BackgroundA cardiac angiotensin II-generating system has been suspected to be involved in various cardiac pathological conditions. Both angiotensin converting enzyme and human chymase can convert angiotensin I to angiotensin II.ObjectiveTo clarify the relative contributions of these two enzymatic pathways to angiotensin II generationin vivo.MethodsWe assessed the expression levels of messenger RNA (mRNA) for collagen type Iα, transforming growth factor-β1, brain natriuretic peptide, angiotensin converting enzyme and chymase in right atrial appendages by competitive polymerase chain reaction and Northern blot analyses. Correlations among the concentrations of these mRNA were analysed to obtain insight that might be important in understanding the formation of angiotensin II in atrial tissue.ResultsThe collagen type Ia and brain natriuretic peptide mRNA concentrations were correlated significantly to the mean pulmonary arterial pressure. Multivariate regression analysis revealed that the collagen type Iα mRNA concentration could be explained in terms of the brain natriuretic peptide (P= 0.0005) and angiotensin converting enzyme (P= 0.0084) mRNA concentrations (r = 0.598,P<0.0001). The chymase mRNA concentration had no significant correlation to the collagen type Ia mRNA concentration. Moreover, multiple regression analysis revealed that the transforming growth factor-β1mRNA concentration could be explained in terms of the angiotensin converting enzyme mRNA concentration alone (r = 0.424,P= 0.014).ConclusionsThe present results suggest that the level of angiotensin converting enzyme affects the tissue angiotensin II level in human atria; however, we could obtain no evidence that chymase is important in determining the tissue angiotensin II level.