June, 1998

Leading U.K. researchers announced that they have been unable to reproduce key results of their 1995 study on octylphenol (OP) which had frequently been cited in support of the endocrine disruption theory.

In a letter in the May edition of Environmental Health Perspectives, which published the original study, lead researcher Dr. Richard Sharpe and his colleagues note that the failure to replicate the study's results "add(s) to growing awareness that endocrine disruption data may be difficult to reproduce" and that "the reason for these inconsistencies remains obscure." (Sharpe, et. al., "Endocrine Disruptors and Testis Development," EHP, May 1998, A220-221)

Although the study's authors "remain confident in the validity" of their original findings, scientists with the APE Panel have noted that these inconsistencies cast serious doubt on the results of the 1995 study.

In the original study, researchers noted small decreases in testicular weight and sperm production of rats which had been exposed to OP during gestation and the first 21 days after birth. Dr. Sharpe and his colleagues now report that a subsequent study using an identical protocol showed an increase in testicular weight.

The authors also report that following the 1995 study, their control colony of rats (which were not exposed to any test material) showed decreased testicular and body weights, comparable to the most severe effect from exposure to DES, a potent pharmaceutical estrogen. They further note that effects of DES on testis weight are inconsistent across various tests using the same dose levels. (DES often has been used in positive control tests for estrogenic effects.)

According to Dr. Sharpe, "We are unable to offer an explanation for either the fall/recovery in testicular weights in our control animals or for our failure to obtain similar effects on testis weight/relative testis weight after exposure to OP."

Dr. Sharpe concludes, "We now consider that biological factors, of which we are unaware and for which we have not controlled, have the potential to exert developmental effects on testis weight which are at least as great as the maximum effects that can be induced by the addition of a potent estrogen (DES) to the mother's drinking water during pregnancy and lactation."

His letter is co-signed by Katie J. Turner, a colleague of Dr. Sharpe at the MRC Reproductive Biology Unit in Edinburgh, Scotland, and John P. Sumpter of the Department of Biology and Biochemistry, Brunel University in Uxbridge, United Kingdom.