Natriuretic peptides maintain sodium homoeostasis during chronic volume loading post-myocardial infarction in sheep

The impaired ability to excrete sodium is a key feature of established congestive heart failure and is also apparent in asymptomatic left ventricular (LV) impairment. However, few studies have examined responses to chronic volume loading immediately post-myocardial infarction (MI). Experimental MI was induced in six sheep by thrombogenic coil coronary artery occlusion, and resulted in significant LV dysfunction with reduced LV ejection fraction ( P =0.001) and subsequent remodelling (increased LV volumes, P =0.015). Chronic volume loading with 2, 3 and 4 litres/day intravenous saline (each for 7 days) showed no evidence of renal sodium or volume retention in sheep with experimental MI compared with six normal control sheep. Plasma levels of brain natriuretic peptide (BNP), N-terminal pro-BNP and cGMP (all P <0.05) were higher in the MI group compared with normal control sheep. There were no differences in haemodynamics, body mass or renin-aldosterone levels between groups. This study provides evidence that natriuretic peptides play a pivotal role in preserving volume/electrolyte balance in the early stages of post-MI cardiac dysfunction.