Ca2+, but not membrane lipid hydrolysis, mediates human chorionic gonadotropin production by luteinizing hormone-releasing hormone in human term placenta.
We postulated a role for lipid metabolism and Ca2+ in the LHRH-induced release of hCG by human placentas. Term placental cells in suspension prelabeled with [3H]myoinositol were stimulated without or with increasing concentrations of LHRH in the presence of 10 mM LiCl, and total inositol phosphate (IP) was measured by ion exchange chromatography; a nonsignificant 0.9 +/- 0.08-fold increase over the control value was observed. In contrast, placental cells stimulated with equimolar concentrations of angiotensin II (AII) induced a 4.6 +/- 0.9-fold increase in total IP (P less than 0.01), while rat pituitary cells showed 1.9 +/- 0.2- and a 2.4 +/- 0.07-fold increases in total IP production after stimulation with LHRH or AII, respectively (P less than 0.05). These increases were blocked by coincubation with specific LHRH and AII antagonists. When 1 x 10(6) placental cells were incubated with 45Ca2+ without and with increasing doses of LHRH for 0-75 s and then filtered under negative pressure, we observed significant incorporation of 45Ca2+. This influx was linear with incubation time, significantly more pronounced in cells exposed to LHRH than in control cells, and showed a dose-response curve to LHRH that reached maximal influx rates of 3.6 +/- 0.3 nM/min.1 x 10(6) cells with 10(-5) M LHRH. This response was completely blocked by coincubation with 10(-5) M LHRH antagonists; cobalt chloride and verapamil reduced it by 60% and 80%, respectively. Compared to placental cells stimulated with LHRH alone, those coincubated with LHRH and specific LHRH or Ca2+ antagonists released from 10-100% less hCG. We conclude that Ca2+ participates in the LHRH action in human placentas, but uncoupled to PI turnover.
Bélisle
S
S
Department of Obstetrics-Gynecology, Faculty of Medicine, University of Sherbrooke, Quebec, Canada.
Petit
A
A
Bellabarba
D
D
Escher
E
E
Lehoux
J G
JG
Gallo-Payet
N
N
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000096:biosynthesis*; D002852:Chromatography, Ion Exchange; D003035:Cobalt / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism* / Q000502:physiology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011263:Pregnancy Trimester, Third; D051381:Rats; D014700:Verapamil / Q000494:pharmacology
D006063:Chorionic Gonadotropin; D007295:Inositol Phosphates; D008563:Membrane Lipids; D000804:Angiotensin II; D007987:Gonadotropin-Releasing Hormone; D003035:Cobalt; D014700:Verapamil; D002118:Calcium