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Human Corpus Luteum: Luteinizing Hormone and Chorionic Gonadotropin Receptors During the Menstrual Cycle^*

Division of Reproductive Endocrinology, Department of Obstetrics and Gynecology, University of Illinois College of Medicine Chicago, Illinois 60612

Address requests for reprints to: M. Yusoff Dawood, M.D., Department of Obstetrics and Gynecology, University of Illinois College of Medicine, 840 South Wood Street, Chicago, Illinois 60612.

To characterize and determine the concentration of LH/hCG receptors in human corpora lutea of the menstrual cycle, we measured occupied and unoccupied receptors and determined the association (K_a) and dissociation (K_d) constants individually in 23 corpora lutea (CL) and 4 corpora albicantia obtained at the time of tubal ligation from 25 normal cycling women. We found no [¹²⁵I]hCG binding in any of the corpora albicantia. Scatchard plot analysis for each CL revealed a linear binding plot indicative of a single set of LH/hCG receptors. The mean concentration of unoccupied receptors was 36 ± 10 (±SE) fmol/mg protein in the early luteal phase (days 15–19; n = 5), 64 ± 11 fmol/mg protein in the midluteal phase (days 20–25; n = 13), and 42 ± 19 fmol/mg protein in the late luteal phase (days 26–30; n = 5). The concentrations of occupied receptors were 56 ± 8, 46 ± 6, and 54 ± 12 fmol/mg protein in the early, mid-, and late luteal phases, respectively. Total (occupied plus unoccupied) receptor concentrations reached maximum levels of 110 ± 11 fmol/mg protein in the midluteal phase. K_a increased progressively from 12 ± 4 x 10⁹ mol/L^–1 in the early luteal phase to 19 ± 7 x 10⁹ and 21 ± 8 x 10⁹ mol/L^–1 in the mid- and late luteal phases. We conclude that in normal CL, 1) total and unoccupied LH/hCG receptor levels parallel progesterone secretion; 2) changes in the binding affinity may be important in sustaining and/or rescuing the CL; and 3) loss of LH/hCG receptors is probably related to luteolysis.

^* Presented in part at the 35th Annual Meeting of the Society for Gynecologic Investigation, March 17–20,1988, Atlanta, GA. This work was supported by an American College of Obstetricians and Gynecologists-Ortho Fellowship Grant and ACOG District VI, Illinois Section, Research Grant.

Received August 26, 1988.