What is the difference between endothelial contraction and endothelial retraction in inflammation?

Endothelial contraction is when the endothelium is pressed together, such as when you have a small cut. The point of endothelial contraction is to prevent blood loss as much as possible. Endothelial contraction also increases vascular permeability (you want the blood vessels to be more permeable so that important fighters during the inflammatory response such as leukocytes, cytokines, T helper cells, etc. can reach the site of injury faster). Histamine is one of the substances that activates endothelial contraction.

Endothelial retraction on the other hand, is essentially the opposite of endothelial contraction. The blodo vessels relax, rather than contract. This happens later, once the injury is under control.