Induction of lordosis in female rats: Two modes of estrogen action and the effect of adrenalectomy

Abstract

In ovariectomized female rats, progesterone treatment alone does not induce lordosis, but following estrogen treatment by an appropriate interval it greatly enhances the performance of lordosis compared to that with estrogen alone. This “facilitating” effect of progesterone is thought to act synergistically with the initial “priming” effect of estrogen. In the present experiments a second estrogen treatment given to estrogen-primed ovariectomized rats in place of progesterone was found to facilitate lordosis. Latency of the facilitation of lordosis following this second estrogen treatment was similar to that of progesterone and was much shorter than that required for the usual “priming” effect, but higher doses were needed for the “facilitatory” effect. Experiments with adrenalectomized-ovariectomized female rats showed that this short latency effect of second estrogen treatment need not be mediated by the adrenals. These results raise the possibility that estrogen acts on the central nervous system in more than one way to induce lordosis.