CHANGES IN HEPATIC ESTROGEN-RECEPTOR CONCENTRATIONS DURING THE ANNUAL REPRODUCTIVE AND OVARIAN CYCLES OF A MARINE TELEOST, THE SPOTTED SEA-TROUT, CYNOSCION-NEBULOSUS

The concentrations of estrogen and vitellogenin in plasma, and hepatic estrogen receptor in cytosolic (ERc) and nuclear (ERn) extracts were elevated throughout the reproductive season in females from a wild population of spotted seatrout, Cynoscion nebulosus. There were significant correlations between plasma estradiol and ERc and between ERn and plasma vitellogenin during the period of ovarian recrudescence (January-May), but not during the remainder of the reproductive season (June-September). During ovarian recrudescence ERc concentrations increased fourfold from 0.78 ± 0.15 pmol/g liver (N = 26) in nonvitellogenic females to 3.23 ± 0.26 pmol/g liver (N = 77) in late vitellogenic females and ERn concentrations increased eightfold from 0.16 ± 0.07 pmol/g liver (N = 26) in nonvitellogenic females to 1.12 ± 0.45 pmol/g (N = 10) in mid vitellogenic females. However, following this period of ovarian recrudescence, estrogen-receptor concentrations and plasma vitellogenin titers did not fluctuate during the remaining stages of the ovulatory cycle (hydration, ovulation, and spawning). In addition, both hepatic ERc and ERn were elevated for the rest of the seasonal reproductive cycle, during which several ovulatory cycles may have occurred in this multiple-spawning species. The affinity of ERc for estradiol did not vary (Kd = 1.26 ± 0.06 nM, N = 68) regardless of the stage of ovarian development. Plasma estradiol titers declined in August, near the end of the reproductive season, prior to the decline in estrogen-receptor concentrations. The persistence of the estrogen receptor during the ovulatory cycle suggests that even if plasma estradiol titers declined between successive ovulatory periods, the hepatic responsiveness to estrogenic stimuli would not be diminished and thus vitellogenin synthesis, if interrupted at all, could be resumed soon after spawning. © 1991.