Physiological role of putative testicular gonadotrophin releasing hormone (GnRH)

Evidence suggests that exogenous GnRH and agonist analogues have short-term stimulatory effects on rat Leydig cell function - when administered intratesticularly. Since rat Leydig cells possess GnRH receptors and their endogenous ligand has not yet been identified the physiological importance of the observations for testis function is unknown. To address this issue we have determined the consequences of blockade of testis GnRH receptors on Leydig cell function under both normogonadotrophic and hypogonadotrophic stimulation of the testis in vivo. A GnRH antagonist (ANT) was used to achieve receptor blockade but during continuous systemic infusion ANT occupied pituitary GnRH receptors and markedly reduced serum LH, FSH, testosterone, and intratesticular testosterone in adult and 30 d old immature male rats. These results were similar to those obtained by administration of a GnRH antiserum which did not bind to testis GnRH receptors. Thus, blockade of testis GnRH receptors during hypogonadotrophism did not produce additional inhibition of steroidogenesis by Leydig cells. However, direct continuous infusion of ANT into one testis produced greater than 90% occupancy of GnRH receptors while reducing GnRH receptors by only 50% in the contralateral testis. Unilateral intratesticular infusion did not reduce serum LH, FSH, Prolactin or testosterone levels despite 75% occupancy of pituitary GnRH receptors. Thus, both ANT infused and saline infused testes were exposed to the same gonadotrophic stimulants but in the former GnRH-R were essentially non-existent. Compared to the control testis, the ANT infused testis showed a 20-30% reduction in LH, FSH, lactogen receptors and 30-40% fall in testosterone content. Identical results were obtained in adult and 30 d-old male rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Deletion of Otx2 in GnRH neurons results in a mouse model of hypogonadotropic hypogonadism

GnRH is the central regulator of reproductive function responding to central nervous system cues to control gonadotropin synthesis and secretion. GnRH neurons originate in the olfactory placode and migrate to the forebrain, in which they are found in a scattered distribution. Congenital idiopathic hypogonadotropic hypogonadism (CIHH) has been associated with mutations or deletions in a number of genes that participate in the development of GnRH neurons and expression of GnRH. Despite the critical role of GnRH in mammalian reproduction, a comprehensive understanding of the developmental factors that are responsible for regulating the establishment of mature GnRH neurons and the expression of GnRH is lacking. orthodenticle homeobox 2 (OTX2), a homeodomain protein required for the formation of the forebrain, has been shown to be expressed in GnRH neurons, up-regulated during GnRH neuronal development, and responsible for increased GnRH promoter activity in GnRH neuronal cell lines. Interestingly, mutations in Otx2 have been associated with human hypogonadotropic hypogonadism, but the mechanism by which Otx2 mutations cause CIHH is unknown. Here we show that deletion of Otx2 in GnRH neurons results in a significant decrease in GnRH neurons in the hypothalamus, a delay in pubertal onset, abnormal estrous cyclicity, and infertility. Taken together, these data provide in vivo evidence that Otx2 is critical for GnRH expression and reproductive competence.     

Pulsatile gonadotropin-releasing hormone treatment of men with idiopathic hypogonadotropic hypogonadism

OBJECTIVES/METHODS: To induce testicular growth and spermatogenesis, 11 patients with idiopathic hypogonadotropic hypogonadism were treated with long-term subcutaneous pulsatile gonadotropin-releasing hormone (GnRH) administration. Three patients had a history of undescended testes. Patients who did not respond to therapy with a sufficient increase in serum testosterone or spermatogenesis were offered additional injections with hCG or, after discontinuation of GnRH, either combined therapy with hCG and hMG or recombinant FSH. RESULTS: During treatment testicular volume and serum levels of FSH, LH and testosterone increased. Semen analysis revealed the presence of spermatogenesis in 9 of the 11 patients (8 on GnRH alone and in 1 when hCG/hMG was subsequently instituted), and 7 pregnancies have resulted thus far. CONCLUSION: Pulsatile GnRH therapy is a well-tolerated and effective therapy for the induction of spermatogenesis in some men with idiopathic hypogonadotropic hypogonadism. It appears that a significant fraction of them should be treated for a minimum of 1-2 years to maximize testicular growth and achieve spermatogenesis. Cryptorchidism was a negative prognostic factor.     

Selective estrogen receptor modulators to prevent treatment-related osteoporosis

The intended therapeutic effect of gonadotropin-releasing hormone (GnRH) agonists is hypogonadism, which is a leading cause of osteoporosis in men. Consistent with this observation, GnRH agonists decrease bone mineral density and increase fracture risk in men with prostate cancer. GnRH agonists markedly decrease serum levels of both testosterone and estrogen. Estrogens play a central role in homeostasis of the normal male skeleton, and the available evidence suggests that estrogen deficiency rather than testosterone deficiency accounts for the adverse skeletal effects of GnRH agonists. The central role of estrogens in male bone metabolism provides a strong rationale to evaluate selective estrogen receptor modulators for prevention of treatment-related osteoporosis in men with prostate cancer. Preliminary evidence suggests that both raloxifene and toremifene increase bone mineral density in GnRH agonist-treated men. An ongoing pivotal study will evaluate the effects of toremifene on fractures and other complications of GnRH agonists in men with prostate cancer.     

Impaired reproductive behavior by lack of GluR-B containing AMPA receptors but not of NMDA receptors in hypothalamic and septal neurons

The roles of ionotropic glutamate receptors in mammalian reproduction are unknown. We therefore generated mice lacking a major subtype of (S)-alpha-amino-3-hydroxy-5-methyl-isoxazolepropionic acid (AMPA) receptors or all N-methyl-d-aspartate (NMDA) receptors in GnRH neurons and other mainly limbic system neurons, primarily in hypothalamic and septal areas. Male mice without NMDA receptors in these neurons were not impaired in breeding and exhibited similar GnRH secretion as control littermates. However, male mice lacking GluR-B containing AMPA receptors in these neurons were poor breeders and severely impaired in reproductive behaviors such as aggression and mounting. Testis and sperm morphology, testis weight, and serum testosterone levels, as well as GnRH secretion, were unchanged. Contact with female cage bedding failed to elicit male sexual behavior in these mice, unlike in control male littermates. Their female counterparts had unchanged ovarian morphology, had bred successfully, and had normal litter sizes but exhibited pronounced impairments in maternal behaviors such as pup retrieval and maternal aggression. Our results suggest that NMDA receptors and GluR-B containing AMPA receptors are not essential for fertility, but that GluR-B containing AMPA receptors are essential for male and female reproduction-related behaviors, perhaps by mediating responses to pheromones or odorants.     

Les hypogonadismes hypogonadotrophiques congénitaux masculins, quelles données récentes ?

Congenital hypogonadotropic hypogonadism (CHH) is a very heterogeneous group of disorders resulting from a deficiency of pituitary gonadotropin secretion that is related to defective migration of GnRH neurons or dysfunction of pituitary or hypothalamic system. Gonadotropin deficiency remains a rare cause of hypogonadism; its prevalence is not definitely established and is thought to be about 1/5,000. It is responsible for clinical symptoms that are related to low testosterone levels. The classification of CHH which was previously based on presence of or lack of anosmia has been enriched in the last two decades by the discovery of many genes involved. This allowed a better understanding of CHH and led to new approaches regarding genetic counselling.     

Mechanism of Testosterone Deficiency in the Transgenic Sickle Cell Mouse

Testosterone deficiency is associated with sickle cell disease (SCD), but its underlying mechanism is not known. We investigated the possible occurrence and mechanism of testosterone deficiency in a mouse model of human SCD. Transgenic sickle male mice (Sickle) exhibited decreased serum and intratesticular testosterone and increased luteinizing hormone (LH) levels compared with wild type (WT) mice, indicating primary hypogonadism in Sickle mice. LH-, dbcAMP-, and pregnenolone- (but not 22-hydroxycholesterol)- stimulated testosterone production by Leydig cells isolated from the Sickle mouse testis was decreased compared to that of WT mice, implying defective Leydig cell steroidogenesis. There also was reduced protein expression of steroidogenic acute regulatory protein (STAR), but not cholesterol side-chain cleavage enzyme (P450scc), in the Sickle mouse testis. These data suggest that the capacity of P450scc to support testosterone production may be limited by the supply of cholesterol to the mitochondria in Sickle mice. The sickle mouse testis exhibited upregulated NADPH oxidase subunit gp91phox and increased oxidative stress, measured as 4-hydroxy-2-nonenal, and unchanged protein expression of an antioxidant glutathione peroxidase-1. Mice heterozygous for the human sickle globin (Hemi) exhibited intermediate hypogonadal changes between those of WT and Sickle mice. These results demonstrate that testosterone deficiency occurs in Sickle mice, mimicking the human condition. The defects in the Leydig cell steroidogenic pathway in Sickle mice, mainly due to reduced availability of cholesterol for testosterone production, may be related to NADPH oxidase-derived oxidative stress. Our findings suggest that targeting testicular oxidative stress or steroidogenesis mechanisms in SCD offers a potential treatment for improving phenotypic changes associated with testosterone deficiency in this disease.     

Effects of chronic smoking on testosterone metabolism in dogs

The effects of long-term cigarette smoking on androgen hydroxylases and peripheral hormones were studied in male beagles. In the testis, chronic smoking of high nicotine/tar cigarettes was associated with decreased activity of the 7 alpha-hydroxylase active on testosterone (68% of control, P less than 0.05). Testicular 6 beta and 16 alpha-hydroxylases were not altered. The hepatic androgen 6 beta-hydroxylase activity in control animals was approximately 6 times the testis levels and was stimulated markedly by smoking. This increase ranged from 221% in the low nicotine/tar group (P less than 0.02) to 304% in the high nicotine/tar group (P less than 0.006). Serum testosterone levels were reduced to 54% of control (P less than 0.02) and prostate size to 44% (P less than 0.001) of control with heavy smoking. Serum LH levels were elevated with smoking. These results suggest that chronic cigarette smoking increased hepatic metabolism of testosterone. In addition, serum testosterone levels and prostate size decreased and LH levels increased. Whether the hepatic and the endocrine effects are causally related cannot be determined from this preliminary study.     

Effect of anti-estrogen and anti-progesterone on spermatogenesis,testosterone production and expression of steroidogenic enzyme genes in adult male rats

The present study was planned to investigate the anti-spermatogenic and anti-steroidogenic effects of Clomiphene Citrate (CC) an anti-estrogen and Mifepristone (MT) an anti-progesterone in the testis of male rats. Following the oral administration of 1.0 mg and 5.0 mg/kg b.w/day of each for the duration of 30 and 60 days, quantitation of spermatogenesis, RIA for serum and intra-testicular testosterone levels, western blotting and RT-PCR for expression of StAR, 3β-HSD and P450arom enzymes in the testis was done. Clomiphene Citrate at 5.0 mg/kg b.w/day for 60 days significantly reduced testosterone (T) levels however the effect was not significant with the lower doses. Reproductive parameters in animals treated by Mifepristone remained mostly unaffected, however, a significant decline in testosterone levels and altered expression of selected genes was observed in 5.0 mg for the 30d treatment group. Clomiphene Citrate at higher doses affected the weights of the testis and secondary sex organs. Seminiferous tubules revealed hypo-spermatogenesis with a significant decrease in the number of maturing germ cells and a reduction in tubular diameter. Attenuation in serum testosterone was associated with the downregulation of expression in StAR, 3β-HSD, and P450arom mRNA and protein levels in the testis even after 30 d of CC administration. The results indicate that the anti-estrogen (Clomiphene Citrate) but not anti-progesterone (Mifepristone) induces hypo-spermatogenesis in rats which are associated with a downregulation of expression of two of the steroidogenic enzymes, 3β-HSD and P450arom mRNA and StAR protein.     

Hypothalamic hypogonadism in congenital adrenal hypoplasia

Congenital adrenal hypoplasia (CAHP) in its X-linked form is associated with hypogonadotropic hypogonadism (HH). A 23 year old man with this disorder received substitution therapy with gluco- and mineralocorticoids starting one week after birth and, recently, pulsatile subcutaneous GnRH treatment via a miniature infusion pump with stepwise increasing doses from 50 to 200 ng/kg body weight/2 hours for a total of 394 days. Testosterone levels increased from prepubertal levels to 409 ng/dl after 2 weeks and to 626 ng/dl after 3 months of treatment. The results of pulsatile GnRH therapy in our patient prove the hypogonadotropic hypogonadism to be of hypothalamic origin. Pulsatile GnRH substitution is a successful therapeutic regimen in patients with CAHP leading to pituitary and gonadal maturation.     

Normal sequence of the gonadotropin-releasing hormone gene in patients with idiopathic hypogonadotropic hypogonadism.

Idiopathic hypogonadotropic hypogonadism (IHH) results from absent or greatly diminished secretion of GnRH. Defects in the GnRH gene have been identified in an animal model of IHH and have been hypothesized as a possible basis for GnRH deficiency in humans. In this study, we used the polymerase chain reaction to clone and sequence the coding regions, promoter, and 3' untranslated tract of the GnRH genes from both alleles of four unrelated patients with IHH. One of the patients studied is a member of a kindred in which X-linked inheritance has been excluded by father-to-son transmission of the disease. No DNA sequence mutations were found. We conclude that most cases of IHH in humans do not involve mutations in the GnRH gene and are presumably caused by mutations at one or more other genetic loci that are required for normal function of GnRH-producing neurons.     

A protein family immunorelated to a sperm-binding protein and its regulation in human semen

In human seminal plasma a family of proteins that is immunologically related to the RSV-IV protein secreted under androgen control from the epithelium of the rat seminal vesicles was detected by a radioimmunoassay. Evidence for the origin of these antigens from human seminal vesicle is presented. Quantitative measurements of this family of proteins were performed in men with low levels of serum testosterone (idiopathic hypogonadotropic hypogonadism) and in individuals having serum testosterone in the normal range of values but carrying sex chromosome aberrations (Klinefelter's syndrome). In the first case we have found a marked decrease in the total amount of the RSV-IV-related proteins. An increase of about 40% in the total amount of these antigens was obtained in these subjects by gonadotropin treatment. A decreased amount of these proteins was also detected in the subjects affected by Klinefelter's syndrome. The possibility that some factor(s) under genetic control is involved, in addition to testosterone, in the regulation of this family of proteins is discussed.     

Déficit Androgénique Lié à l’Age

In contrast with the abrupt cessation of ovarian function at menopause in women, alteration of testicular functions in aging males is partial and progressive. Several cross-sectional studies have demonstrated an age-related decrease of testosterone levels in men. This decrease has also been observed when only men in good health are included in such studies. This age-related decline of testosterone levels has been recently confirmed by a longitudinal study including a large number of subjects. The progressive decline begins early, from the late thirties, and continues at a constant rate throughout the subject’s lifetime. Since SHBG increases with age, free testosterone and non-SHBG-bound testosterone (referred to as bioavailable testosterone) decrease more markedly than total testosterone. As variations of SHBG levels (mainly a decrease in obese and/or insulin-resistant subjects) are often encountered in clinical practice and as it is difficult to reliably measure free testosterone, bioavailable testosterone appears to be the better index to diagnose androgen deficiency in the aging male. Elevation of basal LH levels, decrease of hCG-induced testosterone levels and reduction of Leydig cell number demonstrate the testicular origin of hypogonadism. However, gonadotropic function is also relatively altered with aging. As a result of this alteration of gonadotropic function, LH level is not a reliable index of hypogonadism in the aging male. None of the androgen-dependent functions that are altered with aging, i.e. libido, erectile function, sense of well-being, muscle mass, muscle strength, fat mass, bone mass, etc., are exclusively controlled by androgens. In clinical practice, the indication for androgen replacement therapy must therefore be based on a combination of clinical symptoms and a reduction of bioavailable testosterone below a certain cut-off value, indicating “significant” hypogonadism.     

Expression and function of gonadotropin-releasing hormone (GnRH) receptor in human olfactory GnRH-secreting neurons: an autocrine GnRH loop underlies neuronal migration

Olfactory neurons and gonadotropin-releasing hormone (GnRH) neurons share a common origin during organogenesis. Kallmann's syndrome, clinically characterized by anosmia and hypogonadotropic hypogonadism, is due to an abnormality in the migration of olfactory and GnRH neurons. We recently characterized the human FNC-B4 cell line, which retains properties present in vivo in both olfactory and GnRH neurons. In this study, we found that FNC-B4 neurons expressed GnRH receptor and responded to GnRH with time- and dose-dependent increases in GnRH gene expression and protein release (up to 5-fold). In addition, GnRH and its analogs stimulated cAMP production and calcium mobilization, although at different biological thresholds (nanomolar for cAMP and micromolar concentrations for calcium). We also observed that GnRH triggered axon growth, actin cytoskeleton remodeling, and a dose-dependent increase in migration (up to 3-4-fold), whereas it down-regulated nestin expression. All these effects were blocked by a specific GnRH receptor antagonist, cetrorelix. We suggest that GnRH, secreted by olfactory neuroblasts, acts in an autocrine pattern to promote differentiation and migration of those cells that diverge from the olfactory sensory lineage and are committed to becoming GnRH neurons.     

Effect of continuous infusion of a low dose of GnRH antagonist on serum LH and testosterone concentrations, spermatogenesis and semen quality in the rhesus monkey (Macaca mulatta)

Treatment of 4 adult male rhesus monkeys for 8-12 months with 100-400 micrograms of a GnRH antagonist/day by means of using osmotic minipumps led to suppressed serum concentrations of LH and testosterone followed by various degrees of recovery toward pretreatment values. The serum LH response to a challenge of native GnRH was reduced by 30-75% during antagonist treatment. The serum testosterone response to GnRH was exaggerated above the response in the pretreatment period, suggesting hypersensitivity of the testis to gonadotrophin. Antagonist administration under these conditions did not alter body weight or abolish ejaculatory response. Antagonist infusion caused a 96% decrease in sperm counts. Spermatozoa recovered during the final month of antagonist treatment showed a reduced ability to penetrate denuded hamster ova. Testicular biopsies performed at the end of antagonist treatment revealed persistent spermatogenesis. However, the cellularity of the seminiferous tubules was decreased below that of pretreatment biopsies. The results of this study suggest that the amount of testosterone needed to maintain normal spermatogenesis is greater than that needed to maintain electroejaculatory response in monkeys.     

大鼠急性运动对血清睾酮、睾丸组织丙二醛和超氧化物歧化酶的影响

本实验分别在大鼠衰竭跑后即刻、0.5、1、3及24h同时检测了血清睾酮(T)、黄体生成素、睾丸组织脂质过氧化物丙二醛和超氧化物歧化酶。结果表明,大鼠衰竭跑后恢复30min时,伴随着睾丸组织丙二醛含量的明显升高及超氧化物歧化酶活性的显著降低,血清T水平也明显降低。提示,长时间衰竭跑后血清T浓度的降低很可能与缺血-再灌引起睾丸组织氧自由基剧增及脂质过氧化损伤,从而降低了酶的活性和抑制了T的合成有关。氧自由基清除剂能减轻和预防该损伤,并能有效地防止运动后血清T的降低。     

Effect of casein diet on gonadotropin releasing hormone antagonist induced changes in adrenal gonadal functions in male rats

Adult male rats received daily injections (sc) of gonadotropin releasing hormone antagonist (0.2 mg/kg(-1) x day(-1)) for 21 days when they were sacrificed on day 22, adrenal weight, adrenal A5-3beta (delta 5-3beta) hydroxysteroid dehydrogenase (Delta5-3beta-HSD) activity and serum level of corticosterone were increased significantly while testicular 17beta (17beta) hydroxysteroid dehydrogenase (17beta-HSD) activity and serum level of testosterone and spermatogenesis were decreased in the rats fed on 5% casein diet. GnRH antagonist treated rats fed on 20% casein diet, resulted significant decrease in adrenal weight, serum corticosterone and adrenal A5-3beta-HSD activity while testicular 17beta-HSD activity serum testosterone levels and the weights of sex organs were increased with respect to anti GnRH treated rats fed on 5% casein diet. But the GnRH antagonist treated rats fed on 20% casein diet showed decreased spermatogenesis quantitatively and sperm count appeared similar to anti GnRH treated rats fed on 5% casein diet. These results indicate that high casein diet protects adrenocortical activity and stimulates testosterone synthesis without effecting spermatogenic arrest in GnRH antagonist treated rats. It may be concluded that GnRH antagonist in presence of high milk protein diet may be considered to be a suitable antihormone in the development of an ideal male contraceptive.     

Pituitary and gonadal function in hypogonadotrophic hypogonadal (hpg) mice bearing hypothalamic implants

GnRH receptor values are 30-50% of normal in pituitaries of hpg male mice, and testicular LH receptors only 8% of normal (160.4 +/- 17.6 and 2013 +/- 208.1 fmol/testis respectively). In male hpg mice bearing fetal preoptic area (POA) hypothalamic implants for 10 days there was no change in pituitary GnRH receptors, pituitary gonadotrophin content, or seminal vesicle weight. However, testicular weights and LH receptors were doubled in 4/10 mice and 2 had increased serum FSH levels. Between 26 and 40 days after implantation pituitary GnRH receptors and pituitary LH increased to normal male levels, although at 40 days serum and pituitary FSH concentrations had reached only 50% of normal values. Testicular and seminal vesicle weights increased more than 10-fold by 40 days after implantation and LH receptors to 70% of normal. In hpg female mice bearing hypothalamic implants for 30-256 days pituitary gonadotrophin concentrations were normal, even though GnRH receptors reached only 60% of normal values (6.18 +/- 0.4 and 9.8 +/- 0.4 fmol/pituitary respectively). Serum FSH was substantially increased from values of less than 30 ng/ml in hpg mice to within the normal female range in hypothalamic implant recipients. Ovarian and uterine weights increased after hypothalamic grafting from only 4-5% to over 74% of normal values. LH receptors increased from 6.5 +/- 1.3 fmol/ovary for hpg mice to 566.9 +/- 39.2 fmol/ovary for implant recipients. Vaginal opening occurred about 23 days after implantation and these animals displayed prolonged periods of oestrus.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of steroid milieu on gonadotropin-releasing hormone-1 neuron firing pattern and luteinizing hormone levels in male mice

GnRH neuronal function is regulated by gonadal hormone feedback. In males, testosterone can act directly or be converted to either dihydrotestosterone (DHT) or estradiol (E2). We examined central steroid feedback by recording firing of green fluorescent protein (GFP)-identified GnRH neurons in brain slices from male mice that were intact, castrated, or castrated and treated with implants containing DHT, E2, or E2 + DHT. Castration increased LH levels. DHT or E2 alone partially suppressed LH, whereas E2 + DHT reduced LH to intact levels. Despite the inhibitory actions on LH, the combination of E2 + DHT increased GnRH neuron activity relative to other treatments, reflected in mean firing rate, amplitude of peaks in firing rate, and area under the curve of firing rate vs. time. Cluster8 was used to identify peaks in firing activity that may be correlated with hormone release. Castration increased the frequency of peaks in firing rate. Treatment with DHT failed to reduce frequency of these peaks. In contrast, treatment with E2 reduced peak frequency to intact levels. The frequency of peaks in firing rate was intermediate in animals treated with E2 + DHT, perhaps suggesting the activating effects of this combination partially counteracts the inhibitory actions of E2. These data indicate that E2 mediates central negative feedback in males primarily by affecting the pattern of GnRH neuron activity, and that androgens combined with estrogens have a central activating effect on GnRH neurons. The negative feedback induced by E2 + DHT to restore LH to intact levels may mask an excitatory central effect of this combination.     

Induction of puberty in a patient with hypogonadotropic hypogonadism: effect of sequentially applied hCG and pulsatile GnRH administration

Pulsatile substitution with GnRH appears to be the therapy of choice in patients with Kallmann's syndrome, a well defined type of hypogonadotropic hypogonadism. We tried to simplify the treatment and to limit the subcutaneous GnRH therapy to the period absolutely necessary to induce spermatogenesis. Therefore we applied in sequence first hCG to stimulate testicular growth and second pulsatile GnRH application to induce spermatogenesis. We herein report that with this mode of therapy testicular growth from infantile to adult size and normal spermatogenesis could be achieved. We conclude that pulsatile GnRH application is a new effective therapy of hypogonadotropic hypogonadism which can be simplified considerably by pretreatment with hCG.