HEPATIC ESTROGEN-RECEPTORS IN THE JAPANESE EEL, ANGUILLA-JAPONICA - CHARACTERIZATION AND CHANGES IN BINDING-CAPACITY DURING ARTIFICIALLY-INDUCED SEXUAL-MATURATION

Estrogen receptors were identified in cytosolic and nuclear extracts o f livers of female Japanese eel, Anguilla japonica. A single class of high affinity binding sites was found, with a Kd=0.97 nM for the cytos olic estrogen receptor (cER) and Kd=0.85 nM for the nuclear estrogen r eceptor (nER). Binding of both the cER and the nER was specific for es trogens (diethylstilbestrol: DES >estradiol-17 beta E(2) > > estriol: E(3) >estrone: E(1)). These binding character istics of ERs were quite different from those of the serum estrogen-binding component; [H-3]E( 2) binding to serum was not saturable, and was displaced by testostero ne but not by DES, E(1) or E(3). The relationships between the levels of hepatic ERs, circulating E(2) and vitellogenin (VTG) during artific ial maturation of cultivated female eels were examined, using eels inj ected weekly with chum salmon pituitary homogenate at a dose of 20 mu g/g-body weight. Serum E(2) levels were constantly low during pre- to midvitellogenesis, and dramatically increased in the migratory nucleus stage. However, VTG levels gradually increased from early to midvitel logenesis, and were greatly elevated in the migratory nucleus stage. H epatic cER levels slightly increased in early vitellogenesis, and then increased significantly from midvitellogenesis to the migratory nucle us stage. In contrast, nER levels did not change significantly, althou gh nER levels in the migratory nucleus stage were higher than those at other stages. The changes in cER levels represent increased hepatic r esponsiveness to estrogenic stimuli during artificial maturation. Lack of change in nER levels may be a feature of artificial maturation com pared to sexual maturation in nature.