Diurnal rhythmicity of beta-1- and beta-2-adrenergic receptors in ovariectomized, ovariectomized estradiol-treated and proestrous rats

Abstract

The effect of norepinephrine on LH is complex: the ovarian steroidal milieu appears to determine whether norepinephrine stimulates or inhibits LH secretion. It has been proposed that steroids allow norepinephrine to have opposite effects on LH by altering the relative concentrations of alpha 1-(stimulatory) and beta-(inhibitory) adrenergic receptors in the hypothalamus. Thus, many investigators have argued that estradiol may permit norepinephrine to stimulate LH release by increasing the density of alpha 1- and decreasing the density of beta-adrenergic receptors in one or more key hypothalamic regions. To test this hypothesis specifically, we measured the density of beta 1- and beta 2-adrenergic receptor densities in proestrous, ovariectomized, and ovariectomized estradiol-treated rats at various times of day to determine (1) whether the densities of beta-receptors exhibit diurnal rhythmicity, (2) whether beta-receptors decrease during the time of increased LH secretion and/or (3) how steroidal milieu influences the density and/or the rhythm of receptor densities. The densities of beta 1- and beta 2-receptors exhibit a diurnal rhythm in some brain areas. These rhythms are detectable only in proestrous and ovariectomized rats and only in selected brain regions. Estrogen treatment has opposing effects in different brain regions. It suppresses the rhythm of beta 1-receptor concentrations in ovariectomized rats and also suppresses the average density of receptors in the suprachiasmatic nucleus and pineal gland. In contrast, estrogen increases the density of beta 1-receptors in the medial preoptic nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)