Effects of estradiol on norepinephrine and prostaglandin efflux in medial basal hypothalamus of ovariectomized rats.

The spontaneous and K+-stimulated efflux of norepinephrine (NE) and the release of PGE2 and PGF2 alpha were examined in medial basal hypothalamus (MBH) of ovariectomized rats killed before and during the LH release that follows estradiol treatment. As compared to vehicle-treated, ovariectomized rats, estradiol-primed rats exhibited a 60% more increase in K+-stimulated 3H-overflow of MBH slices preloaded with 3H-NE at morning hours (1000 hours). Estradiol treatment did not result in further increase of K+-induced 3H release from MBH slices at the time of LH release (1700 hours), nor affected labeled NE release in occipital cortex slices. A significant difference between K+-stimulated NE release of vehicle-treated spayed rats killed at 1000 and 1700 hours was observed, the latter showing 54% more release upon stimulus. PGE2 efflux was time-dependent being highest at the evening in both vehicle- and estradiol-treated animals. The MBH of estrogenized rats released significantly more PGE2 at the evening as compared to the controls. The release of PGF2 alpha remained essentially unchanged regardless of estradiol treatment or time of day. The present results offer additional support to the involvement of MBH catecholamines and prostaglandins in the mechanism of LH secretion in the rat.