Heparin releases diamine oxidase (DAO) of enterocytic origin from binding sites located on small bowel microvascular endothelium. In the villus tip enterocytes the enzyme is found in organelles (about 60%) and in cytosol (about 40%), while a negligible activity is present in the brush border. In this study we assessed the changes in DAO distribution into the enterocytes induced by a high dose of intraperitoneal heparin (1000 IU) in the rat, by assaying DAO activity on subcellular fractions obtained from ileal mucosa homogenate. Heparin injection induced a marked reduction of enzyme activity in the S2 fraction (cytosol): after 30 min less than 20% of DAO activity is still found and only 8% after 150 min. In the P1 fraction (organelles) DAO activity significantly decreased only after 60 min and a further consistent reduction was recorded after 150min. Recovery of DAO activity was complete 4 days after the injection, though it was already clearly evident in the first 2 days. These results indicate that enterocytic DAO is distributed in two different compartments: DAO located in the cytosol is quickly released by heparin, while the organelles-linked enzyme is more slowly released. The finding that recovery in DAO activity happens earlier in the P1 fraction suggests that the enzyme supplies the cytosol after being synthesized in the enterocyte organelles.
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