Status of hCG/LH receptor and G proteins in human endometrium during artificial cycles of hormone replacement therapy.
OBJECTIVE
We examined the existence of hCG/LH receptors and associated 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 pool of normal endometrial biopsy specimens (n = 5) was initially used to characterize receptors and G proteins. Subsequently, biopsy specimens (n = 22) were obtained from 11 patients undergoing evaluation cycles of hormone replacement therapy (HRT). From each patient, two specimens were collected on successive cycle days: on day 0 (last day of estrogen) and on either day 3, 6, or 9 of progesterone supplementation. Both hCG/LH receptor and G proteins were determined in membrane (10,000 x g) fractions by immunoblot analysis using specific polyclonal antibodies against synthetic fragments of hCG/LH receptor and against G proteins. Membrane fractions from rat brain and rat corpus luteum were used as controls. Proteins were loaded on the gel under reducing conditions.


RESULTS
The receptor antibody immunoreacted with a protein of approximately 68 kd in endometrial membranes. A similar protein was detected in rat corpus luteum. The G-protein antibodies detected Gs alpha, Gi3 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 kd, respectively. Analysis of membranes obtained during HRT indicated that levels of hCG/LH receptors remained fairly constant throughout the cycle days (days 0, 3, 6, and 9). Similar results were observed for Gi1 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-bound hCG/LH receptors and associated G proteins. During HRT, progesterone supplementation to estrogen therapy enhances the expression of Gs alpha protein subunit, but not hCG/LH receptors.
Bernardini
L
L
Department of Obstetrics and Gynecology, University of California, Irvine, Orange 92613-1491, USA.
Moretti-Rojas
I
I
Brush
M
M
Rojas
F J
FJ
Balmaceda
J P
JP
D000818:Animals; D001706:Biopsy; D002462:Cell Membrane / Q000378:metabolism; D003338:Corpus Luteum / Q000378:metabolism; D004717:Endometrium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004958:Estradiol / Q000627:therapeutic use*; D015914:Estrogen Replacement Therapy; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D018587:Oocyte Donation; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011974:Receptors, LH / Q000378:metabolism*
D011974:Receptors, LH; D011374:Progesterone; D004958:Estradiol; D019204:GTP-Binding Proteins