Effects of Verapamil on PhIP-induced Tumorigenesis in F344 Rats

Possible modifying effects of verapamil on 2-amino-l-methyl-6-phenylimidazo [4, 5-b] pyridine (PhIP) car-cinogenicity were investigated. Male and female F344 rats were administered both PhIP, 0.02% in the diet, and verapamil, 0.05% in the diet (group 1), or either PhIP (group 2) or verapamil (group 3) alone for 52 weeks. Development of mammary tumors induced by PhIP in females was delayed by verapamil coadministration, although the final incidence of adenocar-cinomas was not statistically significant between groups l and 2. These findings were not related to the changes in body weight gain. In males, PhIP induction of intestinal tumors was not affected by verapamil coadministration. In other organs, verapamil did not change the appearance of toxic and neoplastic lesions induced by PhIP. Thus, verapamil exerted only slight inhibitory effect on mammary tumor development.