Plasma and cardiac tissue atrial and brain natriuretic peptides in experimental heart failure

Objectives. This study evaluated the role of changes in heart rate, cardiac filling pressures and cardiac tissue atrial and brain natriuretic peptides in the modulation of their plasma levels in a model of heart failure. Background. Atrial and brain natriuretic peptides constitute a dual natriuretic peptide system that regulates circulator homeostasis. Methods. The effects of 1) acute ventricular pacing, 2) acute volume expansion, and 3) volume expansion after 1 week of continuous pacing on plasma atrial and brain natriuretic peptide levels were compared in eight dogs. Atrial and ventricular tissue levels of the peptides were examined in 5 normal dogs (control group), 21 dogs paced for 1 week (group 1) and 10 dogs paced for 3 weeks (group 2). Results. Both acute pacing and volume expansion increased plasma atrial natriuretic peptide levels (from 53 ± 41 to 263 ± 143 pg/ml [mean ± SD], p < 0.01, and from 38 ± 23 to 405 ± 221 pg/ml, p < 0.001, respectively). After 1 week, there was a marked incerase in plasma levels of atrial natriuretic peptide, but the level did not increase further with volume expansion (from 535 ± 144 to 448 ± 140 pg/ml, p = 0.72). By contrast, plasma brain natriuretic peptide levels increased only modestly with acute pacing (from 12 ± 5 to 20 ± 4 to 20 ± 8 pg/ml, p < 0.05) and after pacing for 1 week (from 13 ± 4 to 48 ± 20 pg/ml, p < 0.05) but did not change with acute or repeat volume expansion. In groups 1 and 2, atrial tissue levels of atrial natriuretic peptide (1.9 ± 1.3 and 2.0 ± 0.9 ng/mg, respectively) were lower than those in the control group (11.e7 ± 6.8 ng/mg, both p < 0.001), whereas ventricular levels were similar to those in the control group. Atrial tissue brain natriuretic peptide levels in groups 1 and 2 were similar to those in the control group. However, ventricular levels in group 2 (0.018 ± 0.006 ng/mg) were increased compared with those in the control group (0.013 ± 0.006 ng/mg, p < 0.05) and in group 1 (0.011 ± 0.006 ng/mg, p < 0.05). Conclusions. Atrial and brain natriuretic peptides respond differently to changes in heart rate and atrial pressures. Reduced atrial tissue atrial natriuretic peptide levels in heart failure may indicate reduced storage after enhanced cardiac release, However, the relatively modest change in the cardiac tissue brain natriuretic peptide levels suggests that the elevated plasma levels may be mediated by mechanisms other than increased atrial pressured.