[Studies on biological damage by active oxygens. III. Generation of hydroxyl radical and inhibition of insulin release in hypoxanthine-xanthine oxidase system in the presence of pancreatic islet cells].

The hydroxyl radicals (HO.) spin adduct of 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) was obtained in the hypoxanthine-xanthine oxidase (HX-X.O.) system in the presence of isolated islet cells by using electron spin resonance spectroscopy. There was a significant increase in the concentration of DMPO-OH spin adduct dependent on the increase in a number of islet cells. In the absence of islet cell, the DMPO-OOH spin adduct formed by superoxide together with a small amount of DMPO-OH spin adduct was detected in HX-X.O. system. These results suggest that HO. is greatly produced in the HX-X.O. system in the presence of islet cells. The generation of HO. was partially inhibited by the addition of superoxide dismutase or catalase and completely by the combined use of both enzymes. Iron-chelator, diethylenetriaminepentaacetic acid and iron-binding protein, apotransferrin also inhibited the generation of HO., suggesting a possible participation of a trace iron in the islet cells. The inhibition of insulin release from islet cell, as well as the amount of DMPO-OH spin adduct, was dependent on the concentration of X.O. These results indicate that the HO. is produced by the site-specific action with islet cells in HX-X.O. system, suggesting a possible involvement of HO. in the oxygen damages of islet cells.