There is evidence that brain noradrenergic systems participate in the feedback regulation of luteinizing hormone (LH) and prolactin (PRL) secretion by ovarian hormones. The present study tested the hypothesis that administration of ovarian hormones in regimens that decrease LH release would also decrease the turnover of norepinephrine (NE), while ovarian hormone treatments that stimulate LH or PRLsecretion would enhance the turnover NE in microdissected brain nuclei. Administration of estradiol to ovariectomized rats reduced circulating LH and decreased the turnover of NE in the periventricular nucleus. Treatment with estradiol, followed by progesterone or estradiol 72 h later enhanced the turnover of NE and of dopamine (DA) in the median eminence, and this was accompanied by elevations of LH and/or PRL. The dual estrogen treatment also increased NE turnover in the arcuate nucleus. Estradiol alone elevated DA turnover in the caudate nucleus and in the interstitial nucleus of the stria terminalis, and this was blocked by subsequent treatment with progesterone or estradiol. These findings indicate that activity in noradrenergic innervation to specific areas of the hypothalamus is altered by ovarian hormones. It is proposed that some of these changes may be involved in the feedback regulation of LH and PRL secretion by estradiol and progesterone.

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