Recovery of the pituitary gland from LRH-induced refractoriness to LRH in the ovariectomized rat.
Recovery of the pituitary gland from LRH-induced refractoriness to LRH was studied in 5-weeks ovariectomized rats. Rats first received over a period of 48 h an infusion of LRH at a rate of 416 ng/h. After discontinuation of this infusion pituitary LH content had decreased to about 50% of its original value and the rate of LH secretion decreased markedly. Over a period of 72 h after discontinuation of the infusion plasma LH values rose to pre-infusion values but pituitary LH content showed such a recovery only partly. In another series of experiments a second infusion of LRH was given during 24 h and again at a rate of 416 ng/h, starting 3, 12, 24 or 72 h after discontinuation of the first infusion. It induced rises of LH secretion which were smaller than those following the first infusion, indicating refractoriness of the pituitary gland to LRH. However, the LH responses became progressively larger with increasing time intervals after the end of the first infusion. This stimulation of LH release was accompanied by a further decrease of pituitary LH content which was still depressed after the first infusion. Comparison of plasma LH levels and pituitary LH content indicated that pituitary responsiveness to LRH can recover independently from pituitary LH content. It can also be concluded that the absolute value of the blood LRH concentration can not be the sole determining factor of LH secretion.
D000818:Animals; D002369:Castration; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone