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.

International Society of Andrology and International Union of Pure and Applied Chemistry, Clinical Chemistry Section, Commission on Nomenclature, and International Federation of Clinical Chemistry Scientific Division. Properties and units in the clinical laboratory sciences XIII. Properties and units in reproduction and fertility (IUPAC-IFCC technical report 1998).

This document is the first recommendation on the presentation of properties in reproduction and fertility and their values in clinical laboratory sciences from The International Society of Andrology, IFCC and IUPAC. It forms part of the ongoing effort to standardise requests and reporting of laboratory data for transmission across cultural and linguistic domains, without attempting to standardise the language used by clinicians and laboratory practitioners. The document is accessible on Internet from C-NPU home page address: http://inet.uni-c.dk/ home/ifcc_iupac_cnpu.

Interrater concordance for faculty grading of student performances in a problem-based learning course.

PURPOSE: To determine whether it is possible for faculty to arrive at consistent, non-idiosyncratic grades in a problem-based learning (PBL) course. METHOD: Integrated Case Studies and Medical Decision Making (ICS) is the final course of the second year at the University of Pittsburgh School of Medicine. In ICS, 16 groups of nine students work in a PBL format over seven weeks. Each group is led by three faculty facilitators who, at the end of the course, independently give each student ratings for overall performance in the course and for each of seven performance categories. In 1993-94 and 1994-95, concordance in grades among the facilitators was determined by computing the intraclass correlation coefficients [ICC (3,1)] for the overall scores, the seven performance category scores, and all eight scores in aggregate. An ICC (3,1) of > or = .1 was considered indicative of statistically significant interrater concordance. An ICC (3,1) of > or = .7 was considered indicative of concordance of practical significance. RESULTS: Because the facilitators occasionally did not rate every student in every performance category, complete information was not available for all 32 groups. Statistically significant concordance was achieved in the aggregate scores in 100% of 23 groups, and in the overall scores in 90% of 18 groups. In six of the seven performance categories, concordance was achieved in at least 75% of the groups (n = 16-20). Practically significant concordance was achieved in the aggregate scores in 83% of 23 groups. CONCLUSION: The study results show that, given specific criteria by which to judge students' performances, it is possible to arrive at consistent, non-idiosyncratic grades for students in PBL courses.

Integrated case studies and medical decision making: a novel, computer-assisted bridge from the basic sciences to the clinics.

This article describes a novel course that was designed to bridge the gap between the basic science years and clinical experiences in medical school by using information science and computer technology as major components of problem-based learning (PBL) sessions. The course, Integrated Case Studies and Medical Decision Making, was first given to second-year students at the University of Pittsburgh School of Medicine in the spring of 1994. It consists of 13 PBL exercises, each of which explores a clinical case. The cases, including images and gated access to information, are housed on a computer. Using one of 16 networked terminals in specially designed small-group rooms, groups of nine students progress through the cases with a faculty facilitator. The responses of students and faculty to the initial year of the course were favorable. In comparison with traditional PBL sessions, enhanced quality of and access to images and accountability for accessing case information in sequential fashion were cited as major strengths of the course. Juxtaposition of basic science and clinical material and utility in reviewing for the United States Medical Licensing Examination were also cited as strengths. The diversity of the basic science material involved in completing the cases drew overwhelming enthusiasm from students and facilitators alike. In conclusion, the course successfully employs computer and information science technology, which will be of increasing importance to future physicians. The course also serves as an effective bridge to the clinical years of medical school and as a study adjunct for the USMLE.

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 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.

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).

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)

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.

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)

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.

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.