INCREASED NEGATIVITY OF INTERSTITIAL FLUID PRESSURE IN RAT TRACHEA AFTER MAST-CELL DEGRANULATION

The present study was performed to investigate whether the increased n egativity of interstitial fluid pressure (P(if)) observed after intrav enous injection of dextran could be mediated via mast cell degranulati on induced by C48/80 and polymyxin B sulfate. Increased negativity of P(if), concomitant with edema formation and increased albumin extravas ation, was seen with both substances. However, the two substances diff ered in that polymyxin B sulfate induced less negativity in P(if) and a larger but transient increase in capillary albumin extravasation and interstitial fluid volume. Total tissue water (TTW) increased from 2. 11 to 2.71 ml/g dry wt 10 min after polymyxin B and returned to contro l level at 30 and 60 min. Injection of C48/80 increased TTW to 2.68 ml /g dry wt at 30 min, and TTW was still elevated at 60 min. Albumin ext ravasation followed a similar pattern; polymyxin B sulfate increased a lbumin extravasation from <0.08 to 1.18 ml/g dry wt during the first 5 min after administration. C48/80 was less potent, and maximal albumin leakage was seen after 10-25 min (0.25 ml/g dry wt). The observations demonstrate the importance of the interstitium and the loose connecti ve tissues as ''active'' participants in the edema-generating process and suggest an interaction with the structural components of the inter stitium, as well as an important role for the mast cells in the chain of events creating increased negativity of P(if).