Physiological factors of atrial natriuretic polypeptide release and its neural regulation in conscious dogs

We have examined physiological factors in atrial natriuretic polypeptide (ANP) release and whether or not the cardiac nerves control release of ANP. Two possible factors were tested, an increase in plasma sodium level (PNa) and an increase in atrial pressure. Injection of 1.0 or 2.0 mEq/kg of sodium ions elevated PNa by 5.3 +/- 0.3 or 7.3 +/- 0.4 mEq/L, respectively, but plasma ANP level (PANP) did not change. Infusion of 18 ml/kg of 3% Dextran-40 over 5 min increased mean left atrial pressure (MLAP) by 7.6 +/- 0.9 mmHg. PANP increased from 206 +/- 17 pg/ml to 260 +/- 25 pg/ml, which was not significant. PANP, corrected for hemodilution, significantly increased to 348 +/- 34 pg/ml. These results suggest that PNa increase does not promote ANP release, but that an atrial pressure increase does. This transient volume load did not induce full response of the ANP releasing system. A prolonged volume load for 45 min increased corrected PANP to 435 +/- 73 pg/ml. A close linear correlation was found between the increases in MLAP and PANP. These facts indicate that prolonged volume expansion is necessary to induce full response of the ANP releasing system. Complete cardiac denervation did not affect the tonic level of plasma ANP, volume expansion-induced increase in PANP, or the sensitivity of the ANP releasing system. Thus we conclude that the cardiac nerves do not control ANP release caused by volume expansion.