Promotion by histamine of carcinogenesis in the forestomach and protection by histamine against carcinogenesis induced by N-nitroso-N-methylnitroguanidine in the glandular stomach in W rats.

The effect of histamine on induction of tumors in the forestomach and the glandular stomach after N-nitroso-N-methylnitroguanidine (MNNG) administration was studied in male inbred W rats. Animals were given 50 micrograms MNNG solution/ml orally for 25 weeks and then 4 mg histamine dihydrochloride sc per day in depot form. Administration of histamine in depot form after MNNG significantly increased the incidence of tumors in the forestomach, but it significantly decreased the incidence of adenocarcinomas in the glandular stomach. All of the tumors induced in the forestomach were of the squamous cell type, and 50% of them were squamous cell carcinomas. Histamine alone had no apparent carcinogenicity in rats.