The Effect on Sperm Production in Adult Sprague-Dawley Rats Exposed by Gavage to Bisphenol A Between Postnatal Days 91-97

M. Sakaue et al. (2001,J. Occup. Health vol. 43, pp. 185-190) have described how oral exposure of sexually mature male rats to bisphenol A (BPA) between postnatal days (PND) 91-97 led to a reduction in daily sperm production (DSP) 5 weeks later (18 weeks of age). Activity was observed over the dose range 20 microgram/kg-200 mg/kg BPA, with an absence of activity over the dose range 2 ng/kg-2 microgram/kg BPA. There was no evidence of a dose response relationship over the active dose range (five orders of magnitude range). The observation of endocrine disruption (ED) effects for BPA at such low doses, and in sexually mature animals, was unexpected. It was therefore decided to mount an independent repeat of their study. A total of four independent studies were conducted according to the protocol used by Sakaue et al. Doses of 20 microgram/kg, 2 mg/kg, or 200 mg/kg BPA were administered to adult Sprague-Dawley (SD) rats over PND 91-97, and the studies were terminated when the rats reached the age of 18 weeks. Three different rodent diets were employed (RM3, Purina 5002, and CE2), the last of which had been used by Sakaue et al. BPA failed to give any evidence of ED activities, including the changes in DSP reported by Sakaue et al. 2001. During the course of these studies, the test protocol was adapted to coincide more precisely with that used by Sakaue et al.; this included restricting the number of animals per cage, removing bedding from the cages, and changing to the use of glass water bottles in the cages. The only thing of interest to emerge from our studies was the observation of a significant difference in DSP between the control groups of our first and second study. As the change in diet from RM3 to Purina 5002 was the major difference between those two studies, we conducted a repeat of the second study, but we were unable to confirm the differences seen between the first and second study. The probability that those differences arose either by chance, or as the result of intrinsic study-to-study variability, was strengthened by the absence of significant differences in the sperm parameters in a final (fifth) study where the sperm parameters for control animals maintained on the three different diets were compared under the conditions of the main experiments. No explanation for our failure to replicate the effects reported by Sakaue et al. is evident. A review of DSP values reported in the recent literature is provided and discussed, and it is concluded that use of the term DSP/g testis rather than DSP/testis could increase the sensitivity of DSP assessments.