FSH Response Research Articles

Low serum free thyroxine index in ambulating elderly is due to a resetting of the threshold of thyrotropin feedback suppression.

Subnormal free T4 index (FT4I) values (less than 80) with inappropriately normal serum TSH concentrations that could not be attributed to illness or drugs were found in 2.5% of ambulating elderly clinic patients. Six such individuals (three men and three women, aged 68.8 +/- 4.8 yr) were selected for their persistent thyroid test abnormalities and were sex and age matched to six subjects (67.7 +/- 4.9 yr) with normal FT4I (greater than 90) and TSH levels. The former also had low serum total T4 (TT4) and rT3 (TrT3) concentrations, but total T3 (TT3) and basal TSH values were normal and did not differ between the groups. Responses of ACTH, LH, FSH, TSH, and PRL to stimulation with CRH, GnRH, and TRH showed no differences between the two groups, indicating that the normal TSH concentration, inappropriate for the low FT4I level, is not due to generalized hypothalamic or pituitary dysfunction. Administration of 3 g iopanoic acid (IOP) daily for 3 days produced significant increases in the TT4 and TrT3 concentrations to the same degree in both groups. Also, in both groups the IOP-induced suppression of T4 to T3 conversion in the pituitary gland provoked similar increases in basal TSH (280 +/- 47% and 288 +/- 33%) and TSH secretion in response to TRH (173 +/- 7% and 156 +/- 13%). These results indicate that the low FT4I is not the consequence of reduced pituitary TSH reserve. In addition, evidence for normal thyroid gland reserve and the secretion of TSH of normal biological activity was obtained by comparing the acute iodothyronine responses to TRH-induced TSH release in both groups. It is concluded that the normal serum TSH concentration, inappropriate for the low FT4I value in some elderly subjects, is due to an apparent resetting of the thyroid hormone feedback regulation threshold of TSH secretion. It may, in turn, be the result of enhanced pituitary conversion of T4 to T3 or increased T4 uptake by the thyrotrophs.

Suppression of the Pituitary-Gonadal Axis in Children with Central Precocious Puberty: Effects on Growth, Growth Hormone, Insulin-Like Growth Factor-I, and Prolactin Secretion*

To assess further the relationship between gonadal sex steroids and PRL, GH, and insulin-like growth factor-I (IGF-I) secretion and to help clarify the mechanism underlying the pubertal growth spurt, we studied 11 children (10 girls) with central precocious puberty before and during gonadal suppression with the GnRH agonist (GnRH-a) leuprolide acetate. Nocturnal sampling for plasma levels of GH and PRL, GH response to GH-releasing factor-(1-44), and plasma IGF-I levels were determined before and 3-6 months after pituitary-gonadal suppression. Treatment caused a significant decrease in the LH and FSH responses to GnRH (P less than 0.01) and the plasma concentration of estradiol (P less than 0.05). The patients' mean height velocity SD score for chronological age, initially 3.8 +/- 1.9, decreased significantly to 0.9 +/- 0.9 with treatment (P less than 0.005). Nocturnal GH secretion (mean GH concentration, sum of GH pulse areas, sum of GH pulse amplitudes, and GH pulse frequency) and mean IGF-I levels (1.38 +/- 0.6 vs. 1.72 +/- 0.34 U/mL) were not significantly altered by treatment. However, the mean peak GH response to GH-releasing factor-(1-44) was 29.2 +/- 6.8 micrograms/L before treatment and declined significantly to 17.7 +/- 3.4 micrograms/L after gonadal suppression (P less than 0.05). PRL secretion was similar before and after GnRH-a-induced suppression. These results indicate that the decrease in height velocity noted during GnRH-a treatment occurred independently of changes in nocturnal GH secretion and IGF-I levels. These data are consistent with the premise that sex steroids can modulate growth by a direct action on skeletal growth.

Plasma concentrations of cortisol, prolactin, luteinizing hormone, and follicle-stimulating hormone in stallions after physical exercise and injection of secretagogue before and after sulpiride treatment in winter

Ten lighthorse stallions were used to determine 1) whether prolactin (PRL) and cortisol responses previously observed after acute exercise in summer would occur in winter when PRL secretion is normally low, 2) whether subsequent treatment with a dopamine receptor antagonist, sulpiride, for 14 d would increase PRL secretion and response to thyrotropin-releasing hormone (TRH) and exercise, and 3) whether secretion of LH, FSH, and cortisol would be affected by sulpiride treatment. On January 11, blood samples were drawn from all stallions before and after a 5-min period of strenuous running. On January 12, blood samples were drawn before and after an i.v. injection of GnRH plus TRH. From January 13 through 26, five stallions were injected s.c. daily with 500 mg of sulpiride; the remaining five stallions received vehicle. The exercise and secretagogue regimens were repeated on January 27 and 28, respectively. Before sulpiride injection, concentrations of both cortisol and PRL increased (P less than .05) 40 to 80% in response to exercise; concentrations of LH and FSH also increased (P less than .05) approximately 5 to 10%. Sulpiride treatment resulted in (P less than .05) a six- to eightfold increase in daily PRL secretion. The PRL response to TRH increased (P less than .05) fourfold in stallions treated with sulpiride but was unchanged in control stallions. Sulpiride treatment did not affect (P greater than .05) the LH or FSH response to exogenous GnRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Gonadotrophin-releasing hormone modulation of gonadotrophins in the ewe: evidence for differential effects on gene expression and hormone secretion

While the regulation of gonadotrophin secretion by gonadotrophin-releasing hormone (GnRH) has been well documented in both rats and sheep, its role in the synthesis of gonadotrophin subunits remains unclear. We have investigated the effects of the specific inhibition of GnRH by a GnRH agonist on the expression of gonadotrophin subunit genes and the subsequent storage and release of both intact hormones and free alpha subunit. Treatment with GnRH agonist for 6 weeks abolished pulsatile LH secretion, reduced plasma concentrations of FSH and prevented GnRH-induced release of LH and FSH. This was associated with a reduction of pituitary LH-beta mRNA and FSH-beta mRNA levels (to 5 and 30% of luteal control values respectively), but not alpha mRNA which was significantly increased (75% above controls). While there was a small decrease in the pituitary content of FSH (30% of controls), there was a drastic reduction in LH pituitary content (3% of controls). In contrast to the observed rise in alpha mRNA, there was a decrease in free alpha subunit in both the pituitary and plasma (to 30 and 80% of control levels). These results suggest that, while GnRH positively regulates the expression of both gonadotrophin beta-subunit genes, it can, under certain circumstances, negatively regulate alpha-subunit gene expression. Despite the complete absence of LH and FSH in response to GnRH, there remained a basal level of beta-subunit gene expression and only a modest reduction (50%) in the plasma levels of both FSH and LH, suggesting that there is a basal secretory pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothalamic-Pituitary Dysfunction in Growth Hormone-Deficient Patients with Pituitary Abnormalities*

Hypothalamic-pituitary function was studied in 45 patients with idiopathic GH deficiency (GHD), 33 of whom had pituitary abnormalities on magnetic resonance imaging: pituitary hypoplasia, undescended stalk and ectopia of the posterior lobe in 8 patients with isolated GHD (IGHD) (group I) and in 12 patients with multiple pituitary hormone deficiency (MPHD) (group II); isolated pituitary hypoplasia in 13 patients with IGHD (group III); no evidence of pituitary abnormalities in the remaining 12 patients with IGHD (group IV). Sellar and pituitary volumes were significantly lower in groups I, II, and III than in group IV (P less than 0.001). No significant differences were observed between group I and group II in the GH response to GHRH1-44 expressed both as peak serum GH and area under the curve. Mean GH peak in group III and IV was significantly higher than that in group I (P less than 0.005) and II (P less than 0.001), as were the mean AUC (P less than 0.005), suggesting hypothalamic defect. Delayed peak serum TSH after TRH was found in all patients of group II, and overt hypothyroidism in 11 of them. Furthermore, basal hyperprolactinemia was present in 6 patients and adrenal insufficiency in 7 cases of group II. Finally, a reduced response of FSH to GnRH was observed in all these patients (P less than 0.005 vs. each of the other groups), and clinical hypogonadism was present in all of them. We suggest that: 1) A high incidence of pituitary abnormalities seems to be present in idiopathic GHD patients; 2) Pituitary hormone deficiencies are more dependent on the type of the hypothalamic-pituitary abnormality than on the size of the pituitary per se: the association of pituitary hypoplasia, undescended stalk and ectopia of the posterior lobe should possibly be considered a distinct entity reflecting an early abnormality in hypothalamic development; 3) The majority of patients with IGHD or MPHD probably have a primary hypothalamic releasing hormone deficiency even if pituitary hypoplasia is associated; 4) Magnetic resonance imaging may have a role in the diagnosis and prognosis of patients with GHD through differentiation between patients who are at risk for developing MPHD vs. those who are candidates for having a persistently isolated GHD.

Evidence That Inhibin Plays a Major Role in the Regulation of Follicle-Stimulating Hormone Secretion in the Fully Adult Male Rhesus Monkey (Macaca mulatto)*

In the juvenile male rhesus monkey in which an adult-like pattern of endocrine activity in the pituitary-testicular axis is imposed by pulsatile stimulation with exogenous GnRH, administration of inhibin antiserum elicits a marked and selective hypersecretion of FSH. This finding suggests that in the monkey, testicular inhibin plays a major role in the postpubertal regulation of this gonadotropin. The purpose of the present study was to confirm this view more directly. To this end, 10 adult male rhesus monkeys were implanted with indwelling venous catheters and housed in specialized cages that permit continuous access to the venous circulation with minimal restraint and without tranquilization. Six of the males received a continuous infusion of an ovine antiserum to the alpha-subunit of human inhibin (iv bolus injection of 2.22 ml/kg BW, followed by a continuous infusion of serum at 0.62 ml/kg BW.24 h), and 4 animals received a similar infusion of control ovine immune serum. The duration of the infusion of the inhibin antiserum ranged from 2.5-7.5 days, and that for the control serum was 7.5 days. The FSH response to immunoneutralization of circulating inhibin was determined by measuring concentrations of this gonadotropin in sequential plasma samples collected between 1900-2300 h on the day before initiation of the anti-serum infusion and, depending on the duration of the infusion, on days 0.5, 1.5, 2.5, 4.5, and 6.5 of antiserum administration. In 5 of the 6 animals that received the inhibin antiserum, a progressive hypersecretion of FSH was observed during the initial 2.5 days of the infusion. This increase in circulating FSH concentration, which reached, by day 2.5 of treatment, a value 2- to 3-fold greater (P less than 0.05) than the pretreatment control level, was not associated with changes in either LH or testosterone levels. Continuation of the infusion of the inhibin antiserum beyond 2.5 days invariably resulted in a marked decline in LH and testosterone secretion, suggesting that the hypophysiotropic drive to the pituitary-testicular axis may have been compromised, presumably by a mechanism related to the infusion of heterologous serum. Infusion of the control immune serum for 2.5 days was not associated with an elevation of circulating FSH concentrations, and changes in circulating concentrations of plasma LH and testosterone were, as expected, unremarkable. Continuation of the infusion of control serum, like that of antiserum, generally resulted in a temporary but precipitous decline in LH and testosterone secretion.(ABSTRACT TRUNCATED AT 400 WORDS)

Macroorchidism and testicular fibrosis associated with autoimmune thyroiditis

A 16-year-old male with long-standing atrophic chronic lymphocytic thyroiditis was evaluated for macroorchidism. A testicular biopsy prior to treatment revealed peritubular and interstitial fibrosis, reduced spermatogenesis and sparse Leydig cells with nonprominent smooth endoplasmic reticulum. Biological/immunological LH and FSH ratios were reduced, I-LH and FSH response to GnRH was blunted, and levels of testosterone and androstenedione were low. Twenty-two months after thyroid treatment, the testicular size was unchanged, and the degree of fibrosis showed minimal regression. Spermatogenesis with normal morphology was present, Leydig cells with Reinke crystals were present, and surface area and diameter of the seminiferous tubules had increased only slightly. There was a normal I-LH and FSH response to GnRH, and normal levels of testosterone and androstenedione. This study, along with previous reports, suggests that the etiology of the hypothyroid state may influence the development of testicular fibrosis.

Reduction of Gonadotropin-Releasing Hormone Pulse Frequency Is Associated with Subsequent Selective Follicle-Stimulating Hormone Secretion in Women with Polycystic Ovarian Disease*

Polycystic ovarian disease (PCO) is characterized by hyperandrogenism, ovulatory dysfunction, and altered gonadotropin secretion. Mean plasma FSH concentrations are low, while LH is elevated in a majority of patients. LH pulsatile secretion has been shown to occur at rapid follicular phase frequencies (approximately one pulse per h) in PCO, suggesting persistent rapid frequency GnRH secretion in this disorder. Anovulatory women with PCO were given estradiol (E2; Estraderm skin patches) and progesterone (P; vaginal suppositories) to produce midluteal concentrations for 21 days. The aim was to determine if E2 and P would slow LH (GnRH) pulse frequency and if this would result in augmented FSH secretion and follicular development after withdrawal of E2 and P. Plasma LH was measured every 10 min for 8 h before, during (days 10 and 20), and 7 days after withdrawal of E2 and P (day 28). On each of these study days FSH was measured hourly, and E2 and P were measured every 2 h. After sampling, GnRH (25 and 250 ng/kg, iv) was given to assess pituitary responsiveness. Follicular development was monitored by vaginal ultrasound through day 34 of the study. Basal LH frequency was 8.5 +/- 0.5 pulses/8 h (mean +/- SEM). During E2 and P, LH pulse frequency fell to 3.3 +/- 1.0 (10 days) and 2.3 +/- 0.8 (20 days), 39% and 27% of the basal value, respectively, and subsequently increased to 5.6 +/- 0.7 (66% of basal) 7 days after withdrawal of E2 and P. LH pulse amplitude (basal, 7.2 +/- 1.5 IU/L) was not reduced until day 20, but remained suppressed (3.9 +/- 1.1 IU/L) on day 28. As a result, mean LH (basal, 21.0 +/- 3.5 IU/L) fell progressively during E2 and P, to 3.8 +/- 1.2 IU/L on day 20, and remained low (39% of basal) 7 days after steroid withdrawal. Mean plasma FSH (basal, 7.1 +/- 0.9 IU/L) also fell during steroid administration, but in contrast to LH, had risen to 93% of the basal value by 7 days after E2 and P. LH release in response to exogenous GnRH revealed marked initial responses which did not decrease until day 20, but remained suppressed (8% of basal) after withdrawal of E2 and P. FSH responses were also suppressed on day 20, but had increased to 75% of the basal value by day 28. Initiation of follicular development occurred in all patients, and the lead follicle measured 12.3 +/- 0.8 mm 13 days post-E2 and P. Ovulation occurred in one patient.(ABSTRACT TRUNCATED AT 400 WORDS)

Patterns of Pulsatile Luteinizing Hormone and Follicle-Stimulating Hormone Secretion in Prepubertal (Midchildhood) Boys and Girls and Patients with Idiopathic Hypogonadotropic Hypogonadism (Kallmann's Syndrome): A Study Using an Ultrasensitive Time-Resolved Immunofluorometric Assay

To study the ontogeny of spontaneous pulsatile LH and FSH secretion before the onset of puberty, plasma LH and FSH were measured by an ultrasensitive time-resolved immunoflurometric assay in 16 boys and 6 girls, aged 6.5 +/- 0.2 yr (+/- SEM; range, 4.4-8.0) with short stature. Eight male patients with idiopathic hypogonadotropic hypogonadism (Kallmann's syndrome), aged 24.1 +/- 3.4 yr, were also investigated. Blood samples were withdrawn at 10- to 20-min intervals for 12 h from 2000-0800 h. Pituitary responsiveness was assessed by a standard iv LHRH challenge test. LH and/or FSH pulses were detectable in all but two prepubertal subjects. In boys, low amplitude LH (0.16 +/- 0.06 U/L) and FSH (0.19 +/- 0.03 U/L) pulses were detectable at mean frequencies of 2.19 +/- 0.37 and 2.13 +/- 0.46 pulses/12 h, respectively. In girls, low amplitude LH (0.29 +/- 0.18 U/L) pulses, but higher (P less than 0.05 compared to boys) amplitude FSH (1.62 +/- 1.05 U/L) pulses were observed at frequencies of 1.71 +/- 0.56 and 1.67 +/- 0.53 pulses/12 h, respectively. Mean FSH in prepubertal girls (1.95 +/- 0.88 U/L) was significantly (P less than 0.05) higher than that in boys (0.46 +/- 0.07 U/L), but mean LH was not different at 0.17 +/- 0.07 and 0.10 +/- 0.03 U/L, respectively. Patients with Kallmann's syndrome had mean LH and FSH levels indistinguishable from those of prepubertal boys. Nocturnal augmentation of pulsatile LH or FSH secretion was observed in 74% of children (71% in girls and 75% in boys), but in none of the eight patients with Kallmann's syndrome. A close temporal association was observed between sleep onset and the appearance of nocturnal pulsatile gonadotropin secretion. The FSH response to exogenous LHRH in prepubertal girls was significantly greater than that in patients with Kallmann's syndrome and prepubertal boys, but LH responses were not different. Our results show that pulsatile LH and FSH secretion occurs in the majority of boys and girls in midchildhood, with a robust association with nocturnal sleep onset. Between the ages of 4-8 yr, these low amplitude and low frequency pulses are unable to activate gonadal function. The regulation of FSH secretion in prepubertal girls appears to be different from that in prepubertal boys.(ABSTRACT TRUNCATED AT 400 WORDS)

Impact of season on seminal characteristics and endocrine status of adult free-ranging African buffalo (Syncerus caffer)

Pituitary, gonadal and adrenal activity were compared in free-living, adult African buffalo bulls during the breeding and nonbreeding seasons. Frequent blood samples were collected for 2 h from anaesthetized bulls treated intravenously with saline, gonadotrophin-releasing hormone (GnRH, 200 micrograms), human chorionic gonadotrophin (hCG, 10,000 i.u.) or adrenocorticotrophic hormone (ACTH, 1.5 mg). Electroejaculates also were collected from anaesthetized bulls during the breeding and nonbreeding seasons. Pretreatment testosterone concentrations among bulls varied more during the breeding (0.17-23.0 ng/ml) than the nonbreeding (0.15-2.21 ng/ml) season. The variation within the breeding season was attributed to 8 of 25 bulls producing higher (P less than 0.05) serum testosterone (High-T; 16.28 +/- 2.03 ng/ml) and testicular LH receptor (1.53 +/- 0.22 fmol/mg testis) concentrations compared with their seasonal counterparts (Low-T; 0.95 +/- 0.26 ng/ml; 0.38 +/- 0.04 fmol/mg) or with all bulls during the nonbreeding season (0.90 +/- 0.27 ng/ml; 0.31 +/- 0.04 fmol/mg). The magnitude of GnRH- and hCG-induced increases in serum testosterone was similar (P greater than 0.05) between Low-T bulls and bulls during the nonbreeding season. In the High-T animals treated with GnRH or hCG, serum testosterone did not increase, suggesting that secretion was already maximal. Peak serum LH concentrations after GnRH were greater (P less than 0.05) in bulls during the nonbreeding than the breeding season; FSH responses were similar (P greater than 0.05). ACTH treatment did not increase serum cortisol concentrations above the 2-fold increase measured in bulls treated with saline, hCG and GnRH (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

GnRH-induced gonadotrophin secretion in ovariectomized Booroola ewes with hypothalamic--pituitary disconnection

To test whether the F gene-specific differences in the plasma concentrations of FSH and LH are due to differences in the pituitary responsiveness to exogenous GnRH, ovariectomized Booroola ewes with hypothalamic-pituitary disconnection (HPD-ovx) were treated with GnRH (250 ng i.v.) once every 2 h for up to 5 weeks. In Exp. 1, jugular venous blood was collected once weekly from 13 FF and 14 ++ HPD-ovx ewes for 6 weeks before GnRH treatment and every 2nd, 3rd or 6th day for 5 weeks during treatment. In Exp. 2, jugular venous blood was collected from another 8 FF and 7 ++ HPD-ovx ewes at 5- or 10-min intervals over 4 GnRH pulses (250 ng i.v. once every 2 h) on 3 separate occasions after the animals had been subjected to the GnRH pulse regimen for approximately 7 days beforehand. Also in Exp. 2, the animals were extensively sampled around a larger (10 micrograms) i.v. injection of GnRH and the pituitary FSH and LH contents assessed after the animals had been re-exposed to the once every 2 h GnRH (250 ng i.v.) pulse regimen for several days following the larger GnRH bolus. In Exp. 3 the distributions of mean plasma concentrations of FSH and LH in individual GnRH-treated HPD-ovx ewes were compared with those in ovariectomized and ovary-intact FF and ++ ewes. During the 6 weeks before GnRH treatment (Exp. 1), the plasma concentrations of FSH (approximately 1 ng/ml) and LH (less than or equal to 0.8 ng/ml) were not different between the genotypes. After GnRH treatment both the mean FSH and LH concentrations increased significantly (P less than 0.01) above basal values after 2 days with F gene-specific differences being noted for FSH but not LH (FSH; FF greater than ++; P less than 0.05). Thereafter, the mean FSH but not LH concentrations increased at a faster rate in FF than in ++ ewes with the overall mean FSH concentrations between the genotypes being significantly different (P less than 0.05). In Exp. 2 considerable between-animal variation in the pulsatile pattern of FSH but not LH concentrations was seen in ewes of both genotypes during GnRH treatment. The overall mean FSH concentrations were higher in FF than in ++ ewes (P less than 0.05) and the mean FSH response to each GnRH pulse was significantly higher in FF than in ++ ewes (P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of luteolysis during late pregnancy on pituitary responsiveness to gonadotrophin-releasing hormone in the rat

We investigated whether the increase in the gonadotrophin response to gonadotrophin-releasing hormone (GnRH) during the last days of pregnancy and the occurrence of parturition on day 22 of pregnancy in rats are due to the increase in the plasma concentrations of oestradiol-17 beta after luteolysis, which occurs around day 20. In a first series of experiments we studied the effects of s.c. implantation of two capsules containing oestradiol on basal and GnRH-stimulated secretion of LH and FSH before and after luteolysis. Before luteolysis, ovariectomy increased basal LH and FSH; oestradiol treatment prevented this increase partly (FSH) or completely (LH). Ovariectomy also lowered the LH response to the infusion of GnRH (100 ng/h). Oestradiol treatment on the other hand, increased the LH and FSH responses of both intact and ovariectomized rats above the level in intact non-treated control rats. After luteolysis, ovariectomy increased basal FSH only. Treatment with oestradiol did not prevent the increase in basal FSH and ovariectomy diminished the LH response to GnRH infusion. Oestradiol treatment maintained the LH response in ovariectomized rats at the control level and increased the FSH responses of both intact and ovariectomized rats to a higher level than in control rats. Furthermore, the LH and FSH responses of the oestradiol-treated groups of intact and ovariectomized rats were higher after luteolysis than before. In a second series of experiments two capsules containing progesterone were s.c. implanted before or after luteolysis. Progesterone treatment suppressed the plasma concentration of oestradiol and the gonadotrophin responses to infusion of GnRH on the expected day of parturition in both groups of rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Basement Membrane Increases G-Protein Levels and Follicle-Stimulating Hormone Responsiveness of Sertoli Cell Adenylyl Cyclase Activity*

On a basement membrane substrate, Sertoli cells in culture have been shown to assume a phenotype similar to that of the in vivo differentiated cells. Sertoli cells from 10-day-old rats were cultured on plastic and on different extracellular matrix substrates [laminin, a reconstituted basement membrane (Matrigel), and a synthetic laminin peptide containing the arginine-glycine-aspartic acid (RGD) tripeptide sequence] to investigate the effects of the extracellular matrix on FSH responsiveness. Both laminin and Matrigel markedly enhanced the cAMP response to FSH and cholera toxin, indicating modifications at the level of guanine nucleotide-binding regulatory (G) proteins. Furthermore, Sertoli cell grown on either of these two substrates responded to physiological levels of FSH (25-50 ng/ml), whereas pharmacological levels of FSH (500 ng/ml) were required for cells grown on either plastic or on the RGD-containing laminin peptide. Immunoblotting of Sertoli cell plasma membranes with antibodies directed against the alpha-subunit of the stimulatory G-protein (Gs alpha) of adenylyl cyclase indicated that Sertoli cell culture on either laminin or Matrigel increased the amounts of Gs alpha. These results were further confirmed by immunoprecipitating the Gs alpha protein from the particulate fraction of [35S]methionine metabolically labeled Sertoli cells. However, Northern blot analysis using a cDNA probe for Gs alpha did not demonstrate changes in gene expression when Sertoli cells were grown on the various substrates. Immunofluorescent studies revealed that the Gs complex of adenylyl cyclase was preferentially located at the base of the Sertoli cells at the site of contact with the extracellular matrix. These data suggest that culture of epithelial Sertoli cells on basement membrane substrates enhances the Gs complex of adenylyl cyclase and the cAMP response to FSH, consistent with the more differentiated morphology and function of the cells.

Dexamethasone Alters Responses of Pituitary Gonadotropin-Releasing Hormone (GnRH) Receptors, Gonadotropin Subunit Messenger Ribonucleic Acids, and Gonadotropins to Pulsatile GnRH in Male Rats*

Dexamethasone (Dex), when administered in high doses, has been shown to suppress spontaneous and GnRH-induced gonadotropin secretion, but the level and the mechanism(s) of this effect are unknown. We administered Dex to castrate testosterone-replaced male rats to determine if gonadotropin gene expression is affected and whether Dex differentially influences GnRH-modulated parameters of gonadotrope function: induction of GnRH receptors (GnRH-R) and gonadotropin synthesis and secretion. GnRH was given iv at 25 ng/pulse at 8, 30, and 120 min intervals for 48 h. Rapid GnRH injection frequency preferentially increased alpha and LH-beta messenger RNA (mRNA) responses to GnRH as well as LH secretion. Slower GnRH injection frequencies were required to increase levels of GnRH-R, FSH-beta mRNA, and FSH secretion. Dex selectively inhibited the serum LH, alpha, and LH-beta mRNA responses to GnRH, but not the serum FSH or FSH-beta mRNA responses. Additionally, it augmented the GnRH-induced increase in GnRH-R. We conclude: 1) induction of GnRH-R, gonadotropin synthesis, and secretion require different modes of GnRH stimulation; 2) Dex acts directly on the gonadotrope to differentially modulate GnRH-induced increases in GnRH-R levels, gonadotropin gene expression, and gonadotropin secretion; and 3) GnRH effects upon induction of GnRH-R, LH, and FSH synthesis and secretion are likely to be mediated via different cellular pathways.

The short-term reproductive toxicity of cyclophosphamide in the female rat

Cyclophosphamide (CTX) is a potent ovarian toxicant. Previous studies of the acute effects of CTX in the rat have demonstrated widespread ovarian follicle atresia, reduced serum estradiol, and progesterone with normal serum LH and FSH. The present investigations demonstrate that a single injection of CTX induces ovarian toxicity that reflects the loss of growing ovarian follicles. CTX induces a sensitization of serum FSH in response to GnRH within 24 h; this sensitization is lost by 7 days, and after 14 days the animals are capable of normal mating behavior. The observed protection of primordial follicles from the acute administration of CTX under these experimental circumstances may be related to the stage of the granulosa cell cycle of these follicles.

Cyclosporine-Induced Alterations in the Hypothalamic Hypophyseal Gonadal Axis in Transplant Patients

We evaluated the response of 20 male patients, 13 cadaveric kidney and 7 heart transplant recipients, to the administration of 100 micrograms GnRH (gonadotropin-releasing hormone) and 500 micrograms TRH (thyrotropic-releasing hormone). All of the heart transplant recipients and 7 of the kidney transplant patients were receiving a combination of cyclosporine, azathioprine and prednisone; while the 6 remaining kidney transplant patients received azathioprine and prednisone. The patients receiving cyclosporine had decreased plasma levels of prolactin, and manifested a blunted response to TRH administration for prolactin and TSH. The heart transplant patients had a blunted response of LH and FSH to the administration of GnRH. The levels of testosterone were found to be low in all patients regardless of the immunosuppressant therapy. Despite the low testosterone levels, no increment in the concentration of LH or FSH was present. Intramuscular administration of HCG (human chorionic gonadotropin) (Ayerst Laboratories, New York, N.Y.) failed to increase the testosterone concentration in 5 of 6 patients with renal transplants, 3 taking cyclosporine and 3 taking azathioprine. This study suggests that cyclosporine has a selective effect on the hypothalamus and/or hypophysis, resulting in lower baseline levels of plasma prolactin and a pituitary insensitivity to TRH administration. In addition, FSH and LH were low or normal in the presence of low testosterone levels, suggesting that the hypothalamic pituitary gonadal axis is impaired. Furthermore, there may be a direct toxic effect of the immunosuppressant medications on the gonads, manifested as lower testosterone levels and inability to respond to the administration of HCG.

LH- and FSH-Secreting Pituitary Adenoma in a Postmenopausal Woman.

Gonadotropin secreting pituitary adenomas have been reported with increasing frequency in men, but they are still rarely recognized in women. We report a 52-year-old postmenopausal woman with LH- and FSH-secreting pituitary adenoma. She had increased LH (37.0 +/- 13.7 IU/l) (mean +/- SD) and FSH (109.9 +/- 26.7 IU/l) but these concentrations were within normal ranges in 80 postmenopausal women (LH: 29.7 +/- 18.3 IU/l, FSH: 104.0 +/- 43.9 IU/l). The administration of GnRH and conjugated estrogen resulted in normal response of LH and FSH. No abnormal response of gonadotropin to TRH and bromocriptine was observed. After transsphenoidal adenomectomy both LH and FSH decreased (LH: 11.1 +/- 4.2 IU/l, FSH: 37.0 +/- 9.6 IU/l). An immunocytochemical study revealed that the adenoma cells synthesize both LH and FSH. The rarity of gonadotropin secreting pituitary adenomas in women could be the result of greater difficulty in recognition due to an increase in serum gonadotropin in postmenopausal women.

INFLUENCE OF HYPOTHALAMIC-RELEASING HORMONE ON AUTONOMIC NERVOUS SYSTEM DETERMINED BY VARIATIONS IN R-R INTERVALS ON ELECTROCARDIOGRAM (ECG)

Hypothalamic hormone is suggested to have an effect on extrapituitary sites. Little information is available about the effects of hypothalamic-releasing hormones on the human autonomic nervous system. Variations in R-R intervals on electrocardiogram (ECG), a parameter of parasympathetic nervous system function, have been used clinically as an indicator of autonomic nervous system dysfunction in various diseases. An attempt was made to determine serial variations in R-R intervals on ECG.Studies were conducted with 23 healthy controls and 52 patients with Graves' disease. Variations in R-R intervals were expressed as the coefficient of variation of 100 resting heart rates (CV%=SD/Mean x 100, CVq).Injection of TRH (500μg, iv) to healthy controls produced a significant elevation of CVq (4.37±0.53% before vs. 5.46±0.40% after TRH, p <0.01) within 15 min. A similar result was obtained in patients with Graves' disease. Pretreatment with atropine (0.5mg, div) or pirenzepine hydrochloride (250mg, po) abolished the stimulatory effect of TRH on CVq. Pretreatment with Clofedanol (75mg, po), which is reported to have an inhibitory effect on the meddula oblongata, and hexamethonium bromide (300mg, po), a ganglionic blocker, resulted in a significant reduction in CVq during TRH test. There was no change in plasma catecholamine concentrations following TRH administrations. Intravenous injection of CRF (50μg) produced a significant decrease in CVq. Pretreatment with propranolol (30mg, po) blocked the effect of CRF. On the other hand, iv administration of GRF (50μg) or LHRH (100μg) had no effect on CVq, while normal responses of serum GH, LH and FSH were observed.In conclusion, TRH stimulates CVq in normal subjects and patients with Graves disease. It is suggested that TRH potentiates the parasympathetic nervous system, regardless of circulating thyroid hormone levels. In contrast, CRF has a suppressive effect on vagal activity in human subjects, probably associated with adrenergic β-effect. Both GRF and LHRH seemed to have little effect on the autonomic nervous system at clinical doses. The present study is the first demonstration that some hypothalamic-releasing hormones affect the autonomic nervous system, as indicated by the variations in R-R intervals on ECG.

Response of gonadotropins to pituitary stimulation with luteinizing hormone releasing hormone is a more specific than sensitive parameter for the polycystic ovary syndrome

Gonadotropin response to exogenous luteinizing hormone-releasing hormone (LHRH) was studied in two groups of patients with the polycystic ovary syndrome (PCOS). Group I (n = 44) was diagnosed as 'overt PCOS' based on clinical and endocrine abnormalities, and the typical ultrasonic picture of multicystic changes in an increased amount of ovarian stroma. Group II patients (n = 34), with similar clinical and hormonal changes, were classified as 'borderline PCOS' because endosonography of the ovaries was not conclusive. Serum gonadotropins were followed 15, 30, 45 and 60 min after administration of 100 micrograms LHRH intravenously. Plasma LH and the peak ratio of luteinizing hormone to follicle stimulating hormone (LH/FSH peak) after LHRH were significantly higher in Group I and II patients (p less than 0.001) than in controls (n = 11). There was a significant positive correlation between LH (r = 0.73 and 0.68, p less than 0.05) and LH/FSH ratio peaks (r = 0.61 and 0.68, p less than 0.05) after LHRH, and the basal values in each group. However, hyperreactivity of LH and the LH/FSH ratio after LHRH (defined as values exceeding the 95th percentile of control values) was only present in Group I in 38.6 and 56.8%, and in Group II in 47.1 and 73.5% of patients. It is concluded that: exaggerated LH release after LHRH is a typical yet not unique feature of PCOS and its sensitivity is inferior to its specificity; a higher rate for sensitivity is achieved when the LH/FSH ratio after LHRH (instead of LH release alone) is used; and that hyperreactivity of LH after LHRH is neither correlated with the plasma concentrations of total testosterone, free plasma testosterone or androstenedione, nor with the ultrasonic picture of the ovaries as significantly higher (p less than 0.05) LH and LH/FSH ratio peaks were found in borderline PCOS patients. While the heterogeneity of gonadotropin response to LHRH clearly limits its routine diagnostic use, the FSH and LH response is useful in patients with inconsistent clinical and ultrasonic features suggestive of PCOS.

Exogenous melatonin enhances the TRH-induced prolactin release in normally cycling women: a sex-specific effect.

The aim of the present study was to analyze the effects of exogenous melatonin (MT) upon pituitary and adrenal responsiveness to releasing hormones in different phases of the menstrual cycle. We evaluated the response of FSH and LH to 100 micrograms gonadotropin releasing hormone, of TSH and prolactin (PRL) to 200 micrograms thyrotropin releasing hormone (TRH), and of cortisol to 10 micrograms ACTH 1-17. We studied eight young women with normal ovulatory cycles in the early follicular (days 5-7) and luteal (days 22-24) phases. Stimulation tests were performed at 18.00 in baseline conditions as well as 1 h after oral intake of exogenous MT (2 mg as a gelatine capsule). We did not observe any significant change in FSH, LH, TSH and cortisol responses to their respective releasing hormones in either phase of the cycle. PRL response to TRH was higher after MT in the follicular phase, when evaluated in terms of net increment and integrated area of response (p less than 0.02 versus baseline conditions for both variables). In the luteal phase, we recorded larger interindividual variability and higher responses after MT were observed in five out of eight subjects. These results suggest that MT may play a facilitatory role in the TRH-induced PRL release in women of reproductive age.