Comparison of the effects of GnRH-I and GnRH-II on HCG synthesis and secretion by first trimester trophoblast.
Gonadotrophin-releasing hormone (GnRH) is an important factor in the regulation of the synthesis and secretion of gonadotrophins from the pituitary gland. An isoform of this decapeptide, GnRH-II, with an amino acid sequence 70% homologous to GnRH-I, has been recently described. Since the physiological effects of GnRH-II are not yet known, we undertook the present study to see whether GnRH-II could be involved in the secretion and synthesis of HCG in first trimester trophoblast. We incubated cytotrophoblastic cells (CTB) with GnRH-I or GnRH-II, for 4 or 96 h and collected the media at different times thereafter. We also performed experiments with placental tissue, where GnRH-I or GnRH-II was added to perifused placental explants, and samples were collected every 3 min. Total amounts of human chorionic gonadotrophin (HCG) were measured in all samples by enzyme-linked immunosorbent assay. GnRH-I was more potent than GnRH-II when incubated for 4 h with CTB, as indicated by increased HCG secretion at 8 h and at 24 h. GnRH-I, but not GnRH-II, down-regulated HCG secretion when incubated for 96 h. GnRH-I significantly increased HCG secretion by the explants, while GnRH-II had a lesser effect. Both induced a pulse of HCG immediately after their injection. Our data show that GnRH-I has more effect than GnRH-II on HCG synthesis and secretion. This difference could be explained by different pathways of GnRH degradation, different receptor affinities, or even by different types of placental GnRH receptor.
Islami
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Department of Obstetrics and Gynaecology, Clinic of Infertility and Gynaecological Endocrinology, WHO Collaborating Centre in Human Reproduction, University Hospital of Geneva, 32 Boulevard de la Cluse, 1211 Geneva, Switzerland. dorina.islami@hcuge.ch
Chardonnens
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D
Campana
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A
Bischof
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P
D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000096:biosynthesis* / Q000378:metabolism*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D006801:Humans; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D020033:Protein Isoforms; D014327:Trophoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D006063:Chorionic Gonadotropin; D020033:Protein Isoforms; D007987:Gonadotropin-Releasing Hormone