Androgen stimulation of Sertoli cell function is enhanced by peritubular cells

Rapid androgen actions on calcium signaling in rat sertoli cells and two human prostatic cell lines: similar biphasic responses between 1 picomolar and 100 nanomolar concentrations

Androgen-induced calcium fluxes and gap junctional intercellular communication (GJIC) were studied in three different cell types. A transient (2-3 min duration) increase in intracellular calcium levels was observed within 20-30 sec of androgen addition, which was followed by a plateau phase with steroid concentrations higher than 1 nM. The kinetics of the calcium responses were similar in immature rat Sertoli cells, which contain normal nuclear receptors; the human prostatic tumor cell line, LNCaP, which contains a mutated nuclear receptor; and the human prostatic cell line, PC3, which does not contain a nuclear receptor. The human A431 tumor cell line did not respond to androgens. Concentrations of testosterone and the synthetic androgen, R1881, between 1-1000 pM induced transient calcium increases with ED(50) values near 1 pM and 1 nM, whereas dihydrotestosterone (DHT) was not active at these concentrations. At concentrations higher than 1 nM, testosterone, R1881, and DHT were equipotent in stimulating an increase in calcium that lasted for more than 10 min, with ED(50) values between 5 and 20 nM. Testosterone covalently bound to albumin was also active, whereas 11 related androstane compounds as well as progesterone and estradiol-17beta were inactive at 1000 nM. The calcium response induced by the three androgens (10 nM) was abolished in all cell types by hydroxyflutamide (1000 nM) and finasteride (1000 nM), but not by cyproterone acetate (1000 nM). The calcium response was also abolished in the absence of extracellular calcium and strongly inhibited by the presence of verapamil. Exposure of the responsive cells to brief (150-sec) pulses of androgens generated calcium responses that were similar to those after continuous exposure. After exposure of Sertoli cells for only 30 sec to 100 nM testosterone, the calcium response lasted for at least 50 min. Although nuclear binding of androgens could be demonstrated, there was no evidence for tight binding to the plasma membrane under similar conditions. When protein synthesis was inhibited, an enhancement of GJIC between rat Sertoli cells, but not between LNCaP cells or PC3 cells, was observed within 15 min of the addition of 10 nM testosterone. Because nuclear androgens are not present in PC3 cells and many functional properties of the responsive system are different from the nuclear receptor in all three cell types, we postulate the existence of an alternative cell surface receptor system with biphasic response characteristics (high and low affinity). The calcium signals are probably coupled to the regulation of gap junctional efficiency between Sertoli cells. The low-affinity receptors may convey complementary androgen signals at elevated local levels such as in the testis, when nuclear receptors are (over)saturated.

Seasonal changes in the immunolocalization of steroidogenic enzymes in the testes of the Japanese black bear (Ursus thibetanus japonicus)

Seasonal changes in sites of immunostaining of steroidogenic enzymes were examined in testes of the Japanese black bear, Ursus thibetanus japonicus. In addition, serum concentrations of testosterone and estradiol-17beta were investigated by radioimmunoassay, and the seasonal changes were compared with the results of immunostaining. On the basis of morphological observations of spermatogenic activity, the reproductive cycle was divided into five periods: an active period in May and June; a degenerative period in November; a resting period in January; an early-resumptive period in March; and a late-resumptive period in April. Serum concentrations of testosterone differed with season accompanied by differences in spermatogenic activity, with baseline levels in November and January, increasing levels in March and April, and high levels in May, and April and June of the next year. Immunoreactivities specific for cholesterol side-chain cleaving cytochrome P450, 17alpha-hydroxylase cytochrome P450 and 30-hydroxysteroid dehydrogenase (3beta HSD) were observed in Leydig cells throughout the year. Only the percentages of Leydig cells immunopositive for 3beta HSD exhibited seasonal differences that correlated with serum concentrations of testosterone. Aromatase cytochrome P450 (P450arom) was immunolocalized in Leydig and Sertoli cells throughout the year, in spermatids in May, and April and June of the next year and in myoid cells in January and March. The percentages of Leydig cells immunopositive for this enzyme increased in May, and January, March and June of the next year. On the other hand, no pattern of seasonal change in serum estradiol-17beta concentration was observed. These results suggest that 3beta HSD is a key enzyme in the regulation of the testosterone production in Leydig cells. Furthermore, estrogen derived from Leydig and myoid cells seems to play a role in the regulation of Leydig cells by negative feedback as a paracrine and/or autocrine mediator.

Restoration of testicular transferrin, insulin-like growth factor-1 (IGF-1), and spermatogenesis by exogenously administered purified FSH and testosterone in medically hypophysectomized rats

To investigate the relation between testicular transferrin and insulin-like growth factor-1 (IGF-1) secreted by Sertoli cells and the differentiation of germ cells in the rat, testosterone and/or purified FSH was administered to rats medically hypophysectomized by an LH-RH agonist. Spermatogenesis was quantitatively analyzed and concentrations of intratesticular transferrin and IGF-1 were measured by radioimmunoassays. The last step of spermatogenesis was quantitatively restored by combined administration of testosterone and purified FSH. Intratesticular IGF-1 concentrations were significantly increased by combined administration of testosterone and purified FSH. From these observations, it is surmised that IGF-1 may have a stimulatory effect on the last step of spermatogenesis.

Rat Sertoli cell extracellular matrix regulates glycosaminoglycan synthesis by peritubular myoid cells in vitro

We have previously reported metabolic cooperation between Sertoli and peritubular myoid cells in terms of synthesis of one of the main testicular extracellular matrix (ECM) constituents, glycosaminoglycans (GAG). This study concerns Sertoli cell ECM-peritubular myoid cell interactions in terms of GAG synthesis. We have examined the responses of hormones and other regulatory agents such as a combination of follicle-stimulating hormone (FSH), insulin, retinol, and testosterone (FIRT) on peritubular myoid cells, and tested if Sertoli cell ECM or serum factor substitute for the stimulation by FIRT. Testicular peritubular myoid cells cultured on Sertoli cell ECM showed significant increases in the levels of cell- and ECM-associated GAG over that when cultured on uncoated plastic. This indicates a specific cell-substratum interaction between Sertoli cell ECM and peritubular myoid cells in the testis in terms of GAG synthesis. Moreover, in terms of cell-associated GAG synthesis, peritubular myoid cell cultured on Sertoli cell ECM or on plastic in the presence of serum substituted for the stimulatory response of FIRT on peritubular myoid cells cultured on uncoated plastic. The data are discussed in relation to the possible role of cell-substratum interaction in maintaining peritubular myoid cell functions.

Cellular localization of IGF-I and IGF-II mRNAs in immature hypophysectomized rat testis and epididymis after in vivo hormonal treatment

IGF-I and II genes expression has been localized by in situ hybridization in testis and epididymis of immature hypophysectomized rats treated in vivo with either pFSH, hLH, bGH, hPRL or with saline. IGF-I mRNA expression was found in both Sertoli and Leydig cells after treatment with either FSH or LH. IGF-I mRNA was highly expressed in germ cells after FSH stimulation and to a lesser extent after GH or LH treatments. However, its expression was very low in hypophysectomized control or PRL treated rats. IGF-I mRNA was also expressed in stromal cells of epididymis after LH treatment and to a lesser extent after GH stimulation. In contrast, IGF-II mRNA expression was detected in all testicular cell types whatever the hormonal treatment (FSH, LH, GH, PRL). For each hormonal treatment testicular sections were examined after immunohistochemical staining with specific antisera against IGF-I and IGF-II. Both in situ hybridization and immunohistochemical data were examined in order to determine the testicular sites of synthesis of IGF-I and IGF-II.

Differentiation of smooth muscle cells in the fetal rat testis and ovary: localization of alkaline phosphatase, smooth muscle myosin, F-actin, and desmin

The histochemical demonstration of alkaline phosphatase (AP) activity and localization of smooth muscle myosin (SMM), F-actin, and desmin were carried out on frozen sections of testes and ovaries from 15-day-old fetal to newborn rats. The presence of immunocytochemically localized SMM and desmin was confirmed by Western blot analysis of proteins from isolated gonads. The development of smooth muscle cells was predominant in the testis. The first SMM-positive cells with an increasing intensity for F-actin and desmin appeared in the testicular tunica albuginea and around the testicular cords by the age of 16 days. A continuous layer of SMM- and F-actin-positive (but not uniformly desmin-positive) myoid cells was detected in the newborn testis. In the early gonads and in the newborn ovary, a majority of the interstitial cells expressed desmin, indicating that, in undifferentiated tissues, non-myogenic cells may also express desmin. During fetal development, male and female gonocytes showed a decrease in F-actin content but retained their high AP activity. In the cortex of the newborn rat ovary, the observed high AP activity and the presence of desmin may be associated with the postnatal histogenesis of the follicles. The presence of SMM-containing cells in the hilus of the ovary may be required for the demarcation of the ovary from the mesonephros by the constriction of the mesovarium. The occurrence of SMM-positive cells predominantly in male fetuses suggests that the development of the contractile cells in the fetal testis may be induced by testicular androgens.

Testosterone and FSH have independent, synergistic and stage-dependent effects upon spermatogenesis in the rat testis

Adult rats were hypophysectomized and treated with ethane dimethanesulphonate (EDS) selectively to eliminate the Leydig cells in the testis. By removing the source of endogenous gonadotrophins and androgens, the subsequent effects on the seminiferous epithelium were studied after 20 days of treatment with vehicle, or FSH (2 x 50 micrograms/day) or a low dose of testosterone (0.6 mg testosterone esters every 3rd day) alone or in combination. Compared to vehicle-treated hypophysectomized rats with Leydig cells, testis weight in saline-treated hypophysectomized rats treated with EDS declined by 50%, spermatogenesis was disrupted severely and only 18% of the tubules contained spermatids, these being confined to stages I-VI of the spermatogenic cycle. Treatment with either FSH or testosterone esters alone significantly (P less than 0.01) increased testis weight compared to vehicle-treated hypophysectomized rats treated with EDS and 40% of tubules contained spermatids either at stages I-VI after FSH, or at all stages I-XIV after testosterone treatment. Treatment with FSH and testosterone esters together maintained testis weights approximately 20% above vehicle-treated hypophysectomized controls; over 70% of the seminiferous tubules contained spermatids and there was a marked stimulation of spermatogenesis at all stages of the spermatogenic cycle. The results suggest, that in the absence of the pituitary gland and the Leydig cells, FSH alone partially supports spermatogenesis up to the development of round spermatids whereas testosterone is capable of maintaining spermatid development at all 14 stages of the cycle. When FSH and testosterone were administered in combination, the effects upon spermatogenesis were far greater than the response expected if their individual effects were simply additive. It is therefore concluded that FSH may play a role in normal spermatogenesis and that this role is essentially that of augmenting the response of the testis to testosterone. The biochemical mechanisms via which this might occur are discussed and hypophysectomized rats treated with EDS used in the present studies should provide a useful approach for their identification.

The role of cell-cell interactions in androgen action

Androgen-regulated mesenchymal-epithelial interactions play an important role during embryonic development of the male urogenital tractus. Studies on the effects of androgens on cultured testicular cells derived from the immature rat testis indicate that, even during postnatal life, similar interactions may be instrumental for normal androgen action. Androgen receptors are found in epithelial Sertoli cells as well as in mesenchymal peritubular cells. The effects of androgens on isolated Sertoli cells, however, are limited. Coculture with peritubular cells increases the sensitivity and/or the responsiveness of a number of Sertoli cell parameters (transferrin, ABP, aromatase activity) to androgens. This effect is at least in part mediated by the secretion of one or more diffusible factors (P-Mod-S) by the peritubular cells. We investigated whether such indirect effects of androgens, relying on mesenchymal-epithelial interactions are also observed in other androgen target tissues. To this end stromal cells were isolated and cultured from the immature rat ventral prostate and the production of factors with P-Mod-S activity was monitored using Sertoli cells as the test system. Under coculture conditions these stromal cells stimulate Sertoli cell transferrin secretion in an androgen-regulated fashion, exactly as peritubular cells. This stimulatory effect is related in part to the collaborative (and androgen-independent) deposition of an extracellular matrix and in part to the secretion of an androgen-regulated diffusible mediator. This mediator has the same physicochemical characteristics as P-Mod-S and it affects other Sertoli cell parameters (ABP, aromatase activity, inhibin, cGMP) in the same way as P-Mod-S. Cultured stromal and peritubular cells look very similar and stain positive after immunostaining for alpha-smooth muscle isoactin. Tissue sections suggest that these cells may be derived from myoid peritubular cells in the testis and similar periacinar cells in the prostate. The hypothesis is advanced that P-Mod-S may be a more universal mediator of indirect effects of androgens in diverse target tissues and that this factor is derived from myoid cells closely associated with the epithelial component.

Cell-cell interactions and the regulation of testis function

Regulatory interactions have been shown to occur between all the testicular cell types considered. The paracrine factors mediating these interactions generally influence either cellular growth or differentiation. The regulation of cellular growth is essential in the developing testis and is required for the maintenance of spermatogenesis in the adult testis. The rapid rate of germinal cell proliferation and the continuous but slowed growth of the peritubular cells and Leydig cells requires the presence of specific growth factors in the adult. Therefore, cell-cell interactions have evolved that involve growth factors such as IGF, TGF-alpha, TGF-beta and NGF. Other growth factors such as FGF or less characterized components like the seminiferous growth factor (SGF) also may be involved in the paracrine regulation of testis cell growth. An alternate cellular parameter to cell growth to consider is the regulation of cellular function and differentiation. A number of endocrine agents and locally produced paracrine factors have been shown to control and maintain testis cell function and differentiation. Cell-cell interactions mediated by factors such as androgens, POMC peptides, and PModS are all primarily directed at the regulation of cellular differentiation. Therefore, the agents which mediate cell-cell interactions in the testis can generally be categorized into factors that regulate cell growth or those which influence cellular differentiation. The specific cell-cell interactions identified will likely be the first of a large number of cellular interactions yet to be investigated. Although a number of potentially important cell-cell interactions have been identified, future research will require the elucidation of the in vivo physiological significance of these interactions. The existence of different cell types and potential cell-cell interactions in a tissue implies that the actions of an endocrine agent on a tissue will not simply involve a single hormone and single cell. The endocrine regulation of testis function will have effects on cell-cell interactions and be affected by local cell-cell interactions. The ability of LH to influence Leydig cell androgen production promotes a cascade of interactions mediated through several cell types to maintain the process of spermatogenesis. FSH actions on Sertoli cells also promote cell-cell interactions that influence germinal cell development, peritubular myoid cell differentiation and Leydig cell function. Therefore, elucidation of the endocrine regulation of testis function requires an understanding of the local cell-cell interactions in the testis.

Effect of epidermal and insulin-like growth factors on vectorial secretion of transferrin by rat Sertoli cells in vitro

Within the seminiferous tubules, the Sertoli cells create an impermeable blood-testis barrier and an unique intratubular microenvironment that fosters the development of spermatozoa. The functional differentiation of spermatozoa therefore requires vectorial secretion by Sertoli cells of substances that cannot cross the blood-testis barrier. We investigated the role of epidermal (EGF) and insulin-like growth factors I and II (IGF-I and IGF-II) in the regulation of vectorial secretion of transferrin by Sertoli cells. In order to study the regulation of vectorial transferrin secretion, we modified culture conditions in the twin chamber culture system to maximise gradients of transferrin secretion. Sertoli cells were plated at high density (3-4 x 10(6) cells/well) into chambers of near equal volume, cultured at 37 degrees C and maintained in simple, fully defined media omitting standard supplements (insulin, EGF, FSH) which affect vectorial transferrin secretion. Using this optimised culture system, maximum gradients of transferrin secretion occurred between days 2 and 3 of culture with preferential secretion (mean ratio 3.7 +/- 0.2) directed towards the apical compartment. The transferrin ratio (ratio of transferrin secreted into the upper over the lower chamber) was decreased by insulin and FSH but not by retinoic acid or testosterone, yet all four stimuli increased total transferrin secretion. IGF-I and IGF-II were effective at physiological concentrations (ED50 = 1 ng/ml) in lowering transferrin ratio and were 100-fold more potent than insulin suggesting that insulin effects on vectorial transferrin secretion by Sertoli cells is mediated through type 1 IGF receptors. EGF also reduced the transferrin ratio (ED50 = 50 ng/ml) as well as stimulating total transferrin secretion. The hormonally mediated reduction in transferrin ratio was consistently due to enhanced secretion of transferrin into the lower chamber. In the first demonstration of a highly polarised response of Sertoli cells to hormonal stimuli, the effects of insulin, FSH and EGF on vectorial transferrin secretion were effected primarily via the basal membrane of the Sertoli cell and operated independent of mechanisms controlling total transferrin secretion. These results establish a potential role for epidermal and insulin-like growth factors in the paracrine regulation of vectorial secretion by the Sertoli cell, in particular the developmental regulation of vectorial transferrin secretion by Sertoli cells. These findings also indicate that previous studies which included insulin and EGF routinely in culture media have systematically underestimated apically directed transferrin secretion.

Stromal regulation of epithelial function

Stromal influences upon epithelia are part of a continuum of cellular interactions that begins at fertilization and extends into adulthood. In parenchymal organs, the most thoroughly characterized interactions have been those that occur during development between mesenchyme, embryonic stroma, and epithelium. Mesenchyme is essential for epithelial proliferation, morphogenesis, and differentiation. Hormones affect stromal-epithelial interactions, and in some cases, steroid hormones may produce their effects on the epithelium indirectly, acting via the mesenchyme. In many adult organs the epithelia continually proliferate and differentiate and consequently may be considered developing systems within the mature organism. This is especially true in organs with a rapidly renewing epithelium, such as the intestine, and in organs that have cycles of functional activity, such as those of the female reproductive system. The mechanisms by which stroma affects epithelial structure and function are not well understood. Current models of how signaling may be accomplished include transmission via diffusible substances, via the extracellular matrix (ECM), and via direct cell-cell contact. Growth factors and organ-specific paracrine factors are candidates for stromal cues that affect the epithelium in some systems. Components of the ECM appear to play a role in permissive interactions and may affect epithelial function by changing cell shape or by binding ECM to the cell surface integrin receptors. Signaling via direct stromal-epithelial contact may be accomplished via interactions between complimentary cell surface adhesion molecules. The importance of stromal-epithelial interactions is reemphasized by several models of carcinogenesis that suggest that perturbations in these interactions may be involved in tumor progression.

Morphological and functional similarities between cultured prostatic stromal cells and testicular peritubular myoid cells

A number of androgen effects on epithelial cells may be mediated by androgen-regulated paracrine factors produced by underlying mesenchymal cells. In previous studies we demonstrated that prostatic stromal cells and testicular peritubular cells, derived from immature rats, produce mediators of androgen action with identical effects on Sertoli cells. In the present paper we further compared the morphological and functional characteristics of both mesenchymal cell types. Cultured prostatic stromal cells and testicular peritubular cells look identical under phase-contrast microscopy, share the ability to form tubular structures and "balls" when cocultured with Sertoli cells, and contain proteins immunoreactive with an antiserum against alpha-smooth muscle isoactin. Two-dimensional gel electrophoresis shows that the pattern of proteins produced by both cell types is nearly identical. Conditioned media from stromal and peritubular cells contain a factor that stimulates transferrin and cGMP production in Sertoli cells. The behavior of the active principle in the media from both cell types is comparable. On reverse-phase HPLC the elution profile of this factor is comparable for media from both cell types. In conclusion, these data point to a striking similarity in the morphological and functional characteristics of mesenchymal cells cultured from the prostate and testis.

Golden hamster myoid cells during active and inactive states of spermatogenesis: correlation of testosterone levels with structure

Myoid cells were examined quantitatively in adult golden hamsters with active spermatogenesis and compared with hamsters in which the testes were regressed due to a modification in the light-dark cycle. A detailed morphometric study was undertaken utilizing animals previously examined. The cell-surface area and volumes of most organelles were not significantly different in animals which were gonadally active as compared with regressed animals. A slight, but significant, increase in nuclear volume (31%) and a slight, but significant, decrease (28%) in cell volume were recorded for regressed animals. The total volume of pinocytotic vesicles was increased dramatically (approximately threefold) in active animals in comparison with inactive animals (P less than 0.01), indicating that an increase in non-specific transport across the myoid cell is associated with spermatogenic activity. Intravascularly injected horseradish peroxidase was capable of entering pinocytotic vesicles in both active and inactive animals. Plasma luteinizing hormone (LH) as well as plasma and testicular testosterone levels were weakly (r = 0.64, 0.68, and 0.65, respectively), but significantly (P less than 0.05), correlated with cell size. Plasma and testicular testosterone were correlated with the total volume of pinocytotic vesicles (r = 0.74 and 0.68, respectively). The data indicate that although the rat myoid cell possesses receptors for testosterone, there are few structural manifestations of the hamster myoid cell that correlate well with testosterone levels. Thus, the hamster myoid cell differs from two other hormone-responsive somatic cells in the testis, the Sertoli cell and the Leydig cell, that show dramatic structural alterations with changes in gonadal activity and striking correlations of structural features with functional measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Follitropin (FSH) stimulation of inhibin biological and immunological activities by seminiferous tubules and Sertoli cell cultures from immature rats

Seminiferous tubules from 20-day-old rats were isolated by mechanical dissection and the conditions to produce optimal inhibin secretion over a 5-day period of culture were established. Inhibin was measured by a specific heterologous radioimmunoassay and by an in vitro bioassay using rat pituitary cells in culture. The tubule production of biologically and immunologically active inhibin was stimulated by ovine follitropin (FSH); however, the ratio of biological to immunological (B:I) activity fell significantly with increasing dose. A similar stimulation of both B and I inhibin activity with a corresponding decrease in B:I ratio with increased FSH dose was also observed using isolated immature Sertoli cells in culture. Fractionation of seminiferous tubule and Sertoli cell culture media by reverse-phase high-performance liquid chromatography (HPLC) revealed the presence of two peaks (I and II) with inhibin biological and immunological activity both of which increased following FSH stimulation. However, while the B:I ratio for peak I remained unchanged following FSH stimulation, the B:I ratio for peak II significantly fell. The molecular weights of peak I and II immunoactivity, determined following fractionation on preparative polyacrylamide gel electrophoresis were 30 kDa and 27 kDa respectively. The 30 kDa peak, based on its inhibin in vitro biological and immunological activity, molecular weight and retention position on HPLC most likely represent 30-32 kDa inhibin. The 27 kDa material remains to be identified.

Stimulation of Sertoli cell inhibin secretion by the testicular paracrine factor PModS

The testicular paracrine factor PModS is produced by peritubular myoid cells under androgen control and modulates Sertoli cell function and differentiation. The observation that luteinizing hormone (LH) stimulates inhibin production in vivo, but has no effect on isolated Sertoli cells in vitro, suggested an indirect mode of LH action, potentially mediated by PModS. The effects of the testicular paracrine factor PModS and hormones on inhibin secretion by Sertoli cells were investigated to provide insight into the endocrine control of inhibin expression. An inhibin radioimmunoassay was utilized which showed essentially parallel displacement curves with purified bovine follicular fluid inhibin, Sertoli cell conditioned medium and concentrated Sertoli cell secreted proteins. An immunoblot analysis of Sertoli cell secreted proteins with the inhibin antisera consistently detected a 32 kDa protein which is the expected size of the mature of inhibin (alpha beta) and periodically detected a 57 kDa protein which is speculated to be an incomplete processed form of the inhibin precursor (alpha 43 beta). Follicle-stimulating hormone (FSH) was found to stimulate inhibin secretion initially between days 2 and 5 of Sertoli cell culture. Insulin and retinol alone had no significant effect on inhibin secretion; however, together they appeared to enhance the ability of FSH to stimulate inhibin secretion. Testosterone had no effect on inhibin production alone or in combination with other regulatory agents. PModS was found to stimulate inhibin secretion approximately 3-fold, but with a delayed time course of stimulation which did not occur until days 5-7 of Sertoli cell culture. Treatment with a combination of PModS and FSH resulted in an apparent maximal stimulation of inhibin secretion. Both forms of PModS, PModS (A) and PModS (B), were found to have equivalent biological activities in their ability to stimulate inhibin production with an apparent half-maximal effective concentration between 10 and 15 ng/ml. The current study provides evidence for the local testicular control of inhibin production and adds to the complexity of the endocrine control of inhibin expression. The cellular interaction is proposed in which LH acts on Leydig cells to stimulate androgen production which in turn acts on peritubular cells to regulate PModS production which subsequently can act on Sertoli cells to control inhibin production. Testicular control of inhibin production provides a potential short feedback loop for the local regulation of androgen production and an additional regulatory element for the pituitary-gonadal axis.

Follicle-stimulating hormone regulates androgen receptor mRNA in Sertoli cells

Follicle-stimulating hormone (FSH) and testosterone stimulate the production of a variety of proteins by immature Sertoli cells. A highly purified Sertoli cell preparation was incubated for 3 days with FSH and testosterone. Both androgen receptor protein and mRNA concentrations were markedly increased by FSH. Testosterone also increased the androgen receptor protein concentration, but did not increase the expression of the androgen receptor mRNA. It is concluded that FSH plays a role in the responsiveness of Sertoli cells to testosterone.

Stromal cells from the rat prostate secrete androgen-regulated factors which modulate Sertoli cell function

Testicular peritubular cells produce paracrine mediators which modulate Sertoli cell function. The production of these mediators (P Mod-S) is controlled by androgens suggesting that mesenchymal-epithelial interactions play an important role in androgen action in the testis. We investigated whether mesenchymal cells from the prostate, another androgen target tissue, produce analogous mediators. To this end rat Sertoli cell cultures were exposed to dialyzed spent media derived from testicular peritubular cells, prostatic stromal cells or footsole fibroblasts. It is demonstrated that the effects of spent media from peritubular cells and stromal cells are nearly identical: they stimulate the production of androgen binding protein and transferrin and they inhibit FSH-inducible aromatase activity. The active principle (or principles) involved is non-dialyzable, heat sensitive and trypsin sensitive. Its production is markedly stimulated by androgens. Fibroblast spent media are inactive. It is concluded that mesenchymal tissue derived from different androgen target tissues may produce identical or similar mediators of androgen action acting on epithelial cells.

Physiology of the male reproductive system: endocrine, paracrine and autocrine regulation

This presentation reviews the male reproductive system, concentrating on newer advances in our knowledge of its physiology, biochemistry, and regulation, and introduces the topic of male reproductive toxicology. GnRH is the hypothalamic peptide responsible for the stimulation of LH and FSH release from the pituitary. It is synthesized as a pro-hormone, processed in the hypothalamus and released into the portal system in a pulsatile fashion. The timing of these pulses is critical to the release of LH and FSH into the general circulation. While LH and FSH are the main trophic hormones for the testis, we now realize the importance of not only endocrine control, but also of paracrine and autocrine regulation. Specifically, the local control of Leydig cells, Sertoli cells, and germ cells appears to be modulated by numerous growth factors and local regulators arising from within the testis. This point is emphasized both during a discussion of the interaction of the various cell types in the testis and during a discussion of spermatogenesis, where techniques which show stage-specific secretions are highlighted. Newest advances in the mechanism of action of steroidal and peptide hormones are also emphasized with special reference to the possible interaction between toxicants and endocrine control of the reproductive system. This update of the reproductive system "sets the stage" for an in-depth examination of the site and mechanism of action of reproductive toxicants.

Relative roles of follicle-stimulating hormone and luteinizing hormone in the control of inhibin secretion in normal men

The glycoprotein hormone inhibin is produced by the Sertoli cells of the testis under the influence of follicle-stimulating hormone (FSH) and is postulated in turn to inhibit FSH secretion. Luteinizing hormone (LH) is not recognized to have an important role in the control of inhibin secretion in any species. To determine the relative roles of FSH and LH in the control of inhibin secretion in man, we examined the effects of selective FSH and LH replacement on serum inhibin levels in normal men whose endogenous gonadotropins were suppressed by testosterone (T). After a 3-mo control period, nine men received 200 mg T enanthate i.m. weekly for 3-9 mo. During T treatment, serum LH and FSH levels were markedly suppressed and serum inhibin levels fell to 40% of control values. While continuing T, 3-5 mo of treatment with purified hFSH (n = 4) or hLH (n = 4) increased the respective serum gonadotropin level into the upper normal range and significantly increased inhibin levels back to 64 and 55% of control values, respectively. Supraphysiological LH replacement with high doses of human chorionic gonadotropin (n = 3) returned serum inhibin levels to 63% of control values. In no case did inhibin levels return fully to control levels. In conclusion, serum inhibin levels fell during gonadotropin suppression and were partially and approximately equally restored by either FSH or LH treatment. FSH presumably acts directly on the Sertoli cell to increase inhibin secretion whereas LH may act via increases in intratesticular T levels and/or other factor(s).

Cell-cell interactions in the testis

In conclusion, the information available indicates that the interactions between different cell types in the testis play an important role in the control and maintenance of testicular functions. Further characterization of these interactions will clearly provide insight into the cell biology of the testis and into the regulation of cellular differentiation, function, and growth. It is apparent that no testicular cell type is autonomous, but that there is communication and cooperation between all cell types in the testis.

Peritubular cells influence Sertoli cells at the level of translation

Conditioned medium from cultured peritubular cells (PTCM) was capable of increasing the incorporation of amino acids into acid-precipitable material in cultured Sertoli cells, while the incorporation of uridine into acid-precipitable material was unaffected. PTCM did not influence intracellular cAMP accumulation in a manner similar to follicle-stimulating hormone (FSH). PTCM was able to stimulate androgen-binding protein (ABP) secretion by Sertoli cells even in the presence of a maximal dose of FSH. PTCM increased the rate at which peptides are elongated 5-fold over control medium or medium from control fibroblasts. These studies indicate that peritubular cells influence Sertoli cells through different mechanisms than FSH and exert their influence, at least in part, at the level of translation by increasing the rate of peptide elongation.

Vectorial secretion of transferrin and androgen binding protein in Sertoli cell cultures: effect of extracellular matrix, peritubular myoid cells and medium composition

We examined the effect of various culture conditions on the polarized secretion of androgen binding protein (ABP) and transferrin (Trf) by Sertoli cells (Sc) in vitro. Sc from 18-day-old rats were cultured as confluent monolayers on permeable membranes in two-compartment chambers for up to 11 days. Coating of the membranes with extracellular matrix (ECM) components: collagen IV + laminin (CL) or reconstituted basement membrane (RBM) enhanced ABP and Trf secretion (200% and 150%, respectively), with RBM being more effective than CL in stimulating ABP but not Trf secretion. Neither CL nor RBM significantly influenced the relative amounts of ABP and Trf secreted into the outer (OC) and inner (IC) compartments of the culture chamber (OC/IC ratio). All of these effects were not significantly influenced by the presence of testosterone and serum. Co-culture of Sc with peritubular myoid cells (Pc) significantly increased the secretion of both ABP and Trf, although the magnitude of stimulation and the time-response patterns were different for each protein. Co-culture with Pc also dramatically increased the OC/IC ratios for ABP and Trf. Testosterone (10(-6) M) enhanced the Pc effects. In cultures of Sc alone, presence of 2% fetal bovine serum increased the OC/IC ratios, whereas testosterone had no effect. Based on these results, we suggest a possible role of Pc in the regulation of Sc polarized secretions.

Intragonadal control mechanisms

On the weight of the evidence presented above, it is concluded that regulation at a local, intragonadal level is an integral part of the overall regulation of gonadal function in both sexes. The interaction between cells within a gonad extends beyond the same cell type to include germ cell-somatic cell interactions as well. We believe this local interaction between cell types facilitates the differing requirements of the various developmental stages of germ cells within the gonad, which would not be possible by simply varying the afferent pituitary hormone supply. We re-emphasize that the local factors responsible for these interactions are acting in conjunction with the pituitary hormones, and, in some cases, may be their proximate regulators. A more controversial phenomenon is the possibility of an interaction between the gonads which does not involve the hypothalamic-pituitary axis. The little evidence which is available to support this hypothesis comes mainly from studies on ovarian function, particularly recruitment and selection of follicles. More research on this phenomenon is warranted. Not surprisingly there are many parallels between the testes and ovaries with respect to the nature and action of local regulators. For example, the intragonadal action of steroids, the local modulation of the response of target cells to FSH, the influence of macrophages on steroidogenesis and the presence of mitotic and meiotic regulators are common to both sexes. It would not be surprising if the chemical nature of these factors in the ovary and testes are similar. If the ever-increasing list of factors and activities being discovered in the gonads is any guide, the phenomena outlined in this review are just the beginning of an extensive list of cell-cell interactions occurring within and between the gonads. No doubt the gonads will share with other organs the same interactions between cells which are required for normal cellular function. The uniqueness of the gonads lies in their protection and production of germ cells. The challenge of the future for reproductive biologists will be to discover and describe the interactions within and between germ cells which are obligatory for normal reproductive function, and to apply that information to devising ways of overcoming infertility and regulating fertility.

Hormonal regulation of Sertoli cell function

The Sertoli cell is clearly influenced, directly and indirectly, by hormones. Among these are FSH, T, insulin and Vitamin A, but others may also be involved. Mechanisms are still not well understood. The biochemical effects of these hormones can be divided into quantitative and qualitative influences, with the former predominating. Specific cellular and secretory proteins and metabolites are affected, in many cases by more than one hormone. Often these same functions are influenced by other factors in the environment of the testis as well. Hormonal responsiveness of the Sertoli cell is determined in part by the maturational state of the cell. Some secreted products bind to specific cell types in the testis and epididymis and may influence the process of spermatogenesis. However, detailed mechanisms are not known at the present time. Understanding Sertoli cell function at the biochemical level and its control by hormones is clearly of key importance in understanding the control of the spermatogenic process.

Paracrine regulation of testicular function

Data from several experimental approaches have been reviewed and the findings clearly indicate the existence of multiple interactions between testicular cells and the potential role of these interactions in the paracrine control of testicular functions. Both testicular interstitial fluid and spent media from cultured Sertoli cells had an acute steroidogenic effect on Leydig cells, and this effect is not species specific. The secretion of this steroidogenic factor(s), which is probably a protein, is enhanced by previous FSH treatment of Sertoli cells. Coculture for 2-3 days of pig Leydig cells with homologous or heterologous Sertoli cells enhances Leydig cell specific functions (hCG receptor number and hCG responsiveness) and induces Leydig cell hypertrophy. A similar but less pronounced trophic effect is seen when Leydig cells are cultured with spent media from Sertoli cells cultured in the presence of FSH and high concentrations of insulin, but the spent media from Sertoli cells cultured in the absence of these two hormones inhibits Leydig cell specific functions. Somatomedin-C might play an important role in the positive trophic effect of Sertoli cells on Leydig cells, since this peptide is secreted by Sertoli cells and it has trophic effects on the specific function of Leydig cells. Moreover, Sertoli cells, probably through a diffusible factor and cell-to-cell contacts, control the multiplication, meiotic reduction and maturation of germ cells. In turn, the activity of Sertoli cells is modulated by the stage of neighbouring germ cells. Thus, if a normal Sertoli cell function (which depends not only on FSH but also on Leydig and myoid cell secretory products) is an absolute requirement for germ cell multiplication and maturation, these cells, in turn, cyclically regulate Sertoli cell function and through these cells the size and probably the function of Leydig cells.

Regulation of androgen production by frog (Rana esculenta) testis: an in vitro study on the effects exerted by estradiol, 5 alpha-dihydrotestosterone, testosterone, melatonin, and serotonin

The possible role of estradiol-17 beta (E2), testosterone (T), 5 alpha-dihydrotestosterone (DHT), melatonin, and serotonin on the regulation of androgen (A) production by the frog, Rana esculenta, testes was studied in vitro. E2 (10(-6) M) inhibited A production whether alone or in combination with oLH (20 micrograms) after 6 hr incubation. After 24 hr incubation. A production was reduced by E2 concentration of around 10(-6) and 10(-9) M. Melatonin and serotonin did not induce any change whichever experimental condition was used. Preincubation for 6 hr with 10(-6) M T or DHT enhanced the oLH-stimulated A production after 18 hr incubation. These data suggest that steroids may regulate their intratesticular levels without passing into the blood stream.

Evidence for a Sertoli cell, FSH-suppressible inhibiting factor(s) of testicular steroidogenic activity

By using a model of immature porcine Leydig and Sertoli cells cultured in serum free defined medium, we evidenced a paracrine control of Leydig cell steroidogenic activity by Sertoli cells via a secreted inhibiting protein(s). This protein(s), partially purified using gel filtration (M.W. 20,000-30,000) suppresses the steroidogenic responsiveness to LH/hCG by decreasing the specific LH/hCG binding (52% decrease) and hormone steroid biosynthesis (73% decrease) at a level(s) located between cAMP production and pregnenolone formation. The suppression of this inhibitor(s) by FSH, in a dose dependent manner, is one mechanism by which FSH "sensitizes" Leydig cell response to LH/hCG stimulation.

Paracrine control of the testis

The mammalian testis is under the overall control of pituitary gonadotropins but the utilization of these signals to achieve normal testicular function involves complex local interactions between the Sertoli and germ cells, the Sertoli and peritubular cells, and the Sertoli and Leydig cells as well as local control of the testicular vasculature. These interactions serve two purposes: (1) to coordinate the functions of the three testicular compartments (seminiferous tubules, interstitium and the vasculature); and (2) to control the complex but orderly sequence of events that constitutes the spermatogenic cycle. This process, which involves multiplication, differentiation and translocation of the germ cells is organized into a sequence of stages, each of which is composed of a constant association of germ cells at four or five different stages of development. At each stage of the spermatogenic cycle, different events occur and the function of the Sertoli cells alters, probably in accordance with the changing requirements of the associated germ cells. As yet, our understanding of these many local events is extremely limited, particularly with respect to the identity of the hormones/factors involved in controlling the various processes. Our knowledge of paracrine control mechanisms in the testis is derived mainly from studies of the rat, but as the process of spermatogenesis is essentially the same in most mammals and involves the same sequence of events, then findings in the rat can probably be applied in general, if not in detail, to the human testis; the limited direct information available on the human testis supports this view. As most cases of infertility in men occur despite normal or raised serum gonadotropin levels and are characterized by the production of reduced or normal numbers of sperm, then it seems likely that malfunction of one or more of the intricate paracrine processes within the testis may be involved in the aetiology of idiopathic oligospermia. It is therefore argued that advances in our knowledge of the paracrine control of the testis should have major repercussions on our ability to understand, and eventually treat, idiopathic infertility in men, and also to induce infertility for contraceptive purposes.

Identification of a non-mitogenic paracrine factor involved in mesenchymal-epithelial cell interactions between testicular peritubular cells and Sertoli cells

Seminiferous peritubular cells have previously been shown to secrete a protein termed P-Mod-S which modulates the functions of Sertoli cells. The present study provides an initial characterization of P-Mod-S and examines the actions of P-Mod-S on Sertoli cells. Gel filtration chromatography demonstrates that P-Mod-S has an apparent molecular weight of 70 000 that could not be dissociated to a lower molecular weight form. A 40- to 90-fold purification of P-Mod-S was obtained with a predicted half maximal effective concentration for Sertoli cells of less than 10(-9) M. Through an analysis of the actions of P-Mod-S on Sertoli cells it is demonstrated that P-Mod-S stimulates the Sertoli cell to a greater extent than any single hormone or vitamin known to influence the cell. P-Mod-S maximally stimulates testicular transferrin and androgen-binding protein production by Sertoli cells, but does not stimulate levels of plasminogen activator activity. P-Mod-S also appears to induce the synthesis of several proteins that are not detected in control non-treated Sertoli cell cultures. One such protein whose synthesis was stimulated by P-Mod-S treatment of Sertoli cells was a component having a molecular mass of 20 kDa. This 20 kDa Sertoli cell-secreted protein was specifically immunoprecipitated with an antibody against an epididymal lactalbumin-like protein. This implies that P-Mod-S can induce Sertoli cells to synthesize and secrete a lactalbumin-like protein. P-Mod-S was found not to contain mitogenic activity. Data presented indicate that testicular peritubular cells synthesize and secrete a 70 kDa non mitogenic paracrine factor termed P-Mod-S which has a dramatic influence on Sertoli cell functions. Results are discussed with respect to modulation of epithelial (Sertoli) cell functions by components produced by mesenchymal (peritubular) cells.