Effect of HCG on the interstitial cells and androgen production in the immature rat testis

Drp1 Phosphorylation Is Indispensable for Steroidogenesis in Leydig Cells

The initial steps of steroidogenesis occur in the mitochondria. Dynamic changes in the mitochondria are associated with their fission and fusion. Therefore, understanding the cellular and molecular relationships between steroidogenesis and mitochondrial dynamics is important. The hypothesis of the current study is that mitochondrial fission and fusion are closely associated with steroid hormone synthesis in testicular Leydig cells. Steroid hormone production, induced by dibutyryl cAMP (dbcAMP) in Leydig cells, was accompanied by increased mitochondrial mass. Mitochondrial elongation increased during the dbcAMP-induced steroid production, whereas mitochondrial fragmentation was reduced. Among the mitochondrial-shaping proteins, the level of dynamin-associated protein 1 (Drp1) was altered in response to dbcAMP stimulation. The increase in Drp1 Ser 637 phosphorylation correlated with steroid hormone production in the MA-10 Leydig cells as well as in the primary adult rat Leydig cells. Drp1 was differentially expressed in the Leydig cells during testicular development. Finally, gonadotropin administration altered the status of Drp1 phosphorylation in the Leydig cells of immature rat testes. Overall, mitochondrial dynamics is directly linked to steroidogenesis, and Drp1 plays an important regulatory role during steroidogenesis. This study shows that Drp1 level is regulated by cAMP and that its phosphorylation via protein kinase A (PKA) activation plays a decisive role in mitochondrial shaping by offering an optimal environment for steroid hormone biosynthesis in Leydig cells. Therefore, it is suggested that PKA-mediated Drp1 Ser 637 phosphorylation is indispensable for steroidogenesis in the Leydig cells, and this phosphorylation results in mitochondrial elongation via the relative attenuation of mitochondrial fission during steroidogenesis.

Origin and evolution of somatic cell testicular tumours in transgenic mice

Transgenic mice bearing a construct in which the expression of the SV40 oncogene is directed by the AMH promoter (AT mice) develop testicular tumours in adult life. We aimed to study early steps of tumour development and characterize tumours at different ages by histological, morphometric, and immunohistochemical techniques. One- to 3-month-old AT mice depicted multifocal Leydig cell hyperplasia. The testicular volume occupied by interstitial tissue was significantly higher in 3-month-old AT mice in comparison with littermate controls. Between 5 1/2 and 7 months, microscopic interstitial tumours developed that progressively evolved to form large confluent areas of high mitotic index in 7- to 14-month-old AT mice. Tumour cells had the characteristics and histoarchitecture of Leydig cells, or formed solid cord-like structures reminiscent of those seen in Sertoli cell tumours. Hyperplastic areas and tumours diffusely expressed 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in Leydig cell areas. AMH expression was negative in Leydig cell conglomerates and tumours and variable in cord-like tumours. The SV40 T antigen and markers of cell proliferation (PCNA) were intensely positive in hyperplastic cells and tumours. Control mice of similar ages showed neither hyperplasia nor tumours, and SV40 T expression was always negative. In conclusion, transgenic mice develop large testicular tumours that are preceded by interstitial hyperplasia and microtumours. The histological and immunohistochemical phenotype of tumours (Leydig and Sertoli cell differentiation, positive 3beta-HSD, and variable AMH) suggests a mixed differentiation of somatic cells of the specialized gonadal stroma. The finding that an oncogene directed by a promoter specifically active in fetal Sertoli cells has given rise to testicular tumours of mixed differentiation is compatible with a common origin of Leydig and Sertoli cells from the specific stroma of the gonadal ridge, as supported by double labelling experiments in fetal mice showing co-localization of the transgene with Sertoli and Leydig cell markers.

Luteinizing hormone receptor-mediated effects on initiation of spermatogenesis in gonadotropin-deficient (hpg) mice are replicated by testosterone

Testosterone (T) is an absolute requirement for spermatogenesis and is supplied by mature Leydig cells stimulated by LH. We previously showed in gonadotropin-deficient hpg mice that T alone initiates qualitatively complete spermatogenesis bypassing LH-dependent Leydig cell maturation and steroidogenesis. However, because maximal T effects do not restore testis weight or germ cell number to wild-type control levels, additional Leydig cell factors may be involved. We therefore examined 1). whether chronic hCG administration to restore Leydig cell maturation and steroidogenesis can restore quantitatively normal spermatogenesis and testis development and 2). whether nonandrogenic Leydig cell products are required to initiate spermatogenesis. Weanling hpg mice were administered hCG (0.1-100 IU i.p. injection three times weekly) or T (1-cm subdermal Silastic implant) for 6 weeks, after which stereological estimates of germinal cell populations, serum and testicular T content, and testis weight were evaluated. Human CG stimulated Leydig cell maturation and normalized testicular T content compared with T treatment where Leydig cells remained immature and inactive. The maximal hCG-induced increases in testis weight and serum T concentrations were similar to those for T treatment and produced complete spermatogenesis characterized by mature, basally located Sertoli cells (SCs) with tripartite nucleoli, condensed haploid sperm, and lumen development. Compared with T treatment, hCG increased spermatogonial numbers, but both hCG and T had similar effects on numbers of spermatocytes and round and elongated spermatids per testis as well as per SC. Nevertheless, testis weight and germ cell numbers per testis and per SC remained well below phenotypically normal controls, confirming the involvement of non-Leydig cell factors such as FSH for quantitative normalization of spermatogenesis. We conclude that hCG stimulation of Leydig cell maturation and steroidogenesis is not required, and that T alone mostly replicates the effects of hCG, to initiate spermatogenesis. Because T is both necessary and sufficient for initiation of spermatogenesis, it is likely that T is the main Leydig cell secretory product involved and that additional LH-dependent Leydig cell factors are not essential for induction of murine spermatogenesis.

Effect of compound CDRI 84/35 and synthetic estrogen on the seminiferous epithelium of immature rat

Compound CDRI 84/35 (a piperazine derivative--a potent antispermatogenic agent) has been shown to cause significant inhibition in testicular spermatogenesis without affecting Leydig cell and accessory sex organ function in adult rats. The present study was conducted to determine its effect on the germ cell population and Leydig cell morphology in immature rats (40-50 gm) administered CDRI 84/35 (100 mg/kg/day p.o.), synthetic estradiol benzoate (EB; 5 microg/rat/day) and vehicle at the age of 21 days. Animals were killed 24 h later following 7 and 14 days' treatments. Bouin's fixed testes were sectioned (at 5 microm) and stained with PAS-hematoxylin. Quantitative determination of Sertoli Cell-Germ Cell ratio was carried out in 150 round seminiferous tubules in each group of 5 rats. Results revealed a significant decrease in number of the spermatocytes (non-pachytene and pachytene) and early (round) spermatids in step 1-8 of spermiogenesis without affecting Leydig cell morphology in rats administered CDRI 84/35 for 7 and 14 days as compared to corresponding controls. In contrast, the testes of rats injected with synthetic EB, caused a marked inhibition in these meiotic and post-meiotic germ cell types, as well as in the diameters of round seminiferous tubules, and Leydig cells nuclei (only in 14 days treatment), and testicular weight on autopsy days 8 and 15 as compared to CDRI 84/35-treated rats. While the number of pre-meiotic spermatogoniae was observed to be slightly decreased after only 14 days treatment in both CDRI 84/35 and EB treatment groups, the Sertoli cell number did not show any significant change as compared to controls. The present investigation confirms the antispermatogenic effect of compound CDRI 84/35 in immature rats similar to that reported in adult rats. Marked inhibition in pachytene spermatocytes and other testicular parameters following synthetic estrogen treatment might be due to its antiandrogenic action, contrasting with the non-hormonal profile of CDRI compound.

Effects of thyroid and luteinizing hormones on the onset of precursor cell differentiation into leydig progenitor cells in the prepubertal rat testis

Leydig cells in the adult rat testis differentiate during the neonatal-prepubertal period. However, the stimulus for the initiation of their differentiation is still not clear. In the present study our objectives were to test the effects of thyroid hormone and LH on the initiation of precursor cell differentiation into Leydig cells in the prepubertal rat testis. Four groups of Sprague-Dawley rats were used. All treatments began at postnatal Day 1. Rats in groups I, II, and III received daily s.c. injections of saline (200 microl, controls), triiodothyronine (T(3), 50 microg/kg body weight, hyperthyroid), and LH (ovine LH 10 microg/rat/day), respectively. Rats in group IV were made hypothyroid from postnatal Day 1 by adding 0.1% propylthiouracil (PTU) to their mother's drinking water. Testes of rats were collected at 7, 8, 9, 10, 11, 12, 16, and 21 days of age, fixed in Bouin's solution, and embedded in paraffin for immunocytochemical studies. Immunoexpression of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and LH receptors (LHR) in testicular interstitial cells (other than the fetal Leydig cells) was observed using the avidin-biotin method. In control rats, out of all spindle-shaped cell types in the testis interstitium, only the peritubular mesenchymal cells showed positive immunolabeling for 3beta-HSD, beginning from the postnatal Day 11. However, positive immunolabeling for LHR was first detected in these cells at Day 12, i.e., after acquiring the steroidogenic enzyme activity. In T(3)-treated rats 3beta-HSD positive spindle-shaped cells were first observed at Day 9 (i.e., 2 days earlier than controls), and LHR-positive cells were first observed on Day 11 (2 days later than obtaining 3beta-HSD immunoactivity); they were exclusively the peritubular mesenchymal cells. The 3beta-HSD- and LHR-positive spindle-shaped cells were absent in the testis interstitium of LH-injected rats from Days 7 through 12 but were present at postnatal Day 16. In addition, more fetal Leydig cell clusters and fetal Leydig cells in mitosis were present in LH-treated rats compared to rats in all other treatment groups. Following their first detection, the number of positive cells for each protein continued to increase at each subsequent age in controls, T(3)-, and LH-injected groups. In PTU rats, 3beta-HSD and LHR-positive spindle-shaped cells were absent throughout the experimental period. From these observations, it is possible to suggest the following regarding the developing rat testis interstitium. 1) The precursor cells for the adult generation of Leydig cells in the postnatal rat testis are the peritubular mesenchymal cells. 2) Luteinizing hormone does not initiate the onset of mesenchymal cell differentiation into Leydig cells, instead it delays this process. However, daily LH treatment causes mitosis in fetal Leydig cells and increase in fetal Leydig cell clusters. 3) Thyroid hormone is critical to initiate the onset of mesenchymal cell differentiation into adult Leydig cells.

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.

Testicular denervation-induced nuclear changes in Leydig cell of hemicastrated adult rats

In the adult male rat, hemicastration (HC) induces a remarkable enhancement of testosterone secretion from the Leydig cells of the remaining testis. We have observed previously that the denervation of inferior spermatic nerves inhibits this enhancement. The present experiments were designed to assess morphometrically whether or not this change had a cytological correlate in Leydig cells. At least five testes from each group (denervation plus HC, sham denervation plus HC and intact rats) were prepared for both optical and electron microscopy studies. The results showed that after 24 h of denervation, the nuclear volume of the Leydig cells in denervation plus HC rats was smaller (p < 0.01) than those of sham denervation plus HC (196.56 +/- 16.53 vs. 280.71 +/- 13.37), whereas both the volume density of heterochromatin (19.84 +/- 3.14 vs. 10.03 +/- 2.47%) and the heterochromatin index (expressed as periphery heterochromatin area divided by nuclear perimeter, 0.149 +/- 0.046 vs. 0.094 +/- 0.026) were significantly (p < 0.01) higher in denervation plus HC rats than in its sham groups. No changes in Leydig cell numbers or cytoplasmic organelles were detected. The results suggest that some nuclear and heterochromatin-associated cellular activity might be inhibited by testicular denervation in hemicastrated rats.

Morphometric study of the testicular interstitial tissue of the monkey Cebus apella during postnatal development

The purpose of this study was to evaluate the developmental changes of the Leydig cells and their precursors during postnatal development in the monkey Cebus apella. Four groups of monkeys were studied: neonatal, infantile, early pubertal and late pubertal. Light microscopy, immunocytochemistry, electron microscopy and stereological studies were performed to determine cytologic and cytochemical characteristics, volume density, absolute volume and cell counts of Leydig cells. In the interstitial tissue two components were recognized: specific interstitium comprising mature and immature Leydig cells and differentiating Leydig cell precursors, and non-specific interstitium including connective tissue and blood vessels. Mature Leydig cells were polygonal with a round, euchromatic nucleus and abundant cytoplasm. Immature Leydig cells were more elongated and the nucleus showed more heterochromatin. Mature and immature Leydig cells showed either a pale- or a dark-stained cytoplasm. Pale Leydig cells showed abundant smooth endoplasmic reticulum (SER), mitochondria with tubular cristae and glycogen granules. The SER of dark Leydig cells consisted of abundant flat cisternae, only few glycogen inclusions and abundant lipid droplets. All Leydig cells were intensely reactive for 3beta-hydrohysteroid dehydrogenase (3beta-HSD). Some peritubular cells acquired nuclear and cytoplasmic characteristics that indicated that they were differentiating to Leydig cells, as evidenced by the strong 3beta-HSD positivity found in scattered elongated cells of the peritubular tissue. Absolute interstitial volume increased from birth to the end of puberty due to an increment in Leydig cells numbers and size. The mature and immature Leydig cell populations showed a different evolution during postnatal development. While immature Leydig cells increased 7-fold from the neonatal to the early pubertal period and increased at a lower rate during puberty, mature Leydig cells remained stable until early puberty and increased significantly during late pubertal development.

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.

Is testosterone essential for maintenance of normal morphology in immature rat Leydig cells?

Selective deprivation of gonadotrophins in prepubertal rats by administration of a GnRH antagonist (Ac-D2Nal1, D4ClPhe2, DTrp3, DArg6, DA1a10-GnRH; GnRH code: 103-289-10, National Institutes of Health, USA) for 3 weeks, initiated at 20-22 days of age, induced morphological changes in the Leydig cells, including thickening and indentation of the nuclear margin, pyknosis and elongation of the nuclei. Mean nuclear diameter was reduced to 22% of that in the controls. Under the electron microscope the cells exhibited reduced volume of the nucleus and cytoplasm and the plasma membrane was irregular. This abnormal appearance of the Leydig cells improved marginally in 20-30% of the Leydig cells and their mean nuclear diameter increased to 39% of the control level after FSH supplementation (20 micrograms ovine FSH/day). Normal morphological integrity of the Leydig cells consisting of round or oval nuclei, a smooth nuclear and cellular margin and the original mean nuclear diameter was restored completely when testosterone (30 micrograms/day) was administered to GnRH antagonist-treated rats, with or without simultaneous administration of FSH; in these rats testosterone levels in blood were also restored to normal. These findings indicate that testosterone may be important for the maintenance of normal Leydig cell morphology in the rat.

Hyperplasia and hypertrophy of Leydig cells associated with testicular germ cell tumours containing syncytiotrophoblastic giant cells

In patients with seminomas and non-seminomatous germ cell tumours of the testis syncytiotrophoblastic giant cells (STGC) are largely responsible for elevated levels of chorionic gonadotropin. In searching for these cells, the question arises whether hyperplasia and/or hypertrophy of Leydig cells in the adjacent testicular tissue is a relevant finding. To elucidate this problem we analysed the tumour-free testicular tissue of 20 seminomas and 20 combined seminomatous and non-seminomatous germ cell tumours with or without immunohistochemically demonstrable STGC morphometrically. Extension of Leydig cell areas and the surface areas of Leydig cells per tubule are increased significantly in seminomas and combined tumours when STGC are present. There is also an apparent increase in the number of Leydig cells per tubule in seminomas and combined germ cell tumours with STGC. The difference, however, is not significant statistically in the group of seminomas. Hypertrophy and/or hyperplasia of Leydig cells must be considered as a relevant finding in germ cell tumours with STGC. It is most easily recorded by evaluating the surface area of Leydig cells per test area or per tubule.

Developmental changes in testicular interstitial cell populations, LH receptors and in the response to hCG in the rat

High doses of hCG were administered to immature rats of different ages and the animals killed 48 h later. Serum testosterone increased 2 to 4-fold over control values 48 h after hCG. In-vitro androgen production showed different patterns according to age. Animals younger than 35 days, when treated with hCG, retained the ability to respond to in-vitro gonadotrophic stimulation. This ability was lost in testes from rats aged 45 days. The number of free LH-receptors 48 h after hCG diminished with increasing age to become non-detectable at 35 and 45 days. In control animals the proportion of differentiated Leydig cells in relation to their mesenchymal precursors increased progressively with age to reach highest values at 45 days. hCG administration induced a shift of the cellular composition of the interstitium toward the more mature cell types. hCG has a predominantly trophic action on mesenchymal precursors in young rats, promoting their differentiation. These effects are minimal in the differentiated Leydig cells in older animals. It is proposed that the observed biochemical responses are the result of the balance between the increase in LH receptors and steroidogenic enzymes in the developing new generation of young Leydig cells and the down-regulation of receptors and enzymatic lesions in fully differentiated Leydig cells.

Transplantation of newborn rat testis under the kidney capsule of adult host as a model to study the structure and function of Leydig cells

Newborn rat testis was transplanted under the kidney capsule of adult castrated and uncastrated male rats to develop and characterize a model system for studies on Leydig cell development. Two weeks after transplantation, the number of Leydig cells and the size of their nuclei in the transplants had increased. Secretion of testosterone was indicated by increased seminal vesicle weights and decreased pituitary LH in the castrated host animals. Pituitary FSH content increased significantly in the uncastrated animals with transplants, which suggested production of an FSH-stimulating factor. Cells with the morphologic features characteristic of fetal- and adult-type Leydig cells were observed in the transplants. The seminiferous tubules with spermatocytes, incipient lumina, and significantly larger average diameters showed more advanced development than those in the normal 2-week-old testis. By the present morphologic and functional criteria, the kidney subcapsular transplantation technique provides a suitable model for studies of fetal and adult Leydig cell development.

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.

Developmental pattern of the testicular androgen response to gonadotrophin stimulation in vitro and its modification by chronic hypoprolactinaemia

Developing male rats were treated chronically with bromocriptine (BR, 3 mg/kg b.w. daily) to maintain severe hypoprolactinaemia throughout postnatal development. This treatment induced a precocious increase in Leydig cell numbers per testis and caused substantial, but age-dependent, modifications of the androgenic responsiveness of incubated hemi-testis preparations to stimulation with hCG. Most conspicuous were: (i) a decrease in sensitivity of the testis to hCG at the approach of adult age (due presumably to reduced responsiveness of the Leydig cells), and (ii) a precocious increase in the steroidogenic maximum of the testis at peripubertal age. This probably resulted from the precocious increase in Leydig cell numbers, which was able to mask the negative consequences of reduced androgenic capacity per Leydig cell. The precocious increase in number of Leydig cells induced by hypoprolactinaemia could have resulted from facilitation of the proliferative action of the high prepubertal LH levels on Leydig cell numbers. There were no clear-cut indications for an important effect of BR-induced changes in LH levels, or of a direct effect of BR on the testis.

Gonadotropin regulation of Leydig cell DNA synthesis

Adult male rats were injected s.c. with either saline, 100 IU hCG, 100 micrograms FSH, 50 micrograms LH, 100 micrograms PRL, 50 micrograms estradiol-17 beta, 500 micrograms or 10 mg testosterone; 50 micrograms estradiol-17 beta; animals were sacrificed at 12-120 h post-injection. Collagenase-dispersed interstitial cells (150-200 X 10(6) cells/2 ml) were incubated in vitro with 10 microCi [3H-methyl]thymidine for 1 h at 32 degrees C. Centrifugation of the cells on discontinuous 11-27% metrizamide gradients revealed thymidine incorporation in the regions of population I and II Leydig cells. A significant increase in thymidine incorporation into DNA after treatment with either hCG or LH was first detectable at 48 h, was equivalent to control values at 72 h and was again significantly increased at 96 h in population I and at 120 h in population II cells. [3H]Thymidine incorporation at 48 h, expressed as dpm/10(6) cells, was 2205 +/- 432 and 4119 +/- 929 vs. 16473 +/- 3795 and 11648 +/- 3427 for control and hCG-treated population I and II cells, respectively. Addition of 20 mM hydroxyurea suppressed [3H]thymidine incorporation, 97% and 96% in hCG-treated population I and II cells, respectively. Autoradiographic analyses revealed that nuclei from control and 48 h hCG-treated population I and II cells exhibited 1.2% and 2.3% vs. 7% and 6.8% silver grains, respectively. PRL had no influence on LH/hCG-enhanced DNA synthesis; however, estradiol-17 beta administration for 48 h dramatically suppressed thymidine incorporation. Population I Leydig cells exhibited a higher level of LH/hCG-stimulated DNA synthesis compared to population II cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Mitosis in adult human Leydig cells

The ultrastructural study of testicular biopsies from 87 adult men revealed mitosis in two mature Leydig cells, each from a different man. The men showed normal hormone levels and had received no previous chemotherapy or hormone treatment, nor had they been exposed to known toxic agents. The presence of mitotic Leydig cells suggests that differentiated Leydig cells may divide and contribute either to the increase in the number of Leydig cells or to the formation of multinucleate Leydig cells.

Selective destruction and regeneration of rat Leydig cells in vivo. A new method for the study of seminiferous tubular-interstitial tissue interaction

The effect of a single i.p. administration of ethane dimethanesulphonate (EDS) upon rat testicular histology was studied by light microscopy and morphometry up to 4 weeks after treatment. One day after injection the interstitial tissue exhibited degenerating Leydig cells, abundant pyknotic interstitial cells, deposition of cellular debris and extensive networks of fibrillar material. Macrophages contained greatly increased numbers of cytoplasmic inclusion bodies. From 3 to 7 days morphometric analysis showed that Leydig cells and cellular debris had disappeared from the interstitial tissue, leaving only macrophages, fibroblasts and lymphatic endothelial tissue. A very small number of new Leydig cells were seen on day 14, often located in peritubular or perivascular positions. Regeneration of foetal-like Leydig cells occurred by 4 weeks, their cytoplasm containing large lipid inclusions and, numerous Leydig cells were often observed closely applied to the walls of the seminiferous tubules. The observations suggest that, after experimental destruction and depletion of Leydig cells, an interstitial precursor cell, as yet unidentified, gives rise to a new Leydig cell population. EDS thus offers a valuable opportunity to study further the interactions between the seminiferous tubules and the interstitial tissue following the destruction and subsequent regeneration of the Leydig cells.

Response to acute hCG stimulation and steroidogenic potential of Leydig cell fibroblastic precursors in humans

The process of early testosterone (T) secretion and Leydig cell differentiation in humans was studied to explore the steroidogenic capacity of Leydig cell fibroblastic precursors. Seven cryptorchid boys received hCG prior to orchidopexy. Patients CP, PB, and MR received one injection of 1000 IU; patients JR and GG, three daily injections of 1000 IU, and patients MP and MM, five daily injections of 1000 IU. A testicular biopsy was obtained at the time of operation, 24 hours after the last injection. Serum T (ng/dl) before and after hCG stimulation and testicular T (ng/g) were determined by RIA. A control prepubertal testis (tumoral orchidectomy) was incubated in vitro and showed a time-dependent accumulation of T both in the medium and the testicular tissue. Testosterone released into the medium at 1, 2, and 4 hours was 0.76, 1.43, and 4.03 ng/ml, respectively. Tissue T at 0, 1, 2, and 4 hours was 9, 11, 16, and 24 ng/g, respectively. This indicates synthesis and secretion of T into the medium. Control testes showed abundant fibroblastic precursors with scanty cytoplasm, few organelles, heterochromatic nuclei, and minute nucleoli. No Leydig cells were present. After 1 day of hCG stimulation, numerous fibroblasts were activated, displaying enlarged cytoplasms with increased numbers of organelles, nuclei rich in euchromatin, and bigger nucleoli. No Leydig cells were present. Basal serum testosterone was 58.2 +/- 45.3 ng/dl and 87.3 +/- 42.0 after hCG administration, while testicular T was 974.0 +/- 686.0 ng/g (control prepubertal testicular T is 10-50 ng/g). After 3 days of hCG, activated fibroblasts increased and immature Leydig cells appeared. Basal serum T was 35.5 +/- 7.8 ng/dl and 394.0 +/- 24.0 after hCG stimulation, while testicular T rose to 2797.5 +/- 1222.6 ng/g. After 5 days, mature Leydig cells appeared for the first time. Serum T was 58 +/- 59.3 ng/dl (basal) and 641.5 +/- 390 ng/dl (after hCG); testicular T was 789 ng/g (patient MM did not have a value for testicular T). HCG induced numerous coated pits and endocytic vesicles in activated fibroblasts and young Leydig cells, suggesting receptor aggregation and internalization of hormone-receptor complexes. Peroxidase-antiperoxidase (PAP) localization of T was positive in peritubular fibroblasts and Leydig cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of bromocriptine-induced hypoprolactinaemia on the developmental pattern of androgen and LH levels in the male rat

In immature male rats, receiving daily injections of bromocriptine (3 mg/kg bw), serum prolactin (Prl) remains low throughout development. In such hypoprolactinaemic males androgen variables are affected: a) the normally low pre-pubertal serum androgen (testosterone, dihydrotestosterone-T, DHT) is considerably increased, in correlation with a precocious development of the testicular Leydig cell population; b) the peri-pubertal rise of androgen is not prevented, but is is followed by significantly lower post-pubertal T, DHT levels, in correlation with moderately reduced Leydig cell counts and with strongly attenuated growth rates of sex accessory organs. Observed alterations of the post-natal androgen pattern cannot be related to LH changes since developmental LH values remained essentially unaltered. Results are in concordance with a marked age-dependent sensibility of androgen variables to a lack of Prl in the developing male.

Stimulation in vivo of testicular 7 alpha-hydroxylase activity in immature rats by LH and hCG

Testicular C19-steroid 7 alpha-hydroxylase activity rises during puberty in the rat. Hormonal mechanisms responsible for this rise are unknown. The present study is to the best of our knowledge the first to report successful stimulation of testicular 7 alpha-hydroxylase in immature rats. Administration of crude and purified hCG every day for 3 or more days to immature rats in doses of 3 I.U. lead to significant stimulation of testicular 7 alpha-hydroxylase activity. Purified preparations of subunits of hCG did not stimulate 7 alpha-hydroxylase activity. Stimulation of testicular 7 alpha-hydroxylase was, however, recorded when purified subunits of hCG were allowed to recombine and then administered to the animals. Several preparations of LH failed to cause stimulation of 7 alpha-hydroxylase when administered to immature rats. Treatment of immature rats with mixtures of LH and FSH, LH and prolactin or LH together with FSH and prolactin was also ineffective in this respect. Large doses of highly purified ovine-LH, rat LH and human LH were, however, able to stimulate testicular 7 alpha-hydroxylase activity in immature rats. Preparations comprising hybrids of ovine-LH and hCG (oLH alpha + hCG beta, hCG alpha + oLH beta) stimulated testicular 7 alpha-hydroxylase activity in immature rats. Administration of the same amounts of a hybrid preparation of human and ovine-LH (oLH alpha + hLH beta) to immature rats was ineffective in this respect. Administration of testosterone or estradiol to immature rats lead to suppression of testicular 7 alpha-hydroxylase activity. Combined treatment of such rats with hCG and testosterone or with estradiol and hCG augmented testicular 7 alpha-hydroxylase activity to the same degree as that of animals treated with hCG only.

Primary cultures of Leydig cells from rat, mouse and pig: advantages of porcine cells for the study of gonadotropin regulation of Leydig cell function

Primary cultures of interstitial cells were prepared from the testis of mice, rats, and pigs. The cells were grown in a defined medium supplemented with low (0.1%) serum and insulin, transferrin and epidermal growth factor. Comparisons of the interstitial cell cultures from the three species were made for plating efficiency, cell survival, maintenance of hCG receptors and maintenance of steroidogenic responsiveness to hCG. The porcine cultures had a higher plating efficiency and higher hCG receptor levels per cell than Leydig cells from either rodent. Additionally, the porcine cells showed an increase in testosterone (T) production with hCG stimulation throughout their lifespan in culture while the rodent cultures showed a decrease in T stimulation with time with no stimulation by day 6 in culture. These data indicate that species differences exist in hCG receptor concentrations per cell, the maintenance of hCG receptors and steroidogenic response in culture. The initial high survival, purity and continued functional response of porcine interstitial cell cultures make them a superior system for the study of gonadotropin regulation of Leydig cell function.

Developmental pattern of testosterone production by the rat testis

We studied the steroidogenic activity of isolated Leydig cells derived from rats on fetal day 19 (F19) and postnatal (N) days 1, 12, 24, 34, 45 and adults. Leydig cells, isolated at all ages by the collagenase method, increased in number throughout development with a doubling time of 8 days. Testicular content and serum concentrations of testosterone showed parallel changes during development. Moderate values were found at the early stages (F19 and N1), with a nadir on day 12, followed by a progressive increment to reach maximal values in adulthood. A reduction in steroidogenic activity of the testis during neonatal life was confirmed by in vitro studies with isolated Leydig cells. Maximal activity was found in group F19; testosterone production diminished after birth to reach a minimum in group N34 and rose thereafter to adulthood. Leydig cells were responsive to hCG stimulation at all ages in the following order: N1 greater than N34 greater than F19 greater than N24 greater than N45 greater than adult. The present study demonstrates the existence of an active and hCG-responsive population of Leydig cells in the rat testis from fetal life to adulthood.

Comparative study of nuclear binding sites for oestradiol in rat testicular and uterine tissue. Determination of low amounts of specific binding site by an [3H] oestradiol-exchange method

1. An [3H]oestradiol-exchange method was developed for the determination of oestradiol-receptor complexes in the nuclear fraction of immature rat testicular tissue. This method permits the determination of nuclear oestradiol-receptor sites in the presence of a relatively large amount of non-specific oestradiol binding present in testicular nuclei. After incubation of nuclei for 60min at 20 degrees C in the presence of [3H]oestradiol with or without a 1000-fold excess of non-radioactive diethylstilboestrol, specific binding can be determined quantitatively in the KCl-extractabe fraction, which contains 40% of the total receptor population. 2. The amount of receptor-bound steroid present in the 0.4m-KCl extract of testicular neclei remained constant during incubation at 20 degrees C. For uterine nuclei incubated with [3H]oestradiol at 37 degrees C a shift of specifically bound [3H]oestradiol occurred from the KCl-soluble fraction to the KCl-insoluble fraction. 3. In intact rat testis, about 20% of the total receptor concentration was present in its nuclear form. Hypophysectomy 5 days before measurement resulted in a twofold decrease in the amount of receptor, which was present mainly in the cytosol. After injection of choriogonadotropin to intact animals, the total receptor concentration increased threefold. 4. This nuclear exchange method might be useful for determination of occupied specific receptor sites in tissues with relatively low contents of specific receptors.

Hormonal regulation of LH stimulation of testosterone production in isolated Leydig cells of immature rats: the effect of hypophysectomy, FSH, and estradiol-17beta

Testosterone production in isolated Leydig cells from testes of immature and adult rats was stimulated by addition of LH in a dose dependent way. Hypophysectomy of adult rats had no influence on LH-stimulated testosterone production in isolated Leydig cells after 5 days. In contrast hypophysectomy of immature rats resulted after 5 days in an almost complete loss of LH sensitivity of isolated Leydig cells. Daily adminitration of FSH during 5 days starting immediately after hypophysectomy maintained LH responsiveness of isolated Leydig cells of immature rats. Also FSH administration starting on day 5 after hypophysectomy resulted in a restoration of LH responsiveness. Estradiol benzoate, injected simultaneously with FSH, abolished the FSH-induced LH responsiveness.