Effect of photoperiod on the size of the Leydig cell population and the rate of recruitment of Leydig cells in adult Syrian hamsters

The number of Leydig cells was determined by stereologic procedures in adult Syrian hamsters housed in long days (14L:10D) to maintain testicular activity (active), in short days (5L:19D) for 12-13 wk to induce testicular regression (photoperiod-induced regressed), or in short days for a period of 21 wk or more to allow spontaneous gonadal recrudescence (spontaneously recrudesced). Testes were removed, sliced, fixed, embedded in Epon 812, and observed by bright-field microscopy. Testicular and seminal vesicle weights, plasma testosterone concentration, total Leydig cell volume per testis, and volume of single Leydig cell were greater (p less than 0.01) in active and recrudesced animals than in regressed animals. The density of Leydig cells was greater in the regressed testes, but the total number per testis was not influenced by photoperiod. In Experiment 2, the rate of recruitment of Leydig cells was determined in 5 adult hamsters exposed to long days (active) or 5 hamsters whose testes were regressed by exposure of animals to short days for 13 wk followed by long-day exposure to initiate testicular growth (photoperiod-induced recrudescing). Hamsters were injected for 3 days/wk for 3 wk with tritiated thymidine, 0.5 or 1 microCi/g body weight. Testes were fixed and tissues prepared, as above, and processed for autoradiography. Again, the photoperiod did not influence the number of Leydig cells per testis. Labeling of Leydig cell nuclei revealed that recruitment of new Leydig cells occurred at approximately 1.3% per day in recrudescing testes but also occurred at approximately 0.6% per day in active testes. Without change in the total number of Leydig cells, new Leydig cells were added continually to the existing population in adult hamsters with either recrudescing or active testes.     

A comparison of Leydig cell function after unilateral and bilateral cryptorchidism and efferent-duct-ligation

Surgical induction of cryptorchidism or ligation of the efferent ducts disrupts spermatogenesis. The response of Leydig cells to disrupted gametogenesis was studied in vitro in tissue and collagenase dispersed Leydig cells obtained from the testes of rats that were made unilaterally or bilaterally cryptorchid or had been efferent-duct-ligated. Four wks after surgery, androgen secretion per mg of tissue or per Leydig cell in response to maximal luteinizing hormone (LH) stimulation was greater in tissue from damaged than from sham-operated testes. It was concluded that disruption of spermatogenesis resulted in Leydig cells that were hyperresponsive to LH stimulation in vitro. Unilateral lesions produced different responsiveness of Leydig cells from the testes ipsilateral and contralateral to the lesion, supporting the hypothesis that intragonadal modulation of Leydig cells function occurs when the function of seminiferous tubules is impaired. Stimulated androgen production of Leydig cells from the contralateral nonligated testis did not differ from that of the sham-operated controls. With unilateral cryptorchidism, which is accompanied by an increase in the temperature of the operated testis, Leydig cells from the scrotal testis were also hyperresponsive compared to those from sham-operated controls. This suggests a possible intergonadal influence of aspermatogenesis caused by cryptorchidism.     

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

Summary 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 was 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 crytorchid group. A new generation of foetal-type Leydig cells was observed in scrotal testes of the 2-week unilateral crytorchid group although their total volume per testis estimated by morphometry, was small, being approximately 1 l. In contrast, the abdominal testis exhibited a remarkable proliferation of foetal-type Leydig cells (total volume per testis, 16 l) 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 l vs 21 l, 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.     

Temporal changes in rat Leydig cell function after the induction of bilateral cryptorchidism

Adult rats were made bilaterally cryptorchid and studied at intervals of 3, 7, 14 or 21 days to study temporal changes in Leydig cell function. Serum FSH and LH levels were measured and the cross-sectional area of the Leydig cells assessed by morphometry. The function of the Leydig cells was judged by the binding of 125I-labelled hCG to testicular tissue in vitro and the testosterone response of the testis to hCG stimulation in vitro. By 3 days after cryptorchidism, the binding of labelled hCG to testicular tissue was significantly decreased compared to that of controls, but the testes were able to respond to hCG stimulation in vitro. At 7, 14 and 21 days after cryptorchidism, an enhanced testosterone response was observed and the size of the Leydig cells was significantly greater than that of the controls, which indicated increased secretory activity by the cryptorchid testis. Although serum FSH levels were significantly elevated after 3 days of cryptorchidism, serum LH levels did not rise until 7 days, thereby suggesting that the loss of receptors is unlikely to result from down-regulation by LH. The reduced testosterone response of the cryptorchid testis in vivo to low doses of hCG and the enhanced response at high doses are probably related to the reduced blood flow to the cryptorchid testis and the decreased sensitivity of the Leydig cells induced by LH/hCG receptor loss.     

Testosterone restores testicular inhibin content in cryptorchid rats

The effects of testosterone administration on testicular inhibin content and histology were studied in bilaterally cryptorchid rats, in which a marked decrease in testicular inhibin content had been observed. Mature male Wistar rats weighing approximately 300 g were made bilaterally cryptorchid by placing the testes in the abdominal cavity. Testosterone in oil, 0.1, 1.0 or 10 mg, was given i.m. each week. Testicular inhibin and testosterone content, histology and plasma LH, FSH and testosterone were studied 2 weeks later. Abnormally decreased testicular inhibin in cryptorchidism was restored toward normal by testosterone in a dose dependent manner in 2 weeks after surgery. Sertoli cell structure also recovered toward normal with increasing amount of testosterone. Decreased testicular testosterone content and Leydig cell atrophy were observed with suppressed plasma LH and FSH after testosterone. These results showed that the increased plasma concentration of testosterone had a stimulatory effect on the Sertoli cell function in cryptorchidism, in which compensated Leydig cell failure was demonstrated.     

Expression of Hsf1, Hsf2, and Phlda1 in cells undergoing cryptorchid-induced apoptosis in rat testes

Surgery‐induced cryptorchidism, in which the testes are prevented from descending into the scrotal sac, results in testicular germ cell death, and it is commonly used as an experimental tool in the study of spermatogenesis. However, the molecular events underlying the activation of germ cell death remain poorly understood. In the present study, we investigate selective cell loss from cryptorchid rat testis by using DNA flow cytometry and by determining protein and mRNA expression of Hsf1, Hsf2, and Phlda1. The hypo‐haploid cell fraction is significantly decreased as early as 3 days after surgical induction of cryptorchidism (from 42.01 ± 5.74% to 15.98 ± 3.88%), followed by a significant decrease in the haploid cell fraction at Day 7. At the latter time point, an apoptotic peak of spermatocytes appears in DNA histograms just before the tetraploid peak; the percentage of aneuploid cells between diploid and tetraploid rises as high as 14.05 ± 2.98% of the total cells in 7‐day cryptorchid testis, suggesting that a large number of spermatocytes are undergoing apoptosis. The expression of Phlda1 mRNA is significantly elevated 3 days after induction of cryptorchidism. After 7 days of cryptorchidism, Hsf1 and Phlda1 are strongly expressed in the nucleus and cytoplasm, respectively, of primary spermatocytes. Numerous apoptotic spermatocytes are also observed at this time point. These results suggest that the Hsf1/Phlda1 pathway plays an important role in the apoptosis of primary spermatocytes in cryptorchid testis. We present evidence suggesting that Hsf2 is also involved in germ cell removal in cryptorchid testis. Mol. Reprod. Dev. 78:283–291, 2011. © 2011 Wiley‐Liss, Inc.     

Cellular localization of cytochrome P450IIA1 in testes of mature Sprague-Dawley rats.

Previous studies have shown that a prominent site of extrahepatic cytochrome P450IIA1 in male rats is the testis. We investigated the cellular location of cytochrome P450IIA1 in the testes of adult rats. Using specific isolation of testicular compartments and individual cell types, as well as in vivo removal of Leydig cells by ethane dimethyl sulfonate, we determined the cellular location of cytochrome P450IIA1 using testosterone hydroxylation assay, Western immunoblotting, and immunohistochemical analysis. Enriched Leydig cell fractions had the greatest testosterone 7 alpha-hydroxylase activity as well as immunoreactivity. Immunohistochemical analysis confirmed that the cellular location of cytochrome P450IIA1 was specific to Leydig cells. The specific localization of enzyme systems that are involved in xenobiotic activation may have important implications for inducing specific cell toxicity by compounds that exert their effects in the testes.     

Changes in the testis interstitium of Sprague Dawley rats from birth to sexual maturity

Changes in the rat testis interstitium from birth to adulthood were studied using Sprague Dawley rats of 1, 7, 14, 21, 28, 40, 60, and 90 days of age. Our objectives were 1) to understand the fate of the fetal Leydig cells (FLC) in the postnatal rat testis, 2) to determine the volume changes in testicular interstitial components and testicular steroidogenic capacity in vitro with age, 3) to differentially quantify FLC, adult Leydig cells (ALC), and different connective tissue cell types by number and average volume, and 4) to investigate the relationship between mesenchymal and ALC numbers during testicular development. FLC were present in rat testes from birth to 90 days, and they were the only steroidogenic cells in the testis interstitium at Days 1 and 7. Except for FLC, all other interstitial cell numbers and volumes increased from birth to 90 days. The average volume of an FLC and the absolute volume of FLC per testis were similar at all ages except at Day 21, when lower values were observed for both parameters. FLC number per testis remained constant from birth through 90 days. The observations suggested that the significance of FLC in the neonatal-prepubertal rat testis is to produce testosterone to activate the hypothalamo-hypophyseal-testicular axis for the continued development of the male reproductive system. ALC were the abundant Leydig cell type by number and absolute volume per testis from Day 14 onwards. The absolute numbers of ALC and mesenchymal cells per testis increased linearly from birth to 90 days, with a slope ratio of 2:1, respectively, indicating that the rate of production of Leydig cells is 2-fold greater than that of mesenchymal cells in the postnatal rat testis through 90 days. In addition, this study showed that the mesenchymal cells are an active cell population during testis development and that their numbers do not decrease but increase with Leydig cell differentiation and testicular growth up to sexual maturity (90 days).     

Influence of experimental cryptorchidism on cholesterol side-chain cleavage enzyme and delta5-3beta-hydroxysteroid dehydrogenase activities in rat testes.

Testicular cholesterol side-chain cleavage enzyme (CSCCE) and delta5-3beta-hydroxysteroid dehydrogenase (delta5-3beta-HSD) activities were assessed 12 hours and 2, 4, 8, 16, and 32 days after surgical induction of bilateral cryptorchidism in adult rats. Within 12 hours after surgery CSCCE activity (expressed as dpm of isocaproic acid-14C formed from cholesterol-26-14C/3 hours/testis) was significantly reduced (P less than 0.01) in cryptorchid testes to approximately 55% of sham-operated control values and remained depressed at less than 50% of control activities 2, 4, 16, and 32 days after surgery. Cryptorchid testis delta5-3beta-HSD activity (measured by a pregnenolone substrate-depletion assay and expressed as mumoles of products/30 minutes/testis) did not differ from controls (P greater than 0.05) 1/2, 2, or 4 days after translocation of testes to the abdominal cavity. By day 8 of cryptorchidism, however, delta5-3beta-HSD activity was reduced to 60% of control values (P less than 0.05) and continued to decline to approximately 30% of controls during the remainder of the experimental period. These observed alterations in enzyme activities suggest an impairment in the ability of cryptorchid rat testes to synthesize androgens and further indicate that testicular CSCCE is more acutely sensitive to the cryptorchid milieu than delta5-3beta-HSD.     

Stimulation of interstitial cell growth after selective destruction of foetal Leydig cells in the testis of postnatal rats

Summary Five-day-old male rats received a single treatment of ethane dimethanesulphonate (EDS), and the response of the testis on days 6–10 and 21 was examined by light microscopy and morphometry, supplemented by measurement of peripheral testosterone levels. One day after treatment, foetal Leydig cells degenerated, showing fragmentation, condensation and nuclear pyknosis. Macrophages phagocytosed the foetal Leydig cells resulting in their disappearance by day 7. Destruction of foetal Leydig cells was followed by an arrest of testicular growth in comparison to testes of intact age-matched control rats. In testes of EDS-treated rats, gonocytes and spermatogonia also degenerated, forming pyknotic bodies within the seminiferous cords. In contrast, interstitial fibroblasts and mesenchymal cells showed proliferative activity, which on days 4 and 5 after treatment resulted in peritubular hyperplasia surrounding each seminiferous cord. Thereafter, on day 21 after EDS administration, the previously depressed serum testosterone levels became markedly elevated coincident with the development of many immature-type Leydig cells, of which the total volume per testis was similar to that of Leydig cells in control testes, despite a four- to five-fold difference in testicular volumes. The results indicate that, although EDS destroys the foetal Leydig cells and impairs spermatogenesis, the interstitial tissue exhibits increased cell growth. The latter probably occurs in response to altered gonadotrophic stimulation and/or disturbances in the interaction between the seminiferous cords and the interstitial tissue.     

Effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion in rats

The effect of uni- and bilateral cryptorchidism on testicular inhibin and testosterone secretion and their relationships to gonadotropins were studied in rats. Mature Wistar male rats weighing approximately 300 g were made either uni- or bilaterally cryptorchid. Testicular inhibin and testosterone content and plasma levels of LH and FSH were examined 2 weeks later. A similar remarkable decrease in testicular inhibin content was found in uni- and bilaterally cryptorchid testes. On the other hand, the testicular testosterone content was significantly decreased only in unilaterally cryptorchid testis with an inverse increase in the contralateral testis. Plasma testosterone levels were normal and plasma LH and FSH increased significantly in both of the cryptorchid groups. These results showed that cryptorchidism impairs both Sertoli and Leydig cell functions. While testosterone production was compensated by increased LH for 2 weeks, neither inhibin secretion nor storage changed in cryptorchid or contralateral testes during the same period.     

Disruption of spermatogenesis is associated with decreased concentration of immunoreactive arginine vasopressin in testicular fluid

We have previously shown that testicular fluid contains factors that can inhibit luteinizing hormone (LH)-stimulated androgen production by Leydig cells, and others have reported the presence of immunoreactive vasopressin (iAVP) in the testes as well as in vitro inhibition by vasopressin of Leydig cell-androgen production. In the current report, we have used an established radioimmunoassay (RIA) to measure the concentration of iAVP in testicular fluid and have related changes in iAVP concentration to disruption of the seminiferous tubules. Spermatogenesis was disrupted in adult rats by surgically establishing bilateral cryptorchidism. The concentration of iAVP decreased progressively from 349 +/- 52 to 61 +/- 5 pg/ml during 4 wk. When cryptorchidism was unilaterally established, the concentration of iAVP in fluid from that testis decreased to 116 +/- 19 pg/ml while the concentration of iAVP in the contralateral scrotal testis remained unaffected. Unilateral ligation of the ductuli efferentes also caused an equivalent unilateral decrease in iAVP to 110 +/- 15 pg/ml. The osmotic pressure of the testicular fluid was not altered by disruption of gametogenesis, and the extracellular "albumin space" was not increased. Therefore, the decrease in concentration of iAVP was probably not due to dilution with increased amounts of interstitial fluid. We conclude that the disruption of spermatogenesis is associated with a decrease in the concentration of iAVP in testicular fluid and suggest that AVP or a similar peptide may be involved in the intratesticular mechanisms associated with increased production of androgen by Leydig cells after disruption of spermatogenesis.     

Rat testicular endogenous steroids and number of Leydig cells between the fetal period and sexual maturity

Endogenous androgens (androstenedione, testosterone, 5 alpha-dihydrotestosterone and 5 alpha-androstane-3 alpha,17 beta-diol), and some of their C21 precursors (pregnenolone, progesterone and 17-hydroxyprogesterone) were measured in rat testes between Day 18.5 of pregnancy and Day 64 postpartum, and correlated with numerical densities of Leydig cells. The latter parameter showed an early maximum on Day 19.5 of the fetal period, a nadir on Day 15 postpartum, and a gradual increase thereafter. The two dominating androgens, testosterone and 5 alpha-androstane-3 alpha,17 beta-diol, had similar levels until 15 days of age, but the 5 alpha-diol predominated thereafter. The total steroid content per Leydig cell was highest on Day 18.5 of gestation (77 ng/10(6) cells). A decline started already in utero, and reached a nadir of 5 ng/10(6) cells on Day 29. Thereafter, a slight increase occurred with advancing age. It is concluded that: The fetal testis has highest Leydig cell and endogenous steroid concentrations. A nadir in these parameters is seen 2-4 wk postpartum. The Leydig cell concentration increases around puberty on Days 40-60, but only a slight concomitant increase occurs in steroids. A sharp decline in steroid content per Leydig cell occurs during the last fetal days, but the postnatal decline of testicular steroids is due to Leydig cell loss. The new Leydig cell generation after 15 days has a persistently low steroid concentration through puberty.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired gonadotrophin uptake in vivo by the cryptorchid rat testis

The specific testicular uptake in vivo of 125I-labelled hCG was compared in control adult rats and adult rats made bilaterally cryptorchid 5 weeks previously. Although a similar temporal pattern of uptake was observed in both groups, uptake of hCG by cryptorchid testes was reduced at all times after injection by up to 70%. The possible causes of this impairment were investigated. It could not be accounted for by differences in the rate of absorption or clearance of 125I-labelled hCG in the two groups. Therefore, because hCG-induced increase in the permeability of testicular capillaries is a crucial factor in determining hCG uptake by the testis, this change was compared in control and cryptorchid testes. Although hCG induced a characteristic increase in testicular capillary wall permeability in both groups, this change was temporally delayed in cryptorchid testes, and occurred after hCG values in the blood had fallen. Even when hCG had crossed the capillary wall into testicular interstitial fluid, its uptake into the testicular tissue was significantly lower in cryptorchid than in control testes. These changes probably account for the impairment of gonadotrophin uptake by the cryptorchid testis and have important implications with respect to the aetiology of Leydig cell changes in cryptorchidism.     

Sertoli cells in the boar testis: changes during development and compensatory hypertrophy after hemicastration at different ages

Changes in Sertoli cell numbers and testicular structure during normal development and compensatory hypertrophy were assessed in crossbred Meishan x White Composite males. Boars were assigned at birth to unilateral castration at 1, 10, 56, or 112 days or to remain as intact controls through 220 days. The first testes removed were compared to assess testicular development. At 220 days, testicular structure was evaluated in boars representing the 25% with the largest (Lg) testis and the 25% with the smallest (Sm) testis in each treatment group. The number of Sertoli cells per testis reached a maximum by Day 56 in Sm testis but not until Day 112 in Lg testis boars, indicating a longer duration of Sertoli cell proliferation in Lg testis boars. Unilateral castration of Lg testis boars on Days 1, 10, 56, and 112 caused the weight of the remaining testis to hypertrophy by 149%, 135%, 119%, and 120%, respectively, and total sperm production to increase to 127%, 128%, 97%, and 106%, respectively. However, Sertoli cell numbers changed little in hemicastrate boars. In Lg testis boars, compensatory hypertrophy primarily involved proliferation of Leydig cells and expansion of existing Sertoli cells with little increase in Sertoli cell numbers, but in Sm testis boars, it involved expansion of existing Leydig and Sertoli cells without increase in cell numbers. These results indicate that Lg and Sm testis boars display intriguing differences during both development and compensatory hypertrophy, and they identify a unique animal model for further studies of factors that program and control Sertoli cell proliferation.     

An in-vivo method for estimating inhibin production by adult rat testes

The concentrations of inhibin in samples of rat testicular venous and arterial blood and interstitial fluid were measured by an in-vitro bioassay using pituitary cells in culture in which the standard was an ovine testicular lymph preparation (assigned potency 1 unit/mg). Inhibin levels were undetectable (less than 2 U/ml) in both blood samples but reached a mean concentration of 120 +/- 7 U/ml in testicular interstitial fluid. After unilateral efferent duct ligation the rate of inhibin accumulation in seminiferous tubules was determined by the difference in the inhibin content of the ligated and unligated testes. Additionally, the rate of seminiferous tubule fluid production was obtained from the difference in weight between the ligated and non-ligated testes. In the 24 h after efferent duct ligation there were linear increases in inhibin (18.5 +/- 1.0 U/h) and in seminiferous tubule fluid production (26 +/- 1 microliter/h), but there were no changes in serum FSH and LH levels. Experimental induction of bilateral cryptorchidism led to a decrease in the inhibin content of the testis after 10 days. The rate of inhibin accumulation after efferent duct ligation declined more rapidly than the inhibin content, being significantly depressed in cryptorchid testes after 3 days, suggesting that this measurement is a more sensitive index of inhibin production than the determination of testicular inhibin content.     

Photoperiodic modulation of testicular LH receptors in the bank vole (Clethrionomys glareolus)

The temporal changes in testicular binding of 125I-labelled hCG in juvenile bank voles (18 days of age, born and reared in a 18L:6D photoperiod) exposed to a long (18L:6D, Group L) or short (6L:18D, Group S) photoperiod for 0, 3, 7, 14 and 42-56 days were investigated. During testicular maturation, in Group L, there was a slight initial decrease in LH receptor numbers per testis followed by a marked prepubertal rise during the initial phase of rapid testicular growth after which a decrease took place. In Group S, during testicular regression, the temporal changes in LH receptor numbers per testis resembled those of Group L except that the corresponding increase in hCG binding during the initial week was considerably less marked and the receptor numbers remained thereafter at a significantly lower level than in Group L. Leydig cell count indicated that the observed changes in LH receptors per testis were due to changes in the number of Leydig cells as well as in LH receptors per Leydig cell. The present results indicate, that (1) photoperiod is an important modulator of testicular LH receptor numbers in this species, (2) photoperiod or age has no significant effect on the binding affinity of LH receptors, (3) short photoperiods arrest the induction of LH receptors as well as the increase in Leydig cell numbers associated with normal testicular maturation, and (4) changes in LH receptor numbers per testis correlate well with the photoperiod-induced changes in androgen biosynthesis, spermatogenesis and Leydig cell morphology observed in our previous studies.     

Effects of the induction of experimental cryptorchidism and subsequent orchidopexy on testicular function in immature rats

Cryptorchidism surgically induced in 14-day-old rats, was allowed to persist until 35 days when one group was killed to assess testicular function. In a second group the cryptorchid testis was returned to the scrotum surgically (orchidopexy) and subsequently killed at 130 days. A third group remained persistently cryptorchid to 130 days, while in a fourth group two sham operations were performed at 14 and 35 days. At 35 days, cryptorchidism resulted in a significant decline in testis weight due to suppressed spermatogenesis. Sertoli cell function as measured by seminiferous tubule fluid (TF) production after unilateral efferent duct ligation and androgen-binding protein (ABP) production was significantly depressed in the cryptorchid group. Serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were significantly elevated with cryptorchidism but serum testosterone levels were unchanged. Although morphometric measurements showed no change in Leydig cells cross-sectioned area, in vitro human chorionic gonadotropin (hCG)-stimulated testosterone production was significantly increased in the cryptorchid group at higher hCG doses. Similar changes were found in cryptorchid testes at 130 days except that Leydig cell cross-sectional area was now significantly increased. Orchidopexy at 35 days restored spermatogenesis and fertility during test mating was not impaired. TF production, ABP accumulation and serum FSH levels returned to normal following orchidopexy.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pubertal development of the boar: age-related changes in testicular morphology and in vitro production of testosterone and estradiol-17 beta

The responsiveness of testicular tissue, in terms of testosterone (T) and estradiol-17 beta (E2) production, to human chorionic gonadotropin (hCG) stimulation in vitro was assessed during pubertal development of the boar. A morphometric investigation was conducted concurrently to quantitate Leydig cell and seminiferous tubule changes in the testes of developing boars. Testicular volume percentage of seminiferous tubules increased from 36% at 40 days of age to a maximum of 72% at 190 days of age. Increases in tubular diameter were from 65 micrometers at 40 days of age to 236 micrometers at 250 days of age. Testicular volume percentage of Leydig cells decreased from 40% at 40 days of age to 10% at 250 days of age. Leydig cell number increased rapidly to 130 days of age, remained constant through 160 days, and then increased steadily to 220 days of age. Volume per Leydig cell changed little from 40 to 130 days of age, increased by 75% at 160 days, and declined thereafter. Total Leydig cell weight increased steadily from 40 to 160 days of age and then declined slightly. The capacity of Leydig cells for T production and testicular tissue for E2 production was greatest (P less than 0.05) after hCG stimulation in boars that were 130 and 160 days of age. In addition, sensitivity, as judged by the regression coefficient of T or E2 production per Leydig cell on log dosage of hCG was greater (p less than 0.05) for T at 130 days of age and for E2 at 160 days of age. The data presented support the hypothesis that one factor in pubertal development of boars is an increased capacity and sensitivity of the testes to gonadotropin stimulation.     

Morphometric studies on hamster testes in gonadally active and inactive states: light microscope findings

This study provides quantitative information on the testes of seasonally breeding golden hamsters during active and regressed states of gonadal activity. Seminiferous tubules occupied 92.5% of testis volume in adult gonadally active animals. Leydig cells constituted 1.4% of the testicular volume. The mean volume of an individual Leydig cell was 1092 microns 3, and each testis contained about 25.4 million Leydig cells. The volume of an average Sertoli cell nucleus during stage VII-VIII of the cycle was 502 microns 3. A gram of hamster testis during the active state of gonadal activity contained 44.5 million Sertoli cells, and the entire testis contained approximately 73.8 million Sertoli cells. Testes of the hamsters exposed to short photoperiods for 12-13 wk displayed a 90% reduction in testis volume that was associated with a decrease in the volume of seminiferous tubules (90.8% reduction), tubular lumena (98.8%), interstitium (72.7%), Leydig cell compartment (79.3%), individual Leydig cells (69.7%), Leydig cell nuclei (50.0%), blood vessels (85.5%), macrophages (68.9%), and Sertoli cell nuclei (34.1%). The diameter (61.1%) and the length (36.8%) of the seminiferous tubules were also decreased. Although the number of Leydig cells per testis was significantly lower (p less than 0.02) after short-photoperiod exposure, the number of Sertoli cells per testis remained unchanged. The individual Sertoli cell in gonadally active hamsters accommodated, on the average, 2.27 pre-leptotene spermatocytes, 2.46 pachytene spermatocytes, and 8.17 round spermatids; the corresponding numbers in the regressed testes were 0.96, 0.20, and 0.04, respectively. The striking differences in the testicular structure between the active and regressed states of gonadal activity follow photoperiod-induced changes in endocrine function and suggest that the golden hamster may be used as a model to study structure-function relationships in the testis.