Luteinizing hormone releasing factor activity in peripheral blood from women during the mid-cycle luteinizing hormone ovulatory surge.

Abstract

Luteinizing hormone (LH) releasing activity was measured in the plas ma of normal women at different stages of menstrual cycle. For the bioassay in rats, 40 ml of plasma were serially extracted with increasing concentrations of methanol. The supernatants were dried and assayed for LH releasing factor (LRF) activity in ovariectomized-estroge n-progesterone-thyroxine treated rats, the end point being the increase in radioimmunoassayable rat LH. 15 samples obtained during the pre- or postovulatory period had low but detectable releasing effects when compared to saline controls (p less than .025). 6 out of 36 specimens obtained between Days 12-16 revealed LRF activity which exceeded the mean of nonovulatory responses by more than 3 standard deviations (SDs) (p less than .01). 4 of the 6 samples with high LRF activity had LH elevations greater than 3 SDs in the same specimens. Plasma LH was a function of plasma LRF as determined by Pearson's coefficient of correlation (r = .419, p less than .004). These results support the view that in the human, the ovulatory LH surge is triggered by estrogen stimulation of hypothlamic LRF release.