Received for publication August 23, 2004.
Revised January 6, 2005.
Accepted for publication January 6, 2005.

Bradykinin Down-regulates Whereas Arginine Analogs Up-regulate eNOS Expression in Coronary Endothelial Cells

Abstract

Bradykinin (BK) is an endogenous vasoactive peptide that promotes vasodilation by stimulating the release of nitric oxide (NO) from endothelial cells via activation of endothelial NO synthase (eNOS). While the role of BK in modulation of eNOS activity is well understood, its possible effect on eNOS expression remains uncertain. Several studies have demonstrated negative feedback regulation of eNOS by NO. Therefore, we hypothesized that sustained stimulation with BK may down-regulate eNOS expression in endothelial cells. Human coronary endothelial cells were incubated for 24 hours with either BK alone or BK plus BK receptor type 1 or type 2 blockers. NO production and eNOS abundance (Western analysis) were determined. In separate experiments, cells were incubated with either an NOS inhibitor alone or in combination with BK. Incubation with BK caused a concentration-dependent rise in NO production and a dose-dependent decline in eNOS protein expression. These effects were abrogated by BK-2 blockade but were unaffected by BK-1 blockade. In contrast, NOS inhibitors lowered NO production and raised eNOS abundance in a dose-dependent fashion. The effects of BK on NO production and eNOS expression were abrogated by the NOS inhibitor. Thus, sustained activation of eNOS by BK results in a compensatory down-regulation of eNOS, whereas, its sustained inhibition leads to a compensatory up-regulation of eNOS. The observed modulations of eNOS expression are mediated by NO and represent an adaptive physiologic response.

Key words: ACE-inhibitors, NOS inhibitors, bradykinin, coronary arteries, endothelial cells, nitric oxide

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