Anoxia-reoxygenation, tumor necrosis factor-alpha (TNF-alpha), and angiotensin II (ANG II) have been shown to induce apoptosis in myocytes. However, the role of these mediators in causing apoptosis of human coronary artery endothelial cells (HCAEC) is not known. This study was designed to examine the interaction of these mediators in induction of apoptosis in HCAEC. Cultured HCAEC were exposed to anoxia-reoxygenation, TNF-alpha, and ANG II. TNF-alpha enhanced apoptosis of HCAEC (determined by DNA nick-end labeling in situ and DNA laddering) caused by anoxia-reoxygenation. ANG II increased apoptosis beyond that caused by anoxia-reoxygenation and TNF-alpha. Apoptosis caused by ANG II was reduced by losartan, a specific ANG II type 1 receptor (AT1R) blocker, whereas PD-123,177, a specific ANG II type 2 receptor blocker, under identical conditions had minimal effect. The proapoptotic effects of ANG II were associated with the activation of protein kinase C (PKC). The importance of PKC activation as a signal transduction mechanism became evident in experiments wherein treatment of HCAEC with a specific inhibitor of PKC activation decreased ANG II-mediated apoptosis. Thus AT1R activation appears to be responsible for apoptosis caused by ANG II in HCAEC, and AT1R activation-mediated apoptosis involves activation of PKC.