What substance is released during inflammation that increases vascular permeability?

Histamine is a key substance released during inflammation that plays a significant role in increasing vascular permeability. When tissues are injured or inflamed, immune cells such as mast cells release histamine into the surrounding area. This release of histamine leads to the dilation of blood vessels and increased permeability of the vascular walls, allowing fluid, proteins, and immune cells to move more easily from the bloodstream into the affected tissues.

This process is crucial for the inflammatory response, as it helps deliver necessary immune components to sites of injury or infection, facilitating healing and defense against pathogens. The increased permeability can also lead to the classic signs of inflammation, including swelling and redness.

While leukocytes are involved in the inflammatory response, they do not directly cause increased vascular permeability. Plasmin is primarily involved in fibrinolysis, the breakdown of fibrin in blood clots, rather than in the acute inflammatory response. Kinins, though also mediators of inflammation, have a more complex role that includes causing pain and acting on the vascular system, but histamine is the primary substance responsible for the immediate increase in vascular permeability during the initial inflammatory response.