Estrogen receptor binding in the hen hypothalamus and pituitary during the ovulatory cycle

The equilibrium dissociation constant (Kd) and the maximum binding capacity (Bmax) of estrogen receptor in soluble (cytosolic) and insoluble (nuclear) fractions in a hypotonic buffer solution of hypothalamus containing preoptic (HPOA) and median eminence (HMEA) areas and of anterior pituitary (AP) of laying and nonlaying hens were examined by Scatchard analysis of specific [3H]estradiol-17 beta ([3H]-E2) binding. The Kd of receptor in all of the tissues was different neither between soluble and insoluble fractions, nor between laying and nonlaying hens. The Bmax in laying hens was greater in the insoluble fraction and lower in the soluble fraction than that in nonlaying hens, but the total binding capacity (sum of Bmax in the soluble and insoluble fractions) was not different between laying and nonlaying hens. In laying hens, the specific [3H]-E2 binding in the insoluble fraction of HPOA was found to increase at 21 h before ovulation and again at 8 to 6 h before ovulation, and of HMEA and AP at 18 to 11 h before ovulation. No change in the specific [3H]-E2 binding in the insoluble and soluble fractions was found in any of the tissues of nonlaying hens during a 24-h period. The results suggest that in laying hens, estrogen may act on the hypothalamus and pituitary at restricted hours during the ovulatory cycle.