The effects of ethane dimethane sulphonate (EDS) on bilaterally cryptorchid rat testes

Ethylene dimethanesulfonate effects on gene promoter activities related to the endocrine function of immortalized Leydig cell lines R2C and MA-10

Ethylene dimethanesulfonate (EDS) is a molecule with known selective cytotoxicity on adult Leydig cells. A single intraperitoneal injection in rats but not mice, leads to male androgen deprivation and infertility. In vitro studies using rat and mouse immortalized Leydig cell lines, showed similar effects of cell death promoted by EDS in rat cells as seen in vivo, and suggest that EDS affects gene transcription, which could firstly compromise steroidogenesis before the apoptosis process. Using gene reporter assay, this study aimed to investigate EDS effects on the promoter activity of genes important for endocrine function (Star, Insl3) and response to toxic agents (Gsta3) in immortalized Leydig cell lines (rat R2C and mouse MA-10 cells), as well as identify possible EDS-responsive elements in the Star gene promoter. EDS exposure of R2C and MA-10 Leydig cells increased Gsta3 promoter activity after 4 h of treatment and decreased Insl3 promoter activity only in R2C cells after 24 h of treatment. EDS also decreased Star promoter activity in both Leydig cell lines. Using R2C cells, the EDS-responsive region in the Star promoter was located between -400 and -195 bp. This suggests that this region and the associated transcription factors, which include MEF2, might be targeted by EDS. Additional somatic gonadal cell lines expressing Star were used and EDS did not affect Star promoter activity in DC3 granulosa cells while Star promoter activity was increased in MSC-1 Sertoli cells after 24 h of treatment. This study contributes to the knowledge regarding the mechanism of EDS action in Leydig cells, and in other gonadal cell lineages, and brings new light regarding the rats and mice differential susceptibility to EDS effects, in addition to providing new avenues for experimental approaches to better understand Leydig cell function and dynamics in different rodent species.

Heat stress response of somatic cells in the testis

The testis is a temperature-sensitive organ that needs to be maintained 2-7 °C below core body temperature to ensure the production of normal sperm. Failure to maintain testicular temperature in mammals impairs spermatogenesis and leads to low sperm counts, poor sperm motility and abnormal sperm morphology in the ejaculate. This review discusses the recent knowledge on the response of testicular somatic cells to heat stress and, specifically, regarding the relevant contributions of heat, germ cell depletion and inflammatory reactions on the functions of Sertoli and Leydig cells. It also outlines mechanisms of testicular thermoregulation, as well as the thermogenic factors that impact testicular function.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

Stem Leydig cells: from fetal to aged animals

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell (ALC) population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Distinct stages of ALC development have been identified and characterized. These include stem Leydig cells (SLCs), progenitor Leydig cells, immature Leydig cells, and ALCs. This review describes our current understanding of the SLCs in the fetal, prenatal, peripubertal, adult, and aged rat testis, as well as recent studies of the differentiation of steroidogenic cells from the stem cells of other organs.

The roles of inhibin and related peptides in gonadal function

Inhibin A and B are dimeric proteins capable of suppressing FSH both in vitro and in vivo. The principal form in the male is inhibin B which is produced in the testis and circulates to inhibit pituitary FSH secretion. Activin A, B and AB are dimeric proteins that share the same beta subunits with the inhibins but, in contrast, stimulate FSH secretion. Although activin A circulates, castration does not lead to a decrease in serum concentrations, indicating that the testis is not the major source of activin A. In the circulation, the activins are bound to a structurally unrelated binding protein, follistatin, that neutralizes the biological actions of these proteins. The subunits of the inhibins/activins as well as follistatin are also produced locally within the pituitary and their levels can be modulated by testosterone and gonadotrophin releasing hormone as well as by autocrine mechanisms. Consequently, the output of FSH is dependent of the balance between local processes and the circulating feedback exerted by testosterone and inhibin. There is increasing data to support the local gonadal production of not only inhibin but also activin and follistatin by both germ cells and somatic cells such as the Sertoli cells. Evidence is accumulating to support the concept that these proteins exert local regulatory mechanisms in the testis.

The pattern of inhibin/activin alpha- and betaB-subunit messenger ribonucleic acid expression in rat testis after selective Leydig cell destruction by ethylene dimethane sulfonate

To further investigate the regulatory mechanisms responsible for the control of testicular inhibin/activin subunit gene expression, inhibin-alpha, -betaA, and -betaB messenger RNA (mRNA) levels were assessed after ethylene dimethane sulfonate (EDS)-induced destruction of Leydig cells (LC) in different animal models: the intact rat, the rat treated with high doses of testosterone, and the unilaterally cryptorchid rat. In intact rats, EDS selectively eliminates the mature adult-type LCs, activating the proliferation and differentiation of preexisting LC precursors into a new population of functionally active LCs. In this model, a single dose of EDS (75 mg/kg BW, ip) induced a significant increase in testicular inhibin-alpha and -betaB mRNA levels 5 days after treatment (5.0- and 5.5-fold increases, respectively), whereas inhibin-betaA mRNA remained undetectable upon Northern hybridization in control and EDS-treated testes. Moreover, in situ hybridization analysis demonstrated that the increased expression of inhibin-alpha and -betaB mRNAs observed 5 days after EDS takes place mainly in Sertoli cells. Along with LC repopulation, the expression level of inhibin-alpha and -betaB messages declined, and inhibin-alpha mRNA returned to control values on day 40 after EDS. This treatment, however, failed to alter the pattern of testicular expression of FSH receptor and androgen-binding protein mRNAs, thus suggesting selectivity for the above effects. In EDS-treated rats supplemented with high doses of testosterone, the preexisting mature LCs are destroyed, but, due to elevated testosterone concentrations, disruption of spermatogenesis is attenuated, and the post-EDS rise in serum gonadotropins is blocked; the latter prevents LC regeneration. In this model, a 5.0-fold increase in inhibin-alpha mRNA levels, similar to that found in intact animals, was detected 5 days after EDS administration, but the rise in inhibin-betaB levels was partially delayed. In addition, the blockade of LC repopulation resulted in permanent elevation of inhibin-alpha and -betaB messages throughout the study period. In unilaterally cryptorchid rats, the abdominal testis shows disrupted spermatogenesis and altered paracrine environment that expedites LC repopulation after EDS treatment. In this model, the abdominal testes showed a significant 2.5-fold increase in inhibin-alpha mRNA levels 5 days after EDS, but no effect was found in those of inhibin-betaB. Further, the faster rate of LC repopulation resulted in precocious decline of inhibin-alpha mRNA levels. Finally, the expression of inhibin/activin subunit mRNAs was monitored during postnatal testicular development, specifically at the time of regression of fetal-type LCs and appearance of those of the adult type. High levels of expression of inhibin-alpha and -betaB mRNAs were detected in neonatal and infantile testes. A sharp decline in both messages took place between days 15-20, i.e. at the time when fetal-type Leydig cells are replaced by adult-type cells. From this time point onward, inhibin-alpha and -betaB mRNA levels remained low, ranging between 15-30% of the maximum. In conclusion, our results suggest that the adult-type LCs differentially modulate the expression of inhibin/activin subunit genes and point to a major inhibitory role in this cell type on expression of the inhibin-alpha gene.

Identification of markers for precursor and leydig cell differentiation in the adult rat testis following ethane dimethyl sulphonate administration

Administration of ethane dimethane sulphonate (EDS) to adult rats results in the destruction of all Leydig cells, followed by a complete regeneration. We investigated this regeneration process in more detail, using different markers for precursor and developing Leydig cells: the LH receptor, 3beta-hydroxysteroid dehydrogenase (3beta-HSD), transforming growth factor alpha (TGFalpha), and a new marker for Leydig cell maturation, relaxin-like factor (RLF). LH receptor immunoreactivity was found in Leydig cell-depleted testes at 3 and 8 days after EDS administration. The positive (precursor) cells had a mesenchymal-like morphology. The number of LH receptor-positive cells 8 days after EDS administration was 15 +/- 4 per 500 Sertoli cell nuclei. Fifteen days after EDS administration, the first new Leydig cells could be observed. These cells stained positively with both the antibodies against the LH receptor and 3beta-HSD, while some cells also stained positively for TGFalpha. After EDS administration, RLF mRNA disappeared from the testis and reappeared again at the time of the appearance of the first Leydig cells. Concomitant with the increase in the number of Leydig cells, the number of RLF-expressing cells increased. The observations of the present study give further support to the hypothesis that Leydig cell development in the prepubertal testis, and in the adult testis following EDS administration, takes place along the same cell lineage and suggest, therefore, that the adult EDS-treated rat can serve as a model for studying the adult-type Leydig cell development that normally occurs in the prepubertal rat testis.

Rodent Leydig cell tumorigenesis: a review of the physiology, pathology, mechanisms, and relevance to humans

Leydig cells (LCs) are the cells of the testis that have as their primary function the production of testosterone. LCs are a common target of compounds tested in rodent carcinogenicity bioassays. The number of reviews on Leydig cell tumors (LCTs) has increased in recent years because of its common occurrence in rodent bioassays and the importance in assessing the relevance of this tumor type to humans. To date, there have been no comprehensive reviews to identify all the compounds that have been shown to induce LCTs in rodents or has any review systematically evaluated the epidemiology data to determine whether humans were at increased risk for developing LCTs from exposure to these agents. This review attempts to fill these deficiencies in the literature by comparing the cytology and ontogeny of the LC, as well as the endocrine and paracrine regulation of both normal and tumorigenic LCs. In addition, the pathology of LCTs in rodents and humans is compared, compounds that induce LC hyperplasia or tumors are enumerated, and the human relevance of chemical-induced LCTs is discussed. There are plausible mechanisms for the chemical induction of LCTs, as typified by agonists of estrogen, gonadotropin releasing hormone (GnRH), and dopamine receptors, androgen receptor antagonists, and inhibitors of 5alpha-reductase, testosterone biosynthesis, and aromatase. Most of these ultimately involve elevation in serum luteinizing hormone (LH) and/or LC responsiveness to LH as proximate mediators. It is expected that further work will uncover additional mechanisms by which LCTs may arise, especially the role of growth factors in modulating LC tumorigenesis. Regarding human relevance, the pathways for regulation of the hypothalamo-pituitary-testis (HPT) axis of rats and humans are similar, such that compounds that either decrease testosterone or estradiol levels or their recognition will increase LH levels. Hence, compounds that induce LCTs in rats by disruption of the HPT axis pose a risk to human health, except for possibly two classes of compounds (GnRH and dopamine agonists). Because GnRH and prolactin receptors are either not expressed or are expressed at very low levels in the testes in humans, the induction of LCTs in rats by GnRH and dopamine agonists would appear not to be relevant to humans; however, the potential relevance to humans of the remaining five pathways of LCT induction cannot be ruled out. Therefore, the central issue becomes what is the relative sensitivity between rat and human LCs in their response to increased LH levels; specifically, is the proliferative stimulus initiated by increased levels of LH attenuated, similar, or enhanced in human vs. rat LCs? There are several lines of evidence that suggest that human LCs are quantitatively less sensitive than rats in their proliferative response to LH, and hence in their sensitivity to chemically induced LCTs. This evidence includes the following: (1) the human incidence of LCTs is much lower than in rodents even when corrected for detection bias; (2) several comparative differences exist between rat and human LCs that may contribute, at least in part, to the greater susceptibility of the rat to both spontaneous and xenobiotic-induced LCTs; (3) endocrine disease states in man (such as androgen-insensitivity syndrome and familial male precocious puberty) underscore the marked comparative differences that exist between rats and man in the responsiveness of their LC's to proliferative stimuli; and (4) several human epidemiology studies are available on a number of compounds that induce LCTs in rats (1,3-butadiene, cadmium, ethanol, lactose, lead, nicotine) that demonstrate no association between human exposure to these compounds and induction of LC hyperplasia or adenomas. (ABSTRACT TRUNCATED)

Local regulation of macrophage subsets in the adult rat testis: examination of the roles of the seminiferous tubules, testosterone, and macrophage-migration inhibitory factor

In the adult rat testis, macrophages belong to one of two subsets differentiated by expression or lack of expression of the resident macrophage surface antigen recognized by monoclonal antibody ED2. Local regulation of the testicular macrophage subsets was investigated in normal and 4-wk experimentally cryptorchid adult rats with and without s.c. testosterone implants (T-implants). Macrophage subsets ED2(+) (resident-type) and ED2(-) (monocyte-like) were identified immunohistochemically and counted in perfusion-fixed frozen testis sections. Depletion of the spermatogenic cells by cryptorchidism had no effect on testicular macrophage numbers. Inhibition of Leydig cell and seminiferous tubule function by low-dose (3 cm) T-implants caused a 40% reduction in ED2(+) resident macrophages in both scrotal and abdominal testes. High-dose (24 cm) T-implants, which inhibit Leydig cell function while maintaining normal seminiferous tubule function, also reduced the number of resident macrophages by approximately 40%, although this reduction was at least partially prevented in the abdominal testes. In the scrotal testis only, the ED2(-) monocyte/macrophage subset was significantly reduced in number by low-dose, but not high-dose, T-implants. The concentration of the Leydig cell-secreted cytokine macrophage-migration inhibitory factor (MIF) in testicular fluid was reduced by cryptorchidism, but not by the T-implants. When data from all experimental groups were combined, ED2(+) resident macrophage numbers showed a significant positive correlation with parameters of Leydig cell function (serum LH and testicular testosterone levels) but a negative correlation with MIF levels. This study indicates that Leydig cells regulate testicular macrophage numbers directly, rather than via an effect upon the seminiferous epithelium, in the adult rat testis. The data also suggest that testosterone and MIF play only a minor role, if any, in this regulation.

Restoration of Leydig cells after repeated administration of ethane dimethanesulfonate in adult rats

Adult male rats were repeatedly treated with ethane dimethanesulfonate (EDS), an agent known to destroy Leydig cells selectively. Following a second injection, changes in serum testosterone levels and histological and morphometric changes of Leydig cells showed the time course to be similar to those after the first treatment. The number and volume of Leydig cells markedly decreased at day 2, began to increase from day 7, and recovered to the values of the control rats at day 30, concomitant with the changes of serum testosterone levels. Cells in the interstitial tissue labeled with bromodeoxyuridine markedly increased in number at day 2, gradually decreased thereafter, and returned to the values of the controls at day 14. During this period, cells undergoing mitosis were seen, their type unable to be determined, but were presumed to be regenerating Leydig cells. Even 30 days following four treatments with intervals of 30 days each, serum testosterone levels were the same as those in the controls. Also the numerical and volume densities of Leydig cells and the volume of an average Leydig cell were the same as those of the controls. Mitosis was observed in mature Leydig cells at this period, if any. It appears that new Leydig cells began to proliferate by division earlier than 14 days after EDS, allowing that there were several stages of proliferation, and that the source of reappearing Leydig cells may not be a limited number of precursor cells, implying the presence of stem cells for Leydig cells.

Effect of seminiferous tubule size on hCG-induced regeneration of peritubular Leydig cells in hypophysectomized, EDS-treated rats

Following their selective destruction 3 weeks previously by administration of ethane dimethanesulphonate (EDS) the regenerative capacity of Leydig cells was assessed in relation to seminiferous tubule morphology in hypophysectomized adult rats administered 7 daily injections of 100 iu hCG. Total Leydig cell volume per testis in hCG-treated rats (30.2 +/- 3.2 microliters, mean +/- SEM) was significantly (p < 0.01) greater than in the testes of rats at 3 and 4 weeks after EDS-treatment (7.6 +/- 0.7 and 22.7 +/- 1.4 microliters, respectively). Regeneration of Leydig cells in hCG-treated rats significantly (p < 0.05) favoured peritubular locations (18.6 +/- 2.8 microliters/testis) compared to central or perivascular sites of origin (11.6 +/- 1.2 microliters/testis). Partial restoration of spermatogenesis occurred in hCG-treated rats (tubule diameters usually > 250 microns) and a significant inverse correlation was found between peritubular Leydig cell percentage, or total volume per testis, and the volumetric proportion of seminiferous tubules (r = -0.94, p < 0.001) or the seminiferous epithelium (r = -0.73 to -0.79, p < 0.05-0.01). No significant (p > 0.4-0.9) correlation existed between centrally-regenerated Leydig cells and these parameters. The results show that in response to hCG stimulation, Leydig cells are more likely to develop around smaller seminiferous tubules, suggesting that hCG alone cannot mimic the expected pattern of Leydig cell regeneration (central and peritubular origins) which occurs during normal sexual maturation or at 3-4 weeks after EDS treatment. It is concluded that other factors, possibly FSH, are required for typical Leydig cell development which in turn may be influenced by local cellular growth factors originating from either the seminiferous tubules or the adjacent intertubular tissue.

Isolation of rat Leydig cells and precursor forms after administration of ethane dimethane sulfonate

The cytotoxic drug ethane dimethane sulfonate (EDS) has been extensively used as a means of studying the regeneration of Leydig cells in the adult rat testis. This study used the EDS-treated rat testis as a source of material for the isolation of regenerating Leydig cells and their precursors and describes the procedures required for the isolation of these cell preparations. As early as 13-15 days after EDS, cells in the precursor fraction can bind low, but detectable, levels of iodinated purified human chorionic gonadotropin. However, no luteinizing hormone (LH) response was detected in terms of steroid production. The precursor fraction of cells isolated from the EDS-treated rat testis 17-19 days after the administration of EDS was heterogeneous in light-microscopic appearance, but identifiable Leydig-like cells were present. The cells in this fraction were the first to exhibit the ability to respond to LH with the production of detectable levels of the reduced androgen, 5 alpha-androstane-3 alpha,17 beta-diol. The amount of androgen produced by both the Leydig cell and precursor fractions had increased by 21 days after EDS and reached the levels produced by immature adultlike Leydig cells, which can be isolated from the 20-day-old rat testes. These studies demonstrate that steroidogenically responsive precursor forms of Leydig cells can be isolated from the EDS-treated testes 17-19 days after depletion of the adult Leydig cell population.

Resumption of testicular activity in Gobius paganellus after administration of ethane 1,2-dimethane sulfonate (EDS)

1. The effect of a single injection of ethane-1,2-dimethane sulfonate (EDS) was studied in the teleost fish, Gobius paganellus in two different periods of the year. 2. During June EDS did not induce any change, while during December the drug was highly effective in promoting testicular activity. 3. Nucleus/cytoplasm ratio of interstitial cells strongly decreased concomitantly with the detection of high testicular androgen levels. 4. The germinal compartment was well developed showing the appearance of all spermatogenic stages and the cavity of lobular compartments filled of spermatozoa. 5. Our data are the first evidence of a stimulatory activity of EDS on testes of a vertebrate species.

The physiology of testicular inhibin and related proteins

The roles of inhibin and related proteins in the male remain unclear, although it is becoming increasingly evident that they play a part in FSH regulation and testicular function, including spermatogenesis. The difficulties associated with these questions have been the limited availability of inhibin and related proteins for in vivo studies, the absence of specific assay methods, and the unclear relationship of inhibin and testosterone in the regulation of FSH secretion. With the availability of human recombinant preparations and the current development of new assays, it is anticipated that many of these questions will be resolved.

Effects of ethane dimethane sulphonate and orchidectomy on luteinizing hormone secretion

Abstract The aim of this study was to determine whether testicular products of non-Leydig cell origin modulate rat luteinizing hormone (LH) secretion in vivo. We therefore compared the effects of ethane dimethane sulphonate (EDS), a toxin regarded as highly selective for Leydig cells, with that of bilateral orchidectomy on LH secretion in mature male Wistar rats. The intention was thereby to compare the effects of selective removal of Leydig cells with that of removing both Leydig cells and seminiferous tubules, respectively. Following a single dose of EDS (75 mg/kg, ip), plasma LH concentrations rose equally with those of castrated rats for the first 3 days. After that time, however, plasma LH concentrations in the EDS-treated rats fell progressively below those of the orchidectomized rats despite the continuing castrate level of circulating testosterone until Day 17. The effects of EDS treatment or orchidectomy on pulsatile LH secretion were then compared after 11 days to castrate levels of testosterone. EDS-treated rats demonstrated reduced LH pulse amplitude, mean plasma LH levels and net LH secretion compared with castrate rats, although LH pulse frequency was unaltered. However, a further group of rats treated with EDS and orchidectomized failed to demonstrate that these changes were fully reversed by the castration and therefore EDS may have direct effects upon pituitary LH secretion. In order to determine the mechanism of the reduced LH pulse amplitude after EDS treatment, a further study was conducted to determine whether EDS treatment resulted in reduced pituitary sensitivity to gonadotropin-releasing hormone (GnRH). Responsiveness of pituitary LH to exogenous GnRH (0.01 to 10 mug/kg body wt) was studied 11 days after removal of testicular testosterone feedback by either EDS or castration. Plasma LH response was linearly related to the log of the GnRH dose. At 10 min after GnRH administration, the plasma LH response in EDS-treated rats was less sensitive than in castrate rats. We conclude that the lesser augmentation of LH secretion between Days 3 and 17 after EDS treatment compared with castrate rats cannot be explained solely by changes in Leydig cell secretion but may involve direct effects of EDS on pituitary LH secretion or non-Leydig cell testicular products. Dampening of LH pulse amplitude without change in LH pulse frequency together with the reduced sensitivity to GnRH in EDS-treated rats suggests that this toxin may have direct effects on pituitary LH secretion independent of its effects on Leydig cell function.

Morphological and hormonal changes in the frog, Rana esculenta, testis after administration of ethane dimethane sulfonate

Apart from mice, in rodents ethane dimethane sulfonate (EDS) selectively destroys Leydig cells. This has been indicated as a new method for the study of seminiferous interstitial compartment interaction. No information on the possible destruction and repopulation of Leydig cells exists in lower vertebrates. This study deals with EDS effects in the frog, Rana esculenta. Animals received a single intraperitonial dose (100 mg/kg body wt) and were sacrificed at 0, 12, and 24 hr and 3, 4, 7, 14, and 28 days postinjection. Androgens (testosterone + DHT) were measured in plasma and right testes. Moreover, left testes were fixed and examined for histological observation. Plasma androgen levels were extremely low on Day 4 after EDS treatment and remained unchanged thereafter. In testes, androgen levels decreased on Day 4 but increased to control levels on Day 14. Leydig cells were damaged within 3 days post-treatment and were completely destroyed on Days 4 and 5. Germinal compartment damage appeared only where the adjacent interstitial tissue presented complete destruction. Pale primary spermatogonia (stem cells) were always present. Testes restored to normal on Day 14 and spermatogenesis resumed to the regenerating interstitial tissue. These results show that regenerating testes in R. esculenta retain androgens and that interstitial-germinal compartment communications may have a role in maintaining spermatogenesis.

Cell-cell interactions in the control of spermatogenesis as studied using Leydig cell destruction and testosterone replacement

This review centers around studies which have used ethane dimethane sulphonate (EDS) selectively to destroy all of the Leydig cells in the adult rat testis. With additional manipulations such as testosterone replacement and/or experimental induction of severe seminiferous tubule damage in EDS-injected rats, the following questions have been addressed: 1) What are the roles and relative importance of testosterone and other non-androgenic Leydig cell products in normal spermatogenesis and testicular function in general? 2) What are the factors controlling Leydig cell proliferation and maturation? 3) Is it the Leydig cells or the seminiferous tubules (or both) which control the testicular vasculature? The findings emphasize that in the normal adult rat testis there is a complex interaction between the Leydig cells, the Sertoli (and/or peritubular) cells, the germ cells, and the vasculature, and that testosterone, but not other Leydig cell products, plays a central role in many of these interactions. The Leydig cells drive spermatogenesis via the secretion of testosterone which acts on the Sertoli and/or peritubular cells to create an environment which enables normal progression of germ cells through stage VII of the spermatogenic cycle. In addition, testosterone is involved in the control of the vasculature, and hence the formation of testicular interstitial fluid, presumably again via effects on the Sertoli and/or peritubular cells. When Leydig cells regenerate and mature after their destruction by EDS, it can be shown that both the rate and the location of regenerating Leydig cells is determined by an interplay between endocrine (LH and perhaps FSH) and paracrine factors; the latter emanate from the seminiferous tubules and are determined by the germ cell complement. Taken together with other data on the paracrine control of Leydig cell testosterone secretion by the seminiferous tubules, these findings demonstrate that the functions of all of the cell types in the testis are interwoven in a highly organized manner. This has considerable implications with regard to the concentration of research effort on in vitro studies of the testis, and is discussed together with the need for a multidisciplinary approach if the complex control of spermatogenesis is ever to be properly understood.

Stimulation of the proliferation and differentiation of Leydig cell precursors after the destruction of existing Leydig cells with ethane dimethyl sulphonate (EDS) can take place in the absence of LH

In hypophysectomized rats, 2 days after the administration of the cytotoxic drug ethane dimethyl sulphonate (EDS), the proliferative activity of Leydig cell precursors increased six-fold. Thus, factors other than LH act locally to stimulate the proliferation of precursor cells after EDS. Twenty-six days after EDS administration, neither cells with the morphological characteristics of Leydig cells nor histochemical enzyme activities, such as 3 beta-HSD and alpha-naphtyl esterase, could be detected in testis tissue. In hypophysectomized rats treated daily with hCG (100 iu) for 7 days, starting at 26 days after EDS, the number of Leydig cells was increased to 48 +/- 11 cells (per 1000 Sertoli cells), which is approximately 4.5% of the intact control level. 3 beta-HSD and alpha-naphtyl esterase activity could be detected, and plasma testosterone levels had increased 15-fold compared with the hypophysectomized controls. These results show that proliferation and some differentiation of precursor cells along the Leydig cell lineage can occur independent of LH, but the final stages of the differentiation process require hCG stimulation.

The testes of moles (Talpa europaea) retain a considerable microsomal capacity for androgen synthesis during seasonal regression

Seasonal changes in testicular histology and steroidogenesis were investigated in the mole (Talpa europaea). Androgen synthesis was examined by incubating [4-14C]pregnenolone (P) and [4-14C]dehydroepiandrosterone (DHA) with testicular minces in a static incubation system. The metabolites formed were characterized by thin-layer chromatography. Morphological changes were studied by routine histological methods. During sexual quiescence spermatogenesis was arrested. The regressive seminiferous tubules consisted predominantly of Sertoli cells and spermatogonia. On the other hand, histological quantification suggested that season has no significant effects on the number or the nuclear dimensions of Leydig cells in this species. The capacity of the regressive testes (per unit weight) to metabolize P and DHA to testosterone (T) was somewhat greater in regressive (48.5%, 49.4%) than in active (33.2%, 41.6%) testes. The results also suggest that the greater in vitro T production encountered during reproductive quiescence is due possibly to an increase in the activity of 17 beta-hydroxysteroid dehydrogenase (per unit weight). Our data on Leydig cell numbers indicate, however, that the capacity of the individual Leydig cells to produce T is decreased during sexual regression. T. europaea appears to be quite exceptional among seasonally breeding small mammals exhibiting pronounced annual changes in spermatogenesis in that the testes retain a considerable enzymatic capacity to produce testosterone from pregnanes during sexual quiescence. The results suggest that pituitary as well as paracrine regulation of the annual testicular cycle in this species differs from that generally encountered in seasonal breeders.

Inhibin secretion is influenced by Leydig cells: evidence from studies using the cytotoxin ethane dimethane sulphonate (EDS)

Adult male rats given a single intraperitoneal injection of the Leydig cell cytotoxin ethane dimethane sulphonate (EDS) show a significant decrease in testosterone from 7 to 14 days, and elevation of serum FSH and LH levels commencing 7 days after treatment, returning to normal at 28 days for LH and 49 days for FSH. A significant rise in serum inhibin levels was seen at day 14 after EDS treatment with levels returning to normal at day 49. In a second series of experiments, silastic implants of testosterone, either 2.5 cm or 22.5 cm in length, were introduced subcutaneously into adult male rats which were treated with EDS 10 days later. Both doses of testosterone suppressed basal LH levels but did not significantly change FSH levels. The rise in FSH and LH levels seen in normal rats after EDS treatment did not occur in either group of testosterone-implanted rats. However, serum inhibin levels rose significantly in both groups after EDS treatment, suggesting that the rise in serum inhibin levels was not due to stimulation arising from the increase in FSH levels after EDS treatment. The data suggest that the rise in serum inhibin levels after EDS treatment is linked to destruction of the Leydig cells through mechanisms that require further investigation.

Plasma inhibin levels in men with chemotherapy-induced severe damage to the seminiferous epithelium

Immunoreactive plasma inhibin levels and free testosterone index (FTI) were estimated in 17 patients who had previously received combination chemotherapy for Hodgkin's disease and in 16 age-matched controls. In the same patients we had previously found significantly raised FSH and LH levels in the presence of normal basal and HCG-stimulated total testosterone levels. Mean plasma inhibin levels were not different between the patients (601 +/- 321 U/l) and controls (530 +/- 174 U/l) nor were FTI values (81.5 +/- 35 vs 91 +/- 47 respectively). There was a positive correlation (r = 0.53, P less than 0.05) between FSH and inhibin levels and a negative correlation between FSH and FTI (r = -0.51, P less than 0.05) in the patients but not in the controls. No such correlations with inhibin or FTI existed for LH but there was a positive correlation between LH and FSH levels in the patients. In four patients inhibin levels were pathologically raised and in this group mean FSH values (21.7 +/- 4.7 IU/l) were higher (P less than 0.001) and mean FTI (59.1 +/- 22.6) lower (P less than 0.001) than respective values (13.6 +/- 5.3 IU/l and 88.4 +/- 35) for the remainder of the patients. These data are not compatible with the hypothesis that inhibin is the major negative feedback signal for the control of FSH secretion.

The regulation of the proliferation and differentiation of rat Leydig cell precursor cells after EDS administration or daily HCG treatment

The proliferation and differentiation of possible Leydig cell precursors in adult rats were studied after destruction of the existing Leydig cells with EDS or after daily treatment with hCG. After 2 days with either treatment, a 12- to 16-fold increase in the number of [3H]thymidine-incorporating interstitial cells was found. In the case of hCG treatment, this was probably due to the high plasma hCG levels. However, after EDS treatment, LH levels start to rise between days 1 and 3, suggesting a paracrine stimulation of the proliferation of interstitial cells. After hCG treatment, a substantial increase in the numbers of Leydig cells was already found at day 2. It was concluded that hCG induced a rapid differentiation, without cell division, of existing precursor cells into recognizable Leydig cells. In rats treated with both EDS and hCG, new Leydig cells were not formed during the first 10 days. This indicates that EDS destroys not only mature Leydig cells but also those Leydig cell precursors that are able to differentiate rapidly into recognizable Leydig cells.

In vitro effects of ethylene-dimethane sulfonate (EDS) on Leydig cells: inhibition of steroid production and cytotoxic effects are dependent on species and age of rat

A number of proteins in Leydig cells isolated from immature rats, mature rats and tumour tissue as well as protein in Sertoli cells, hepatocytes and blood plasma are alkylated after incubation of cells with 14C-labelled ethylene-dimethane sulfonate (EDS) for 5 h. LH-stimulated and 22R-hydroxycholesterol-supported steroid production by Leydig cells from immature and mature rats and from rat tumour tissue but not from testes of mature mice was strongly or completely inhibited after incubation with EDS. EDS had no effects on ATP levels in Leydig cells from mature rats after an incubation period of 24 h but ATP levels were almost zero after 72 h. In Leydig cells from tumour tissue the ATP level was decreased to 10% of the original value after 24 h EDS and decreased further during the following 48 h period. In Leydig cells from immature rats EDS had no effect on ATP levels after 72 h incubation. Ultrastructural evidence of cell damage by EDS was observed in cells from mature rats and tumour tissue but not in cells from immature rats. Discrepancies between biochemical and morphological indications for cell damage were noticed after 24 h incubation with EDS but not after 72 h. The results show that EDS exerts a direct inhibitory effect on both mature and immature rat Leydig cells but does not affect LH-stimulated steroid production by mouse Leydig cells. A cytotoxic response to EDS develops in rat Leydig cells during maturation. However, the molecular basis for these very specific effects of EDS on Leydig cells is at present not understood.