Comparison of relative binding affinities of endocrine active compounds to fathead minnow and rainbow trout estrogen receptors.

Twelve chemicals were tested for binding affinity to rainbow trout liver estrogen receptor (rbtER) and fathead minnow liver ER (fhmER). The chemicals included estradiol (E2), diethylstilbestrol (DES), ethinylestradiol (EE2), estrone (El), estriol, tamoxifen (TAM), genistein (GEN), p-nonylphenol (PNP), p-tert-octylphenol (PTOP), methoxychlor (MXC), testosterone, and methyltestosterone (MT). Relative binding affinity (RBA) was calculated for each chemical as a function of E2 binding to the receptor. The estrogens DES, EE2, and E1 bound with high affinity to both receptors, with respective RBAs of 583, 166, and 28% (fathead minnow) and 179, 89, and 5% (rainbow trout). Relative binding affinity of E3, TAM, and GEN for both fhmER and rbtER were moderate, with values between 0.3 and 5%. The alkylphenols had weak affinity for the ERs with RBAs for the fhmER of 0.1 and 0.01 for PNP and PTOP, respectively. Corresponding values for the rbtER are 0.027 and 0.009. Estradiol ([3H]E2) only partially was displaced from both the fhmER and the rbtER by MXC, T, and MT. Comparison of RBAs of the chemicals tested for fhmER and rbtER indicates that the rank order of RBAs essentially are the same for both species.