[Effect of orally administered zinc on the inducibility of experimental brain tumors in the rat].

The effect of orally administered zinc on induction and growth of brain tumours in rats was investigated. The brain tumours were induced experimentally by N-ethyl-N-nitrosourea injected subcutaneously in a single dose (17 mg/kg body weight) into newborn BD IX rats. The rats were killed after 180 days. Their brains were cut in serial sections and investigated histologically. The incidence of brain tumours of a control group of rats (group 1) was compared with that of rats which received drinking-water containing 22.8 mmol/l (5.0 g/l) zinc acetate from the 4th week (group 2) or from the 150th day (group 3) after birth. The rats of group 2 developed three times more brain tumours than the rats of the control group. This difference is statistically significant. The incidence of brain tumours in rats of group 3 corresponds to that of the control group. The average size of the tumours was the same in all groups. In the brains of the rats that received zinc with the drinking-water up to the 180th day but without administration of a cancerogen immediately after birth (group 4) we could not find any tumour, neither after 180 nor after 380 days. Our results indicate a cocancerogenic (promotion) effect of zinc in experimental neurooncogenesis of the rat.