Comparison of study controls.

In the article "Natural Variability and the Influence of Concurrent Control Values on the Detection and Interpretation of Low-Dose or Weak Endocrine Toxicities," Ashby et al. (2004) discounted a number of studies reporting low-dose effects caused by endocrine-disrupting chemicals, including bisphenol A (BPA), based on variability in control values in experiments conducted at different times. They cited data from four experiments that we reported in three published studies (Ohsako et al. 2001; Sakaue et al. 1999, 2001). Ashby et al. stated that the marked reduction in daily sperm production (DSP) caused by BPA that we observed in two experiments (Sakaue et al. 2001) should be discounted because the DSP values in BPA-exposed males were not significantly different from those in controls we reported in another study (Ohsako et al. 2001). Ashby et al. (2004) proposed that our conclusion that BPA significantly decreased DSP is incorrect because of a difference in control values for DSP from different experiments conducted at different times.

We would like to point out that it is absolutely inappropriate to compare these sets of data not only because the experiments were conducted at different times but also because they included different experimental conditions and different animals (Table 1). First, we used Sprague-Dawley rats in the two experiments in the BPA study (Sakaue et al. 2001) and Holtzman rats in another study of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Ohsako et al. 2001). Second, the Sprague-Dawley rats used in the BPA study were purchased from a laboratory animal breeder, whereas the Holtzman rats used in the TCDD experiment were bred at the National Institute for Environmental Studies (NIES). Third, animal maintenance conditions were not the same for the three studies: Holtzman rats were housed in polycarbonate cages with wooden chips, and Sprague-Dawley rats were kept in hanging stainless wire-mesh cages.

There are many reasons why males from different rat strains obtained from different breeding facilities using different animal feed and housing conditions might differ in DSP. We thus disagree with the interpretation by Ashby et al. (2004) that this variability between rats from different strains invalidates the conclusion drawn by Sakaue et al. (2001) that exposure to BPA reduces DSP in Sprague-Dawley rats. We also disagree with their attempt to discount effects caused by BPA and other endocrine-disrupting chemicals due to variability in control animals from entirely different experiments in which low-dose effects were reported by other researchers.

The authors declare they have no competing financial interests.

REFERENCES

Ashby J, Tinwell H, Odum J, Lefevre P. 2004. Natural variability and the influence of concurrent control values on the detection and interpretation of low-dose or weak endocrine toxicities Environ Health Perspect 112:847-853.

Ohsako S, Miyabara Y, Nishimura N, Kurosawa S, Sakaue M, Ishimura R, et at. 2001. Maternal exposure to a low dose of 2,3,7,8-tetrachlorodibennzo-p-dioxin (TODD) suppressed the development of reproductive organs of male rats: dose dependent increase of mRNA levels of 5-reductase type 2 in contrast to decrease of androgen receptor in pubertal ventral prostate. Toxicol Sci 60:132-143.

Sakaue M, Ohsako S, Ishimura R, Kurosawa S, Kurohmaru M, Hayashi Y, et al. 1999. Preliminary BPA experiment [Abstract]. In: 127th Annual Meeting of the Japanese Society of Veterinary Science, 2-4 April, Fujisawa, Japan. Abstract 47.

Sakaue M, Ohsako S, Ishimura R, Kurosawa S, Kurohmaru J, Hayashi Y, et al. 2001. Bisphenol A affects spermatogenesis in the adult rat even at a low dose. J Occup Health 43:185-190.

Seiichiroh Ohsako

Environmental Health Sciences Division

National Institute for Environmental Studies

Tsukuba, Japan

E-mail: [e-mail]

Chiharu Tohyama

Center for Disease Biology and

Integrative Medicine

Graduate School of Medicine

The University of Tokyo

Tokyo, Japan

E-mail: [e-mail]

Table 1. Comparison of conditions of the three experiments.

                                               Sakaue et al 1999

Rat strains                                         Holtzman
Place of birth                          Animal breeding facility (NIES)
Age at the time of purchase                            NA
Cage type                                     Stainless wire-mesh
Bedding                                               None
Age at the time of tissue collection                 PND126
Place for examination                   Animal breeding facility (NIES)
Test compound                                         BPA
Vehicle                                             Corn oil
Control DSP value (a)                        39.0 [+ or -] 1.6 (4)
  (x [10.sup.6]/testis)

                                               Ohsako et al. 2001

Rat strains                                         Holtzman
Place of birth                             Chemical hazard area (NIES)
Age at the time of purchase                            NA
Cage type                                     Polycarbonate plastic
Bedding                                             Wood chip
Age at the time of tissue collection                 PND120
Place for examination                      Chemical hazard area (NIES)
Test compound                                         TCDD
Vehicle                                       Corn oil/4% n-nonane
Control DSP value (a)                       34.6 [+ or -] 2.0 (12)
  (x [10.sup.6]/testis)

                                               Sakaue et al. 2001

Rat strains                                      Sprague Dawley
Place of birth                                     CLEA Japan
Age at the time of purchase                          PND77
Cage type                                     Stainless wire-mesh
Bedding                                               None
Age at the time of tissue collection                 PND126
Place for examination                   Animal breeding facility (NIES)
Test compound                                         BPA
Vehicle                                      Corn oil/6.5% ethanol
Control DSP value (a)                      44.0 [+ or -] 2.2 (5) (b)
  (x [10.sup.6]/testis)                    49.3 [+ or -] 5.3 (8) (c)

Abbreviations: NA, not applicable, PND, postnatal day.

(a) Mean [+ or -] SE (number of animals). (b) First experiment.
(c) Second experiment.