Evidence for the existence of a functional cardiac renin-angiotensin system in humans

Background The presence of mRNA for the essential components of the renin-angiotensin system (RAS) has been found in animal and human hearts. The present study was designed to provide evidence for the existence of a (functional) cardiac RAS. Methods and Results Twenty-four patients with atypical chest pain undergoing coronary angiography for diagnostic purposes were investigated. The cardiac production rate of angiotensins was estimated by measurement of the cardiac extraction of I-125-angiotensin I and I-125-angiotensin II associated with the determination of endogenous angiotensins in aortic and coronary sinus blood in normal, low, or high sodium diets. In a normal sodium diet, angiotensin I and II aorta-coronary sinus gradients were tendentially negative (-1.8+/-2.5 and -0.9+/-1.7 pg/mL, respectively), and the amounts of angiotensin I and II added by cardiac tissues were 6.5+/-3.1 and 2.7+/-1.3 pg/mL, respectively. The low sodium diet caused a significant increase in both plasma renin activity (PRA) and angiotensin I concentration in aortic but not in coronary sinus blood, resulting in a more negative aorta-coronary sinus gradient (-9.7+/-3.1 pg/mL, P<.01). Angiotensin formation by PRA in blood during transcardiac passage increased (P<.001), whereas angiotensin I formed by cardiac tissues de creased dramatically. Accordingly, in the low sodium diet, I-125-angiotensin II extraction did not change, the cardiac fractional conversion rate of I-125-angiotensin I to I-125-angiotensin II notably decreased (P<.01), and angiotensin II formation by cardiac tissues was undetectable. The high sodium diet caused a decrease in PRA and no changes in cardiac extraction of radiolabeled angiotensins; conversely, angiotensin I formed by cardiac tissues, cardiac Ang I fractional conversion rate, and angiotensin II formed during transcardiac passage significantly (P<.01 for all) increased. Conclusions These results provide evidence for the existence of a functional cardiac RAS independent of but related to the circulating RAS.