The annual testicular cycle in the turtle, Chrysemys picta: a histochemical and electron microscopic study

This work is a study of testicular function in Chrysemys picta using changes in ultrastructure and steroid histochemistry as indices of Leydig and Sertoli cell activity. The cytological features of these cells are described in reference to four periods of tubular development. Leydig and Sertoli cells show distinct changes in morphological appearance during the seasonal cycle. Leydig cells are hypertrophic with an active 3 beta-hydroxysteroid dehydrogenase (HSD) and abundant smooth endoplasmic reticulum (SER) in early spring when androgen levels are high and animals mate and atropic in mid-summer when spermatogenesis is proceeding. Leydig cell atrophy is associated with a reduction in the volume of cytoplasm and SER. Leydig cells become active again in the fall showing a return toward the spring condition, with an increase in 3 beta-HSD activity. In contrast, although Sertoli cells show variations in abundance of organelles and inclusions during the annual cycle, no obvious degenerative changes could be seen and SER is always present. 3 beta-HSD enzyme activity in Sertoli cells is weak or absent in spring but intense during summer. Taken together, these observations suggest that Sertoli and Leydig cell functions are asynchronous.     

Androgens and spermatogenesis

Male infertility contributes to 50% of all cases of infertility. The main cause is low quality and quantity of sperm. In humans, spermatogenesis starts at the beginning of puberty and lasts lifelong. It is under the control of FSH and testicular androgens, and mainly testosterone (T), and therefore requires a normal gonadotroph axis, intratesticular T production by Leydig cells and functional androgen receptors (ARs) within testicular Sertoli cells. Various clinical cases illustrate the roles of T in human spermatogenesis. Men with complete congenital hypogonadotropic hypogonadism (HH) are usually azoospermic. Treatment by exogenous testosterone injection and FSH is not able to produce sperm. However, combined treatment with FSH and hCG is effective. This example shows that intratesticular T plays a major role in spermatogenesis. Furthermore, testicular histology of men with LH receptor mutations shows Leydig cell hypoplasia/agenesis/dysplasia with conserved Sertoli cell count. The sperm count is reduced, as in males with partial inactivating mutation of the androgen receptor. Some protocols of hormonal male contraception or exogenous androgen abuse induce negative feedback in the hypothalamic pituitary axis, decreasing FSH, LH and T levels and inducing sperm defects and testicular atrophy. The time to recovery after cessation of drug abuse is around 14 months for sperm output and 38 months for sperm motility. In summary, abnormal androgen production and/or AR signaling impairs spermatogenesis in humans. The minimal level of intratesticular T for normal sperm production is a matter of debate. Interestingly, some animal models showed that completely T-independent spermatogenesis is possible, potentially through strong FSH activation. Finally, recent data suggest important roles of prenatal life and minipuberty in adult spermatogenesis.     

Seasonal cycles in gonadal activity and plasma gonadotropin in the musk turtle, Sternotherus odoratus

Plasma gonadotropin cycles were examined in relation to the seasonal gonadal cycle in freshly captured musk turtles, Sternotherus odoratus, from South Carolina. Acute and chronic stress effects of captivity on testicular growth and circulating plasma testosterone (T) and follicle-stimulating hormone (FSH) also were examined. Monthly mean FSH levels in freshly captured males were correlated significantly with plasma T. Both T and FSH were minimal in spring when testes were small, and highest in the fall in males that had begun spermiation and whose testes had begun to regress. Individual plasma T and FSH values were significantly correlated during the fall when both hormones were at elevated levels. In contrast, plasma luteinizing hormone (LH) remained undetectable throughout the year in males. Females had nondetectable levels of both plasma LH and FSH throughout the year. There was a seasonal pattern in plasma 17 beta-estradiol which was correlated with follicular growth. Holding males in captivity (outdoors) reduced plasma T by 35-60% within 24 hr of capture (depending on season) and plasma T remained at these lower levels after 2 weeks. However, FSH was not significantly affected by such short-term "stress." Testicular weight and FSH cycles of captive males were similar to those of males in the field. Monthly plasma T of long-term captives also exhibited a seasonal cycle but at a level significantly lower than in the field and with a delayed peak. Thus, while the data suggest that FSH may be important to both seasonal testicular growth and androgen secretion, fluctuations in FSH alone cannot account for all observed patterns or changes in spermatogenesis or plasma androgen levels.     

Seasonal reproduction in the mongoose,Herpestes auropunctatus: I. Androgen,luteinizing hormone,and follicle-stimulating hormone in the male

The mongoose is a small carnivore that exhibits a distinct seasonal rhythm in reproductive activity. Feral mongooses were trapped alive on the island of Oahu (Hawaii) between May 1977 and December 1979. The animals were autopsied shortly after capture and testes and prostate glands were weighed and serum collected for later measurement of androgen, LH, and FSH. The validations of radioimmunoassays for mongoose LH and FSH are described. Testes and prostate gland weights were significantly larger during the breeding season than during the inactive season. Serum androgen, LH, and FSH levels were significantly higher during the breeding season than during the inactive season. Significant annual variations were found in testes and prostate gland weights and serum androgen and FSH levels. During testicular regression (August to September) changes in gonadotropin levels paralleled changes in serum androgen levels; however, during the recrudescence phase (December to February) gonadotropin levels appeared to rise much more rapidly than serum androgen levels. Possible factors involved in the regulation of the seasonal pattern in serum gonadotropin levels and testicular activity are discussed.     

New perspectives in the diagnosis of pediatric male hypogonadism: the importance of AMH as a Sertoli cell marker

Sertoli cells are the most active cell population in the testis during infancy and childhood. In these periods of life, hypogonadism can only be evidenced without stimulation tests, if Sertoli cell function is assessed. AMH is a useful marker of prepubertal Sertoli cell activity and number. Serum AMH is high from fetal life until mid-puberty. Testicular AMH production increases in response to FSH and is potently inhibited by androgens. Serum AMH is undetectable in anorchidic patients. In primary or central hypogonadism affecting the whole gonad and established in fetal life or childhood, serum AMH is low. Conversely, when hypogonadism affects only Leydig cells (e.g. LHβ mutations, LH/CG receptor or steroidogenic enzyme defects), serum AMH is normal or high. In pubertal males with central hypogonadism, AMH is low for Tanner stage (reflecting lack of FSH stimulus), but high for the age (indicating lack of testosterone inhibitory effect). Treatment with FSH provokes an increase in serum AMH, whereas hCG administration increases testosterone levels, which downregulate AMH. In conclusion, assessment of serum AMH is helpful to evaluate gonadal function, without the need for stimulation tests, and guides etiological diagnosis of pediatric male hypogonadism. Furthermore, serum AMH is an excellent marker of FSH and androgen action on the testis.     

Effects of FSH on Leydig cell morphology and function in the hypogonadal mouse.

The hypogonadal (hpg) mouse has a congenital deficiency in gonadotrophin-releasing hormone and the gonads consequently lack exposure to endogenous gonadotrophins during development. To determine the effect of FSH on Leydig cell function in these animals adult hpg mice were injected twice daily with FSH (2 micrograms injections) or LH (40 ng injections, the presumed LH contamination of FSH used). Following FSH treatment there was a clear stimulation of the seminiferous epithelium and in animals injected with FSH plus [3H]thymidine, the incorporation of label was largely confined to the germ cells with no apparent uptake by the Sertoli cells. In FSH-treated testes the Leydig cells contained numerous large lipid droplets, similar to the unstimulated hpg testis. There was no evidence of the interstitial hyperplasia which is observed following injection of high doses of LH (2 micrograms twice daily). There was no change in basal androgen content of the testis in vivo following FSH treatment but injection of a maximal dose of human chorionic gonadotrophin (hCG), 1 h before death, markedly increased testicular androgen content only in the FSH-treated group. Testicular androgen production in vitro was significantly increased following FSH treatment both under basal conditions (FSH-treated, 17.4 pmol/testis; control, 1.46 pmol/testis) and during stimulation by hCG (FSH-treated, 940 pmol/testis; control, 81 pmol/testis). Associated with the increased androgen production following FSH treatment there were significant increases in the activities of three steroidogenic enzymes; cholesterol side-chain cleavage (186-fold increase over control), 17 alpha-hydroxylase (103-fold increase) and 17-ketosteroid reductase (177-fold increase).(ABSTRACT TRUNCATED AT 250 WORDS)     

Increased serum inhibin B levels after varicocele treatment

OBJECTIVE: Inhibin B is secreted by Sertoli cells in response to FSH and is the major feedback regulator of FSH secretion in man. The serum inhibin B level has emerged as a good marker of spermatogenesis and Sertoli cell function. Varicocele has been associated with infertility and disturbed spermatogenesis. We have studied the effect of varicocele treatment on serum inhibin B levels, with the aim of investigating the effect on spermatogenesis and the involvement of the Sertoli cell in varicocele pathophysiology. DESIGN AND PATIENTS: In a pre-post test design, the effect of varicocele surgery on inhibin B levels was studied in 30 infertile men. MEASUREMENTS: Endocrinology (inhibin B, FSH, LH, SHBG and testosterone) and semen analysis (sperm concentration, motility and morphology). RESULTS: In men receiving varicocele treatment, a significant increase in serum inhibin B levels was observed from 133.9 +/- 13.4 pretreatment to 167.8 +/- 16.1 ng/l after treatment (mean +/- SEM, P < 0.0001). No significant changes were observed in serum levels of FSH, LH and testosterone. The serum SHBG level decreased from 32.9 +/- 3.5 to 28.6 +/- 3.4 nmol/l (mean +/- SEM, P = 0.04) and the free androgen index was significantly increased from 66 +/- 5.9 pretreatment to 85 +/- 6.8 after treatment (P = 0.02, mean +/- SEM). Semen analysis showed a significant improvement in sperm concentration, from 6.5 +/- 1.9 pretreatment to 19.3 +/- 4.9 x 106/ml after treatment (P = 0.003, mean +/- SEM), and in sperm motility from the baseline level of 17 +/- 3 to 32 +/- 4% after treatment (P = 0.001, mean +/- SEM). CONCLUSIONS: Varicocele treatment can increase serum inhibin B levels, indicating improvement of spermatogenesis and Sertoli cell function. This finding suggests that the pathophysiology of varicocele involves impairment of Sertoli cell function or a different distribution of germ cell stages.     

Permanent effects of neonatal estrogen exposure in rats on reproductive hormone levels, Sertoli cell number, and the efficiency of spermatogenesis in adulthood.

This study aimed to identify the mechanism(s) for impairment of spermatogenesis in adulthood in rats treated neonatally with estrogens. Rats were treated (days 2-12) with 10, 1, or 0.1 microg diethylstilbestrol (DES), 10 microg ethinyl estradiol (EE), 10 mg/kg of a GnRH antagonist (GnRHa), or vehicle and killed in adulthood. DES/EE caused dose-dependent reductions in testis weight, total germ cell volume per testis, and Sertoli cell volume per testis. Sertoli cell number at 18 days of age in DES-treated rats was reduced dose dependently. GnRHa treatment caused changes in these parameters similar to those in rats treated with 10 microg DES. Plasma FSH levels were elevated (P < 0.001) to similar levels in all treatment groups regardless of differences in Sertoli cell number and levels of inhibin B; the latter reflected Sertoli cell number, but levels were disproportionately reduced in animals treated with high doses of DES/EE. Neonatal estrogen treatment, but not GnRHa, caused dose-dependent reductions (40-80%) in plasma testosterone levels in adulthood, but did not alter LH levels. Preliminary evidence suggests that the decrease in testosterone levels in estrogen-treated rats is not due to reduced Leydig cell volume per testis. GnRHa-treated rats exhibited a significant increase in germ cell volume per Sertoli cell and a reduction in germ cell apoptosis, probably because of the raised FSH levels. Despite similar raised FSH levels, rats treated with DES (10 or 1 microg) or EE (10 microg) had reduced germ cell volume/Sertoli cell and increased germ cell apoptosis, especially when compared with GnRHa-treated animals. The latter changes were associated with an increase in lumen size per testis, indicative of impaired fluid resorption from the efferent ducts, resulting in fluid accumulation in the testis. Rats treated neonatally with 0.1 microg DES showed reduced germ cell apoptosis comparable to that in GnRHa-treated animals. The changes in apoptotic rate among treatment groups occurred across all stages of the spermatogenic cycle. It is concluded that 1) neonatal estrogen treatment results in dose-dependent alterations in Sertoli cell numbers, germ cell volume, efficiency of spermatogenesis, and germ cell apoptosis in adulthood; 2) the relatively poor spermatogenesis in estrogen-treated animals is most likely due to altered testis fluid dynamics and/or altered Sertoli cell function; 3) as indicated by FSH (LH) and testosterone levels, the hypothalamic-pituitary axis and Leydig cells are probably more sensitive than the Sertoli cells to reprogramming by estrogens neonatally; and 4) elevated FSH levels in adulthood may improve the efficiency of spermatogenesis.     

Seasonal changes in testicular structure and function and the effects of gonadotropins in the freshwater turtle,Chrysemys picta

Plasma testosterone was measured at stages during the reproductive cycle of control male turtles (Chrysemys picta) and following hypophysectomy and/or mammalian FSH or LH injection. Testosterone levels were highest in April and December when large Leydig cells were observed in the interstitium but the epithelium was inactive. During active spermatogenesis (July, October) plasma steroid levels were basal, and not significantly reduced by hypophysectomy. While LH injections had no effect, FSH was a potent stimulus to plasma testosterone in both intact and hypophysectomized turtles. Histologic observations during the testicular cycle and after hypophysectomy indicated that the tubular epithelium was dependent on endogenous pituitary hormone secretion but the interstitium did not atrophy during the experimental period. Injections of FSH in May increased testicular weight and caused disappearance of vacuoles and granules from apical portions of the Sertoli cell with a consequent reduction in cell height. Neither FSH nor LH had obvious effects on the morphology of the interstitium in control or hypophysectomized turtles either in July or November.     

Testicular gonadotrophins and their receptors in human cryptorchidism as revealed by immunohistochemistry and radioreceptor assay

The localisation of endogenous FSH and LH was studied in 4 inguinal adult human testes by the immunoperoxidase technique utilising antisera against the beta-subunits of human FSH and LH. The content of available FSH and LH receptors was determined by radioreceptor assay. The Sertoli cells and about 10% of cells in the intersitium the Leydig cells, possibly the testicular macrophages, were similarly FSH-positive in cryptorchidism and control testes. The FSH receptor levels per testis were significantly lower in cryptorchidism than in control testes. Also the localisation of LH in Leydig cells in cryptorchidism was similar to the control testes, but the LH receptor level was significantly lower. These data bring further evidence for Leydig and Sertoli cell malfunction in the inguinal human testis.     

Functional analysis of LHbeta knockout mice

LH and FSH act on gonadal cells to regulate steroidogenesis and gametogenesis. To model human reproductive disorders involving loss of LH function and to define LH-responsive genes, we produced knockout mice lacking the hormone-specific LHbeta subunit. LHbeta null mice are viable but demonstrate postnatal defects in gonadal growth and function resulting in infertility. Mutant males have decreased testes size, a block in Leydig cell differentiation, and a reduction in serum and intra-testicular testosterone levels. Furthermore, spermatogenesis is blocked at the round spermatid stage resulting in a total absence of the elongated spermatids. Mutant female mice are hypogonadal and demonstrate decreased levels of serum estradiol and progesterone. Ovarian histology reveals normal thecal layer, defects in folliculogenesis including many degenerating antral follicles and absence of corpora lutea. The defects in both sexes are not secondary to aberrant FSH regulation, since FSH levels were unaffected in null mice. Finally, the null mice can be pharmacologically rescued by exogenous hCG indicating that LH-responsiveness of the target cells is not irreversibly lost. Thus, LHbeta null mice provide a useful model to study the consequences of an isolated deficiency of LH ligand in reproduction, while retaining normal LH-responsiveness in target cells.     

Stimulatory effects of recombinant follicle-stimulating hormone on Leydig cell function and spermatogenesis in immature hypophysectomized rats

Although earlier reports suggest a stimulatory effect of FSH on Leydig cell function, controversy exists due to unavailability of FSH preparations free of contaminating LH. Recent availability of recombinant human FSH preparations made it possible to reinvestigate this question. Immature male rats were hypophysectomized (21-22 days old at surgery) and implanted with osmotic minipumps releasing 8 IU recombinant FSH or 18 IU purified human pituitary FSH (hpFSH)/day, whereas control animals received vehicle alone. After 7 days of treatment, testicular weight increased in the recombinant FSH and hpFSH-treated animals to values 2.3- and 2.5-fold those of controls, respectively. Analyses of the steroidogenic capacity of Leydig cells in testes of rats treated with recombinant FSH or hpFSH also revealed 2.9- and 3.8-fold androgen production in vitro compared to controls. In these rats recombinant FSH and hpFSH increased the LH receptor number in testicular homogenate by 50% and 70%, respectively. The increase in LH receptor number was associated with increases in the LH receptor mRNA levels. In hypophysectomized control rats, small seminiferous tubules contained spermatogonia and zygotene/early pachytene spermatocytes. In contrast, treatment with either FSH preparation enhanced the progression of meiosis, as evidenced by large number of pachytene spermatocytes and appearance of round spermatids. The present results show that LH-free recombinant FSH, like purified pituitary FSH, is capable of increasing the LH receptor content and steroidogenic responsiveness of Leydig cells through paracrine mechanisms together with a stimulatory effect on spermatogenesis. These observations suggest that prepubertal elevation of FSH secretion may be important for increasing Leydig cell steroidogenic capacity and spermatogenic progression.     

Annual cycles of gonadotropins and androgens in the hibernating golden-mantled ground squirrel

Ground squirrels, captured in the field, were housed at ambient temperatures of 23 degrees (photoperiod = 10L:14D) for 13 months. Plasma was sampled at 3 to 4-week intervals and measured for gonadotropin and androgen levels. Testis size was examined monthly by laparotomy. Male ground squirrels showed clear circannual cycles in body mass, testis size, and levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), and dihydrotestosterone (DHT). During summer and fall, FSH, LH and androgen levels were low, testes were undeveloped, and body mass was increasing. Testes began to rapidly enlarge in January and reached maximum size in February. A rise in FSH preceded gonadal growth but LH remained low until near the time of testis mass peak. LH remained elevated during spring while FSH levels fell and testes regressed. Plasma T and DHT levels generally paralleled LH concentrations; DHT levels were approximately one-fifth those of T levels. During winter animals lost weight but were only occasionally found in a slightly hypothermic condition. Females had elevated plasma LH levels (greater than 1 ng/ml) predominantly in the spring but displayed no cycle in plasma FSH levels. A second group of males held at 4 degrees for 8 months (photoperiod = stimulated natural for 47 degrees N) were regularly torpid during a hibernation season that lasted between November and May. Most (15/21) of these males did not show gonadal development by spring; these non-reproductive males had had restricted body mass gains the previous fall. Plasma FSH was low in both reproductive and non-reproductive males during fall and winter but increased in March while animals were still hibernating. FSH levels continued to increase in April only in reproductive males and reached maximal levels after hibernation was spontaneously terminated. LH titers were elevated in individual males in winter during torpor and were greater in reproductive than in non-reproductive males in May. Androgen levels were undetectable in torpid squirrels, elevated in animals sampled during periodic arousals, and elevated in most males within 3 weeks after terminating hibernation.     

Heterodimers and homodimers of inhibin subunits have different paracrine action in the modulation of luteinizing hormone-stimulated androgen biosynthesis.

Inhibin, a gonadal hormone capable of preferential suppression of pituitary follicle-stimulating hormone (FSH) secretion, has recently been purified. The major form of this protein is an alpha beta heterodimer encoded by two separate genes. In contrast to the FSH-suppressing action of the alpha beta heterodimer, the beta beta homodimer stimulates FSH secretion. Luteinizing hormone (LH)-secreting pituitary cells and gonadal androgen-producing cells have long been shown to form a closed-loop feedback axis. Based on recent studies demonstrating the FSH stimulation of inhibin biosynthesis by ovarian granulosa and testis Sertoli cells, an additional closed-loop feedback axis exists between pituitary FSH- and gonadal inhibin-producing cells. Because uncharacterized Sertoli cell factors have been suggested to either stimulate or inhibit androgen production by testicular Leydig cells, we have tested the intragonadal paracrine actions of heterodimers and homodimers of inhibin subunits. In primary cultures of testis cells, the alpha beta heterodimer of inhibin enhances Leydig cell androgen biosynthesis stimulated by LH, whereas the beta beta homodimer suppresses androgen production. Furthermore, similar modulatory actions of inhibin-related proteins were found in cultured ovarian theca-interstitial cells and theca explants treated with LH. In contrast, treatment with the inhibin-related proteins alone did not affect gonadal steroidogenesis. Our data indicate that the inhibin-related gene products synthesized by Sertoli and granulosa cells may form heterodimers or homodimers to serve as intragonadal paracrine signals in the modulation of LH-stimulated androgen biosynthesis and allow cross-communication between the two feedback loops.     

Gonadotropin dynamics in XX males

Hypothalamic-pituitary gonadotropin function was evaluated in two postpubertal XX males. Serum levels of LH and FSH were moderately elevated, and the serum testosterone level was low. A subnormal response by testicular Leydig cells to hCG was observed. The LH and FSH responses to LRH were normal. A significant LH increase was observed after castration. Weekly administration of testosterone enanthate (250 mg) for 10 consecutive weeks caused a reduction (greater than 75%) in gonadotropins and abolishment of the LRH pituitary response. No differences were observed in terms of gonadotropin dynamics compared with other forms of hypergonadotropic hypogonadism. These results indicate that XX males exhibit hypergonadotropic hypogonadism secondary to testicular failure with a preserved androgen responsiveness of the hypothalamic-pituitary unit.     

The influence of luteinizing hormone on the Leydig cells of cryptorchid rat testes

The influence of circulating LH levels on Leydig cells from cryptorchid adult rats was examined after ablation of the pituitary. After 2 weeks cryptorchidism, serum FSH and LH levels rose 2-fold while serum testosterone (T) remained unchanged. Leydig cells were hypertrophied and showed an increased response to in vitro hCG stimulation. Two weeks after hypophysectomy (hypox), serum hormone levels (LH, FSH and T), Leydig cell size, cytoplasm, organelle content and in vitro T production were all dramatically reduced. However, when hypophysectomy was combined with cryptorchidism (hypox/crypt), there was an increase in Leydig cell size, compared to hypophysectomy alone, in the presence of very low levels of serum FSH, LH and T. Compared to the hypophysectomised state, the mitochondria were larger and the cytoplasm contained more smooth endoplasmic reticulum. The response of the hypox/crypt testes to in vitro hCG stimulation, though significantly less than the cryptorchid testes, was significantly greater than the hypox testes. These results demonstrate that the changes observed in the Leydig cell after cryptorchidism can occur in the absence of peripheral pituitary hormones and are consistent with the hypothesis that a local feedback loop exists within the testis.     

Hormonal control of inhibin B in men

Serum inhibin B (IB) and testosterone (T) levels, secreted by Sertoli cells (SC) and Leydig cells (LC), respectively, are parameters of the functional state of these cells. Whereas LC activity and, consequently, T secretion are regulated by serum LH, factors regulating IB secretion by SC are still partially unknown. There is evidence that under certain conditions such as puberty, aging or some spermatogenesis defects, LH levels or Gn-independent factors might contribute to regulating SC activity and IB secretion. Among these factors, GH and IGF-I as well as PRL might have a role. Therefore, in order to explore the possible effects of either LH alone and FSH alone or a combination of both Gn, respectively, on SC function, IB plasma levels and spermatogenesis, we studied their effects in 6 patients with hypogonadotropic hypogonadism (HH), whereas the effects of GH on these parameters were studied in 6 men with panhypopituitarism (PH). Finally, the possible effects of PRL on SC function and spermatogenesis were studied in 6 patients with hyperprolactinemia (HPRL); 24 normal, fertile adults served as control group. In men with HH, neither human chorionic Gn (hCG) nor FSH, respectively, were able to increase serum IB after 3 months of therapy, whereas combined Gn therapy for 24 months increased IB plasma levels and stimulated spermatogenesis in 4 out of 6 hypogonadal men. In panhypopituitaric men, GH added to the classical Gn therapy did not have an additional effect on serum IB levels or spermatogenesis. Surprisingly, in our hyperprolactemic men, IB plasma levels were increased and positively correlated (p<0.01) with serum PRL levels, whereas normalization of the latter by cabergoline treatment caused a decrease of IB levels and a moderate increase in T, LH and FSH. In conclusion, the lack of SC response to FSH therapy alone, as opposed to the response to combined Gn therapy, might indicate that normalization of serum T by hCG is required to obtain IB secretion by SC. Addition of GH did not affect SC function, serum IB levels or spermatogenesis. Finally, our data suggest that PRL plasma levels might have a direct role on IB secretion, suggesting that the hypogonadism found in patients with HPRL might be a consequence of both central (inhibition of Gn secretion) and peripheral (stimulation of IB secretion) origin.