Influence of zinc on onset and progression of oral carcinogenesis in rats.

Three-week-old female rats were fed 0.09 (zinc-deficient), 0.77 (zinc-adequate) or 3.98 (zinc-supplemented) mmol zinc/kg diet in three experimental groups and the palatal mucosa was painted with the water-soluble carcinogen 4-nitroquinoline N-oxide (4NQO) three times a week for 20 weeks. The zinc-supplemented diet seemed to retard the induction of carcinogenesis, whereas a low-zinc diet had the opposite effect. Once initial cellular changes had been induced the supplementary zinc seemed to accelerate their further advancement. Zinc-deficiency in animals fed a copper/zinc low-zinc diet was reflected in the plasma and liver zinc levels as well as in the copper/zinc ratio. The development of cancer was accompanied by a decrease in plasma zinc and an increase in the plasma copper/zinc ratio as well as in the liver zinc. These changes were most remarkable in the zinc-supplemented group.