Relationship Between the Plasma Levels of Luteinizing Hormone and Progesterone During the Normal Menstrual Cycle1

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Abstract
The temporal relationship between the concentrations of luteinizing hormone (LH) and progesterone in peripheral plasma has been determined during the course of the normal human menstrual cycle. Daily plasma samples were assayed, in duplicate, for progesterone by the competitive protein-binding method of Murphy (0.5 ml aliquots of plasma) and for LH by a radioimmunologic procedure (0.1 ml aliquots of plasma). Plasma progesterone levels remained consistently low (after the midcycle surge of LH became fully evident. Following the decline in plasma LH concentrations, the plasma progesterone levels increased rapidly, reaching maximal concentrations of 10–19 mμg/ml in 3–5 days. Progesterone concentrations remained elevated for 4–6 days and then fell abruptly to the initial low levels approximately 24 hr before the onset of menstruation without concomitant changes in LH concentration.