STATUS OF HCG LH RECEPTOR AND G-PROTEINS IN HUMAN ENDOMETRIUM DURING ARTIFICIAL CYCLES OF HORMONE REPLACEMENT THERAPY/

OBJECTIVES: We examined the existence of hCG/LH receptors and associat ed GTP-binding (G) proteins in membrane fractions of nonpregnant human endometrium and investigated whether their expression is affected, in vivo, by estrogen and progesterone replacement therapy. METHODS: A po ol of normal endometrial biopsy specimens (n = 5) was initially used t o characterize receptors and G proteins. Subsequently, biopsy specimen s (n = 22) were obtained from 11 patients undergoing evaluation cycles of hormone replacement therapy (HRT). From each patient, two specimen s weve collected on successive cycle days: on day 0 (last day of estro gen) and on either day 3, 6, or 9 of progesterone supplementation. Bot h hCG/LH receptor and G proteins were determined in membrane (10,000 x g) fractions by immunoblot analysis using specific polyclonal antibod ies against synthetic fragments of hCG/LH receptor and against G prote ins. Membrane fractions from rat brain and rat corpus luteum were used as controls. Proteins were loaded on the gel under reducing condition s. RESULTS: The receptor antibody immunoreacted with a protein of appr oximately 68 kd in endometrial membranes. A similar protein was detect ed in rat corpus luteum. The G-protein antibodies detected Gs alpha, G i3 alpha, Gi1 alpha/Gi2 alpha, and common beta subunits in endometrial membranes with a molecular weight of 48-42 kd, 41 kd, 40 kd, and 37 k d, respectively. Analysis of membranes obtained during HRT indicated t hat levels of hCG/LH receptors remained fairly constant throughout the cycle days (days 0, 3, 6, and 9). Similar results were observed for G i1 alpha/Gi2 alpha and Gi3 alpha. In great contrast, Gs alpha was low at day 0 but increased with the administration of progesterone (days 3 , 6, and 9). CONCLUSIONS: Human endometrium contains both membrane-bou nd hCG/LH receptors and associated G proteins. During HRT, progesteron e supplementation to estrogen therapy enhancer the expression of Gs al pha protein subunit, but not hCG/LH receptors.