Influence of mast cells on leukocyte-independent plasma extravasation during endotoxemia

Introduction

Endotoxemia is characterized by increased microvascular permeability. Endothelial factors and mast cell activation seems to promote microvascular permeability independently from leukocyte adherence [1]. The aim of our study was to investigate the influence of mast cells on leukocyte-independent microvascular permeability changes. Therefore, microvascular permeability was determined during endotoxemia after inhibition of the L-selectin mediated leukocyte-endothelium interaction by fucoidin. Mast cells were either degranulated with compound 48/80 (CMP48/80) prior to the experiment or pre-treated with the mast cell stabilizing agent cromolyn.

Methods

In male Wistar rats, microvascular permeability (MP), leukocyte adherence (LA) and mast cell activation (MCA) were determined in mesenteric postcapillary venules using intravital microscopy at baseline, and at 60, and 120 min after start of a continuous infusion of endotoxin (groups A-C, n = 8 each). Animals underwent laparotomy and the mesentery was exposed beneath an in vivo videomicroscope. MCA was determined in vivo by superfusion of the mesentery with ruthenium red. MP was measured using fluorescein isothiocyanate (FITC) labeled albumin. Leukocyte-endothelial interaction was blocked by fucoidin 10 min before laparotomy in groups A, B, and C. Animals in group B additionally received CMP48/80 (1 mg/kg b.w. i.p.) 48 h before the start of the experiment. Animals in group received cromolyn (20 mg/kg b.w. i.v.) prior to baseline measurement followed by a continuous superfusion of the mesentery with cromolyn. Group D (control, n = 8) only received equivalent volumes of NaCl 0.9%. Statistical analysis was performed using student's t-test. A P value < 0.05 was considered significant.

Results

In the endotoxin and fucoidin treated groups (A-C), LA was attenuated to levels similar to control group (D). Endotoxin-induced MCA was prevented in both the CMP48/80- and the cromolyn-treated animals (groups B + C) (P < 0.05 vs group A). However, in the CMP48/80- and the cromolyn-treated groups the endotoxin-induced increase in microvascular permeability tended to be reduced too, but without being significant (P > 0.05 vs group A). Differences in MP between group A and the control group were significant at 120 min.

Conclusions

The results of this study demonstrate that mast cells are only less involved in the pathophysiology of leukocyte-independent plasma extravasation during endotoxemia. Further patho-mechanisms must be discussed.