Hormonal effects of lead acetate in the male rat: mechanism of action

The Effects of Toxic Heavy Metals Lead, Cadmium and Copper on the Epidemiology of Male and Female Infertility

Infertility is a major problem in modern society that affects a significant number of couples around the world. Heavy metals and a number of other factors have been causally linked to infertility. The aim of this study was to determine the effect of heavy metals lead, cadmium, and copper on the epidemiology of male and female infertility. Searches for articles published from 1982 to 2020 using related keywords such as male and female infertility and heavy metals were performed in scientific databases PubMed, Google Scholar, Science Direct, and others. The results showed that, in recent years, the number of infertile individuals has increased. Various environmental, occupational, and genetic factors have been described as potential causes. Heavy metals lead, cadmium, and copper cause infertility in couples through various mechanisms, such as changes in sperm motility factors, decreased semen quality, or effects on the egg. Exposure to physical phenomena such as radiation (ionized or microwave) and heat; stress and mental disorders; chemicals from cigarettes, respiratory pollutants (lead), insecticides and pesticides; anesthetic gases; and mercury and cytotoxic drugs may also contribute to the onset of infertility.

The Effects of Chronic Lead Exposure on Testicular Development of Japanese Quail (Coturnix japonica): Histopathological Damages, Oxidative Stress, Steroidogenesis Disturbance, and Hypothalamus-Pituitary-Testis Axis Disruption

Lead (Pb) becomes a global public health concern for its high toxicology. Birds are sensitive to environmental pollution and Pb contamination exerts multiple negative influences on bird life. Pb also impacts on avian reproductive system. Thus, in this study, we attempted to determine toxicological effects and possible mechanistic pathways of Pb on avian testicular development by using the model species-Japanese quail (Coturnix japonica). Male quail chicks of 1-week-old were exposed to 0, 50, 500, and 1000 ppm Pb concentrations in drinking water for 5 weeks when reaching sexual maturation. The results showed that high Pb doses (500 and 1000 ppm) induced testis atrophy and cloacal gland shrinkage. Microstructural damages of both hypothalamus and testis indicated the disruption of the hypothalamus-pituitary-gonadal (HPG) axis by Pb exposure. The decrease of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and testosterone (T) may also imply HPG axis disruption. Moreover, excess testicular oxidative damages featured by increasing reactive oxygen species (ROS) and malondialdehyde (MDA) and decreasing catalase (CAT), glutathione (GSH), superoxide dismutase (SOD), glutathione-S-transferase (GST), and total antioxidant capacity (T-AOC) indicated increasing risks of reproductive dysfunction by Pb. Furthermore, increasing apoptosis and upregulation of gene expression associated with cell death suggested testicular abnormal development. In addition, molecular signaling involved with steroidogenesis in the testis was disturbed by Pb treatment. The study showed that Pb could impair testicular development and reproductive function by morphological and histological injury, hormone suppression, oxidative stress, cell death, and HPG axis disruption.

The effect of ferulic acid against lead-induced oxidative stress and DNA damage in kidney and testes of rats

Oxidative stress is an imbalance between free radicals and antioxidants which leads to reactive oxygen species (ROS) production in cells. Reactive oxygen species contains oxygen radicals that easily react with other molecules in the biological system. For decades, lead acetate (Pb(C₂H₃O2)₂) is used as an additive for many widely used chemical products such as insecticides, hair dyes, and cosmetics; however, contact with lead acetate may irritate skin, eyes, and mucous membranes.In the present study, the antioxidant and anti-inflammatory effect of using ferulic acid to inhibit lead acetate-induced toxicity in rats is investigated. Lead acetate was orally given at a dose of 20 mg/kg body weight for 10 days, either alone or with ferulic acid at dose 25 mg/kg. Serum luteinizing hormone (LH), total testosterone, and follicle-stimulating hormone (FSH) levels were measured. Also, reactive oxygen species (ROS), lipid peroxidation (LPO), total antioxidant capacity (TAC), and catalase (CAT) activities were determined. In addition, histopathological changes of testes and kidney were examined. Results showed that administration of lead acetate induced oxidative stress through attenuation of luteinizing hormone, total testosterone, and follicle-stimulating hormone levels in serum. Moreover, the kidney and testes of lead acetate-treated animals exhibited elevation of ROS level, lipid peroxide levels, as well as lysosomal enzyme activity such acid phosphatase and N-acetyl-β-glucosminidase. DNA fragmentation and histological changes were also observed in lead acetate-treated group. In contrast, ferulic acid treatment reduced the deleterious effects induced by lead acetate in both testes and kidney tissues. These results illustrated that ferulic acid has a protective action against toxicity caused by lead acetate in rats. In conclusions, ferulic acid may have future therapeutic relevance in the prevention of lead acetate-induced testicular and renal toxicity in rats.

Thymoquinone attenuates testicular and spermotoxicity following subchronic lead exposure in male rats: Possible mechanisms are involved

AIMS

The testis is one of the main target organs for lead (Pb) toxicity. The current study was investigated the mechanism (s) of the therapeutic potential of thymoquinone (TQ), the active principle of Nigella sativa seed, against testicular toxicity following subchronic Pb exposure in the light of cytopathic effects, apoptotic signaling pathways, oxidative stress, serum sex hormones levels and testicular aromatase gene expression.

MATERIALS AND METHODS

Thirty-two male albino rats were randomly allocated into control, PbAc (20 mg PbAc/kg bwt, orally), TQ (5 mg TQ/kg bwt dissolved in corn oil, orally), and PbAc + TQ groups for 56 successive days.

KEY FINDINGS

PbAc-treated rats showed significant decrease of testes and epididymes weights, sperm count, motility and viability, spermatogenesis score and serum FSH, LH, testosterone and estradiol levels, as well as a significant decreased testicular antioxidant molecules (Superoxide dismutase enzyme and reduced glutathione), and a significant elevation of sperm abnormalities, oxidative biomarkers (Malondialdehyde and Nitric oxide) compared to a control group. In addition, Pb induced significant downregulation of aromatase gene expression, activation of Bax and Caspase-3 apoptotic pathways. Moreover, Pb caused complete seminiferous tubules hyalinization (38%), germinal epithelium sloughing (15%) and hypocellularity (8%). However, administration of TQ with PbAc improved sperm quality, testicular histology and oxidative/antioxidative status, and serum levels of LH, testosterone and E2 with respect to PbAc group. Additionally, TQ with PbAc significantly lessen the staining intensity and the area of Bax and Caspase-3 immunoexpression.

SIGNIFICANCE

TQ might exert its acceptable therapeutic potential against Pb-induced testicular and spermotoxicity via anti-oxidative, endocrine and anti-apoptotic pathways.

Effect of Low-Level Environmental Lead Exposure on the Onset of Male Puberty

The objective of this study was to evaluate male pubertal changes associated with environmental low-level lead (Pb) exposure. The study was conducted on 180 boys aged 15 years divided into 3 equal size groups: group 1 from El-Newayrat village, group 2 from Al-Shorafaa (0.5 and 10 km, respectively, from an industrialized area), and group 3 from Talla (25 km). Blood Pb levels (BLLs) were measured and pubertal changes evaluated by measurement of testicular volume (TV), and estimation of the follicle-stimulating hormone, luteinizing hormone, testosterone, estradiol, and prolactin. Blood Pb levels of children of El-Newayrat and Al-Shorafaa were significantly higher (6.38 [1.32] and 3.84 [0.79] μg/dL, respectively) than that of Talla children (1.85 [0.72]; P < 0.001), while height, weight, and TV were lower in boys in groups 1 and 2, compared to group 3. Genitalia and pubarche staging showed greatest retardation and marked bone growth delay in boys of group 1. Hormonal assays reported significant differences in boys of the industrialized areas when compared to that of Talla. Low-level Pb exposure in boys located near an industrial area was accompanied with altered male puberty indicators.

Protective effect of diallyl sulfide against lead-mediated oxidative damage, apoptosis and down-regulation of CYP19 gene expression in rat testes

AIMS

The present study aimed to investigate the potential therapeutic effect of diallyl sulfide (DAS), a natural component of garlic (Allium sativum), in the improvement of lead (Pb)-induced testicular toxicity and its underlying mechanisms.

MATERIALS AND METHODS

Thirty-two male albino rats were randomly divided into control, PbAc (20 mg lead acetate/kg bwt, orally), DAS (200 mg/kg bwt, orally), and PbAc + DAS groups for 49 successive days. The investigation based on the following criteria: Paired testes and epididymides weights, epididymal sperm analysis, level of serum sex hormones (Testosterone and17β-estradiol (E2)), aromatase (CYP19) expression, Malondialdehyde (MDA), Nitric oxide (NO), Superoxide dismutase (SOD) enzyme, reduced glutathione (GSH), testicular histopathology, spermatogenesis score and apoptosis detection (Caspase-3 immunoexpression).

KEY FINDINGS

Pb caused significant decline in epididymal sperm count and motility, testes and epididymes weights, spermatogenesis score and serum testosterone and1E2, as well as a significant decrease in SOD and GSH level, and a significant elevation of MDA and NO compared to a control group. In addition, Pb induced significant downregulation of CYP19 gene expression, increase of Caspase-3 immunoreactivity, various testicular degenerative and necrotic changes. Whereas, co-treatment of rats with DAS improved sperm analysis, and testicular histology and antioxidative status. Furthermore, DAS co-administration regulated testicular CYP19 and Caspase-3 expressions.

SIGNIFICANCE

Collectively, DAS seemed to be a promising agent for protection against Pb-induced testicular toxicity through antioxidative properties, beside regulation of testicular apoptosis and aromatase expression.

Impaired hypothalamic-pituitary-testicular axis activity, spermatogenesis, and sperm function promote infertility in males with lead poisoning

Lead poisoning is a stealthy threat to human physiological systems as chronic exposure can remain asymptomatic for long periods of time before symptoms manifest. We presently review the biophysical mechanisms of lead poisoning that contribute to male infertility. Environmental and occupational exposure of lead may adversely affect the hypothalamic-pituitary-testicular axis, impairing the induction of spermatogenesis. Dysfunction at the reproductive axis, namely testosterone suppression, is most susceptible and irreversible during pubertal development. Lead poisoning also appears to directly impair the process of spermatogenesis itself as well as sperm function. Spermatogenesis issues may manifest as low sperm count and stem from reproductive axis dysfunction or testicular degeneration. Generation of excessive reactive oxygen species due to lead-associated oxidative stress can potentially affect sperm viability, motility, DNA fragmentation, membrane lipid peroxidation, capacitation, hyperactivation, acrosome reaction, and chemotaxis for sperm-oocyte fusion, all of which can contribute to deter fertilization. Reproductive toxicity has been tested through cross-sectional analysis studies in humans as well as in vivo and in vitro studies in animals.

Red Palm Oil Attenuates Lead Acetate Induced Testicular Damage in Adult Male Sprague-Dawley Rats

To study the protective effect of Red Palm Oil (RPO) on testicular damage induced by administration of lead acetate on male Sprague-Dawley rats, 28 rats divided into four groups of 7 animals each were used. They were administered orally with RPO (1 mL and 2 mL) and lead acetate (i.p.) 6 mg/kg body weight/day, respectively. Treatment was conducted for 8 weeks, and 24 hrs after the last treatment the rats were sacrificed using cervical dislocation. Sperms collected from epididymis were used for seminal fluid analyses; while the testes sample was used for ROS and oxidative enzyme activities assessment. Statistical analysis was carried out using GraphPad Prism 5.02 statistical analysis package. Administration of lead acetate increased generation of reactive oxygen species (ROS) significantly (p < 0.05) as evidenced by the elevated value of H2O2 and LPO and decreased GSH level. Also there was reduced epididymal sperm count, poor grade of sperm motility, and lower percentage of normal sperm morphology significantly. Coadministration with RPO, however, has a protective effect against lead toxicity by decreasing H2O2 production, increased GSH level, and increased sperm qualities especially. This shows that RPO has a potential to attenuate the toxic effect of lead on testicular cells preventing possible resultant male infertility.

Recovery of lead-induced suppressed reproduction in male rats by testosterone

The objective of the present study was to investigate the effects of testosterone in recuperation of lead-induced suppressed reproduction in adult male rats. Lead acetate was administered orally to adult male rats (95 ± 5 days) at dosage level of 0.05 and 0.15% for 55 days through drinking water and injected intraperitoneally with either testoviron depot at a dose of 4.16 mg kg(-1) body weight or vehicle alone on days 1, 7 and 14 respectively. At the end of treatment, control and treated males were cohabited with untreated normal-cycling females. After cohabitation for 5 days, all the male rats were killed and weights of reproductive organs were determined. Significant increase in the indices of testis, epididymis, seminal vesicles, vas deferens and prostate glands was observed in testosterone (T)-treated rats when compared to those of lead-exposed rats. Testosterone treatment significantly increased epididymal sperm count, motile spermatozoa, viable spermatozoa and HOS tail-coiled spermatozoa and also the activity levels of testicular 3β- and 17β-hydroxysteroid dehydrogenases when compared to those of lead-exposed males. From the results, it can be hypothesised that supplementation of testosterone mitigated lead-induced suppressed reproduction in male rats.

INHIBITORY ACTIONS OF LEAD ON STEROIDOGENESIS IN MA-10 MOUSE LEYDIG TUMOR CELLS

The inhibitory actions of Pb on StAR protein expression and steroidogenic enzymes on steroidogenesis were analyzed by both linear and 2nd order polynomial models in MA-10 mouse Leydig tumor cells. Lead acetate, ranging from 10(-8) M to 10(-5) M, caused inhibitory effects on StAR protein expression and steroidogenic enzymes. The correlation coefficients R2 (linear vs. 2nd order polynomial) were 0.93 vs. 0.96 for human chorionic gonadotropin-stimulated progesterone production, 0.38 vs. 0.79 for dibutyryl cAMP-stimulated progesterone production, 0.03 vs. 0.99 for the expression of StAR protein, 0.6 vs. 0.92 for P450 side-chain cleavage enzyme activity, and 0.52 vs. 0.96 for 3beta-hydroxysteroid dehydrogenase activity. Thus, 2nd order polynomial model showed higher correlation coefficients than the linear model for predicting inhibitory actions of Pb on StAR protein expression and the activities of steroidogenic enzymes after exposure of Pb on steroidogenesis in MA-10 cells.

Association of blood lead levels with onset of puberty in Russian boys

BACKGROUND

Epidemiologic studies suggest a temporal trend of earlier onset and longer duration of puberty, raising concerns regarding the potential impact of environmental factors on pubertal development. Lead exposure has been associated with delayed pubertal onset in girls; however, epidemiologic data in boys are limited.

METHODS

We used multivariable logistic regression models to explore the cross-sectional association of blood lead levels with growth and pubertal onset based on physician-assessed testicular volume (TV) and pubertal staging in 489 boys 8-9 years of age from Chapaevsk, Russia. We used multivariable linear regression models to assess associations of blood lead levels with somatic growth at the study entry visit.

RESULTS

The median (25th-75th percentile) blood lead level was 3 microg/dL (2-5 microg/dL). Height, weight, body mass index, birth weight, and gestational age were predictive of the onset of puberty as assessed either by TV (> 3 mL), genitalia stage (G2), or both. Blood lead level was inversely associated with height (p < 0.001) and weight (p = 0.06) after adjustment for birth weight, gestational age, and age at examination. In multivariable adjusted analyses, boys with blood lead levels > or = 5 microg/dL had 43% reduced odds of having entered G2 compared with those with lower levels (odds ratio = 0.57; 95% confidence interval, 0.34-0.95, p = 0.03).

CONCLUSIONS

Relatively low environmental blood lead levels were associated with decreased growth and differences in pubertal onset in periadolescent Russian boys. Future analyses of this prospective cohort will address pubertal onset and progression in relation to lead and other environmental chemicals.

Endocrine disruptors and estrogenic effects on male reproductive axis

Endocrine disruptors (e.g., polychlorinated biphenyls [PCBs], dichlorodiphenyl-trichloroethane [DDT], dioxin, and some pesticides) are estrogen-like and anti-androgenic chemicals in the environment. They mimic natural hormones, inhibit the action of hormones, or alter the normal regulatory function of the endocrine system and have potential hazardous effects on male reproductive axis causing infertility. Although testicular and prostate cancers, abnormal sexual development, undescended testis, chronic inflammation, Sertoli-cell-only pattern, hypospadias, altered pituitary and thyroid gland functions are also observed, the available data are insufficient to deduce worldwide conclusions. The development of intra-cytoplasmic sperm injection (ICSI) is beyond doubt the most important recent breakthrough in the treatment of male infertility, but it does not necessarily treat the cause and may inadvertently pass on adverse genetic consequences. Many well-controlled clinical studies and basic scientific discoveries in the physiology, biochemistry, and molecular and cellular biology of the male reproductive system have helped in the identification of greater numbers of men with male factor problems. Newer tools for the detection of Y-chromosome deletions have further strengthened the hypothesis that the decline in male reproductive health and fertility may be related to the presence of certain toxic chemicals in the environment. Thus the etiology, diagnosis, and treatment of male factor infertility remain a real challenge. Clinicians should always attempt to identify the etiology of a possible testicular toxicity, assess the degree of risk to the patient being evaluated for infertility, and initiate a plan to control and prevent exposure to others once an association between occupation/toxicant and infertility has been established.

Effects of lead exposure on sperm concentrations and testes weight in male rats: a meta-regression analysis

The correlation between exposure to lead (PB) and sperm concentrations and testes weight are important in risk assessment of metal toxicity to male reproductive functions. The authors carried out two systematic reviews and meta-analyses of rats. In addition, a meta-regression analysis was taken to explore a dose-response relationship between the mean difference of testes weight (MD(testes)) and available confounding factors. Data were obtained from computerized literature searches of several databases from their inception through December 2005. The reference lists of identified articles were examined further for relevant articles. The authors identified 6 and 12 studies, separated into 16 and 28 subgroups, in the two meta-analyses. The authors conducted random- or fixed-effect models toward the effect size. Heterogeneity between study results was explored through chi-square tests and meta-regression. Results showed that a decrease in sperm concentrations was found as low as mean difference of sperm concentrations (MD(sperm)) = 30.9 and 95%CI = (25.43-36.37) in a fixed-effect model or MD(sperm) = 35.47 and 95%CI = (15.27-55.68) in a random-effect model after Pb exposure. Similarly, a significantly lower testes weight was also evident: MD(testes) = 0.033 and 95%CI = (0.021-0.046) in a fixed-effect model or MD(testes) = 0.047 and 95%CI = (0.0044-0.089) in a random-effect model. In the meta-regression analysis, two confounders, age and body weight, explained part of the observed heterogeneity. The body weight after Pb exposure was inversely associated with MD(testes). These findings support the notion that Pb exposure produced decreased sperm concentrations and testes weight in rats.

Lepidium meyenii (Maca) reversed the lead acetate induced—Damage on reproductive function in male rats

Rats were treated with 0, 8, 16 and 24 mg/kg of lead acetate (LA) (i.p.) for 35 days with or without Maca. Maca was co-administrated orally from day 18 to day 35. The lengths of stages of the seminiferous epithelium were assessed by transillumination. Also, sex organ weights, testicular and epididymal sperm count, sperm motility, daily sperm production, sperm transit rate and serum testosterone levels were measured. Lead acetate treatment resulted in a dose-response reduction of lengths of stages VIII and IX-XI, and serum testosterone levels. However, rats treated with 8 and 16 mg/kg but not 24 mg/kg of lead acetate showed a low number of testicular spermatids, low daily sperm production (DSP) and low epididymal sperm count. Administration of Maca to rats treated with lead acetate resulted in higher lengths of stages VIII and IX-XI with respect to lead acetate-treated rats. Moreover, treatment with Maca to lead acetate-treated rats resulted in lengths of stages VIII and IX-XI similar to the control group. Maca administration also reduced the deleterious effect on DSP caused by lead acetate treatment. Maca prevented LA-induced spermatogenic disruption in rats and it may become in a potential treatment of male infertility associated with lead exposure.

Lead-induced cell signaling cascades in GT1-7 cells

The effects of lead on the signal transduction pathways that may be involved in the release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus have not been well defined. Using the GT1-7 cell line, an in vitro model for GnRH-secreting neurons, we examined signal transduction pathways directly affected by lead. We found that lead-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1 and ERK2), as well as p90RSK and cAMP response element-binding protein (CREB), but did not induce IkappaB degradation. MEK1/2 inhibitor (PD98059) suppressed lead-induced ERK and p90RSK activation. Neither PKC inhibitors (Go6983, Go6976) nor CaMKII inhibitor (KN-62) had a pronounced effect on lead-induced ERK1 and ERK2 phosphorylation. However, MEK1/2 inhibitor, CaMKII inhibitor, and PKC inhibitor significantly suppressed lead-induced CREB phosphorylation. These results indicate that lead-activated PKC, CaMKII and MEK/ERK/p90RSK pathways simultaneously, all of which contributed to CREB phosphorylation. Our results also indicate that lead-induced p90RSK and CREB activation does not alter expression of early response genes like c-fos. We conclude that lead activates PKC, CaMKII or MEK-ERK-p90RSK pathways in GT1-7 cells, leading to CREB phosphorylation and modulation of gene expression.

Inhibitory mechanisms of lead on steroidogenesis in MA-10 mouse Leydig tumor cells

Lead can directly influence Leydig cell steroidogenesis, which results in reduction of testosterone and causes low sperm counts in human beings and animals. This study investigated the effect of 6 h incubation time of lead on steroidogenesis in MA-10 mouse Leydig tumor cells. Lead acetate, ranging from 10(-8) to 10(-5) M, caused profounder inhibitory effects on human chorionic gonadotropin (hCG)- and dibutyryl cAMP (dbcAMP)-stimulated progesterone production for 6 h in MA-10 mouse Leydig tumor cells. Lead acetate significantly inhibited hCG- and dbcAMP-stimulated progesterone production from 20 to 35% in MA-10 cells at 6 h. Lead suppressed the expression of steroidogenesis acute regulatory (StAR) protein from 30 to 55%. Moreover, the activities P450 side-chain cleavage (P450scc) enzyme and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) were reduced by lead from 15 to 25%. Thus, after 6 h exposure to lead caused profounder inhibitory effects on StAR protein expression and steroidogenic enzymes and then progesterone production compared to 2- or 3-h lead treatments in MA-10 mouse Leydig tumor cells.

Concentration dependency in lead-inhibited steroidogenesis in MA-10 mouse Leydig tumor cells

Lead acetate (Pb) decreases the expression of steroidogenic acute regulatory (StAR) protein and the enzymatic activities of cytochrome P-450 side-chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in a concentration-dependent manner in Leydig cells at 2 h, the duration of submaximal inhibition. This study was undertaken at 3 h of Pb incubation to compare the effects at maximal metal inhibition of steroidogenesis. Quantitatively a 3-h Pb incubation with MA-10 cells resulted in higher decreases in human chorionic gonadotropin (hCG)-stimulated progesterone production, expression of StAR protein, and the activity of 3beta-HSD compared to 2 h. In contrast, lead inhibited dibutyryl cAMP (dbcAMP)-stimulated progesterone production but lacked this effect at 2 h. Surprisingly, Pb at 3 h of incubation did not affect P450scc enzyme activity, yet this enzymatic activity was inhibited at 2 h. Data indicate that incubation time is a factor in Pb-induced alterations in MA- 10 cell steroidogenesis.

Cell Junction Dynamics in the Testis: Sertoli-Germ Cell Interactions and Male Contraceptive Development

Spermatogenesis is an intriguing but complicated biological process. However, many studies since the 1960s have focused either on the hormonal events of the hypothalamus-pituitary-testicular axis or morphological events that take place in the seminiferous epithelium. Recent advances in biochemistry, cell biology, and molecular biology have shifted attention to understanding some of the key events that regulate spermatogenesis, such as germ cell apoptosis, cell cycle regulation, Sertoli-germ cell communication, and junction dynamics. In this review, we discuss the physiology and biology of junction dynamics in the testis, in particular how these events affect interactions of Sertoli and germ cells in the seminiferous epithelium behind the blood-testis barrier. We also discuss how these events regulate the opening and closing of the blood-testis barrier to permit the timely passage of preleptotene and leptotene spermatocytes across the blood-testis barrier. This is physiologically important since developing germ cells must translocate across the blood-testis barrier as well as traverse the seminiferous epithelium during their development. We also discuss several available in vitro and in vivo models that can be used to study Sertoli-germ cell anchoring junctions and Sertoli-Sertoli tight junctions. An in-depth survey in this subject has also identified several potential targets to be tackled to perturb spermatogenesis, which will likely lead to the development of novel male contraceptives.

Role of early GnRH administration in sexual behavior disorders of rat pups perinatally exposed to lead

The effects of maternal exposure to lead (Pb) during the perinatal (1% and 0.1% Pb) periods of sexual brain differentiation were studied in adult male offspring. Maternal Pb levels were measured after treatment. Behavioral (open field and sexual behavior), physical (sexual maturation, body and organ weights), and biochemical (testosterone levels and hypothalamic monoamine and respective metabolite levels) data were assessed in perinatally exposed offspring. The effects of gonadrotopin-releasing hormone (GnRH) administration to pups at birth on puberty and sexual behavior were also investigated in offspring postnatally exposed to the metal. Results showed that perinatal administration of the two Pb concentrations did not modify maternal weight gain; 1% Pb exposure reduced offspring body weight during the 7 days of treatment while no changes were observed after 0.1% Pb exposure; neither Pb concentration altered offspring sexual maturation; the higher Pb concentration improved sexual behavior while the 0.1% concentration reduced it; exposure to 0.1% Pb caused decrease in testis weight, an increase in seminal vesicle weight and no changes in plasma testosterone levels; hypothalamic VMA levels were increased compared to the control group; GnRH administration reversed the effects of 0.1% Pb administration on male sexual behavior. These results show that perinatal exposure to Pb had a dose-dependent effect on the sexual behavior of rats and that a decrease in GnRH source in the offspring was probably involved in the reduction of their sexual performance.

Male reproductive toxicity of lead in animals and humans. ASCLEPIOS Study Group

OBJECTIVE

To critically review the literature on male reproductive toxicity of lead in animals and humans.

METHODS

A systematic literature search identified a total of 32 experimental studies in animals and 22 epidemiological studies, one case report on humans and five review articles or documents. The studies were evaluated by paying attention mainly to sample size, study design, exposure, and dose characterisation, analytical method standardisation, and quality assurance.

RESULTS

Several studies on rats and other rodents indicated that blood lead concentrations > 30-40 micrograms/dl were associated with impairment of spermatogenesis and reduced concentrations of androgens. However, other animal studies, mainly about histopathological, spermatozoal, and hormonal end points, indicated that certain species and strains were quite resistant to the reproductive toxicity of lead and that different testicular lead concentrations could account for these differences. The human studies focused mainly on semen quality, endocrine function, and birth rates in occupationally exposed subjects, and showed that exposure to concentrations of inorganic lead > 40 micrograms/dl in blood impaired male reproductive function by reducing sperm count, volume, and density, or changing sperm motility and morphology. No relevant effects were detected on endocrine profile.

CONCLUSION

Several factors make it difficult to extrapolate the animal data to the human situation. The difficulties are mainly due to differences between species in reproductive end points and to the level of exposure. Concentrations of blood lead > 40 micrograms/dl seemed to be associated with a decrease in sperm count, volume, motility, and morphological alterations and a possible modest effect on endocrine profile. Dose-response relation, in particular at a threshold level, is poorly understood, and site, mode, or mechanism of action are unknown. Also, the effects were not always the same or associated in the same on sperm count and concentration. Some methodological issues and indications for future studies are discussed.

Effects of lead exposure on GnRH and LH secretion in male rats: response to castration and alpha-methyl-p-tyrosine (AMPT) challenge

Animal and clinical studies suggest that lead exposure disrupts the hypothalamic-pituitary axis. To define more precisely the toxic action of lead on the hypothalamic-pituitary unit, a series of in vivo and in vitro experiments were performed. The first experiment was designed to determine whether lead exposure exerts an inhibitory effect on GnRH secretion as reflected by an enhanced inhibition of luteinizing hormone (LH) secretion in response to the tyrosine hydroxylase inhibitor methyl-p-tyrosine (AMPT). In the control animals, the AMPT dose had no significant effect on LH secretion, whereas LH fell significantly in the lead-treated animals. In experiments designed to evaluate the effects of lead exposure on the pattern of pulsatile release of gonadotropins castrated control and lead-dosed animals were cannulated, and serial blood sampling was performed. Baseline LH and follicle-stimulating hormone values were not statistically different between the control and lead-treated group. There were no significant differences noted in pulsatile patterns when the data were analyzed as groups. Pituitary cells harvested from lead-treated animals released significantly more LH that did the control animals. These data are consistent with the hypothesis that the signals between the hypothalamus and pituitary gland are disrupted by lead exposure in the intact animal. However, the lead-exposed castrated rat's hypothalamic-pituitary unit is able to adapt to the toxic effects of lead.

Impairment of testicular endocrine function after lead intoxication in the adult rat

To clarify the mechanism of the action of lead on male reproductive function, adult male rats were injected intraperitoneally (i.p.) with lead acetate (8 mg/kg/day of lead), 5 days a week for 35 days. Despite this high dose, germ cells and Sertoli cells did not appear to be major targets of lead. However, lead determination in the reproductive organs showed that the accessory sex glands are such a target. Epididymal function was unchanged. In lead-exposed rats, plasma and testicular testosterone dropped by about 80%, but plasma luteinizing hormone (LH) only dropped by 32%. After luteinizing hormone releasing hormone (LHRH) stimulation of the pituitary, the plasma LH level reached the control one, but plasma testosterone remained significantly reduced by 37%. The sharp decrease in the testosterone:LH ratio in lead-exposed rats, combined with the significant reduction of intertubular tissue volume in the testes, indicate impaired Leydig cell function.

Time-dependent effects of lead on rat reproductive functions

The effects of exposure to lead on endocrine function and the reproductive parameters were studied in pubertal rats treated with 1.0 g l-1 lead acetate in drinking water for 20 days (subacute group) or 9 months (chronic group) in addition to i.v. injections of lead acetate (0.1 mg 100 g-1 body wt.) every 10 (subacute group) or 15 days (chronic group). Although basal levels of testosterone were higher both in plasma and in testes of acutely intoxicated animals, the circulating levels of luteinizing hormone (LH) were not affected in either group, nor was the LH-releasing hormone content of the median eminence. The density of [125I]LH/human chorionic gonadotrophin (hCG) binding sites in testicular homogenates was reduced by saturnism in both groups, concomitant with a significantly increased apparent affinity constant of the hormone-receptor complex. These data can be viewed as the result of a mixture of specific lead toxicity (e.g. at the enzyme level) with other more general actions (e.g. at the level of the hypothalamus-pituitary-testicular axis).

Lead (Pb) alters the norepinephrine-induced secretion of luteinizing hormone releasing hormone from the median eminence of adult male rats in vitro

In the present study, we evaluated the in vitro effects of lead (Pb) on basal and stimulated luteinizing hormone releasing hormone (LHRH) and Prostaglandin E2 (PGE2) secretion. Median eminences (ME) were removed from brains of adult male rats and preincubated for 15 minutes in Krebs-Ringer bicarbonate glucose buffer in an atmosphere of 95% O2-5% CO2. These media were discarded and all MEs were subjected to one of the following experiments. In Experiment 1, all MEs were incubated for 30 minutes in medium only. These media were collected and replaced with medium only (controls) or with medium containing Pb doses ranging from 5 to 20 microM. After this 60-minute incubation, media were collected, then replaced with new medium containing 60 microM norepinephrine (NE), or NE plus each dose of Pb, then incubated for a final 30-minute period. Experiment 2 was conducted as above, except PGE2 (2.8 microM) replaced the NE. In both experiments, the amounts of LHRH released was measured by RIA. In experiment 3, NE was again used for the challenge; however, this time, the amount of PGE2 released was measured by RIA. Results indicate that Pb did not alter basal LHRH release, but compared with controls, significantly blocked NE-induced LHRH release in a dose-related manner. Conversely, Pb had no effect on the PGE2-induced release of LHRH. Additionally, Pb did not alter basal PGE2 release; however, it significantly blocked the NE-induced release of PGE2. Since NE-induced LHRH release is mediated by PGE2, these results support the hypothesis that Pb is capable of altering the hypothalamus and suggest that this effect is due, at least in part, to the diminished PGE2 synthesis/release within the ME, resulting in diminished LHRH secretion.

Reproductive endocrine effects of chronic lead exposure in the male cynomolgus monkey

The reproductive endocrine effects of chronic lead exposure were investigated in 9 year old male (n = 16) cynomolgus monkeys, orally dosed with lead acetate (1500 micrograms/kg/day) according to the following dosing regimens: continuous exposure from birth onward (lifetime, n = 4), beginning at postnatal day 300 (post-infancy, n = 5) and postnatal days 0 to 400 (infancy, n = 4), or vehicle only (control, n = 3). Altered Sertoli cell function was shown by a significant (P = 0.0286) decrease in the inhibin/follicle stimulating hormone (INH/FSH) ratio in both the lifetime and post-infancy groups compared to the control group. Gonadotropin releasing hormone (GnRH) stimulated levels of luteinizing hormone (LH) were significantly (P = 0.0370) lower in the lifetime group compared to the control group as determined by comparisons of the area under the curve. These data suggest that chronic lead exposure exerts a subtle effect on the pituitary as well as on Sertoli cell function.

Effect of ingestion and inhalation of lead on the reproductive system and fertility of adult male rats and their progeny

Ninety-day-old Sprague-Dawley rats were intoxicated for 70 d with lead, given either as 0.3% lead acetate in drinking water or by inhalation as 5 mg m-3 lead oxide. Direct or transmitted lead toxicity for the male reproductive system was assessed in the rats and their offspring from pituitary and genital organ weights after exposure, the numbers of Sertoli and germ cells, the number, motility and morphology of epididymal spermatozoa, the levels of plasma testosterone, LH and FSH and fertility tests. Whole blood lead levels were similar after lead ingestion and after inhalation (58.0 +/- 1.7 micrograms dl-1 vs. 51.1 +/- 1.8 micrograms dl-1). Lead acetate ingestion did not affect the reproductive system or fertility of rats. Inhalation of lead oxide did not affect fertility either, but seminal vesicle weight dropped significantly, which might suggest an alteration in the pattern of testosterone secretion. In the male progeny of sires that inhaled lead, the number of epididymal spermatozoa decreased but this did not interfere with fertility. Our results show that for the doses studied, lead inhalation and lead ingestion do not produce strikingly different effects on the male rat's reproductive system. Differences between the present findings and those of others might be due to difference of rat strain or of age at exposure.

Lead acetate does not impair secretion of Sertoli cell function marker proteins in the adult Sprague Dawley rat

This study was conducted to determine the effects of lead on Sertoli cell function. Androgen binding protein and inhibin in testicular fluids and classical parameters of the hypothalamic-pituitary-gonadal axis were measured in adult male rats. For 10 wk, the rats were given water that contained 0.05%, 0.1%, 0.5%, and 1% lead acetate. Serum follicle-stimulating hormone, luteinizing hormone, and testosterone levels in all animals that ingested lead were normal at the middle and end of the experiment, as was the pituitary content of follicle-stimulating hormone and luteinizing hormone. Histologic examination revealed no disruption of spermatogenesis. Distribution of androgen binding protein in serum, seminiferous tubular fluid, and interstitial fluid was normal, as was the concentration of inhibin in interstitial fluid and seminiferous tubular fluid. However, a significant increase in epididymal androgen binding protein level and a decrease in seminal vesicle weight were observed in rats that ingested water containing 1% lead acetate. These results suggest that the effect of lead on spermatogenesis is not marked in adult Sprague Dawley rats, nor does Sertoli cell function appear to be affected adversely. Lead has been reported to alter in vitro metabolic function of Sertoli cells obtained from 16- to 21-d-old Sprague Dawley rats, and the Sertoli cells of juvenile animals may be more susceptible to lead than those of adult animals. The significant decrease in seminal vesicle weight and the abnormal epididymal androgen binding protein content indicate that lead could affect the male reproductive function in Sprague Dawley rats via its action on male accessory organs.

Effects of low-level lead exposure on hypothalamic hormones and serum progesterone levels in pregnant guinea pigs

Pregnant guinea pigs were given a daily oral dose of 0, 5.5, or 11 mg lead (as lead acetate) per kg body weight during days 22-52 or 22-62 of gestation. Maternal serum progesterone levels were measured at the end of treatment, as well as hypothalamic levels of gonadotropin-releasing hormone (GnRH) and somatostatin (SRIF) in both the mothers and fetuses. Lead-treated dams had lower serum concentrations of progesterone at the end of treatment than did vehicle-treated animals. This effect was statistically significant for the higher Pb dose only. Hypothalamic levels of GnRH and SRIF were reduced in a dose-dependent manner by lead treatment in both dams and fetuses. The reduction of SRIF levels in 52-day-old fetuses was particularly severe (92%) in the 11 mg group. However, neither litter size nor body and organ weights, including placental weight, of the dams and fetuses was significantly affected. The relevance of these hormonal decreases is unknown, but could include decreased reproductive capacity in both the dams and fetuses that does not become apparent until later in the life-cycle.

Prenatal lead exposure in the rat during the third week of gestation: long-term behavioral, physiological, and anatomical effects associated with reproduction

Sprague-Dawley dams were administered lead acetate (0.1%) in their drinking water from Day 14 of gestation to parturition to determine whether exposure of the fetus to elevated lead (Pb) levels during a period of rapid differentiation of the hypothalamic-pituitary-gonadal (HPG) axis would disrupt HPG function in adulthood. At birth, offspring from 20 Pb-treated and 10 control dams were weighed and 2 litter representatives from each sex were fostered to untreated dams. Animals were weaned at 26 days of age and subsequently group housed by sex and treatment. Blood Pb levels in prenatally exposed pups were below the limits of detectability at weaning. Female offspring from Pb-treated dams were found to have a significant delay in the day of vaginal opening. In a sample of lead exposed females, 50% were found to exhibit prolonged and irregular periods of diestrous which was accompanied by an absence of observable corpora lutea when they were euthanized at 83 days of age. Male offspring from these dams were found to have decreased sperm counts at 70 and 160 days of age and to exhibit significantly less territorial scent marking and masculine sex behavior in adulthood compared to controls. Azoospermia was observed in 1 lead exposed animal at 70 days of age and 2 animals at 160 days. Enlarged prostates were observed in Pb-exposed males measured at 160 days, but other sex organ weights were normal. Volume of the sexually dimorphic nucleus of the preoptic area of the hypothalamus in adulthood was significantly reduced by approximately 35% in Pb-exposed males. Pulsatile release of gonadotropins, measured in castrated adult animals of both sexes, revealed irregular release patterns of both FSH and LH in some Pb animals which were not observed in controls. The overall pattern of results suggests that multiple levels of the HPG axis can be affected by exposure to Pb during a period of gestation when structures related to the HPG axis are undergoing rapid proliferation. These data indicate that lead exposure during this period places the exposed animal at significant risk for reduced reproductive capacity in adulthood.

The effect of age of exposure on lead-induced testicular toxicity

The present study was designed to assess the significance of age of exposure on the expression of lead toxicity on the male gonad. Male Wistar rats, age 42 days, 52 days and 70 days were treated with lead acetate in their water for 30 days prior to sacrifice. The lead treated groups in all cases had blood lead values significantly greater than control animals. Blood lead levels in control animal groups were less than 7 micrograms/dl. Serum testosterone and sperm concentration and production rate were significantly suppressed in those animals that were exposed to lead acetate starting at age 52 days and 70 days, but not 42 days. These data indicate that prepubertal rats may be less sensitive to the toxic effects of lead than are rats whose exposure begins after puberty has been initiated.

Mechanistic approaches in the study of testicular toxicity: toxicants that affect the endocrine regulation of the testis

This review will expand on the themes presented by Heindel and Treinen (1988). As a prelude to describing where selected compounds act on the endocrine regulation of the testis and the theories about their mechanisms, we will briefly review some of the central pathways that underlie this control. After reviewing some studies that define the site of action of lead on the reproductive system, we will discuss the "signature" lesion caused by androgen deficiency, and then move on to an evaluation of the effects of an antiandrogen (flutamide) on the male reproductive system. Finally, some consideration will be given to alterations in hepatic function which modify circulating levels of androgens.

Occupational lead exposure and pituitary function

Twenty-five moderately exposed lead workers (mean blood-lead level 1.9 mumol/l) had lower plasma levels of follicle stimulating hormone than 25 individually matched controls without occupational lead exposure (blood-lead level 0.2 mumol/l). In addition, the ten most heavily exposed individuals had higher levels of thyroid stimulating hormone, and the 14 workers under the age of 40 had decreased plasma levels of luteinizing hormone and serum levels of cortisol, as compared to the controls. All values were within "normal" reference limits. There was no significant change of the plasma testosterone level. These data indicate a complex effect on the endocrine system by moderate lead exposure, possibly mediated by changes at the hypothalamic-pituitary level. Besides the effect on hormone levels, there was also a decrease in plasma selenium level for the lead exposed workers.

Reversibility of the toxic effect of lead on the male reproductive axis

The present study investigates the reversibility of the toxic effects of lead on the hypothalamic-pituitary-testicular axis in prepubertal and pubertal male rats. Male Wistar rats, 27 days and 52 days old, were given ad libitum access to 0.0% or 0.6% lead acetate containing water. Groups of animals were sacrificed at the end of 30 days of exposure or after a 30-day recovery period. Blood lead and free erythrocyte porphyrin (FEP) levels in the lead-treated groups were significantly higher than in the control animals (P less than 0.001). The animals in the recovery groups had lower, albeit not normal, blood lead and FEP levels 30 days after discontinuing treatment. Serum testosterone, intratesticular sperm counts, and sperm production rates were suppressed in the lead-treated groups (P less than 0.001). Serum testosterone and sperm parameters normalized at the end of the recovery period in the prepubertal animals but not in the pubertal animals.