Role of atrial appendages in modulating stimulated plasma atrial natriuretic peptide levels in conscious rats

To evaluate the role of the atrial appendages in modulating plasma levels of atrial natriuretic peptide (ANP), we applied a series of both acute and chronic stimuli in conscious, chronic, bilaterally atrial-appendectomized (APP) and sham-operated control rats. Basal plasma ANP levels and urinary sodium excretion were normal in all rats after APP. The release of ANP was markedly blunted to acute volume expansion (+67% vs. +357% in controls, P < 0.01) but was only moderately reduced after norepinephrine infusion (+106% vs. +212%, P < 0.05) and was normal after acute salt load [+148% vs. +180% in controls, not significant (NS)]. Furthermore, plasma levels of ANP were increased normally in APP rats treated with deoxycorticosterone acetate (270 + 18 vs. 296 + 14 pg/ml in controls, NS) and in APP rats with congestive heart failure induced by a large arteriovenous (a-v) fistula between the aorta and the vena cava (306 ± 18 vs. 302 ± 12 pg/ml, NS). Sodium excretion patterns were similar in chronically stimulated APP and control rats. The results demonstrate that, although APP reduces the response of ANP release to acute volume expansion, it does not do so to other stimuli of either acute or chronic nature, suggesting that there is no permanent defect in the ability of APP rats to secrete ANP. These studies confirm that the atria are the major source for ANP release into the circulation after acute intravascular volume expansion. However, other tissue sources may contribute significantly to the levels of circulating ANP in response to this and other acute and chronic stimuli.