Attrition of the human Leydig cell population with advancing age

Aging and androgens: Physiology and clinical implications

In men >  ~35 years, aging is associated with perturbations in the hypothalamus-pituitary-testicular axis and declining serum testosterone concentrations. The major changes are decreased gonadotropin-releasing hormone (GnRH) outflow and decreased Leydig cell responsivity to stimulation by luteinizing hormone (LH). These physiologic changes increase the prevalence of biochemical secondary hypogonadism-a low serum testosterone concentration without an elevated serum LH concentration. Obesity, medications such as opioids or corticosteroids, and systemic disease further reduce GnRH and LH secretion and might result in biochemical or clinical secondary hypogonadism. Biochemical secondary hypogonadism related to aging often remits with weight reduction and avoidance or treatment of other factors that suppress GnRH and LH secretion. Starting at age ~65-70, progressive Leydig cell dysfunction increases the prevalence of biochemical primary hypogonadism-a low serum testosterone concentration with an elevated serum LH concentration. Unlike biochemical secondary hypogonadism in older men, biochemical primary hypogonadism is generally irreversible. The evaluation of low serum testosterone concentrations in older men requires a careful assessment for symptoms, signs and causes of male hypogonadism. In older men with a body mass index (BMI) ≥ 30, biochemical secondary hypogonadism and without an identifiable cause of hypothalamus or pituitary pathology, weight reduction and improvement of overall health might reverse biochemical hypogonadism. For older men with biochemical primary hypogonadism, testosterone replacement therapy might be beneficial. Because aging is associated with decreased metabolism of testosterone and increased tissue-specific androgen sensitivity, lower dosages of testosterone replacement therapy are often effective and safer in older men.

Leukemia inhibitory factor-receptor signalling negatively regulates gonadotrophin-stimulated testosterone production in mouse Leydig Cells

Testicular Leydig cells (LCs) are the principal source of circulating testosterone in males. LC steroidogenesis maintains sexual function, fertility and general health, and is influenced by various paracrine factors. The leukemia inhibitory factor receptor (LIFR) is expressed in the testis and activated by different ligands, including leukemia inhibitory factor (LIF), produced by peritubular myoid cells. LIF can modulate LC testosterone production in vitro under certain circumstances, but the role of consolidated signalling through LIFR in adult LC function in vivo has not been established. We used a conditional Lifr allele in combination with adenoviral vectors expressing Cre-recombinase to generate an acute model of LC Lifr-KO in the adult mouse testis, and showed that LC Lifr is not required for short term LC survival or basal steroidogenesis. However, LIFR-signalling negatively regulates steroidogenic enzyme expression and maximal gonadotrophin-stimulated testosterone biosynthesis, expanding our understanding of the intricate regulation of LC steroidogenic function.

Hallmarks of Testicular Aging: The Challenge of Anti-Inflammatory and Antioxidant Therapies Using Natural and/or Pharmacological Compounds to Improve the Physiopathological Status of the Aged Male Gonad

The evolutionary theory of aging supports a trade-off relationship between reproduction and aging. Aging of the male reproductive system primarily affects the testes, leading to a decrease in the levels of sexual hormones, alterations in sperm quality and production, and a decline in fertility that does not necessarily involve a complete cessation of spermatogenesis. Inflammation, oxidation, and apoptosis are events considered as predictors of pathogenesis and the development of age-related diseases that are frequently observed in aged testes. Although the molecular mechanisms are still poorly understood, accumulating evidence points toward pro-inflammatory molecules and reactive oxygen species as primary contributing factors for testicular aging. However, the real impact of aging-related testicular alterations on fertility, reproductive health, and life span is far from being fully revealed. This work discusses the current knowledge on the impact of aging in the testis, particularly of aging-related dysregulated inflammation and oxidative damage on the functioning of its different cell populations. More interestingly, this review covers the potential benefits of anti-aging interventions and therapies using either pharmacological compounds (such as non-selective non-steroidal anti-inflammatory medication) or more natural alternatives (such as various nutraceuticals or even probiotics) that exhibit anti-inflammatory, antioxidant, and anti-apoptotic properties. Some of these are currently being investigated or are already in clinical use to delay or prevent testicular aging.

Reproductive aging and telomeres: Are women and men equally affected?

Successful reproduction is very important for individuals and for society. Currently, the human health span and lifespan are the object of intense and productive investigation with great achievements, compared to the last century. However, reproduction span does not progress concomitantly with lifespan. Reproductive organs age, decreasing the levels of sexual hormones, which are protectors of health through their action on several organs of the body. Thus, this is the starting point of the organismal decay and infertility. This starting point is easily detected in women. In men, it goes under the surface, undetected, but it goes, nevertheless. Regarding fertility, aging alters the hormonal equilibrium, decreases the potential of reproductive organs, diminishes the quality of the gametes and worsen the reproductive outcomes. All these events happen at a different pace and affecting different organs in women and men. The question is what molecular pathways are involved in reproductive aging and if there is a possible halting or even reversion of the aging events. Answers to all these points will be explained in the present review.

Age-related changes in human Leydig cell status

STUDY QUESTION

What are the consequences of ageing on human Leydig cell number and hormonal function?

SUMMARY ANSWER

Leydig cell number significantly decreases in parallel with INSL3 expression and Sertoli cell number in aged men, yet the in vitro Leydig cell androgenic potential does not appear to be compromised by advancing age.

WHAT IS KNOWN ALREADY

There is extensive evidence that ageing is accompanied by decline in serum testosterone levels, a general involution of testis morphology and reduced spermatogenic function. A few studies have previously addressed single features of the human aged testis phenotype one at a time, but mostly in tissue from patients with prostate cancer.

STUDY DESIGN, SIZE, DURATION

This comprehensive study examined testis morphology, Leydig cell and Sertoli cell number, steroidogenic enzyme expression, INSL3 expression and androgen secretion by testicular fragments in vitro. The majority of these endpoints were concomitantly evaluated in the same individuals that all displayed complete spermatogenesis.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Testis biopsies were obtained from 15 heart beating organ donors (age range: 19-85 years) and 24 patients (age range: 19-45 years) with complete spermatogenesis. Leydig cells and Sertoli cells were counted following identification by immunohistochemical staining of specific cell markers. Gene expression analysis of INSL3 and steroidogenic enzymes was carried out by qRT-PCR. Secretion of 17-OH-progesterone, dehydroepiandrosterone, androstenedione and testosterone by in vitro cultured testis fragments was measured by LC-MS/MS. All endpoints were analysed in relation to age.

MAIN RESULTS AND THE ROLE OF CHANCE

Increasing age was negatively associated with Leydig cell number (R = -0.49; P < 0.01) and concomitantly with the Sertoli cell population size (R= -0.55; P < 0.001). A positive correlation (R = 0.57; P < 0.001) between Sertoli cell and Leydig cell numbers was detected at all ages, indicating that somatic cell attrition is a relevant cellular manifestation of human testis status during ageing. INSL3 mRNA expression (R= -0.52; P < 0.05) changed in parallel with Leydig cell number and age. Importantly, steroidogenic capacity of Leydig cells in cultured testis tissue fragments from young and old donors did not differ. Consistently, age did not influence the mRNA expression of steroidogenic enzymes. The described changes in Leydig cell phenotype with ageing are strengthened by the fact that the different age-related effects were mostly evaluated in tissue from the same men.

LIMITATIONS, REASONS FOR CAUTION

In vitro androgen production analysis could not be correlated with in vivo hormone values of the organ donors. In addition, the number of samples was relatively small and there was scarce information about the concomitant presence of potential confounding variables.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides a novel insight into the effects of ageing on human Leydig cell status. The correlation between Leydig cell number and Sertoli cell number at any age implies a connection between these two cell types, which may be of particular relevance in understanding male reproductive disorders in the elderly. However aged Leydig cells do not lose their in vitro ability to produce androgens. Our data have implications in the understanding of the physiological role and regulation of intratesticular sex steroid levels during the complex process of ageing in humans.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from Prin 2010 and 2017. The authors have no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Effect of paternal age on offspring birth defects: a systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis was aimed at determining whether paternal age is a risk factor for offspring birth defects.

RESULTS

A total of 38 and 11 studies were included in the systematic review and meta-analysis, respectively. Compared with reference, fathers aged 25 to 29, young fathers (< 20 years) could increase the risk of urogenital abnormalities (OR: 1.50, 95 % CI: 1.03-2.19) and chromosome disorders (OR: 1.38, 95 % CI: 1.12-1.52) in their offsprings; old fathers (≥ 40 years) could increase the risk of cardiovascular abnormalities (OR: 1.10, 95 % CI: 1.01-1.20), facial deformities (OR: 1.08, 95 % CI: 1.00-1.17), urogenital abnormalities (OR: 1.28, 95 % CI: 1.07-1.52), and chromosome disorders (OR: 1.30, 95 % CI: 1.12-1.52).

CONCLUSIONS

Our study indicated that paternal age is associated with a moderate increase in the incidence of urogenital and cardiovascular abnormalities, facial deformities, and chromosome disorders.

METHODS

PubMed, Web of Science, the Cochrane Library, and Embase were searched for relevant literatures from 1960 to February 2020. The systematic review follows PRISMA guidelines. Relevant meta-analyses were performed.

Testosterone and Dehydroepiandrosterone Treatment in Ageing Men: Are We All Set?

Although demographic statistics show that populations around the world are rapidly ageing, this rising life expectancy is accompanied by an increase in the number of people living with age-related chronic conditions, such as frailty, cognitive decline, depression, or sexual dysfunction. In men, a progressive decline in androgens occurs with increasing age, and low androgen levels are associated with age-related chronic conditions. However, androgen administration studies are inconclusive, showing differing results according to the androgen used (testosterone [T], dehydroepiandrosterone [DHEA]), the group of men examined (younger vs. older; eugonadal vs. hypogonadal) and the conditions studied (frailty, cognitive decline, depression, sexual dysfunction). In this review, the current state for the use of T and DHEA therapy in men for the age-related conditions is examined. Due to the progressive age-related decline in androgens leading to a higher rate of older men having low androgen levels, the effects of androgen treatment in elderly males will be of particular interest in this review. Dose-response relationships, the role of potential moderators, and the androgen treatment-related risk for adverse events will be discussed. Studies have suggested that T treatment - more so than DHEA treatment - may be an effective therapy against age-related chronic conditions in men with low T levels; especially older men. Such conditions include frailty, depression, or sexual dysfunction. However, T treatment does not emerge as an effective therapy against cognitive decline. Nevertheless, more high-quality, randomised controlled trials using T treatment for age-related chronic conditions are necessary if further conclusions are to be made.

Aging and Senescence in Canine Testes

Senescent cells accumulate with age but tissue-based studies of senescent cells are limited to selected organs from humans, mice, and primates. Cell culture and xenograft studies have indicated that senescent cells in the microenvironment may play a role in tumor proliferation via paracrine activities. Dogs develop age-related conditions, including in the testis, but cellular senescence has not been confirmed. We hypothesized that senescent cells accumulate with age in canine testes and in the microenvironment of testicular tumors. We tested the expression of the established senescence markers γH2AX and p21 on normal formalin-fixed, paraffin-embedded testes from 15 young dogs (<18 months of age) and 15 old dogs (7-15 years of age) and correlated the findings with age-dependent morphological changes. A statistically significant age-dependent increase in the percentage of p21-expressing cells was observed for testicular fibroblasts (4-fold) and Leydig cells (8-fold). However, p21-expressing cells were still a rare event. In contrast, the percentage of γH2AX-positive cells did not increase with age. P21- and γH2AX-expressing cells were rare in the microenvironments of tumors. Age-dependent morphological changes included an increased mean number of Leydig cells per intertubular triangle (2.95-fold) and a decreased spermatogenesis score. To our surprise, no age-related changes were recorded for interstitial collagen content, mean tubular diameter, and epithelial area. Opposed to our expectations based on previous in vitro data, we did not identify evidence of a correlation between age-associated accumulation of senescent cells and testicular tumor development. Understanding the role of the microenvironment in senescence obviously remains a challenging task.

A young testicular microenvironment protects Leydig cells against age-related dysfunction in a mouse model of premature aging

Testicular Leydig cells (LCs) are the primary source of circulating androgen in men. As men age, circulating androgen levels decline. However, whether reduced LC steroidogenesis results from specific effects of aging within LCs or reflects degenerative alterations to the wider supporting microenvironment is unclear; inability to separate intrinsic LC aging from that of the testicular microenvironment in vivo has made this question difficult to address. To resolve this, we generated novel mouse models of premature aging, driven by CDGSH iron sulfur domain 2 (Cisd2) deletion, to separate the effects of cell intrinsic aging from extrinsic effects of aging on LC function. At 6 mo of age, constitutive Cisd2-deficient mice display signs of premature aging, including testicular atrophy, reduced LC and Sertoli cell (SC) number, decreased circulating testosterone, increased luteinizing hormone/testosterone ratio, and decreased expression of steroidogenic mRNAs, appropriately modeling primary testicular dysfunction observed in aging men. However, mice with Cisd2 deletion (and thus premature aging) restricted to either LCs or SCs were protected against testicular degeneration, demonstrating that age-related LCs dysfunction cannot be explained by intrinsic aging within either the LC or SC lineages alone. We conclude that age-related LC dysfunction is largely driven by aging of the supporting testicular microenvironment.—Curley, M., Milne, L., Smith, S., Jørgensen, A., Frederiksen, H., Hadoke, P., Potter, P., Smith, L. B. A Young testicular microenvironment protects Leydig cells against age-related dysfunction in a mouse model of premature aging.

Lower birthweight and left-/mixed-handedness are associated with intensified age-related sex steroid decline in men. Findings from the Men's Health 40+ Study

In males, age‐related decline in free testosterone (T) and dehydroepiandrosterone (DHEA) by 2–3% per year has been reported. Estradiol (E2) and progesterone (P) seem to decrease as well, but to a lesser extent. Lower sex steroid levels in men have been related to physical and mental symptoms. Low birthweight and left‐/mixed‐handedness (L/MH) are indicators of an adverse fetal environment during pregnancy, and both have been linked to morbidity in later life. The aim of this study is to examine the relationship between lower birthweight as well as L/MH and age‐related sex steroid decline. In a cross‐sectional study design, saliva samples were collected under standardized conditions from healthy men for subsequent steroid hormone analysis using standard luminescence immunoassays. T (M = 67.57 pg/mL), DHEA (M = 247.91 pg/mL), E2 (M = 1.29 pg/mL), and P (M = 28.20 pg/mL) have been quantified leading to a final sample of 256 men providing complete data on sex hormones (M_Age=57.8; SD_Age = 10.8). Information on participants’ birthweight was obtained from birth reports (N = 134), and participants were asked about their handedness (right‐handed, left‐handed, mixed‐handed) (N = 256). Multivariate‐adjusted linear regression models relating each sex hormone individually and the principal component of declining steroid hormones (DSH)—an integrated hormonal parameter—with handedness and birthweight did not identify significant associations except for handedness and E2. Moderation analysis using robust regression accounting for bias due to influential data points detected a significant association between age and DSH for handedness (β = −0.0314, p = 0.040) but only a trend for birthweight (β = 0.0309, p = 0.073). For lower birthweight, a trend toward intensified age‐related sex steroid decline in men was observed, while for L/MH, a significant association with intensified age‐related sex steroid decline was identified. These results indicate that L/MH and potentially also lower birthweight might be considered as early risk factors for endocrine health in later life.

Reproductive genetics and the aging male

PURPOSE

To examine current evidence of the known effects of advanced paternal age on sperm genetic and epigenetic changes and associated birth defects and diseases in offspring.

METHODS

Review of published PubMed literature.

RESULTS

Advanced paternal age (> 40 years) is associated with accumulated damage to sperm DNA and mitotic and meiotic quality control mechanisms (mismatch repair) during spermatogenesis. This in turn causes well-delineated abnormalities in sperm chromosomes, both numerical and structural, and increased sperm DNA fragmentation (3%/year of age) and single gene mutations (relative risk, RR 10). An increase in related abnormalities in offspring has also been described, including miscarriage (RR 2) and fetal loss (RR 2). There is also a significant increase in rare, single gene disorders (RR 1.3 to 12) and congenital anomalies (RR 1.2) in offspring. Current research also suggests that autism, schizophrenia, and other forms of "psychiatric morbidity" are more likely in offspring (RR 1.5 to 5.7) with advanced paternal age. Genetic defects related to faulty sperm quality control leading to single gene mutations and epigenetic alterations in several genetic pathways have been implicated as root causes.

CONCLUSIONS

Advanced paternal age is associated with increased genetic and epigenetic risk to offspring. However, the precise age at which risk develops and the magnitude of the risk are poorly understood or may have gradual effects. Currently, there are no clinical screenings or diagnostic panels that target disorders associated with advanced paternal age. Concerned couples and care providers should pursue or recommend genetic counseling and prenatal testing regarding specific disorders.

Sertoli Cell Number Defines and Predicts Germ and Leydig Cell Population Sizes in the Adult Mouse Testis

Sertoli cells regulate differentiation and development of the testis and are essential for maintaining adult testis function. To model the effects of dysregulating Sertoli cell number during development or aging, we have used acute diphtheria toxin-mediated cell ablation to reduce Sertoli cell population size. Results show that the size of the Sertoli cell population that forms during development determines the number of germ cells and Leydig cells that will be present in the adult testis. Similarly, the number of germ cells and Leydig cells that can be maintained in the adult depends directly on the size of the adult Sertoli cell population. Finally, we have used linear modeling to generate predictive models of testis cell composition during development and in the adult based on the size of the Sertoli cell population. This study shows that at all ages the size of the Sertoli cell population is predictive of resulting testicular cell composition. A reduction in Sertoli cell number/proliferation at any age will therefore lead to a proportional decrease in germ cell and Leydig cell numbers, with likely consequential effects on fertility and health.

Cellular changes in the hamster testicular interstitium with ageing and after exposure to short photoperiod

The aim of this study was to evaluate the cellular changes that occur in the hamster testicular interstitium in two very different physiological situations involving testicular involution: ageing and exposure to a short photoperiod. The animals were divided into an ‘age group’ with three subgroups – young, adult and old animals – and a ‘regressed group’ with animals subjected to a short photoperiod. The testicular interstitium was characterised by light and electron microscopy. Interstitial cells were studied histochemically with regard to their proliferation, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP in situ nick end labelling (TUNEL+) and testosterone synthetic activity. We identified two types of Leydig cell: Type A cells showed a normal morphology, while Type B cells appeared necrotic. With ageing, pericyte proliferation decreased but there was no variation in the index of TUNEL-positive Leydig cells. In the regressed group, pericyte proliferation was greater and TUNEL-positive cells were not observed in the interstitium. The testicular interstitium suffered few ultrastructural changes during ageing and necrotic Leydig cells were observed. In contrast, an ultrastructural involution of Leydig cells with no necrosis was observed in the regressed group. In conclusion, the testicular interstitium of Mesocricetus auratus showed different cellular changes in the two groups (age and regressed), probably due to the irreversible nature of ageing and the reversible character of changes induced by short photoperiod.

The total number of Leydig and Sertoli cells in the testes of men across various age groups - a stereological study

The aim of this study was to estimate the total number of Sertoli and Leydig cells in testes from male subjects across the human lifespan, using an optimized stereological method for cell-counting. In comparison with many other organs, estimation of the total cell numbers in the testes is particularly sensitive to methodological problems. Therefore, using the optical fractionator technique and a sampling design specifically optimized for human testes, we estimated the total number of Sertoli and Leydig cells in the testes from 26 post mortem male subjects ranging in age from 16 to 80 years. The mean unilateral total number of Sertoli cells was 407 × 10(6) [range: 86 × 10(6) to 665 × 10(6) , coefficient of variation (CV) = 0.33], and the mean unilateral total number of Leydig cells was 99 × 10(6) (range: 47 × 10(6) to 245 × 10(6) , CV = 0.48). There was a significant decline in the number of Sertoli cells with age; no such decline was found for Leydig cells. Quantitative stereological analysis of post mortem tissue may help understand the influence of age or disease on the number of human testicular cells.

The changes of stage distribution of seminiferous epithelium cycle and its correlations with Leydig cell stereological parameters in aging men

PURPOSE

To evaluate the changes of stage distribution of seminiferous epithelium cycle and its correlations with Leydig cell stereological parameters in aging men.

METHODS

Point counting method was used to analyze the stereological parameters of Leydig cells. The stage number of seminiferous epithelium cycle was calculated in the same testicular tissue samples which were used for Leydig cell stereological analysis.

RESULTS

The aging group had shown more severe pathological changes as well as higher pathologic scores than the young group. Compared with the control group, the volume density (VV) and surface density (NA) of Leydig cells in the aging group were increased significantly. The stage number of seminiferous epithelium cycle in the aging group was decreased coincidently compared to the young group. Leydig cell Vv in the young group has a positive relationship with stages I, II, III, V and VI of seminiferous epithelium cycle, and Leydig cell NA and numerical density (NV) were positively related to stage IV. However, only the correlation between NV and stage II was found in the aging group.

CONCLUSIONS

The stage number of seminiferous epithelium cycle was decreased in aging testes. Changes in the stage distribution in aging testes were related to the Leydig cell stereological parameters which presented as a sign of morphological changes.

Association between serum inhibin-B levels and coronary artery disease in aging males

INTRODUCTION

Atherosclerosis is a systemic disorder. It is a frequent leading cause of coronary artery disease (CAD). Similarly, atherosclerotic vascular alterations could lead to testicular arterial blood flow reduction and impairment of testicular function with age. Inhibin-B has been validated as a valuable serum marker of testicular functions and its correlation with testicular volume was shown in some studies done before. The purpose of this study is to investigate the association between serum inhibin-B levels and CAD in elderly men.

MATERIAL AND METHODS

Between March 2009 and March 2010, fifty-two 50-80-year-old consecutive patients with Gensini score over 20 and ejection fraction (EF) > 50% were included in the study as the CAD group. Fifty healthy men without any cardiac disease history were recruited as the control group. All patients in the CAD group who had indications for coronary artery angiography underwent selective coronary artery angiography.

RESULTS

Inhibin-B, total testosterone and testicular volume levels were found to be significantly lower in the CAD group in comparison with the control group (p = 0.004, p < 0.0001, and p = 0.001 respectively).

CONCLUSIONS

In this study, although no correlation was found in CAD patients between Gensini score and inhibin-B or testicular volume, inhibin-B levels and testicular volume were significantly lower in patients with CAD than in healthy men. In order to fully assess the relationship between serum inhibin-B levels and CAD, multi-centered prospective and longitudinal studies must be done in elderly male patients.

(18)F-FDG Uptake of Human Testis on PET/CT: Correlation with Age, Sex Hormones, and Vasectomy

PURPOSE

The purpose of this study was to evaluate glucose metabolism of normal human testis on (18)F-FDG PET/CT and to assess possible correlations among age, the serum levels of sex hormones, and vasectomy.

METHODS

(18)F-FDG PET/CT was performed in 66 normal healthy men (50.8 ± 13.6 years, range 22-81), and mean standard uptake values (SUV) of (18)F-FDG in testis and adductor muscle were measured. Testis-muscle SUV ratios (T/M ratios) were calculated. Serum levels of total testosterone, free testosterone, estradiol, and of sex-hormone binding globulin (SHBG) were measured. We searched for correlations between T/M ratios and age and the serum concentrations of sex hormones. (18)F-FDG PET/CT was also performed in 32 vasectomized men (55.7 ± 7.8 years, range 38-71) and 52 nonvasectomized men (55.4 ± 11.6 years, range 37-72). Mean SUVs of testis and adductor muscle were measured, and T/M ratios were calculated.

RESULTS

A significant age-related decline was found in T/M ratio (r = -0.509, p < 0.0001). Serum levels of total testosterone and free testosterone were also found to be positively correlated with T/M ratio (r = 0.427, p = 0.0003; r = 0.435, p = 0.0003, respectively). The mean SUV and T/M ratio of vasectomized men were significantly lower than those of nonvasectomized men (p < 0.0378 and p = 0.0001, respectively).

CONCLUSIONS

Glucose metabolism in the testis in an adult population was found to be correlated with age, serum sex hormone level, and vasectomy history. These results indicate that testicular (18)F-FDG uptake may have attributed to testicular function and testicular histology. Our findings may have important implications for the interpretation of testicular (18)F-FDG uptake in the normal adult population.

Leydig cell transplantation restores androgen production in surgically castrated prepubertal rats

Prepubertal testicular dysfunction and the subsequent development of hypogonadism affects an estimated one in 200 children worldwide. As the testosterone levels are dynamic during development and puberty, traditional hormone treatment regimens are often inadequate, thereby leaving associated physiological conditions unresolved. Therefore, we have investigated the potential therapeutic effect of mature Leydig cell transplantation for the treatment of prepubertal primary hypogonadism through the use of a surgically induced hypogonadistic rat model system. In the experiment, Leydig cells were surgically isolated from mature Sprague-Dawley rats and transplanted into prepubertal recipients. Serum testosterone levels and microscopic analysis of the stained testicular interstitium were compared with sham-treated controls, as well as with castrated and intact rats during sexual development. At 4 weeks post-implantation, serum testosterone was detectable in Leydig cell recipients, but not in surgical controls, and progressively increased as a function of time until reaching levels comparable with sexually mature males at 12 weeks post-implantation. Histological analysis revealed a high rate of Leydig cell survival as well as steroidogenic secretory activity. Therefore, we conclude that mature Leydig cell transplantation in prepubertal hypogonadism recipients has therapeutic potential in rats and merits further investigation for clinical application.

Associations between andrological measures, hormones and semen quality in fertile Australian men: inverse relationship between obesity and sperm output

BACKGROUND

The World Health Organization developed a time to pregnancy (TTP) study (number of menstrual cycles taken to conceive) to determine whether the average TTP is increasing and semen quality decreasing with time. The present study describes clinical, semen and hormone characteristics obtained from male partners of pregnant women in Melbourne, Australia, and examines the associations between these characteristics.

METHODS

Male partners (n = 225) of pregnant women (16-32 weeks) who conceived naturally had physical examination, health and lifestyle questionnaires, semen and hormone (FSH, LH, sex hormone-binding globulin, testosterone and Inhibin B) analyses.

RESULTS

Previously known associations between semen, hormone and clinical variables were confirmed as significant: sperm numbers (concentration and total sperm count) correlated positively with Inhibin B and inversely with FSH and left varicocele, while total testicular volume correlated positively with sperm numbers and Inhibin B and inversely with FSH. However, only abstinence, total testicular volume, varicocele grade and obesity (BMI > 30 kg/m2) were independently significantly related to total sperm count. Compared with those with BMI < 30 (n = 188), obese subjects (n = 35) had significantly lower total sperm count (mean 324 versus 231 million, P = 0.013) and Inhibin B (187 versus 140 pg/ml, P < 0.001) but not FSH (3.4 versus 4.0 IU/l, P = 0.6).

CONCLUSIONS

Obese fertile men appear to have reduced testicular function. Whether this is cause or effect, i.e. adiposity impairing spermatogenesis or reduced testicular function promoting fat deposition, remains to be determined.

Normal uptake of 18F-FDG in the testis: an assessment by PET/CT

OBJECTIVE

The aim of this study was to assess the physiological uptake of 18F-fluoro-2-deoxyglucose (FDG) by an apparently normal testis with combined positron emission tomography-computed tomography (PET/CT) and its correlation with age, blood glucose level, and testicular volume.

METHODS

The testicular uptake of 18F-FDG, expressed as the standardized uptake value (SUV), was measured on PET/CT images in 203 men. The correlation between SUV and age, blood glucose level, and testicular volume was assessed.

RESULTS

The SUV in the total of 406 testes was 2.44 +/- 0.45 (range 1.23-3.85). The SUV was 2.81 +/- 0.43 (2.28-3.85) for 30-39 years (n = 12), 2.63 +/- 0.45 (1.77-3.75) for 40-49 years (n = 64), 2.46 +/- 0.35 (1.44-3.15) for 50-59 years (n = 82), 2.51 +/- 0.41 (1.50-3.46) for 60-69 years (n = 86), 2.43 +/- 0.47 (1.42-3.29) for 70-79 years (n = 86), and 2.18 +/- 0.45 (1.23-3.03) for 80-89 years (n = 76). When we calculated the mean SUV of bilateral testes in each patient, there were significant statistical differences between those in the age group of 30-39 years and 80-89 years, 40-49 years and 80-89 years, and 50-60 years and 80-89 years, when using an unpaired test with Bonferroni correction. The laterality index (|L - R|/(L + R) x 2) in 203 men was 0.066 +/- 0.067 (0-0.522). There was a mild correlation between the mean SUV and age (r = -0.284, P < 0.001) as well as between the mean SUV and mean volume (r = +0.368, P < 0.001). There was no correlation between the mean SUV and glucose blood level (r = -0.065, P = 0.358).

CONCLUSIONS

Some uptake of FDG is observed in the normal testis and declines slightly with age. Physiological FDG uptake in the testis should not be confused with pathological accumulation.

The seminiferous epithelium cycle length in the black tufted-ear marmoset (Callithrix penicillata) is similar to humans

Marmosets are New World small primates phylogenetically close to humans and are commonly used in biomedical research. Although the reproductive biology of the common marmoset Callithrix jacchus is fairly well investigated, there are few data available for testis function for its close relative, Callithrix penicillata. In this regard, the present study was performed to investigate testis structure, spermatogenic cycle length, and spermatogenic and Sertoli cell efficiencies in eight captive C. penicillata. These animals received (3)H-thymidine injections and had their testes perfused-fixed with glutaraldehyde and embedded in plastic at different time periods after (3)H-thymidine injections, for histomorphometric and autoradiographic evaluation. The analysis of the different germ cell associations showed that two or more stages were observed in about 30% of the seminiferous tubule cross sections investigated. The values found for spermatogenic cycle length and for total duration of spermatogenesis in the marmoset C. penicillata, 15.4 and 69.3 days respectively, were very close to those cited in the literature for humans. However, the results observed for Sertoli cell efficiency (number of round spermatids per Sertoli cell; 8:1) and spermatogenic efficiency (daily sperm production per gram of testis; 18.4 million) were substantially higher than those observed for humans. The results found in the present investigation suggest that the black tufted-ear marmoset C. penicillata might represent an alternative and useful experimental model to perform comparative studies regarding the spermatogenic process, particularly in investigations related to the expansion of spermatogonial stem cells and the establishment of spermatogenic waves.

A histomorphometric and cytogenetic study of testis from men 29–102 years old

OBJECTIVE

To evaluate the influence of aging on testicular histology and the aneuploidy rate in testis postmeiotic cells.

DESIGN

Comparison between older men and younger men.

SETTING

Deceased donors and patients who requested assisted reproductive technology (ART).

PATIENT(S)

Thirty-six older men (61-102 years old) and 10 younger men (29-40 years old).

INTERVENTION(S)

Testes were obtained from 35 deceased donors, and testicular biopsies were obtained from 11 patients who requested ART.

MAIN OUTCOME MEASURE(S)

Histomorphometry of testis and fluorescent in situ hybridization (FISH), with a three-probe set X, Y, and 18.

RESULT(S)

The histomorphometric study showed a thickening of the basal membrane when spermatogenesis was arrested. The number of germinal and Sertoli cells decreased as age increased. The rate of aneuploidy of postmeiotic cells was 1.1% for the control group, 1.29% for older subjects with preserved spermatogenesis, and 14.28% for the subjects with an arrested spermiogenesis. Only this last figure was higher than the control group.

CONCLUSION(S)

The rate of aneuploidy in older subjects (61-95 years old) with preserved spermatogenesis was not statistically different from that found in the control group; it was increased in older subjects with arrested spermatogenesis.

Testicular histological examination of spermatogenetic activity in captive gorillas (Gorilla gorilla)

To clarify the reproductive state of male gorillas, we performed histological examinations on the testicles of 10 male gorillas (Gorilla gorilla). The testicular samples were obtained by autopsy, and ordinal histological preparations were made for light microscopy. The poor spermatogenesis of this species was characterized by the following findings: First, spermatogenesis was evident in only four samples. Meiosis progressed in two samples, but they lacked spermatogenesis. In the remaining four specimens, seminiferous tubules hyalinized without any sign of spermatogenesis. Second, seminiferous epithelia were thin even in the males in which spermatogenesis was observed. Third, degenerated seminiferous tubules were found in all specimens. Fourth, abnormally large syncytial cells were found in the tubules. Six stages in the epithelial cycle of the seminiferous tubules were identified. Testosterone staining made it clear that there were many Leydig cells with spherical or fusiform nuclei in an abundance of interstitial tissue. The relevance of the testicular architecture of gorillas to the mating system is discussed.

Gestational exposure to ethane dimethanesulfonate permanently alters reproductive competence in the CD-1 mouse

Although the adult mouse Leydig cell (LC) has been considered refractory to cytotoxic destruction by ethane dimethanesulfonate (EDS), the potential consequences of exposure during reproductive development in this species are unknown. Herein pregnant CD-1 mice were treated with 160 mg/kg on Gestation Days 11-17, and reproductive development in male offspring was evaluated. Prenatal administration of EDS compromised fetal testosterone (T) levels, compared with controls. EDS-exposed pups recovered their steroidogenic capacities after birth because T production by hCG-stimulated testis parenchyma from prepubertal male offspring was unchanged. However, prepubertal testes from prenatally exposed males contained seminiferous tubules (STs) devoid of germ cells, indicating a delay in spermatogenesis. In adults, some STs in exposed males still contained incomplete germ cell associations corroborating observed reductions in epididymal sperm reserves, fertility ratios, and litter size. Morphometry revealed an EDS-induced increase in interstitial area and a concomitant decrease in ST area, but stereology revealed an unexpected decrease in the number and size of the LCs per testis in exposed males. Paradoxically, there was an increase in both serum LH and T production by adult testis parenchyma, indicating that the LCs were hyperstimulated. These data demonstrate permanent lesions in LC development and spermatogenesis caused by prenatal exposure in mice. Thus, although adult mouse LCs are insensitive to EDS, EDS appears to have direct action on fetal LCs, resulting in abnormal testis development.

Recent neuroendocrine facets of male reproductive aging

We recently identified consistent attenuation of LH and testosterone secretory pulse amplitude and associated disruption of their orderly patterns of release in healthy older men. These dynamic changes emerge despite young-adult concentrations of LH and total testosterone. Moreover, we could document disruption of synchrony between LH secretion and oscillations in FSH, prolactin, sleep-stage and NPT (nocturnal penile tumescence), thus pointing to loss of coordinate neurohormone outflow. Such data suggest that CNS-hypothalamically based regulatory defects may be important in aging, as inferred indirectly in the old male rat and mouse more than 15 years ago. How such alterations are related to specific hypothalamic neurotransmitter changes in aging will be critical to unravel.

Ageing and testicular function in Octodon degus

The present study analyses cell loss and proliferation which account for the decrease in the number of germ cell populations in the senile male Octodon degus. This is a good model to study ageing in wild animals, since it has recently been incorporated as a laboratory animal but still has a high degree of genetic heterogeneity, thus representing a situation found in natural systems. The cell loss from pachytene spermatocytes to round spermatids is estimated by cell counts in the cross section of seminiferous tubules. DNA testicular synthesis is measured by scintillation counting and the index of labelling of spermatogonia by radioautography of testes comparing sexually mature young animals and senile animals. Other determinations in both groups are testis weight, thickness of the albuginea and tubular wall, daily sperm production, percentage of depleted seminiferous tubules and nuclear cell diameters of germ cells. The results suggest a decrease in the number of cell population in the senile animals resulting from an increase in physiological cell loss coupled with a decreased proliferative spermatogonial activity. There is also a decreased yield of meiosis in terms of round spermatid production. Lowered testosterone levels both in plasma and testicular parenchymal fluid are found in senile animals. All these senescent changes reflect an altered remodelling activity of the seminiferous epithelium and presumably also of Leydig cells.

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

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

Efficiency of spermatogenesis

Spermatogenesis is a process of division and differentiation by which spermatozoa are produced in seminiferous tubules. A measure of efficiency of spermatogenesis is the estimated number of spermatozoa produced per day per gram of testicular parenchyma. This measure is not influenced by species differences in testicular size; however, it is influenced by species differences in the numerical density of germ cells and in the life spans of these cells. Seminiferous tubules are composed of somatic cells (myoid cells and Sertoli cells), and germ cells (spermatogonia, spermatocytes, and spermatids). Activity of these three germ cells divide spermatogenesis into spermatocytogenesis, meiosis, and spermiogenesis, respectively. Spermatocytegenesis involves mitotic cell division to increase the yield of spermatogenesis and to produce stem cells and primary spermatocytes. Meiosis involves duplication and exchange of genetic material and two cell divisions that reduce the chromosome number and yield four spermatids. Spermiogenesis is the differentiation of spherical spermatids into mature spermatids which are released at the luminal free surface as spermatozoa. The spermatogenic cycle is superimposed on the three major divisions of spermatogenesis. Spermatogenesis and germ cell degeneration can be quantified from numbers of germ cells in various steps of development throughout spermatogenesis, and quantitative measures are related to number of spermatozoa in the ejaculate. Germ cell degeneration occurs throughout spermatogenesis; however, the greatest impact occurs during spermatocytogenesis and meiosis. Efficiency of spermatogenesis is related to the amount of germ cell degeneration, pubertal development, season of the year, and aging of humans and animals. Number of Sertoli cells and amount of smooth endoplasmic reticulum of Leydig cells (but not Leydig cell number) are related to efficiency of spermatogenesis. In humans, efficiency of spermatogenesis is reflected in number of spermatogenic stages per cross-section and number of missing generations within each stage; however, the arrangement of stages along the tubular length does not reflect differences in the efficiency of spermatogenesis. In short, spermatogenesis involves both mitotic and meiotic cell divisions and an unsurpassed example of cell differentiation in the production of the spermatozoon, and daily sperm production per g parenchyma is a measure of its efficiency.

Neuronal hypertrophy in the hypothalamus of older men

A striking neuronal hypertrophy occurs in the infundibular nucleus of postmenopausal women. To determine the gender specificity of this response, we measured the areas of neuronal profiles in the infundibular nucleus of young (21, 32, and 41 years) and older (60, 61, and 68 years) men and compared them to data reported previously from the hypothalami of pre-(28, 32, and 40 years) and postmenopausal women (58, 62, and 74 years). Sagittal blocks of formalin-fixed hypothalami were paraffin embedded, serially sectioned and stained with cresyl-violet. The profile areas of 2,429 infundibular neurons were manually digitized using an image-combining computer microscope. The contralateral hypothalamus of each subject was cryoprotected, frozen-sectioned in the coronal plane and also stained with cresyl violet. The infundibular nuclear volume and the total number of neurons were estimated from the coronal sections using stereological methods. The mean profile area of infundibular neurons from older men (176.6 +/- 1.7 microns 2) was significantly larger than that of young men (147.0 +/- 1.3 microns 2). There was also a significant increase in the density of hypertrophied neurons (> 226 microns 2 profile area) in the infundibular nucleus of older men. There was no difference in infundibular nucleus associated with an average neurons was significantly increased in the older men. A comparison with previous data obtained from pre- and postmenopausal women revealed that the profile area of infundibular neurons was equal in young men and young women. However, the profile area of neurons in the postmenopausal women (190.4 +/- 2.1 microns 2) was significantly greater than that of older men.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of age on male reproductive function

When couples elect to defer child bearing, the effects of age on reproductive potential must be considered. The impact of advancing age on female reproductive potential has been well documented. Relatively less attention, however, has been directed toward the effect of age on male reproductive function. Although less pronounced than its effect on female fertility, advancing age does have an impact on male reproduction. Among men, increasing age is associated with a decrease in sexual function as well as changes in testicular histology and a decline in basic fertility parameters. Additionally, there is an identifiable association between advanced paternal age and subsequent birth defects. These issues should be borne in mind when men are counseled regarding the age at which they elect to establish families.

Ultrastructure and morphometry of testicular Leydig cells and the interstitial components correlated with testosterone in aging rats

The ultrastructure of testicular interstitium in young and aged adult rats was analysed using morphometric methods, and the plasma testosterone concentration was measured. With increasing age there was an augmentation in the volume of collagen fibrils in the intercellular matrix and in blood vessels. During the aging process (approximately two years) the average volume of the Leydig cell decreased from 1364 microns 3 to 637 microns 3, but the number of Leydig cells in paired testes increased from 53 x 10(6) to 113 x 10(6). The absolute volume of smooth surfaced endoplasmic reticulum (SER) per Leydig cell amounted in aged rats to 78% of that in young adult rats. The total amount of SER in paired testes increased by 62% with aging. The present analysis suggests that the ability of SER to maintain peripheral testosterone concentration decreases with age. In young adult rats the absolute volume of peroxisomes per Leydig cell correlated significantly with the concentration of testosterone in blood and also with the absolute volume of SER per Leydig cell. These results combined with ultrastructural observations of close apposition of peroxisomes and SER suggest that peroxisomes have a role in testosterone secretion by Leydig cells.

Structural response of the hamster Sertoli cell to hypophysectomy: a correlative morphometric and endocrine study

Reproductively active hamsters were hypophysectomized and examined 6 or 20 days later in a combined morphometric and endocrine study of the Sertoli cell to determine 1) the morphological and endocrine effects of hypophysectomy of both short- and long-term duration, 2) if regression of Sertoli cells after hypophysectomy in a seasonal breeder resembles regression due to seasonal changes, and 3) if effects of hypophysectomy in a seasonal breeder are equivalent to the effects of hypophysectomy in a nonseasonal breeder. Six days after hypophysectomy, at a period when germ cell degeneration is first noted, there was a significant decrease in testis weight, interstitial space, tubule diameter and length, volume of seminiferous tubule, and tubular lumen. There were no significant changes in Sertoli cell nuclear and cytoplasmic volume although cell surface area was decreased significantly. Most organelles exhibited no significant change in volume or surface area except for secondary lysosomes which expectedly increased in volume as the result of phagocytosis of germinal cells. Thus at an early time period when functional changes in germ cells and Leydig cells are clearly evident (Russell et al. [1992] Endocrinology), the Sertoli cell shows minimal changes. Twenty days after hypophysectomy, the cell, nuclear and cytoplasmic volumes and surface area of the Sertoli cells, and volumes and surface areas of nearly all organelles were significantly decreased from values measured in normal and in short-term hypophysectomized hamsters. The exceptions were the total volumes of lipid which increased significantly and lysosomes which were similar to normal but significantly lower than short-term hypophysectomized animals. The long-term hypophysectomized hamster Sertoli cell, like that of the short-day hamster (Sinha Hikim et al. [1989b] Endocrinology, 125:1829-1843) is structurally regressed as a whole rather than exhibiting selective decreases in cellular and subcellular components. The size of the Sertoli cell in pituitary-intact, long- and short-term hypophysectomized animals showed positive and significant correlations with the volumes and surface areas of all its cytoplasmic organelles except the volume of lipid which showed a negative, significant correlation. Comparisons of long-term hypophysectomized hamsters (in long-day light exposure) and short-day exposed animals (Sinha Hikim et al. [1989b] (Endocrinology, 125:1829-1843) suggested that hypophysectomy, in general, resulted in similar, but slightly more severe regressive changes in the testis and germ cell population than those seen during seasonal regression.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional cytology of the human testis

The seminiferous tubular compartment of the human testis occupies about two thirds of the volume of the organ and is supported by loose connective tissue containing the Leydig cells. Sertoli cells extend from the basal lamina to the lumen of the seminiferous tubule and provide structural and functional support to the germ cells which proliferate and mature through the complex process of spermatogenesis, lasting for approximately 70 days. Histological examination of the human seminiferous epithelium gives the impression of a very irregular pattern of germ cell development but recent cytological, ultrastructural and computer-modelling studies have shown that the arrangement of germ cells within the seminiferous tubules is in fact highly organized into a helical pattern based upon the geometry of concentric spirals. Thus the human spermatogenic cycle is precisely regulated in accordance with the more familiar ordered arrangements of germ cells seen in most non-human primates and other mammalian species. The population of Leydig cells in the adult human testis represents the third and final phase of their developmental history, preceded by distinct neonatal and, earlier, fetal Leydig cell generations. Human Leydig cells are irregular in outline, deeply staining with basophilic dyes and exhibit a characteristic circular or ovoid nucleus. The density of their cytoplasm is attributed to extensive domains of smooth endoplasmic reticulum, characteristic of steroidogenic tissue. Mitochondria are numerous and lipid droplets and lipfuscin inclusions accumulate with advancing age. Crystals of Reinke up to 30 microns in length are often noted in the Leydig cell cytoplasm although their function remains unknown. The intertubular tissue contains small calibre lymphatic vessels, fibroblasts, collagen, blood vessels and occasional macrophages. With increasing age, declining sperm production and lowered androgen levels are correlated with decreases in the numbers of Sertoli cells and Leydig cells although the mechanisms responsible for this attrition have not been defined. Continued collaboration between morphologists and physiologists is necessary if we are to understand fully the endocrine regulation of spermatogenesis and the factors contributing to disturbances of spermatogenic function.

Reinitiation of spermatogenesis by exogenous gonadotropins in a seasonal breeder, the woodchuck (Marmota monax), during gonadal inactivity

The present study was undertaken (1) to document structural and functional changes in the testes of seasonally breeding woodchuck during active and inactive states of spermatogenesis and (2) to evaluate the ability of exogenous gonadotropins to reinitiate spermatogenesis outside the breeding season. During seasonal gonadal inactivity, there were significant (P less than 0.05) reductions in volumes of several testicular features (testis, seminiferous tubules, tubular lumen, interstitial tissue, individual Leydig cells, Leydig cell nuclei, and Leydig cell cytoplasm) as compared with gonadally active animals. The diameter of the seminiferous tubules was decreased by 26%, and Leydig cell numbers also declined in the regressed testes. These changes were accompanied by a decline in testosterone (T) levels in both plasma and testis, and reduction in epithelial height of accessory reproductive organs. A hormonal regimen was developed that would reinitiate spermatogenesis in captive, sexually quiescent woodchucks. A combination of PMSG and hCG markedly stimulated testicular growth and function and restored spermatogenesis qualitatively. Quantitatively normal spermatogenesis was restored in 2 of 6 treated males. Morphometric analyses revealed substantial increases in seminiferous tubular diameter and in the volume of seminiferous tubules, tubular lumen, total Leydig cells, and individual Leydig cells in the hormone-treated animals. These increased values corresponded to 99, 75, 68, 51, and 200%, respectively, of the values measured in naturally active woodchucks. Leydig cell numbers, however, remained unchanged and approximated only 31% of the number found in naturally active testes. Hormonal stimulation also resulted in a significant rise in serum T as well as in the total content of testicular T, and a marked increase in epithelial height in various accessory reproductive glands. The most effective hormonal protocol for stimulating spermatogenesis was treatment with 12.5 IU of PMSG twice a week for 4 weeks followed by 12.5 IU of PMSG + 25 IU of hCG twice a week for 4 weeks.

Ultrastructure of the seminiferous epithelium and intertubular tissue of the human testis

The ultrastructural features of the human testis are reviewed with emphasis upon the process of spermatogenesis and the cytology of the Leydig cells. The seminiferous epithelium is structurally partitioned by the Sertoli cells into basal and adluminal compartments via the specialized tight junctions between the Sertoli cells. Spermatogonia reside in the basal compartment, and, via a series of cell divisions, produce the primary spermatocytes, which at the commencement of their development move into the adluminal compartment, and thus the lengthy process of meiotic maturation is initiated. The fine structure of primary spermatocytes is described together with the complex transformation of the spermatids into spermatozoa during the process of spermiogenesis. Earlier studies of the organization of the human seminiferous epithelium showed that germ cells at different developmental stages formed identifiable collections termed cell associations or stages, but since several stages were seen in a single tubule cross-section, this gave the impression of an extremely irregular pattern of spermatogenic development. When the topographic arrangement of germ cells was re-examined with the aid of computer modelling, a highly ordered distribution was revealed, conforming to a helical pattern based on the geometry of spirals. Thus spermatogenesis in the human testis is subjected to a precise regulation in keeping with the ordered arrangement of the germ cells seen in other mammalian species. The intertubular tissue of the human testis is composed of loose connective tissue containing blood vessels, occasional lymph capillaries, macrophages, mast cells, and the Leydig cells which occur either as single cells or form small clusters. The Leydig cell cytoplasm contains an abundant supply of smooth endoplasmic reticulum and mitochondria with tubular cristae, both features being characteristic of steroidogenic cells. Human Leydig cells contain large Reinke crystalloids of variable size and number, but their function remains obscure. The frequent occurrence of paracrystalline inclusions within the cytoplasm of the human Leydig cell suggests that these elements are precursors of the Reinke crystalloids.

Ultrastructure of the aging human testis

The ultrastructure of the progressive testicular involution with advancing age in men is reviewed. There is no definite age at which testicular involution begins, and the onset and severity of testicular lesions are subjected to pronounced individual variations. Hormone studies also indicate great individual variations, and subtle changes in both the testis and the pituitary develop progressively with age. Testicular size, sperm quality, and numbers of all germ cell types, Sertoli cells, and Leydig cells decrease with age. The volume occupied by the seminiferous tubules decreases, whereas that occupied by the testicular interstitium remains constant. The most frequent histological pattern of the aging testis is a mosaic of different seminiferous tubule lesions, varying from tubules with complete, although reduced, spermatogenesis, to completely sclerosed tubules. The tubules with complete spermatogenesis may show numerous morphological abnormalities in the germ cells, including multinucleation. Abnormal germ cells degenerate causing Sertoli cell vacuolation. These vacuoles correspond to dilations of the extracellular spaces resulting from the premature exfoliation of germ cells. Degenerating cells that are phagocytosed by the Sertoli cells give rise to an accumulation of lipid droplets in the Sertoli cell cytoplasm. The loss of germ cells begins with the spermatids, but progressively affects the earlier germ cell types, and tubules with maturation arrest at the level of the spermatocytes or spermatogonia are observed. The Sertoli cells show morphological abnormalities such as dedifferentiation, mitochondrial metaplasia, and multinucleation. Germ cell loss is associated with thickening of the tunica propria. When all seminiferous epithelial cells have disappeared, only an intensely collagenized tunica propria with myoid cells remains (sclerosed tubules). The Leydig cells progressively dedifferentiate with a decrease in the quantity of both smooth endoplasmic reticulum and mitochondria, together with an accumulation of lipid droplets, crystalline inclusions, and residual bodies, and formation of multinucleate cells. The development of tubular involution with age is similar to that observed after experimental ischemia, suggesting that vascular lesions may play an important role in age-related testicular atrophy.

Age-related decline of plasma bioavailable testosterone in adult men

Plasma bioavailable and total testosterone (T), gonadotropins (FSH, LH) and prolactin (PRL) were determined in 70 ambulatory men subdivided into 3 groups according to age: group I (n = 22; age 20-35 yr), group II (n = 22; age: 36-50 yr) and group III (n = 26; age 51-70 yr). Bioavailable T levels declined significantly with age (r = -0.42; P less than 0.01) while those of total T decreased less significantly (r = -0.28; P less than 0.05). In addition, the decrease of bioavailable T occurred earlier. FSH was shown to increase with age (r = 0.41; P less than 0.01) whereas LH and PRL were not found to change significantly. Bioavailable T was correlated with total T (r = 0.25; P less than 0.05) and inversely correlated with FSH (r = -0.26; P less than 0.05). No correlation could be demonstrated between LH and either bioavailable or total T. In view of the age-related increase of sex hormone binding globulin, a fact generally observed in the literature, bioavailable T may be considered a more reliable index than total T for the evaluation of T production. Thus it may be concluded that the early decrease of bioavailable T in ambulatory men not known to have any pathology or any medication altering testicular function corresponds in fact to age-related decline of T secretion by the testes.

Photoperiodic variation of Leydig cell numbers in the testis of the golden hamster: a possible mechanism for their renewal during recrudescence

Golden hamster testes regress after short day exposure. The present study asks: 1) are Leydig cell numbers depleted during short days, and 2) if so, how are they replenished during recrudescence. Control hamsters were shown 14 h of light and 10 h of dark (LD 14:10) for 10 weeks (n = 12). Testicular regression was induced by LD 6:18 for 10 weeks (n = 4), and recrudescence by switching regressed hamsters to LD 14:10 for 3 and 5 weeks (n = 8 for each group). All hamsters were injected with [3H]thymidine [3 microCi/gm body wt., intraperitoneally (i.p.)] 1 h or 2 weeks before sacrifice. Leydig cell number per testis was determined by stereological analysis of sections of perfusion-fixed testes, and labeling indices were determined by autoradiography. Leydig cell numbers were reduced significantly from 18.2 X 10(6) in control to 9.0 X 10(6) in regressed testes (p less than 0.05); then increased to 14.0 X 10(6) and 17.9 X 10(6) in 3- and 5-week recrudesced hamsters. The labeling index was nondetectable (n.d.) for regressed hamsters. In control and recrudescing hamsters the labeling index was measured at two times (t1 = 1 h vs. t2 = 2 weeks post-injection): in controls, t1 = 0.22 +/- 0.15% (mean +/- SEM) vs. t2 = 0.28 +/- 0.22%; in 1 week recrudesced, n.d. vs. 1.92 +/- 0.77% (p less than 0.05); at 3 wk, n.d. vs. 4.58 +/- 1.74% (p less than 0.05); at 5 weeks, 1.92 +/- 0.61% vs. 2.25 +/- 0.59%.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphometric analysis of the components of the neonatal and the adult rat testis interstitium

Leydig cells in the foetal rat testis are still present at birth and it has been hypothesized that they commence to degenerate immediately after birth, based on the decrease in their volume density (v/v%) with age. In this study the interstitium of the rat testis was studied quantitatively at 1, 5, 10, 15, 20 and 90 days after birth: the latter are considered to be adults. The absolute volumes of connective tissue cells and blood vessels increased with age. The absolute volumes of macrophages and lymphatic spaces were greater at 90 days than at any other age. The absolute volume of foetal Leydig cells per testis was unchanged from 1 to 15 days, despite a decrease in the % volume occupied per testis. The number of foetal Leydig cells per testis did not decline from days 1-20 although on day 20 an average foetal Leydig cell was smaller in volume than at earlier ages (days 1-15). Adult Leydig cells were recognized at day 10 and their absolute volume and number per testis increased from 15 to 90 days. Adult Leydig cells were similar in morphology to foetal Leydig cells at 20 days except for a reduced volume of cytoplasmic lipid.

Testicular involution in elderly men: comparison of histologic quantitative studies with hormone patterns

An endocrinologic and quantitative histologic study was carried out in 64 elderly men who underwent orchidectomy owing to prostatic carcinoma. The men were classified into age groups (decade of life), and each group was subdivided into group A (testes with complete spermatogenesis in most tubules) and group B (testes showing maturation arrest of spermatogenesis in most tubules). Up to 80 years of age, men of group A showed hormone levels and testicular parameters similar to those of young control men. From 50 to 60 years of age, men of group B showed a significant decrease in testicular volume, tubular volume, tubular length, number of germ cells, Sertoli cells and Leydig cells per testis, and plasma testosterone levels, whereas the tunica propria thickness and plasma levels of both follicle-stimulating hormone and luteinizing hormone were increased.

Quantitative analysis of germ cells and Leydig cells in rat made infertile with gossypol

This study utilized improved methods of fixation and plastic embedding to quantitatively evaluate the effects of gossypol on germ cells and Leydig cells in testes of rats made infertile with gossypol. Rats were fed by gavage with 10, 20 or 30 mg/kg per day of gossypol for 9 weeks; control animals received the vehicle alone. Numbers of A spermatogonia, preleptotene and pachytene spermatocytes, and step 7 or 8 spermatids per Sertoli cell were counted in stages VII-VIII of the cycle of the seminiferous epithelium. Although high doses (30 mg/kg) of gossypol produced a significant decrease in the relative number of germ cells compared with vehicle-treated controls, no significant deviation in the relative number of germ cells was noted between controls and rats made infertile with 10 or 20 mg/kg/day of gossypol. Stereologic techniques were used to assess the changes in the Leydig cells. No significant deviation in the Leydig cell morphology, cell number, or cell volume was noted as a result of gossypol treatment at the dose levels employed. It appears that germ cell depletion, such as that caused by high doses of gossypol, is not mediated by a change in Leydig cell function. The present report emphasizes the importance of studies to determine the minimal effective doses for gossypol's antifertility activity in animal models as well as in man.

Decrease in the number of human Ap and Ad spermatogonia and in the Ap/ Ad ratio with advancing age. New data on the spermatogonial stem cell

The numbers of Ap and Ad spermatogonia per unit section of the testis were calculated in autopsy specimens from young adults and elderly men without testicular pathology. The number of Ap spermatogonia decreased from the 6th decade of life, whereas that of Ad spermatogonia began to decrease in the 8th decade. Although it has been reported that Ad spermatogonia are more sensitive to noxious agents than Ap spermatogonia, the involution of Ap spermatogonia precedes that of Ad spermatogonia. These findings provide new information on concepts relating to the spermatogonia precedes that of Ad spermatogonia. These findings provide new information on concepts relating to the spermatogonial stem cell in man.