There has been increasing concern over the role of dietary and environmental steroids, and steroid mines on the increased occurrence of various abnormalities in steroidally responsive target tissues in both males females. In mammals, these compounds often appear to elicit their effect at the transcriptional level through their competitive interaction for the estrogen/androgen receptors. However, the tight focus on mammalian models of endocrine disruption at the receptor level has resulted in a tendency to overlook at the importance of the effects of these compounds on other susceptible pathways critical for normal reproductive behavior. The environmental pollutant tributyltin (TBT) may represent a new class of endocrine disruptor that elicits its effects by directly perturbing the pathways governing steroidogenesis rather than acting indirectly via the estrogen receptor. The compound can act as a potent 'anti-estrogen' causing sex reversal in certain species of mollusc at concentrations as low as o.5ng1-1. This condition, termed imposex, describes a state of pseudo- hermaphrodism where afflicted females exhibit spermatogenic activity and secondary male characteristics including a penis where a penal duct and a vas deferens. At this present time, the mechanisms by which TBT causes masculinization in these organisms is unknown and its potential for causing similar perturbations in sex differentiation and expression in other species, including mammals, remains to be established. The primary, long-term goal of the proposed study is to determine the sub-lethal model of toxicity of the compound and assess whether TBT and other toxicological analogues could constitute an environmental hazard to humans. Preliminary data indicate that TBT may cause imposex by three independent mechanisms that either directly, or indirectly, collectively increase the androgenic titer of steroids, thereby inducing maleness. In this proposal, a series of in vivo and in vitro experiments using the TBT-sensitive mollusk, Nucella emarginata, and human prostate cancer and hepatoma cell lines have been designed to specifically test each of the identified mechanisms of action and determine if TBT acts via perturbing aromatase activity, androgen conjugation and elimination or by potentiation gonadotrophin neuropeptide release.