NATRIURETIC PEPTIDE RESPONSES TO ACUTE AND CHRONIC VENTRICULAR PACINGIN SHEEP

The responses of atrial natriuretic peptide (ANP) and brain natriureti c peptide (BNP) were investigated in six conscious sheep paced at 120, 155, 190, and 225 beats/min for 1.5 h at each rate and at 180, 225, a nd 180 beats/min for 4 days at each rate. Increased pacing reduced art erial pressure, cardiac output, and urine and Na excretion and increas ed left atrial pressure and plasma ANP, BNP, and C-type natriuretic pe ptide, with delayed activation of the renin-angiotensin system (RAS). Acute pacing increased plasma ANP and BNP levels 8.6- and 3.6-fold, re spectively (both P < 0.001), whereas chronic pacing increased ANP and BNP 7.8- and g-fold, respectively (both P < 0.001). Thus the ANP-to-BN P ratio increased during acute pacing (P < 0.001) and decreased propor tionately during chronic pacing (P < 0.05). Reduction in pacing improv ed hemodynamic status, reduced natriuretic peptides (BNP less than ANP ), normalized the RAS, and induced diuresis and natriuresis. In conclu sion, BNP is less responsive than ANP to acute changes in intracardiac pressure but is proportionately more responsive to chronic hemodynami c changes such as occur in congestive heart failure.