Chemical interference with genomic and nongenomic actions of steroids in fishes: role of receptor binding.

The characteristics of steroid nuclear and membrane receptors and their interactions with xenobiotic chemicals in two marine perciform species, Atlantic croaker (Micropogonias undulatus) and spotted seatrout (Cynoscion nebulosus) are briefly reviewed. Several organochlorines that bind to the nuclear progesterone receptor in mammals show negligible binding to the nuclear progestogen receptor in seatrout ovaries. Two distinct nuclear androgen receptors with different tissue distributions have been identified in croaker, but only one of them binds xenobiotic anti-androgens previously identified in mammals. Multiple forms of the nuclear estrogen receptor (ER) have been identified in fishes. The ER in croaker testis has a higher affinity than the croaker liver ER for estrogens and xenoestrogens and may be more susceptible to chemical interference. In addition, differences in the feedback effects of estrogens and xenoestrogens on gonadotropin secretion in croaker are observed, depending on the stage of the reproductive cycle. Finally, the first clear evidence in any vertebrate for xenobiotic chemical interference with the nongenomic actions of steroids by binding to steroid membrane receptors was obtained with the seatrout ovarian progestogen membrane receptor and since has been confirmed with progestogen and estrogen membrane receptors in croaker sperm and testes. These various factors that influence chemical/steroid receptor interactions are likely to significantly modify steroid hormone actions at target tissues and consequently the toxicological effects of chemical exposure.