Nitrogen intake and tumorigenesis in rats injected with 1,2-dimethylhydrazine

Tumor incidence was studied in 1,2-dimethylhydrazine (DMH) injected male rats assigned at weaning to isoenergetic casein-sucorse deits containing 7.5%, 15%, or 22.5% protein with or without 2.5% urea. Twenty rats fed each diet were given weekly intraperitoneal injections of DMH (15 mg/kg body weight/week) for the first 24 weeks and 20 were given saline. Of 96 DMH-injected rats necropsied after 28 weeks, 88 were necropsied during the 32nd or final week of the experiment. Adenocarcinomas of the small and large intestine were larger and significantly more numberous in rats fed 15% and 22.5% dietary protein. Keratin producing papillomas of the sebaceous glands of the external ear were observed first at 21 weeks in DMH-injected rats fed 22.5% protein. These were subsequently observed in some rats from all DMH-treated groups. As time progressed, the ear tumors increased in size and number in all groups but the greatest incidence was in the group fed 22.5% protein. No tumors were observed in saline-injected rats. Urea feeding did not increase the number of tumors nor cause changes in pH, urease activity or ammonia concentration of contents of the colon or cecum, or blood cholesterol. As dietary protein increased, cecal ammonia concentrations rose while both colon and cecal pH dropped. Portal blood urea and cholesterol reose as dietary protein was increased. DMH-treated rats had significantly higher concentrations of colon and cecal ammonia and lower blood cholesterol. Altough the rats fed 7.5% protein gained significantly less weight during 0 to 6 weeks of feeding, their weight gain was significantly higher during 6 to 26 weeks. No tumors were found in rats necropsied at 16 weeks.