Circulating Luteinizing Hormone Levels Research Articles

Effects of Low Luteinizing Hormone Serum Levels on Oocyte Retrieval, Fertilization Rate, and Embryo Quality during Controlled Ovarian Stimulation: Results from a Prospective Cohort Analysis

Objectives: Luteinizing hormone (LH) plays a key role in normal follicular development and oocyte maturation in controlled ovarian stimulation. LH stimulates the proliferation and differentiation of theca cells for the secretion of androgens, synergistically increasing estrogen production. This study aimed to investigate the effects of low LH concentrations on oocyte retrieval, fertilization, and embryo development in patients undergoing in vitro fertilization/intracytoplasmic sperm injection. Design: We prospectively (ClinicalTrials ID: NCT05755529) analyzed patients undergoing in vitro fertilization/intracytoplasmic sperm injection, subdividing them into three groups according to their age. Serum LH levels were evaluated on day 3, during stimulation (day 10) and before ovulation induction (day 12). Participants/Materials, Setting, Methods: Forty-three consecutive women were scheduled for IVF and received ovarian stimulation with follitropin alfa (Gonal F, Merck Serono, Germany) and ganirelix (Fyremaldel, Sun Pharma, Italy). Statistical analysis was performed with InStat 3.10, GraphPad software, San Diego, CA, USA. Normal distribution was tested by the Shapiro-Wilk test. Continuous variables were expressed as the mean and standard deviation. Categorical variables are expressed as frequencies and percentages. Results: Our data analysis suggests that serum LH levels progressively decrease during controlled ovarian stimulation, and this effect is more evident in the early phase of this procedure. From this perspective, circulating LH levels may significantly decrease during the late follicular phase due to the negative feedback of ovarian hormones from multiple follicular developments or after the suppressive effects of gonadotropin-releasing hormone antagonists. Limitations: Although our study confirms that exogenous LH can be considered a strategy in women with reduced LH levels during ovarian stimulation to improve oocyte quality and reproductive outcome, the generalizability of the results is limited by the low number of participants enrolled. Conclusions: Exogenous LH may be considered a strategy in women with a decrease in LH levels during ovarian stimulation to improve oocyte quality and reproductive outcome.

Carbon Black Nanoparticles Selectively Alter Follicle-Stimulating Hormone Expression in vitro and in vivo in Female Mice.

Toxic effects of nanoparticles on female reproductive health have been documented but the underlying mechanisms still need to be clarified. Here, we investigated the effect of carbon black nanoparticles (CB NPs) on the pituitary gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are key regulators of gonadal gametogenesis and steroidogenesis. To that purpose, we subjected adult female mice to a weekly non-surgical intratracheal administration of CB NPs at an occupationally relevant dose over 4 weeks. We also analyzed the effects of CB NPs in vitro, using both primary cultures of pituitary cells and the LβT2 gonadotrope cell line. We report here that exposure to CB NPs does not disrupt estrous cyclicity but increases both circulating FSH levels and pituitary FSH β-subunit gene (Fshb) expression in female mice without altering circulating LH levels. Similarly, treatment of anterior pituitary or gonadotrope LβT2 cells with increasing concentrations of CB NPs dose-dependently up-regulates FSH but not LH gene expression or release. Moreover, CB NPs enhance the stimulatory effect of GnRH on Fshb expression in LβT2 cells without interfering with LH regulation. We provide evidence that CB NPs are internalized by LβT2 cells and rapidly activate the cAMP/PKA pathway. We further show that pharmacological inhibition of PKA significantly attenuates the stimulatory effect of CB NPs on Fshb expression. Altogether, our study demonstrates that exposure to CB NPs alters FSH but not LH expression and may thus lead to gonadotropin imbalance.

Development of a giant grouper Luteinizing Hormone (LH) Enzyme-Linked Immunosorbent Assay (ELISA) and its use towards understanding sexual development in grouper

A recombinant giant grouper Luteinizing Hormone (LH) consisting of tethered beta and alpha subunits was produced in a yeast expression system. The giant grouper LH β-subunit was also produced and administered to rabbits for antibody development. The recombinant LH and its antibody were used to develop an Enzyme Linked Immunosorbent Assay (ELISA). This ELISA enabled detection of plasma LH levels in groupers at a sensitivity between 391 pg/ml and 200 ng/ml. Different species of grouper were assayed with this ELISA in conjunction with gonadal histology and body condition data to identify links between circulating LH levels and sexual development. We found that circulating levels of LH decreased when oocytes began to degenerate, and sex-transition gonadal characteristics were apparent when LH levels decreased further. When circulating LH levels were related to body condition (body weight/ body length), transitioning-stage fish had relatively high body condition but low plasma LH levels. This observation was similar across multiple grouper species and indicates that plasma LH levels combined with body condition may be a marker for early male identification in the protogynous hermaphrodite groupers.

The skeleton gets a (reproductive) life

The skeleton gets a (reproductive) life

Alarin stimulates food intake and gonadotrophin release in male rats

Alarin is a recently discovered member of the galanin peptide family encoded by a splice variant of galanin-like peptide (GALP) mRNA. Galanin and GALP regulate energy homeostasis and reproduction. We therefore investigated the effects of alarin on food intake and gonadotrophin release. Alarin was administered into the third cerebral ventricle (i.c.v.) of rats, and food intake or circulating hormone levels were measured. The effect of alarin on the hypothalamo-pituitary-gonadal axis was investigated in vitro using hypothalamic and anterior pituitary explants, and immortalized cell lines. Receptor binding assays were used to determine whether alarin binds to galanin receptors. The i.c.v. administration of alarin (30 nmol) to ad libitum fed male rats significantly increased acute food intake to 500%, and plasma luteinizing hormone (LH) levels to 170% of responses to saline. In vitro, 100 nM alarin stimulated neuropeptide Y (NPY) and gonadotrophin-releasing hormone (GnRH) release from hypothalamic explants from male rats, and 1000 nM alarin increased GnRH release from GT1-7 cells. In vivo, pretreatment with the GnRH receptor antagonist cetrorelix prevented the increase in plasma LH levels observed following i.c.v. alarin administration. Receptor binding studies confirmed alarin did not bind to any known galanin receptor, or compete with radiolabelled galanin for hypothalamic binding sites. These results suggest alarin is a novel orexigenic peptide, and that it increases circulating LH levels via hypothalamic GnRH. Further work is required to identify the receptor(s) mediating the biological effects of alarin.

A Potential Means of Investigating the Role of Luteinizing Hormone in the Pathogenesis of Alzheimer Disease

Editor - I read with great interest the recent review article, “The Contribution of Luteinizing Hormone to Alzheimer Disease Pathogenesis” by Webber et al.1 In this paper and in another article,2 the authors present some intriguing data from various lines of basic, epidemiological and clinical research supporting their hypothesis implicating luteinizing hormone (LH) in the pathogenesis of Alzheimer disease. One might speculate that women who have undergone oophorectomy and men who have undergone orchiectomy might be at increased risk according to this model. Conversely, one would expect that people with lower levels of LH might be less predisposed to Alzheimer disease. If this is true, pharmacological intervention to lower LH levels might potentially decrease this risk. The authors mention Phase II data suggesting stabilization of cognitive function in men with Alzheimer disease from a trial specifically designed to test the potential of leuprolide acetate (leuprolide) (Lupron).3 Leuprolide, along with a similar agent, goserelin acetate (goserelin) (Zoladex), are gonadotropin-releasing hormone (GnRH) agonist analogues that decrease circulating LH levels. GnRH is a hypothalamic hormone that stimulates LH release from the anterior pituitary gonadotrophs when the pituitary is exposed to GnRH in the physiologically normal pulsatile fashion. Although leuprolide and goserelin are agonists at the receptor level, continuous stimulation of the anterior pituitary gonadotrophs by these synthetic analogues paradoxically diminishes LH release. Both agents are commonly used in the treatment of endometriosis, precious puberty and metastatic prostate cancer. Radiation oncologists also frequently use them as adjuvant therapy for locally advanced or high-risk localized prostate cancer. Long-term follow-up has documented improved local control, biochemical control, disease specific survival and overall survival compared to radiotherapy alone for high-risk prostate cancer patients. Given that these studies were prospective, randomized clinical trials, which began in the 1980s, they could perhaps provide additional evidence supporting or refuting the hypothesis. For instance, in the clinical trial RTOG 85–31,4 patients with high-risk prostate cancer were randomized to either indefinite use of goserelin acetate or no treatment following radiation therapy. Thus, a cohort of patients given goserelin (and thus having suppressed LH levels) dating back to 1985 can be compared to a very similar cohort who did not receive such therapy. Definite conclusions, of course, will be limited due to the high percentage of patients who eventually crossed over to the goserelin arm when their disease progressed, the high number of deaths since the trial began, and the possibility that data on Alzheimer disease development over the years was not fully documented. Of note, certain other clinical trials of goserelin or leuprolide and radiation therapy may not be as useful as cohort studies to test the role of LH inAlzheimer disease pathogenesis. A European study5 had an outcome very similar to the RTOG study4 as far as prostate cancer control goes, and many of these men never fully recovered testicular function following withdrawal of the use of adjuvant goserelin for 3 years. Although men in both trials had long-term reductions in testosterone levels and improved prostate cancer control compared to radiotherapy alone, at the completion of the EORTC trial,5 LH levels presumably increased, whereas in the RTOG study4 LH levels remained suppressed. Similarly, although the effect of orchiectomy may be similar to long-term goserelin or leuprolide therapy (i.e. testosterone is decreased to castration levels), the effects on LH will be drastically different with orchiectomy leading to increased LH and “chemical castration” leading to lowered LH. In light of this intriguing hypothesis, it might be interesting and worthwhile to investigate the effects of LH suppression on Alzheimer disease development in these completed, long-term cohorts.

Effect of a high-fat diet on 24-h pattern of circulating levels of prolactin, luteinizing hormone, testosterone, corticosterone, thyroid-stimulating hormone and glucose, and pineal melatonin content, in rats

Circadian rhythmicity is affected in obese subjects. This article analyzes the effect of a high-fat diet (35% fat) on 24-h changes circulating prolactin, luteinizing hormone (LH), testosterone, corticosterone, thyroid-stimulating hormone (TSH) and glucose, and pineal melatonin content, in rats. When body weight of rats reached the values of morbid obesity, the animals were sacrificed at six different time intervals throughout a 24-h cycle, together with age-matched controls fed a normal diet (4% fat). Plasma hormone levels were measured by specific radioimmunoassays and glucose concentration by an automated glucose oxidase method. In rats under a high-fat diet, a significant disruption of the 24-h pattern of plasma TSH, LH, and testosterone and a slight disruption of prolactin rhythm were found. Additionally, high-fat fed rats showed significantly lower total values of plasma TSH and testosterone and absence of correlation between testosterone and circulating LH levels. Plasma corticosterone levels increased significantly in high-fat fed rats and their 24-h variation became blunted. In obese animals, a significant hyperglycemia developed, individual plasma glucose values correlating with circulating corticosterone in high-fat fed rats only. The amplitude of the nocturnal pineal melatonin peak decreased significantly in high-fat fed rats. The results underlie the significant effects that obesity has on circadian organization of hormone secretion.

Insulin-Like Factor 3: A New Circulating Hormone Related to Luteinizing Hormone-Dependent Ovarian Hyperandrogenism in the Polycystic Ovary Syndrome

Insulin-like factor 3 (INSL3), a circulating peptide hormone and a member of the relaxin-insulin family, is produced in the testicular Leydig cells and, to a lesser extent, in ovarian theca interna cells of antral follicles, the corpora lutea, and the ovarian stroma. Recent studies in rats suggest an important role for luteinizing hormone (LH) in stimulating gonadal expression of INSL3. Most women with polycystic ovary syndrome (PCOS) have a hyperplastic theca intema and cortical stroma and an increased number of small antral follicles. A majority-specially non-obese patients-have elevated circulating LH levels. This study estimated circulating levels of INSL3 by radioimmunoassay in 22 women with PCOS and normal body weight and 22 others who were overweight (body mass index [BMI] of 25-30 kg/m 2 ) or obese (BMI exceeding 30 kg/m 2 ). Each was matched for age and body weight with a non-PCOS control subject. Compared with control women, those with PCOS had greater insulin responses to oral glucose, higher androgen levels, and less frequent menstruation. Differences in androgen levels were most evident in normal-weight subjects, while differences in insulin responses to glucose were more evident in overweight/obese women. Baseline LH levels were highest in PCOS women of normal body weight. Serum levels of INSL3 were significantly higher in PCOS women than in control subjects, but only in those of normal body weight. In all women, serum INSL3 correlated positively with levels of total and free testosterone and with LH levels. In women with PCOS, concentrations of INSL3 were associated with greater responses of 170H-progesterone to buserelin, an index of ovarian hyperandrogenism. Levels of INSL3 also correlated positively with the number of ovarian follicles in women with PCOS. In contrast, women with PCOS exhibited no significant correlation between baseline LH levels and the number of follicles. These findings could be interpreted to mean that INSL3 is a circulating hormone related to LH-dependent ovarian hyperandrogenism in women with PCOS and normal body weight.

Use of a Vascular Access Port for the Measurement of Pulsatile Luteinizing Hormone in Old Broiler Breeders

Techniques used to measure circulating hormone concentrations in avian species over extended periods routinely involve cannulation or multiple venipunctures under physical restraint, resulting in sepsis and stress. We adapted a method for serial blood sampling in chickens using a vascular access port (VAP) surgically implanted under the skin of the neck and connected to a catheter inserted in the right jugular vein. The system was used to measure circulating luteinizing hormone (LH) profiles in six, 21-mo-old broiler breeders at the end of their laying period. The VAP were implanted under general anesthesia, and, after a period of recovery, serial blood samples (every 10 min for 6 h) were collected using an extension line connected to a push–pull system. Birds were unrestrained and had free access to food and water. Red blood cells were recovered by centrifugation, reconstituted in saline solution, and returned to the donor bird through the VAP once every 90 min. Luteinizing hormone levels were subsequently measured in plasma by radioimmunoassay. With the exception of 1 hen that developed valvular endocarditis, no sign of disease or infection was observed throughout the study, and the VAP remained functional in all birds for at least 3 mo. Thus, our results suggest that VAP are a safe, reliable, and less stressful technique for serial blood sampling and long-term studies. Radioimmunoassay results revealed that in old birds, circulating LH levels followed a pulsatile pattern, with pulse amplitudes ranging from 1.35 to 2.02 ng/mL and pulse frequencies ranging from 5 to 6 peaks per 6 h. Although not significant, amplitude of LH pulses in out-of-lay hens appeared to be lower than in laying hens.

Orthotopic transplantation of LH receptor knockout and wild-type ovaries

Luteinizing hormone (LH) receptor knockout animals have an ovarian failure due to an arrest in folliculogenesis at the antral stage. As a result, the animals have an infertility phenotype. The present study was undertaken to determine whether this phenotype could be reversed by orthotopic transplantation of wild-type ovaries. The results revealed that transplanting wild-type ovaries into null animals did not result in resumption of estrus cycles. Although the number of different types of follicles increased, none progressed to ovulation. The serum hormone profiles improved, reflecting the ovarian changes. The wild-type animals with null ovaries also failed to cycle and their ovaries and serum hormone levels were more like null animals with their own ovaries. Although the lack of rescue of null ovaries placed into wild-type animals was predicted, the failure of wild-type ovaries placed in null animals was not, which could be due to chronic exposure of transplanted tissue to high circulating LH levels and also possibly due to altered internal milieu in null animals. These findings may have implications for potential future considerations of grafting normal donor ovaries into women who have an ovarian failure resulting from inactivating LH receptor mutations.

Steroid-induced changes in the morphology of GnRH neurons in the male leopard frog, Rana pipiens: correlation with plasma gonadotropin and gonadal size

Previously, we reported that hypothalamic explants isolated from male leopard frogs ( Rana pipiens) implanted with 17β-estradiol (E 2), but not 5α-dihydrotestosterone (DHT), released significantly higher levels of gonadotropin-releasing hormone (GnRH) in response to a veratridine challenge. In this study, we measured changes in GnRH soma size, circulating luteinizing hormone (LH), and gonadosomatic index (GSI) in response to these two steroid hormones to further assess the impact of these hormones on the hypothalamic–pituitary–gonadal axis. Sexually mature male R. pipiens were implanted with silastic capsules containing cholesterol (Ch; control), E 2, or DHT for 20 days. GnRH immunocytochemistry (ICC) revealed that both E 2 and DHT significantly enlarged GnRH soma size without affecting the total number of GnRH neurons in the forebrain. The effects of E 2 and DHT were specific, since neither hormone altered the soma size of tyrosine hydroxylase neurons in the dorsomedial posterior tuberculum. Circulating LH levels were significantly reduced in animals treated with both steroid hormones, with E 2 exerting the most potent inhibitory effect. A significant inverse correlation was observed between the GSI and GnRH soma size in Ch controls, suggesting animals with larger GnRH neurons tended to have smaller gonads. Overall, our results showed that both steroid hormones induced the accumulation of GnRH and ultimately the swelling of the GnRH soma. Further, larger GnRH neurons were associated with smaller gonads and lower circulating levels of LH, suggesting a link between enlarged GnRH neurons and an overall decrease in the reproductive activity of R. pipiens.

Circulating LH Levels and the Response to Exogenous GnRH in the Common Mole-Rat: Implications for Reproductive Regulation in This Social, Seasonal Breeding Species

The effects of breeding season and reproductive status on male and female reproduction were investigated in the common mole-rat, Cryptomys hottentotus hottentotus, a cooperatively breeding rodent which exhibits a unique combination of seasonal breeding and a reproductive division of labor. Pituitary function was examined by measuring the luteinizing hormone (LH) responses to single doses of 2 μg exogenous gonadotrophin-releasing hormone (GnRH) and physiological saline in 69 males and 58 females from 35 wild-caught colonies. Neither males nor females exhibited any apparent manifestation of season on basal LH concentrations or on pituitary sensitivity to stimulation by exogenous GnRH. The continuance of reproductive function during the nonbreeding period is essential in common mole-rat males and females, as this period coincides with the period of maximal dispersal opportunity in the winter rainfall area they inhabit. Normal circulating levels of reproductive hormones in dispersing animals may aid intersexual recognition, assist pair-bond formation, and thus prime animals for independent reproduction. Circulating basal concentrations of LH as well as LH levels measured in response to a single exogenous GnRH challenge were not significantly different between the reproductive and non-reproductive groups of either sex, suggesting the absence of a physiologically well-defined suppression of reproduction in subordinate common mole-rats.

Age-related decrease in hypothalamic gonadotropin-releasing hormone (GnRH) gene expression, but not pituitary responsiveness to GnRH, in the male Brown Norway rat.

As is the case in humans, aging male Brown Norway (BN) rats exhibit both primary and secondary (hypothalamic/pituitary) testicular failure. We hypothesized that secondary testicular failure in aging BN rats is due to alterations in both hypothalamic and pituitary function. In order to determine whether gonadotropin-releasing hormone (GnRH) gene expression is altered with aging, we compared hypothalamic preproGnRH (ppGnRH) mRNA by in situ hybridization histochemistry and GnRH peptide content in microdissected brain areas by radioimmunoassay in intact (or sham-operated) young, middle-aged, and old male rats. In addition, we determined hypothalamic-pituitary responsiveness to the removal of testicular feedback by comparing ppGnRH messenger RNA (mRNA) and gonadotropin levels in sham-operated and orchidectomized young, middle-aged, and old rats. In sham-operated rats, both the cellular ppGnRH mRNA content and the number of neurons expressing ppGnRH mRNA were lower in old compared with young and middle-aged rats. In addition, GnRH content decreased with aging in intact rats in 2 of the 3 brain areas examined, and GnRH content tended to decrease with aging in the third region. Morning serum luteinizing hormone (LH) levels were unchanged with aging, whereas follicle-stimulating hormone (FSH) was significantly increased in old compared with younger intact rats. The cellular ppGnRH mRNA content also decreased with aging in orchidectomized rats, although the number of neurons expressing ppGnRH mRNA was unchanged with aging in these rats. Within age groups, the cellular ppGnRH mRNA content was higher in orchidectomized than in sham-operated rats, though there was no effect on the number of neurons expressing GnRH. In a second study, we compared pituitary responsiveness to GnRH by measuring serum LH and FSH levels after GnRH administration in intact BN rats of different ages. The LH response to GnRH was unchanged with aging, whereas the FSH response to GnRH tended to increase with aging. Despite similar LH responses, the testosterone (T) response to GnRH declined progressively with aging. A third study assessed age-related changes in the circadian rhythm of circulating LH, T, and corticosterone (B) levels. LH levels over a 24-hour period decreased with aging and tended to be lower in the morning hours in all age groups, and circadian rhythmicity was blunted in middle-aged and old compared with young rats. T levels over 24 hours declined progressively with aging, and these levels showed a bimodal diurnal variation in young rats, a variation that was not evident in older animals. B levels over a 24-hour period were lower in old than in younger animals, and with aging, there was dampening of the amplitude of the circadian rhythm of B. Taken together, these findings suggest that secondary testicular failure in aging male BN rats is due in part to decreased GnRH gene expression rather than to decreased pituitary responsiveness to GnRH. This reduction in GnRH gene expression with aging is not dependent on testicular feedback factors. Finally, the blunted circadian rhythmicity of LH and T secretion with aging provides further evidence of altered hypothalamic regulation of gonadal hormone secretion in old animals.

The reversible effects of raloxifene on luteinizing hormone levels and ovarian morphology in mice

Raloxifene is a selective estrogen receptor modulator that has estrogen agonist effects on bone and serum lipids and estrogen antagonist effects on breast and uterine tissues. This study assessed the effects of raloxifene hydrochloride (HCl) treatment on circulating luteinizing hormone (LH) levels and ovarian morphology in sexually mature, 15-week-old, female CD-1 mice. Mice were maintained on diets providing average daily doses of 0 or 233 mg/kg raloxifene for 2 weeks (Study 1) or 0, 7.9, or 236 mg/kg raloxifene for 4 weeks (Study 2). At the end of the treatment period, blood samples were collected every 2 hours for 24 h in Study 1 (5 mice per group) and at 10:00 a.m. and 10:00 p.m. in Study 2 (8 mice per group). Serum LH levels were measured by radioimmunoassay. Ovarian histomorphology was evaluated in the 10 mice per group (Study 1) and the 8 mice per group (Study 2). For the reversibility phase (Study 2), mice were fed untreated diets for 3 weeks; serum LH levels and ovarian histomorphology were then assessed. Raloxifene treatment at 233 mg/kg/day for 2 weeks (Study 1) significantly elevated circulating LH levels by 4- to 7-fold compared with control. Raloxifene-treated mice had elevated LH levels sustained over the 24-h sampling period and did not exhibit the preovulatory LH surge evident in some control mice at the 4:00 p.m., 6:00 p.m., and 8:00 p.m. time points. Mice treated with 236 mg/day raloxifene for 4 weeks (Study 2) had elevated LH levels (4.4-fold compared to control), whereas mice exposed to 7.9 mg/kg/day raloxifene had a slight, nonsignificant increase in LH (2-fold compared to control). In both dose groups, LH levels were indistinguishable from controls 3 weeks after raloxifene treatment was discontinued. The ovaries in six of the eight mice treated with 7.9 mg/kg/day raloxifene had dilated and/or anovulatory follicles. One mouse in this group had a single hemorrhagic follicle; however, corpora lutea distribution was normal, indicating that ovulation was occurring. Raloxifene-treated mice in Study 1 and mice treated with a comparable raloxifene dose (236 mg/day) in Study 2 had histomorphological changes in the ovary indicative of arrested follicular maturation, including anovulatory hemorrhagic follicles, some developing follicles, and very few corpora lutea. At the end of the reversibility phase, hemorrhagic follicles were no longer evident and follicular maturation and corpora lutea distribution were normal. Raloxifene treatment in mice produces a dose-dependent, sustained elevation in serum LH levels and is associated with changes in ovarian follicular morphology. These changes are reversible upon discontinuation of raloxifene treatment.

Sex steroids and the initiation of puberty in male African catfish (Clarias gariepinus).

The effects of sex steroids on spermatogenesis and testicular androgen secretion were studied in juvenile (spermatogonia present in testes) African catfish. Fish were implanted with Silastic pellets containing 11-ketotestosterone (KT), 11beta-hydroxyandrostenedione (OHA), androstenetrione (OA), androstenedione (A), testosterone (T), 5alpha-dihydrotestosterone (DHT), or estradiol-17beta (E2). Control groups received steroid-free pellets. Two weeks later, testis tissue fragments were incubated with African catfish luteinizing hormone (LH) and the amount of OHA secreted in vitro (the main androgen produced by African catfish testes) was quantified. Tissue fragments were then fixed for histological analysis of spermatogenesis. Treatment with KT, OHA, and OA stimulated testicular growth and spermatogenesis (spermatocytes and spermatids were found), whereas T, DHT, A, or E2 had no such effects. All steroids, except for DHT and E2, reduced OHA secretion in the absence and presence of LH to approximately 10% of the control values. Previous studies have shown that KT, OHA, and OA have little effect on circulating LH levels in juvenile male African catfish, so that these androgens probably had direct effects on the testis. Inasmuch as OHA, OA, and KT have largely similar effects and because OHA and OA are converted to KT in vivo, we suggest that KT is physiologically the most relevant androgen for the initiation of spermatogenesis in African catfish.

Tamoxifen-induced light and electron microscopic changes in the rat testicular morphology and serum hormonal profile of reproductive hormones

The effects of oral administration of tamoxifen at doses of 40 and 200 μg/kg/day on testicular histology, testicular ultrastructure and serum hormonal profile were studied. The drug was administered to adult male rats over a period of 90 days and the effect was assessed at 10-day intervals. The morphometry, microscopic structures of the testis, including ultrastructure and daily sperm production rate, were evaluated. The hormone profiles of luteinizing hormone (LH), follice-stimulating hormone (FSH), testosterone, and estradiol were studied. The testes from treated animals showed disorganization of tubular elements with increased intercellular space. At day 50, the changes were extensive including presence of phagosomes. Morphometric studies showed a reduction in the spermatid and spermatozoan population (69.3%) with no changes in tubular diameter. The mean Leydig cell area was significantly lowered at day 50, at both doses. The daily sperm production rate was reduced as compared with controls. An array of degenerative changes were revealed by ultrastructural studies. The changes were extensive at day 50 at both doses. The characteristic features were lost in most of the cells with phagolysosomes becoming abundant. The cytoplasm of the cells was dense with poorly defined cytoplasmic organelles. Circulating LH levels were not modified at the 40 μg/kg/day dose but at 200 μg/kg/day, LH levels were significantly decreased. Initial transitory rise in FSH was seen with both doses. Both doses of tamoxifen decreased testosterone levels. Changes in the circulating estradiol levels were inconsistent, and no apparent relationship between dose and days of treatment was observed. Thus, this study supports our thesis of tamoxifen as a potential male contraceptive agent.

Role of endogenous opioid peptides in central glucocorticoid Receptor (GR)-induced decreases in circulating LH in the male rat

While it has been shown that intracerebral administration of exogenous glucocorticoids diminishes pituitary luteinizing hormone (LH) release, it is not known if these hormones act directly on gonadotropin-releasing hormone (GnRH)-synthesizing neurons, or if their central inhibitory effects are mediated by specific neural substrates. In the present study, we examined whether the opioid receptor antagonist, naltrexone (NALT), alters patterns of LH release elicited by either systemic or intracerebroventricular (i.c.v.) delivery of GR agonists. Subcutaneous (s.c.) injection of the GR agonist, RU362 (2.5 mg/kg), promoted a significant reduction in circulating LH levels; pretreatment by i.c.v. injection of 1.0 μg NALT, however, attenuated this inhibitory hormonal response. It was also found that rats treated sequentially with NALT and RU362 exhibited significantly lower plasma LH levels compared to rats injected with NALT alone. In other experiments, intracranial delivery of the synthetic glucocorticoid, dexamethasone (DEX), into either the ventricular system or the hypothalamic ARC resulted in significantly decreased plasma LH concentrations; the central inhibitory effects of DEX on peripheral LH release were reversed, however, by i.c.v. pretreatment with NALT. In summary, the present studies show that opioid receptor blockade attenuates systemic, as well as intracerebral inhibitory effects of GR agonists on the GnRH-pituitary LH axis, suggesting that circulating glucocorticoids inhibit LH, in part, through central actions involving endogenous opioid receptors. The observed decline in peripheral plasma LH following intra-ARC injection of DEX suggests that local GR may be functional target sites for glucocorticoid effects on LH. Since i.c.v. administration of NALT reversed the inhibitory LH response to these localized effects of DEX, opioid receptors may reside within neural pathways mediating the inhibitory effects of ARC GR on pituitary LH.

Changes in pulsatile release of neuropeptide-Y and luteinizing hormone (LH)-releasing hormone during the progesterone-induced LH surge in rhesus monkeys.

In previous studies we have shown that the pulsatility of LH-releasing hormone (LHRH) release in gonadectomized monkeys is modulated by input from neuropeptide-Y (NPY) neurons: 1) the endogenous release of NPY in the stalk-median eminence (S-ME) was pulsatile; 2) NPY pulses were temporally correlated with LHRH pulses, with NPY pulses preceding LHRH pulses by approximately 5 min; and 3) infusion of NPY into the S-ME stimulated LHRH release, whereas 4) infusion of antiserum to NPY suppressed endogenous LHRH pulses. It is not known, however, whether ovarian steroid hormones alter the pulsatility of NPY and LHRH release or whether the temporal correlation of NPY and LHRH pulses is maintained during the LH surge. In the present study we examined the changes in pulsatile release of NPY and LHRH in ovariectomized monkeys treated with estradiol benzoate (EB) followed by progesterone or oil. Using push-pull perfusion, perfusate samples from S-ME were collected at 10-min intervals for 15 h. NPY and LHRH concentrations in the perfusates were measured by RIA. Circulating LH levels were also monitored by periodic blood sampling and RIA. Injection of progesterone (sc) after EB induced an LH surge with a peak latency of 7.3 +/- 1.3 h (mean +/- SE) in seven of seven monkeys, whereas oil injection after EB elicited an LH surge in none of seven monkeys. The progesterone-induced LH surge was associated with an increase in LHRH release; the mean, pulse amplitude, and pulse frequency increased significantly (for all, P < 0.05) 4-8 h after progesterone. NPY pulse frequency also increased significantly (P < 0.05) 4-8 h after progesterone treatment, whereas mean release and pulse amplitude did not change in response to progesterone. Oil treatment after EB administration did not alter any parameter of LHRH and NPY pulses. Interestingly, the NPY and LHRH pulses were highly correlated (P < 0.001) in monkeys treated with either EB-progesterone or EB-oil, and NPY pulses preceded LHRH pulses by 4.8 +/- 0.7 and 5.1 +/- 0.6 min, respectively. In summary, 1) an episode of increased LHRH release occurs before and during the progesterone-induced LH surge; 2) acceleration of LHRH pulse frequency and the increase in LHRH pulse amplitude after progesterone are accompanied by acceleration of NPY pulse frequency; and 3) ovarian steroids do not affect the temporal correlation between NPY and LHRH pulses.(ABSTRACT TRUNCATED AT 400 WORDS)

In Vivo GnRH Responsiveness of LH Secretion in the Female Turtle, Trachemys scripta, in Relation to the Reproductive Stage

The effects of several forms of gonadotropin-releasing hormone (GnRH) on the in vivo secretion of luteinizing hormone (LH) were investigated in the female turtle Trachemys scripta. Serial injections of large vitellogenic turtles with 1-2 μg (ca. 0.15 μg/100 g turtle) of chicken GnRH-I (cGnRH-I) and multiple blood sampling revealed that mature females were unresponsive to GnRRH. In contrast, both forms of avian GnRH, cGnRH-I and cGnRH-II, and an avian GnRH analogue (GnRHa) significantly increased circulating levels of LH in previtellogenic turtles. In these turtles, plasma LH increased within 10 min after the initial injection of 0.5 μg GnRHa or cGnRH-I, but this increase in LH was generally transient and could not be sustained for more than 2 hr even with repeated GnRH injections. Turtles treated with GnRHa on Day 1 showed attenuated pituitary responsiveness to subsequent GnRH challenges on Day 2, whereas turtles treated with both native forms of chicken GnRH remained equally responsive on Day 2. In vitro, GnRHa was more resistant to degradation in plasma than both native forms of GnRH, and the clearance rate of GnRHa in vivo was also slower than that of cGnRH-I. The results show, for the first time, that in vivo GnRH administration stimulates and desensitizes LH secretion in the turtles, but the GnRH responsiveness is related to reproductive status. Furthermore, the results suggest that the desensitizing effects of various forms of GnRH in vivo may be related to their clearance rate.

Effects of subchronic implantation of hydrocortisone phosphate-releasing osmotic pumps on peripheral gonadotropin levels and estradiol feedback to gonadotropin secretion in the cynomolgus monkey.

The purpose of our study was to investigate subchronic effects of moderate hypercortisolemia on serum gonadotropin and estradiol (E2) levels in the primate using a repeated-measures experimental design. Osmotic pumps which released hydrocortisone 21-phosphate (HP) at a dose of 5 mg/day were implanted subcutaneously (s.c.) in each of five cynomolgus monkeys for one menstrual cycle. The pumps were filled with saline for the two control cycles, one of which preceded and one of which followed hormone infusion. Subsequently, osmotic pumps which released HP at a higher dose of 15 mg/day were implanted s.c. in four of the initial five monkeys for the longer period of two menstrual cycles. The pumps were filled with saline for the two additional control cycles, one of which preceded and one of which followed HP infusion at 15 mg/day. The control cycle which followed HP infusion at 5 mg/day and the control cycle which preceded HP infusion at 15 mg/day were separated by at least one menstrual cycle. Administration of HP at the lower dose elevated serum cortisol levels 1.4-fold and decreased serum adrenal androgens to 0.6 of the pretreatment baseline. The higher dose of HP elevated serum cortisol levels 1.7-fold and suppressed serum adrenal androgens to 0.4 of the baseline. In the menstrual cycle following HP infusion serum cortisol levels were depressed to 0.8 and 0.6 of the pretreatment levels after the lower and the higher dose of HP, respectively. Serum levels of adrenal androgens returned to the baseline after the lower dose of HP, but were still suppressed to 0.5 of the baseline after the higher treatment dose. Implantation of pumps which released 5 mg/day of HP did not affect gonadotropin levels in the serum, either in the follicular phase (FP) or the luteal phase (LP) of the menstrual cycle. Serum E2 levels were increased by 77% in the FP during HP infusion at 5 mg/day (p < 0.001), but returned to control values in the LP. Implantation of pumps which released 15 mg/day of HP raised serum luteinizing hormone (LH) levels throughout the two menstrual cycles of treatment, by 111 and 96% in FPs (p < 0.001), and by 84 and 70% in LPs (p < 0.001). Conversely, serum follicle-stimulating hormone (FSH) levels were decreased by 45 and 50% in FPs (p < 0.05), and by 54 and 50% in LPs (p < 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)