Developmental changes in the hormonal regulation of rat testis Sertoli cell adenylyl cyclase

The stimulatory effects of FSH on Sertoli cell functions such as cAMP accumulation, protein kinase activation, and RNA and protein synthesis wane during testis maturation. However, FSH receptors increase with age and addition of cAMP stimulates these biochemical events in Sertoli cells from animals of any age. In order to determine if this loss of responsiveness to FSH was due to an inability to stimulate adenylyl cyclase, the hormonal responsiveness of this enzyme was investigated as a function of testicular development. In agreement with intact cell studies, adenylyl cyclase activity was found to be stimulated by FSH 2- to 3-fold in homogenates of testes from immature (5-20 days of age) Sertoli cell-enriched rats, while no stimulation of the enzyme by FSH was observed in similar homogenates from Sertoli cell-enriched animals 20 days of age or older. The possibility of a decrease in enzyme sensitivity to the gonadotropin as a function of maturation ws ruled out by dose-response studies. Catalytic activity of the enzyme was retained with increasing animal age as evidenced by the ability of fluoride (10 mM) to stimulate basal activity 4-fold. Hormonal responsiveness of the Sertoli cell adenylyl cyclase of mature animals could be restored, however, either by addition of the nonmetabolizable guanosine 5'-triphosphate analog, 5'-guanylyl-imidodiphosphate to homogenates or by preparation of membrane particles. We found that 5'-guanylyl-imidodiphosphate selectively potentiated FSH effects on cyclase in testicular homogenates from mature animals while having no effect on the relative degree of hormone stimulation in homogenates from immature animals, and that in contrast to homogenates, testicular membrane preparations retain their FSH responsiveness upon animal maturation.     

Follicle-stimulating hormone activation of glycogen phosphorylase in the Sertoli cell-enriched rat testis

The potential role of glycogen phosphorylase in providing energy for the Sertoli cell-enriched testis has been investigated. This enzyme is detectable in testes from rats 6-54 days of age. Glycogen phosphorylase in isolated Sertoli cell-enriched testes is specifically stimulated by FSH. Maximal activation (2-fold) is obtained within 10 min after adding 0.5 micrograms FSH/ml to isolated immature testes (16 days old). There is only a 1.1-fold activation by FSH in testes from mature (34 days old) animals. The sensitivity to the gonadotropin can be restored by adding 1-methyl-3-isobutylxanthine, a phosphodiesterase inhibitor, with the FSH. Phosphorylase can be activated by effectors that mimic the actions of the two proposed mediators of FSH action, cAMP and Ca+2. Phosphorylase from testis of either age is maximally activated by an analog of cAMP, 8-bromo-cAMP. While phosphorylase is rapidly activated 1.4-fold by incubating isolated testis for 2 min with A23187, a Ca+2 ionophore, the age, time, and dose dependence of FSH activation are consistent with conversion mediated by cAMP. Phosphorylase was localized in cultured Sertoli cells by indirect immunofluorescence microscopy. Affinity-purified antiphosphorylase decorated cytoskeletal structures that resemble stress fibers, suggesting that phosphorylase may function in Sertoli cells to provide energy for cytoskeletal motility.     

Follicle-stimulating hormone regulates in vivo testicular phosphodiesterase

The effect of FSH on testicular phosphodiesterase was studied in immature rats in order to verify that the regulation of response to hormone in the gonad involves an increased cyclic AMP catabolism. Hydrolysis of cyclic AMP and cyclic GMP was measured in the homogenates of seminiferous tubules and interstitium of control animals and animals injected i.p. with 50 micrograms ovine FSH twice, 24 h and 12 h before necroscopy. After hormonal treatment, cyclic AMP phosphodiesterase activity in the seminiferous tubules was markedly increased whether results were expressed per testis or per mg protein, while cyclic GMP phosphodiesterase present in the same compartment was apparently unaffected. In the interstitium, cyclic nucleotide hydrolysis was usually decreased after FSH injection. The stimulation of phosphodiesterase, a slow process reaching maximal stimulation after 12 h, was dependent on the dose of FSH injected. In addition, DEAE-cellulose chromatography of cytosol prepared from control and treated seminiferous tubules confirmed that stimulation was restricted to a cyclic AMP hydrolysing enzyme while the activity of the cyclic GMP hydrolysing form was not modified. Thus it is demonstrated that testicular phosphodiesterase is under FSH control. It is proposed that this in vivo regulation is a relevant phenomenon in the modulation of Sertoli cell function and contributes to the refractoriness that follows gonadotropin treatment.     

Synergistic effects of follicle-stimulating hormone and testosterone on the maintenance of spermiogenesis in hypophysectomized rats: relationship with the androgen-binding protein status

The present study examined the relationship between the functional status of Sertoli cells and the maintenance and restoration of spermatogenesis in immature hypophysectomized (HPX) rats given various doses of exogenous testosterone with or without daily injections of FSH for 90 days. Subcutaneous implantation of a 2- to 10-cm testosterone capsule (TC) increased serum testosterone levels of HPX rats 2-10 times above the normal control levels, but did not significantly increase the testicular testosterone level. Daily injections of FSH significantly increased the accumulation of testosterone in testes of TC-implanted HPX rats. Maintenance of early spermiogenesis was observed in all TC-implanted animals. Although elongated spermatids were present, step 18-19 spermatids at the luminal edge of stages VII-VIII epithelium were only observed in rats bearing 10-cm TC implants. Daily injection of FSH resulted in the completion of spermiogenesis in all TC-implanted animals, and the number of step 18-19 spermatids was dependent on the length of TC implants used. These results demonstrate the importance of the synergism of FSH and testosterone in the final steps of spermiogenesis. The androgen-binding protein (ABP) content per testis of the HPX rats was stimulated by TC implants. However, a significant increase in epididymal ABP was only noted in rats bearing 10-cm TC implants. Injection of FSH resulted in a significant increase in the testicular ABP content in rats bearing 2- or 5-cm TC, but not in those with 10-cm TC implants. In addition, the epididymal ABP content was significantly stimulated by FSH in all TC-implanted animals. The ABP status in the testis and its transport toward the epididymis are closely related to the extent of maintenance of spermiogenesis. It is speculated that the production of ABP by Sertoli cells and the biochemical properties of ABP molecules may have some role in the control of the final steps of spermiogenesis.     

Measurement of a follicle-stimulating hormone-responsive protein of Sertoli cell origin using an enzyme-linked immunoblot assay

Many proteins secreted by Sertoli cell-enriched cultures are maximally stimulated by a combination of FSH and testosterone. Since very few are stimulated primarily by FSH, we thought it pertinent to identify such proteins. Sertoli cell-enriched cultures were prepared from testes of 20-day-old rats and grown in serum-free medium containing insulin, transferrin, and epidermal growth factor and in such medium supplemented with FSH, testosterone, or FSH plus testosterone. Media were fractionated using HPLC, and proteins were identified by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. A protein designated CMB-2, with an apparent mol wt of 22,000, was shown to increase in response to FSH. Antiserum was raised using denatured protein eluted from SDS-polyacrylamide gels as the antigen, and a specific immunoassay using a combination of SDS-polyacrylamide gel electrophoresis and Western blotting was developed. The production of CMB-2 by primary Sertoli cell-enriched cultures was found to increase in a dose-dependent manner in response to FSH (30-1000 ng/ml); secretion was not significantly affected by testosterone (2 X 10(-13) M). An investigation of the tissue distribution of CMB-2 showed that the puberty, CMB-2 is secreted into the rete testis and accumulates in the epididymis in high concentration. We conclude that CMB-2 will be a useful marker to study the action of FSH on the rat testis.     

Effects of follicle-stimulating hormone on cultures of Sertoli cell preparations.

Sertoli cell-enriched preparations were obtained by sequential enzyme treatment of testes of 18-20 day old rats, and were maintained in culture in a chemically defined medium. The addition of highly purified follicle-stimulating hormone (FSH) to cells immediately after preparation, or after 48 h in culture, elicited an increase in the level of cyclic adenosine 3',5'-monophosphate (cAMP) when incubated in the presence of 3-isobutyl-1-methylxanthine (MIX). Luteinizing hormone (LH) had no effect on the cAMP levels. The cells cultured in the presence of FSH or dibutyryl cAMP for 48 h incorporated more [3H]leucine into trichloroacetic acid (TCA)-insoluble material than did cells cultured in the basal medium. Cycloheximide abolished the amino acid incorporation into protein precipitated by TCA. The data demonstrate that the Sertoli cell is a target cell for FSH action, and indicate that added dibutyryl cAMP can duplicate the enhancement of amino acid incorporation into protein elicited by FSH.     

Hormonal control of spermatogenesis.

FSH and testosterone (T) secretion are essential for the successful completion of spermatogenesis. Because there are no receptors for FSH or testosterone on germ cells, there are intermediate steps in this action, the nature of which are unknown. However, as the Sertoli cell contains receptors for both FSH and T, it is likely that these hormones exert their influence on germ cells by modulating Sertoli cell function. Both FSH and T exert synergistic actions on germ cells, but T has a specific action on the later stages of spermatid maturation. FSH, by its ability to stimulate Sertoli cell mitosis during testicular development, can influence the spermatogenic capacity of the adult testis.     

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.     

Influence of germ cells upon Sertoli cells during continuous low-dose rate gamma-irradiation of adult rats

The effects of continuous gamma-irradiation of adult rats at two low-dose rates (7 cGy and 12 cGy/day; up to a total dose of 9.1 Gy and 10.69 Gy 60Co gamma-ray, respectively) were investigated. Over a period of 3-131 days of irradiation, groups of experimental and control animals were killed. Body weight, testis, epididymis, prostate and seminal vesicle weights, the number of germ cells and Sertoli cells, tubular ultrastructure, epididymal and testicular levels of biologically active androgen-binding protein (ABP), and the plasma concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were monitored. Irradiation had no effect on body weight, whereas testicular and epididymal weight began to decrease following 35 and 50 days of irradiation at 7 and 12 cGy, respectively. At 7 cGy the target cells of the gamma-rays were essentially A spermatogonia, whereas at 12 cGy A spermatogonia and preleptotene spermatocytes were primarily affected. This resulted in a progressive and sequential dose-related reduction in the number of pachytene spermatocytes, round spermatids and late spermatids (LS). Under both irradiation procedures the Sertoli cell number remained unchanged whereas partial (7 cGy) or no change (12 cGy) was seen at the Leydig cell level. Whatever the irradiation protocol, from the time LS numbers decreased, vacuolisation of the Sertoli cell cytoplasm progressively occurred, followed by thickening and folding of the peritubular tissue. Moreover, in parallel to the drop in the number of these germ cell types, ABP production fell whereas FSH levels rose. A highly significant positive correlation was found between LS numbers and these Sertoli cell parameters. This study supports our previous concept of a control of certain important aspects of Sertoli cell function by late spermatids in the adult rat.     

Effect of cryptorchidism in the ram: changes in the concentrations of testosterone and estradiol and receptors for LH and FSH in the testis, and its histology

Cryptorchidism was induced in 5 pre-pubertal lambs and 7 adult rams, 5 months after surgery, testicular weight and membrane protein content were 4-fold lower than in the control. The total number of Leydig cells per testis was markedly decreased but their size was not changed. In contrast, the total number of Sertoli cells per testis was not affected but their nuclear size was smaller. Induced cryptorchidism had no effect on the length of seminiferous tubules; blood vessel volume was reduced; and the production of germ cells was completely disrupted. The number of LH receptors estimated per Leydig cell was not changed in pre-pubertal lambs but decreased 4-fold in adult rams. The number of FSH receptors calculated per Sertoli cell was reduced by 95% in both pre-pubertal and adult animals. No effect on the binding affinities of LH (Ka = 1 X 10(10) M-1) and FSH (Ka = 4.5 X 10(9) M-1) to their testicular receptors was observed. Although testicular concentrations of testosterone and estradiol-17 beta were increased, the total content of testosterone within the testis was increased only in pre-pubertal lambs. The estimated ratio of testosterone per Leydig cell was higher in cryptorchid animals than in controls, suggesting that, despite their reduction in number and the decrease of LH receptors, the Leydig cells of cryptorchid rams have an enhanced steroidogenic capacity. This study also confirms the important dysfunction of the Sertoli cells in cryptorchid rams.     

Regulation of protein kinase inhibitor by follicle-stimulating hormone in Sertoli cells in vitro

The heat-stable protein inhibitor of cAMP-dependent protein kinase is specifically regulated by hormones in cultures of rat Sertoli cells maintained under completely defined conditions. Hormones that are known to elevate Sertoli cell cAMP concentrations, namely FSH and isoproterenol, produce a 4- to 5-fold increase in the specific activity of protein kinase inhibitor, whereas testosterone and LH have no effect. The stimulatory effects of FSH or isoproterenol on protein kinase inhibitor are completely mimicked by dibutyryl cAMP. The ability of FSH to stimulate protein kinase inhibitor is dependent upon the age of the animals used as a source for the Sertoli cells. FSH stimulates protein kinase inhibitor activity in cells from 9- and 16-day-old animals, but not in cells from 32-day-old animals. On the other hand, isoproterenol or dibutyryl cAMP will stimulate protein kinase inhibitor in cells from both young and old animals. FSH can stimulate protein kinase inhibitor activity in older cells only in the added presence of the phosphodiesterase inhibitor, 1-methyl-3-isobutyl xanthine. Using specific antibodies to protein kinase inhibitor, we have shown that this protein is regulated by hormones via preferential stimulation of de novo synthesis of the inhibitor. (Endocrinology 108: 427, 1981)     

Concerning the hormonal regulation of androgen binding protein in rat testis.

Androgen binding protein (ABP) was measured in testis following an acute injection of FSH to ascertain whether this protein could serve as an endpoint marker of FSH action in the Sertoli cell. A single intravenous injection of oFSH (200 mug NIH-S-10) resulted in a rapid stimulation of ABP activity in testis of either 10- or 14-day old rats. Maximal increases were noted by 2 h in both cases (undetectable to 0.9, and 0.3 to 1.5 pmol ABP/mg protein in 10- and 14-day old rats, respectively) and by 4h ABP activity had again returned to control values. Although FSH failed to acutely stimulate ABP in 60-day-old rats, hypophysectomy of these animals resulted in a return of sensitivity within 3 days. The acute stimulation of ABP by FSH was also shown to be dependent upon both the route of hormone administration and the dose of FSH. Finally, the rapid decrease in ABP activity following FSH could be prevented by injection of a second dose of hormone. ABP activity was also increased by intratesticular injection of an analog of cyclic AMP, 8-bromo cAMP. This response was also dose-dependent and the time course of response was indistinguishable from that resulting following FSH. A test of nucleotide specificity revealed that any adenine nucleotide would stimulate ABP, whereas guanine compounds were ineffective. Peptide hormone specificity was next examined. It was determined that 200 mug of a variety of crude pituitary hormone preparations (LH, GH, PRL and ACTH) were stimulatory. However, when highly purified hormones were utilized, hFSH (LER-1577) did not increase testicular ABP whereas 1 mug of oLH (Papkoff) was maximally stimulatory. Further studies revealed that all compounds (including peptide hormones and nucleotides) which resulted in acute elevation of ABP activity also increased the intratesticular concentration of testosterone. Moreover, a single ip injection of testosterone produced a steroid specific stimulation of ABP which reached maximal levels within 1 h. These findings suggest that the acute regulation of ABP activity in the testis may be a result of the intratesticular concentration of testosterone and not due to a direct effect of FSH as had been previously hypothesized.     

Evidence from Sertoli cell-depleted rats indicates that spermatid number in adults depends on numbers of Sertoli cells produced during perinatal development

To probe the relationship between the size of the Sertoli cell population, established during perinatal development, and production of germ cells in the adult testis, a Sertoli cell-depleted rat model was developed. This was accomplished by delivering an antimitotic drug, cytosine arabinoside (araC), directly to the testis of newborn pups. Initial studies of these araC-treated neonates indicated that 1) the drug is cleared rapidly from the testis; 2) it substantially reduces the level of Sertoli cell proliferation; 3) Sertoli cell division ceases at a normal time in spite of the previous drug treatment; and 4) araC itself has no residual effect on germ cell proliferation, which begins several days after the injection. Pups given araC were allowed to reach maturity, and their testes were perfuse-fixed for light microscopic morphometry. When the numbers of Sertoli cells in adult rats given araC as were compared with those in normal littermates, a 54% decrease in the size of the Sertoli cell population was detected in treated rats, now referred to as Sertoli cell-depleted. Moreover, when round spermatids were quantified and compared in normal and Sertoli cell-depleted adults, testes of the latter were found to contain 55% fewer round spermatids. Since, in the araC-treated group, the decrease in Sertoli cell population size was paralleled by a reduction in spermatid production of equal magnitude, the number of round spermatids per Sertoli cell was essentially identical in normal and Sertoli cell-depleted animals. Measurements of serum androgen-binding protein (ABP) and FSH in both groups indicated that the circulating level of ABP in Sertoli cell-depleted rats was approximately half, and the concentration of FSH approximately twice, that in normal animals. Thus, even though FSH is elevated in Sertoli cell-depleted rats, the production of ABP per Sertoli cell is unchanged. In addition, collective volume of Leydig cells and ventral prostate weights were normal in the Sertoli cell-depleted group, suggesting that Leydig cell function in these rats is normal. In summary, a Sertoli cell-depleted rat model has been produced by interfering specifically with Sertoli cell proliferation early in postnatal life, before onset of germ cell division. Moreover, our findings with this model indicate that production of normal numbers of germ cells in adults depends, at least in part, on the size of the Sertoli cell population. Thus, our observations identify the perinatal period, when the Sertoli cell population is established, as critical for development of quantitatively normal spermatogenesis in the adult.     

Prolonged exposure to androgens suppresses follicle-stimulating hormone-induced aromatase activity in rat Sertoli cell cultures

We studied the effects of androgens on basal and FSH-stimulated aromatase activity in Sertoli cell-enriched monolayers. Daily exposure to androgens from the first day of culture results in a time- and dose-dependent decrease in inducible aromatase activity. The inhibition is observed whether FSH, L-isoproterenol or (Bu)2cAMP is used as inducer of the aromatase activity. Basal activity is not affected by preincubation with androgens and the inhibitory effect is not observed after short-term exposure (24 h) to these hormones. The ability of different androgens to decrease inducible aromatase activity does not depend on their ability to serve as a substrate for the aromatase but parallels their ability to stimulate the production of androgen-binding protein. Moreover, the effect of testosterone is neutralized by the antiandrogen cyproterone acetate, suggesting that it is mediated by the androgen receptor. These data suggest that testicular androgens may be responsible for the decrease in FSH-inducible aromatase activity observed in intact rats between days 10 and 30 of life. Similarly, the removal of these androgens during the preparation of Sertoli cell cultures may explain the spontaneous increase in inducible aromatase activity observed when these cultures are maintained in the absence of androgens.     

Sertoli cell origin of testicular androgen-binding protein (ABP)

In this report it is suggested that the specific androgen-binding protein (ABP), previously shown to originate in the testis of rat and other species, is produced by the Sertoli cells. This suggestion is based upon the following experimental findings: 1) ABP was found in high concentrations in testicular efferent duct fluid but only in trace amounts in inter-tubular lymph. 2) ABP could be recovered from crude preparations of testis tubules, but not from Leydig cells from the same testes. 3) Testes whose germinal epithelium had been severely damaged by gamma irradiation showed no decrease in ABP content. The transport of ABP to epididymis was also preserved as judged from the levels of ABP in caput epididymis. 4) Testes that were completely devoid of germ cells following prenatal gamma irradiation showed high levels of ABP. These high levels approached zero following hypophysectomy, but could be restored by FSH administration to the hypophysectomized animals. ABP has been well characterized and now provides a valuable experimental tool as an indicator of Sertoli cell function.     

Basic fibroblast growth factor (bFGF) gene expression and protein production during pubertal development of the seminiferous tubule: follicle-stimulating hormone-induced Sertoli cell bFGF expression.

The potential role of basic fibroblast growth factor (bFGF) as a mediator of cell-cell interactions in the growth and development of the testis was examined. Nuclease protection analysis was used to evaluate bFGF gene expression in the testis and other male reproductive tract tissues. bFGF expression was evident in seminal vesicle, prostate, epididymis, and, at low levels, testis of 20-day-old rats. The developmental expression of bFGF in whole testis and isolated somatic cells types was determined. Mesenchymal-derived peritubular cells and epithelial-like Sertoli cells were isolated from prepubertal, midpubertal, and late pubertal rat testes. In whole testis, bFGF expression is predominant early in prepubertal testicular development and decreases with sexual maturity. Both freshly isolated peritubular and Sertoli cells express bFGF at relatively constant levels during pubertal development, with a slight suppression at the late pubertal stages. Freshly isolated mature Leydig cells also expressed low levels of bFGF. Cultured Sertoli and peritubular cells produced bFGF-like proteins, including 18- and 24-kilodalton forms. Interestingly, FSH increased Sertoli cell bFGF gene expression and protein production. Previously, FSH and bFGF have been shown to stimulate immature Sertoli cell growth. The results of the current study suggest that the ability of FSH to regulate testis and Sertoli cell proliferation may in part be indirectly mediated through the local production and action of bFGF. bFGF has also previously been shown to localize in developing germinal cells. Therefore, FSH-induced Sertoli cell bFGF expression may mediate Sertoli-germinal cell interactions involved in the control of the spermatogenic process. Observations demonstrate the presence of bFGF at a time coinciding with active growth of the somatic cell populations of the seminiferous tubule. Potential roles for bFGF in the seminiferous tubule to consider include angiogenesis of the tubule, prepubertal Sertoli cell proliferation, and mediating Sertoli-germinal cell interactions.     

Hypoandrogenism and abnormal regulation of gonadotropin secretion in rats fed a low protein diet.

The function of the hypothalamic-pituitary-testicular axis was evaluated in rats fed a low protein diet for 4 weeks beginning at 21 days of age. Compared to control, the low protein group had decreased seminal vesicle and prostate weights as well as decreased testicular testosterone output in vitro, although serum testosterone was not different. The low protein group showed no consistent alterations in serum LH (basal, post-LHRH, and postcastration) compared to control although serum FSH (basal and post-LHRH) was lower in the low protein group. Despite this lower basal FSH, the low protein group had supranormal serum FSH after castration. Seminiferous tubule diameter and testicular histology were normal in the low protein group although testicular androgen-binding protein was absent. Testicular androgen-binding protein was also undetectable in a modestly food-restricted control group which had normal testicular size, testicular histology, androgen output, and serum FSH. This finding suggests that loss of testicular androgen-binding protein may be a sensitive sign of undernutrition. We conclude that rats fed a low protein diet have hypoandrogenism, normal testicular histology, and supranormal FSH after castration despite subnormal basal FSH. The latter combination suggests overproduction of an FSH inhibitor of testicular origin.     

Impaired sertoli cell function in experimental cryptorchidism in the rat

The production of testicular androgen-binding protein (ABP), as a measure of Sertoli cell function, was studied after unilateral or bilateral experimental cryptorchidism in adult rats. Two or 4 weeks after the testis had been translocated to the abdomen, no major changes were found in the concentration of ABP per mg protein, although there was a marked and progressive decrease in ABP content per testis. However, the rate of ABP production was greatly decreased, as measured by the accumulation of ABP during 16-h ligation of the efferent ducts or by the production of ABP by testis mince in an in vitro system. This indicates that the Sertoli cell function is severely impaired by the intra-abdominal position.     

Testicular recrudescence in the golden hamster (Mesocricetus auratus): a possible model of sexual maturation

The ability of cultured hamster Sertoli cells to respond to FSH was studied during sexual maturation and photoperiodically induced regression and recrudescence. Serum gonadotropins were also measured in donor animals to determine if changes in LH and FSH were associated with changes in Sertoli cell response (accumulation of intracellular cAMP). There was a maturational peak of gonadotropins and an age-related decline in the ability of Sertoli cells to respond to FSH; the decline began before the peak of either gonadotropin. During regression, LH and FSH levels fell to or below prepubertal values, and the Sertoli cell response to FSH returned after the testicular weight had fallen from 2000 to 1400 mg/testis. Maximal Sertoli cell response to FSH occurred at approximately 800 mg/testis. During recrudescence, the low serum gonadotropin levels rose, reached a peak, and declined again to adult levels. The peak of gonadotropins during recrudescence was larger than that observed during maturation, and the loss of Sertoli cell response to FSH during recrudescence was delayed until after the gonadotropin peak. These data suggest that testicular recrudescence in the hamster is a dynamic process that approximates sexual maturation, but may be regulated in a somewhat different manner.     

Hormonal regulation of protein synthesis, secretion, and phosphorylation in cultured rat Sertoli cells.

The accumulation of two polypeptides, SCm1 and SCm2, in the medium of Sertoli cell cultures is enhanced by follicle-stimulating hormone (FSH) but is unaffected by either the cAMP analog, N6,O2'-dibutyrl cAMP or luteinizing hormone. The assigned molecular weights of SCm1 and SCm2 differ from those of androgen-binding protein subunits or any other previously identified Sertoli cell secretory product. Incubation of Sertoli cell cultures with either FSH or N6,O2'-dibutyryl cAMP also stimulates the incorporation of [35S]methionine into two intracellular polypeptides, SCc1 and SCc2. In addition, the phosphorylation of three intracellular polypeptides, SCc3, SCc4, and SCc5, is intensified when Sertoli cell cultures are treated with either FSH or N6,O2'-dibutyryl cAMP. Based on these results and on previous work, we conclude that (i) SCm1 and SCm2 may, like androgen-binding protein, be secreted by Sertoli cells and function extracellularly while SCc1 and SCc2 are involved in FSH-dependent intracellular activity; (ii) SCc3, SCc4, and SCc5 are possible substrates for FSH-stimulated, cAMP-dependent protein kinase activity; and (iii) SCc5 is an isoelectric variant of vimentin-type intermediate filament protein presumably involved in FSH- and N6,O2'-dibutyryl cAMP-induced Sertoli cell shape changes.