at the hypothalamic level , during the estrous cycle in rats , beta-end concentrations were highest on diestrus i in the arcuate nucleus , median preoptic area and median eminence and lowest at the time of the preovulatory 17 beta-e2 surge on proestrus , before the subsequent preovulatory hypothalamic gnrh and plasma lh surges .
C0020663
hypothalamic
C0023610
gnrh