Inhibitory effects of prostaglandin F2 alpha on mammary carcinogenesis induced by ethyl methanesulphonate in rats

The effect of prostaglandin F2 alpha (PGF2 alpha) on mammary carcinogens was examined for a new system in female rats, using ethyl methanesulphonate (EMS). The rats were given EMS orally for a period of 12 weeks starting at age 4 weeks. Mammary carcinomas were first detected at the 16th week and were found in all surviving rats at the 32nd week. The concomitant administration of PGF2 alpha for 8 weeks made the development of tumor retarded; i.e., the carcinomas were first detected at the 30th week and final tumor incidence at the 44th week was 61.1%. The incidence of developing mammary carcinomas and multiplicity (number of mammary carcinomas per rat) were significantly lower in PGF2 alpha treated rats than in those given EMS alone. The inhibitory effect of PGF2 alpha on tumor development was apparent when PGF2 alpha was concomitantly given to the rats with EMS at age 4 weeks, while PGF2 alpha injections after oral administration of EMS at age 16 weeks did not significantly retard tumor development. Histologically, no significant difference in morphology was observed between PGF2 alpha-treated and PGF2 alpha-non-treated rats in either the cancerous or noncancerous mammary tissues. The finding demonstrates that PGF2 alpha inhibits the development of EMS-induced mammary carcinomas when given to younger rats, presumably by affecting the hormonal status rather than by direct action on the mammary glands.