Weibel-Palade bodies--sentinels of acute stress.

Weibel-Palade bodies are uniquely present in endothelial cells and harbor a range of bioactive substances that participate in hemostasis, vasomotion, inflammation and fibrinolysis, in addition to modulating vascular permeability, angiogenic sprouting, and stem cell mobilization. This Perspectives article examines the latest insights into the biogenesis of these organelles and the cellular and molecular mechanisms of their exocytosis. In addition, we advance two hypotheses on the pathogenic role of these organelles: first, in the development of endothelial dysfunction associated with the reduction of nitric oxide bioavailability and accumulation of peroxynitrite and second, as a first-line response to acute stress that determines the balance between regenerative and proinflammatory signals.