Hypothalamic changes in norepinephrine release in rats with estradiol valerate-induced polycystic ovaries

Abstract

Chronic anovulation and polycystic ovaries (PCO) can be induced by a single i.m. injection of estradiol valerate (EV, 2 mg in oil) in the rat. Constant exposure to high plasma levels of estradiol provokes a neurotoxic effect on the hypothalamic neurons, including those from the arcuate nucleus. Because of the important participation of hypothalamic norepinephrine (NE) in the regulation of GnRH release and the possible noxious effect of prolonged exposure of these neurons to estradiol, our interest was to study the activity of the noradrenergic neurons innervating the hypothalamus. We analyzed the biosynthesis, content, and release of NE from the noradrenergic nerve terminals of the hypothalamus during the PCO condition. We found a decrease in tyrosine hydroxylase (TH) activity and in the content of dopamine (DA) in the anterior hypothalamus after 2 mo of EV injection, whereas dopamine-β-hydroxylase (DβH) was increased without changes in NE content. No variations in TH activity or in DA