Effects of hypercalcemia and ouabain on plasma atrial natriuretic polypeptide in anesthetized dogs

For the purpose of examining the role of calcium ion in the secretory process of atrial natriuretic polypeptide (ANP), we studied the effects of hypercalcemia and ouabain on plasma concentration of immunoreactive ANP (irANP). Pentobarbital sodium-anesthetized dogs were treated with calcium chloride infusion (0.136 mmol.kg-1.min-1, 10 min) or ouabain injection (30 micrograms/kg), and plasma irANP concentration, right atrial pressure, mean arterial pressure, heart rate, and serum calcium concentration were measured. To evaluate the effect of rising arterial pressure, plasma irANP concentration was also measured in dogs treated with phenylephrine hydrochloride (10 micrograms/kg). With calcium chloride infusion, serum calcium concentration and plasma irANP concentration, respectively, increased to about three times and about four times their basal levels. This increase of plasma irANP concentration was not attenuated by pretreatment with adrenoceptor blockers. Ouabain increased plasma irANP concentration to approximately 2.5 times the initial level. Neither calcium chloride nor ouabain produced any effect on right atrial pressure and heart rate, but both significantly increased mean atrial pressure. Phenylephrine caused a greater increase in mean arterial pressure than both calcium chloride and ouabain. However, there was no significant increase in plasma irANP concentration. These results suggest that the calcium ion may play a key role in the secretory process of ANP.