Effect of rapid sodium load on circulating atrial natriuretic polypeptide

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Abstract
The hypothesis that an increase in plasma sodium concentration (PNa) causes an increase in circulating atrial natriuretic polypeptide (ANP) was examined in conscious dogs. NaCl solution in small volume (0.3 ml/kg body wt) and at high concentration (20%) was injected intravenously within 2 s to rapidly increase PNa. PNa rapidly increased to 5.1 .+-. 0.3 meq/l. Urinary excretion of sodium and water increased to 4.1 and 2.5 times the control levels, respectively. Plasma vasopressin level increased to 3.7 times the control level. Plasma ANP level (PANP) did not change significantly. PANP corrected for sodium-induced hemodilution did not change either. On a different day, a double amount of sodium (0.6 ml/kg body wt of 20% NaCl solution) was intravenously injected into the dogs. PNa increased by 7.3 .+-. 0.4 meq/l, which was significantly more than the increase after the 0.3 ml/kg injection. PANP with or without correction for hemodilution again did not change. These results indicate that a rapid increase in PNa within the physiological range does not cause elevation of circulating ANP. This suggests that ANP does not contribute to the regulation of plasma sodium concentration.