AJP - Endocrinology and Metabolism, Vol 240, Issue 5 550-E555, Copyright © 1981 by American Physiological Society
Human placental lactogen release in vitro: paradoxical effects of calcium
S. Handwerger, P. M. Conn, J. Barrett, S. Barry and A. Golander
To study the effects of calcium on the release of human placental lactogen
(hPL), placental explants were exposed to media containing lower or higher
concentrations of calcium than normally available to the placenta. Explants
exposed for 2 h to calcium-poor medium or medium containing either 2 mM
EDTA or 2 mM EGTA released 160, 248, and 253% more hPL, respectively, than
control explants. In contrast, explants exposed to medium containing higher
than normal calcium concentrations released the same amounts of hPL as the
control explants. At lower than normal extracellular calcium
concentrations, the increased hPL release was inversely proportional to the
calcium concentration. The increased release in calcium-poor medium was
inhibited by subsequent exposure of the explants to medium containing
calcium and was prevented by either barium or magnesium. Changes in barium
or magnesium concentrations, however, had no effects on hPL release in the
presence of normal extracellular calcium concentrations. Methoxyverapamil
(D 600), an inhibitor of calcium flux, stimulated hPL release. Because low
extracellular calcium and methoxyverapamil both inhibit calcium influx,
these experiments suggest that calcium influx inhibits hPL release. The
role of calcium in the regulation of hPL release therefore appears to be
different from that reported in other release systems.
