Direct formation of angiotensin II without renin or converting enzyme in the ischemic dog heart.

An in vivo study was done to determine whether angiotensin II is directly formed by kallikrein or kallikrein-like proteases. Dogs were bilaterally nephrectomized 24 hours before ligation of the coronary artery. This acute coronary artery occlusion led to a regionally increased acidic state in the ischemic tissue and resulted in an elevation of immunoreactive angiotensin II (IR-Angiotensin II) levels in the coronary sinus blood, but not in systemic aortic blood. Elevation of the IR-Angiotensin II level was specifically inhibited by aprotinin, a kallikrein inhibitor. It was not affected by either captopril, a potent angiotensin converting enzyme inhibitor, or by pepstatin, a renin inhibitor. The concentrations of immunoreactive angiotensin I (IR-Angiotensin I), plasma renin activity and angiotensin converting enzyme activity remained unaltered in the presence of coronary artery occlusion. These results suggest that IR-Angiotensin II in the ischemic heart may be generated directly by kallikrein or kallikrein-like proteases, independently of the systemic renin angiotensin system.