Facilitation of lordosis in guinea pigs by an alpha-noradrenergic agonist is independent of progestin receptor stimulation.

Because manipulations of the noradrenergic system affect both lordosis behavior and progestin receptor levels in female guinea pigs, the present study attempted to determine if the noradrenergic (NE) system affects lordosis solely because of its impact on progestin receptors. Although the progestin receptor antagonist RU486 significantly reduced progesterone-facilitated lordosis, it had no effect on lordosis induced by the alpha-NE agonist clonidine in estrogen-primed female guinea pigs. This indicates that although progesterone may facilitate lordosis in female guinea pigs via activation of progestin receptors, the alpha-noradrenergic agonist clonidine does not mediate lordosis through the same mechanism.