Changes In Gonadotropin-releasing Hormone Research Articles

Chronological Changes in Gonadotropin-Releasing Hormone 1, Gonadotropins, and Sex Steroid Hormones along the Brain-Pituitary-Gonadal Axis during Gonadal Sex Differentiation and Development in the Longtooth Grouper, Epinephelus bruneus.

(1) Fshβ and Lhβ showed stronger signals and higher transcript levels from 590 to 1050 dph than at earlier stages, implying their active involvement during primary oocyte development. (2) Fshβ and Lhβ at lower levels were detected during the phases of ovarian differentiation and oogonial proliferation. (3) E2 concentrations increased significantly at 174, 333, and 1435 dph, while T concentrations exhibited significant increases at 174 and 333 dph. These findings suggest potential correlations between serum E2 concentrations and the phases of oogonial proliferation and pre-vitellogenesis.

Changes in gonadotropin-releasing hormone in the cerebral ganglion of the Manila clam Ruditapes philippinarum during gonadal development

Gonadotropin-releasing hormone (GnRH) plays an important role in reproduction in both vertebrates and invertebrates; however, little is known about GnRH during gonadal development in bivalves. We developed a time-resolved fluoroimmunoassay (TR-FIA) for Manila clam Ruditapes philippinarum GnRH (rpGnRH) and measured the amount of rpGnRH in the cerebral ganglion (CG) and sex steroid hormones in the hemolymph during gonadal development. The cross-reactivity of the anti-rpGnRH antibody against other forms of GnRH was <0.15%, and the displacement curve obtained for serially diluted CG extracts was parallel to the rpGnRH standard curve, confirming the suitability of the TR-FIA system. Based on histological observation, gonadal development of the clams was classified into early developing (stage 1), late developing (stage 2), ripe (stage 3), and partially spent (stage 4). In female clams, rpGnRH levels in the CG peaked at stage 1, and 17β-estradiol (E2) levels in the hemolymph peaked at stage 2. The rpGnRH levels in males and hemolymph testosterone levels in both sexes did not differ significantly across stages. Hemolymph E2 levels in males were below the detection limit for the TR-FIA. These results suggest that rpGnRH and E2 secretion in females can activate ovarian development of the Manila clam at the early and late developing stages, respectively.

Trans-seasonal activation of the neuroendocrine reproductive axis: Low-temperature winter dormancy modulates gonadotropin-releasing hormone neurons in garter snakes.

All animals use external cues from the environment to accurately time life-history events. How the brain decodes environmental stimuli to effect changes in physiology and behavior, however, is poorly understood, particularly with regard to supplementary environmental cues such as temperature. We asked if low-temperature dormancy alters the synthesis and/or release of gonadotropin-releasing hormone (GnRH). We used the well-studied red-sided garter snake (Thamnophis sirtalis) for this study, as low-temperature exposure is both necessary and sufficient to induce reproduction in northern populations of this species. Snakes were collected from the field and hibernated at 4°C or 10°C in complete darkness for up to 16 weeks. In males, increasing duration of low-temperature dormancy significantly increased GnRH-immunoreactive cell number and GnRH soma size (a proxy for relative cell activity) in the forebrain. These changes mirrored those in male reproductive behavior (reported previously) and plasma androgen concentrations. The changes in GnRH cell area observed in males were specific to the neuroendocrine population of cells in the medial preoptic area; soma size in the rostral GnRH cells did not change. Finally, temperature-induced changes in GnRH were sexually dimorphic: neither hibernation temperature nor the duration of winter dormancy significantly modulated GnRH cell number or soma size in females, despite the fact that plasma estradiol and corticosterone increased significantly in response to both. These data demonstrate that the neuroendocrine GnRH system is sensitive to environmental temperature and suggest that GnRH neurons play a conserved but trans-seasonal role in mediating changes in reproductive physiology and behavior in dissociated breeders.

Effect of cortisol on gonadotropin inhibitory hormone (GnIH) in the cinnamon clownfish, Amphiprion melanopus

Hypothalamic peptides, gonadotropin-releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH), play pivotal roles in the control of reproduction and gonadal maturation in fish. In the present study we tested the possibility that stress-mediated reproductive dysfunction in teleost may involve changes in GnRH and GnIH activity. We studied expression of brain GnIH, GnIH-R, seabream GnRH (sbGnRH), as well as circulating levels of follicle stimulating hormone (FSH), and luteinizing hormone (LH) in the cinnamon clownfish, Amphiprion melanopus. Treatment with cortisol increased GnIH mRNA level, but reduced sbGnRH mRNA and circulating levels of LH and FSH in cinnamon clownfish. Using double immunofluorescence staining, we found expression of both GnIH and GnRH in the diencephalon region of cinnamon clownfish brain. These findings support the hypothesis that cortisol, an indicator of stress, affects reproduction, in part, by increasing GnIH in cinnamon clownfish which contributes to hypothalamic suppression of reproductive function in A. melanopus, a protandrous hermaphroditic fish.

Brain aromatase (cyp19a1b) and gonadotropin releasing hormone (gnrh2 and gnrh3) expression during reproductive development and sex change in black sea bass (Centropristis striata)

Teleost fish exhibit diverse reproductive strategies, and some species are capable of changing sex. The influence of many endocrine factors, such as gonadal steroids and neuropeptides, has been studied in relation to sex change, but comparatively less research has focused on gene expression changes within the brain in temperate grouper species with non-haremic social structures. The purpose of the present study was to investigate gonadotropin releasing hormone (GnRH) and brain aromatase (cyp19a1b) gene expression patterns during reproductive development and sex change in protogynous (female to male) black sea bass (Centropristis striata). Partial cDNA fragments for cyp19a1b and eef1a (a reference gene) were identified, and included with known gnrh2 and gnrh3 sequences in real time quantitative PCR. Elevated cyp19a1b expression was evident in the olfactory bulbs, telencephalon, optic tectum, and hypothalamus/midbrain region during vitellogenic growth, which may indicate changes in the brain related to neurogenesis or sexual behavior. In contrast, gnrh2 and gnrh3 expression levels were largely similar among gonadal states, and all three genes exhibited stable expression during sex change. Although sex change in black sea bass is not associated with dramatic changes in GnRH or cyp19a1b gene expression among brain regions, these genes may mediate processes at other levels, such as within individual hypothalamic nuclei, or through changes in neuron size, that warrant further research.

Social opportunity rapidly regulates expression of CRF and CRF receptors in the brain during social ascent of a teleost fish, Astatotilapia burtoni.

In social animals, hierarchical rank governs food availability, territorial rights and breeding access. Rank order can change rapidly and typically depends on dynamic aggressive interactions. Since the neuromodulator corticotrophin releasing factor (CRF) integrates internal and external cues to regulate the hypothalamic-pituitary adrenal (HPA) axis, we analyzed the CRF system during social encounters related to status. We used a particularly suitable animal model, African cichlid fish, Astatotilapia burtoni, whose social status regulates reproduction. When presented with an opportunity to rise in rank, subordinate A. burtoni males rapidly change coloration, behavior, and their physiology to support a new role as dominant, reproductively active fish. Although changes in gonadotropin-releasing hormone (GnRH1), the key reproductive molecular actor, have been analyzed during social ascent, little is known about the roles of CRF and the HPA axis during transitions. Experimentally enabling males to ascend in social rank, we measured changes in plasma cortisol and the CRF system in specific brain regions 15 minutes after onset of social ascent. Plasma cortisol levels in ascending fish were lower than subordinate conspecifics, but similar to levels in dominant animals. In the preoptic area (POA), where GnRH1 cells are located, and in the pituitary gland, CRF and CRF1 receptor mRNA levels are rapidly down regulated in ascending males compared to subordinates. In the Vc/Vl, a forebrain region where CRF cell bodies are located, mRNA coding for both CRFR1 and CRFR2 receptors is lower in ascending fish compared to stable subordinate conspecifics. The rapid time course of these changes (within minutes) suggests that the CRF system is involved in the physiological changes associated with shifts in social status. Since CRF typically has inhibitory effects on the neuroendocrine reproductive axis in vertebrates, this attenuation of CRF activity may allow rapid activation of the reproductive axis and facilitate the transition to dominance.

Immunohistochemical localization of GnRH and RFamide-related peptide-3 in the ovaries of mice during the estrous cycle

Gonadotropin releasing hormone (GnRH) has now been suggested as an important intraovarian regulatory factor. Gonadotropin inhibitory hormone (GnIH) a hypothalamic dodecapeptide, acts opposite to GnRH. GnRH, GnIH and their receptors have been demonstrated in the gonads. In order to find out the physiological significance of these neuropeptides in the ovary, we aim to investigate changes in the abundance of GnRH I and GnIH in the ovary of mice during estrous cycle. The present study investigated the changes in GnRH I, GnRH I-receptor and RFRP-3 protein expression in the ovary of mice during estrous cycle by immunohistochemistry and immunoblot analysis. The immunoreactivity of GnRH I and its receptor and RFRP-3 were mainly localized in the granulosa cells of the healthy and antral follicles during proestrus and estrus and in the luteal cells during diestrus 1 and 2 phases. The relative abundance of immunoreactivity of GnRH I, GnRH I-receptor and RFRP-3 undergo significant variation during proestrus and thus may be responsible for selection of follicle for growth and atresia. A significant increase in the concentration of RFRP-3 during late diestrus 2 coincided with the decline in corpus luteum activity and initiation of follicular growth and selection. In general, immunolocalization of GnRH I, GnRH I-receptor and RFRP-3 were found in close vicinity suggesting functional interaction between these peptides. It is thus, hypothesized that interaction between GnRH I-RFRP-3 neuropeptides may be involved in the regulation of follicular development and atresia.

Identification of a functional corpus luteum in the Atlantic hagfish, Myxine glutinosa

Hagfish represent the oldest extant craniates and are an important link between invertebrates and vertebrates. However, key elements of the reproductive system have not been elucidated in hagfish. There is new evidence from our recent studies that Atlantic hagfish may have a seasonal reproductive cycle. These data include seasonal changes in gonadotropin-releasing hormone, gonadal steroids, estradiol, and progesterone, corresponding to gonadal reproductive stages along with the putative identification of a functional corpus luteum. The corpus luteum in non-mammalian vertebrates secretes mainly progesterone thought to be involved in the retention of eggs and down regulation of vitellogenin synthesis. The most ancient vertebrate that is known to have a functional corpus luteum is the dogfish, Squalus acanthias. However, brown bodies, hypothesized to be corpora lutea, have been observed by scientists for over 100 years in the gonad of the hagfish. To date, data in support of these brown bodies acting as corpora lutea have consisted mainly of observational studies. Therefore, we examined the putative corpora lutea (post-ovulatory follicles) in hagfish by histology, electron microscopy, and production of progesterone and estradiol. Progesterone concentrations from post-ovulatory follicles were significantly higher (12 ± 1.5 pg/mg gonad tissue wet weight) compared to controls containing only gonadal tissues and oocytes (3.6 ± 1.5 pg/mg gonad tissue wet weight) ( p < 0.05). Estradiol was detected in seven of the 13 samples containing only gonadal tissue with oocytes and ranged between 0.6 and 0.18 pg/mg gonad tissue wet weight and was not detected in any of the media containing only corpora lutea samples. Light and electron microscopy analysis supported that these structures were corpora lutea like structures (post-ovulatory follicles). From these results, we hypothesize that hagfish have functional corpora lutea like structures that produce progesterone.

Current Knowledge of Hagfish Reproduction: Implications for Fisheries Management

This review briefly summarizes the latest findings on reproductive endocrinology of Atlantic hagfish (Myxine glutinosa) and implications for fisheries management. In response to a major decline or collapse of the fisheries (groundfish and anadromous species) industry in the Northeast, species that were once considered alternative or underutilized have and are being identified that may be suitable for commercial harvest, one such example is the hagfish. Hagfish in recent years have been sought after as valuable fish not only for their flesh, but also their skin. Currently, there are no regulations governing the harvesting of hagfish along the East Coast. There has been little to no information of the life history of hagfish including growth rate, age determination, reproductive biology, life span, and larval size at hatching. Thus, the level at which a sustainable fisheries for this species can be maintained is unknown. In some parts of the world, hagfish stocks are being depleted due to overfishing. In order for fisheries management to manage its hagfish stocks and develop a sustainable commercial hagfish fishery, critical information is needed to assist in determining the optimal use of this valuable resource.Key elements of the reproductive system have not been elucidated in hagfish. However, there is new evidence from recent reproductive studies that Atlantic hagfish may have a seasonal reproductive cycle. These data include seasonal changes in gonadotropin-releasing hormone (GnRH), gonadal steroids, estradiol and progesterone, corresponding to gonadal reproductive stages along with the putative identity of a functional corpus luteum. This newly acquired data may provide important information to fisheries managers of the East Coast.

Long-term effects of the mammary carcinogen 7,12-dimethylbenz(a) anthracene on hypothalamic gonadotropin-releasing hormone and its pituitary receptor gene expression, during the promotion stage, in female Sprague-Dawley rats.

A single intragastric administration of 7,12-dimethylbenz(a)anthracene (DMBA) has been shown to induce mammary tumors in young cycling female Sprague-Dawley rats. The appearance of these tumors is preceded by a series of neuroendocrine disturbances, including attenuation of the preovulatory luteinizing hormone (LH) surge and amplification of the preovulatory 17beta-estradiol surge, and gonadotropin-releasing hormone (GnRH) released in vitro. In this study, we examined the hypothesis that DMBA administration decreases levels of GnRH mRNA in the preoptic area-anterior hypothalamus (POA-AH) and GnRH receptor (GnRH Rc) mRNA and protein in the anterior pituitary gland. Sprague-Dawley rats, 55-60 days of age with regular estrous cycles, received a single dose of 15 mg DMBA in 1 ml sesame oil delivered by intragastric intubation. A first series of experiments was performed for the measurement of hypothalamic GnRH mRNA and pituitary GnRH Rc mRNA levels. A second series of experiments was performed for the measurement of pituitary GnRH receptor. In both experiments, animals were sacrificed by decapitation at 11.00, 16.00, 18.00 and 20.00 h on each day of the 7th or 8th estrous cycle (28-32 days) after treatment. GnRH and GnRH receptor mRNAs were quantified using solution hybridization-RNase protection assay. The GnRH Rc was quantified using the 125I-D-Ala6-N-Met-Leu6-des-Gly10-ethylamide GnRH. DMBA-treatment produced no significant effect on the overall mean values of GnRH mRNA. GnRH mRNA levels in control rats rose significantly between 16.00 and 20.00 h on proestrus and between 18.00 and 20.00 h on diestrus I. DMBA-treated rats had a surge in GnRH mRNA levels at 18.00 h on proestrus, and showed additional surges at 18.00h on diestrus II and estrus. GnRH receptor mRNA content in the anterior pituitary gland surged at 16.00h on certain days of the cycle in both groups of rats. In control rats, only the surge on diestrus II proved significant, whereas DMBA-treated rats exhibited significant surges on diestrus I, diestrus II and proestrus. GnRH receptor mRNA values were significantly lower on both days of diestrus in DMBA-treated rats compared with controls. GnRH Rc peptide content, like GnRH receptor in RNA surged at 16.00h in both groups with the exception of a marked fall on proestrus day for DMBA treated rats. A reduction in the amplitude of the surge was also seen on the day of estrous and to a lesser extend on the day of diestrus DII in DMBA treated animal. Overall, there was a disruption of the GnRH Rc pattern which culminate on the day of proestrus in DMBA-treated animals. Interestingly, the daily rise between 11.00 and 16.00h which is the more pronounced on the day of proestrus in control animals, was completely blunted in DMBA-treated rats. Overall, the results are consistent with the hypothesis that the carcinogen attenuates, directly or indirectly, preovulatory biosynthesis of the GnRH receptor and LH release. Obviously, the changes in GnRH might occur simultaneously, independently from mammary tumorigenesis, but may play a role, in association with others DMBA-induced neuroendocrine disorders, in the promotion stage of mammary tumors in the Sprague-Dawley female rat.

Neuroendocrine effects of progesterone

Progesterone (P) is secreted by the corpus luteum under the control of gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH). Progesterone (P) is essential for reproduction because: (1) it induces in the endometrium the transcription of specific genes involved in the implantation of the blastocyst, (2) it modulates GnRH/LH secretion by decreasing GnRH pulse frequency, which in turn enriches the gonadotroph cells in FSH and avoids a second LH surge. Using the ewe as a model, we investigated the immediate GnRH and LH responses to acute changes of circulating P levels. Our results show that P changes cause dramatic modifications in GnRH pulse frequency: P removal induces an acceleration of the pulse generator, while P administration slows the pulse frequency. LH secretion was modified in parallel to the changes in GnRH. Other experiments proved that these neuroendocrine effects of P are mediated by P itself, not by its hydroxylated metabolites, and occur at the level of P receptors. Finally, these effects require priming by estradiol. Additionally, in the final stage of the follicular phase, P plays a role in the triggering of the LH surge. This has been shown in rodents, non-human primates, and in women. Such a phenomenon is not observed in ewes, although in these species luteal P modulates the amplitude of the estradiol-induced LH surge.

Changes in the hypothalamic gonadotropin‐releasing hormone gene expression and the pituitary luteinizing hormone immunoreactivity in male rats: Comparison of clozapine with typical antipsychotics

Evidence suggested that atypical antipsychotics (APs) such as clozapine show less side effects than those of typical APs such as haloperidol and sulpiride. However, little is known about chronic effects of these drugs on changes in gonadotropin releasing hormone (GnRH) mRNA expression and luteinizing hormone (LH) immunoreactivity. Male rats were divided into water‐, haloperidol‐, sulpiride‐, and clozapine‐treated groups, and these drugs were administered orally for 4 weeks. The changes in the expression of GnRH mRNA and the LH immunoreactivity were determined in the hypothalamus and pituitary, respectively, using in situ hybridization and immun‐ohistochemistry. GnRH mRNAs were clearly expressed in the water‐treated control rats. This was significantly reduced by the chronic treatments with the typical APs, especially with haioperidoi, but not with atypical APs clozapine. Likewise, LH immunoreactivity was clearly stained in the control group. While its immunoreativity was significantly reduced by the chronic APs treatments, clozapine treatment showed only slight attenuation. The results show that the atypicaj APs clozapine has less side effects in the gonadal function than the typical APs haloperidol and the suipiride. These results suggest that clozapine is a safer drug than the typical APs, at least in the reproductive system.

Rapid photoperiod-induced increase in detectable GnRH mRNA-containing cells in Siberian hamster.

To determine whether changes in gonadotropin-releasing hormone (GnRH) neurons are early indicators of photostimulation, Siberian hamsters were placed in short days (6:18-h light-dark) at 3 (experiment 1) or 6 (experiment 2) wk of age where they were held for 3 (experiment 1) or 4 (experiment 2) wk. Hamsters were then moved to long photoperiod (16:8-h light-dark). In experiment 1, brains were collected 1-21 days after transfer from short to long days. In experiment 2, brains were collected only on the second morning of long day exposure. Long and short day controls were included in both experiments. Cells containing GnRH mRNA, as visualized by in situ hybridization, were counted. As expected, there were no differences in the number of detectable GnRH mRNA-containing cells among animals chronically exposed to long or short photoperiods. However, on the second morning after transfer from short to long photoperiod, a positive shift in the distribution of GnRH mRNA-containing cells occurred relative to the respective controls in the two experiments. Increases in follicle-stimulating hormone secretion and gonadal growth occurred days later. In conclusion, a rapid but transient increase in the distribution of detectable GnRH mRNA-containing cells is an early step in the photostimulation of the hypothalamic-pituitary-gonadal axis.

Gonadotropin-Releasing Hormone and NMDA Receptor Gene Expression and Colocalization Change during Puberty in Female Rats

During development, an increase in gonadotropin-releasing hormone (GnRH) release occurs that is critical for the initiation of puberty. This increase is attributable, at least in part, to activation of the GnRH neurosecretory system by inputs from neurotransmitters, such as glutamate, acting via NMDA receptors. We examined changes in GnRH and NMDA-R1 gene expression by RNase protection assay of preoptic area-anterior hypothalamic (POA-AH) dissections of female rats undergoing normal puberty or in which precocious puberty was induced by treatment with the glutamate agonist NMA. GnRH mRNA levels increased significantly throughout normal development; this was accelerated by treatment with NMA. NMDA-R1 mRNA levels increased only between P10 and P20. The acceleration of the elevation in GnRH mRNA levels by NMDA suggests that a stimulation of GnRH gene expression may be a rate-limiting factor for the onset of puberty. This is attributable to a post-transcriptional mechanism because GnRH primary transcript levels, an index of proGnRH gene transcription, were not observed to change during puberty. Alterations in the colocalization of GnRH neurons with the NMDA-R1 subunit during puberty also were assessed immunocytochemically. The percentage of GnRH neurons that double-labeled with NMDA-R1 was 2% in prepubertal rats and 3% in pubertal rats; this increased to 19% in postpubertal rats. Taken together, these studies suggest that an increase in glutamatergic input to GnRH neurons plays a role in the increase in GnRH release and gene expression that occurs at the initiation of puberty.

Gonadotropin‐Releasing Hormone mRNA and Gonadotropin β‐Subunit mRNA Expression in the Adult Female Rat Exposed to Ethanol In Utero

Previous studies have demonstrated that exposure of female rats to ethanol in utero results in long-term deficits in reproductive function, including a delayed onset of puberty and an early onset of acyclicity. In the present studies, we determined if changes in reproduction are correlated with changes in gonadotropin-releasing hormone (GnRH) mRNA expression in the brain or gonadotropin subunit mRNA expression in the anterior pituitary gland. We used in situ hybridization histochemical techniques to examine the density of GnRH mRNA and the distribution of GnRH mRNA-containing cells in the basal forebrain, and reverse transcription-polymerase chain reaction (RT-PCR) to quantitate the beta-subunit mRNA of luteinizing hormone (LH beta) and follicle-stimulating hormone (FSH beta) in the anterior pituitary gland of adult (3 months of age) fetal alcohol-exposed (FAE) female rats. For GnRH mRNA measurements, animals were gonadectomized 4 days before use. Three groups of animals were examined. FAE females were derived from pregnant dams fed a liquid diet containing 35% ethanol-derived calories from gestational day 14 until parturition. Dams of control animals were either pair-fed (PF) an isocaloric diet with sucrose substituted for ethanol or maintained on normal laboratory rat chow [chow-fed (CF)]. Serial blood samples taken by indwelling right atrial cannulae demonstrated significantly smaller pulses of LH (p < 0.05) and FSH (p < 0.05) in ovariectomized FAE females at 3 months of age, compared with PF and CF controls. Distribution of GnRH mRNA-containing cells was mapped throughout the forebrain, and the number of autoradiographic silver grains/cell was determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in brain gonadotropin-releasing hormone, plasma estradiol 17-beta, and progesterone during the final reproductive cycle of the female sea lamprey, Petromyzon marinus.

Changes in ovarian morphology, brain gonadotropin-releasing hormone (GnRH), plasma estradiol, and progesterone were examined during the 1988 and 1989 spawning migrations of the adult female sea lamprey, Petromyzon marinus. There were significant increases through time in brain GnRH (1989) and plasma estradiol (1988 and 1989), with progesterone levels fluctuating (1988 and 1989) during the freshwater phase of the spawning migrations. In 1989, brain GnRH and plasma estradiol levels gradually increased through time until just prior to spawning when levels decreased. During 1988, there were no significant changes in GnRH, which may reflect lower temperatures in that year. These data provide new information on brain GnRH during the final maturational processes in the female sea lamprey.

Pituitary responsiveness to GnRH, hypothalamic content of GnRH and pituitary LH and FSH concentrations immediately preceding puberty in gilts.

To determine whether pituitary concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) or hypothalamic content of gonadotropin releasing hormone (GnRH) change before puberty, 40 prepubertal gilts averaging 7 mo of age were slaughtered before or on the second, third or fourth day after relocation and boar exposure. Some gilts responded to relocation and boar exposure as indicated by swollen vulvae, turgid uteri and enlarged ovarian follicles at the time of slaughter. Pituitary concentrations of LH and FSH and hypothalamic content of GnRH were similar between gilts that responded to relocation and boar exposure and gilts that did not respond. In addition, boar exposure and relocation had no effect on pituitary concentrations of LH and FSH or on hypothalamic content of GnRH. To determine whether pituitary responsiveness to GnRH changes before puberty, a third experiment was conducted in which 72 gilts were injected with 400 micrograms of GnRH either before or on the second, third or fourth day after relocation and boar exposure. In gilts that subsequently responded (i.e., ovulated) as a result of relocation and boar exposure, pituitary responsiveness to GnRH was reduced as compared with gilts that failed to ovulate after relocation and boar exposure. Peak concentrations of serum LH after GnRH injection were 4.6 +/- 1.3 vs 9.8 +/- .8 ng/ml for responders vs nonresponders. Peak serum FSH after GnRH injection was also lower for responders than for nonresponders (29.5 +/- 4.2 vs 41.2 +/- 2.4 ng/ml). When compared with controls, relocation and boar exposure did not significantly affect GnRH-induced release of LH and FSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary content of gonadotropins and receptors for gonadotropin-releasing hormone (GnRH) and hypothalamic content of GnRH during the periovulatory period of the ewe.

Studies were undertaken to determine if the number of hypophyseal receptors for GnRH changes at the time of the preovulatory surge of LH in ewes. Concentrations of LH, FSH, progesterone, and estradiol in serum and concentrations of LH and FSH in pituitary were measured. The content of GnRH in the hypothalamus was also determined. Estrus was synchronized in 35 cross-bred ewes by injecting prostaglandin F2 alpha (PGF2 alpha) at 0 and 4 h (7.5 mg each, im) on day 14 of a naturally occurring estrous cycle, followed 30 h later by the injection of estradiol (25 micrograms in safflower oil, im). Five ewes were killed at each of the following times relative to the first injection of PGF2 alpha: 0, 24, 32, 44, 50, 56 and 96 h. Blood samples were collected throughout the course of the experiment. Concentrations of progesterone in serum decreased markedly by 8 h after PGF2 alpha and were uniformly undetectable (less than 300 pg/ml) by 34 h. Concentrations of estradiol in serum increased after the injection of estradiol and returned to basal values 10 h later. Surges of LH, which were usually coincident with surges of FSH, occurred between 43 and 53 h. Concentrations of both LH and FSH in the pituitary declined after the LH surge. There were no significant changes in the amount of GnRH contained in the preoptic area, the median eminence, or the hypothalamus. The number of receptors for GnRH increased at 24 and 32 h compared to the 0 h value and remained elevated at 44 and 50 h. After the LH surge (56 h), the number of GnRH receptors declined and at 96 h was not different from the number measured at 0 h. Since an increase in the number of receptors will result in the formation of more receptor-hormone complex and may lead to an augmented response, these data suggest that an increase in the number of hypophyseal receptors for GnRH may contribute to the preovulatory LH surge in ewes.

Estimation of GnRH pulse amplitude during pubertal development.

Fourteen children between 2.5 and 16 years of age were studied to provide a quantitative estimate of the changes in gonadotropin-releasing hormone (GnRH) pulse amplitude in hypophysial portal plasma during puberty. Responses to physiologic doses of synthetic GnRH were measured [induced luteinizing hormone (delta LH) and induced follicle-stimulating hormone (delta FHS)] and compared with spontaneous fluctuations in gonadotropins [spontaneous luteinizing hormone (delta sLH) and spontaneous follicle-stimulating hormone (delta FHS)]. One to four low-dose (0.0125 or 0.025 microgram/kg IV) pulses of GnRH were given every 2 hr between 0800 ad 1600 or 2200 and 0400 hr. Maximal peripheral plasma concentrations of GnRH one min after pulses averaged 107 +/- 25 pg/ml (S.E.) (0.0125 microgram/kg dose) and 218 +/- 33 pg/ml (0.025 microgram/kg dose). In early pubertal children the maximal delta LH was similar to or less than the maximal nocturnal delta sLH (maximum, delta LH 7.0 +/- 0.2 versus maximum delta sLH 7.0 +/- 1.3 mIU/ml in boys, 7.0 +/- 1.2 versus 16.0 +/- 3.0 mIU/ml in girls). Luteinizing hormone (LH) responses were low or undetectable in children whose bone ages were less than 10 years. When discernible, LH pulse frequency was similar during daytime and nighttime sampling periods in early pubertal boys. However, two hourly injections of GnRH given during the day did not simulate the initial nocturnal rise in LH. Overall mean delta FSH and delta sFSH were similar in three prepubertal female patients (3.0 +/- 0.2 versus 2.8 +/- 0.2 mIU/ml). delta FSH was greater than delta sFSH in two patients with gonadal dysgenesis (bone ages, 2.5 and 5 years) and in one prepubertal girl. The gonadotropin responses seen in early pubertal children suggests that the amplitude of nocturnal GnRH pulses is equal to or greater than that previously reported in normal men.