Effect of calcium depletion on the secretion of newly synthesised human chorionic gonadotropin by first trimester human placenta.

Depletion of calcium in the extracellular medium used to incubate first trimester human placental minces resulted in a significant decrease in the quantity of immunoreactive hCG in the medium and a corresponding increase in the tissue. In contrast, when secretion of newly synthesised hCG was monitored in the absence of calcium by using a radioactive amino acid precursor, a significant increase in the secretion of newly synthesised hCG in the medium was noticed. This was true of secretion of other proteins also as evidenced by the increase in the trichloroacetic acid precipitable radioactivity in the medium in the absence of calcium. These results suggest that newly synthesised hCG is preferentially released over stored hormone in the absence of calcium.