In acute inflammation, contraction of endothelial cells results in the following:

Endothelial cell contraction leading to intercellular gaps in postcapillary venules is the most common cause of increased vascular permeability. Endothelial cell contraction occurs rapidly after binding of histamine, bradykinin, leukotrienes, and many other mediators to specific receptors, and is usually sho lived (15-30 min). Ref: Robbins Basic Pathology edited by Vinay Kumar, Abul K. Abbas, Jon C. Aster, 2012, Page 34.