The role of C-type natriuretic peptide in the heart: study in an experimental model of pacing-induced heart failure.

Purpose: C-type natriuretic peptide (CNP), a member of the family of natriuretic peptides, was recently found to be produced in the myocardium, but its cellular source and possible difference between atrium and ventricle production are so far lacking. Aim: to evaluate, in an experimental model of pacing-induced heart failure (HF), plasmatic levels of CNP and mRNA and protein expressions. Methods: Adult male minipigs (n=5) were chronically instrumented with a unipolar pacemaker connected to the anterior left ventricular (LV) wall. HF was induced by rapid pacing (180 beats/min) for 4 weeks. End-stage HF occurred at 24±2 days of pacing when the LV end-diastolic pressure was >=25 mmHg. As control, we studied 5 adult male minipigs. Blood samples were collected (aprotinin and EDTA) at rest (control) and at 10 min, 1, 2, 3 and 4 weeks of pacing stress. At 4 weeks, myocardial samples were collected. Both CNP mRNA and proteins were extracted from a same sample of different cardiac chambers with the method of phenol/guanidine-thiocyanate/chloroform. CNP levels in plasma and in cardiac extracts were determined by a radioimmunoassay after a preliminary extraction on Sep-Pak C18, while the expression of mRNA coding for CNP in myocardial tissue by RT-PCR. As overall control, a parallel RT-PCR assay for BNP mRNA expression was carried out in the same samples. Results: Compared to control, plasmatic CNP levels were increased after 1 week of pacing stress (36.9±10.4 pg/ml vs.16.7±1.1, p=0.013, mean±sem). As to myocardial extract, at rest CNP was found in all cardiac chambers and its content was ten fold higher in atria than in ventricles (RA: 13.7±1.9 pg/mg; LA: 8.7±3.8 pg/mg; RV: 1.07±0.33 pg/mg; LV: 0.93±0.17 pg/mg). At 4 weeks of pacing stress, myocardial levels of CNP in left ventricle were higher than in controls (15.8±9.9 pg/mg vs.0.9±0.17 pg/mg, p=0.01). The expression of mRNA coding for CNP was observed at 4 weeks of pacing althought CNP gene expression appears to be noticeable lower than that of BNP. Conclusions: Althought further investigations are necessary, the high plasmatic levels of CNP found after pacing stress as well as the myocardial CNP expression suggest an important role of this peptide in HF pathophysiology.