Interrelated calcium ion and cyclic AMP inhibition of placental lactogen secretion by cultured human term trophoblast

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Abstract
Calcium ion has been been shown to have a negative regulatory effect on the secretion of human placental lactogen (hPL). We report an inhibitory effect of cyclic AMP on hPL secretion in a model system of cultured human term trophoblast. Similar results were obtained by modulation of cyclic AMP-phosphodiesterase. The effects of ionophore A23187 and cyclic AMP were non-additive. In searching for the sequence of the common pathway, we found that the inophore A23817 reduced cyclic AMP concentration and that the inhibitory effect of cyclic AMP was abolished by verapamil, a calcium channel blocker and by trifluoperazine, a calcium-calmodulin inhibitor. Cyclic AMP seems to mobilize intracellular calcium, and the latter, by way of a calcium-calmodulin complex, modulates the secretion of hPL.

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