Increased negativity of interstitial fluid pressure in rat trachea after mast cell degranulation.

The present study was performed to investigate whether the increased negativity of interstitial fluid pressure (Pif) observed after intravenous injection of dextran could be mediated via mast cell degranulation induced by C48/80 and polymyxin B sulfate. Increased negativity of Pif, concomitant with edema formation and increased albumin extravasation, was seen with both substances. However, the two substances differed in that polymyxin B sulfate induced less negativity in Pif 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 control 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 extravasation followed a similar pattern; polymyxin B sulfate increased albumin 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 connective tissues as "active" participants in the edema-generating process and suggest an interaction with the structural components of the interstitium, as well as an important role for the mast cells in the chain of events creating increased negativity of Pif.