Influence of osmolality and ionic environment on the secretion of prolactin by human decidua in vitro

The effects of extracellular osmolality and ions on the secretion of prolactin were examined in human decidual explants incubated for 4 h in modified Krebs-Ringer buffer. Explants incubated in media made hypersomotic (280-336 mosM/kg) with sodium, lithium or mannitol or in media made hypo-osmotic (280-224 mosM/kg) by decreasing the sodium concentration secreted the same amount of prolactin as explants incubated in control medium (280 mosM/kg). Explants incubated in calcium-deficient medium secreted 64 +/- 8% (P less than or equal to 0.001) less prolactin than controls (1.65 mmol Ca2+/1). Secretion was restored to control values by the addition of calcium (0.33 mmol/l) or barium (0.5, 1.0 or 2.0 mmol/l) to the medium. Prolactin secretion was unaffected by higher than control extracellular calcium concentrations, calcium ionophore A23187 (10-6, 10-9 mol/l) or lanthanum (0.5, 1.0 or 2.0 mmol/1). Changes in extracellular magnesium (0-20 mmol/l), potassium (0-55 mmol/l) or bicarbonate (0-32 mmol/l) had no effect on prolactin secretion. These results indicate that marked changes in extracellular osmolality and concentrations of sodium, magnesium and bicarbonate have no effects on decidual prolactin secretion. Calcium, however, is essential for the basal secretion of decidual prolactin.