The modifying effects of the naturally occurring antioxidants γ-oryzanol, phytic acid, tannic acid and n-tritriacontane-16, 18-dione (TTAD) were investigated in a rat wide-spectnim organ carcinogenesis model. Animals were initiated with two i.p. injections of 1000 mg/kg body wt 2,2′-dihydroxy-di-n-propylnitrosamine (DHPN) followed by two i.g. administrations of 1500 mg/kg body wt N-ethyl-N-hydroxyethylnitrosamine (EHEN), and then three s.c. injections of 75 mg/kg body wt 3,2′-dimethyl-4-amlnobiphenyl (DMAB) during the first 3 weeks. Starting 1 week after the last injection, groups of rats received diet containing 1% γ-oryzanol, 2% phytic acid, 0.2% TTAD or 1% tannic acid or basal diet alone for 32 weeks. Animals were then killed and complete autopsy was performed at the end of week 36. Histological examination revealed enhancement of lung carcinogenesis by γ-oryzanol, and the incidence of urinary bladder papillomas to be increased by phytic acid. On the other hand, TTAD inhibited hepatic and pancreatic carcinogenesis. Phytic acid and tannic acid were marginally effective in inhibiting hepatic and colon carcinogenesis respectively. The results thus indicated that naturally occurring antioxidants each exert specific modifying effects depending on the organ site and indicate that wide-spectrum carcinogenesis models are useful for defining complex influences.

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