EFFECT OF IONIC ENVIRONMENT ON THE RELEASE OF HUMAN PLACENTAL LACTOGEN IN VITRO

Abstract

SUMMARY: Short-term incubation of human placental tissue in Krebs–Ringer bicarbonate buffered media with various concentrations of K⁺ and Ca²⁺ showed a graded response in human placental lactogen (HPL) release at different Ca²⁺ concentrations, but no effect at increased K⁺ concentration. Media with high Ca²⁺ caused an inhibition of release, while Ca²⁺-free media caused a stimulation in HPL release. High concentrations of Mg²⁺ inhibited release minimally, while Ba²⁺ had no effect. There was no change in HPL release when Na⁺ concentration was increased. La³⁺-Locke's solution markedly inhibited release of HPL but the significance of this effect is unknown. These results suggest that Ca²⁺ is not required for HPL secretion from placental tissue. It seems that HPL secretion in vitro does not follow the usual pattern where a physiological stimulus or high K⁺ concentration causes inward movement of calcium which couples stimulation to secretion.