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

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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 which attained a peak 14 and 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.