Priming action of estrogen: minimum duration of exposure for feedback and behavioral effects.

The minimum duration of the centrally-mediated "priming" effects of estrogen on "positive feedback" release of LH and sexual receptivity (lordosis) was studied. Spayed rats were given Silastic implants of estradiol followed 3 days later by an s.c. injection of progesterone and testing. 30-min implantation of preincubated estradiol capsules sufficed for behavioral responses, but did not stimulate the LH surge. When the capsules were not preincubated, however, LH surges did occur, presumably because of the greater release of estrogen. It is concluded that the minimum duration of the estrogen priming effects is considerably less than the period of natural preovulatory surge of estrogen at proestrus.