Methylguanidine (MG) which is known as a uremic toxin, is synthesized from creatinine(Cre). We have clarified that active oxygen plays an important role on MG synthesisin vitro and in rat hepatocytes. On the other hand, hyperoxia is very injurious in various tissues, and it has been reported that active oxygen produced in hyperoxia plays an important role on the tissue injury. This study was performed to investigate the effect of hyperoxia on MG synthesis in vivo. The subjects in this study were patients who were treated by hyperbaric oxygen therapy (HBO), Serum Cre, MG, and urinary Cre, MG before and after HBO were measured in these subjects. The subjects were classified into four groups. Group 1-III were undergone HBO with condition of 100% 02, 2 atomosphere absolute (ATA), 1 hour, (I: Ccr<10 ml/min, II: l0≤Ccr<50 m1/min, III: Ccr≥50ml/min) and group IV (Ccr≥50ml/min) with 100%O2, 3ATA. 1 hour. Urinary excretion rate of MG (urine MG/urine Cre) significantly increased after HBO therapy in every group. Urine MG/urine Cre/serum Cre ratio which was used as a index of MG synthesis rate also increased. In this study, it is clarified that MG excretion rate increases in hyperoxic condition. These results suggest that active oxygen plays an important role on MG synthesis in vivo, and that the urine MG/urine Cre/serum Cre ratio can be a uaeful maker of the active oxygen products in vivo.
