The structure and reactions of the microcirculation in a subcutaneous air pouch in the rat

Studies by a combination of vascular perfusion, histological and electron microscopic techniques show that subcutaneous injection of air into rats excites no acute inflammatory response, but leads to the formation of a pouch lined by avascular fibrous tissue. Existing subcutaneous blood vessels are displaced by the pouch but no new blood vessels are formed. By contrast injection of carrageenan with the air or into a preformed air pouch leads to a severe inflammatory reaction and the rapid development of a thick layer of granulation tissue. Either type of pouch is a useful system in which to study inflammation. However because the distribution and ultrastructure of small blood vessels in the pouch wall is quite different from the known characteristics of the microcirculation of synovial membrane, the air pouch is an unsuitable model for the study of injury to joints or experimental arthritis.