title: Binding characteristics of estrogen receptor (ER) in Atlantic croaker (Micropogonias undulatus) testis: different affinity for estrogens and xenobiotics from that of hepatic ER.
abstract: An estrogen receptor (ER) was identified in cytosolic and nuclear fractions of the testis in a marine teleost, Atlantic croaker (Micropogonias undulatus). A single class of high affinity, low capacity, and displaceable binding sites was identified by saturation analysis, with a Kd of 0.40 nM in cytosolic extracts and a Kd of 0.33 nM in nuclear extracts. Competition studies demonstrated that the receptor was highly specific for estrogens (diethylstilbestrol > estradiol >> estriol = estrone) and also bound several antiestrogens. Testosterone and 5alpha-dihydrotestosterone had much lower affinities for the receptor, whereas no displacement of specific binding occurred with 11-ketotestosterone or any of the C21 maturation-inducing steroids. A variety of xenoestrogens, including o,p'-dichlorodiphenyltrichloroethane (DDT), chlordecone (Kepone), nonylphenol, hydroxylated polychlorinated biphenyls (PCBs), and the mycotoxin zearalenone, bound to the receptor with relatively low binding affinities, 10(-3) to 10(-5) that of estradiol. A comparison of the binding affinities of various ligands for the testicular ER and the hepatic ER in this species revealed that the testicular ER was saturated at a lower [3H]estradiol concentration (1 nM vs. 4 nM). The binding affinities of several compounds, including testosterone and nafoxidine, exhibited marked differences for the two ERs; and most of the estrogens and xenoestrogens tested had higher binding affinities for the testicular receptor. Minor amounts of estradiol (0.12 ng/g tissue/h) were produced by testicular tissue fragments incubated in vitro, and estradiol was detected in male Atlantic croaker plasma. The identification of a testicular ER and evidence that estradiol is produced by the testes in croaker suggest that estrogens participate in the hormonal control of testicular function in teleosts.
authors.affiliation: Department of Marine Science, Marine Science Institute, University of Texas at Austin, Port Aransas, Texas 78373, USA.
authors.forename: A K
authors.initials: AK
authors.lastname: Loomis
authors.forename: P
authors.initials: P
authors.lastname: Thomas
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004958:Estradiol / Q000096:biosynthesis / Q000097:blood / Q000378:metabolism; D004967:Estrogens / Q000378:metabolism*; D005399:Fishes / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D009256:Nafoxidine / Q000378:metabolism; D011960:Receptors, Estrogen / Q000378:metabolism*; D013737:Testis / Q000378:metabolism* / Q000648:ultrastructure; D013739:Testosterone / Q000378:metabolism; D015262:Xenobiotics / Q000378:metabolism*
chemical_list: D004967:Estrogens; D011960:Receptors, Estrogen; D015262:Xenobiotics; D013739:Testosterone; D009256:Nafoxidine; D004958:Estradiol