Effect of sex hormones on carcinogenesis in the stomachs of rats.

We have been investigating possible effects of sex hormones on the carcinogenesis of stomach cancer in Wistar rats that were given N-methyl-N'-nitro-N-nitrosoguanidine in drinking water (50 micrograms/ml) for 4 months. The incidences of stomach cancer in intact male, intact female, castrated male, and castrated female rats at Month 4 of the experiment were 5, 0, 0, and 0% respectively; and those at Month 8 were 40, 10, 0, and 0% respectively; indicating that the incidence in intact males was much higher than in the other groups. The difference in the incidence became more evident when the animals were sacrificed at Month 12 of the experiment (81, 0, 29, and 5%, respectively). Hypertrophy and dissociation of the lamina muscularis mucosae which are considered to occur in the carcinogenic process were observed only in the male rats at the earlier months, but not in female nor in castrated rats. In N-methyl-N'-nitro-N-nitrosoguanidine carcinogenesis, female and castrated rats had a lower incidence of gastric cancers with less change in the lamina muscularis mucosae than did the nontreated male rats. These findings, therefore, suggest that, in addition to the suppressive action of female hormones, male hormones facilitate carcinogenesis.