Bisphenol A (BPA) causes reproductive toxicities, but the mechanisms are still unclear. In the present study, we sought to clarify these mechanisms in comparison with those of 17beta-estradiol (E2). Prepubertal Wistar/ST male rats (4 weeks old) were subcutaneously administered BPA (0, 20, 100 and 200 mg/kg/day) or E2 (10 and 100 microg/kg/day) for 6 weeks. Both BPA and E2 treatments decreased plasma and testicular testosterone levels, and plasma luteinizing hormone (LH), but not E2 and follicle-stimulating hormone levels, though E2 treatment increased its plasma level. In relation to the decreased testosterone levels, BPA and E2 decreased expressions of steroidogenic enzymes and cholesterol carrier protein in Leydig cells. Thus, decreased testosterone levels in plasma might have resulted from decreased expressions of these enzymes and protein as well as from decreased plasma LH levels. Interestingly, the changes in steroidogenic enzymes and carrier protein were observed at lower levels of exposure to BPA or E2 than those inhibiting plasma LH levels. Microscopically, 200 mg/kg BPA and 100 microg/kg E2 significantly decreased Leydig cell numbers in the testis. In addition, BPA and E2 also decreased expression of estrogen receptor alpha-mRNA, which might be related to the decreased numbers of Leydig cells. Thus, BPA directly affects not only the Leydig cells but also the pituitary gland, but the former may be impaired at lower exposure concentrations than the latter.
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