Enhanced mucosal permeability and nitric oxide synthase activity in jejunum of mast cell deficient mice

Abstract

Background—Recent reports have described a modulating influence of nitric oxide (NO) on intestinal mucosal permeability and have implicated a role for mast cells in this NO mediated process. 
Aims—To assess further the contribution of mast cells to the mucosal permeability changes elicited by the NO synthase (NOS) inhibitor N^G-nitro-L-arginine methylester (L-NAME), using mast cell deficient (W/W^V) and mast cell replete mice (+/+). 
Methods—Chromium-51 EDTA clearance (from blood to jejunal lumen), jejunal NOS and myeloperoxidase (MPO) activities, and plasma nitrate/nitrite levels were monitored. 
Results—The increased EDTA clearance elicited by intraluminal L-NAME in W/W^V mice (4.4-fold) was significantly greater than the response observed in control (+/+) mice (1.8-fold). The exacerbated response in W/W^v mice was greatly attenuated by pretreatment with either dexamethasone (1.3-fold) or the selective inducible NOS inhibitor, aminoguanidine (1.4-fold), and partially attenuated by the mast cell stabiliser, lodoxamide (2.9-fold). Jejunal inducible NOS activity was significantly higher in W/W^V than in +/+ mice, while jejunal MPO was lower in W/W^V mice than in +/+ mice, suggesting that the higher inducible NOS in W/W^V does not result from the recruitment of inflammatory cells into the gut. The higher inducible NOS activity in the jejunum of W/W^V was significantly reduced by dexamethasone treatment. 
Conclusions—Our results suggest that mast cells normally serve to inhibit inducible NOS activity tonically in the gut and that inhibitors of NOS elicit a larger permeability response when this tonic inhibitory influence is released by mast cell depletion. 



Keywords: aminoguanidine; c-kit; dexamethasone; epithelium; neutrophils

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Figure 1 .

: (A) Time course of mucosal permeability changes in untreated controls (+/+) (n=5), and elicited by L-NAME in +/+ (n=6), and mast cell deficient (W/W^V) mice (n=6). (B) L-NAME induced mucosal permeability changes expressed as a ratio of the maximum clearance to baseline value (10-20 minute clearance value) in the following groups: +/+, W/W^V, W/W^V pretreated with lodoxamide (Lod) (n=5), W/W^V pretreated with dexamethasone (Dex) (n=5), and W/W^V pretreated with aminoguanidine (AG) (n=6) and ICR mice (n=6). *p<0.05 relative to respective baseline value, †p<0.001 relative to L-NAME-treated +/+, *p<0.05, ‡p<0.001 relative to the peak clearance response of W/W^V. 


Figure 2 .

: Nitric oxide synthase (NOS) activity in control (+/+) mice (n=7), mast cell deficient (W/W^V) mice (n=8), W/W^V mice pretreated with dexamethasone (DEX) (n=8), and W/W^V mice pretreated with aminoguanidine (AG) (n=6). *p<0.05, **p<0.001 relative to +/+, †p<0.05 relative to W/W^V. 


Figure 3 .

: Plasma levels of nitrite and nitrate in control (+/+) (n=6), mast cell deficient (W/W^V) (n=6), and W/W^V mice pretreated with either dexamethasone (Dex) (n=6) or aminoguanidine (AG) (n=6). *p<0.01 relative to +/+.