Endocrine disruptors are hormonally active compounds which can disturb the physiological function of mammalian endogenous hormones. Two of these substances, tetrabrombisphenol A (TBBA) and zearalenone (ZEA), were tested. TBBA is a substance widely used in industry as a flame retardant. ZEA is a mycotoxin produced by fungi of the species Fusarium, which is a common contaminant of grain. In a mouse model, we examined the effect of both substances on the reproductive parameters, spermatogenesis, semen quality and expression of testicular genes playing an important role during spermatogenesis, in the process of apoptosis and in hormonal response. TBBA in the dose of 35 μg/kg b.w. per day increased incidence of apoptosis in the testes and changes in the morphometry of seminiferous tubules. We also found changes in the expression pattern of selected genes encoding proteins that play an important role during spermatogenesis. ZEA was administered in two different doses (25 µg/kg b.w. and 25 ng/kg b.w. per day). ZEA decreased sperm concentration (by 40%) and quality and altered expression of the selected genes. Surprisingly, we observed a stronger effect after exposure to the lower dose of ZEA. This phenomenon is quite common in endocrinology, where lower dosages of hormones are effective, while high dosages have no effect. Also, the higher doses may potentially lead to greater recourse to compensatory mechanisms. Both substances (TBBA and ZEA) cause changes in the reproductive parameters and in the expression of selected genes that influence spermatogenesis, and may subsequently affect the sperm quality and finally reproduction.

Acknowledgement
This work was supported by the Grant Agency of the Czech Republic, grant No. 503/12/1834 and by BIOCEV project CZ.1.05/1.1.00/02.0109 from the ERDF.