There is presently considerable interest in endocrine disruption which is a new area of endocrinology concerned with chemicals that mimic hormones, in particular sex steroids. It has been hypothesised that exposure to such chemicals may be responsible for adverse effects in both humans and wildlife. Until now, chemicals that mimic oestrogens (so-called xenoestrogens) have been the main focus of endocrine disruption research. However, recent evidence suggests that many abnormalities in the male reproductive system may be mediated via the androgen receptor. By blocking androgen action, exposure to an anti-androgen may cause changes similar to those associated with oestrogen exposure.We have used in vitro yeast-based assays to detect oestrogenic, anti-oestrogenic, androgenic and antiandrogenic activities in a variety of chemicals of current interest. We show that many of the so-called 'environmental oestrogens' also possess anti-androgenic activity. The previously reported anti-androgenic activities of vinclozolin and p,p -1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE) were confirmed. We also found that o,p -1,1,1,-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), bisphenol A and butyl benzyl phthalate were anti-androgenic. However, not all xenoestrogens are also anti-androgenic, because nonylphenol was found to be a weak androgen agonist. Our results demonstrate that hormone-mimicking chemicals can have multiple hormonal activities, which may make it difficult to interpret their mechanisms of action in vivo.Although not a specific objective of this study, our results also demonstrate that yeast-based assays are powerful tools with which to investigate both agonist and antagonistic hormonal activities of chemicals.

Bisphenol A (BPA), a high-volume chemical used to make polycarbonate plastic, epoxy resins, and other chemicals has been reported to be weakly estrogenic. To investigate the effects of long-term exposure to Bisphenol A, a multigeneration study was conducted in which fathead minnows (Pimephales promelas) were exposed to water concentrations of BPA in the range from 1 to 1280 micrograms/L. In this paper, we report the growth and reproductive effects of BPA on sexually mature adults in the F0 generation (after 43, 71, and 164 d of exposure) and the effects on hatchability in the F1 generation. Mean measured concentrations of BPA in the water for all doses, over a 164-d exposure period, were between 70% and 96% of nominal. An inhibitory effect of BPA on somatic growth (length and weight) occurred in adult male fish exposed to 640 and 1280 micrograms/L (after 71 and 164 d). BPA induced vitellogenin synthesis (VTG; a biomarker for estrogen exposure) in males at concentrations of 640 and 1280 micrograms/L after 43 d and 160 micrograms/L after 71 d. In females, plasma VTG concentrations were elevated above controls only after 164-d exposure to 640 micrograms/L. Inhibition of gonadal growth (as measured by the gonadosomatic index) occurred in both males and females at concentrations of 640 and 1280 micrograms/L after 164 d. In males, a concentration of 16 micrograms/L altered the proportion of sex cell types in the testis, suggesting inhibition of spermatogenesis. Concentrations of BPA that induced VTG synthesis and affected gonadal development were lower than those that resulted in discernible effects on reproductive output. Egg production was inhibited at a BPA concentration of 1280 micrograms/L, and hatchability in the F1 generation was reduced at a BPA concentration of 640 micrograms/L (there were not enough eggs spawned in the 1280 micrograms/L group for hatchability studies to be conducted). The results demonstrate that BPA acts as a weak estrogen to fish when administered via the water, with effects on breeding at and above 640 micrograms/L.

To date, within the field of endocrine disruption, much focus has been placed on chemicals that mimic oestrogens (so-called xenoestrogens), and the number of such chemicals apparently detected continues to grow steadily. Less effort has been expended on investigating chemicals that mimic, or antagonize, other hormones. Nevertheless, a number of chemicals have been reported to have a weak affinity for the androgen receptor, all of which have, to date, been found to have anti-androgenic activity in vivo. In this report, we present evidence that the insecticide fenitrothion can interact with the androgen, but not with the oestrogen, receptor. Using recombinant yeast expressing the human androgen receptor, we found that fenitrothion behaved as an androgen agonist in vitro when tested alone, and that it could antagonize the androgen DHT when both chemicals competed for the androgen receptor in vitro. In vivo studies using both intact and castrated male rats showed no conclusive androgenic or anti-androgenic responses. Changes in organ weights suggestive of anti-androgenic effects were mitigated against by the reduced body weights of fenitrothion-treated rats. The toxicity of the compound precluded the use of higher dose levels to substantiate any tentative findings. Interestingly, fenitrothion (and related insecticides) is structurally similar to flutamide, an anti-androgen used clinically that gives clearly positive responses in both intact and castrated rats.