Subcellular compartmentalization of the progesterone receptor in cat uteri following the acute administration of progesterone.

Cytosol and nuclear progesterone receptors in the cat uterus were measured by Scatchard analysis to determine the relationships between dose of progesterone administered and the time following administration with the content of receptor in these two cellular compartments. Cats were ovariectomized, treated for 7 days with estradiol and then injected via the saphenous vein with progesterone. One uterine horn was removed prior to, and the other uterine horn after the injection of progesterone. The amount of cytosol receptor translocated was found to be dose-dependent over the range of 0-200 micrograms of progesterone. A maximum of 40% of the cytosol receptor was depleted even when the amount of progesterone injected was increased. In non-estradiol-primed animals it was also found that approximately 40% of the cytosol receptor was depleted following a progesterone injection. Within 3 h of the injection of 300 micrograms of progesterone, the cytosol and nuclear receptor levels had returned to preinjection values. A second administration of progesterone at 1 or 3 h after the first injection of progesterone caused a partial depletion of the cytosol receptor and an increase in nuclear progesterone receptor concentration. These data suggest that the translocation of cytosol receptor and the appearance of nuclear receptor is dose-dependent until approximately 40% of the cytosol receptor is depleted following a single injection of progesterone, that the retention of nuclear receptor after an acute injection of progesterone is of short duration (less than 1 h), and that the replenishment of cytosol receptor is complete within 3 h.