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

Potential new targets involved in 1,3-dinitrobenzene induced testicular toxicity

1,3-Dinitrobenzene (DNB) causes testicular injury, particularly to Sertoli cells, and induces apoptosis in the surrounding germinal cells in rodents; however, the mechanisms causing this toxicity are poorly understood. Our studies, using standard and molecular tools, were conducted to better understand the pathogenesis of the testicular effects. Four daily oral doses of 0.1-8mg/kg/day caused marked testicular lesions in rats from 4mg/kg/day. Global transcriptomics revealed cell cycle and cell death as the major biological processes affected with the expression of genes associated with cell cycle progression ("mitotic roles of polo-like kinase") being particularly altered. In a single dose time course study (4mg/kg), no adverse changes were recorded; however, in contrast to the data from the multiple dose study, plasma testosterone and testicular steroidogenesis-related gene expression were affected. These steroid hormone effects were confirmed in vitro using the H295R steroidogenesis assay. With this global approach we show that DNB not only induces apoptosis and interferes with cell cycle in the testes but that DNB can also modulate steroid hormone biosynthesis, suggesting an interference with the endocrine system. However, the contribution of the endocrine changes to the severe testicular lesions is presently unknown and requires further investigation.

The estrogenic and antiandrogenic pesticide methoxychlor alters the reproductive tract and behavior without affecting pituitary size or LH and prolactin secretion in male rats

This study was designed to determine if long-term exposure to high doses of methoxychlor (M) would alter pituitary or testicular endocrine functions in either an estrogenic or antiandrogenic manner. Weanling male Long-Evans hooded rats were dosed daily with M (po) at 0, 200, 300, or 400 mg kg-1 day-1 for 10 months. Methoxychlor treatment delayed puberty by as much as 10 weeks and reduced fertility and copulatory plug formation in a dose-related manner at the initial mating. During mating, M-treated males exhibited shorter latencies to mount and ejaculate versus control males, but the number of intromissions prior to ejaculation was unaffected, indicating that M enhanced the arousal level in the males in an estrogen-dependent manner. Most treated males eventually mated but time-to-pregnancy was lengthened. Very low sperm counts were associated with infertility, while prolonged delays in puberty reduced fecundity. Methoxychlor treatment with 200 to 400 mg kg-1 day-1 failed to mimic the chronic effects of a sustained (8 months) low dose of estradiol-17 beta (3-mm silastic implants) on pituitary or testicular hormone levels. Estradiol administration increased pituitary weight 4-fold, serum levels of luteinizing hormone (LH) were reduced by almost 50%, and serum prolactin was increased 40-fold, while M did not affect any of these measures. These data demonstrate that M affects the CNS, epididymal sperm numbers, and the accessory sex glands and delays mating without significantly affecting the secretion of LH, prolactin, or testosterone. These data indicate that M did not alter pituitary endocrine function in either an estrogenic or antiandrogenic manner. To our knowledge, these data provide the first in vivo example of such a pronounced degree of target tissue selectivity to an environmental endocrine-disrupting chemical.

1,3-Dinitrobenzene metabolism and toxicity in seminiferous tubules isolated from rats of different ages

Previous in vivo studies in rats have shown that susceptibility to 1,3-dinitrobenzene (DNB)-induced testicular damage increases with age. The present study has used an in vitro approach to investigate the possibility that differences in testicular metabolism contribute to the age-related differences in toxicity. Seminiferous tubules were isolated from Sprague-Dawley rats (30, 75 and 120 days old) and incubated with 100 microM DNB for 22 h. Formation of metabolites and tubular levels of ATP and glutathione (GSH) were monitored over time. There was no difference in seminiferous tubule metabolic capacity among the three ages of rats examined. After 22 h of incubation with DNB, ATP levels were 20-30% of control and GSH levels were 70-90% of control, but neither parameter showed an age-related difference in decline. Based on these biochemical indicators of cell health, this study would suggest that the lack of testicular toxicity in young animals in vivo may be due to the previously described shorter half-life with consequent reduced exposure of the testis to DNB and that the age-related increase in severity of lesion between 75 and 120 days of age cannot be explained by differences in tubular metabolism of DNB or whole-animal toxicokinetics.

Urinary creatine profiles after administration of cell-specific testicular toxicants to the rat

Cell-specific testicular toxicants have been used to examine the distribution of creatine within the rat testis, and to examine the potential use of creatinuria as a non-invasive indicator of testicular damage. Groups of rats were administered single doses of various toxicants: a germ cell toxicant (methoxyacetic acid, MAA), one of two Sertoli cell toxicants (di-n-pentyl phthalate, DPP or 1,3-dinitrobenzene, 1,3-DNB), or a Leydig cell toxicant (ethane-1,2-dimethane sulphonate, EDS). Urinary creatine and creatinine levels were monitored in 24 h periods over the following 48 h, after which time the testes were removed, weighed and, after processing, sections were examined by light microscopy. All four treatments resulted in reductions in relative testis weight (RTW) and produced morphological changes similar to those which have been previously reported. In addition, MAA, DPP and 1,3-DNB all caused significant elevations in urinary creatine excretion and the urinary creatine:creatinine ratio (Cr/Crn) within 24 h. EDS had no such effect. We conclude that creatine is associated with the cells of the seminiferous epithelium, and that elevated urinary excretion of creatine may serve as a non-invasive marker for damage to these cells in vivo.