Sex-specific effects of estradiol on hypothalamic noradrenaline turnover in gonadectomized rats

In long-term gonadectomized rats of either sex a single injection of estradiol-17 beta 3-benzoate acutely decreased the turnover rates of noradrenaline in the preoptic-anterior hypothalamic brain area (POAH) and reduced the serum concentrations of luteinizing hormone (LH). On the afternoon of day 3, between 72 and 78 h after estrogen priming, an increase of noradrenaline turnover was observed in female rats, whereas the turnover remained low in males. The increase of noradrenergic activity in female rat brain occurred at the time when LH release could be stimulated by progesterone. On the other hand, the low noradrenergic activity in the POAH of male rats correlated with the lack of stimulatory progesterone effects on LH secretion. The data indicate that estradiol induces a sex-specific increase of noradrenaline turnover in the POAH. This increase appears to be a prerequisite for the induction of LH surges.