Blunt cell growth potential in carcinogen resistant inbred DRH rats

A carcinogen-resistant inbred strain DRH/Sea has been developed from the Cr j:Donryu strain. The rats had a very low incidence of liver tumors when the y were fed diets containing a hepatocarcinogen such as 3'-methyl-4-dimethyl amino-azobenzene (3'-Me-DAB). Despite using 3'-Me-DAB during the stage of s election, the DRH/Sea rats developed normally, reproduced and did not have any spontaneous tumor in the lung, liver or uterus at over I year of age. A lthough their growth curves were similar to the Crj:Donryu rats, the progre ssion of polyploidization in the liver was significantly delayed when compa red with Crj:Donryu rats, Mitogenic changes that occurred in the liver caus ed by either 3'-Me-DAB or lead nitrate were less significant in the DRH rat s than in Crj:Donryu rats. Furthermore, the growth rate of cultured fibrobl asts derived from the DRH rats was slower than that of Crj:Donryu rats. The se results, together with our previous results, suggest that slow growth po tential is present under certain conditions in DRH rats. These findings may explain partly the meaning of the different susceptibility to hepatocarcin ogens.