Effects of calcium and ouabain on the release of atrial natriuretic factor

In order to examine the role of calcium in the secretory process of atrial natriuretic factor (ANF), we studied the effects of hypercalcaemia and ouabain on the plasma concentration of immunoreactive ANF, and the effect of calcium on immunoreactive ANF release from isolated rat atria. Anaesthetized dogs were treated with CaCl2 infusion, ouabain or phenylephrine injection. With CaCl2 infusion, serum calcium and plasma immunoreactive ANF respectively increased to three and four times their basal levels. Ouabain increased plasma immunoreactive ANF to two and a half times the initial level. Neither CaCl2 nor ouabain produced any effect on right atrial pressure and heart rate, but they both significantly increased arterial pressure. Phenylephrine caused a greater increase in arterial pressure than both CaCl2 and ouabain. However, there was no significant increase in plasma immunoreactive ANF. Moreover, calcium stimulated the release of immunoreactive ANF from isolated rat atria. These results suggest that the calcium may play a key role in the secretory process of ANF.