Developmental changes in testicular inhibin and androgen-binding protein during sexual maturation in the cynomolgus monkey, Macaca fascicularis

Inhibin was measured by RIA in testicular extracts and plasma of cynomolgus monkeys during four stages of sexual maturation. Immunoactive inhibin levels were compared to those of another Sertoli cell secreted protein, androgen-binding protein (ABP). ABP steroid-binding (bioactive) activity was measured in testes and epididymal segments using the radiolabeled ligand [3H]dihydrotestosterone (DHT). Testicular immunoreactive inhibin concentrations were maximal in late prepubertal monkeys, 2.5-3.5 yr old, while the total testicular content of inhibin progressively increased with age into adulthood. Bioactive testicular ABP concentrations were maximal during the pubertal period of the cynomolgus monkey (3.5-4.0 yr old), while the total ABP content of the testes also increased with sexual maturation. Mean (+/- SE) plasma concentrations of inhibin and testosterone (T) in adults, 6-8 yr old (17.72 +/- 3.5 microliters inhibin equivalents/ml and 7.07 +/- 2.45 ng/ml T, respectively), were significantly higher (P less than 0.05 and P less than 0.001, respectively) than those in early prepubertal, juvenile monkeys, aged 1.5-2.5 yr (5.85 +/- 2.1 microliters inhibin equivalents/ml and 0.27 +/- 0.02 ng/ml T). The increased plasma levels of inhibin and T in adults were associated, respectively, with the increased inhibin and androgen contents of the testes in these same animals. The developmental changes in testicular steady state mRNA concentrations for the inhibin alpha-, beta A-, and beta B-subunits as well as ABP were examined during sexual maturation by Northern blot analysis using heterologous human cDNA probes. Densitometric analysis of the autoradiograms revealed that the inhibin alpha-subunit mRNA concentrations were higher than those of inhibin-beta A and -beta B and ABP mRNA during all stages of pubertal development. Although the relative concentrations of each inhibin subunit mRNA were decreased in the adult animals relative to those in the juvenile monkeys, the total amount of steady state mRNA for the subunits was greater than that in the immature animals. A similar situation existed for the ABP mRNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of castration on luteinizing hormone and follicle-stimulating hormone secretion by pituitary cells from male rats

Because the role of the pituitary in the testicular control of gonadotropin secretion remains controversial, we examined the effects of castration on the release of LH and FSH under basal conditions and in response to GnRH stimulation by dispersed pituitary cells in monolayer culture as well as by cells perifused with pulses of GnRH. These effects were compared to changes in LH beta, FHS beta, and alpha-subunit mRNA levels determined by Northern blot analysis. Pituitary cells were prepared from 7-week-old intact rats and rats orchidectomized 2 weeks previously. Castration increased basal FSH secretion from monolayer cultures, interpulse FSH release from perifused pituitary cells, FSH beta mRNA concentrations and serum FSH levels each approximately 2-fold, whereas pituitary FSH contents were similar in cells from intact and castrated rats. Pituitary LH content rose 3-fold, LH beta mRNA rose 5.6-fold, and basal LH secretion increased 6-fold, but serum LH levels increased 22-fold. Thus, the change in FSH synthesis inferred from the increase in FSH beta mRNA was proportional to the increase in FSH secretion both in vitro and in vivo. Whereas the basal release of LH in vitro was also proportional to the change in LH beta mRNA, secretion of LH in vivo exceeded these changes, underscoring the importance of increased GnRH to the serum LH castration response. Castration resulted in an increase in the sum of FSH content and secretion during 10 days in culture in the absence of GnRH, indicating ongoing FSH synthesis. Total LH declined in cells from intact rats, and this decline was prevented by castration; this effect may be due to a castration-related decrease in intracellular LH degradation or increased LH synthesis in the absence of GnRH. Castration also augmented the GnRH-stimulated release of LH and FSH from monolayer cultures 4.5- and 1.8-fold, respectively, and increased the amplitude of GnRH-stimulated LH and FSH pulses 5- and 2-fold in experiments with perifused pituitary cells. The EC50 for GnRH was unaffected by castration.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum immunoreactive inhibin levels before and after luteectomy in the cynomolgus monkey (Macaca fascicularis)

Whereas studies in women have demonstrated that serum immunoreactive inhibin concentrations peak during the luteal phase of the menstrual cycle and that the corpus luteum (CL) encodes mRNA for the inhibin subunits, a clear link between the presence of the CL and circulating inhibin has not been established in primates. Therefore, we measured serum immunoreactive inhibin levels in monkeys before and after luteectomy as well as immunoreactive inhibin concentrations and mRNA encoding the alpha-inhibin subunit in luteal tissue. Monkeys were assigned to one of four groups depending on which day of the luteal phase luteectomy was performed: group A, days 4-5; group B, days 7-8; group C, days 9-10; and group D, days 11-12 (the day after the estrogen surge = day 1 of the luteal phase). Daily blood samples were obtained for 3 days before luteectomy, immediately before surgery, and for 2 days after luteectomy. Immunoreactive inhibin concentrations were measured with a double antibody RIA using an antiserum to bovine 31-kDa inhibin, bovine 31-kDa inhibin for iodination, and a human follicular fluid inhibin preparation as standard. Total RNA was isolated from luteal tissue and transferred by Northern blot onto a Zeta-probe membrane. The probe used for hybridization was the PstI/NcoI restriction enzyme fragment (381 basepairs) of alpha-inhibin DNA generated from a human ovarian cDNA library. Serum inhibin concentrations decreased (P less than 0.05) 24 h after removal of the corpus luteum in each of the four groups studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Pituitary glycoprotein hormone alpha-subunit secretion after thyrotropin-releasing hormone stimulation in normal men and men with idiopathic hypogonadotropic hypogonadism

Although TRH stimulates the release of uncombined alpha-subunit into the circulation in patients with primary hypothyroidism, it is not clear whether alpha-subunit is released from the thyrotrophs in euthyroid subjects. We hypothesized that spontaneous fluctuations in circulating alpha-subunit released from gonadotrophs by GnRH in normal adults could obscure the detection of small changes in alpha-subunit after TRH administration. We, therefore, examined alpha-subunit responses to TRH in five euthyroid men with idiopathic hypogonadotropic hypogonadism (IHH), who produce little or no GnRH, five normal men, and four postmenopausal women. Mean (+/- SEM) basal serum alpha-subunit levels were significantly (P less than 0.05) less in men with IHH (0.26 +/- 0.07 microgram/L) than in the normal men (0.80 +/- 0.20 microgram/L) or postmenopausal women (3.54 +/- 0.60 microgram/L). alpha-Subunit levels rose after TRH administration in all men with IHH to a peak level of 0.86 +/- 0.25 ng/ml; TSH levels also increased from 1.9 +/- 0.4 to 13.0 +/- 5.6 mU/L. The increment in TSH and alpha-subunit levels was highly positively correlated (r = 0.96). alpha-Subunit levels also increased 2-fold in normal men given TRH, whereas alpha-subunit levels in postmenopausal women were unchanged. We conclude that thyrotrophs release alpha-subunit into the circulation in normal men and euthyroid men with IHH. Thus, both thyrotrophs and gonadotrophs appear to contribute to circulating alpha-subunit in men with IHH; however, most of the uncombined alpha-subunit in normal men appears to be from gonadotrophs.

Inhibin is released together with testosterone by the human testis

The secretion of inhibin by the testis into the circulation was studied by measuring immunoreactive inhibin concentrations in spermatic vein blood samples drawn at 15 min intervals for 4 h. Mean spermatic vein inhibin levels were four times the levels in peripheral blood whereas spermatic vein testosterone (T) levels were 60-fold increased. Inhibin was released in well-defined pulses which coincided with episodes ot T release; both the duration and relative amplitude of inhibin and T pulses were similar. Inhibin pulses were undetectable in peripheral blood. These data suggest that the mechanism responsible for releasing T from the testis also stimulates inhibin release. This mechanism appears to involve LH and Leydig cells.

Effect of inhibin from primate Sertoli cells and GnRH on gonadotropin subunit mRNA in rat pituitary cell cultures

Partially purified inhibin from primate Sertoli cell culture medium (pSCl) suppresses both LH and FSH secretion from cultured rat pituitary cells stimulated with GnRH. To examine the mechanism of action of pSCl, we have measured steady state levels of mRNAs for the gonadotropin subunits in pituitary cell cultures exposed to 10 nM GnRH for 6 h in control or pSCl-containing medium (short term) and after 72-h pretreatment with pSCl or control medium (long term). Messenger RNA levels were determined by Northern analysis using specific cDNA probes for rat FSH beta, LH beta, and the common alpha-subunit. In the long term experiments, pSCl inhibited GnRH-stimulated release of FSH (47.4 +/- 3.3% of control), LH (69.2 +/- 2.3%), and free glycoprotein alpha-subunit (74.2 +/- 4.5%), and intracellular FSH declined to 88.4 +/- 3.5% of control. Concentrations of the subunit mRNAs were all decreased: FSH beta to 54.4 +/- 5.0%, LH beta to 79.6 +/- 9.4%, and alpha to 70.8 +/- 8.7% of control. In the short-term experiments, pSCl also suppressed FSH, LH, and alpha-subunit secretion to 75.9 +/- 3.6%, 79.5 +/- 2.1%, and 90.9 +/- 1.8% of control, respectively. Intracellular LH and alpha-subunit levels were significantly increased in cells treated for 6 h with GnRH and pSCl (155 +/- 18%, 145 +/- 14% of control), while FSH was comparable to control. After 6 h, pSCl selectively reduced the level of mRNA for FSH beta (56.5 +/- 5.8% of control).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of oxytocin administration upon the pulsatile secretion of luteinizing hormone in humans

The effect of iv administration of synthetic oxytocin upon the pulsatile pattern of LH secretion was studied in 5 healthy men and 10 healthy women. Five of the women were studied in the follicular phase of a menstrual cycle and the other 5 were studied in the luteal phase of a cycle. Synthetic oxytocin in 0.9% saline or saline alone was administered via continuous iv infusion for 8 h on 2 consecutive days. Infusions were administered using a double-blinded and radomized schedule. The rate of the oxytocin infusion commenced at 1 mU min and was increased 1 mU/min every 40 min to a final rate of 12 mU min. The plasma oxytocin concentration during oxytocin infusion ranged from 2-70 fmol 1. Blood for LH determination was sampled every 20 min in the 5 follicular phase women and every 10 min in the 5 men and 5 luteal phase women. The detect algorithm was used to analyze LH pulsatile secretion. Oxytocin infusion was without significant effect on mean LH, number of LH pulses, or area under the LH curve in men or women studied for the period of observation. Thus it is unlikely that increases in plasma oxytocin regulate the pulsatile secretion of LH in humans.

Hypogonadism following long-term treatment with diethylstilbestrol

The authors describe the abnormalities of gonadal function developing in a patient with prostate cancer who had received estrogen therapy continuously for 6 years. The pretreatment prostate biopsy showed well developed acini consistent with normal androgenization and adenocarcinoma. Twelve years later, 6 years after discontinuation of estrogen treatment, the patient presented with severe hypogonadism, gynecomastia, and primary hypothyroidism. Testicular biopsies showed ghosts of seminiferous tubules with absence of Leydig cells, and prostatic biopsies showed atrophic acini without evidence of malignancy. Despite undetectable serum testosterone levels, serum gonadotropins were inappropriately normal and responded minimally to gonadotropin-releasing hormone (GnRH) administration. Replacement therapy with levothyroxine did not correct gonadal dysfunction. Thus, prolonged estrogen therapy may result in irreversible testicular destruction and loss of the feed-back response of the hypothalamic pituitary gonadal axis.

Nature of alpha subunit secretion in men: circadian rhythms, pulsatile release and secretory profiles

Alpha subunit complements LH as a marker of the activity of the hypothalamic GnRH pulse generator. To characterize episodes of alpha subunit release and to determine if a circadian pattern of alpha subunit secretion is present in man, spontaneous alpha subunit pulsatility was analyzed in six healthy young men by blood sampling every 5 min for 24 h. The resulting alpha subunit concentration time series were analyzed by two statistically based independent peak detection methods, and subjected to Fourier transformation to assess underlying circadian rhythms. Cross-correlation analyses and multiple parameter deconvolution were used to estimate the concordance of spontaneous and exogenous GnRH-stimulated LH and alpha subunit secretion. These analyses revealed that two independent discrete peak detection algorithms yielded similar estimates of spontaneous alpha subunit pulse frequency, namely, 21 +/- 1.1 (Cluster) and 21 +/- 1.5 (Detect) alpha subunit peaks/24 h. Sampling intensity markedly influenced the estimate of endogenous alpha subunit pulse frequency, inasmuch as estimates from 5-min sampling were significantly greater than those of 10-min or 20-min sampling. Fourier transformation unmasked a significant circadian alpha subunit rhythm in all six men, with maximal concentrations at 0836 h and an average amplitude of 28% of the 24-hr mean hormone concentration. Cross-correlation analysis of spontaneous glycoprotein release revealed that serum LH and alpha subunit concentrations were highly cross-correlated when considered simultaneously, but not at various lags. Finally, deconvolution analysis of exogenous GnRH-stimulated glycoprotein release disclosed distinct half-times of alpha subunit and LH clearance with virtually simultaneous underlying secretory bursts. These data indicate that human alpha subunit is secreted in both a circadian and a discrete pulsatile fashion at a pulse frequency that is significantly underestimated at conventional sampling rates. The approximately hourly alpha subunit interpulse interval (68 +/- 4.6 min) is similar to that reported earlier for LH in peripheral blood and for testosterone in gonadal vein blood in healthy men. Moreover, cross-correlation analysis of endogenous GnRH-driven alpha subunit and deconvolution analysis of exogenous GnRH-stimulated alpha subunit and LH secretion suggest that these glycoproteins are secreted virtually simultaneously, but have significantly different endogenous clearance properties. The remarkably similar in vivo pulse frequencies for alpha subunit, LH, and testosterone in man suggest that the release of these three hormones is coordinately regulated.

Rapid and profound suppression of messenger ribonucleic acid encoding follicle-stimulating hormone beta by inhibin from primate Sertoli cells

We showed previously that inhibin, partially purified from cynomolgus monkey Sertoli cell culture medium (primate Sertoli cell inhibin referred to as pSCI), selectively suppressed basal FSH secretion from dispersed rat pituitary cells and decreased total cellular FSH, but not LH content, suggesting a decrease in FSH biosynthesis. In order to investigate the mechanism of action of inhibin at the molecular level, we have now examined the effects of pSCI on steady state levels of the subunit mRNAs encoding LH and FSH and correlated these with release and intracellular content of LH, FSH, and glycoprotein alpha-subunit. Dispersed pituitary cells from 7- to 8-week-old adult male rats were cultured in the presence of pSCI or control medium for 2-72 h. FSH secretion was reduced significantly by 6 h (P less than 0.05) and reached a nadir (38% of control) by 48 h. LH secretion was unchanged, while release of the alpha-subunit was decreased to 89% of control at 72 h (P less than 0.05). Also by 72 h, cell content of both FSH (73% of control) and alpha-subunit (81% of control) were significantly suppressed (P less than 0.001, P less than 0.01), while LH was slightly affected. Total RNA was extracted from the pituitary cell cultures, electrophoresed in 1.2% agarose-formaldehyde gels, transferred to nylon membranes, and hybridized with 32P-labeled cDNA probes for the rat alpha-, LH beta-, and FSH beta-subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of gonadal steroids on gonadotropin secretion in males: studies with perifused rat pituitary cells

The feedback effects of testosterone (T) and estradiol (E2) on FSH and LH secretion were compared in dispersed pituitary cells from adult male rats perifused with pulses of GnRH. Cells were stimulated with 10 nM GnRH for 2 min every 1 h. T (10 nM) pretreatment for 24 h reduced the amplitude of FSH and LH pulses to 77 +/- 4% (mean +/- SE) and 47 +/- 3% of control values, respectively (P less than 0.01), whereas 6-h T treatment was without effect. By contrast, interpulse secretion of FSH was increased after 24 h T to 184 +/- 7% of the control value (P less than 0.01), but interpulse LH release was unchanged (104 +/- 5%). E2 (0.075 nM) treatment of pituitary cells reduced GnRH-stimulated FSH and LH release within 2 h to 75 +/- 2% and 73 +/- 3% of control values, respectively (P less than 0.01). E2 pretreatment for 24 h stimulated (P less than 0.025) GnRH-induced FSH (136 +/- 10%) and LH (145 +/- 8%) release and also increased (P less than 0.01) interpulse FSH (127 +/- 5%) and LH (145 +/- 8%) secretion. These data indicate that the suppression of FSH and LH secretion by T in males is due in part to a direct effect on the pituitary. The findings that T suppresses GnRH-stimulated FSH less than LH, and that T stimulates interpulse FSH, but not LH, provide evidence for differential regulation of FSH and LH secretion by T. The dissimilar actions of T on GnRH-stimulated pulses and interpulse gonadotropin secretion suggest that interpulse secretion is unrelated to stimulation by GnRH, although its physiological significance is unknown. Since E2, in physiological levels for males, increased pituitary FSH and LH secretion, the suppression of gonadotropin secretion by E2 in vivo in males may result from an effect on the hypothalamic pulse generator; however, additional studies are needed before extending these conclusions to higher mammals and men.

Gonadotropin therapy in men with isolated hypogonadotropic hypogonadism: the response to human chorionic gonadotropin is predicted by initial testicular size

This study was designed to determine whether exogenous hCG alone can complete spermiogenesis in men with isolated hypogonadotropic hypogonadism (IHH). hCG was administered to 22 men with IHH until maximal testicular growth was achieved. Their mean testicular volume increased from 5.5 +/- 1.1 (+/- SE) mL (pretreatment) to 10.8 +/- 1.6 mL (maximum) during treatment (P less than 10(-6)). The maximum mean testicular volume was highly positively correlated with initial volume (r = 0.84; P less than 10(-6)). All men attained normal serum testosterone levels, and 7 of 22 men achieved supraphysiological serum estradiol levels. During hCG treatment, 14 of the 22 men had sperm appear in their semen. Six of 11 men with complete gonadotropin deficiency, defined as an initial mean testicular volume less than 4 mL, became sperm positive during hCG treatment. In contrast, 9 of 11 men with partial gonadotropin deficiency (initial mean testicular volume of 4 mL or more) produced sperm during treatment (P less than 0.001). Sperm concentration was highly positively correlated with both pretreatment (r = 0.65; P less than 0.01) and final testicular volume (r = 0.73; P less than 0.0001). Of 13 men attempting to impregnate their partners, 7 were successful in initiating conception; a total of 8 pregnancies ensued. The sperm concentration at the time of conception was less than 10 million/mL in all but 1 man. Our study demonstrates that hCG, in the absence of exogenous FSH, can complete spermiogenesis in men with partial gonadotropin deficiency. The response to hCG in men with IHH is predicted by the initial testicular volume.

Effects of inhibin from primate Sertoli cells on follicle-stimulating hormone and luteinizing hormone release by perifused rat pituitary cells

We used a pituitary cell perifusion system to investigate the time course and selectivity of the inhibin effect on pulsatile GnRH-stimulated LH and FSH release. Dispersed pituitary cells from 7- to 8-week-old male rats were perifused on a Cytodex bead matrix and stimulated with 10 nM GnRH for 2 min every hour for 8-11 h. The addition of a preparation of inhibin partially purified from primate Sertoli cells reduced pulsatile FSH release within 2 h. After removal of inhibin from the perifusion medium, the effect was reversed within 3 h. GnRH-stimulated LH release was also influenced by inhibin, although the decline in LH was less than that in FSH (80 +/- 3% vs. 68 +/- 4% of control; P less than 0.025). Smaller doses of inhibin suppressed GnRH-induced FSH secretion, but had no effect on LH release. Further, prolonged incubation of pituitary cells with inhibin at the higher dose reduced its FSH inhibitory effect and eliminated the effect on LH. These results indicate that inhibin can reduce both LH and FSH secretion in vitro, although the specificity and magnitude of the effect are a function of both the dose and duration of inhibin treatment. Further, the actions of inhibin and GnRH on the pituitary may be interrelated.

Alpha-subunit secretion in men with idiopathic hypogonadotropic hypogonadism

We studied the regulation of glycoprotein hormone alpha-subunit secretion in four men with idiopathic hypogonadotropic hypogonadism due to presumed GnRH deficiency. Immunoreactive alpha-subunit was present at low but usually detectable levels in blood samples drawn at 10- to 20-min intervals for 12-24 h; however, no characteristic pattern of pulsatile alpha-subunit secretion was found. Serum from each man was examined by gel filtration chromatography. Each sample tested contained an immunoreactive alpha-subunit peak with a slightly lower elution volume than [125I]hCG alpha, as we had previously found in serum from normal men. To determine if this peak represented TSH alpha, two men were treated with 0.3 mg L-T4 daily for 7-14 days. Serum TSH levels decreased to less than 1.5 mU/L, and neither TSH nor alpha-subunit levels increased after the iv administration of 500 micrograms TRH. An alpha-subunit peak that eluted before [125I]hCG alpha was again found in the serum of T4-treated men. We conclude that glycoprotein hormone alpha-subunit is present in the serum of men with idiopathic hypogonadotropic hypogonadism in whom TSH secretion is completely suppressed by L-T4. The gonadotrophs represent the most likely source of this alpha-subunit. The finding of more normal alpha-subunit than LH secretion in these men indicates that the production of the gonadotropin subunits is differentially regulated in man and supports the hypothesis that factors in addition to GnRH regulate alpha-subunit gene expression.

Identification of inhibin secreted by cynomolgus monkey Sertoli cell cultures

An inhibin was identified in the media of primary Sertoli cell-enriched cultures from the cynomolgus monkey, Macaca fascicularis, and some of its biochemical properties were studied. Conditioned monkey Sertoli cell culture medium (m-SCCM), when added to pituitary cells from 6-week-old male rats, inhibited the basal secretion of FSH but not that of LH. This specificity was lost after the addition of GnRH; mSCCM inhibited not only FSH but also LH release, determined by both RIA and mouse interstitial cell bioassay, from pituitary cells exposed for 6 h to 10 nM GnRH. FSH-inhibiting activity persisted when m-SCCM was boiled for 30 min, but activity was lost after incubation for 1 h at 37 C with 0.1% trypsin. m-SCCM inhibin activity was completely retained by Concanavalin A-Sepharose and could be eluted with 0.2 M alpha-methyl-D-glucoside. Gel filtration high pressure liquid chromatography with a Superose-12 column revealed inhibin activity between 20-60K, with the greatest activity at 40K. Our results indicate that primate Sertoli cells produce an inhibin-like factor which could play a role in controlling gonadotropin secretion in males.

Testosterone and estradiol are co-secreted episodically by the human testis

In spite of a striking pulsatile pattern of luteinizing hormone (LH) secretion, testosterone (T) fluctuations in peripheral blood in normal adult men are irregular and of low amplitude. To determine whether T secretion by the human testis is episodic, T was measured in blood samples drawn at 15-min intervals for 4 h through a catheter placed in the testicular vein of six men with varicocele-associated infertility. Estradiol (E2) concentrations were also determined in each sample. Each subject released testosterone in well-defined pulses. Gonadal vein T levels ranged from 1 to 1,540 ng/ml. Mean (+/- SE) pulse amplitude was 176 +/- 42 ng/ml, with a frequency of 4.0 +/- 0.3 pulses per 4 h. Testicular vein E2 levels ranged from 0.01 to 6.8 ng/ml. E2 secretory episodes were generally coincident with T pulses, and their amplitudes were highly positively correlated (r = 0.90, P less than 0.01). These results indicate that T secretion by the adult human testis is pulsatile, and suggest a functional relationship between intermittent LH secretion and normal testicular steroidogenesis in men. The failure to appreciate these fluctuations as hormone pulses in peripheral blood may relate to their absolute amplitude and frequency. The concordance between E2 and T pulses suggests that the Leydig cell, under LH control, is the source of most of the E2 secreted by the adult human testis.

Testicular control of prostaglandin E2 production in rat vas deferens

Orchidectomy decreased and testosterone (T) replacement restored prostaglandin E2 (PGE2) concentrations in adult rat vas deferens. To explain this finding, phospholipase A (PLase-A) and PG synthetic activity were studied in vas tissue from 9-week-old rats orchidectomized with or without T replacement as well as in rats in which the cauda epididymidis was ligated. PG synthetic activity fell to 3% of intact levels in 14-day castrate rats and was restored to normal by T replacement. Although vas PLase-A activity was also significantly (P less than 0.01) reduced to 38% of the control level in 14-day castrate rats, this change appears in part to reflect a castration-related increase in endogenous phospholipid concentrations. Further, T replacement only partially restored PLase-A activity to 59% of intact levels. Ligation of the cauda epididymidis in intact rats reduced vas PLase-A activity to castrate levels without altering vas T concentration. These results demonstrate both a direct effect of T on the biosynthesis of PGs in rat vas deferens as well as a paracrine effect, which appears to be mediated by a factor(s) other than T. These data suggest the existence of a new mechanism through which testicular products contribute to the function of the vas deferens.

Seminiferous tubule androgen receptors in experimental cryptorchidism

As an initial approach to the study of seminiferous tubule androgen receptors in disordered spermatogenesis, cytosol androgen receptors were studied in rats with experimental cryptorchidism. Two weeks after the testis had been repositioned in the abdomen of 6-week-old rats, the animals were hypophysectomized to deplete the testis of androgen, and 1 week later they were killed. Androgen receptor binding was studied in seminiferous tubule cytosol using [3H]methyltrienolone as the radiolabelled probe. The androgen-binding capacity of cryptorchid testis, when expressed as fmol bound/testis, was reduced to 50% of control, in parallel with the decline in testis weight. No change in binding affinity was found. Sucrose density gradient centrifugation using a vertical tube rotor revealed a 9S molybdate-stabilized receptor under low-salt conditions in both cryptorchid and scrotal seminiferous tubule cytosol. Receptor-complex stability studies, analysis by gel filtration and DEAE-cellulose chromatography produced similar results in cryptorchid and scrotal tubules. The mechanism for the reduction in testicular receptor content of an abdominal testis remains to be clarified. The demonstration that testicular androgen receptors can be reduced by cryptorchidism suggests that further studies may indicate the role of receptor binding in testicular function.

Assay of primate seminiferous tubule androgen receptors using [3H]mibolerone

The synthetic radiolabelled androgen mibolerone (7 alpha, 17 alpha-dimethyl-19-nortestosterone) was used to characterize androgen receptor binding in the seminiferous tubules from Cynomolgus monkey testis. Mibolerone binding was of high affinity (Kd = 0.6-5.4 nM) and limited capacity (37-50 fmol/mg protein), and was androgen specific. Sucrose density gradient centrifugation using a vertical tube rotor permitted the identification of a 9S molybdate-stabilized receptor under low salt conditions. The receptor bound to DEAE-cellulose. Methyltrienolone, but not mibolerone, also bound to a low affinity high capacity binding site in tubule cytosol, which probably represents glucocorticoid receptor binding, since it could be displaced by excess dexamethasone. However, occupancy of this low-affinity binding site by dexamethasone in an androgen receptor assay with [3H]methyltrienolone lead to a 33% underestimation of receptor binding, which appeared to relate to radioactive decomposition. Mibolerone, as well as methyltrienolone, bound to a progestin-binding protein in seminiferous tubule cytosol. These studies provide methods for the study of seminiferous tubule androgen receptors in subhuman primates and indicate that, due to its greater stability and lack of binding to glucocorticoid receptor, mibolerone is a useful new ligand in the study of androgen receptors in testis and its constituent cells.

Evidence for a role of endogenous estrogen in the hypothalamic control of gonadotropin secretion in men

To examine the mechanism by which endogenous estrogens inhibit gonadotropin secretion in men, blood samples were drawn every 10 min for 12 h in five men before and at the completion of 3 weeks of treatment with the estrogen antagonist clomiphene citrate (50 mg twice daily). Samples were analyzed for LH and alpha-subunit by RIA. Clomiphene produced a 3-fold rise in circulating LH levels, which was associated with a 80% increase in pulse frequency and a 70% increase in pulse amplitude. Immunoreactive alpha-subunit secretion was also pulsatile before and after clomiphene treatment. Mean alpha-levels rose 70%, together with a 39% increase in pulse frequency and a 41% increase in pulse amplitude. Circulating testosterone and estradiol levels increased 2-fold and FSH levels increased 3-fold after clomiphene treatment. Insofar as each LH and uncombined alpha-subunit pulse reflects a LHRH secretory episode, our data indicate that endogenous estrogens tonically restrain the hypothalamic release of LHRH. From these results and those of previous studies, we conclude that estrogens as well as androgens are important in the testicular feedback inhibition of the hypothalamic oscillator that governs pulsatile gonadotropin secretion.

Identification of androgen-binding protein from testis cytosol and sertoli cell culture medium of the cynomolgus monkey, Macaca fascicularis

The biochemical and immunological properties of monkey androgen-binding protein (mABP) from the cynomolgus monkey, Macaca fascicularis, have been examined in testis cytosol and medium of primary Sertoli cell-enriched cultures. mABP in testis tissue was separated from the serum protein testosterone-estradiol-binding globulin (mTeBG) by affinity chromatography on Concanavalin A-Sepharose (Con A). mTeBG from serum extracts was completely retained by the lectin and could be displaced with buffer containing alpha-methyl-D-glucoside. In contrast, mABP from testis extracts either did not interact with the Con A and appeared in the void volume or was partially retained by the column and could be eluted with buffer alone. A third component retained by the Con A may represent mTeBG contamination, a form of mABP which binds to Con A, or both. The specific 5 alpha-dihydrotestosterone (DHT)-binding activity in the void volume of the Con A column was designated mABP and was further studied. [3H]DHT binding to mABP was saturable and of limited capacity (0.163 +/- 19 pmol/mg protein). Scatchard analysis of the data was consistent with a single class of binding sites with an apparent dissociation constant (Kd) at 4 C of 2.6 +/- 0.2 X 10(-9) M. DHT was the most effective competitor of [3H]DHT binding to mABP, followed by 2-methoxyestradiol, testosterone, estradiol, and cyproterone acetate. Concentrated Sertoli cell culture medium subjected to steady state polyacrylamide gel electrophoresis produced a single peak of specifically bound [3H]DHT with a mobility similar to that of other androgen-binding proteins. [35S]Methionine-labeled medium proteins were immunoprecipitated with a rabbit anti-human TeBG antiserum. Two bands, corresponding to mol wt of approximately 46,000 and 48,000, were observed by fluorography, with the lighter component being more intense. After androgen affinity chromatography of radiolabeled medium proteins, these two bands were again observed on sodium dodecyl sulfate-urea-containing polyacrylamide gels. These results demonstrate that 1) mABP may be separated from mTeBG by lectin affinity chromatography, as in humans; 2) hTeBG and mABP are antigenically related; and 3) mABP consists of subunits of different mol wt in unequal ratios.

An analysis of the age-related decline in testicular steroidogenesis in the rat

The effect of aging in rats on serum and intratesticular testosterone levels, microsomal steroidogenic enzyme activities and microsomal cytochrome P-450 was studied. Serum testosterone levels were highest in 11-wk-old rats, declined at age 16 wk and further declined between ages 7 and 21 mo. Intratesticular testosterone levels in 21-mo-old rats were significantly lower than those of the other groups. The activity of 17 alpha-hydroxylase and C17-20 lyase, as well as cytochrome P-450, decreased significantly in 21-mo-old rats. The activity of 17 beta-hydroxysteroid oxidoreductase increased from 11 wk to 16 wk of age and then declined by 21 mo of age to the levels of 11-wk-old animals. Similar changes in delta 5-3,3-hydroxysteroid dehydrogenase coupled with delta 5-delta 4 isomerase activities were observed, but were not statistically significant. These results suggest that the decline in testosterone production in old rats is predominantly a result of decreased oxygenase activity. Inasmuch as oxygenases are gonadotropin dependent, our results support the hypothesis that gonadotropin deficiency is the major factor responsible for Leydig cell dysfunction in old rats. Further, the decline in the ratio of 17 alpha-hydroxylase to C17-20 lyase with aging suggests that other factors affect these enzymes as well as the reduction in cytochrome P-450.

Pulsatile secretion of immunoreactive alpha-subunit in man

We compared the secretion of uncombined alpha-subunit with LH secretion, as measured by RIA in six normal men, an agonadal adult man, and an adult woman with testicular ferminization. Blood samples were drawn every 10 min for 12 h to evaluate pulsatile LH and free alpha secretion. Spontaneous alpha pulses occurred every 120 +/- 60 min (mean +/- SD; range, 40-260) in eugonadal men. The mean alpha pulse amplitude was 0.49 +/- 0.11 ng/ml, representing an increase of 60 +/- 18% above the preceding nadir value. alpha pulses were generally associated with LH pulses, and the amplitudes of concordant alpha and LH pulses were highly positively correlated (r = 0.58; P less than 0.01). The absolute amplitude of concordant alpha peaks was 1.5 +/- 0.7% that of corresponding LH peaks. Additional alpha pulses were noted in each subject for which simultaneous LH fluctuations failed to meet the criteria for pulses. Studies in the agonadal man and in the patient with testicular feminization revealed that the frequency of both spontaneous alpha and LH pulses was increased to approximately twice that in normal men. Gel filtration analysis indicated that all alpha radioimmunoactivity in normal male sera coeluted with [125I]alpha. By contrast, in hypogonadal sera, only 50-60% of alpha immunoreactivity coeluted with [125I]alpha, the remaining activity appeared in the region of LH and FSH and resulted from RIA cross-reactivity. We conclude that uncombined alpha-subunit, as well as LH is normally released into the peripheral blood in discrete pulses. In the absence of exposure to androgen, the frequency of these pulses increases, presumably as a consequence of the accelerated release of LRH. However, alpha RIAs overestimate the concentration of uncombined alpha in hypogonadal sera. We propose that the coanalysis of LH and alpha secretory episodes may prove useful in resolving some of the complexities associated with gonadotropin secretory patterns.

Studies of the human testis. XIX. Preparation of an antibody to human testosterone-oestradiol-binding globulin and its application to the study of testicular androgen-binding protein

Human testosterone-oestradiol-binding globulin (hTeBG) was purified from pregnancy serum by ammonium sulphate precipitation, preparative flatbed electrofocusing, Concanavalin A-Sepharose affinity chromatography, Sephadex G-150 gel filtration, DEAE-Sephadex chromatography and preparative polyacrylamide gel electrophoresis. The yield was 0.3 mg of hTeBG with a specific acitivity of 1.1 nmoles DHT bound per mg. An antiserum to TeBG was raised in rabbits. Anti-hTeBG IgG was separated from rabbit TeBG by DEAE-Affi-Gel-Blue chromatography. Anti-hTeBG was titrated using protein A-Sepharose which quantitatively binds IgG and therefore bound [3H]DHT-hTeBG-anti-TeBG complexes. The androgen binding components from human testis were separated on Concanavalin A-Sepharose columns into excluded and retained fractions. The antibody bound both testis fractions with titration curves which paralleled that of TeBG, indicating that these androphilic proteins share common immunodeterminants with hTe-BG. The possibility that these testicular proteins are identical in amino acid sequence to TeBG and differ only in carbohydrate content will require further verification. Finally, these results indicate that antibodies to TeBG can be used to study human testicular androgen-binding protein.