Stimulatory effects of extracellular calcium on chorionic gonadotrophin and placental lactogen release by human placental explants

The effects of sudden modifications of extracellular calcium ion concentration on human chorionic gonadotrophin (hCG) and human placental lactogen (hPL) release were investigated using term placental explants incubated in Krebs Ringer solution. The hCG and hPL releases were both stimulated when the extracellular Ca2+ concentration was increased. The hCG and hPL secretions elicited by the addition of extracellular Ca2+ were larger when placental explants were preincubated in alpha-calcium (no added calcium + EGTA) than in normo-calcium (1.5 mM). Removal of extracellular Ca2+ from the medium also elicited an increase in hCG and hPL release. However, this stimulatory effect of Ca2+ omission was partly suppressed by washing the explants prior to incubation in the alpha-calcium medium, and was completely abolished when alpha-calcium medium was supplemented with 1 mM cobalt. Our results indicate that changes in Ca2+ modify hCG and hPL release from term placental explants in a manner concordant with the 'stimulus-secretion coupling' concept.