Stimulation of LH secretion in constant estrous rats under constant illumination by rat hypothalamic extract.

Adult female rats were rendered anovulatory by continuous illumination. Pituitary LH of these constant estrous rats decreased with the time length of illumination. Acidic extract from the rat hypothalamus was injected into these rats through the carotid artery for testing LH-RF activity. The extract, if a dose more than 2 hypothalamic fragments per rat was given, induced ovulation. Ovulatory response was determined by observation of tubal ova and formation of new corpora lutea. Cerebral cortical extract, lysine vasopressin and oxytocin were not active in stimulation of ovulation. Pituitary LH and plasma LH shortly after intracarotid injection of the hypothalamic extract were estimated by the OAAD method. A single injection produced a transient rise in pituitary LH, and the maximum occurred 20 mins. after injection. Sixty mins. after injection pituitary LH showed a significant decrease. Corresponding to this fall in pituitary LH, plasma LH showed a significant rise. Both pituitary LH and plasma LH returned to near-initial levels 4 hrs. after injection. These results suggest that hypothalamic extract may stimulate the sysnthesis of LH by the anterior pituitary of constant estrous rat as well as the release of LH.