Circulating Gonadotropin Levels Research Articles

PUBLIC HEALTH CONCERNS OF ENVIRONMENTAL EXPOSURE CONNECTED WITH FEMALE INFERTILITY

This study reviewed recent articles on prevalence and risk exposure of pollutants connected with female sterility. Occupational and regular exposure to mixtures of metals and other chemicals induce oxidative stress which further induce hormonal imbalance and result to damage cell membrane, cell apoptosis, damage proteins, lipid and nucleic acid, reduced growth and development of oocytes, increase mRNA in anterior pituitary, reduced follicular development and growth, poor oocytes quality, poor reproductive outcome, damage DNA, embryo fragmentation, implantation failure, abortion, ovarian aging and steroidogenesis, folliculogenesis, impaired placentation, congenital abnormalities and formation of numerous developmental abnormalities. This study revealed an association between environmental contaminants and unexplained infertility, women with unexplained infertility have decreased ovarian sensitivity to gonadotropins, resulting in higher circulating gonadotropin levels, including higher mean serum follicle stimulating hormone (FSH) and luteinizing hormone (LH) levels. Asides from environmental contaminant effects on female infertility, exposure to environmental contaminants could also increase the risk of suffering spontaneous abortion, stillbirths, premature delivery, gestational diabetes mellitus, pregnancy hypertension, preeclampsia, premature rupture of membranes, intrauterine growth restriction, low birth weight, harm the growing baby leading to foetal abnormality and congenital disabilities To manage female infertility, risk exposures to heavy metals should be reduced to minimal or zero level.

Effect of timing of restricted feeding on sexual maturation in female yellowtail, Seriola quinqueradiata

In aquaculture of species with a large body size such as tuna and yellowtail, a major problem still is that broodstock management for egg collection requires high feeding cost and labor. In order to reduce feeding costs, development of restricted feeding techniques without affecting the reproductive performance may be useful. To gain a better understanding of reproductive responses to food supply, we examined the effect of restricted feeding during the previtellogenic and vitellogenic phases on sexual maturation in female yellowtail, Seriola quinqueradiata. Restricted feeding during the vitellogenic phase tended to reduce ovary weight relative to normally fed controls at the end of the experiment. Histological observations revealed that both restricted feeding regimes do not affect the percentage of atretic follicles as compared to the control group. Nevertheless, the mean diameter of the most advanced follicles of the females subjected to restricted feeding during the vitellogenic phase was significantly smaller to normally fed controls. These results suggest that reduced food intake during the vitellogenic phase is likely to delay oocyte growth, and lead to low ovarian weight. Endocrine analyses showed that restricted feeding during the vitellogenic phase reduced plasma 17β-estradiol levels, but not plasma and pituitary gene expression levels of gonadotropins (follicle-stimulating hormone and luteinizing hormone) at the end of the experiment. Transcripts for ovarian steroidogenesis-related genes, such as P450 side-chain cleavage (cyp11a1) and 3β-hydroxysteroid dehydrogenase (hsd3b) after food restriction during the vitellogenic phase tended to be high. Therefore, the effects of restricted feeding on reproduction would not be mediated by alterations in circulating gonadotropin levels, but rather through direct effects on the ovarian steroid production in yellowtail females.

Circulating gonadotropins and ovarian adiponectin system are modulated by acupuncture independently of sex steroid or β-adrenergic action in a female hyperandrogenic rat model of polycystic ovary syndrome

Acupuncture with combined manual and low-frequency electrical stimulation, or electroacupuncture (EA), reduces endocrine and reproductive dysfunction in women with polycystic ovary syndrome (PCOS), likely by modulating sympathetic nerve activity or sex steroid synthesis. To test this hypothesis, we induced PCOS in rats by prepubertal implantation of continuous-release letrozole pellets (200 µg/day) or vehicle. Six weeks later, rats were treated for 5–6 weeks with low-frequency EA 5 days/week, subcutaneous injection of 17β-estradiol (2.0 µg) every fourth day, or a β-adrenergic blocker (propranolol hydrochloride, 0.1 mg/kg) 5 days/week. Letrozole controls were handled without needle insertion or injected with sesame oil every fourth day. Estrous cyclicity, ovarian morphology, sex steroids, gonadotropins, insulin-like growth factor I, bone mineral density, and gene and protein expression in ovarian tissue were measured. Low-frequency EA induced estrous-cycle changes, decreased high levels of circulating luteinizing hormone (LH) and the LH/follicle-stimulating hormone (FSH) ratio, decreased high ovarian gene expression of adiponectin receptor 2, and increased expression of adiponectin receptor 2 protein and phosphorylation of ERK1/2. EA also increased cortical bone mineral density. Propranolol decreased ovarian expression of Foxo3, Srd5a1, and Hif1a. Estradiol decreased circulating LH, induced estrous cycle changes, and decreased ovarian expression of Adipor1, Foxo3, and Pik3r1. Further, total bone mineral density was higher in the letrozole–estradiol group. Thus, EA modulates the circulating gonadotropin levels independently of sex steroids or β-adrenergic action and affects the expression of ovarian adiponectin system.

Androgens directly stimulate spermatogonial differentiation in juvenile Atlantic salmon (Salmo salar)

We studied the effects of androgens on early stages of spermatogenesis along with androgen receptor binding characteristics and the expression of selected testicular and pituitary genes. To this end, immature Atlantic salmon postsmolts received testosterone (T), adrenosterone (OA, which is converted in vivo into 11-ketotestosterone, 11-KT) or a combination of the two androgens (T+OA). Treatment with OA and T elevated the plasma levels of 11-KT and T, respectively, and co-injection of OA with T lead to high 11-KT levels but prevented plasma T levels to reach the levels observed after injecting T alone. Clear stimulatory effects were recorded as regards pituitary lhb and gnrhr4 transcript levels in fish receiving T, and to a lesser extent in fish receiving OA (but for the lhb transcript only). The two androgen receptors (Ara1 and Ara2) we cloned bound T and 11-KT and responded to these androgens in a similar way. Both androgens down-regulated testicular amh and increased igf3 transcript levels after 1week of treatment, but effects on growth factor gene expression required sustained androgen stimulation and faded out in the groups with the decreasing T plasma levels. In fish exhibiting a sustained elevation of 11-KT plasma levels (OA and T+OA groups) for 2weeks, the number of differentiating spermatogonia had increased while the number of undifferentiated spermatogonia decreased. Previous work showed that circulating gonadotropin levels did not increase following androgen treatments of gonad-intact immature male salmonids. Taken together, androgen treatment of immature males modulated testicular growth factor expression that, when sustained for 2weeks, stimulated differentiation, but not self-renewal, of undifferentiated type A spermatogonia.

In Vivo Actions of the Sertoli Cell Glucocorticoid Receptor

We determined the functional role of the Sertoli cell glucocorticoid receptor (GR) in vivo using a transgenic Cre-loxP approach to conditionally disrupt GR expression. Sertoli cell GR knockout (SCGRKO) was shown by absent Sertoli cell-specific GR immunolocalization and reduced levels of glucocorticoid-responsive Stc1 and Tsc22d3 mRNA in SCGRKO relative to control testes. Adult SCGRKO testes exhibited distinct morphological changes, including reduced seminiferous tubular lumen formation, decreased total Sertoli cell numbers, and parallel reductions in meiotic spermatocyte and postmeiotic spermatid numbers. Conversely, tubular diameter was increased and testis size was normal in SCGRKO males. Decreased serum FSH and testicular Fshr mRNA levels were consistent with reduced Sertoli cell number. Adult SCGRKO testes also displayed atypical germ cells and interstitial focal accumulations of hypertrophic lipid-laden, immature-like Leydig cells. Circulating LH, and testicular Lhr mRNA, testosterone, dihydrotestosterone, and 3α/3β-diol levels were all reduced in mature SCGRKO mice, whereas serum testosterone and dihydrotestosterone levels remained normal. Moreover, Sertoli cell GR disruption caused differential changes to steroidogenic enzyme transcripts, with down-regulated testicular Cyp11a1 contrasting with up-regulated Hsd17b3 expression. Reduced SCGRKO testicular expression of Hsd11b2, encoding an enzyme for corticosterone inactivation, supports a dynamic coupling between Hsd11b and androgen production. Our novel SCGRKO model has revealed that Sertoli cell-mediated GR actions support normal testicular function. Sertoli cell GR is required to maintain normal testicular Sertoli/germ cell numbers and circulating gonadotropin levels, as well as optimal Leydig cell maturation and steroidogenesis, providing new insight into gluocorticoid-mediated impact on male reproduction.

Circulating kisspeptin and pituitary adenylate cyclase-activating polypeptide (PACAP) do not correlate with gonadotropin serum levels

Kisspeptins are known to be the principle regulators of the hypothalamic-pituitary gonadal (HPG) axis. In addition, the role of pituitary adenylate cyclase-activating polypeptide (PACAP) in the regulation of pituitary gonadotropins has been elucidated. We measured plasma concentrations of kisspeptin and PACAP and determined whether the levels of these peptides varied in proportion to circulating gonadotropin levels. Plasma luteinizing hormone (LH) levels were higher in postmenopausal women and in patients with premature ovarian failure (POF) and lower in patients with idiopathic hypogonadotropic hypogonadism (IHH) compared with the LH level in normally menstruating women. Similarly, serum follicle-stimulating hormone levels were higher in postmenopausal women and in patients with POF but lower in pregnant women and patients with IHH compared with normally menstruating women. Plasma levels of kisspeptins were significantly higher in pregnant women compared with normally menstruating women. However, no significant differences were observed in postmenopausal women, patients with POF, and patients with IHH. On the other hand, plasma levels of PACAP were significantly lower in pregnant women, patients with POF, and in IHH patients when compared with normally menstruating women. No significant differences were observed in PACAP concentration between postmenopausal women and in normally menstruating women. Our observations suggest that the serum levels of kisspeptins and PACAP did not correlate with variations in serum gonadotropin levels.

Microdose gonadotropin-releasing hormone agonist in the absence of exogenous gonadotropins is not sufficient to induce multiple follicle development

Because the effectiveness of the "microdose flare" stimulation protocol often is attributed to the dramatic endogenous gonadotropin release induced by the GnRH agonist, the aim of this study was to determine whether use of microdose GnRH agonist alone could induce multiple ovarian follicle development in normal responders. Based on these data, the duration of gonadotropin rise is approximately 24 to 48 hours and is too brief to sustain continued multiple follicle growth.

Morphological restoration of gonadotrope population by thymulin gene therapy in nude mice.

The integrity of the thymus during the first week of life is necessary for a proper maturation of the pituitary-gonadal axis as revealed by the significantly reduced levels of circulating gonadotropins in congenitally athymic (nude) mice. In the present work we studied the impact of athymia and the effect of neonatal thymulin gene therapy on the pituitaries of adult nude mice. Also circulating thymulin and gonadotropin levels were evaluated. We used an adenoviral vector expressing a synthetic gene for the thymic peptide thymulin (metFTS) termed RAd-FTS. On postnatal day 1, each experimental heterozygous (nu/+) and homozygous (nu/nu) pup of both sexes received a single bilateral i.m. injection of RAd-FTS or RAd-GFP/TK, a control vector expressing green fluorescent protein. On postnatal days 51-52, mice were bled and sacrificed, their pituitaries were immediately dissected, fixed and immunostained. Morphometry was performed by means of an image analysis system. The following parameters were calculated: volume density (VD: cell area/reference area), cell density (CD: number of cells/reference area), and cell size (expressed in microm(2)). Serum thymulin levels were measured by a bioassay and gonadotropin levels were assayed by RIA. It was observed that neonatal thymulin gene therapy in the athymic mice restored their serum thymulin levels and prevented the reduction in circulating gonadotropin levels. The histometrical analysis revealed that the treatment prevented the reduction in gonadotrope CD and the VD in athymic mice. Our data suggest that thymulin gene therapy may be an effective strategy to approach reproductive deficits associated with endocrine thymus dysfunction.

Long term effects of dibromochloropropane (DBCP) on male rats' reproductive system.

Adult male rats were injected s.c. once a week for 3 weeks with DBCP, 20 mg/kg B.W. Animals were sacrificed 5, 9, 13, 17, 25 and 50 weeks after last injection. Body weight was recorded once a week. Prior to sacrifice each male was presented with proestral females in order to determine the male's mating behaviour and fertility. Testes were removed, weighed and taken for standard histological examination. DBCP treatment caused a reduction of body weight which reverted back to control levels some 17 weeks post injection. Testes weights were reduced and remained low despite the recovery of body weight. Generally, all males showed normal mating behaviour but most of them were infertile. Testicular histology showed a correlation between decreasing testicular weight and increasing percentage of degenerated seminiferous tubules, which was on the other hand correlated with decreasing tubular diameter. Serum levels of FSH and LH were significantly increased in the infertile DBCP treated males while values for the fertile ones were similar to those of controls. There were no differences in serum testosterone levels between DBCP treated and control animals. It is concluded that in DBCP treated rats testicular degenerative damages are associated with increased circulating gonadotrophin levels and with normal testosterone levels. Although mating behaviour is unaffected fertility is depressed and does not recover for at least 50 weeks post injection. It is suggested that DBCP treatment affects mainly the activity of the Sertoli cells while the Leydig cells are affected to a much lesser degree.

Relationship between follicle growth and circulating gonadotrophin levels during postnatal development of sheep

This study investigates the number and size of ovarian antral follicles in relation to plasma follicle stimulating hormones (FSH) and luteinizing hormone (LH) concentrations from birth to 26 weeks of age in ewe lambs of the Ouled Djellel breed, a non-seasonal breed of sheep. Plasma was collected from 10 ewe lambs at 14 sampling times (Week 0, i.e. <24 h, Week 1 and every two weeks from Week 4 to Week 26, inclusive). At each of these stages, four ewe lambs were slaughtered, the ovaries recovered and weighed, and the number and size of the follicles determined from histological examination. The pattern for plasma FSH showed a peak at Week 10, a smaller peak at Week 18 and a very small peak at Week 24. The pattern for LH was similar until Week 24 when the largest peak occurred. Paired ovarian weight increased rapidly from birth to four weeks and then more slowly to 10 weeks, followed by a decline at 12 weeks and a gradual increase from 14 to 24 weeks of age. The number and total diameter of follicles ≥3 mm in diameter showed similar patterns of development – rising gradually from birth to Week 14, falling to Week 16 and then rising more rapidly to a peak at Week 24. Maximum follicle diameter declined from birth to Week 1, then rose rapidly to Week 4, followed by a more gradual rise to Week 14 and, thereafter, a more rapid increase to a peak of 7.23 ± 0.16 mm at 24 weeks old. The number of follicles (<3 mm diameter) increased rapidly from birth to Week 10 and then declined to values similar to those at Weeks 1 and 4. First behavioural oestrus was observed at Week 24 and a corpus luteum was present on the ovary of one lamb at Week 24 and two lambs at Week 26. It was concluded that two or three peaks in plasma FSH and LH levels precede puberty and first ovulation in Ouled Djellel ewe lambs, and first ovulation occurred at 24–26 weeks of age. The increase in follicle number and size generally reflected the pattern of plasma FSH and LH levels.

Thymulin gene therapy prevents the reduction in circulating gonadotropins induced by thymulin deficiency in mice

Integrity of the thymus during perinatal life is necessary for a proper maturation of the pituitary-gonadal axis in mice and other mammalian species. Thus congenitally athymic (nude) female mice show significantly reduced levels of circulating gonadotropins, a fact that seems to be causally related to a number of reproductive derangements described in these mutants. Interestingly, a number of in vitro studies suggest that the thymic peptide thymulin may be involved in thymus-pituitary communication. To determine the consequences of low serum thymulin in otherwise normal animals, we induced short (8 days)- and long (33 days)-term thymulin deficiency in C57BL/6 mice by neonatally injecting (intraperitoneally) an anti-thymulin serum and assessed their circulating gonadotropin levels at puberty and thereafter. Control mice received an irrelevant antiserum. Gonadotropins were measured by radioimmunoassay and thymulin by bioassay. Both long- and short-term serum thymulin immunoneutralization resulted in a significant reduction in the serum levels of gonadotropins at 33 and 45 days of age. Subsequently, we injected (intramuscularly) an adenoviral vector harboring a synthetic DNA sequence (5'-ATGCAAGCCAAATCTCAAGGTGGATCCAACTAGTAG-3') encoding a biologically active analog of thymulin, methionine-FTS, in newborn nude mice (which are thymulin deficient) and measured circulating gonadotropin levels when the animals reached 52 days of age. It was observed that neonatal thymulin gene therapy in the athymic mice restored their serum thymulin levels and prevented the reduction in circulating gonadotropin levels that typically emerges in these mutants after puberty. Our results indicate that thymulin plays a relevant physiological role in the thymus-pituitary-gonadal axis.

Pituitary progesterone receptor expression and plasma gonadotrophin concentrations in the reproductively dysfunctional mutant restricted ovulator chicken

Female mutant restricted ovulator (RO) chickens of the White Leghorn strain carry a naturally occurring single nucleotide mutation in the very low density lipoprotein receptor (VLDLR) gene. Due to this mutation, RO hens fail to express a functional VLDLR protein on the oocyte membrane, which results in an impaired uptake of circulating yolk precursor macromolecules. Mutant RO hens subsequently develop hyperlipidemia and generally fail to lay eggs due to follicular atresia. Since RO hens also reportedly have three-fold higher basal plasma estrogen concentrations, combined with four-fold lower levels of circulating progesterone as compared to wild-type (WT) hens, we hypothesized that RO hens would have an increased abundance of pituitary progesterone receptor (PR) mRNA and PR isoforms A and B as well as alterations in circulating gonadotrophin levels. Quantitative PCR assays revealed significantly greater ( P ≤ 0.05) pituitary PR mRNA abundance in RO hens as compared to WT hens. Similarly, pituitary PR isoforms A and B quantities were significantly greater ( P ≤ 0.05) in the RO hens compared to WT hens. In addition, mutant RO hens had significantly greater plasma concentrations of luteinizing hormone, follicle stimulating hormone, estrone, and estradiol, but lower circulating progesterone levels. Collectively, elevated circulating estrogen and/or decreased progesterone levels may have contributed to the upregulation of PR mRNA and PR isoforms A and B in the RO hen pituitary gland. Lastly, in order to gain a more complete understanding of why RO hens are reproductively dysfunctional, a model is proposed that links humoral and ovarian factors to observed and putative changes in the hypothalamic-pituitary axis.

The Serotonin Type 3&lt;SUB&gt;A&lt;/SUB&gt; Receptor Facilitates Luteinizing Hormone Release and LHβ Promoter Activity in Immortalized Pituitary Gonadotropes

The 5-hydroxytryptamine type 3A receptor (5-HT3AR) is a ligand-gated cation channel activated by serotonin. This receptor is expressed throughout the nervous system as well as in the pituitary gland. Although it has been documented that the 5-HT3AR modulates exocytosis in neurons, its role in the pituitary gland has not been determined. Previous research has shown that the 5-HT3AR modulates circulating gonadotropin levels in vivo. It is unclear, however, if its activation in the pituitary gland mediates these effects or if receptors elsewhere in the hypothalamus-pituitary-gondal axis are responsible. To investigate the potential for the 5-HT3AR to modulate gonadotropin release from pituitary gonadotropes, the gonadotrope-derived LbetaT2 cell line was used as a model system and radioimmunoassays were employed to investigate how 5-HT3AR activation influences luteinizing hormone (LH) release. Our studies demonstrate that gonadotropin releasing hormone (GnRH)-stimulated LH release was decreased by the 5-HT3AR-specific antagonist MDL 72222 in a concentration-dependent manner. In addition, it was found that overexpressing the 5-HT3AR in LbetaT2 cells enhanced both basal and GnRH-stimulated LH release and also increased LHbeta gene promoter activity. These results suggest that the 5-HT3AR may participate in the hypothalamus-pituitary-gonadal axis at the level of the pituitary gonadotrope to mediate pituitary hormone release.

Evidence for a causal role of low energy availability in the induction of menstrual cycle disturbances during strenuous exercise training.

Cross-sectional and short-term prospective studies in humans support the concept that low energy availability, and not other factors associated with exercise, causes the development of exercise-induced reproductive dysfunction. To rigorously test this hypothesis, we performed a longitudinal study, examining the role of low energy availability on both the development and the reversal of exercise-induced amenorrhea, using a monkey model (Macaca fascicularis). Eight adult female monkeys developed amenorrhea (defined as absence of menses for at least 100 d, with low and unchanging concentrations of LH, FSH, E2, and P4) after gradually increasing their daily exercise to 12.3 +/- 0.9 km/d of running over a 7- to 24-month period. Food intake remained constant during exercise training. To test whether amenorrhea is caused by low energy availability, four of the eight amenorrheic monkeys were provided with supplemental calories (138-181% of calorie intake during amenorrhea) while they maintained their daily training. All four monkeys exhibited increased reproductive hormone levels and reestablished ovulatory cycles, with recovery times for circulating gonadotropin levels ranging from 12-57 d from the initiation of supplemental feeding. The rapidity of recovery within the reproductive axis in a given monkey was directly related to the amount of energy that was consumed during the period of supplemental feeding (r = -0.97; P < 0.05). Repeated measurements of plasma T3 concentrations, a marker of cellular energy availability, revealed a tight correlation between the changes in reproductive function and T3 levels, such that T3 significantly decreased (27%) with the induction and significantly increased (18%) with the reversal of amenorrhea (P < 0.05). These data provide strong evidence that low energy availability plays a causal role in the development of exercise-induced amenorrhea.

Photoperiodic effects on gonadotropin-releasing hormone (GnRH) content and the GnRH-immunoreactive neuronal system of male Siberian hamsters.

Despite profound photoperiodic differences in circulating gonadotropin levels, consistent differences in the GnRH system have not been observed in Siberian hamsters (Phodopus sungorus) housed chronically in short or long days. During the transition from short to long days, however, male hamsters exhibit a transient increase in the number of cells expressing prepro-GnRH mRNA on the morning of the second long day. Here, we present two experiments designed to examine whether or not this change in mRNA level is associated with changes in GnRH protein synthesis. In the first experiment, we used RIA to measure GnRH content in preoptic area-mediobasal hypothalamic homogenates. We observed a significant increase in GnRH protein levels on the morning of the second long day relative to short- and long-day controls. The latter two groups did not differ from one another. In the second experiment, we used immunocytochemistry to quantify GnRH cell number in the various treatment groups. GnRH-immunoreactive (-ir) cell number did not increase significantly after long-day transfer relative to that in short-day controls; however, both of these groups had significantly more GnRH-ir neurons than long-day controls. We hypothesize that during the transition from short to long days, male Siberian hamsters experience a transient increase in GnRH production in a stable population of neurons. When GnRH secretion subsequently increases on long days, peptide content within neuronal cell bodies declines, leading to a decrease in the number of immunoreactive neurons detected. The rapid response of the hypothalamo-pituitary-gonadal axis in Siberian hamsters to a change in day length defines a narrow temporal window in which to identify the physiological, cellular, and molecular mechanisms mediating the photoperiodic regulation of reproduction.

Neonatal hypothyroidism permanently alters follicle-stimulating hormone and luteinizing hormone production in the male rat.

Transient neonatal hypothyroidism, induced with the goitrogen 6-n-propyl-2-thiouracil (PTU), results in dramatic increases in both testis size and sperm production in the adult rat. The observed increases in testis size and function occur in the presence of normal circulating testosterone levels. However, circulating gonadotropin levels are chronically reduced by 30-50% at all times in treated males. To better understand the permanent reduction in serum gonadotropin levels following transient neonatal hypothyroidism, we conducted a series of experiments to evaluate pituitary and hypothalamic function in the adult male PTU-treated rat. PTU treatment led to a significant reduction in GnRH-stimulated LH production. Castration resulted in 3.9- to 8.5-fold increases in circulating gonadotropin levels in both treated and control males; however, the absolute increases were significantly reduced in treated males. In contrast to circulating levels, pituitary gonadotropin contents did not increase in treated males after castration. PTU treatment did not lead to a reduction in the density of either luteotropes or folliculotropes, and both cell types increased in size and density after castration. The relative concentrations of both gonadotropin beta-subunit messenger RNAs increased more slowly in treated males than in controls after castration. Thus, although treated rats have the intrinsic ability to produce normal circulating levels of LH and FSH, gonadal feedback and an overall reduction in gonadotrope synthetic ability combine to produce the chronically reduced circulating levels of these hormones.

Pituitary-testicular axis in cardiomyopathic Syrian hamsters.

Testicular function and other endocrine parameters were studied in cardiomyopathic hamsters. In these animals, the major defect is an intracellular calcium overload, which is due to defective voltage-sensitive calcium channels. Basal circulating gonadotropin, prolactin, and triiodothyronine levels were lower in cardiomyopathic hamsters than in normal hamsters, but thyroxine, progesterone, and testosterone levels were not. In cardiomyopathic hamsters, the luteinizing hormone receptor (LHR) positive autoregulation by human chorionic gonadotropin (hCG) reached a maximum faster and at a lower dose than in normal hamsters. Similar results were observed for the response of circulating testosterone to hCG administration. The data indicate that, in spite of deficient pituitary function, cardiomyopathic hamsters have a normal or more efficient testicular function. This is probably the result of the cellular calcium overload, which would stimulate Leydig cell gene transcription, specifically that for LHR.

Cyclosporin-Mediated Depression of Luteinizing Hormone Receptors and Heme Biosynthesis in Rat Testes: A Possible Mechanism for Decrease in Serum Testosterone*

The toxic side-effects of the immunosuppressive drug cyclosporin (CsA) include testicular dysfunction and a decline in circulating testosterone. However, mechanisms for the consistently observed CsA-mediated depression of serum testosterone levels are unclear because of conflicting reports concerning circulating gonadotropin levels and incomplete studies of intratesticular steroidogenesis. To elucidate these mechanisms, endocrine-regulated testicular steroidogenesis and heme metabolic parameters were studied in male rats given sc injections of either 25 or 40 mg/kg.day CsA for 6 days and then killed on the seventh day. Consistent with earlier reports, CsA treatment dramatically suppressed serum testosterone levels (less than 20% of control at both CsA doses). Additionally, the intratesticular testosterone content declined with the higher CsA dose. Serum LH and FSH levels were elevated up to 2- to 4-fold after the higher CsA treatment regimen. Measurement of decreases in testicular receptors for LH revealed for the first time that CsA treatment significantly reduced the ability of the testes to respond to normal or elevated circulating levels of LH. In animals receiving higher dose of the drug, cytochrome P-450-dependent mitochondrial cholesterol side-chain cleavage activity, which is the rate-limiting step in steroidogenesis, was markedly reduced to a mere 30% of the control value. Additionally, the activity of the microsomal cytochrome P-450-dependent 17 alpha-hydroxylase was decreased to less than half of the control value. Biotransformation of the prototype drug, benzo(a)pyrene, as well as microsomal cytochrome P450 levels declined significantly after the higher CsA dose, suggesting that CsA has an adverse affect on testicular cytochromes P-450 in general. In addition, CsA treatment altered heme metabolic parameters; significant increases in the activity of uroporphyrinogen-I synthetase and total porphyrin content were noted. Conversely, the activity of ferrochelatase, the enzyme that incorporates iron into porphyrin to form heme molecule, decreased significantly, as did the total heme levels. The latter was reduced to only 61% of control values. The findings suggest the likelihood that the observed inhibition of heme formation may contribute substantially to the reduced levels of microsomal cytochromes P-450 and steroidogenic activities that depend on them. Taken collectively, these data suggest a plausible mechanism by which CsA may induce testicular dysfunction; as the result of a combination of reduction in the number of LH receptors and a suppression of heme formation, the hemoprotein-dependent steroidogenic enzymes activities are compromised, leading to an impairment of normal testicular function.

Patterns of Circulating Gonadotropins and Ovarian Steroids during the First Periovulatory Period in the Developing Sheep1

This report provides evidence that an increment in serum gonadotropin levels occurs at puberty in the sheep and that this reflects the critical hormonal event culminating in first ovulation in this species. Blood samples were collected from 6 female lambs at 4-h intervals for a period of approximately 2 mo around the expected time of puberty (32 wk of age) until behavioral estrus was observed and ovulation was verified by assay of serum progesterone. Patterns of circulating LH, FSH, progesterone, and estradiol concentrations were characterized during the peripubertal period for each lamb. A rise in serum levels of both LH and FSH began approximately 7-10 days before the first preovulatory surge of gonadotropins. Although the increase in gonadotropin levels occurred gradually over several days, serum estradiol levels rose only during the final 40-60 h prior to the preovulatory surge of gonadotropin. Serum progesterone profiles revealed, however, that normal (14-16-day) luteal phases were induced in only 2 of 6 females as a result of the first surge. In four lambs, a short luteal phase of 2.5 days' duration occurred, which was followed by another estradiol rise and a preovulatory surge that then resulted in a full luteal phase of 14 days' duration. These data demonstrate clearly that the precipitating event at puberty in the female sheep is an increase in circulating gonadotropin levels and that the estradiol secreted from the newly stimulated follicle provides the signal for the first preovulatory surge.

Response of circulating gonadotropin levels to GnRH agonist treatment in prostatic cancer.

Luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T) responses to 6-month treatments with a gonadotropin-releasing hormone (GnRH) agonist (buserelin) and subsequent orchiectomy were studied in patients with advanced prostate cancer. For treatments, either an intranasal (600 micrograms, 3/day, n = 8) or subcutaneous depot preparation (6.6 mg every other month, n = 5) were used. A third group of patients received intranasal buserelin (400 micrograms, 3/day, n = 12) for 35 months. LH and FSH were measured using radioimmunoassay (RIA) and a sensitive (0.04 IU/L) immunofluorometric assay (IFMA). In addition, selected samples were analyzed for bioactive (bio) LH. The RIA-LH levels decreased 70% with intranasal treatment. In contrast, when monitored by IFMA, the reduction was greater than 90%: 0.2 to 0.3 IU/L with intranasal and 0.044 to 0.052 IU/L with depot treatment (P less than 0.01). Gonadotropin suppression was stable up to 35 months. Bio-LH and IFMA-LH levels decreased in parallel during treatment, with no apparent changes in the bio/immuno ratio. FSH levels were suppressed temporarily during the treatments. After castration and cessation of buserelin treatment, serum LH and FSH increased rapidly in the intranasal treatment group but only marginally during 3 months in the depot group. Serum T reached the castrate range when IFMA-LH decreased below 0.5 IU/L. A further decrease in LH (less than 0.1 IU/L) still suppressed the intratesticular T concentration measured after orchiectomy. In conclusion, IFMA offers an improved method to monitor the antigonadotropic effect of GnRH agonist treatment. The results emphasize the necessity of profound LH suppression to achieve maximal inhibition of testicular androgen production.