Changes in pituitary LH content and LH secretion in the long-term ovariectomized rat during prolonged infusion of LRH.

LH secretion and the depletion of the pituitary LH stores caused by continuous infusion of LRH, were studied in the 5-weeks ovariectomized rat. After 1 day of infusion at the rate of 416 ng/h, pituitary LH content decreased to about 40% of its initial value. Upon continuation of the infusion the LH content increased slowly until, after 7 days, it increased to about 54% of the original value. The plasma LH concentrations, after having reached peak values of 7122 +/- 291 ng/ml after 2 h of infusion, declined to a plateau at about 300 ng/ml but it took 5 days to reach this value. When after either 2 or 8 days of LRH infusion at the rate of 416 ng/h the infusion was changed to a 'supramaximal' rate of 10,400 ng/h for 24 h, a transient secondary rise of LH secretion was induced. The magnitude of the secondary response, was essentially the same after 2 or 8 days of LRH infusion, but these secondary responses were significantly smaller than the LH-response during a similar LRH-infusion in previously untreated ovariectomized rats.