How is increased vascular permeability occurring in endothelial cells?

Retraction of endothelial cells (opening interendothelial spaces, elicited by histamine, bradykinin, leukotrienes, other chemicals. Occurs after exposure to mediator short lived, immediate transient response. Occurs at post-capillary venules Endothelial injury also increases vascular permeability due to necrosis and detachment, so direct damage to endothelium is encountered in severe injuries, neutrophils adhere to injured endothelia and amplify this reaction. Starts just with the injury and stays hours until damaged vessels are thrombosed or repaired