Extracted and nonextracted atrial natriuretic peptide in rabbits during tachycardia

The time course of changes in the plasma concentration of immunoreactive atrial natriuretic peptide (iANP) accompanying tachycardia was measured in anesthetized rabbits. In contrast to the hemodynamic changes, which occurred within the 1st min of tachycardia, the plasma iANP increased gradually and did not reach significantly elevated levels until 10 min into the stimulation period. After 20 min of tachycardia iANP was almost 200 pg/ml. Immunoreactive ANP was measured prior to and following extraction. Although the basal levels of iANP were higher in the unextracted than in extracted plasma (62 vs. 22 pg/ml), the time course of changes in iANP was identical in both. The gradual increase in iANP suggests that the release of iANP in this model may not simply be a consequence of the increase in atrial pressure.