Evidence for Leydig cell dysfunction in rats with seminiferous tubule damage

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.

Identification and characterization of telocytes in rat testis

In this study, we investigated the localization, morphological features and cellular interactions of telocytes in the rat testicular interstitium. Transmission electron microscopy (TEM) and immunohistochemical and immunofluorescence analyses of the rat testicular interstitium showed a distinct layer of telocytes surround the seminiferous tubules along with inner layer of peritubular myoid cells. The majority of the telocytes were made up of a small cell body and moniliform prolongations that contained mitochondria and secretory vesicles. Some other telocytes were observed possessing large cell bodies. Within the testicular interstitium, the telocytes formed a network connecting peritubular myoid cells, Leydig cells as well as blood vessels. Immunohistochemical and double immunofluorescence analyses showed that rat testicular telocytes express CD34 and PDGFRα, but are negative for vimentin and α-SMA. Our findings demonstrate the presence of telocytes in the rat testicular interstitium. These cells interact with peritubular myoid cells, seminiferous tubules, Leydig cells and blood vessels via long telopode extensions, which suggests their vital role in the intercellular communication between different cell types within the rat testis.

Leydig cell insufficiency in hypospermatogenesis: a paracrine effect of activin-inhibin signaling?

Clinical findings and a variety of experimental models indicate that Leydig cell dysfunction accompanies damage to the seminiferous tubules with increasing severity. Most studies support the idea that intratesticular signaling from the seminiferous tubules to Leydig cells regulates steroidogenesis, which is disrupted when hypospermatogenesis occurs. Sertoli cells seem to play a pivotal role in this process. In this review, we summarize relevant clinical and experimental observations and present evidence to support the hypothesis that testicular activin signaling and its regulation by testicular inhibin may link seminiferous tubular dysfunction to reduced testosterone biosynthesis.

Significance of Leydig Cell Neoplasia in Rats Fed Lactitol or Lactose

Lactitol is a disaccharide sugar alcohol (polyol) which is derived from lactose by catalytic hydrogenation and which may be used as a noncariogenic, reduced calorie sugar substitute in different foods. In the context of the safety evaluation of lactitol, a chronic carcinogenicity/toxicity study was conducted in a Wistar-derived strain of rats. In addition to effects that occur commonly in rats fed high doses of polyols, an increased incidence of Leydig cell tumors was observed in rats fed a diet with 10% lactitol for their lifetime. A comparison group receiving a diet with 20% lactose exhibited the same effect. At the 5% dose level of lactitol, no testicular changes were seen. Although lactitol is not genotoxic in standard in vitro tests and was also not associated with tumor formation in female rats and mice of either sex, it was necessary to assess the relevance of the testicular neoplastic growth for human safety. A comparative evaluation of the spontaneous and chemically induced formation of Leydig cell tumors in rats and humans demonstrates that the spontaneous occurrence is extremely low in humans but rather high in rats. Chemical agents or experimental conditions that in rats are associated with interstitial cell hyperplasia or neoplasia have not been associated with similar effects in humans. This is also true for lactose which, in Western countries, is consumed regularly and in substantial amounts with dairy products. Since lactitol is essentially not hydrolyzed in the small intestine, it gains access to the metabolism only after fermentation by the intestinal flora. It is therefore reasonable to assume that the testicular effects of lactitol and lactose were mediated by changes in the digestive tract such as by the known increase of calcium absorption which occurs in lactitol- and lactose-fed rats but not in humans or by effects of these compounds on the enterohepatic cycling of steroid hormones. Although these mechanisms are not yet elucidated, the available data on Leydig cell tumors indicate that the effects seen in male rats are not relevant to humans. The major lines of evidence supporting the human safety of lactitol and lactose are: (1) the lack of genotoxicity of lactitol, (2) the rat specificity of the testicular effects of lactose and lactitol, (3) the long history of safe consumption of lactose in humans, (4) the insensitivity of the human Leydig cells to agents and conditions that are known to cause neoplastic growth of Leydig cells in rats, (5) the generally very low spontaneous incidence of Leydig cell tumors in the human population, and (6) the absence of any epidemiological evidence establishing a link between nutritional factors and the occurrence of Leydig cell tumors in humans.

Prenatal and lactation nicotine exposure affects Sertoli cell and gonadotropin levels in rats

Nicotine is largely consumed in the world as a component of cigarettes. It can cross the placenta and reach the milk of smoking mothers. This drug induces apoptosis, affects sex hormone secretion, and leads to male infertility. To investigate the exposure to nicotine during the whole intrauterine and lactation phases in Sertoli cells, pregnant rats received nicotine (2 mg/kg per day) through osmotic minipumps. Male offsprings (30, 60, and 90 days old) had blood collected for hormonal analysis (FSH and LH) and their testes submitted for histophatological study, analysis of the frequency of the stages of seminiferous epithelium cycle, immunolabeling of apoptotic epithelial cells (TUNEL and Fas/FasL), analysis of the function and structure of Sertoli cells (respectively using transferrin and vimentin immunolabeling), and analysis of Sertoli-germ cell junctional molecule (β-catenin immunolabeling). The exposure to nicotine increased the FSH and LH plasmatic levels in adult rats. Although nicotine had not changed the number of apoptotic cells, neither in Fas nor FasL expression, it provoked an intense sloughing of epithelial cells and also altered the frequency of some stages of the seminiferous epithelium cycle. Transferrin and β-catenin expressions were not changed, but vimentin was significantly reduced in the early stages of the seminiferous cycle of the nicotine-exposed adult rats. Thus, we concluded that nicotine exposure during all gestational and lactation periods affects the structure of Sertoli cells by events causing intense germ cell sloughing observed in the tubular lumen and can compromise the fertility of the offspring.

Transcriptome profiling of mice testes following low dose irradiation

BACKGROUND

Radiotherapy is used routinely to treat testicular cancer. Testicular cells vary in radio-sensitivity and the aim of this study was to investigate cellular and molecular changes caused by low dose irradiation of mice testis and to identify transcripts from different cell types in the adult testis.

METHODS

Transcriptome profiling was performed on total RNA from testes sampled at various time points (n = 17) after 1 Gy of irradiation. Transcripts displaying large overall expression changes during the time series, but small expression changes between neighbouring time points were selected for further analysis. These transcripts were separated into clusters and their cellular origin was determined. Immunohistochemistry and in silico quantification was further used to study cellular changes post-irradiation (pi).

RESULTS

We identified a subset of transcripts (n = 988) where changes in expression pi can be explained by changes in cellularity. We separated the transcripts into five unique clusters that we associated with spermatogonia, spermatocytes, early spermatids, late spermatids and somatic cells, respectively. Transcripts in the somatic cell cluster showed large changes in expression pi, mainly caused by changes in cellularity. Further investigations revealed that the low dose irradiation seemed to cause Leydig cell hyperplasia, which contributed to the detected expression changes in the somatic cell cluster.

CONCLUSIONS

The five clusters represent gene expression in distinct cell types of the adult testis. We observed large expression changes in the somatic cell profile, which mainly could be attributed to changes in cellularity, but hyperplasia of Leydig cells may also play a role. We speculate that the possible hyperplasia may be caused by lower testosterone production and inadequate inhibin signalling due to missing germ cells.

Histological and hormonal testicular function in oligo/azoospermic infertile men

We characterised and correlated the histological and hormonal aspects of a cohort of 261 azo/oligozoospermic men, applying a quantitative/qualitative evaluation of testicular tissue and serum and intratesticular hormonal measurements. One hundred and 93 azo⁄oligozoospermic patients were diagnosed as: complete sertoli cell only syndrome (cSCOS), n = 76; focal SCOS, n = 31; maturation arrest, n = 34; hypospermatogenesis, n = 17; mixed atrophy, n = 25; and severe atrophy, n = 10. Normal spermatogenesis was observed in 68 infertile men (controls). Patients with cSCOS, focal SCOS, mixed and severe atrophy had larger LC/clusters (11.5; 11.0; 10.7; 18.9 LC/cluster) than controls (6 LC/cluster; P < 0.001). cSCOS, focal SCOS, mixed and severe atrophy patients had higher FSH, LH and lower T/LH ratio serum levels than the other groups. Intratesticular testosterone concentrations were higher in tissues with complete or focal SCOS (45.6 ng mg(-1) protein) and mixed atrophy (79.0 ng mg(-1) protein) than normal tissues (20.3 ng mg(-1) protein; P = 0.03 and P = 0.007). Considering all subjects, significant correlations were found between T/LH ratio and Leydig cells/cluster (r = 0.510, P < 0.001), FSH levels (r = -0.692, P < 0.001) and with intratesticular testosterone (r = -0.354, P = 0.001); these correlations follow the pattern of severity of spermatogenic damage. By a thorough histological evaluation, we validate the concept that the severity of spermatogenic impairment is associated with major morphological and functional disturbance of the Leydig cell compartment.

Impaired male fertility and atrophy of seminiferous tubules caused by haploinsufficiency for Foxa3

Foxa1, 2 and 3 (formerly HNF-3alpha, -beta and -gamma) constitute a sub-family of winged helix transcription factors with multiple roles in mammalian organ development. While all three Foxa mRNAs are present in endoderm derivatives including liver and pancreas, only Foxa3 is expressed in the testis. Here we demonstrate by genetic lineage tracing that Foxa3 is expressed in postmeiotic germ and interstitial Leydig cells. The germinal epithelium of Foxa3-deficient testes is characterized by a loss of germ cells secondary to an increase in germ cell apoptosis that ultimately leads to a Sertoli cell-only syndrome. Remarkably, not only the Foxa3(-/-) mice but also Foxa3(+/-) mice exhibited loss of germ cells. This cellular phenotype caused significantly reduced fertility and testis weight of both Foxa3(-/-) and Foxa3(+/-) mice. Using microarray analysis, we found a dramatic downregulation of the zinc finger protein 93 and the testicular tumor-associated paraneoplastic Ma antigen (PNMA) and increased expression of a number of genes including zinc finger protein 94 and several kallikrein 1-related peptidases which could account for at least part of the observed phenotype. In summary, we have identified Foxa3 as a transcriptional regulator with a dominant phenotype in germ cell maintenance and suggest FOXA3 as a potential candidate gene for subfertility in man.

Effects of gamma radiation on luteinizing hormone (LH) receptor expression, signal transduction and steroidogenesis in cultured rat Leydig cells

PURPOSE

To investigate the dose-dependent effects of gamma radiation on rat Leydig cell luteinizing hormone (LH) receptor expression, signal transduction and steroidogenesis.

MATERIALS AND METHODS

Leydig cells isolated from testicles of adult male albino rats were cultured and exposed to different doses (2, 4, 6, 8 and 10 Gy) of fractioned gamma radiation for three days. Normal as well as irradiated cells were used for the quantification of cell surface LH receptor or LH/cyclic adenosine monophosphate (cAMP) stimulation test or total ribonucleic acid (RNA) isolation to study the LH receptor messenger RNA (mRNA) expression by reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

Radiation was found to have dose-dependent effects on rat Leydig cell surface LH receptor, basal and LH-stimulated cAMP production, basal, LH and cAMP-stimulated steroidogenesis. Lower doses (2 and 4 Gy) of radiation did not induce any change, whereas higher doses (6, 8 and 10 Gy) of radiation exposure diminished the above said parameters significantly. In spite of the low level of cell surface LH receptors following higher doses of radiation exposure, its mRNA level was not altered under any dose level.

CONCLUSION

From these observations, it is concluded that gamma radiation has dose-dependent inhibitory effects on Leydig cell LH signal transduction and steroidogenesis. Decreased cell surface LH receptor following higher doses of radiation exposure is not coupled with altered LH receptor mRNA level.

A repository of ENU mutant mouse lines and their potential for male fertility research

Many of the proteins and their encoding genes involved in spermatogenesis are unknown, making the specific diagnosis and treatment of infertility in males difficult and highlighting the importance of identifying new genes that are involved in spermatogenesis. Through genome-wide chemical mutagenesis using N-ethyl-N-nitrosourea (ENU) and a three-generation breeding scheme to isolate recessive mutations, we have identified mouse lines with a range of abnormalities relevant to human male fertility. Abnormal phenotypes included hypospermatogenesis, Sertoli cell-only (SCO) seminiferous tubules, germ-cell arrest and abnormal spermiogenesis and were accompanied, in some, with abnormal serum levels of reproductive hormones. In total, from 65 mouse lines, 14 showed a reproductive phenotype consistent with a recessive mutation. This study shows that it is feasible to use ENU mutagenesis as an effective and rapid means of generating mouse models relevant to furthering our understanding of human male infertility. Spermatozoa and genomic DNA from all mouse lines, including those with abnormal reproductive tract parameters, have been cryopreserved for the regeneration of lines as required. This repository will form a valuable resource for the identification and analysis of key regulators of multiple aspects of male fertility.

Actions of radiation on living cells in the "post-bystander" era

Over the past 20 years there has been increasing evidence that cells and the progeny of cells surviving a dose of ionizing radiation can exhibit a wide range of effects inconsistent with the level of dose received. Recently, the cause of these delayed effects has been ascribed to so-called bystander effects, occurring in cells not directly hit by an ionizing track, but which are influenced by signals from irradiated cells. These effects are not necessarily deleterious, although most of the literature deals with adverse delayed effects. What is important to consider is what, if anything, these effects mean for what is still the central dogma of radiobiology and radiation protection, i.e., that DNA double-strand breaks are the primary radiation-induced lesion that can be quantifiably related to received dose, and which determine the probability that a cancer will result from a radiation exposure. In this chapter we review the history of radiation biology which led to the DNA paradigm. We explore the issues and the evidence which are now challenging the view that dose deposition in DNA is all important. We conclude that in the low-dose region, the primary determinant of radiation exposure outcome is the genetic and epigenetic background of the individual and not the dose. This effectively dissociates dose from effect as a quantitative relationship, but it does not necessarily mean that the effect is unrelated to DNA damage somewhere in the system.

Infertility with defective spermatogenesis and hypotestosteronemia in male mice lacking the androgen receptor in Sertoli cells

Androgens and the androgen receptor (AR) play important roles in male fertility, although the detailed mechanisms, particularly how androgen/AR influences spermatogenesis in particular cell types, remain unclear. Using a Cre-Lox conditional knockout strategy, we generated a tissue-specific knockout mouse with the AR gene deleted only in Sertoli cells (S-AR(-/y)). Phenotype analyses show the S-AR(-/y) mice were indistinguishable from WT AR mice (B6 AR(+/y)) with the exception of testes, which were significantly atrophied. S-AR(-/y) mice were infertile, with spermatogenic arrest predominately at the diplotene premeiotic stage and almost no sperm detected in the epididymides. S-AR(-/y) mice also have lower serum testosterone concentrations and higher serum leuteinizing hormone concentrations than B6 AR(+/y) mice. Further mechanistic studies demonstrated that S-AR(-/y) mice have defects in the expression of anti-Müllerian hormone, androgen-binding protein, cyclin A1, and sperm-1, which play important roles in the control of spermatogenesis and/or steroidogenesis. Together, our Sertoli cell-specific AR knockout mice provide in vivo evidence of the need for functional AR in Sertoli cells to maintain normal spermatogenesis and testosterone production, and ensure normal male fertility.

Differential regulation of endobiotic-oxidizing cytochromes P450 in vitamin A-deficient male rat liver

1. The hepatic CYP4A-dependent omega-hydroxylation of arachidonic acid and CYP2C11-dependent 2alpha-/16alpha-hydroxylations of testosterone were decreased to 74 and 60% of respective control in microsomal fractions from vitamin A-deficient rats. Decreases in the rates of arachidonic acid omega-1-hydroxylation and testosterone 6beta-, 7alpha- and 17alpha-hydroxylations were less pronounced. 2. Corresponding decreases in microsomal CYP4A and CYP2C11 immunoreactive protein expression to 64 and 68% of respective control were observed in vitamin A-deficient rat liver. Expression of CYP3A proteins was unchanged from vitamin A-adequate control. 3. Northern analysis revealed a selective decrease in CYP4A2 mRNA expression in vitamin A-deficient rat liver to approximately 5% of control; expression of the related CYP4A1/4A3 mRNAs was not decreased. CYP2C11 mRNA expression was also decreased in vitamin A-deficient male rat liver to 39% of control levels. 4. Intake of the deficient diet containing all-trans-retinoic acid (ATRA) during the final week of the experiment restored CYP4A2 mRNA and CYP4A protein. Administration of exogenous androgen or episodic growth hormone was ineffective. In contrast, CYP2C11 expression was restored by ATRA and androgen, but not by growth hormone. 5. From these studies it emerges that CYP4A2, a fatty acid omega-hydroxylase in rat liver, is highly dependent on vitamin A for optimal expression, whereas CYP2C11 is indirectly down regulated by androgen deficiency resulting from vitamin A-deficiency. Altered CYP expression in vitamin A-deficiency provides insights into the relationship between dietary constituents and the intracellular formation of vasoactive eicosanoids as well as the clearance of androgenic steroids.

Multiple effects of retinoids on the development of Sertoli, germ, and Leydig cells of fetal and neonatal rat testis in culture

We investigated the effect of retinoids on the development of Sertoli, germ, and Leydig cells using 3-day culture of testes from fetuses 14.5 and 18.5 days post-conception (dpc) and from neonates 3 days postpartum (dpp). Addition of 10(-6) M and 3.10(-8) M retinoic acid (RA) caused a dose-dependent disruption of the seminiferous cords in 14.5-day-old fetal testes, without any change in the 5-bromo-2'-deoxyuridine (BrdU) labeling index of the Sertoli cells. RA caused no disorganization of older testes, but it did cause hyperplasia of the Sertoli cells in 3-dpp testes. Fragmentation of the Sertoli cell DNA was not detected in control or RA-treated testes at any age studied. The cAMP produced in response to FSH was significantly decreased in RA-treated testes for all studied ages. Both 10(-6) M and 3.10(-8) M RA dramatically reduced the number of gonocytes per 14.5-dpc testis. This resulted from a high increase in apoptosis, which greatly exceeded the slight increase of mitosis. RA caused no change in the number of gonocytes in testes explanted on 18.5 dpc (the quiescent period), whereas it increased this number in testes explanted on 3 dpp (i.e., when gonocyte mitosis and apoptosis resume). Lastly, RA and retinol (RE) reduced both basal and acute LH-stimulated testosterone secretion by 14.5-dpc testis explants, without change in the number of 3beta-hydroxysteroid dehydrogenase-positive cells per testis. Retinoids had no effect on basal or LH-stimulated testosterone production by older testes. In conclusion, RE and RA are potential regulators of the development of the testis and act mainly negatively during fetal life and positively during the neonatal period on the parameters we have studied.

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)

Colony-stimulating factor-1 plays a major role in the development of reproductive function in male mice

Colony-stimulating factor-1 (CSF-1) is the principal regulator of cells of the mononuclear phagocytic lineage that includes monocytes, tissue macrophages, microglia, and osteoclasts. Macrophages are found throughout the reproductive tract of both males and females and have been proposed to act as regulators of fertility at several levels. Mice homozygous for the osteopetrosis mutation (csfm[op]) lack CSF-1 and, consequently, have depleted macrophage numbers. Further analysis has revealed that male csfm(op)/csfm(op) mice have reduced mating ability, low sperm numbers, and 90% lower serum testosterone levels. The present studies show that this low serum testosterone is due to reduced testicular Leydig cell steroidogenesis associated with severe ultrastructural abnormalities characterized by disrupted intracellular membrane structures. In addition, the Leydig cells from csfm(op)/ csfm(op) males have diminished amounts of the steroidogenic enzyme proteins P450 side chain cleavage, 3beta-hydroxysteroid dehydrogenase, and P450 17alpha-hydroxylase-lyase, with associated reductions in the activity of all these steroidogenic enzymes, as well as in 17beta-hydroxysteroid dehydrogenase. The CSF-1-deficient males also have reduced serum LH and disruption of the normal testosterone negative feedback response of the hypothalamus, as demonstrated by the failure to increase LH secretion in castrated males and their lack of response to exogenous testosterone. However, these males are responsive to GnRH and LH treatment. These studies have identified a novel role for CSF-1 in the development and/or regulation of the male hypothalamic-pituitary-gonadal axis.

Leydig cell hyperplasia and adenoma formation: mechanisms and relevance to humans

Leydig cell adenomas are observed frequently in studies evaluating the chronic toxicity of chemical agents in laboratory animals. Doubts have been raised about the relevance of such responses for human risk assessment, but the question of relevance has not been evaluated and presented in a comprehensive manner by a broad group of experts. This article reports the consensus conclusions from a workshop on rodent Leydig cell adenomas and human relevance. Five aspects of Leydig cell biology and toxicology were discussed: 1) control of Leydig cell proliferation; 2) mechanisms of toxicant-induced Leydig cell hyperplasia and tumorigenesis; 3) pathology of Leydig cell adenomas; 4) epidemiology of Leydig cell adenomas; and 5) risk assessment for Leydig cell tumorigens. Important research needs also were identified. Uncertainty exists about the true incidence of Leydig cell adenomas in men, although apparent incidence is rare and restricted primarily to white males. Also, surveillance databases for specific therapeutic agents as well as nicotine and lactose that have induced Leydig cell hyperplasia or adenoma in test species have detected no increased incidence in humans. Because uncertainties exist about the true incidence in humans, induction of Leydig cell adenomas in test species may be of concern under some conditions. Occurrence of Leydig cell hyperplasia alone in test species after lifetime exposure to a chemical does not constitute a cause for concern in a risk assessment for carcinogenic potential, but early occurrence may indicate a need for additional testing. Occurrence of Leydig cell adenomas in test species is of potential concern as both a carcinogenic and reproductive effect if the mode of induction and potential exposures cannot be ruled out as relevant for humans. The workgroup focused on seven hormonal modes of induction of which two, GnRH agonism and dopamine agonism, were considered not relevant to humans. Androgen receptor antagonism, 5 alpha-reductase inhibition, testosterone biosynthesis inhibition, aromatase inhibition, and estrogen agonism were considered to be relevant or potentially relevant, but quantitative differences may exist across species, with rodents being more sensitive. A margin of exposure (MOE; the ratio of the lowest exposure associated with toxicity to the human exposure level) approach should be used for compounds causing Leydig cell adenoma by a hormonal mode that is relevant to humans. For agents that are positive for mutagenicity, the decision regarding a MOE or linear extrapolation approach should be made on a case-by-case basis. In the absence of information about mode of induction, it is necessary to utilize default assumptions, including linear behavior below the observable range. All of the evidence should be weighed in the decision-making process.

Temperature and germ cell regulation of Leydig cell proliferation stimulated by Sertoli cell-secreted mitogenic factor: a possible role in cryptorchidism

Local control of Leydig cell morphology and function by seminiferous tubules was suggested in previous in vivo studies, especially those that used experimental cryptorchid rat testis as a model. These studies reported changes in morphology, increases in cell number and mitotic index and decreases in testosterone formation and luteinizing hormone/human chorionic gonadotropin receptor levels of Leydig cells. However, little is known about how these changes are mediated. We recently observed that a novel Sertoli cell-secreted mitogenic factor stimulated proliferation, decreased testosterone formation and luteinizing hormone/human chorionic gonadotropin receptor levels, and dramatically altered the morphology of Leydig cells in culture. In the present studies, we demonstrate that an increase in coculture temperature from 33 to 37 degrees C increased [3H]-thymidine incorporation (5.6- vs. 19.2-fold) and labelling index (4.3% vs. 15.8%), and accelerated proliferation (2.1- vs. 3.9-fold) of cultured immature Leydig cells. In addition, testosterone formation and luteinizing hormone/human chorionic gonadotropin receptor levels of Leydig cells cocultured with Sertoli cells were further decreased following a 4 degrees C increase in coculture temperature. This elevation in culture temperature increased both the secretion of this factor by Sertoli cells and responsiveness of Leydig cells to this factor. In addition, the presence of germ cells, especially pachytene spermatocytes, inhibited the secretion of the mitogenic factor by Sertoli cells. These temperature- and germ cell-associated effects mimicked the morphological and functional changes of Leydig cells reported following experimental cryptorchidism. These observations suggest a possible role of this Sertoli cell-secreted mitogenic factor in explaining Leydig cell changes following experimental cryptorchidism.

Evidence that α5β1 integrins mediate Leydig cell binding to fibronectin and enhance Leydig cell proliferation stimulated by a Sertoli cell-secreted mitogenic factor in vitro

We reported previously that coculture of immature rat Sertoli cells with Leydig cells or the addition of a concentrate from Sertoli cell-conditioned medium (SCCM) stimulated Leydig cell [(3)H]-thymidine incorporation, increased cell number, and altered Leydig cell morphology (Wu and Murono, 1994). In the present studies, the effect of various extracellular matrix proteins on immature Leydig cell binding, proliferation and response to SCCM concentrate was investigated. Pretreatment of culture wells with 50 μg/mL collagen I or 10 μg/mL laminin inhibited Leydig cell binding to culture wells about 95 and 89%, respectively; however, 5 μg/mL fibronectin did not change the level of attachment. The binding of Leydig cells to fibronectin was reduced by antifibronectin or-β1 integrin antibodies (66 and 91%, respectively). Treatment of culture wells with five or 50 μg/mL fibronectin alone increased [(3)H]thymidine incorporation about twofold. When Leydig cells were cultured in wells precoated with increasing concentrations of fibronectin and then treated with SCCM concentrate for 2 d, [(3)H]-thymidine incorporation increased progressively with the concentration of fibronectin, beyond the levels observed with SCCM concentrate alone. This response was associated with increases in both Leydig cell number and labeling indices. When Leydig cells were cultured on fibronectin, their numbers increased by 3.7-and 5.1-fold following treatment with SCCM concentrates or coculture for 6 d, respectively; whereas, they increased 2.6- and 3.9-fold, respectively, when cultured on plastic. Labeling indices of Leydig cells cultured on plastic for 2 d and treated with SCCM or cocultured were 6.9 and 11.9%, respectively, while labeling indices of Leydig cells grown on fibronectin increased further to 17.6 and 26.3%, respectively. α5β1 integrin complexes and α5 integrin mRNA were expressed in Leydig cells, suggesting that binding to fibronectin may be mediated by α5β1 integrins, a fibronectin receptor. These results suggest that Leydig cell proliferation stimulated by a Sertoli cell-secreted mitogenic factor(s) is enhanced by Leydig cell binding fibronectin, and that this binding may be mediated by α5β1 integrins.

In vivo regulation of rat epididymal proteins by retinoids: analysis by two-dimensional electrophoresis

The role of retinoids in the regulation of epididymal fluid protein expression was investigated. We compared the patterns of two-dimensional electrophoretic gels of proteins from luminal fluids, cytosols and spermatozoa (from control rats only) of control, retinoid-depleted, retinoid-depleted retinoic acid-complemented and retinoid-depleted testosterone-supplemented rats. This study compared the luminal fluid patterns from the 4 diets and observed 13 proteins whose expression was dependent on nutritional status. Eight were either absent or very weakly expressed in retinoid-depleted animals only, while their presence was obvious in control rats and in the retinoid-deficient retinoic acid- and testosterone-complemented groups. The expression of 8 proteins was greatly enhanced in retinoid-depleted testosterone-supplemented fluids as compared to control fluids. Five of the regulated proteins seemed to be captured by spermatozoa as they were observed in sperm protein patterns of control rats. These results clearly show that the synthesis of several epididymal proteins is influenced by retinoids. Since testosterone-supplemented animals on retinoid-free diet elicited the same response as retinol and retinoic acid ones, testosterone is likely to be the mediator of retinoid action on epididymal protein synthesis. Nevertheless, the observation of one protein whose expression is stimulated by retinoic acid only and is totally independent of testosterone also favors the direct influence of this retinoid.

Identification of a stimulator of steroid hormone synthesis isolated from testis

Gonadal steroidogenesis is regulated by pituitary gonadotropins and a locally produced, unidentified factor. A 70-kilodalton (kD) protein complex secreted from rat Sertoli cells was isolated. The complex, composed of 28- and 38-kD proteins, stimulated steroidogenesis by Leydig cells and ovarian granulosa cells in a dose-dependent and adenosine 3',5'-monophosphate-independent manner. The follicle-stimulating hormone-induced 28-kD protein appeared to be responsible for the bioactivity, but the 38-kD protein was indispensable for maximal activity. The 28- and 38-kD proteins were shown to be identical to the tissue inhibitor of metalloproteinase-1 (TIMP-1) and the proenzyme form of cathepsin L, respectively. Thus, a TIMP-1-procathepsin L complex is a potent activator of steroidogenesis and may regulate steroid concentrations and, thus, germ cell development in both males and females.

A Sertoli cell-secreted paracrine factor(s) stimulates proliferation and inhibits steroidogenesis of rat Leydig cells

Previous studies have shown that disruption or damage to the seminiferous tubules by radiation, antiandrogen, vitamin A deficiency or experimental cryptorchidism causes Leydig cell hypertrophy and hyperplasia, suggesting that Sertoli cells secrete a mitogenic factor(s) that stimulates Leydig cell proliferation. To study the possible paracrine regulation of Leydig cell proliferation by Sertoli cells, highly purified Leydig cells and Sertoli cells were co-cultured in a two-chambered co-culture system. Our results revealed that co-culture of immature rat Sertoli cells with Leydig cells stimulated Leydig cell DNA synthesis by 19-fold, increased cell number by about 3.9-fold and increased the labeling index from 0.5% to 15.8%. In addition to these changes, co-culture reduced Leydig cell testosterone formation and luteinizing hormone (LH) receptor levels, and dramatically altered the morphology of Leydig cells. The addition of concentrates from Sertoli cell conditioned medium (SCCM) mimicked these biological effects. The Leydig cell mitogenic activity in SCCM was trypsin sensitive and inactivated by boiling for 2 h, suggesting that it is a protein. However, it was resistant to acid and dithiothreitol. The molecular weight of this putative factor(s) is above 10 kDa. The responsiveness of Leydig cells to this mitogenic protein(s) decreased with age, whereas the secretion of this protein(s) by Sertoli cells in culture did not change with age. The addition of 10 ng/ml of follicle stimulating hormone (FSH) dramatically decreased the mitogenic activity in SCCM, indicating that the secretion of this mitogenic factor(s) is inhibited by FSH. This paracrine factor(s) may be as yet an unidentified testicular growth factor(s) because it differs in molecular weight, stability and other characteristics from all previously reported Sertoli cell-produced or expressed growth factors.

Response of the seminiferous epithelium of the rat testis to withdrawal of androgen: evidence for direct effect upon intercellular spaces associated with Sertoli cell junctional complexes

The morphological response of the Sertoli cells to partial or complete withdrawal of testosterone was studied in adult rats following hypophysectomy or administration of ethane dimethanesulphonate (EDS), a toxicant known to destroy selectively the Leydig cells of the testis. To assess the role of germ cells in effecting changes to Sertoli cells following withdrawal of testosterone, germ cell-deficient rats with Sertoli-cell-only testes (SCO) were treated with EDS to remove the source of testosterone. At 6 days after hypophysectomy or 4, 6 and 8 days after EDS treatment, stage VII and VIII seminiferous tubules showed degenerating germ cells and numerous basally-located vacuoles approximately 1-15 microns in diameter. Ultrastructural analysis indicated that most of the vacuoles were multiple focal dilations of the intercellular space associated with Sertoli cell junctional complexes. In SCO rats, treatment with EDS resulted in a significant (P < 0.05) increase in the formation of many vacuoles particularly in the base but also in the trunk of the Sertoli cells and again electron microscopic analysis showed multiple, localized expansions of the intercellular space associated with Sertoli cell junctional complexes. The appearance of intercellular spaces in SCO testes following androgen withdrawal cannot be attributed to shrinkage of degenerating germ cells since the seminiferous tubules did not contain germ cells. It is concluded that withdrawal of androgen induces early morphological alterations of the Sertoli cell junctional complexes in which the sites of membrane fusions representing tight junctions remain intact whereas the intercellular spaces exhibit major focal dilations.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term stimulatory effect of Sertoli cell conditioned medium on Leydig cell steroidogenesis is not mediated by inhibin

Addition of concentrated rat Sertoli cell conditioned medium (rSCCM) to isolated Leydig cells from immature rats stimulated steroid production more than 13-fold within 4 h. LH-stimulated steroidogenesis was not enhanced by addition of rSCCM. The biological activity of the concentrated rSCCM was higher after incubation of Sertoli cells with FSH, whereas FSH alone did not stimulate steroid production. This effect of rSCCM was not due to inhibin, since highly purified 32 kDa rat inhibin, in doses equivalent to those present in rSCCM, had no effect on steroidogenesis during the 4 h incubation period. Furthermore, inhibin could be separated from the Leydig cell stimulating factor by anion-exchange chromatography. These results indicate a short-term paracrine control of Leydig cell steroidogenesis by Sertoli cell derived factors, which differ from inhibin.

Patchy basement membrane of rat Leydig cells shown by ultrastructural immunolabeling

Rat testes were examined by conventional and immunolabeling transmission electron microscopy. Ultrastructurally identifiable continuous basement membranes were found around seminiferous tubules and the interstitial capillaries. Patches of basement membrane were, additionally, found on free surfaces of Leydig cells, between two Leydig cells, and in macrophage-Leydig cell contact sites. The ultrastructural findings were confirmed by immunocytochemical localization of laminin and collagen type IV in the same areas. A close association between the capillary basement membranes and the surfaces of perivascular Leydig cells was also observed. The possible basement membrane-mediated interactions of Leydig cells with other testicular structures, together with the novel bioactive products and regulators of Leydig cells, support the role of these cells as exceptionally complex regulatory centers of testicular functions.

Changes of basal and steroidal precursor-stimulated testosterone secretion in isolated Mongolian gerbil and guinea pig testes after a single episode of heating

1. In the absence of steroidal precursors, testosterone secretion by Mongolian gerbil testes incubated at 37 degrees C was 340 ng/g tissue/4 hr. Addition of 1 microgram progesterone or DHEA drastically stimulated testosterone secretion by testes incubated at 37 degrees C (progesterone: 3281 ng/g tissue/4 hr, DHEA: 4654 ng/g tissue/4 hr). 2. While neither basal nor DHEA-stimulated production of testosterone was significantly affected by a single episode of heating (43-44 C for 30 min), progesterone-stimulated testosterone secretion markedly decreased during the 4-hr incubation period. 3. In contrast, in isolated testes of adult guinea pigs, a single episode of heating (44 degrees C for 30 min) resulted in a drastic reduction of basal and precursor-stimulated testosterone production during the 4-hr incubation period. 4. From these data it appears that enzymatic activities in the testes of the two species do not have their maxima at the same temperature, but rather in each case at, or close to, the temperature prevailing in the scrotal testis.

Changes in testicular and serum hormone concentrations in the male rat following treatment with m-dinitrobenzene

m-Dinitrobenzene (m-DNB)-induced testicular atrophy has been attributed to a direct effect upon the germinal epithelium. However, such degenerative changes in the germinal epithelium should induce shifts in the testicular hormonal milieu, which would in turn alter the hypothalamic-pituitary gonadal axis in general. This study evaluated the endocrine status of male rats (killed 3 hr, 24 hr, 1 week, and 2 weeks) following a single oral dose of m-DNB (32 mg m-DNB/kg). Serum and pituitary leuteinizing hormone, follicle-stimulating hormone (FSH), and protactin and hypothalamic gonadotropin-releasing hormone (GnRH) concentrations were determined. Testosterone and androgen-binding protein concentrations in serum, interstitial fluid, seminiferous tubule fluid, and caput epididymis were also determined. In vitro basal and hCG-stimulated testosterone release was determined in the decapsulated testis. Results of the present study indicate that pituitary hormone concentrations and hypothalamic GnRH were unaffected after a single oral dose of m-DNB. Serum FSH was elevated at 2 weeks. There was a transient decrease in serum testosterone at 24 hr, which returned to control values at 1 and 2 weeks. Interstitial fluid, seminiferous tubule fluid, and caput epididymal testosterone concentrations were increased at 1 and 2 weeks. Basal testosterone release in vitro was increased at 2 weeks, while hCG-stimulated testosterone release was increased at 1 and 2 weeks. Androgen-binding protein concentrations in serum and interstitial fluid were increased at 1 and 2 weeks. Androgen-binding protein was increased at 24 hr and 1 week in seminiferous tubule fluid, but returned to control concentrations by 2 weeks. However, the total tubular content of androgen-binding protein was dramatically decreased at 2 weeks. Androgen-binding protein in the caput epididymis was unaltered following m-DNB treatment. These data demonstrate that m-DNB exerts a direct effect on the testes and not through alterations in hypothalamic and pituitary control of gonadal function.

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.

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.

Variation in the effect of a nongonadotropic Leydig cell stimulating factor in testicular interstitial fluid after exposure of the testis to a single episode of heat treatment

The activity of a nongonadotropic factor present in rat testicular interstitial fluid and capable of stimulating Leydig cell testosterone production was measured at intervals for 8 weeks after exposure of the testis to a single episode of heat treatment (43 C for 15 minutes). The activity of this factor was determined using a Leydig cell bioassay and the testicular albumin space (a measure of the interstitial fluid volume) was determined after the injection of 125I-labeled bovine serum albumin. Additionally, the response of interstitial cells to hCG stimulation was measured at each time point after heat treatment. The response of interstitial cells to hCG and the activity of the interstitial fluid were both increased transiently 2 or 3 weeks after heat treatment coincident with the disruption of spermatogenesis. These data provide further evidence for the local interaction of the tubules and interstitium and imply a role for the testicular interstitial fluid factor in these local regulatory mechanisms.

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.

Regeneration of Leydig cells in unilaterally cryptorchid rats: evidence for stimulation by local testicular factors

Leydig cells in testes of adult rats were selectively destroyed by a single intraperitoneal injection of ethane dimethane sulphonate. Four days later rats were made unilaterally cryptorchid and 1, 2 and 4 weeks later the histology of the testes were examined by light microscopy and morphometry. After induction of unilateral cryptorchidism, the volume of abdominal compared to scrotal testes was reduced by 45-60% due to rapid impairment of spermatogenesis in abdominal testes. Leydig cells were not present in either scrotal or abdominal testes in the 1-week unilateral cryptorchid group. A new generation of foetal-type Leydig cells were observed in scrotal testes of the 2-week unilateral cryptorchid group although their total volume per testis estimated by morphometry, was small, being approximately 1 microliter. In contrast, the abdominal testis exhibited a remarkable proliferation of foetal-type Leydig cells (total volume per testis, 16 microliter) which predominantly surrounded the peritubular tissues of the seminiferous tubules. A similar morphology and pattern of Leydig cell development was observed in scrotal and abdominal testes of the 4-week unilateral cryptorchid group where total Leydig cell volume was 7 microliter vs 21 microliter, respectively. The results show that regeneration of a new population of Leydig cells occurs more rapidly in the abdominal testis than in the scrotal testis of the same animal. These observations suggest the possibility that augmentation of Leydig cell growth is mediated by local intratesticular stimulatory factors within the abdominal testis. Development of new Leydig cells from the peritubular tissue provides circumstantial evidence that the seminiferous tubules and in particular the Sertoli cells, are a likely source of agents that stimulate the growth of Leydig cells.

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

A single dose of ethane dimethane sulphonate (EDS) given to adult male rats has a specific destructive effects on Leydig cells, which are removed from the intertubular area by macrophages. This is associated with a decrease in testosterone (T) and a rise in serum FSH and LH for 21-28 days after EDS. Recovery of Leydig cells occurs from connective tissue precursors. This study uses the bilaterally cryptorchid rat to investigate the influence of local factors from the seminiferous tubules on the restoration of Leydig cell morphology and function. Morphometric data of intertubular tissue, hCG binding, serum T, FSH and LH levels all indicate that the Leydig cell population in cryptorchid testes is more rapidly restored from connective tissue cells when compared to the normal situation. The precise mechanism for this faster recovery will require further study.

Paracrine control of Leydig cell activity by FSH dependent proteins from Sertoli cells: an in vitro study

The regulating effect of follicle-stimulating hormone (FSH) on Leydig cell function was studied using a model of immature porcine Leydig and Sertoli cells cultured in a hormone supplemented defined medium. FSH pretreatment for 2 days of Leydig cells cultured alone was with no effect. FSH pretreatment of Leydig cells cocultured with Sertoli cells increases Leydig cell activity in an FSH dose-dependent manner with a maximal effect observed at 50 ng/ml porcine FSH (pFSH). Leydig cells cultured for 2 days in conditioned medium (CM) by FSH stimulated (FSH-CM) Sertoli cells, as compared to CM by unstimulated (control) (C-CM) Sertoli cells show an increase of their activity with a maximal effect observed at 50 ng/ml pFSH. Leydig cells cultured in CM as compared to non CM, show a marked development of organelles (smooth endoplasmic reticulum and mitochondria) involved in the steroidogenic activity. The activity of FSH-CM as compared to C-CM on Leydig cell function was non dialyzable and trypsin sensitive. These data suggest that Sertoli cells exert a regulatory action on Leydig cell steroidogenic activity via FSH dependent secreted proteins.

Dose and time related responses of the irradiated prepubertal rat testis. I. Leydig cell function

The testes of prepubertal rats were locally irradiated with 300 kVp x-rays to doses of between 1 and 15 Gy. Leydig cell function was assessed between 2 and 36 weeks post-irradiation. Dysfunction was observed at two weeks as evidenced by a reduction in serum levels of testosterone to between 40 and 70% of control, with a threshold dose of about 5 Gy. Endocrine deficiencies in the Leydig cell population were indicated at later times by increased serum levels of LH, although serum testosterone concentrations recovered to control levels. The elevations in serum LH increased with time suggesting progressive Leydig cell failure.

Stage-specific inhibition of interstitial cell testosterone secretion by rat seminiferous tubules in vitro

The stage-specific influence of the secretions from rat seminiferous tubules on the LH-stimulated testosterone production by rat Leydig cells in vitro was studied. The spent media from incubated seminiferous tubules (SMST) from stages VII-VIII of the seminiferous epithelial cycle caused about 50% inhibition of the LH-dependent testosterone production by a crude preparation of rat interstitial cells. The SMST from other stages had no effect on testosterone production. Mixed tubules of unidentified stages gave an intermediate response. When SMST from ten different stages of the seminiferous wave were compared, the most pronounced inhibitory activity was found in stages VI and VIII-XI, while SMST from stages I, VII and XIII-XIV had no inhibitory effects on interstitial cell testosterone production. No stimulation was found in this system. Prolonged incubation of the interstitial cells with SMST from stages VIII-XI resulted in loss of inhibitory activity after 12 h of incubation. Maximum inhibitory activity was noted after 3 h of incubation. The inhibitory activity of the SMST from stages VIII-XI was retained after prolonged dialysis, and was unchanged after heating the medium at 60 degrees C for 1 h. The activity did not seem to be due to the presence of proteolytic enzymes, since it was not influenced by addition of protease inhibitors. SMST from stages VIII-XI had no effect on the metabolism of [3H]testosterone added to the interstitial cell preparations. No inhibitory effect was observed when Leydig cells were incubated with dibutyryl cAMP instead of LH, suggesting an early influence on the LH-receptor-adenylate cyclase chain of events.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal irradiation increases androgen production by dispersed leydig cells of the rat

Damage to the seminiferous epithelium of the rat has been shown to decrease the concentration of serum testosterone. In these animals, compared to controls, the structure of the Leydig cells suggests hyperactivity. In an attempt to understand the functional changes at the Leydig cell level, we measured in vitro androgen production by whole testes, testicular fragments, and Leydig cell preparations. The androgen production of adult rats that had received 1.6 Gy of gamma radiation on day 20 of gestation was compared to that of nonirradiated controls. Leydig cells obtained from fetally-irradiated adult rats demonstrated increased basal (1.3 X) and LH-stimulated (4.4 X) testosterone production and increased hCG binding (4.8 X) per histochemically identified Leydig cell, as compared to cells obtained from nonirradiated control animals. Although the irradiated testicular tissue showed an increased responsiveness per mg/tissue compared to controls, basal and stimulated in vitro testosterone production per irradiated testis calculated from this data was diminished because of the five-fold decrease in testis size. In addition, the circulating levels of testosterone were reduced in irradiated animals. We suggest that fetal irradiation is associated with an increase of hCG binding and testosterone production per Leydig cell, and a decrease in the number of these Leydig cells per testis.

Interactions between immature porcine Leydig and Sertoli cells in vitro. An ultrastructural and biochemical study

Interactions between Leydig and Sertoli cells, as well as a stimulatory effect of FSH on Leydig cell activity, have been reported in many studies. In order to investigate these interactions, the ultrastructure of immature pig Leydig cells under different culture conditions has been studied. When cultured alone in a chemically defined medium, there is a marked regression of the Leydig cell smooth endoplasmic reticulum and a swelling of the mitochondria. Addition of FSH or hCG does not prevent these phenomena. Co-culturing of Leydig cells with Sertoli cells from the same animal maintains the smooth endoplasmic reticulum at the level seen in vivo and in freshly isolated Leydig cells. The addition of FSH to the co-culture stimulates its development and increases Leydig cell activity, as assessed by an increase in hCG binding sites and an increased steroidogenic response to hCG. These results suggest that Sertoli cells exert a trophic effect on Leydig cells, and that the stimulatory effect of FSH on Leydig cell function is mediated via the Sertoli cells. These results reinforce the concept of a local regulatory control of Leydig cell steroidogenesis.

Changes in testicular function induced by short-term exposure of the rat testis to heat: further evidence for interaction of germ cells, Sertoli cells and Leydig cells

This study was designed to determine the effects of a short episode of testicular heating (43 degrees C for 15 min) on spermatogenesis and Sertoli and Leydig cell function. Rats killed at intervals up to 156 days after heating were assessed by histological examination, and by measurement of serum FSH and LH, and by tests of Sertoli cell function consisting of fluid production, androgen binding protein (ABP) content of the ligated and unligated tests, together with the binding of [125I]FSH. Leydig cell function was assessed by in vitro testosterone production, serum testosterone levels and [125I]hCG binding to testes homogenates. Testis weight declined 7 days after heating to 70% of control and remained lower until 82 days, whereas epididymal weight did not decrease significantly until 26 days and also recovered by 82 days. Fluid production was significantly lower in heated testes at 26 days and returned to normal at 56 days. ABP production measured as the difference between the ABP content of ligated and unligated testes was significantly reduced at 14 and 26 days, but subsequently recovered. Serum FSH levels were significantly elevated from 14-26 days in the heat treated group and the binding of [125I]FSH was reduced at 26 days post-heating. Basal and stimulated in vitro T production was significantly increased in the heat-treated testes at 14 days and subsequently returned to normal whilst [125I]hCG binding was significantly lower in the heat-treated testes from 7-26 days. Serum T and LH did not alter significantly during the study. Primary spermatocytes and young spermatids were the most heat sensitive germ cell type and a reduction in spermatogenesis was noted from 7 to 26 days, although recovery appeared complete by 56 days and thereafter. These results demonstrate that the transient spermatogenic disruption induced by heating is accompanied by significant alterations in Sertoli and Leydig cell function which are identical to those produced in other models of spermatogenic dysfunction. The results suggest that the duration of these changes appears to correlate closely with alterations occurring in the germ cell compartment.

The secretion, measurement, and function of a testicular LHRH-like factor

In this paper we have demonstrated the presence and secretion within the testis of a factor that is immunologically distinct from LHRH, but that has receptor-binding and bioactive features similar to LHRH. The major source of this LHRH-like factor is probably the Sertoli cell and, as its site of action appears to be restricted to the Leydig cells, it is possible that it is one of the means by which the Sertoli cell has been postulated to regulate the Leydig cell. All of the available evidence suggests that the action of the LHRH-like factor on the Leydig cell is inhibitory, and it may mediate some or all of the negative effects on the Leydig cell of LH and hCG. The precise role of the LHRH-like factor, particularly under physiological conditions (i.e., low level stimulation with LH), remains to be determined, but the availability of methods for its extraction, measurement, and inactivation should enable this problem to be resolved within the near future. Moreover, the recognition that Leydig cell function may be regulated by local factors within the testis should open up new avenues of research that may lead to improved methods for the regulation of fertility in the male.

Local differences in Leydig cell morphology in the adult rat testis: evidence for a local control of Leydig cells by adjacent seminiferous tubules

In order to test the hypothesis that Leydig cell function in the adult rat testis is influenced by the surrounding tubules, Leydig cell morphology was compared in different types of interstitial areas. Triangular interstitial areas surrounded by 3 cross-sectioned tubules in nearly the same stage of spermatogenesis were chosen for quantitative light microscopy. It was found that the volume density of Leydig cells in such areas was about 30%, except when the surrounding tubules were in stages IX-X or XI-XII, when it was only about 20%. This variation in total Leydig cell mass seemed to be due to a variation in Leydig cell size and not in Leydig cell number. The largest Leydig cell profile area, 118 +/- 6 micrometers 2 (mean +/- SE n = 6 rats), was observed when the surrounding tubules were in stages VII-VIII, i.e. just prior to sperm release. The smallest Leydig cells were seen when the surrounding tubules were in stages IX-X and XI-XII (68 +/- 3 and 66 +/- 4 micrometers 2). The present results indicate that there may be a Leydig cell cycle in the adult rat testis, which is regulated by the adjacent tubules.

Raised plasma oestrogens in infertile men with elevated levels of FSH

In twenty oligospermic or azoospermic patients with elevated plasma FSH, the mean concentrations of plasma oestrone sulphate (843 +/- 233 pg/ml), oestrone (54 +/- 10.4 pg/ml) and oestradiol (46.6 +/- 12.6 pg/ml) were found to be significantly higher than in twenty-one normal fertile men of comparable age (593 +/- 220 pg/ml, 40.6 +/- 8.8 pg/ml and 33.1 +/- 10.9 pg/ml respectively). SHBG binding capacity was elevated in the infertile group (infertile 3.35 +/- 0.82 x 10(-8) M/l v. normal 2.76 +/- 0.89 x 10(-8) M/l) but the total plasma testosterone concentrations were comparable (infertile 5435 +/- 1578 pg/ml v. normal 5046 +/- 1102 pg/ml). Evidence was cited to support the view that Sertoli cells, in response to an unphysiological FSH stimulation, are a likely source of excessive oestrogen production. The possible significance of increased intra-testicular and circulating oestrogen in the altered state of testicular steroidogenic function in men with primary seminiferous tubular defects was discussed.