Relationship between the changes in cytoplasmic progesterone receptor concentration and in nuclear progesterone binding sites in the hen hypothalamus and pituitary during the ovulatory cycle.

The amount of specific [3H]-progesterone bindings was measured in cytosols and in nuclear fractions of the hen hypothalamus and pituitary during the ovulatory cycle. In both tissues, a decrease in cytosol binding from the peak at 18 and 8 hr before ovulation was coincident with an increase in nuclear binding attained a peak 14 to 6 hr before ovulation. The results suggest that progesterone may act on the hypothalamus and pituitary 18-14 hr before ovulation and 8-6 hr before ovulation.