Effects of luteinizing hormone, follicle stimulating hormone, prostaglandin E1 and other hormones on adenosine-3':5'-cyclic monophosphate and testosterone production in rat testis tissues

The site and specificity of LH action on cAMP and testosterone production in rat testis have been investigated. In tissue from hypophysectomized rats LH added in vitro specifically stimulated cAMP production in interstitial tissue, whereas FSH added in vitro specifically stimulated cAMP production in seminiferous tubules. No synergistic effect of FSH and LH was found in either tissue. LH markedly stimulated testosterone production in the interstitial tissue whereas only a very small increase was obtained in the seminiferous tubules using tissue from hypophysectomized rats. These results suggest that seminiferous tubules do not significantly contribute to testis testosterone biosynthesis. No stimulatory effect of testosterone production attributable to FSH could be demonstrated in either tissue or in whole testis tissue when this hormone was added alone or with LH in vitro.LH-stimulated testosterone production in total testis tissue from intact rats, when expressed in terms of mg of interstitial tissue present, was two times higher compared with interstitial tissue obtained by dissection. Addition of seminiferous tubules to the interstitial tissue did not increase the testosterone production. In contrast cAMP production per mg interstitial tissue present was the same in all three preparations.Prostaglandin E₁ caused a small but significant increase in cAMP production in interstitial tissue but had no effect on testosterone biosynthesis. None of the other hormones tested (oestradiol-17β, ACTH, GH, prolactin, testosterone) had any effect on cAMP or testosterone production by rat testes preparations in vitro.     

Localization of 17beta-hydroxysteroid dehydrogenase/17-ketosteroid reductase isoform expression in the developing mouse testis--androstenedione is the major androgen secreted by fetal/neonatal leydig cells

The final step in the biosynthesis of testosterone is reduction of androstenedione by the enzyme 17beta-hydroxysteroid dehydrogenase/ 17-ketosteroid reductase (17betaHSD/17KSR). In this study, we have examined expression of the four known reductive isoforms of 17betaHSD/ 17KSR (types 1, 3, 5, and 7) in the developing mouse testis and have determined changes in the localization of isoform expression and testosterone secretion during development. Using RT-PCR isoforms 1, 3, and 7 were shown to be expressed in the seminiferous tubules of neonatal testis, whereas isoforms 3 and 7 were expressed in the interstitial tissue of the adult testis. The type 7 isoform is unlikely to be involved in androgen synthesis and further study concentrated on the type 3 isoform. Developmentally, isoform type 3 was expressed in the seminiferous tubules up to day 10, showed little or no expression on day 20 and from day 30 was confined to the interstitial tissue. In situ hybridization confirmed that the type 3 isoform was expressed only in the seminiferous tubules in fetal testes and in the interstitial tissue in adult testes. In accordance with the localization of enzyme messenger RNA expression 17-ketosteroid reductase enzyme activity was very low in isolated interstitial tissue from neonatal testes while interstitial tissue from adult testes showed high activity. Seminiferous tubules from both neonatal and adult testes showed high levels of enzyme activity. The major androgen secreted by the interstitial tissue of prepubertal animals was androstenedione up to day 20 while 5alpha-androstanediol and/or testosterone were the major androgens secreted from day 30 onwards. These results show that fetal Leydig cells do not express significant levels of a reductive isoform of 17betaHSD/ 17KSR and that androstenedione is the major androgen secreted by these cells. Production of testosterone up until puberty is dependent upon 17betaHSD/17KSR activity in the seminiferous tubules--a "two cell" requirement for testosterone synthesis. Expression of the 17betaHSD/17KSR type 3 isoform (the main reductive isoform in the testis) declines in the seminiferous tubules before puberty but then reappears in the developing adult Leydig cell population.     

Mechanism of action of the factor(s) secreted by rat seminiferous tubules and inhibiting interstitial cell testosterone production in vitro

Rat seminiferous tubules secrete a factor which inhibits LH-dependent steroidogenesis by interstitial cells. The inhibitory activity was found to be specific for the testes, as cytosols from other rat tissues such as the kidney, heart, spleen, liver and epididymis had no significant effect on testosterone production by interstitial cells. Preliminary characterization by Ultrogel AcA 44 gel chromatography demonstrated that the active substance in SMST has a molecular weight between 40-50 kD. Spent medium from incubation of seminiferous tubules (SMST) caused a dose-dependent inhibition of LH-or cholera toxin-stimulated in vitro testosterone production by rat interstitial cells. However, SMST failed to inhibit forskolin-stimulated steroidogenesis. The effect of SMST was not altered by pre-incubating the cells with the sulfhydryl reagent, N-ethylmaleimide. Considering the proposed mode of action of these modulators of adenylate cyclase activity, the present studies suggest that a high molecular weight testis specific factor acts through the guanine nucleotide-binding stimulatory regulatory protein of the adenylate cyclase complex to inhibit LH-dependent testosterone production by Leydig cells.     

Follicle-stimulating hormone induction of Leydig cell maturation

The effects of FSH on the testes of immature hypophysectomized rats were investigated by comparing functional changes in Leydig cells with changes in their number and morphological appearance. Rats were treated twice daily for 7 days with 0.5 ml saline vehicle, 10 micrograms rat FSH, or 20 ng ovine LH (an equivalent amount of LH known to contaminate the FSH preparation). FSH treatment caused a significant increase in testis weight and stimulated more advanced spermatogenic activity compared to saline or LH treatment. Morphometric analysis of glutaraldehyde perfusion-fixed testes showed no significant increase in Leydig cell number after LH treatment [saline, 4.63 +/- 0.14 million cells; LH, 6.38 +/- 0.55 million mean +/- SE)], but a significant (P less than 0.001) increase after FSH treatment (11.55 +/- 0.79 million). FSH, but not LH or saline, treatment resulted in Leydig cell hypertrophy and ultrastructural features identical to those of adult Leydig cells, these changes being reflected by enhanced hCG- and LHRH agonist-stimulated testosterone production in vitro by whole testes or dispersed interstitial cells. FSH and LH treatment caused minor but significant decreases in LH receptor numbers on dispersed interstitial cells compared to saline treatment. LHRH receptor numbers on interstitial cells were significantly increased only by FSH treatment. It is suggested that since FSH acts only on the seminiferous epithelium, then the hypertrophy, hyperplasia, and functional enhancement of Leydig cells after FSH treatment may be mediated by the secretion of one or more factors from the seminiferous tubules, providing additional evidence to support the view that gonadotropic regulation of testicular function is modulated by local interactions between the seminiferous tubules and the interstitial tissue.     

On the androgen microenvironment of maturing spermatozoa

Adult anesthetized male rats were submitted to in vivo micropuncture of the seminiferous and epididymal tubules and reproductive tract vasculature to obtain fluids for analysis of testosterone, 5 alpha-dihydrotestosterone, and androgen-binding protein (ABP). Androgen and ABP concentrations were determined by RIA. The highest concentrations of testosterone (73.14 +/- 5.12 ng/ml) were in testicular interstitial fluid. A significant downhill concentration gradient exists between testosterone concentrations in testicular interstitial fluid and seminiferous tubule fluid (50.24 +/- 2.26 ng/ml); another significant decrease occurs between seminiferous tubule fluid and rete testis fluid (17.85 +/- 2.11 ng/ml). 5 alpha-Dihydrotestosterone concentrations were highest in intraluminal caput epididymidal fluids (58.73 +/- 6.48 ng/ml) as were ABP concentrations (33.30 +/- 2.40 mu leq/microliter). Intraluminal sperm concentrations were also determined, and from these data, fluid reabsorption by the efferent ducts and epididymal tubules were calculated. Eighty-nine percent of the fluid leaving the testis is reabsorbed between the rete testis and caput epididymidis, and 96% is reabsorbed between rete and cauda. It was calculated that large losses of androgen and ABP also occur from the lumen of the excurrent duct system. These losses may be due to metabolism, diffusion from the lumen, or uptake by cells.     

Endocrinological and histological changes induced by flutamide treatment on the hypothalamo-hypophyseal testicular axis of the adult male rat and their incidences on fertility

Adult male Wistar rats were treated with flutamide from 90 to 105 days of age. In a first experiment, testis and accessory sex organs were weighed. In the same animals, hypothalamic LRH content, pituitary gonadotrophin concentrations, plasma LH, FSH, prolactin and testosterone levels, and testicular gonadotrophin receptors were evaluated. In a second experiment, fertility was tested at the end of the treatment, and histology of the testis was performed. All the results were compared to those obtained in control animals of the same age. Accessory glands of genital tract were significantly lower in flutamide-treated animals (P less than 0.01). Hypothalamic LRH, pituitary and plasma FSH, and prolactin concentrations were unchanged, while pituitary and plasma LH level and especially plasma testosterone concentration were increased (P less than 0.001). Flutamide therefore exerted a strong inhibition on testosterone-dependent organs, and blocked the negative feedback of testosterone on the hypothalamo-pituitary axis, increasing the LH levels. Testis weight, intertubular tissue volume, total number and total volume of Leydig cells/testis, as well as total length and diameter of seminiferous tubules were unchanged in flutamide treated rats. However number of LH receptors/Leydig cell, nuclear area of Sertoli cells, number of FSH receptors/Sertoli cell, number of leptotene spermatocytes and of round spermatids per cross section, and yield of spermatogonial divisions were decreased after treatment. Flutamide treatment also decreased fertility by 48% (P less than 0.05). This lowered fertility is likely the result of impaired spermatogenesis and/or a dysfunction of accessory sex organs.     

Inhibition of testicular and somatic development after treatment of the postnatal rat with the Leydig cell cytotoxic ethylene dimethanesulphonate

The Leydig cell cytotoxic ethylene dimethanesulphonate (EDS) was administered s.c. daily (50 mg/kg) to male rats aged 5-16 days. Apart from loss of weight and that the eyelids unfused earlier, no gross toxicity was observed during treatment. On day 17 testis weights, serum testosterone concentrations, testicular serum testosterone content and 125I-labelled human chorionic gonadotrophin (hCG) binding to testicular homogenates were reduced. Serum LH and FSH concentrations were elevated. The testes did not recover from EDS treatment and at 63 and 120 days were minute (less than 2% of control), and the prostate and seminal vesicles were small although not completely atrophied. In addition, body weights were substantially reduced. Serum and testicular testosterone and 125I-labelled hCG binding to testicular homogenates were reduced but not absent. Serum LH and FSH concentrations were increased. Light microscopy of the adult testes showed that EDS treatment inhibited the development of the seminiferous tubules. Most of the tubules were devoid of germ cells and Sertoli cells were rare. Occasionally tubules also contained spermatogonia and spermatocytes but no signs of spermiogenesis. The testes were composed mainly of closely packed interstitial tissue with no lymphatic space. The interstitial cells resembled Leydig cells and stained for 3 beta-hydroxysteroid dehydrogenase. Histochemically identified Leydig cells were absent during treatment but reappeared when treatment was withdrawn.(ABSTRACT TRUNCATED AT 250 WORDS)     

Suppression of the intratesticular testosterone is associated with quantitative changes in spermatogonial populations in intact adult rats

To investigate the interactions between testosterone and FSH on quantitative aspects of spermatogenesis, intact adult rats were implanted sc with 0.5- to 50-cm long testosterone-filled silastic capsules (TC) for 8 weeks. Serum testosterone levels were suppressed slightly in rats bearing 1-cm TC implants but were elevated 6- to 30-fold when 5 cm or longer TC implants were used. These changes in serum testosterone were associated with a biphasic, dose-dependent response in testicular testosterone concentrations, reaching a minimum of 10-15% of the control values in rats bearing the 1- or 5-cm TC implants, but rebounding to 80% when 50-cm long TC implants were used. Meanwhile, serum FSH was comparably suppressed by 40-70%. Complete spermatogenesis was observed in all experimental animals with the exception of three rats with 1-cm TC implants in which elongated spermatids were absent or reduced in number. Enumeration of various cell types in the basal compartment of whole mounted seminiferous tubules revealed a 20% increase in type A1 spermatogonia in rats with the 1-cm TC implants. On the other hand, a 15-20% reduction in type B spermatogonia and preleptotene spermatocytes was noted in rats receiving 5-cm or longer TC implants. These results demonstrate that complete spermatogenesis can be maintained in intact animals in the presence of 10-15% of the normal testicular testosterone concentration. Failure to maintain normal testis weight, testicular testosterone concentration, or germ cell number at a 30-fold increase in serum testosterone demonstrates that high levels of serum testosterone may not be beneficial for quantitative spermatogenesis. Furthermore, both quantitative and qualitative differences were observed in different phases of spermatogenesis in the presence of comparable serum FSH and testicular testosterone concentrations. These results suggest that factors other than these two hormones are also involved in the regulation of spermatogenesis.     

Histochemical studies on steroid dehydrogenases in the testis of the goat (Capra hircus)

Detailed histochemical localization of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 17 beta-HSD was made in the goat testis using both NAD and NADP coenzymes. The substrates used for 3 beta-HSD were dehydroepiandrosterone (DHA) and pregnenolone whereas 17 beta-HSD was localized with testosterone and oestradiol. In general, the activity of the enzymes varied with the cell type, substrate and coenzyme. In seminiferous tubules, DHA and NAD were the preferred substrate and coenzyme respectively for 3 beta-HSD. In addition, in interstitial tissue, NAD was the preferred coenzyme with DHA whereas no such preference existed with pregnenolone. 17 beta-Hydroxysteroid dehydrogenase showed a similar pattern in the two main compartments of the testis, as testosterone and oestradiol were equally utilized and NAD was the preferred coenzyme in both these compartments. The activities of the enzymes increased during the process of spermiogenesis and were higher in seminiferous tubules than in interstitial tissue, especially in elongated spermatids and spermatozoa.     

The restricted penetration of iodinated rat FSH and LH into the seminiferous tubules of the rat testis.

The penetration of 125I-iodinated rat follicle-stimulating hormone (FSH; labelled by three different techniques) and luteinizing hormone (LH) through the walls of the seminiferous tubules of the rat testis has been studied by injecting the labelled hormone into rats with the efferent ducts of one testis ligated 16 h before the collection of samples of blood and tissues. The concentration of trichloracetic acid-precipitable and immunoprecipitable radioactivity was measured in blood plasma and rete testis fluid and calculated for the total secreted fluid retained in the testis by the ligature, and for the additional tubular fluid from the ligated testis, separated by centrifugation after decapsulating the testis and dispersing the cells. Very little intact hormone penetrated into the testicular fluids, even 16 h after injection of the labelled hormone, and the volume of distribution in the unligated testis of the trichloracetic acid-precipitable radioactivity was only slightly greater than that for markers known to be confined to the extracellular interstitial fluid. This suggests that the labelled hormones do not penetrate readily through the walls of the semiferous tubules into their lumina. Injected inorganic iodiide and trichloracetic acid-soluble 125I-circulating after the injection of iodinated hormones penetrated more rapidly into the tubules, but had not reached equilibrium between the testicular fluids and blood plasma 16 h after injection. Labelled FSH was reasonably stable in the circulation after injection, but 80% of the 125I was not protein-bound 16 h after injection of labelled LH.     

To what extent can spermatogenesis be maintained in the hypophysectomized adult rat testis with exogenously administered testosterone?

In a previous study it was demonstrated that spermatogenesis can be maintained quantitatively with exogenously administered testosterone in adult intact rats that lack LH. The studies described herein were designed to examine the extent to which spermatogenesis can be maintained quantitatively with exogenously administered testosterone in adult rats that lack all pituitary hormones. Adult male rats were hypophysectomized and testosterone was administered at the time of hypophysectomy via sustained release polydimethylsiloxane (PDS) capsules of increasing lengths. We used the PDS capsules to clamp testosterone at defined concentrations within the seminiferous tubule fluid over a 2- to 3-month treatment period. Mean testis weights and advanced spermatid numbers per testis stabilized by 8 weeks of testosterone treatment regardless of testosterone dose. Both testis weight and advanced spermatid number responded to testosterone dose, reaching plateaus of 1.2 g and 170 x 10(6) per testis, respectively. These values were 60% of, and significantly less than, the respective control values. This result was in striking contrast to the results of our previous study of LH-suppressed intact rats, in which exogenously administered testosterone resulted in testis weights and advanced spermatid numbers that plateaued at values not significantly different from those in controls. These different effects of testosterone in intact and hypophysectomized rats occurred despite the fact that the seminiferous tubule fluid testosterone concentrations achieved in the hypophysectomized rats (up to 25 ng/ml) were greater than the minimal testosterone concentration found previously to be required to maintain spermatogenesis quantitatively in LH-suppressed intact rats (13 ng/ml). Taken together, these results demonstrate clearly that intratesticular testosterone doses that are as high as or higher than those that maintain spermatogenesis quantitatively in intact rats lacking LH fail to maintain spermatogenesis quantitatively in rats lacking all pituitary hormones.     

Ethan-1,2-dimethanesulphonate reduces testicular oxytocin content and seminiferous tubule movements in the rat

An oxytocin-like peptide is present in the interstitial cells of the testis, and testicular concentrations of oxytocin have been shown to increase seminiferous tubule movements in vitro. We have used the drug ethan-1,2-dimethanesulphonate (EDS), which depletes the Leydig cell population of the adult rat testis, to examine further the relationships between the Leydig cell, testicular oxytocin and tubular movements. Adult rats were injected i.p. with a single dose of EDS (75 mg/kg) or of vehicle (25% dimethyl sulphoxide). Histological study 3 and 10 days after treatment with EDS showed a reduction in the number of interstitial cells, and levels of oxytocin immunoreactivity were undetectable by radioimmunoassay. Immunostaining revealed very few oxytocin-reactive cells. Spontaneous contractile activity of the seminiferous tubules in vitro was also dramatically reduced, but could be restored by the addition of oxytocin to the medium. Four weeks after EDS treatment, the interstitial cells were similar to those in the control animals both in number and in immunostaining; immunoassayable oxytocin was present and tubular movements were normal. The EDS effect, seen at 3 and 10 days, was not altered by daily treatment with testosterone. However, repopulation of the testes with oxytocin-immunoreactive cells was not seen until 6 weeks in the testosterone-treated animals. We suggest that the Leydig cells are the main source of oxytocin immunoreactivity in the testis and that this oxytocin is involved in modulating seminiferous tubule movements and the resultant sperm transport. The results also imply that testosterone does not play a major role in controlling tubular activity in the mature rat.     

In vivo and in vitro production of inhibin by cryptorchid testes from adult rats

Adult male rats were made bilaterally cryptorchid for 3, 7, 10, and 14 days, and the peripheral serum, testicular vein serum, and interstitial fluid levels of inhibin were measured by RIA, and compared with values obtained in intact animals. The levels of inhibin in peripheral serum, testicular vein, and interstitial fluid were significantly elevated (P less than 0.01) after 3 days of cryptorchidism but declined significantly thereafter. The secretion of inhibin was also studied in vitro using isolated segments of seminiferous tubules from scrotal and abdominal testis in adult rats made unilaterally cryptorchid for 3, 6, and 12 days. The basal inhibin secretion by 3-day cryptorchid seminiferous tubules incubated at 37 C was significantly greater when compared with the scrotal seminiferous tubules at 32 C. If seminiferous tubules from scrotal testes were incubated at 37 C, the secretion of inhibin was greatly increased to similar levels observed by the 3-day abdominal seminiferous tubule cultures. In addition inhibin secretion was significantly higher when tubules from 5-week hypophysectomized rats were cultured at 37 C compared to 32 C. The inhibin secretion by seminiferous tubules from 6-day abdominal testes had returned to scrotal seminiferous tubule levels but then decreased below scrotal seminiferous tubule levels after 12 days of cryptorchidism. Seminiferous tubules from cryptorchid testes remain responsive to FSH stimulation (500 ng/ml) up to 12 days of cryptorchidism. FSH-stimulated inhibin production was increased at 3 and 12 days after cryptorchidism, but similar at 6 days after cryptorchidism, compared to the response of tubules obtained from scrotal testes. Furthermore, using seminiferous tubules from normal adult rats, FSH-stimulated inhibin production was increased by raising the incubation temperature from 32 C to 37 C. These in vivo and in vitro data suggest a dual stimulatory and inhibitory effect of higher temperature on inhibin production with an initial rise in basal and FSH-stimulated inhibin secretion by the cryptorchid testis which seems to be due to a direct effect of temperature on Sertoli cells. The subsequent decline in inhibin secretion could be due to the disruption of the seminiferous epithelium.     

Differential production and regulation of inhibin subunits in rat testicular cell types

The distributions of the alpha-, beta A-, and beta B subunits of inhibin/activin polypeptides were studied in the testis of adult (60-day-old) and immature (12-day-old) rats. Immunohistochemical techniques using antisera selective for each subunit were used to localize the polypeptide chains. In situ hybridization using radiolabeled complementary RNA probes enabled localization of the messenger RNAs (mRNAs) encoding these subunits. In 12-day-old rats, immunostaining and mRNA signal for the alpha-subunit was found in Leydig cell clusters. The beta A- and beta B-subunit staining and beta A-subunit message were detectable in isolated interstitial cells, but the clusters appeared to lack these subunits. Positive immunostaining for each subunit was localized in a Sertoli cell-like pattern in seminiferous tubules, as was a positive mRNA signal for the alpha- and beta B-subunit over regions containing these cell types. Treatment with human CG (hCG) and PMSG greatly enhanced the production of the alpha-subunit in the Leydig cell clusters, but not within the tubules, of these young rats. In adult rats, alpha- and beta B-subunit staining, and alpha-subunit mRNA signal, was observed in the interstitial cells. As in the immature animals, all three subunits were localized in a Sertoli cell-like pattern in the tubules, and a positive mRNA signal for the alpha- and beta B-subunits was found over these cells. There was, however, no obvious change in the expression of the subunits in the testis of adult rats after gonadotropin treatment. The present findings suggest that: 1) in the rat testis, both Sertoli and interstitial cells produce inhibin/activin subunits; 2) the alpha- and beta-subunits are produced by different types of interstitial cells in immature rats; and 3) the production of the alpha-subunit in the Leydig cells of immature rats is regulated by LH-like hormones.     

Re-evaluation of the intratesticular level of testosterone required for quantitative maintenance of spermatogenesis in the rat

The amount of testosterone required for quantitative maintenance of spermatogenesis has been re-evaluated using techniques aimed at minimizing the synthesis of testosterone after removal of the testis. Adult male rats were treated with ethane dimethane-sulphonate (EDS) to destroy the Leydig cells, and were supplemented with 25, 5 or 1 mg testosterone esters by injection every 3 days for 21 days. Serum hormone levels, testicular morphology and spermatogenesis were assessed and the intratesticular levels of testosterone compared in testes either removed under ether anaesthesia and placed in liquid nitrogen (right testis) or removed after collection of blood and placed in ice (left testis). Data for testosterone-supplemented rats were compared with those for control rats and rats treated with EDS alone. All doses of testosterone suppressed LH and FSH levels in serum to within the hypophysectomized range, and Leydig cell regeneration in EDS-treated rats was prevented completely. Treatment of EDS-injected rats with 25 or 5 mg testosterone maintained testicular weight, the number of germ cells and the diameter of seminiferous tubules at stage VII within or above the control range, although there was a significant increase in the number of degenerating pachytene spermatocytes at stage VII with 5 but not 25 mg testosterone; none of these parameters was maintained at control levels by a dose of 1 mg testosterone. Levels of testosterone in testosterone-supplemented rats differed little between testes collected in ice and liquid nitrogen, but in controls and rats treated with EDS alone, testosterone levels were overestimated by 75 and 27% respectively when comparing testes collected in ice with those collected in liquid nitrogen.(ABSTRACT TRUNCATED AT 250 WORDS)     

LH- and FSH-stimulating of adenylate cyclase in seminiferous tubules from young rats: functional FSH and LH receptors unmasked by homogenization.

LH- and FSH-sensitive adenylate cyclase activity was present in homogenates of whole testis tissue as well as in microdissected seminiferous tubules derived from young rats. In homogenates of seminiferous tubules a single adenylate cyclase appears to interact with both LH and FSH through separate hormone-specific receptors. Disruption of testis tissue by homogenization exposes functional FSH and LH receptors which are inaccessible to the hormones in intact cell preparations. These results indicate that in certain seminiferous tubule cell types only a fraction of the total functional receptors present is accessible to the cell surface for interaction with hormone.     

Cytological reactions in the pars intermedia of the hypophysis of the salpa, Boops salpa L. (a marine teleost fish, Sparidse) to variations in salinity]

Two fractions, one of them possessing enhanced follicle-stimulating hormone (FSH) activity and the other luteinizing-hormone (LH) activity when bioassayed with rats, were prepared from chicken adenohypophyses. The effects of these fractions on the testis of the newly hatched cockerel were examined. Injection of either the FSH- or the LH-like fraction increased the weight of testes, although the former fraction was more potent. The FSH-like fraction caused hypertrophy of the Sertoli cells and a proliferation of spermatogonia, consequently producing a widening in seminiferous tubule diameter. It induced slight development of interstitial cells. The LH-like fraction stimulated hypertrophy and proliferation of the interstitial cells, but stimulated only slight division of the spermatogonia. It is concluded that the chicken adenohypophysis contains two kinds of gonadotropins which are homologous to mammalian FSH and LH both in their action on the testis and in their behavior chromatographically. However, it is still not known whether these two gonadotropins are secreted from the adenohypophysis as a complex or separate hormones.     

Maintenance of advanced spermatogenic cells in the adult rat testis: quantitative relationship to testosterone concentration within the testis

The studies described herein were designed to examine whether there is a threshold concentration of testosterone (T) within the seminiferous tubules that is required to maintain spermatogenesis in the rat, or alternatively, whether there is a dose-response relationship between the intratesticular T concentration and the maintenance of spermatogenesis. T was administered to intact adult male rats via sustained release polydimethylsiloxane capsules in order to experimentally clamp T at well defined concentrations within the seminiferous tubules. Implantation of T-filled capsules of increasing sizes resulted in linear increases in T concentrations in serum, interstitial fluid, and seminiferous tubule fluid (STF). We examined the effect of step decreases in intratesticular T concentration on the numbers of advanced spermatogenic cells maintained by the testis over a 2-month period. Quantitatively complete spermatogenesis was maintained despite an 80% reduction in the STF T concentration (to approximately 13 ng/ml) from control values. The ability of the testis to maintain complete spermatogenesis was extremely sensitive to further decreases in STF T concentration. Thus, reduction of the STF T concentration from approximately 13 to 9 ng/ml resulted in a reduction in the number of advanced spermatids that were maintained in the testis by approximately 100 x 10(6). Reduction of the STF T concentration to approximately 4 ng/ml resulted in a further reduction in the number of advanced spermatids per testis by 100 x 10(6). Taken together, these data support the contention that there is far more T present within the seminiferous tubules of intact rat testes than is required to maintain quantitatively normal spermatogenesis and reveal for the first time that there is a dose-response relationship between the STF T concentration and the quantitative maintenance of advanced spermatogenic cells in the rat testis.     

Prepubertal treatment of rats with clomiphene citrate affects postpubertal testicular development

A previous study showed that clomiphene citrate (clomiphene) reduced serum and pituitary gonadotropins and impaired testis growth and steroidogenesis in 10-day-old rats treated for up to two weeks. The present study was conducted to assess the effect of prepubertal clomiphene treatment on postpubertal pituitary-testicular function. Rats were implanted with pellets that released 0, 0.05, 0.5 or 5.0 mg clomiphene.kg-1.day-1 between 10-31 days of age and were killed at 90 days of age. Testis and prostate weights in treated rats were reduced (P less than 0.05), whereas serum LH, FSH and testosterone, and pituitary gonadotropin and GnRH receptor concentrations had recovered to levels observed in control rats. Testicular FSH receptor concentrations were not altered; however, FSH receptor content was decreased (P less than 0.05) in clomiphene-treated rats proportional to the reduction in testicular weight. In contrast, testicular LH and GnRH receptor concentrations were increased (P less than 0.05) in treated animals, resulting in similar receptor contents. Daily sperm production per gram of parenchyma was unaffected, while daily sperm production per testis was decreased in treated rats (P less than 0.05). These data show early postnatal treatment with clomiphene does not permanently impair pituitary function. Despite reduced testicular mass, normal serum testosterone concentrations and testis LH receptor content of treated rats suggest recovered Leydig cell function. The decreased content of testicular FSH receptors and reduced sperm production suggest seminiferous tubule function was compromised in the adult rat.     

Effects of flutamide or of supplementation with testosterone in prepubertal male rats prenatally treated with busulfan

Male rats treated prenatally with busulfan in order to render them aspermatogenic were treated between 23 and 38 days of age either with testosterone, or flutamide. In such aspermatogenic rats, testosterone supplementation stimulated the growth of accessory sex organs, markedly decreased the secretion of gonadotrophins (by 61% for LH and 83% for FSH), decreased testicular weight (-60%) as well as all parameters relating to testicular histology. Flutamide treatment decreased the weight of accessory sex organs, stimulated the secretion of both LH (+200%) and FSH (+63%) by inhibition of the negative feedback of testosterone; endogenous testosterone secretion was increased by 363%. Testicular weight was increased by 44% and the total volume and the cytoplasmic and nuclear area of Leydig cells were increased by 254 and 28%, respectively, but their number per testis was unchanged. The number of Sertoli cells per testis was increased by 49%, but their nuclear area was not modified. In aspermatogenic prepubertal rats, the large increase in plasma FSH demonstrated that FSH release was partly under the control of inhibin, secreted by Sertoli cells when germinal cells were present. Nevertheless, FSH levels after testosterone (inhibition) or flutamide treatment (stimulation) clearly demonstrated that, in the growing rat, FSH secretion is also partly dependent on the negative feedback of testosterone. In the absence of germ cells, FSH was able to re-initiate Sertoli cells mitoses, but not their functional activity. LH secretion was solely controlled by the negative feedback of androgens and, even in the absence of germinal cells, Leydig cells were able to respond to LH stimulation by an increase in testosterone secretion.