Nitric oxide inhibits numerous features of mast cell-induced inflammation

We previously reported that mast cell degranulation causes histamine and P-selectin-dependent leukocyte rolling and platelet-activating factor (PAF)- and CD18-associated leukocyte adhesion, whereas others have reported serotonin-induced edema formation. The purpose of the present study was to determine whether nitric oxide (NO) could inhibit the mast cell-induced multistep recruitment of leukocytes and the associated microvascular dysfunction in single inflamed venules.

Intravital fluorescence microscopy was used to demonstrate increased leukocyte rolling and adhesion and increased albumin extravasation in single 25- to 40-microns venules that were treated with the mast cell-degranulating agent compound 48/80 (CMP 48/80). The mast cell-induced histamine-dependent rolling and PAF-dependent adhesion were completely inhibited by the addition of the NO donor spermine NO. However, spermine NO did not directly inhibit histamine-induced leukocyte rolling and only partly affected PAF-induced leukocyte adhesion. Compound 48/80-activated mast cells evoked a significant increase in PAF-dependent neutrophil adhesion in vitro. Spermine-NO prevented the mast cell-dependent neutrophil adhesion but failed to affect direct adhesion with PAF. The mast cell-induced albumin leakage was also inhibited by the NO donor.

Taken together, these results suggest that exogenous NO can modulate leukocyte recruitment and microvascular permeability alterations elicited by mast cell activation and raises the possibility that the use of NO donors may be a reasonable therapeutic approach to reducing mast cell-dependent inflammation.