Noradrenergic regulation of cytosol estrogen receptors in female rat hypothalamus: possible role of ga 2-noradrenergic receptors

Abstract

Because of the previous work demonstrating that the α 1-noradrenergic receptor antagonist , prazosin, decreases the concentration of cytosol estrogen receptors in rat mediobasal hypothalamus, a series of experiments was performed to determine the specificity of this effect of the α 1-noradrenergic system. Injection of the α 2-noradrenergic antagonist, yohimbine, caused a decreased in the concentration of estrogen receptors in mediobasal hypothalamus. In addition, the down-regulation of cytosol estrogen receptors by either the α 1-noradrenergic antagonist, prazosin, or the α 2noradrenergic antagonist, yohimbine, could be blocked by pretreatment with the α 2noradrenergic agonist, clonidine. The α 1-noradrenergic agonist, phenylephrine, was ineffective in blocking the effects of the α 1-noradrenergic antagonist, prazosin. These results add further support to the hypothesis that the α-noradrenergic system modulates the concentration of cytosol estrogen receptors in the rat hypothalamus. They suggest that the modulation may occur by way of α 2-noradrenergic receptors in addition to, or instead of, α 1-noradrenergic receptors.