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Luteinizing Hormone Releasing Factor Activity in Peripheral Blood from Women During the Midcycle Luteinizing Hormone Ovulatory Surge¹

Departments of Physiology and of Medicine, University of Connecticut School of Medicine Farmington, Connecticut and Medical Service, Veterans Administration Hospital Newington, Connecticut

To test the hypothesis that the ovulatory surge of LH secretion in humans is induced by the release of LRF, peripheral plasma of women during the menstrual midcycle has been bioassayed for its effects on LH secretion in rats. Forty ml of plasma were serially extracted with increasing concentrations of methanol. The supernatant of each extraction was dried and redissolved in methanol. The final dry extract dissolved i n saline was assayed for LRF activity in the ovariectomized—estrogen—progesterone—thyroxine treated rat, the end point of the assay being the increase in radioimmunoassayable rat LH. I n preliminary studies this extraction method recovered all the LRF activity from porcine hypothalamic extracts added to plasma. Fifteen samples taken during the pre- or postovulatory period had low but detectable releasing effects when compared to saline controls (p < 0.025). Of 36 plasma samples taken between days 12–16, 6 specimens had LRF activity which exceeded the mean of nonovulatory responses by more than 3 standard deviations. Human radioimmunoassayable LH was elevated more than 3 SD above mean ovulatory normal in 4 of the 6 specimens. Responses were not due to injected LH, since methanol extracts of plasma contain trace amounts or no LH. Plasma HLH was significantly correlated with LRF activity (r = 0.419, p < 0.004). Although it is reasonable to assume on the basis of previous studies in animals that the circulating LRF is hypothalamic in origin, this has not been proven for the human. If the LRF activity being measured was authentic LRF, these results would indicate that normal women have small amounts of circulating LRF, and that increased amounts of LRF appear during the midcycle.

¹ Supported in part by NIH Grant USPHS AM13695 and by a grant from the Veterans Administration.

² Postdoctoral Research Fellow of the Population Council, New York, New York. Present address, University of Guanajuato, Leon, GTO, Mexico.

Received December 14, 1970.

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