Regulation of Human Gonadotropins: X. Episodic Fluctuation of LH During the Menstrual Cycle1

Abstract

Serum concentrations of LH and FSH in 49 samples obtained at consecutive hourly intervals from seven women at different phases of the menstrual cycle have been determined by radioimmunoassay. In all cases, hourly analysis indicated that serum concentrations of LH, and possibly FSH, are maintained as a series of peaks of variable magnitude. The sampling interval was too long to permit an exact determination of the frequency of the peaks which appeared to occur at approximately 2½ hour intervals. The largest LH excursions were noted during the ascending and descending phases of the major LH peak at midcycle and during the luteal phase of the cycle. These observations are compatible with the hypothesis that serum concentrations of LH, and possibly FSH, are maintained by brief periods of release followed by periods of little or no release.