NITRIC-OXIDE MODULATES EPITHELIAL PERMEABILITY IN THE FELINE SMALL-INTESTINE

The objective of this study was to assess whether inhibition of nitric oxide production leads to increased epithelial permeability in feline small intestine. Local intra-arterial infusion of the nitric oxide synthesis inhibitor N(G)-nitro-L-arginine-methyl ester (L-NAME; 0.025-mu-mol . ml-1 . min-1) was performed in autoperfused segments of cat ileum for 90 min. An exogenous source of nitric oxide, sodium nitroprusside (SNP) was infused (0.025-mu-mol.ml-1.min-1) for the last 30 min of the 90-min L-NAME infusion. Epithelial permeability was quantitated by measuring blood-to-lumen clearance of Cr-51-labeled EDTA throughout the experiment. An increase of approximately sixfold in mucosal permeability was observed within 30 min Of L-NAME infusion and this effect was completely reversed by infusion of either SNP or L-arginine (0.125-mu-mol . ml-1 . min-1). N(G)-nitro-D-arginine-methyl ester (D-NAME) had no effect on mucosal permeability. The increase in epithelial permeability was sufficiently large that rhodamine-dextran (mol wt = 17,200) clearance from interstitium to lumen was increased. Pretreatment with IB4, a monoclonal antibody directed against the leukocyte adhesive glycoprotein complex (CD11/CD18) did not prevent the L-NAME-induced increase in epithelial permeability. These data suggest that inhibition of nitric oxide production leads to a reversible circulating leukocyte-independent increase in epithelial permeability.