A discontinuous schedule of estradiol treatment is sufficient to activate progesterone-facilitated feminine sexual behavior and to increase cytosol receptors for progestins in the hypothalamus of the rat.

Abstract

In this study, we demonstrate that a surprisingly small and discontinuous period of estradiol (E2) treatment is sufficient to induce progesterone-facilitated sexual receptivity in the female rat. We used this temporal paradigm to measure associated changes in nuclear E2 and cytosol progestin receptors (CPRs) in the mediobasal hypothalamus-preoptic area (MBHPOA) and pituitary (PIT). The lordosis quotient, lordosis quality, and preceptivity scores of animals which received E2 in Silastic capsules for 24 or 6 continuous h were not significantly different at 24 h. CPRs in the MBH-POA and PIT in animals which received E2 for 24 or 6 continuous h were equivalent at 24 h. Receptivity comparable to 24 or 6 h of continuous E2 treatment was seen in animals which received only two 1-h periods of E2, provided that the second treatment began not fewer than 4 h, or more than 13 h, after the end of the first period (sufficient treatment). If animals received only two 0.5-h periods of E2 treatment during these times, rec...