INCREASED NEGATIVITY OF INTERSTITIAL FLUID PRESSURE CONTRIBUTES TO DEVELOPMENT OF EDEMA IN RAT SKIN FOLLOWING APPLICATION OF XYLENE

Intradermal interstitial fluid pressure (P(i)) has been studied in rat skin during formation of inflammatory oedema caused by application of xylene. P(i) was measured with sharpened micropipettes connected to a servocontrolled counter-pressure system. Control P(i) averaged -1.3 ± 0.6 (SP) mmHg. Following xylene application P(i) decreased to -5.0 mmHg after 5 min and then increased to stabilize at about 0 mmHg at 45-60 min and later. When the transvascular fluid shifts accompanying the inflammatory reaction were prevented by inducing circulatory arrest prior to xylene application, P(i) fell to -7.5 mmHg within 5 min and remained at this level throughout the observation period of 90 min. Aprotinin in large doses (80,000 KIE kg-1) before xylene application reduced the fall in P(i), whereas indomethacin had no effect. The increased negativity in P(i) will add directly to a normal transcapillary net filtration pressure of about 0.5 mmHg, resulting in a 10- to 20-fold increase in this pressure. The present experiments therefore suggest that the interstitium plays an active role in oedema formation in the initial phase of xylene-induced inflammation in rat skin through the development of an increased negativity of P(i).