Plasma Follicle-stimulating Hormone Research Articles

Plasma Inhibin Levels in Relation to Steroids and Gonadotrophins during Oestrous Cycle in Buffalo

The study was conducted on six Murrah buffalo synchronized and induced to oestrus. An indwelling catheter was placed in the jugular vein of each buffalo 4 days before the expected onset of the oestrus following the induced oestrus and blood samples were collected at 8 h intervals from each animal throughout the oestrous cycle. Plasma immunoreactive inhibin, follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17 beta and progesterone were estimated by radioimmunoassay to study the variations in the peripheral levels of these hormones and their inter-relationships in order to elucidate the feedback systems controlling them during the oestrous cycle of buffalo. Plasma inhibin levels ranged between 391.25 and 631.97 pg/ml during various phases of the oestrous cycle and were found to be higher than reported in cows. Peak LH and FSH levels during oestrus were 38.40 +/- 9.21 and 24.04 +/- 4.75 ng/ml, respectively and estradiol-17 beta and progesterone were 19.50 +/- 5.51 pg/ml and 0.61 +/- 0.25 ng/ml, respectively. The mean plasma inhibin concentration on the day of oestrus was 562.5 +/- 18.9 pg/ml. Levels of FSH in the plasma showed three mid-cycle elevations which corresponded to comparatively lower inhibin and elevated estradiol-17 beta levels during the same period. From this observation it was deduced that both inhibin and estradiol-17 beta have a feed-back regulatory effect on FSH secretion in buffalo.

Factors affecting gonadal function after bone marrow transplantation during childhood.

Conditioning for bone marrow transplantation (BMT) may alter viability of germ cells and production of gonadal hormones. We analyzed the risk factors for gonadal failure after 12 Gy total body irradiation (TBI) given as six fractions (n = 31, group 1), 10 Gy (one dose) TBI (n = 20, group 2), 6 Gy (one dose) total lymphoid irradiation (TLI, n = 17, group 3) and chemotherapy alone (n = 7, group 4), given at 7.7 +/- 0.4 (0.6-13.6) years. Among the 34 girls, seven (20.6%) had normal ovarian function with regular spontaneous menstruation and normal plasma follicle-stimulating (FSH) and luteinizing (LH) hormones, five (14.7%) had partial ovarian failure with regular menstruation but increased FSH and/or LH, and 22 (64.7%) had complete ovarian failure. The 24 girls with chronological and bone ages >13 years included similar percentages, with increased FSH or LH in all four groups. There was a positive correlation between age at BMT and FSH (r = 0.54, P < 0.01), but not with lh, and between fsh and lh (r = 0.8, P = 0.0003). Plasma FSH concentrations had returned to normal spontaneously in six cases, and those of LH in two cases. Among the 41 boys, 16 (39%) had normal testicular function and 25 (61%) had tubular failure and increased FSH. Of these, 10 also had Leydig cell failure (three complete and seven partial). The 18 boys with chronological and bone ages >15 years included similar percentages with increased FSH or LH in groups 1 to 3, and testicular volume was significantly lower in group 2 than in group 3 (P = 0.008). There was no correlation between age at BMT and FSH, LH or testosterone, but there was a negative correlation between FSH and inhibin B (rho = -0.87, P < 0.003). we conclude that girls are more likely to suffer ovarian failure the older they are at bmt, and that early ovarian recovery is possible. the negative correlation between fsh and inhibin b in boys suggests that this parameter is an additional indicator of tubular function.

Testicular effect of mustard gas

Objectives. To explain the testicular effect of mustard gas. Methods. Eighty-one patients who had been exposed to sulfur mustard and had the presenting symptom of infertility underwent evaluation of their reproductive system. Three semen analyses, serum hormonal determinations (luteinizing hormone, follicle-stimulating hormone, and testosterone), and genital examinations were completed for all patients, as were testicular biopsies in 24 patients. Results. Azoospermia and severe oligospermia were diagnosed in 42.5% and 57.5% of patients, respectively. Hormone studies revealed an elevated plasma follicle-stimulating hormone level and normal plasma luteinizing hormone and testosterone concentrations. Testicular biopsy showed selective atrophy of the germinal epithelium, intact Sertoli cells, and normal-appearing Leydig cells. Conclusions. Mustard gas can cause defective spermatogenesis years after exposure.

Nonylphenol Affects Gonadotropin Levels in the Pituitary Gland and Plasma of Female Rainbow Trout

Female rainbow trout (Oncorhynchus mykiss) were exposed to 4-nonylphenol (NP) at (mean measured) concentrations of 0.7, 8.3, and 85.6 micrograms/L for 18 weeks, during early ovarian development. Fish were sampled sublethally every six weeks, and terminal samples were taken at 18 weeks. NP induced an estrogenic effect (the synthesis of vitellogenin) at concentrations of 8.3 and 85.6 micrograms/L. An effect on gonadotropin synthesis and secretion was also observed. Plasma follicle stimulating hormone (FSH) levels and FSH gene expression in the pituitary were the most sensitive endpoints assessed, being reduced at the lowest dose employed (0.7 microgram NP/L). Pituitary gland luteinizing hormone (LH) content was significantly lower in fish exposed to 85.6 micrograms NP/L, and LH gene expression was suppressed in fish exposed to 8.3 and 85.6 micrograms NP/L. In contrast, plasma LH concentration increased in these fish, but by a very minor absolute amount, and returned to control levels by the final sampling time. Gonadal development ceased in the fish exposed to 85.6 micrograms NP/L, and steroidogenesis in these fish was also markedly inhibited. Although the mechanisms underlying these responses are unknown, this study demonstrates that NP has adverse effects on pituitary function that can result in inhibition of ovarian development.

Cadmium effects on hypothalamic-pituitary-testicular axis in male rats.

This study analyzes cadmium effects at the hypothalamic-pituitary-testicular axis. Male rats were given cadmium during puberty or adulthood. Cadmium exposure through puberty increased norepinephrine content in all hypothalamic areas studied, but not in the median eminence. Metal exposure increased serotonin turnover in median eminence and the anterior hypothalamus, while decreased it in mediobasal hypothalamus. Also, decreased plasma levels of testosterone were found. Cadmium exposure during adulthood increased norepinephrine content in posterior hypothalamus and decreased the neuro-transmitter content in anterior and mediobasal hypothalamus. Decreased circulating levels of luteinizing hormone (LH) and testosterone and increased plasma follicle stimulating hormone (FSH) levels were also observed. Cadmium accumulated in all analyzed tissues. Various parameters showed age-dependent changes. These data suggest that cadmium globally effects hypothalamic-pituitary-testicular axis function by acting at the three levels analyzed and that an interaction between cadmium exposure and age emerge.

Plasma and pituitary concentrations of gonadotropins (FSH and LH) in minke whales ( [formula omitted]) during the feeding season

This study investigated plasma and pituitary concentrations of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and steroid hormones (progesteron: P 4, testosterone: T, estradiol-17β: E 2 by enzyme-immunoassay (EIA) in minke whales ( Balaenoptera acutorostrata ) captured during the feeding season (December to March) in the Antarctic Ocean. Plasma FSH and LH levels in female minke whales were higher P < 0.05) than in male whales. Although the pituitary weight was not significantly different between male and female whales, pituitary FSH and LH levels were higher in females than in males (P<0.01) and mature whales than immature whales (P<0.05). Plasma levels of FSH, T and E 2 were not significantly different between immature and mature male whales, but plasma LH and pituitary FSH and LH levels were higher (P<0.05) in mature than in immature whales. In both immature and mature whales regardless of gender, pituitary FSH and LH levels were correlated significantly (r=0.69: P<0. 01). In mature male whales, plasma T and E 2 levels (r=0.60: P<0.01), and testis weight and plasma T levels (r=0.46: P <0.05) were correlated. In immature female whales, plasma FSH and LH levels were highly correlated (r=0.68: P<0.001), but were not for mature female whales. The results show that gender and maturity influence gonadal and pituitary function of minke whales during the feeding season.

Estrogen replacement therapy in postmenopausal women: a study of the efficacy of estriol and changes in plasma gonadotropin levels

The purpose of this study was to clarify the efficacy of estriol for estrogen replacement therapy in postmenopausal women with undefined symptoms and to evaluate endocrinological changes during therapy in relation to clinical outcome. Administration of 2 mg estriol in 168 postmenopausal patients was markedly effective in 22.6% of cases, effective in 45.2%, fairly effective in 14.3%, and ineffective in 17.9% of cases. The plasma concentration of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) after administration of estriol decreased significantly (p < 0.001), by 52.2% and 32.9%, respectively for markedly effective cases, and by 39.1% and 48.0% for effective cases. In contrast, the plasma estradiol concentration remained unchanged. On the other hand, decreases in FSH and LH concentration were 13.9% and 5.9% for the fairly effective and 8.2% and 1.9% for ineffective cases, demonstrating a significantly lower decrease in plasma FSH and LH levels than in the markedly effective and effective cases (p < 0.001). For cases showing side-effects, the plasma FSH and LH levels decreased by 52.0% and 64.3%, respectively, whereas the plasma estradiol level remained unchanged. In conclusion, the efficacy of estriol was significantly correlated to the degree of decrease in plasma FSH and LH levels in patients with undefined symptoms. In addition, efficacy appeared to be correlated to the incidence of side-effects. The degree of reduction of FSH (39.1-52.2%) and LH (48.0-64.3%) from the baseline may possibly be used as a guide to the therapeutic hormone levels during HRT. The present results suggest that plasma gonadotropin levels could be a useful indicator in the management of patients undergoing estrogen replacement therapy.

Oxidative stress and male IGF-1, gonadotropin and related hormones in diabetic patients.

Elevation of glucose concentration in diabetes may induce generation of oxygen free radicals such as superoxide (O2*-) and hydroxyl (*OH). The aim of the present study was to investigate the effect of the oxidative stress on the activities of blood superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GSSG-R) and aldose reductase, the levels of reduced glutathione (GSH), lipid peroxidation (thiobarbituric acid reactive substances; TBARS) and plasma levels of insulin-like growth factor-1 (IGF-1), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone in type 2 (non-insulin-dependent diabetes) patients and in healthy controls. Blood SOD, CAT, GSH-Px and GSSG-R were lower in type 2 diabetic patients compared with the the control group. Blood aldose reductase activity was elevated in patients with type 2 diabetes compared with the control group. GSH was decreased while TBARS concentration was increased in red blood cells (RBC) and leukocytes from the patients with type 2 diabetes mellitus in comparison to the control group. The mean values of plasma LH, FSH and testosterone were decreased, whereas the mean plasma IGF-1 concentration was increased in type 2 diabetes compared with controls. These findings support the hypothesis that hyperglycemia enhances the activity of the polyol pathway and impairs the antioxidant status, particularly glutathione redox cycle, resulting in poorer defense against oxidative stress. In addition, decreased circulating testosterone and gonadotropin levels may reflect the oxidative stress exerted by diabetes.

Increased plasma follicle-stimulating hormone concentrations in prepubertal gilts from lines selected for increased number of corpora lutea.

Plasma follicle-stimulating hormone (FSH) was evaluated in gilts from two studies in which ovulation rate was increased through direct selection for number of corpora lutea (CL) to determine whether selection for ovulation rate affected FSH secretion during prepubertal development. In the first study, 76 control and 110 selected gilts of University of Nebraska gene pool lines were bled twice during prepubertal development. Plasma FSH concentrations were greater (P < 0.05) at 53 (13.5%) and 75 (21.3%) d of age in selected than in control gilts. In the second study, 254 control gilts, 261 gilts from a line selected for ovulation rate, and 256 gilts from a line selected for uterine capacity were bled at three prepubertal ages. Plasma FSH was greater (P < 0.05), relative to controls, on d 34 (> 24%), 55 (> 13%), and 85 (> 10%) in White Composite gilts selected for either increased ovulation rate or for greater uterine capacity. Unilateral ovariectomy and hysterectomy were performed at 160 d of age on random gilts in these three lines (n = 377); weights of these organs were evaluated to determine whether selection affected their development. Ovarian and uterine weights were less (P < 0.01) in the control than in the ovulation rate line. Subsequently, ovulation rate was determined during pregnancy (n > or = 130 gilts/line). Controls had fewer (P < 0.01) CL (14.6) than gilts of the ovulation rate line (17.7) but numbers similar (P > 0.10) to those of gilts of the uterine capacity line (14.7). Within each line, plasma FSH only on d 85 correlated positively with subsequent ovulation rate (P < 0.03, 0.001, and 0.08; r = 0.17, 0.30, and 0.15 for control, ovulation rate, and uterine capacity lines, respectively). Ovarian weight at 160 d of age also correlated with subsequent ovulation rate (P < 0.03 and 0.001; r = 0.23 and 0.38) in control and ovulation rate gilts but not in uterine capacity gilts (P > 0.10; r = 0.11). Gilts selected for increased number of CL, in two independent studies, had greater concentrations of FSH during prepubertal development than respective controls. The modest but significant, positive association of FSH at 85 d of age with subsequent ovulation rate provides additional support for using plasma FSH in prepubertal gilts to indirectly select for ovulation rate.

Estrogen replacement therapy in postmenopausal women: a study of the efficacy of estriol and changes in plasma gonadotropin levels

The purpose of this study was to clarify the efficacy of estriol for estrogen replacement therapy in postmenopausal women with undefined symptoms and to evaluate endocrinological changes during therapyin relation to clinical outcome. Administration of 2 mg estriol in 168 postmenopausal patients was markedly effective in 22.6% of cases ,effective in 45.2% ,fairly effective in 14.3% ,and ineffective in17.9% of cases. The plasma concentration of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) after administration of estriol decreased significantly (p < 0.001) ,by 52.2% and 32.9%,respectively for markedly effective cases ,and by 39.1% and 48.0% for effective cases. In contrast ,the plasma estradiol concentration remained unchanged. On the other hand ,decreases in FSH and LH concentrationwere 13.9% and 5.9% for the fairly effective and 8.2% and 1.9% for ineffective cases ,demonstrating a significantly lower decrease in plasma FSH and LH levels than in the markedly effective and effectivecases (p < 0.001). For cases showing side-effects ,the plasma FSH and LH levels decreased by 52.0% and 64.3% ,respectively ,whereas the plasma estradiol level remained unchanged.In conclusion,the efficacy of estriol was significantly correlated to the degree of decrease in plasma FSH and LH levels in patients with undefined symptoms. In addition ,efficacy appeared to be correlated to the incidenceof side-effects. The degree of reduction of FSH (39.1-52.2%) and LH (48.0-64.3%) from the baseline may possibly be used as a guide to the therapeutic hormone levels during HRT. The presentresults suggest that plasma gonadotropin levels could be a useful indicator in the management of patients undergoing estrogen replacement therapy.

Contribution of endogenous inhibin to the decline of the secondary surge of follicle-stimulating hormone in the rat.

The involvement of inhibin in the decline of the secondary surge of follicle-stimulating hormone (FSH) was investigated in the rat. After ovariectomy or treatment with inhibin antiserum conducted at 2300 hours during pro-oestrus, plasma concentrations of FSH were maintained at high levels compared with control rats. However, plasma FSH started to decline at 0500 hours during oestrus in both the groups. The same treatments conducted during metoestrus markedly increased plasma FSH after 24 h (twofold compared with the treatments during pro-oestrus), suggesting that the treatments sufficiently depleted circulating inhibin. To examine whether the decline of plasma FSH occurred through a transcriptional mechanism or through a translational mechanism, FSH-beta mRNA expression and the pituitary concentration of FSH were measured. Neither ovariectomy nor inhibin immunization conducted during the night of pro-oestrus, affected the pituitary concentration of FSH after 24 h, whereas a noticeable increase was observed after the treatments conducted during metoestrus. In both stages, both ovariectomy and inhibin immunization significantly increased FSH-beta mRNA expression compared with control rats. In contrast with the pituitary concentration of FSH, the effect of inhibin immunization on FSH-beta mRNA expression was not different between the stages. The present data demonstrate the involvement of inhibin in the decline of the secondary surge of FSH, and suggest that a factor or factors other than inhibin may also be responsible for the fall in FSH. Changes in the pituitary concentration of FSH and FSH-beta mRNA expression suggest that post-transcriptional mechanisms may be involved in the suppression of FSH secretion during oestrus.

Regulatory Role of Inhibin in Follicle-Stimulating Hormone Secretion and Folliculogenesis in the Guinea Pig.

The effects of unilateral and bilateral ovariectomy and passive immunization against inhibin on follicle-stimulating hormone (FSH) secretions and follicular development in the guinea pig were investigated. Bilateral ovariectomy decreased plasma immunoreactive (ir-) inhibin rapidly and increased plasma FSH significantly. Unilateral ovariectomy decreased plasma ir-inhibin and increased plasma FSH temporarily, and doubled the number of ova released from the remaining ovary at the subsequent ovulation in guinea pigs. Injection of 1.0 ml inhibin antiserum significantly increased concentrations of plasma FSH at 6 hr onwards and the number of small follicles (100-200 microm in diameter) at 48 hr after the injection in guinea pigs bearing progesterone-containing implants. In vitro bioassay showed that inhibin antiserum could neutralize the suppression of ovarian homogenate on FSH secretion from cultured rat anterior pituitary cells. These results confirm the evidence that the ovary is the main source of inhibin secretion and both in vitro bioassay and passive immunization against inhibin show that the inhibin is a major regulator in the follicular development through FSH secretion in guinea pigs.

Effects of cyproheptadine clorhydrate ,a serotonin receptor antagonist ,on endocrine parameters in weight-loss related amenorrhea

The aim of the study was to evaluate the possible interactions and/or modulations of the serotoninergic system on hormonal parameters and the reproductive axis in amenorrheic subjects. Hypogonadotropic,underweight ,amenorrheic patients (n = 8) were studied before and during cyproheptadine clorhydrate administration (4 mg/day for 3 months). A pulsatility study (4 hours ,sampling every 10 minutes) and analoxone test were performed before and after 4 and 12 weeks of treatment. Plasma luteinizing hormone (LH) ,follicle-stimulating hormone (FSH) ,growth hormone (GH) ,estradiol ,thyroid-stimulating hormone(TSH) ,free tri-iodothyronine (fT3) ,free thyroxine (fT4) and total triiodothyonine (total T3) ,insulin-like growth factor-I (IGF-I) concentrations were determined. Pulsedetection analysis was performed using the DETECT program.Serotoninergic receptor blockade affected neither the naloxone-inducted LH response nor the gonadotropin pulsatile parameters. Body mass index(BMI) did not vary; conversely ,integrated mean gonadotropins ,GH and fT3 concentrations increased during the treatment. In conclusion ,cyproheptadine administration affects some of the abnormalendocrine parameters of underweight amenorrheic subjects with no modulation of the opioidergic system. It is likely that the gonadotropin and the fT3 increases take place owing to a change inthe metabolic signals modulating hypothalamic function and/or an increased energy availability. Our study suggests a specific central effect of cyproheptadine on the serotonergic pathway controlling foodintake at the hypothalamic level.

Modulation of pituitary dopamine D1 or D2 receptors and secretion of follicle stimulating hormone and luteinizing hormone during the annual reproductive cycle of female rainbow trout.

The two gonadotrophins follicle stimulating hormone (FSH) and luteinizing hormone (LH) have distinct temporal expression and release profiles in fish, but little is known regarding their neuroendocrine control, especially for FSH. The present experiments were performed on previtellogenic, mature and preovulatory female trout. The catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine, increased plasma LH and FSH concentrations of mature fish. The dopamine agonist apomorphine decreased and the dopamine antagonist domperidone increased plasma LH concentration of preovulatory fish and delayed ovulation, but did not modify plasma FSH concentration. The dopamine D2 agonist bromocryptine inhibited LH release in cultured gonadotrophs from mature and preovulatory fish, but not from previtellogenic fish. Bromocryptine also significantly inhibited basal and salmon gonadotrophin releasing-hormone (sGnRH)-induced FSH release from cultured gonadotrophs of mature fish, but not of preovulatory fish, and increased FSH release from gonadotrophs of previtellogenic fish. The dopamine D1 agonist SKF 38393 had no observed effect on the release of FSH and LH, at any reproductive stage studied. The D1 agonist SKF 38393, the D2 agonist bromocriptine and sGnRH had no observed effects on cell contents of FSH and LH. Taken together, these data suggest that, at the level of the pituitary, dopamine inhibits LH release as vitellogenesis proceeds, via activation of dopamine D2 receptors. We demonstrate for the first time in fish a control of FSH release (a dopamine control), especially in mature fish which have low circulating concentrations of FSH.

Seminal plasma nitrite/nitrate and intratesticular Doppler flow in fertile and infertile subjects.

The objective of the present study was prospectively to evaluate the role of nitric oxide (NO) in modulating intratesticular blood flow and sperm function. A total of 56 males, undergoing assisted reproduction, were divided into three groups according to semen analysis: (i) normozoospermic (n = 16); (ii) oligozoospermic (n = 21); and (iii) azoospermic (n = 19). All the subjects were submitted to hormone analysis [luteinizing hormone, follicle stimulating hormone (FSH), growth hormone, testosterone, androstenedione, insulin], and to ultrasonographic (testicular volume) and Doppler (transmediastinal artery) evaluations. Plasma and seminal plasma nitrite/nitrate concentrations, and plasma insulin-like growth factor-I were assayed. All 56 patients completed the study. In normozoospermic patients, significantly greater testicular volume, lower transmediastinal resistances, and higher seminal plasma nitrite/nitrate concentrations were observed in comparison with both oligo- and azoospermic subjects. Testicular volume was inversely correlated with plasma FSH (r = -0.589; P = 0.005) and pulsatility index of transmediastinal artery (r = -0.402; P = 0.049). Furthermore, the seminal plasma nitrite/nitrate concentrations were inversely correlated with pulsatility index of transmediastinal artery (r = -0.511; P = 0.015). It was concluded that NO is involved in vascular modulation of testicular vessels and ultimately in sperm output.

Antireproductive effect of the calcium channel blocker amlodipine in male rats

The purpose of the present study was to investigate whether treatment of male rats with the calcium antagonist amlodipine, used in the treatment of hypertension and angina, interferes with the reproductive function of male rats. Amlodipine treatment (0.04 mg amlodipine besylate/rat/day for 30 days) decreased plasma follicle-stimulating hormone and testosterone but not luteinizing hormone or prolactin concentrations (measured by double-antibody radioimmuno-assay). A significant reduction (23%) was observed in sperm density (sperm suspension collected from the cauda epididymidis) as well as in the amount of mature spermatids (14%) and Sertoli cells (9%) counted in seminiferous tubule cross-sections (400 x magnification). The results reveal the deleterious effects of subacute amlodipine treatment on the reproductive function of male rats.

Effects of Salmon Gonadotropin-Releasing Hormone on Follicle Stimulating Hormone Secretion and Subunit Gene Expression in Coho Salmon (Oncorhynchus kisutch)

Previous work has indicated that, during the process of gametogenesis in salmon, follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are differentially synthesized and released. Although substantial information is available on the regulation of LH in many fish species, relatively little is known about the regulation of FSH biosynthesis and secretion or the regulation of two types of α subunit in salmon. In this study, the effects of salmon gonadotropin-releasing hormone (sGnRH) on in vitro secretion of FSH, and α1, α2, LH β, and FSH β subunit gene expression were investigated in coho salmon (Oncorhynchus kisutch) using primary pituitary cell cultures. To quantify FSH β, LH β, α1, and α2 subunit transcript levels, a multiplex RNase protection assay (RPA) was developed. Probes for the β subunits of coho salmon FSH and LH were available from previous studies. To generate probes for the α subunit RPAs, α1 and α2 subunit cDNAs were cloned using reverse transcriptase PCR. Release of FSH and LH into cell culture medium was quantified by radioimmunoassays. The effects of sGnRH on gonadotropin release and gene expression were tested at two points during the spring (April and May) prior to spawning in the autumn; a period when plasma and pituitary FSH levels are increasing and females are in early stages of secondary oocyte growth. In both experiments, sGnRH increased steady-state mRNA levels of FSH β, α1, and α2, whereas LH β mRNA levels were not detectable. Secretion of FSH was stimulated by sGnRH in a concentration-dependent manner. Medium LH was not detectable in the first experiment (April) and was measurable only after sGnRH treatment in the second experiment (May). Control levels of medium FSH and transcripts for FSH β and α1 subunits increased approximately fourfold between April and May, whereas α2 transcript levels remained relatively constant, suggesting that the seasonal increase in FSH release may involve increased production of α1. Therefore, sGnRH has direct stimulatory effects on both secretion of FSH and FSH subunit biosynthesis, most likely due to increased transcription. However, alterations in rates of transcript degradation cannot be ruled out.

Inhibin is an important factor in the regulation of FSH secretion in the adult male hamster.

We investigated the importance of inhibin and testosterone in the regulation of gonadotropin secretion in adult male golden hamsters (Mesocricetus auratus). After castration, plasma concentrations of inhibin and testosterone were reduced to undetectable, whereas plasma follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were increased. After hemicastration, plasma FSH and LH increased moderately and plasma inhibin decreased to one-half its initial level. Plasma testosterone levels in hemicastrated animals decreased 3 h after hemicastration but returned to those in sham-operated animals at 6 h. Plasma LH in the castrated hamster declined comparably to intact animals with testosterone treatment; plasma FSH also decreased but still remained at levels higher than those in intact animals. After treatment with inhibin in long-term-castrated animals, plasma FSH decreased, whereas plasma LH was not altered. Intact males treated with flutamide, an anti-androgen, showed a significant increase in plasma LH but not in FSH. On the other hand, treatment with anti-inhibin serum induced a significant elevation in plasma FSH, but not in LH. Using immunohistochemistry, we showed that the inhibin alpha-subunit was localized to both Sertoli and Leydig cells. The present study in adult male hamsters indicates that FSH secretion is regulated mainly by inhibin, presumably from Sertoli and Leydig cells, and that LH secretion is controlled primarily by androgens produced from the Leydig cells. This situation is more similar to that of primates than of rats.

High serum follicle stimulating hormone (FSH) during perimenopause at high altitude

The current data provide evidence that women living at high altitude may experience accelerated w x menopause than at sea level 1 , although the precise mechanisms are unknown. It has been suggested that early age at menopause may be due to high levels of serum FSH observed in regularly menstruating women at high altitude w x than at sea level 2 . The loss of ovarian oocytes, the cause of menopause, accelerates in the decade before menopause. This accelerated oocyte loss may in turn be caused by a selective elevation of w x plasma follicle-stimulating hormone 3 . Serum FSH levels increase significantly after the age of 40, and this elevation seems to be related to the high rate of follicular atresia, determining age at w x menopause 3 . It could be interesting to determine serum FSH levels in women in their forties living at high altitude.

Annual Variation of Body Composition, Reproductive Hormones, and Blood Constituents of Red Foxes

We tested the hypothesis that there is seasonal variation in the body composition of red foxes ( Vulpes vulpes ) maintained outdoors in captivity and receiving a fixed high-quality ration. We monitored body components (water, fat, protein, minerals) of 12 wild foxes kept at the Jardin zoologique du Quebec monthly from February 1995 to January 1996. We estimated mass of body components using regression models that relied on body mass, linear measurements, and electrical resistance. We also monitored plasma follicle-stimulating hormone, testosterone, and progesterone together with serum phosphorus and albumin. Total body mass increased slightly during the study probably due to limited activity and a constant high-quality diet. Fat reserves exhibited an annual cycle, decreasing by 50% in summer (May–October). In contrast, protein, water, minerals, and phosphorus peaked at that time. Follicle-stimulating hormone reached high levels in December–March and in September–January for females and males, respectively. Progesterone peaked in April for females, and testosterone peaked in January–March for males. Albumin concentration did not exhibit any clear seasonal pattern.