Real time PCR evaluation for c-type natriuretic peptide and for its specific receptor, NPR-B in cardiac tissue of normal and chronic heart failure animals

Background. C-type natriuretic peptide (CNP) was recently found in the myocardium, but possible differences between atrium and ventricle production are so far lacking. Aim. To evaluate the expression of transcripts coding for CNP and for its specific receptor, NPR-B, in cardiac tissue (right and left atrium and ventricle) of normal and HF animals. Methods. Cardiac tissue was collected from male adult minipigs without (control, n=5) and with pacing-induced HF (n=5). HF was induced by rapid pacing (180 beats/ min) for 3 weeks. mRNA was extracted with the method of phenol/guanidine-thiocyanate/chloroform. The expression of mRNA coding for CNP and NPR-B was determined in myocardial tissue (n=40) by Real Time-PCR with DDCt method. As overall control, a parallel Real Time-PCR assay for BNP mRNA expression was carried out in the same samples. Results. CNP gene expression was observed in controls and at 3 weeks of pacing resulting lower than that of BNP (left ventricle: p=0.05 controls vs. HF). As expected, BNP gene expression in all the cardiac chambers resulted higher after 3 weeks of pacing compared to normal heart (right atrium and left ventricle: p=0.003 controls vs. HF). Moreover, BNP mRNA expression was higher in atrium than in ventricle. We also observed higher, but not significantly, levels of CNP mRNA expression between normal and HF animals in all chambers. The NPR-B resulted to be expressed in all cardiac regions analyzed, and a down- regulation was observed in ventricles after HF (right ventricle p=0.001 controls vs. HF). Conclusions. In the present study, we provided the first evidence of CNP and NPR-B expression in tissue from normal and HF. The increased myocardial CNP synthesis was associated to the NPR-B down regulation in HF. The co-localization of the CNP system and its specific receptor suggests a possible role of this peptide in a complex pathology such as HF and the present results may prompt novel therapeutical strategies targeting NPR-B