PHORBOL-MYRISTATE ACETATE EX-VIVO MODEL OF ENHANCED COLONIC EPITHELIAL PERMEABILITY - REACTIVE OXYGEN METABOLITE AND PROTEASE INDEPENDENCE

The initiating mechanisms involved in colonic injury are currently unk nown. The goal of the current study was to examine the role of the inf lammatory mediators reactive oxygen metabolites and proteases in an ex vivo model of selective epithelial permeability. Rats were prepared w ith exteriorized colonic chambers to which the protein kinase C (PKC) activator phorbol myristate acetate (PMA) was added in doses ranging f rom 5 to 800 mu g. PMA caused a dose-dependent transient increase in e pithelial permeability, but had no significant effect on microvascular permeability. There was no accumulation of neutrophils and no apparen t histological changes. PMA acts via a PKC-dependent mechanism, as ass essed using the PKC-inactive phorbol analog 4 alpha-phorbol didecanoat e, and the response is tachyphylactic. The mechanism is independent of reactive oxygen metabolites and proteases, as shown by the lack of ef fect of the free radical scavengers superoxide dismutase and catalase and the general serine protease inhibitor soybean trypsin inhibitor. T he classic inflammatory process does not appear to be involved in the PMA-induced epithelial permeability changes. This finding suggests tha t noninflammatory mechanisms may regulate the increased epithelial per meability induced by PMA. Further study to elucidate these mechanisms is of importance for understanding both normal gastrointestinal physio logy and initiation of pathology.