Alpha 1 noradrenergic antagonism decreases hormonally-induced and hormonally-independent lordosis.

Manipulations of the alpha noradrenergic (NE) system affect both lordosis and the concentration of hypothalamic steroid receptors. The present studies explored whether NE affects lordosis in guinea pigs via changes in hypothalamic estrogen or progestin receptors or through some other mechanism. The alpha 1 NE antagonist prazosin blocked lordosis which was induced with estradiol benzoate (EB) followed by progesterone (P), lordosis which was induced by EB alone and lordosis which is not dependent upon gonadal hormones for its display. These results suggest that NE modulation of lordosis in the guinea pig is not exerted solely through progestin receptors or estrogen receptors. Because prazosin blocked hormonally-independent lordosis, it is apparent that the NE system modulates some nonhormonal component of lordosis in guinea pigs.