Mammary carcinogenesis induced in Wistar : Han rats by the combination of ionizing radiation and dimethylbenz(a)anthracene: prevention with melatonin

The primary cancer chemoprevention is an important topic of experimental on cology. We have analyzed the possible oncostatic properties of melatonin in a combined model of radiation plus chemocarcinogen-induced mammary carcino genesis. Virgin female rats of Wistar:Han strain were continuously irradiat ed with daily dose 96 mGy of gamma rays up to 15 days. At the end of irradi ation, between 52-60 postnatal days, 7,12-dimethylbenz(a)anthracene was adm inistered by gavage, in three 10 mg/rat consecutive doses. A part of animal s drank melatonin in a concentration 100 mu g/ml of tap water, continuously from the beginning of irradiation and 26 weeks after its end. The aim of t he experiment was to investigate the preventive effect of melatonin on mamm ary tumor patterns. Relatively low incidence of mammary tumors in the nonin fluenced group was probably connected with generally very low sensitivity o f Wistar:Han female rats to single dose of chemocarcinogen in mammary carci nogenesis induction. In our trial melatonin decreased markedly the volume o f mammary tumors, but did not influence any other tumor characteristics. The chemopreventive effect of melatonin, derived from in vivo realized mamm ary carcinogenesis study in female Wistar:Han rats was limited. The cancer preventive properties of melatonin should be investigated in the future esp ecially from the standpoint of susceptible strain, effective doses, and mod e plus sufficient length of application.