Leydig cell insufficiency in hypospermatogenesis: a paracrine effect of activin-inhibin signaling?

Clinical findings and a variety of experimental models indicate that Leydig cell dysfunction accompanies damage to the seminiferous tubules with increasing severity. Most studies support the idea that intratesticular signaling from the seminiferous tubules to Leydig cells regulates steroidogenesis, which is disrupted when hypospermatogenesis occurs. Sertoli cells seem to play a pivotal role in this process. In this review, we summarize relevant clinical and experimental observations and present evidence to support the hypothesis that testicular activin signaling and its regulation by testicular inhibin may link seminiferous tubular dysfunction to reduced testosterone biosynthesis.

Identification of gene networks modulated by activin in LbetaT2 cells using DNA microarray analysis

Activins, members of the TGFbeta family of proteins, are widely expressed in a variety of tissues. First identified based on their ability to regulate biosynthesis and secretion of follicle-stimulating hormone (FSH), activins have also been shown to modulate development, cell growth, apoptosis, and inflammation. Despite their many known functions, the precise mechanisms and downstream signaling pathways by which activins mediate their diverse effects remain unknown. We have used a DNA microarray assay to identify genes that are regulated by activin, alone or in combination with gonadotropin-releasing hormone (GnRH), another major regulator of FSH, in a murine gonadotrope-derived cell line (LbetaT2). We used mRNA from these cells to screen Affymetrix Mu74av2 mouse Gene Chip oligonucleotide microarrays, representing approximately 12,400 mouse genes. Treatment of LbetaT2 cells with activin A, a gonadotropin-releasing hormone agonist (GnRHA) or activin A plus GnRHA resulted in alterations in levels of gene expression that ranged in magnitude from 15 to 67-fold. Data analysis identified 268 transcripts that were up- or down-regulated by two-fold or more. Distinct sets of genes were affected by treatment with activin, GnRHA and activin plus GnRHA, suggesting interactions between activin and GnRHA. Changes in expression of seven randomly selected representative genes identified by the microarray technique were confirmed by real-time quantitative PCR and semi-quantitative reverse transcription/PCR (RT/PCR). Modulation of expression of genes by activin suggests that activin may mediate its effects through a variety of signaling pathways.

Testosterone, sex hormone-binding globulin, and body composition in young adult African American and Caucasian men

This study examined the diurnal variation in circulating total and free testosterone and sex hormone-binding globulin (SHBG) levels in young adult African American and Caucasian men in order to investigate whether there are differences in the secretion of these plasma hormones in populations at different risks of developing prostate cancer as they age. A significant and similar diurnal rhythm for total and free testosterone was found for both groups. Serum levels of total testosterone were 29.4% and 23.9% lower at 8:00 PM than at 8:00 AM in African American and Caucasian men, respectively. Significantly higher serum levels of total testosterone (P<.01) and SHBG (P <.02) were found in the African American than in the Caucasian men in both the morning and evening, whereas free testosterone levels were similar in both groups. The higher SHBG levels appear to have an environmental/metabolic basis in that the waist circumference, waist-to-hip ratio, and fasting insulin concentration were lower (P <.05) in African Americans than in Caucasians. In summary, these data indicate that racial differences in central adiposity in men are established in early adulthood and influence circulating SHBG and thereby testosterone levels. In light of the findings by others that SHBG increases cyclic adenosine monophosphate (cAMP) production in the prostate and that cAMP-dependent protein kinase A is a coactivator of the androgen receptor, these studies provide a possible mechanism by which circulating androgens may contribute to the increased risk for prostate cancer among African American men.

Pituitary follistatin and activin gene expression, and the testicular regulation of FSH in the adult Rhesus monkey (Macaca mulatta)

In rats, FSHbeta gene expression and FSH secretion are increased and decreased, respectively, by pituitary activin and follistatin. Because little information is available on the paracrine control of FSH secretion in the primate, follistatin and activin/inhibin beta(B) messenger RNA (mRNA) levels were measured in pituitaries of adult male rhesus monkeys 6 weeks after castration or sham surgery (n = 5/group). Follistatin mRNA was determined by quantitative RT-PCR assay using oligonucleotide primers designed to span exons 3-5 of the human follistatin gene. Activin/inhibin beta(B) mRNA levels were measured by ribonuclease protection. Orchidectomy resulted in a 100-fold increase in plasma FSH concentrations and a 60-fold rise in those of LH. In castrated monkeys, levels of mRNA encoding FSHbeta, LHbeta, alpha- subunit, and GnRH receptor (GnRH-R) were increased 21-, 2.1-, 1.7-, and 1.7-fold, respectively (P < 0.01). Levels of pituitary follistatin and activin/inhibin beta(B) mRNAs, however, were similar in castrated and intact animals. These data suggest that the paracrine control of FSH secretion in the male differs substantially in primates and rodents. Specifically, the relatively greater postcastration rise in FSHbeta gene expression and FSH secretion in the adult male monkey may result because in this species pituitary follistatin gene expression does not increase after orchidectomy, as it does in the rat.

Follistatin production by skin fibroblasts and its regulation by dexamethasone

Activin and follistatin (FS) appear to play a role in the development of the skin and its appendages, in the inflammatory process, angiogenesis, and in wound healing. Although there is information on the expression of activin subunits and receptors in fibroblasts and keratinocytes, there are no reports on the regulation of FS expression in these cells. In the present study we analyzed the splicing variants of FS mRNAs in fibroblasts from genital and nongenital skin by RT-PCR and northern analysis, and examined the induction of FS mRNA and protein by hormones and growth factors in skin fibroblasts from human and nonhuman primates. FS mRNA was highly expressed in all fibroblast strains with similar expression regardless of donor species (human or monkey), donor age (neonate or adult), or the organ from which the fibroblast strains were established (skin or pituitary, genital or non-genital skin). Moreover, the band density corresponding to FS-288 was <5-10% of the value for FS-315 in skin fibroblasts as in all other tissues examined. Fibroblast FS mRNA and protein production were biphasically regulated by dexamethasone: low concentrations (0.01 and 0.1 nM) increased whereas higher concentrations (>1 nM) suppressed FS expression. On the other hand, androgens, activin and PACAP38 were without effect. These data establish cultured skin fibroblasts as a model to study FS gene expression in humans, and support a role for follistatin in the normal immune response and in the anti-inflammatory actions of glucocorticoids.

Serum testosterone levels decrease in middle age in women with the polycystic ovary syndrome

OBJECTIVE

To determine whether testosterone levels change as women with the polycystic ovary syndrome (PCOS) grow older.

DESIGN

A follow-up cross-sectional study of a cohort of women with PCOS identified up to 20-25 years ago.

SETTING

Women with PCOS were recruited primarily from practice records between 1970 and 1990. Voter registration tapes and household directories were used to identify age-, race-, and neighborhood-matched controls.

PARTICIPANT(S)

Eighty-four women with PCOS, 20-57 years of age, and 37 age-matched controls participating in a study of the risk for cardiovascular disease in women with PCOS.

INTERVENTION(S)

Clinical data were collected by questionnaire and fasting blood samples were obtained randomly throughout the menstrual cycle.

MAIN OUTCOME MEASURE(S)

Total and non-SHBG-bound testosterone levels.

RESULT(S)

Total and non-SHBG-bound testosterone levels were similar in women with PCOS who were 20-42 years of age but were reduced by approximately 50% among women 42-47 years of age and remained stable in women older than 47 years of age. Testosterone levels were increased in younger and older women with PCOS compared with controls but were similar to controls in women 42-47 years of age.

CONCLUSION(S)

Hyperandrogenism partly resolves before menopause in women with PCOS. This change may explain the tendency of women with PCOS to cycle regularly as they grow older. Testosterone levels remain elevated in older women with PCOS, however, and may contribute to their increased risk for cardiovascular disease, endometrial cancer, and other diseases.

Partial characterization of circulating inhibin-B and pro-alphaC during development in the male rhesus monkey

Gel filtration chromatography and ELISAs for inhibin-B and pro-alphaC were used to examine the circulating forms of inhibin in the neonatal (age 2-6 weeks), juvenile (age 1-2 yr), and adult male rhesus monkey. In all samples, isoforms of inhibin-B of 26-36K and 150K were found. Both forms were significantly greater in the adult. The alpha-subunit assay detected major peaks at 45-60 and 29-31K, and a minor peak of greater than 100K. As for inhibin-B, the major forms of inhibin pro-alphaC were highest in adulthood. Inhibin-B and pro-alphaC were measurable in peripheral plasma at age 1 week, increased with the neonatal rise in plasma FSH, and then decreased but remained detectable through age 1 yr. Values in adult males were higher than at any time during the first year of life. Finally, mean values of plasma inhibin-B and pro-alphaC in five monkeys, based on multiple blood samples drawn between age 1 week and 1 yr, were rank ordered and were found to be highly positively correlated (r = 0.96), suggesting that inhibin levels in the first year of life may be a marker of Sertoli cell number, and may predict the spermatogenic capacity of the testis in adulthood.

Regulation of lutenizing hormone secretion and subunit messenger ribonucleic acid expression by gonadal steroids in perifused pituitary cells from male monkeys and rats

The mechanisms by which gonadal steroids regulate gonadotropin secretion remain incompletely understood. As previous studies suggest that the pituitary actions of testosterone (T) and estradiol (E) differ in male primates and rodents, we compared the effects of 10 nM T, 0.1 nM E, and 10 nM dihydrotestosterone (DHT) on the LH response to hourly pulses of GnRH as well as the GnRH receptor (GnRH-R) and LH subunit messenger RNA (mRNA) levels in dispersed pituitary cells from intact male monkeys and rats. T suppressed (P < 0.01) and E increased (P < 0.05) GnRH-stimulated LH secretion by rat pituitary cells. With monkey pituitary cells, on the other hand, there was no significant effect of either T or DHT on GnRH-stimulated LH secretion. In E-treated monkey cells, a period of initial enhancement (P < 0.05) was followed by significant suppression (P < 0.05) of LH secretion. GnRH-R mRNA was unchanged by T or E in either rat or monkey cells. T suppressed LHbeta (P < 0.01) and alpha-subunit (P < 0.01) mRNAs, whereas E increased alpha-subunit (P < 0.01), but did not alter LHbeta mRNA levels in rat cells. In monkey cells, however, neither T nor E affected LHbeta or alpha-subunit mRNA levels significantly. Our results identify different regulatory mechanisms by which testicular steroid hormones control LH secretion by the pituitary in male primates and rodents. We propose that the primary site of androgen negative feedback in the male primate is to restrain GnRH pulsatile secretion, whereas in the male rat T also decreases gonadotropin synthesis and secretion by directly affecting the pituitary. E suppresses GnRH-stimulated LH secretion in the primate pituitary, but amplifies the action of GnRH in the rat. Our data also reveal that the action of T to suppress LH secretion and subunit mRNA in male rats is not through decreased GnRH-R gene expression.

Visceral obesity and insulin resistance are associated with plasma aldosterone levels in women

OBJECTIVE

Both obesity and insulin resistance increase the risk of hypertension and other cardiovascular diseases, but the mechanisms linking these abnormalities are unknown. The current study was undertaken to examine the effects of obesity, fat distribution, and insulin resistance on plasma levels of aldosterone and other adrenal steroids that might contribute to sequelae of obesity.

RESEARCH METHODS AND PROCEDURES

Twenty-eight normotensive premenopausal women and 27 normotensive men with a wide range of body fat underwent measurements of visceral adipose tissue by CT scan, total fat mass by dual energy X-ray absorptiometry, blood pressure, insulin sensitivity, and plasma levels of three adrenal steroid hormones.

RESULTS

Plasma aldosterone in women correlated directly with visceral adipose tissue (r=0.66, p<0.001) and inversely with insulin sensitivity (r=-0.67, p<0.001), and these associations were independent of plasma renin activity. There were no corresponding correlations in men. Plasma aldosterone was significantly correlated with plasma cortisol and dehydroepiandrosterone sulfate in women. Seventeen women and 15 men completed a weight-reduction regimen, losing an average of 15.1+1.2 kg. After weight loss, plasma aldosterone was significantly lower and insulin sensitivity higher; however, the correlations of aldosterone with visceral adipose tissue and insulin sensitivity in women persisted (p = 0.09 and 0.07, respectively). Although none of the women were hypertensive, blood pressure correlated with plasma aldosterone both before and after weight loss.

DISCUSSION

We conclude that visceral adiposity and insulin resistance are associated with increased plasma aldosterone and other adrenal steroids that may contribute to cardiovascular diseases in obese women.

Current status of testosterone replacement therapy in men

Testosterone plays an essential role in the development of the normal male and in the maintenance of many male characteristics, including muscle mass and strength, bone mass, libido, potency, and spermatogenesis. Androgen deficiency occurs with disorders that damage the testes, including traumatic or surgical castration (primary testicular failure) or disorders in which the gonadotropin stimulation of the testes is reduced (hypogonadotropic hypogonadism). The clinical manifestations of androgen deficiency depend on the age at onset and the severity and duration of the deficiency. In adult males, these manifestations may include reduced body hair, decreased muscle mass and strength, increased fat mass, decreased hematocrit, decreased libido, erectile dysfunction, infertility, osteoporosis, and depressed mood. The forms of androgen replacement currently available in the United States are intramuscular depot injections of testosterone esters, oral tablets of testosterone derivatives, and transdermal patches. For most patients, androgen replacement therapy with testosterone is a safe, effective treatment for testosterone deficiency.

Secretion of testosterone and its delta4 precursor steroids into spermatic vein blood in men with varicocele-associated infertility

Insight into the mechanisms by which steroid hormones are released from the testes was sought by examining the concentrations of progesterone, 17alpha-hydroxyprogesterone, and androstenedione as well as testosterone in spermatic vein blood every 15 min for 4 h in men with varicocele-associated infertility. Coincident discrete secretory episodes of all four steroids were found, and spermatic vein concentrations of testosterone were highly positively correlated to the concentrations of progesterone (r = 0.79), 17alpha-hydroxyprogesterone (r = 0.81), and androstenedione (r = 0.82), respectively. The sum of the four measured steroids per mL plasma was calculated, and testosterone was found to account for 70%, 17alpha-hydroxyprogesterone for 24%, androstenedione for 5%, and progesterone for 1% of the total. In a previous study of the intratesticular steroids in a separate population of men with varicocele-associated infertility, the sum of these four steroids per g tissue was similarly calculated. Testosterone accounted for 70% of the four measured steroids, 17alpha-hydroxyprogesterone for 22%, androstenedione for 4%, and progesterone for 3% of the total. Thus, the relative concentrations of these four steroids are nearly identical in testicular tissue and spermatic vein plasma. From these data we hypothesize that steroids in the testicular interstitium are cosecreted into peripheral plasma in response to stimulation by LH and propose that the mechanism initiating this pulsatile mode of secretion oftestosterone and its precursor steroids may not be coupled to testosterone biosynthesis.

The analog free testosterone assay: are the results in men clinically useful?

Men with low testosterone concentrations are usually hypogonadal. However, because variations in the testosterone transport protein, sex hormone-binding globulin (SHBG), directly influence the total testosterone concentration, confirmation of a low testosterone with a measurement of free testosterone or "bioavailable" testosterone (BAT) is recommended. In the present study, we examined the relationship of SHBG with free testosterone (Coat-A-Count assay, Diagnostic Products) and with BAT in men (n = 29) and women (n = 28) who participated in a study of the metabolic determinants of body composition. As expected, total testosterone was strongly positively correlated with SHBG among men (r = 0.68; P <0.01). Although the BAT was independent of SHBG in men (r = 0.02), SHBG was an important predictor of free testosterone (r = 0.62; P <0.01). In contrast, in women serum concentrations of total testosterone (r = -0.26; P = 0.17), free testosterone (r = -0.30; P = 0.17), and BAT (r = -0.46; P = 0.013) all tended to be lower with increasing SHBG. Free testosterone was nearly perfectly positively correlated with total testosterone (r = 0.97) in men, among whom free testosterone represented a relatively constant percentage of the total testosterone (0.5-0.65%), and the percentage of free testosterone was unrelated to SHBG. Thus the Coat-A-Count free testosterone concentration in men, like the total testosterone concentration, is determined in part by plasma SHBG. Accordingly, androgen deficiency may be misclassified with this assay in men with low SHBG. Moreover, the previous findings of reduced free testosterone concentrations with hypertension or hyperinsulinemia or as a risk factor for developing type 2 diabetes, conditions in which SHBG is reduced, may have been methodology-related.

The time course of follicle-stimulating hormone suppression by recombinant human inhibin A in the adult male rhesus monkey (Macaca mulatta)

In higher primates, FSH secretion appears to be regulated by a control system consistent with that described by the classical inhibin hypothesis. The purpose of the present experiment was to examine the time course of inhibin's action to suppress FSH secretion in the intact adult male rhesus monkey. To this end, five adult males implanted with indwelling venous catheters and exhibiting typical episodic patterns of LH and testosterone (T) secretion received a 4-day i.v. infusion of recombinant human (rh) inhibin A (832 ng/h x kg) followed, after a 4-week interval, by vehicle infusion of similar duration. Changes in circulating FSH concentrations during the inhibin and vehicle infusions were determined using a sensitive homologous macaque RIA, whereas enzyme-linked immunosorbent assays were employed to track inhibin A, inhibin B, and inhibin pro-alpha-C levels during the experiment. Normal pulsatile activity in the hypothalamic-pituitary-Leydig cell axis was confirmed by monitoring changes in circulating concentrations of LH and T in 12-h windows of sequential blood collection (1200-2400 h; every 20 min) before, during, and after the rh inhibin A and vehicle infusions. Although infusion of rh inhibin A, which led to a 12 ng/ml square wave increment in circulating levels of this inhibin dimer, produced a marked decline in circulating FSH concentrations, significant suppression of the secretion of this gonadotropin was not manifest until 54 h after initiation of the infusion. Despite the marked decline in FSH secretion during the last 24 h of the 4-day infusion of recombinant hormone, circulating inhibin B and pro-alpha-C concentrations were maintained at preinfusion control levels (1 ng/ml). The finding that imposition of an exaggerated circulating inhibin signal led to suppression of FSH secretion in the male monkey only after 2 days of exposure to the hormone indicates that in this species the feedback action of testicular inhibin on FSH secretion is heavily lagged. Moreover, as the decrease in FSH did not lead to changes in native inhibin secretion, it seems reasonable to propose that the FSH-inhibin feedback loop that governs testicular function in higher primates operates with considerable hysteresis at both the pituitary and gonadal levels. The failure of dramatically elevated inhibin A levels to influence the pulsatile secretion of LH in the monkey reinforces the idea that in this species the pituitary action of testicular inhibin is specific for FSH and does not involve modulation of GnRH receptor levels.

Procedures for the isolation and culture of Sertoli cells from the testes of infant, juvenile, and adult rhesus monkeys (Macaca mulatta)

The purpose of the present study was to establish culture conditions for the in vitro study of the rhesus monkey Sertoli cell (Sc) at three major stages of development, namely infancy, adulthood, and the intervening prepubertal period. Conditions for the culture of Sc from juveniles were first established using collagenase and pancreatin digestion of seminiferous tubules. The addition of 1% fetal bovine serum for the first 24 h of culture was necessary for attachment of Sc clusters. Confluency of Sc from juveniles was reached as early as 4 days of culture. Histochemical and ultrastructural observations confirmed that the cultures were enriched with Sc and that contamination by peritubular cells was minimal (2%). Although application of similar culture conditions was successful in establishing cultures of Sc from infants, significant modification of the procedure was required before Sc from adults could be cultured. Specifically, adult testicular tissue required two sequential collagenase digestions at elevated temperature. The yield of adult Sc, however, remained low. Cultures of juvenile Sc produced substantial quantities of 31-kDa inhibin, which was bioactive as reflected by its ability to suppress FSH secretion from rat pituitary cells in vitro. Although aromatase activity in juvenile Sc cultures was stimulated by FSH, inhibin synthesis, as reflected by immunoactive inhibin production and steady-state levels of alpha inhibin mRNA, was not increased by FSH. The establishment of conditions for the culture of infant, juvenile, and adult Sc from the rhesus monkey will provide a model for study of the postnatal ontogeny of Sc function in higher primates.

Transcriptional regulation of the glycoprotein hormone alpha-subunit gene by pituitary adenylate cyclase-activating polypeptide (PACAP) in alphaT3-1 cells

We showed previously that pituitary adenylate cyclase-activating polypeptide (PACAP) increases glycoprotein hormone alpha-subunit gene expression and secretion in alphaT3-1 cells. We have now used 5'-flanking deletion and clustered point mutations of the mouse alpha-subunit promoter fused to the luciferase (LUC) reporter gene in transient transfection assays to further characterize the cell signaling pathways and sequences involved in responsiveness to PACAP. PACAP stimulated LUC activity at a lower concentration than VIP, supporting the notion that PACAP acts through type 1 receptors. The effect of PACAP on LUC activity was observed by 2 h, peaked at 4-12 h, and persisted until at least 20 h. alphaT3-1 cells were transfected with mouse alpha-LUC constructs truncated at -507, -424, -288, -205, -146, and -133, and treated with PACAP, a cell-permeable cAMP analog (8Br-cAMP), phorbol myristate acetate (PMA), or control medium. Transcriptional activation by PACAP was highest with the -288 and -205 mouse alpha-LUC vectors (7-8-fold stimulation) and decreased significantly with truncation of the 5'-flanking region to -146 or -133. The pattern of alpha-subunit stimulation by cAMP closely paralleled that of PACAP. With PMA, stepwise decrements in LUC activity were observed between -507 and -424 and, especially, -424 and -288, and there was no further loss of activity with deletion to -205, -146, or -133. Clustered point mutations in the pituitary glycoprotein hormone basal element (-337 to -330) or the gonadotropin-releasing hormone response element (GnRH-RE)(-406 to -399) of the -507 to +46 mouse alpha-promoter significantly (P < 0.05) increased and decreased, respectively, PACAP's effect on transcriptional activity. These results indicate that there are several regions of the mouse alpha-subunit promoter that mediate responsiveness to PACAP. The co-localization of PACAP and cAMP responsiveness as well as the results of studies involving specific inhibitors of protein kinase A (H-89) or protein kinase C (PKC) (bisindolylmaleimide) suggests that the action of PACAP on alpha-subunit transcription is mediated primarily by the protein kinase A (PKA) pathway.

Evidence that pituitary adenylate cyclase activating polypeptide suppresses follicle-stimulating hormone-beta messenger ribonucleic acid levels by stimulating follistatin gene transcription

There is accumulating evidence to suggest that pituitary adenylate cyclase-activating polypeptide (PACAP) may be an important modulator ofgonadotrope function. One of the actions of PACAP identified previously is to decrease FSHbeta messenger RNA (mRNA) levels. In the present series of experiments we demonstrate that PACAP-induced suppression of FSHbeta mRNA correlates with a rise in follistatin mRNA levels in primary pituitary cell cultures. Transient transfection of gonadotrope-derived alphaT3-1 cells with a rat follistatin promoter-luciferase reporter plasmid reveals that PACAP stimulates follistatin gene transcription. PACAP stimulation of LUC activity was maximal at concentrations as low at 1 nM. Furthermore, in alphaT3-1 cells PACAP activation of the follistatin promoter appears to be via the cAMP-dependent protein kinase A pathway. Accordingly, we propose that PACAP stimulates follistatin transcription, which neutralizes activin activity and thereby reduces FSHbeta mRNA. Since PACAP and follistatin are colocalized in multiple tissues including the brain, adrenals, and gonads, our findings may reflect a broadly distributed autocrine/paracrine mechanism for modification of activin effects that is under PACAP control.

Serum LH concentrations in hypogonadal men during transdermal testosterone replacement through scrotal skin: further evidence that ageing enhances testosterone negative feedback. The Testoderm Study Group

OBJECTIVE

The present study was designed to explore further the mechanism for the decline in androgen production as men age by studying the influence of ageing on testosterone negative feedback control of gonadotrophin secretion.

DESIGN

Circulating testosterone, dihydrotestosterone, oestradiol, SHBG and LH concentrations were measured during long-term treatment of men with primary hypogonadism using transdermal testosterone via scrotal skin.

PATIENTS

Results were compared in 12 hypogonadal men below age 40 years (34 +/- 1.1 years; mean +/- SEM), 13 middle-aged men, aged 51 +/- 2.2 years, and 10 men age 64 years or older (68 +/- 1.4 years).

RESULTS

During the course of therapy, circulating LH levels were suppressed 48% (F = -2.42, P = 0.018) from 19.6 +/- 6.0 IU/I at baseline to 10 +/- 7.7 IU/I during month 15 in elderly men. By contrast, LH levels were unchanged (F = 0.31; P = 0.97) in young men (20.3 +/- 7.4 IU/I at baseline and 17.7 +/- 14.9 IU/I during treatment month 15). Intermediate results were observed in middle-aged men in whom LH levels declined slightly (F = 1.34; P = 0.24). Transdermal testosterone treatment produced similar circulating testosterone levels (F = 1.49; P = 0.24) and oestradiol levels (F = 0.60; P = 0.42) in elderly and young men. Mean plasma DHT levels were approximately 20% higher (F = 9.91; P = 0.01) during treatment in elderly men overall mean values of 8.03 +/- 0.37 nmol/l) than in young men (6.68 +/- 0.08 nmol/l). When total DHT was adjusted for higher plasma SHBG levels in elderly men, the free DHT index during treatment was similar (F = 0.23; P = 0.64) in both groups.

CONCLUSIONS

These data provide further evidence that the set point for androgen negative feedback control of gonadotrophin accretion in men is altered by ageing. Taken together with previous findings, these results provide a potential explanation for the unchanged or slightly increased plasma LH levels and reduced testosterone production characteristic of elderly men. Accordingly, ageing-associated Leydig cell insufficiency leads to a decline in testosterone production, but circulating LH levels do not rise appropriately because the set-point for negative feedback is decreased.

Circulating concentrations of dimeric inhibin A and B in the male rhesus monkey (Macaca mulatta)

The purpose of this study was to determine the relative concentrations of inhibin A and B in peripheral serum of the adult male rhesus monkey and to examine the testicular contribution to these circulating forms of inhibin. In addition, inhibin B concentrations were also determined in peripheral sera of neonatal and juvenile males and in spermatic vein blood of adults. Immunoradiometric assays specific for the measurement of inhibin A and B were used. These assays also provided an opportunity to reexamine the physiological significance of a replacement infusion of recombinant human (rh)-inhibin A previously employed to study the role of this hormone in regulating FSH secretion in the monkey. In intact adults, the mean (+/-SE) serum concentration of inhibin B was 1008 +/- 184 pg/mL. In contrast, circulating inhibin A concentrations were very low (< 46 pg/mL). Inhibin B was consistently detected in neonatal monkey serum (275 +/- 57 pg/mL), and concentrations of this inhibin dimer increased throughout postnatal development, reaching maximum values in adulthood. Circulating inhibin A concentrations in neonatal and juvenile monkeys were undetectable (< 7 pg/mL). Both forms of inhibin were generally undetectable in castrate sera. The ratio of inhibin B concentrations in testicular venous blood to those in the peripheral circulation was 1.4:1. These findings indicate that, in the male monkey, inhibin B is the principal form of circulating dimeric inhibin, and that this hormone is derived exclusively from the testis. The elevated levels of circulating inhibin B in the juvenile male monkey suggest that, during this phase of development, testicular inhibin B secretion is relatively gonadotropin independent. Additionally, we found that the concentration of circulating inhibin A in castrate animals that had earlier received an iv infusion of rh-inhibin A (832 ng/h/kg BW) was 9881 +/- 2135 pg/mL, indicating that this mode of inhibin replacement may not have been entirely physiological.

A study of the relative roles of follicle-stimulating hormone and luteinizing hormone in the regulation of testicular inhibin secretion in the rhesus monkey (Macaca mulatta)

The purpose of this study was to examine the relative roles of FSH and LH in stimulating testicular inhibin secretion in the male rhesus monkey. Recombinant human (rh) FSH and rhCG were used as the gonadotropic stimuli, and juvenile rhesus monkeys, in which the endocrine activity of the pituitary-testicular axis was being driven in an adult manner with an intermittent i.v. GnRH infusion, were studied. Immunoactive inhibin levels were measured by the Monash RIA. Initiation of an intermittent i.v. infusion of rhFSH (10 IU every 3 h) resulted, after a delay of 5-6 h, in a progressive increase in the concentrations of immunoactive inhibin, which achieved, after 48 h of stimulation, a value twice that observed during vehicle treatment. Gel filtration chromatography revealed that the FSH-induced elevation in immunoactive inhibin was the result of an increase in three distinct mol wt fractions: peak I (100 kDa), peak II (50-60 kDa), and peak III (31 kDa). Although peak III accounted for most of the inhibin immunoactivity in vehicle-treated animals, peaks I and II were most responsive to FSH stimulation. Application of recently developed enzyme-linked immunosorbent assays for inhibin B and pro-alpha-C-related peptides provided additional insights into the nature of the FSH-sensitive forms of circulating immunoactive inhibin. Most notably, the 31-kDa fraction (peak III) was comprised of inhibin B and pro-alpha-C. In contrast to FSH stimulation, an intermittent infusion of rhCG (40 IU every 3 h), which markedly elevated testicular testosterone secretion, failed to increase immunoactive inhibin concentrations. These findings indicate that various forms of immunoactive inhibin are present in the circulation of the rhesus monkey, and that in this species, FSH is the principal stimulus of the secretion of testicular inhibins, including inhibin B. Additionally, they further underline the importance of the FSH-inhibin feedback loop in governing testicular function in primates.

Effects of continuous inhibin administration on gonadotropin secretion and subunit gene expression in immature and adult male rats

To begin to examine inhibin as a male contraceptive, recombinant human (rh) inhibin-A was administered for 3 days via osmotic minipumps to male rats. Doses of inhibin of 0-150 mg/kg per day did not produce a concentration-dependent suppression of FSH secretion or pituitary FSH beta mRNA levels in adult rats. Treatment of immature rats at a dose of 145 micrograms/kg per day, which was without effect in adults, reduced plasma FSH levels by 49% (p < 0.01), and FSH beta mRNA levels to 47 +/- 11% of control (p < 0.01). Inhibin also decreased levels of LH beta mRNA (63 +/- 8% of control; p < 0.01), alpha-subunit mRNA (86 +/- 10% of control; p < 0.05), and GnRH-receptor mRNA (77 +/- 17% of control; p <0.01) in immature rats. Rh inhibin-A was more effective in immature than in adult animals; plasma inhibin levels were increased (p = 0.03) by rh inhibin-A treatment only in immature rats. Pharmacokinetic studies revealed that the weight-adjusted clearance was greater (p < 0.01), and the elimination half-life of rh inhibin A was shorter (p < 0.01) in adult than in juvenile rats. These data indicate that partial suppression of FSH beta mRNA inhibin is associated with a decline in GnRH receptor gene expression, suggesting that the notion that inhibin can act as a male contraceptive through selective and complete inhibition of FSH production, without effect on LH and Leydig cell function, may be mistaken. In addition, increased inhibin clearance appears to contribute to the fall in plasma inhibin levels with maturation in the male rat.

Relationship between gonadotropin subunit messenger ribonucleic acid levels and plasma gonadotropin concentrations in intact and orchidectomized adult rats

To gain further insight into the factors regulating FSH, LH, and uncombined alpha subunit secretion in the male rat, pituitary levels of the gonadotropin subunit mRNAs and plasma levels of FSH, LH, and alpha subunit were measured in 7-wk-old intact male rats and rats castrated 2 wk previously. A highly positive correlation was found between pituitary FSH beta mRNA levels and plasma FSH concentrations in intact (r = 0.60; p = 0.039) but not in castrated rats (r = -0.13; p = 0.66). On the other hand, neither pituitary alpha subunit nor LH beta mRNA levels were predictive of plasma alpha subunit or LH concentrations in intact or orchidectomized rats. This observation is consistent with the proposal that a pretranslational mechanism is the major determinant of FSH secretion in the intact adult male rat but not in the castrated male.

Exercise increases serum testosterone and sex hormone-binding globulin levels in older men

We examined the effects of moderate physical activity on serum luteinizing hormone (LH), sex hormone-binding globulin (SHBG), and testosterone levels in seven sedentary but otherwise healthy men aged 66 to 76 years (mean +/- SD, 70 +/- 4). Blood samples were obtained at 10-minute intervals for 4 hours before, during, and 4 hours after 60 minutes of cycle ergometry. Blood samples were also obtained every 10 minutes for 9 hours during a separate day to control for normal diurnal variation in serum testosterone levels. Serum testosterone increased 39%, SHBG 19%, total serum protein 13%, and the free testosterone index 23% during exercise (P < .01 for all). Testosterone and SHBG levels during the 4-hour sampling period after exercise were similar to values obtained before exercise and on the morning and afternoon of the control day. LH concentrations were unaltered during or after exercise. The change in SHBG levels during exercise correlated positively with the change in testosterone concentrations (r = .74, P = .09). We conclude that short-term exercise produces a transient elevation in serum testosterone levels in elderly men, which is partly due to an increase in serum SHBG concentrations. The concomitant increase in total protein and the rapid return of total protein and SHBG to baseline values after exercise indicate that hemoconcentration partly contributes to the exercise-associated increase in circulating testosterone levels.

Regulation of alpha-subunit mRNA transcripts by pituitary adenylate cyclase-activating polypeptide (PACAP) in pituitary cell cultures and alpha T3-1 cells

Pituitary adenylate cyclase activating polypeptide (PACAP) increases glycoprotein hormone alpha-subunit mRNA levels suggesting a role for PACAP in maintaining the high levels of alpha-subunit protein characteristic of the pituitary. The present study used primary pituitary cell cultures and the alpha T3-1 pituitary cell line to investigate how PACAP affects alpha-subunit mRNA transcripts. Stimulation of cultured pituitary cells with 10 nM PACAP38, 10 nM GnRH, or the combination, for 24 h increased alpha-subunit mRNA levels 1.5-fold, whereas GnRH more effectively (P<0.01) stimulated alpha-subunit protein release than did PACAP38 (3.2- vs. 2.0-fold). alpha-Subunit mRNA levels in alphaT3-1 cells were also increased by PACAP38 and by GnRH to maximum values at 12 h (P<0.05), and alpha-subunit protein secretion rose proportionately and in parallel with alpha-subunit mRNA levels. PACAP38 was a 100-fold more potent stimulator of alpha-subunit mRNA than was VIP, and a VIP-antagonist failed to block the stimulatory effect of PACAP38, suggesting an effect via type PACAP 1 receptors. Type I receptor mRNA transcripts were identified by Northern analysis in alphaT3-1 cells. Depletion of PCK activity by PMA failed to block the stimulatory effect of PACAP38, but prevented GnRH from increasing alpha-subunit mRNA levels and alpha-subunit secretion. PACAP38, like 8Br-cAMP and forskolin, stimulated (P<0.05) luciferase (LUC) activity in alphaT3-1 cells transfected with a plasmid containing the first 846 of 180 base pairs of the 5'-flanking region of the human alpha-subunit gene linked upstream to a LUC reporter gene. Finally, experiments using the transcription inhibitor DRB reveal that PACAP does not appreciably change alpha-subunit mRNA half-life. These findings are consistent with the proposal that PACAP contributes to the high levels of alpha-subunit protein characteristic of the pituitary by activating Type I receptors and stimulating alpha-subunit gene transcription in part by the cAMP/PKA pathway.

Replacement with recombinant human inhibin immediately after orchidectomy in the hypophysiotropically clamped male rhesus monkey (Macaca mulatta) maintains follicle-stimulating hormone (FSH) secretion and FSH beta messenger ribonucleic acid levels at precastration values

This study directly tested the inhibin hypothesis by examining the ability of replacement with recombinant human (rh-) inhibin, either alone or in combination with testosterone (T), to maintain FSH secretion and FSH beta messenger RNA (mRNA) at intact levels after orchidectomy in the hypophysiotropically clamped juvenile rhesus monkey. Thirteen male monkeys (11-21 months of age) received an intermittent i.v. infusion of GnRH (0.1 microgram/min for 3 min every 3 h). After 4-6 weeks of GnRH stimulation, 10 animals were orchidectomized, and 3 monkeys were sham castrated. Hormone replacement was initiated at castration and maintained for 4 days. Three monkeys received a combination of inhibin and T replacement, 4 monkeys received replacement with inhibin alone, and 3 monkeys received T replacement alone. A continuous i.v. infusion of rh-inhibin (832 ng/h.kg) was used to replace the testicular protein, whereas SILASTIC capsules were implanted sc for T replacement. The FSH response to castration and hormone replacement was determined by measuring circulating concentrations of this gonadotropin before a GnRH pulse and for 3 h thereafter on the day before surgery and on days 2 and 4 postcastration. Circulating immunoactive inhibin was measured by a RIA that recognizes the free alpha-subunit of inhibin as well as inhibin dimers. At the end of the study, anterior pituitaries were collected for analysis of steady state levels of FSH beta, LH beta, and alpha-subunit mRNAs. Steroid replacement alone, which produced circulating T concentrations in the upper physiological range, failed to prevent the postcastration increases in circulating FSH concentrations and pituitary FSH beta mRNA levels. In contrast, when circulating immunoactive inhibin in T-replaced monkeys was maintained at precastration levels (approximately 2 ng/ml) by infusion of rh-inhibin, FSH secretion and synthesis were held at control values. When T was omitted from combined replacement, the FSH-suppressing action of the recombinant hormone was not compromised. These results demonstrate that rh-inhibin is biologically active in the monkey, and the action of inhibin to suppress FSH synthesis and secretion does not require a concomitant action of T. Moreover, because the hypophysiotropic drive to the pituitary-testicular axis was clamped, the FSH-suppressing action of rh-inhibin must be at the pituitary.

Inhibin in normal and abnormal pregnancy: maternal serum concentration and partial characterization

OBJECTIVE

This study evaluated maternal serum inhibin concentration and molecular distribution in normal and abnormal pregnancies.

STUDY DESIGN

Serum inhibin levels were measured by radioimmunoassay in 33 abnormal pregnancies (23 singleton and 10 multiple gestations) and 33 matched controls and were compared with pregnancy variables.

RESULTS

In the controls serum inhibin concentrations rose with gestational age (correlation coefficient 0.358, p < 0.01) and were higher in mothers with female fetuses (p < 0.05). Inhibin levels were higher in the abnormal singleton pregnancies (2.69 +/- 1.41 ng/ml) than in controls (1.26 +/- 0.32 ng/ml, p < 0.0001) and increased more rapidly with gestational age in multiple pregnancies (p < 0.05). Gel filtration chromatographic analysis of immunoreactive inhibin revealed three peaks with the major form having an apparent molecular weight of 55 to 60 kd.

CONCLUSION

Maternal serum inhibin concentrations are affected by gestational age, fetal gender, and complications of pregnancy. Most of the immunoreactive inhibin in maternal circulation is a large-molecular-weight form.

Effects of pulsatile pituitary adenylate cyclase activating polypeptide (PACAP) on gonadotropin secretion and subunit mRNA levels in perifused rat pituitary cells

The effects of pituitary adenylate cyclase activating polypeptide (PACAP) administered intermittently on gonadotropin secretion and subunit mRNA levels in anterior pituitary cells from 7wk old intact and orchidectomized rats were studied. Cells were perifused for 9 h with hourly pulses of 2.5 nM GnRH or 10 nM PACAP, or with medium alone. Pulsatile PACAP initiated episodes of LH, FSH and alpha-subunit secretion, but was much less effective than GnRH. Responsiveness declined with repeated pulses of PACAP, although interpulse secretion increased gradually throughout the experiment. PACAP was a slightly more effective stimulator of LH release by pituitary cells from castrated than intact rats. At the completion of perifusion, pituitary RNA from castrated rats was extracted for measurement of gonadotropin subunit mRNA levels. Pulsatile PACAP stimulated alpha-subunit and LHbeta mRNA levels but did not affect FSHbeta mRNA. By contrast, continuous PACAP increased alpha-subunit mRNA levels, but suppressed FSHbeta mRNA without affecting LHbeta mRNA. We conclude that pulsatile PACAP is a relatively ineffective stimulator of gonadotropin secretion when administered alone, and regulates gonadotopin subunit gene expression quite differently than continuous PACAP. We propose that the mode of PACAP secretion in vivo may be a determinant of the differential expression of the gonadotropin subunit genes.

Endocrine evaluation of testicular function

This article reviews currently available endocrine tests that are used to evaluate adult testicular function. In many patients, all that is needed is a thorough medical history and physical examination with measurement of total testosterone, FSH, and LH levels. For others, various secondary tests are appropriate. The usefulness and pitfalls of these endocrine tests are discussed.

Effects of pituitary adenylate cyclase-activating polypeptide on gonadotropin secretion and subunit messenger ribonucleic acids in perifused rat pituitary cells

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP38) is a neuropeptide related to vasoactive intestinal peptide-secretin-glucagon which stimulates adenylate cyclase in cultured rat pituitary cells and stimulates LH and FSH release in vitro and in vivo. Because the cAMP-protein kinase-A pathway regulates the gonadotropin subunit messenger RNAs (mRNAs) and modulates GnRH-stimulated gonadotropin secretion in vitro, we examined the effects of PACAP38 on gonadotropin secretion and subunit mRNA levels. Anterior pituitary cells were prepared from 7-week-old male rats castrated at 5 weeks of age. In monolayer cultures stimulated with GnRH, 0.1-10 nM PACAP38 decreased (P < 0.05) the EC50 for GnRH dose-dependently without affecting the maximum LH secretory response. Cells were next stimulated with 1-min pulses of 2.5 nM GnRH every hour for 9 h in the absence or presence of 10 nM PACAP38, which was perifused continuously. The amplitude of GnRH-induced LH, FSH, and alpha-subunit secretory episodes from PACAP38-treated cells rose (P < 0.01) gradually to 233 +/- 54%, 197 +/- 44%, and 378 +/- 104%, respectively (mean +/- SEM; n = 5 experiments), of the value for control cells lacking PACAP38. This enhancement was sustained for at least 3 h after PACAP38 was removed from the perifusion medium. With PACAP treatment, interpulse secretion of LH and alpha-subunit increased gradually (P < 0.01) to 174 +/- 21% and 212 +/- 64% of the value for chambers stimulated with GnRH alone (control), respectively, whereas interpulse secretion of FSH declined (P < 0.001) to 75 +/- 7% of the control value. In contrast to the gradual effect of PACAP38 to enhance GnRH-induced hormone secretion, PACAP38 alone produced a transient burst of gonadotropin secretion. At the completion of the perifusions, total RNA was extracted and gonadotropin subunit mRNA levels were determined by Northern analysis. GnRH increased (P < 0.01) FSH beta mRNA to 438 +/- 52% of the level in cells stimulated with medium alone (control). Adding PACAP38 to the perifusion medium partially blocked (P < 0.01) the effect of GnRH (178 +/- 20% of the control value), and PACAP38 alone reduced (P < 0.01) FSH beta mRNA levels to 31 +/- 3% of the control value. By contrast, alpha-subunit mRNA levels were increased by both PACAP38 (143 +/- 4% of the control value; P < 0.01) and GnRH (121 +/- 2% of the control value; P < 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

FSH is produced by GnRH-deficient men and is suppressed by testosterone

Because there is an unexpected action of testosterone (T) to increase follicle-stimulating hormone (FSH) production in the absence of gonadotropin-releasing hormone (GnRH) in the rat, the effects of T treatment on circulating FSH were studied in men with GnRH deficiency. FSH immunoreactivity was identified in serum using a sensitive two-site immunoassay in each of five untreated GnRH-deficient men. Analysis by gel filtration chromatography revealed that circulating immunoreactive FSH coeluted with radiolabeled authentic FSH. T enanthate treatment suppressed serum FSH levels in each subject from (mean +/- standard error of the mean [SEM]) 1.02 +/- 0.94 to 0.26 +/- 0.21 mIU/ml (P = 0.061, Wilcoxon rank sum test). Thus, FSH is produced in GnRH-deficient men, but there is no evidence for the stimulatory effect of T on FSH production in the absence of GnRH, as observed in the rat. These preliminary data provide further evidence that male contraceptive strategies using GnRH antagonists to suppress LH and FSH production in normal men will not be counteracted by T replacement therapy, although the issue deserves further attention in that study population.

Pattern of oxytocin concentrations in the peripheral blood of healthy women and men: effect of the menstrual cycle and short-term fasting

A sensitive and specific radioimmunoassay was used to measure basal oxytocin (OT) concentrations in samples of peripheral blood drawn q 10 min for 8 hrs from women during the follicular and luteal phases of the menstrual cycle and from men before and after 20 hrs of fasting. Few, if any, pulses of OT were found in the blood of men and women in this study. The pattern of OT concentrations in the circulation was the same during both stages of the menstrual cycle and was not affected by short-term fasting. The use of frequent sampling and the present assay system for OT did not detect a pulsatile pattern of OT concentrations in the blood of men and women in the basal state.

Endocrine consequences of weight loss in obese, hyperandrogenic, anovulatory women

OBJECTIVE

To determine whether weight loss in obese, hyperandrogenic, anovulatory women is associated with resumption of ovulation and/or with changes in insulin, androgen, and gonadotropin concentrations.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research center.

PATIENTS

Twelve obese, hyperandrogenic, anovulatory women.

INTERVENTIONS

Twelve-week weight loss program in treatment (n = 6); 12-week "waiting list" in control group (n = 6).

MAIN OUTCOME MEASURES

[1] Ovulation; [2] fasting insulin and glucose measurements; [3] sex hormone-binding globulin (SHBG), total and non-SHBG T concentrations; [4] LH pulse frequency, amplitude, and concentration; and [5] FSH concentration.

RESULTS

In contrast with the control group who showed no change in weight, ovulation status, or hormone levels, women in the treatment group lost an average of 16.2 kg and showed a significant increase in SHBG, a significant decline in non-SHBG T, and a decline (though nonsignificant) in fasting insulin. Four of six subjects resumed ovulation. However, no changes were evident in LH pulse frequency or amplitude or in mean LH and FSH concentrations.

CONCLUSIONS

Weight loss in obese, hyperandrogenic, anovulatory women appears to reduce insulin and non-SHBG T concentrations despite the absence of a change in gonadotropin secretion and may lead to resumption of ovulation.

Role of testosterone in the induction of hepatic peroxisome proliferation by clofibrate

Hepatic peroxisome proliferation is induced by a number of agents, including clofibrate. Sustained proliferation of peroxisomes is associated with the development of hepatocellular carcinoma. In the present study, we have investigated the role of testosterone in peroxisome proliferation induced by clofibrate. Three groups of male rats (intact, castrated, and castrated replaced with testosterone) were studied. Proliferation of peroxisomes was induced by feeding clofibrate (0.25%, 0.50%, and 1.0% of diet) for 2 weeks. Peroxisome proliferation was monitored by measuring total peroxisomal beta-oxidation activity. In intact rats, the peroxisomal beta-oxidation activity (nmol/min/mg protein) increased in a dose-dependent manner and was 7.2 +/- 0.4, 52.6 +/- 7.5, 63.2 +/- 3.7, and 92.4 +/- 4.0 at clofibrate doses of 0%, 0.25%, 0.50%, and 1.0%, respectively. In contrast, in castrated rats, the total peroxisomal beta-oxidation activity was significantly (P < .01) lower at clofibrate levels of 0.25% and 0.50% (25.8 +/- 2.7 and 42.5 +/- 2.2, respectively), but not at the clofibrate level of 1.0% (85.0 +/- 6.3). Testosterone replacement of castrated rats restored the peroxisomal beta-oxidation activity. To determine whether the above results were related to the metabolism of clofibrate in the absence or presence of testosterone, we measured serum clofibrate levels. These levels were 50% lower in castrated rats than in intact rats or in testosterone-treated castrated rats. The activity of hepatic uridine diphosphate (UDP)-glucuronyltransferase, the enzyme catalyzing the glucuronidation of clofibrate, was measured using either bilirubin or 4-methylumbelliferone as substrates and was found to be unaffected by castration or testosterone treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The follicle stimulating hormone-inhibin feedback loop in male primates

This paper reviews our current knowledge of the role of testicular inhibin in the regulation of follicle stimulating hormone (FSH) secretion in the rhesus monkey. Species differences between monkey and rat are described, and evidence for and against the hypothesis that control of FSH secretion in the human male is similar to that for the monkey is presented.

Evidence for a role for the cyclic adenosine 3',5'-monophosphate/protein kinase-A pathway in regulation of the gonadotropin subunit messenger ribonucleic acids

cAMP regulation of gonadotropin secretion and subunit mRNA levels was studied in pituitary cells perifused with pulses of GnRH. Pituitary cells from 7-week-old male rats castrated at 5 weeks of age were stimulated hourly for 9-24 h with 1-min pulses of GnRH, the adenylate cyclase activator forskolin, the cell-permeable cAMP analog 8-bromo-cAMP (8Br-cAMP), or control medium. Cells were also treated with the nonsteroidal antiinflammatory drug flufenamic acid, which reduces pituitary cAMP levels. During perifusion, the effluent was collected in 10-min fractions for FSH and LH assay. At the completion of perifusion, total RNA was extracted, and gonadotropin subunit mRNA levels were quantitated by Northern analysis. Continuous administration of flufenamic acid gradually reduced the amplitude of GnRH-stimulated FSH and LH pulses to nadir values of 40 +/- 4.7% and 62 +/- 12% of the control value, respectively. Flufenamic acid decreased (P < 0.05) FSH beta and alpha-subunit mRNA levels and blocked the effect of GnRH to lengthen LH beta mRNA. Pulses of forskolin or 8Br-cAMP released LH and FSH, and continuous forskolin or 8Br-cAMP potentiated the gonadotropin stimulatory effect of GnRH. Forskolin or 8Br-cAMP increased (P < 0.05) FSH beta mRNA and alpha-subunit mRNA levels when administered in pulses, but not when administered continuously, and lengthened LH beta mRNA. The Nal-Glu GnRH antagonist blocked the effects of GnRH pulses, but not the effects of 8Br-cAMP or forskolin. In conclusion, lowering intracellular cAMP levels with flufenamic acid attenuated GnRH-stimulated gonadotropin secretion, decreased alpha-subunit and FSH beta mRNA levels, and blocked the effect of GnRH to lengthen LH beta mRNA, whereas 8Br-cAMP or forskolin produced the opposite effect. These data extend previous results which suggested that cAMP modulates gonadotropin secretion and indicate that the cAMP/A-kinase pathway regulates each of the gonadotropin subunit mRNAs.

Increased luteinizing hormone and alpha-subunit secretion in women with hyperandrogenic anovulation

Women with hyperandrogenic anovulation (HAA) have increased circulating levels of LH relative to those of FSH. The cause of this disturbance in gonadotropin secretion is uncertain. Previous investigations have sought to determine if increased GnRH drive is responsible for the excessive LH concentrations. Because previous results have conflicted, we addressed this question by comparing the 24-h secretory patterns of alpha-subunit and LH in women with HAA (n = 9) to those in eumenorrheic women in the midfollicular phase (n = 9). The mean (+/- SEM) pulse frequency was increased in women with HAA compared to that in eumenorrheic women of comparable age and percent ideal body weight for both LH (23.0 +/- 0.7 pulses/24 h vs. 3 17.1 +/- 1.7; P = 0.002) and alpha-subunit (23.0 +/- 0.8 vs. 19.1 +/- 1.2; P = 0.02). LH and alpha-subunit, but not FSH, responses to a submaximal dose of exogenous GnRH were increased in HAA, as were basal LH and alpha-subunit levels (P < 0.01). The present observations provide evidence for increased GnRH drive, including pulse frequency, in HAA. Although the results confirm the presence of a disturbance in gonadotropin secretion and suggest that its proximate cause may be of hypothalamic origin, they do not exclude the possibility that other factors, perhaps of ovarian origin, play a role in the establishment and/or maintenance of the altered gonadotropin secretory patterns and the chronic anovulation characteristic of HAA.

Decay of follicle-stimulating hormone-beta messenger RNA in the presence of transcriptional inhibitors and/or inhibin, activin, or follistatin

In primary cultures of rat pituitary cells, inhibin and follistatin reduce steady state levels of FSH beta mRNA to less than 10% of control within 4-6 h, while activin increases this mRNA 2- to 3-fold after 2-4 h of treatment. The effects of these three gonadal polypeptide hormones on the LH beta and common alpha-subunit mRNAs are more gradual and of lesser magnitude. The present study was designed to determine whether inhibin, activin, and/or follistatin act at the posttranscriptional level by altering the stability of the gonadotropin subunit mRNAs. To determine the decay rates of FSH beta, LH beta, and alpha-subunit mRNAs, primary pituitary cell cultures were treated for 1-24 h with either of two transcriptional inhibitors, actinomycin-D or 5,6-dichloro-1-beta-ribofuranosyl benzimidazole (DRB), in the presence or absence of recombinant human inhibin-A, recombinant human activin-A, or purified bovine follistatin. The decay of preexisting gonadotropin subunit mRNAs was followed by Northern blot analysis. Levels of LH beta and alpha-subunit mRNAs remained constant or increased during the 24-h exposure to transcriptional inhibitors; therefore, it was not possible to calculate their half-lives. The stability of these mRNAs was not altered by inhibin, activin, or follistatin. In contrast, FSH beta mRNA turned over rapidly: the estimated half-life was 2.6 +/- 0.19 h (mean +/- SEM of eight determinations) after actinomycin-D treatment and 1.9 +/- 0.14 h (mean +/- SEM of 12 determinations) after DRB treatment. When new RNA synthesis was blocked by either actinomycin-D or DRB, there were no significant effects of inhibin, activin, or follistatin on the stability of FSH beta mRNA (n = 2-4 for each hormone). The decay of FSH beta mRNA in the presence of inhibin or follistatin alone, however, was even more rapid than that determined after the administration of transcriptional inhibitors (P < 0.005). After an initial lag of 1-2 h, the half-life of FSH beta mRNA was 0.88 +/- 0.15 h (n = 4) or 0.62 +/- 0.11 h (n = 3), in the presence of inhibin or follistatin, respectively. The most likely interpretation of these results is that inhibin/follistatin reduces steady state levels of FSH beta mRNA by inducing a labile protein that accelerates the degradation of this mRNA species, and the synthesis of this protein is blocked by actinomycin-D or DRB treatment. It is not clear at present whether inhibin, follistatin, and activin have additional effects on transcription of the gonadotropin subunit genes.

Effect of gonadotropin-releasing hormone pulse frequency on gonadotropin secretion and subunit messenger ribonucleic acids in perifused pituitary cells

Slow frequency GnRH pulses have been proposed to preferentially increase circulating FSH levels by increasing FSH synthesis and pulsatile release. Examination of this proposal using various in vivo models, however, has produced conflicting results. To examine directly the effects of GnRH pulse frequency on the pituitary, we compared the effects of 2.5-nM GnRH pulses administered every 1 h or every 4 h vs. no GnRH, using perifused rat pituitary cells. FSH secretion (total area under the response curve) was 2-fold greater (P less than 0.01) with every hour than with every 4 h GnRH pulses. This difference resulted from the increased number of GnRH pulses and increased (P less than 0.05) interpulse FSH secretion, whereas FSH pulse amplitude was unchanged. FSH beta mRNA levels at the completion of the 11-h perifusion were increased 4.5-fold by GnRH every h (P less than 0.01) and 3.3-fold by GnRH every 4 h (P less than 0.05) above levels in untreated cells. FSH beta mRNA levels were greater (P less than 0.05) at the faster GnRH pulse frequency. Because more frequent stimulation delivered more GnRH during the study, cells were next stimulated with 2.5 nM GnRH every 1 h for nine pulses, 7.5 nM GnRH every 4 h for three pulses to equalize the GnRH dose, or 2.5 nM GnRH every 4 h for three pulses. Interpulse FSH secretion and FSH beta mRNA levels were again greater (P less than 0.05) with every hour than every 4 h GnRH pulses. Interpulse LH secretion, FSH and LH pulse amplitude, and LH beta and alpha-subunit mRNA levels were not different between the groups. GnRH doses of 0.1-10 nM every hour increased FSH and LH pulsatile secretion dose-dependently, but FSH beta, LH beta, and alpha-subunit mRNA levels were similar. In conclusion, our data reveal that reducing the frequency of GnRH pulses from every hour to every 4 h reduces both FSH beta mRNA levels and FSH interpulse secretion, but does not change GnRH-stimulated FSH pulsatile release. We suggest that the finding by others that slow frequency GnRH pulses increase circulating FSH levels under certain experimental conditions in vivo may instead be explained by complex hormonal interactions or changes in FSH clearance.

Effects of orchidectomy on gonadotropin and inhibin subunit messenger ribonucleic acids in the pituitary of the rhesus monkey (Macaca mulatta)

Our research programs required the preparation of hypophysectomized and orchidectomized rhesus monkeys. This afforded us the possibility to characterize and compare levels of the gonadotropin and inhibin subunit mRNAs in pituitaries from intact and castrate monkeys. Eighteen adult male monkeys, four of which had been bilaterally orchidectomized 5-9 months previously, were used in this study. Plasma concentrations of LH and FSH were, respectively, 188.5 +/- 5.3 and 246.8 +/- 25.2 ng/ml in the castrate monkeys and 25.8 +/- 4.5 and 4.1 +/- 1.1 ng/ml (mean +/- SEM) in the intact animals. Total pituitary RNA was hybridized to cDNA probes for cynomolgus monkey gonadotropin subunits (FSH beta, LH beta, and the common alpha-subunit) and for human inhibin subunits (alpha, beta B, and beta A) by Northern blot analysis, and mRNA levels were normalized by subsequent hybridization to cyclophilin. Each of the gonadotropin subunit probes hybridized to a single RNA species with the approximate sizes of 1.6 kilobases (kb; FSH beta), 0.7 kb (LH beta), and 0.8 kb (alpha). Levels of LH beta and alpha-subunit mRNAs in pituitaries from castrate monkeys were about 5- and 2-fold higher, respectively, than those in pituitaries from intact monkeys. FSH beta mRNA, on the other hand, was elevated about 27-fold in castrate monkeys [mean +/- SEM, 3176 +/- 408 cpm bound (n = 4 castrate) and 116 +/- 30 cpm bound (n = 8 intact]). Inhibin beta B-subunit mRNA was present in the monkey pituitary as a doublet of about 5 kb, and it was approximately twice as abundant in intact pituitaries as in castrate pituitaries. Hybridizations involving inhibin beta A cDNA revealed a faint band in the region expected for monkey beta A mRNA (6.5 kb) in three of six RNA samples from intact monkeys and a 0.3- to 0.4-kb mRNA species. mRNA encoding the inhibin alpha-subunit was undetectable by Northern blot hybridization. These results indicate that the postpubertal testis imposes an inhibition on the expression of the genes encoding FSH beta, LH beta, and glycoprotein hormone alpha-subunit and that this suppression of the FSH beta gene in the monkey is much greater than that in the rat. In addition, the monkey pituitary may be a source of activin, which may act locally to modulate FSH gene expression and secretion.

Antide bioavailability: single dose administration for suppression of testosterone and inhibin in male monkeys

The pharmacokinetics and pharmacodynamics of a single sc injection of Antide on testosterone (T) and inhibin secretion in intact male cynomolgus monkeys were examined. Fifteen primates were randomized to three groups receiving: propylene glycol and water vehicle, 3 mg/kg Antide, and 10 mg/kg of Antide. Antide at the 10 mg/kg dose caused long-term suppression of T ranging from 24-56 days. At the 3 mg/kg dose, suppression of T was of shorter duration. Serum Antide levels were significantly greater in the 10 mg/kg group than the 3 mg/kg group (p less than 0.02), both initially and through 35 days post-treatment. The duration of testosterone inhibition and sustained Antide levels were significantly correlated (p less than 0.01). Inhibin concentrations followed the same general pattern as testosterone reaching a nadir on day 21 post-treatment before subsequent recovery. The prolonged suppressive effect of Antide on T without detectable side effects makes this compound an excellent candidate for clinical evaluation.

Effects of testosterone on gonadotropin subunit messenger ribonucleic acids in the presence or absence of gonadotropin-releasing hormone

There is accumulating evidence that the negative feedback actions of testosterone on the pituitary may contribute to the differential regulation of FSH and LH secretion in males. In the present study we measured steady state levels of the mRNAs encoding the gonadotropin subunits in pituitary cell cultures treated with 10 nM testosterone (T) as well as in T-treated pituitary cells perifused with pulses of GnRH to explore further the direct actions of T on the pituitary. T treatment of pituitary cells in monolayer culture for 72 h increased FSH beta mRNA 1.5-fold (P less than 0.05), decreased alpha-subunit mRNA to 45% of the control level (P less than 0.05), and decreased LH beta mRNA to 75% of the control level (P less than 0.05). FSH and uncombined alpha-subunit secretion were increased and decreased by T, respectively, whereas basal LH secretion was unchanged. Treatment with 0.1 nM estradiol, a physiological concentration for males, did not change gonadotropin secretion or subunit mRNA concentrations. Between days 2 and 5 in culture in the absence of steroid treatment, steady state levels of LH beta and alpha-subunit mRNA declined (P less than 0.01) 52% and 61%, respectively, but FSH beta mRNA levels were unchanged. Pulsatile stimulation with 2.5 nM GnRH every 1 h for 10 h increased FSH beta mRNA 2.8-fold (P less than 0.05) and increased (P less than 0.05) alpha-subunit mRNA to 117% of the control level. When cell cultures were pretreated with T for 48 h and then perifused with pulses of GnRH, FSH beta, LH beta, and alpha-subunit mRNA levels were 66%, 74%, and 70% of the value during GnRH alone (P less than 0.05). T treatment also reduced (P less than 0.01) the amplitudes of FSH, LH, and alpha-subunit secretory pulses by 18%, 26%, and 41%, respectively. These data indicate that a portion of the negative feedback action of T is at the pituitary to regulate gonadotropin subunit gene expression. Our data reveal two opposing effects of T on FSH beta mRNA: a stimulatory action, which is GnRH independent, and an inhibitory effect, which is related to the actions of GnRH. These divergent actions of T represent one mechanism through which FSH and LH are differentially regulated.

A comparison of moment to moment and diurnal changes in circulating inhibin and testosterone concentrations in male rhesus monkeys (Macaca mulatta)

The secretion of inhibin by the testis was studied in the rhesus monkey, a species which exhibits marked episodic and diurnal patterns of testosterone (T) secretion. Inhibin and T were measured by RIA in blood samples drawn every 20 min for 24 h from 5 adult male monkeys. The molecular size of circulating inhibin, estimated by gel chromatography, was approximately 31 kDA. Plasma inhibin levels were undetectable in long term castrates. T was secreted episodically at a frequency of 6.0 +/- 0.9 pulses/24 h. The computer algorithm also identified 4.6 +/- 0.8 inhibin pulses/24 h. Of 30 T pulses among the 5 animals, however, only 7 coincided with low amplitude inhibin secretory bursts. Each animal demonstrated a significant diurnal periodicity in T secretion, with mean maximum concentrations at 0108 h (range, 2100-0640 h). By contrast, there was no significant diurnal rhythm for inhibin in any of the animals. The pulsatile administration of GnRH (0.1 micrograms/min, iv, for 3 min every 3 h) was used to activate the pituitary testicular axis in 6 juvenile monkeys. After 5 weeks of GnRH priming, a pulse of GnRH produced an immediate 4-fold rise in serum LH concentrations, followed within 30-50 min by a 5-fold increase in circulating T levels. FSH levels rose 50%. During the 3-h GnRH interpulse interval, however, there was no change in serum inhibin levels. Two GnRH-treated juvenile monkeys underwent bilateral orchidectomy. In each animal, circulating inhibin levels declined rapidly, with estimated first phase half-lives of 23 and 32 min, respectively. In conclusion, circulating inhibin concentrations in male rhesus monkeys exhibit neither the prominent moment to moment changes nor the circadian pattern characteristic of T secretion in this species. The relatively constant inhibin levels cannot be explained by prolonged metabolic clearance. The data are consistent with the proposal that most of the inhibin in the circulation is released across the apical surface of Sertoli cells into the seminiferous tubular fluid with passage into the rete testis from which it is continuously absorbed. The intermittent LH signal, by contrast, appears to make a minor contribution to the release of inhibin from the primate testis into the circulation.

Diurnal rhythm of testosterone and luteinizing hormone in hypogonadal men

To determine the relationship between increasing luteinizing hormone (LH) production and the diurnal secretion of LH and testosterone (T) in adult men, studies were performed on five men with gonadotropin insufficiency associated with prolactinoma, five eugonadal men, and five men with primary testicular failure. Blood samples were drawn every 10 to 20 minutes for 24 hours beginning at 8:00 to 8:30 AM to evaluate diurnal periodicity. Mean (+/- SEM) LH levels in the three groups were 7.67 +/- 1.46 mlU/ml, 13.9 +/- 3.2 mlU/ml, and 62.3 +/- 14.4 mlU/ml, respectively, and mean serum T levels were 8.05 +/- 1.49 nmol/L, 13.9 +/- 3.5 nmol/L, and 9.15 +/- 1.3 nmol/L, respectively. Cosinor analysis revealed that each hyperprolactinemic man had a T rhythm with a significant 24-hour periodicity; the mean acrophase was at 5:00 AM. Testosterone levels were 35.0 +/- 10.6% less at 4:00 PM than at 8:00 AM. Eugonadal men also demonstrated a significant diurnal T rhythm with an acrophase at 6:00 AM, and T levels were 15.8 +/- 5.3% less at 4:00 PM than at 8:00 AM. By contrast, there was no significant diurnal rhythm in T secretion among the men with testicular failure, although serum T levels were 11.5 +/- 3.7% less at 4:00 PM than at 8:00 AM. For LH, hyperprolactinemic men demonstrated a significant 24-hour rhythm with an acrophase at 1:30 AM, whereas no significant 24-hour periodicity was identified among either eugonadal men or men with testicular failure.(ABSTRACT TRUNCATED AT 250 WORDS)

Interrelationship between the actions of testosterone and primate Sertoli cell inhibin in the control of gonadotropin secretion by cultured pituitary cells

There is accumulating evidence that the differential regulation of LH and FSH secretion in the male is partly accomplished by the direct actions of testosterone (T) and inhibin on the pituitary. The present study was designed to examine the interaction between T and inhibin, in the presence and absence of GnRH, using dispersed pituitary cells in monolayer culture and cells perifused with pulses of GnRH from intact, 2-week castrated, and castrated T-replaced young adult male rats. The effect of partially purified inhibin from primate Sertoli cell culture medium (pSCI) to suppress basal FSH secretion was similar with pituitary cells from intact and castrated rats. T increased basal FSH secretion in the presence or absence of pSCI but did not alter the dose-dependent suppression of FSH by pSCI with cells from either intact or castrate rats. Castration increased basal FSH and LH secretion, whereas only basal FSH release was increased with cells from T-replaced castrates. T pretreatment increased the action of pSCI to suppress GnRH-stimulated FSH and LH release from perifused pituitary cells. These data indicate that T and inhibin exert opposite but independent effects on basal FSH release. The action of inhibin to suppress basal FSH secretion is not impaired by the absence of T and inhibin subsequent to castration. By contrast, the actions of T and inhibin to suppress GnRH-stimulated gonadotropin secretion are coordinated and interrelated.

Effects of gonadal steroids on follicle-stimulating hormone and luteinizing hormone secretion by pituitary cells from castrated and intact male rats

The effectiveness of androgens in suppressing gonadotropin secretion declines with time following orchidectomy; however, the mechanism for this acquired resistance to androgen action is unknown. The role of the pituitary was studied by use of perifused rat pituitary cells and cells in monolayer culture. Pituitary cells from 7-wk-old intact male rats and rats that had been castrated 2 wk previously were treated with 10 nM testosterone (T) for 24 h; cells were then packed into perifusion chambers and stimulated with 2.5 nM GnRH for 2 min every hour for 8 h during which time T treatment was continued. T suppressed GnRH-stimulated LH secretion and LH pulse amplitude equally in both groups to approximately 60% of control values. Interpulse LH secretion was unchanged by T in either group. GnRH-stimulated FSH release was suppressed more (p less than 0.05) by T with cells from castrated rats than with cells from intact rats (76 +/- 4% vs. 90 +/- 2% of control; mean +/- SEM). By contrast, the action of T to increase interpulse basal FSH secretion was less (p less than 0.05) with cells from castrated rats (115 +/- 10% of control) than with cells from intact rats (146 +/- 6% of control). T treatment for 72 h also increased basal FSH secretion by pituitary cells in monolayer culture to a lesser extent with cells from castrated rats than with cells from intact rats (151 +/- 14% vs. 191 +/- 16% of control, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effects of cycloheximide and inhibin on the gonadotropin subunit messenger ribonucleic acids

Cycloheximide (CHX) has been shown to mimic the action of inhibin on gonadotropin secretion by pituitary cell cultures. We showed previously that suppression of FSH secretion by inhibin is associated with a rapid and profound suppression of FSH beta mRNA levels. The present study was designed to examine the mechanism of action of CHX and to determine whether inhibin's actions involve new proteins synthesis. Pituitary cell cultures were treated with control medium or medium containing inhibin, CHX, or inhibin plus CHX for 2 or 6 h. At 6 h, secretion of FSH was decreased by inhibin (72% of control), CHX (58% of control), and the combined inhibitors (56% of control). LH secretion was not significantly changed, while that of free alpha-subunit was reduced only by CHX (68% of control). Levels of FSH beta, LH beta, and alpha-subunit mRNAs were measured by Northern analysis. At 2 h inhibin decreased FSH beta mRNA to 49% of the control value. CHX alone had no effect, while CHX plus inhibin produced intermediate levels (77% of control). By 6 h, however, inhibin and CHX each decreased FSH beta mRNA to very low levels (12% and 15% of control, respectively), and in cultures treated with both inhibin and CHX, this RNA was barely detectable. To determine the reversibility of the effects of these inhibitors, cells were incubated with fresh control medium after 6 h. Secretion of FSH and free alpha-subunit remained suppressed 4 h later; recovery was complete by 16 h in inhibin treated cultures. FSH beta mRNA returned to control levels by 4 h in inhibin-treated and by 16 h in CHX-treated cultures. Levels of LH beta and alpha-subunit mRNA were comparable to control values at all times. In conclusion, 1) CHX, like inhibin, suppresses FSH beta mRNA levels, although its actions are less rapid and less rapidly reversible; 2) inhibin requires ongoing protein synthesis for full expression of its inhibitory effects; 3) the synthesis and secretion of LH are much less sensitive to inhibition by either inhibin or CHX than are the synthesis and secretion of FSH; and 4) secretion of free alpha-subunit involves a labile protein(s).