The Effects of the Natriuretic Peptide System on Alveolar Epithelium in Heart Failure.

Alveolar active sodium transport is essential for clearing edema from airspaces, in a process known as alveolar fluid clearance (AFC). Although it has been reported that atrial natriuretic peptide (ANP) attenuates AFC, little is known about the underlying molecular effects of natriuretic peptides (NPs). Therefore, we examined the contribution of NPs to AFC and their effects as mediators of active sodium transport. By using the isolated liquid-filled lungs model, we investigated the effects of NPs on AFC. The expression of NPs, Na(+), K(+)-ATPase, and Na(+) channels was assessed in alveolar epithelial cells. Congestive heart failure (CHF) was induced by using the aortocaval fistula model. ANP and brain NP (BNP) significantly reduced AFC rate from 0.49 ± 0.02 mL/h in sham rats to 0.26 ± 0.013 and 0.19 ± 0.005 in ANP and BNP-treated groups, respectively. These effects were mediated by downregulating the active Na(+) transport components in the alveolar epithelium while enhancing the ubiquitination and degradation of αENaC in the lungs, as reflected by increased levels of Nedd4-2. In addition, AFC was reduced in compensated CHF rats treated with ANP, while in decompensated CHF, ANP partially restored AFC. In conclusion, NPs regulate AFC in health and CHF. This research could help optimize pharmacological treatments for severe CHF.