Characterization of a nuclear estrogen receptor in the testis of Atlantic croaker (Micropogonias undulatus) and effects of estrogen on testicular steroidogenesis

An estrogen receptor (ER) was identified in the nuclear and cytosolic fractions of the testis in the marine teleost, Atlantic croaker (Micropogonias undulatus). Competition studies demonstrated that the receptor was highly specific for estrogens and that a variety of xenoestrogens bound to the receptor with relatively low binding affinities. A comparison of the binding affinities of ligands for the testicular and hepatic ERs in this species revealed that the testicular ER saturated at a lower estradiol concentration and also had higher binding affinities for most of the estrogens and xenoestrogens tested. Minor amounts of estradiol were produced by testicular tissue fragments incubated in vitro. Incubation of testicular fragments in vitro with estradiol caused a concentration-dependent decrease in gonadotropin-stimulated 11-ketotestosterone (11-KT) production. Estradiol is acting on the cell surface via a non-genomic mechanism to alter 11-KT production