The release of human chorionic gonadotrophin and placental lactogen by placental explants can be stimulated by Ca2+ entry through a Na(+)-Ca2+ exchange process.
Isosmotical replacement of extracellular Na+ ([Na+]o) by K+, choline and to a lesser extent by saccharose stimulated the release of chorionic gonadotrophin and placental lactogen from human term placental explants. The effect of [Na+]o removal on the release of both hormones was concentration-dependent and was inhibited in the absence of extracellular Ca2+ or in the presence of 0.5 mM Co2+, a Ca2+ entry blocker. Blockers of the voltage-sensitive Ca2+ channels (20 microM nifedipine and 50 microM methoxyverapamil) or Na+ channels (5 microM tetrodotoxin) did not affect the stimulatory effects of [Na+]o omission. By contrast, Mg2+ and Sr2+ (10 mM) as well as amiloride (2 mM) and its analogue 2',4'-dimethylbenzamil (50 microns), all known to affect the Na(+)-Ca2+ exchange, markedly reduced the increase in hormone release elicited by [Na+]o removal. Lastly, the secretory responses to [Na+]o deprivation were increased in the presence of 2 mM ouabain, an inhibitor of the Na(+)-K+ ATPase. These results indicate for the first time that [Na+]o omission provokes a Ca(2+)-dependent stimulation of human chorionic gonadotrophin and placental lactogen releases. The pharmacological dissection of the secretory effects of [Na+]o removal supports the existence of a process of Na(+)-Ca2+ exchange in placental cells.
Polliotti
B
B
Research Laboratory on Reproduction, Faculty of Medicine (CP626), Free University of Brussels (ULB), Belgium.
Lebrun
P
P
Robyn
C
C
Meuris
S
S
D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism; D006063:Chorionic Gonadotropin / Q000187:drug effects / Q000378:metabolism*; D046508:Culture Techniques; D005260:Female; D006801:Humans; D010920:Placenta / Q000187:drug effects / Q000378:metabolism*; D010928:Placental Lactogen / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D006063:Chorionic Gonadotropin; D015222:Sodium Channels; D010928:Placental Lactogen; D012964:Sodium; D002118:Calcium