Sex differences in in-vitro activation and in-vivo carcinogenicity

Metabolic activation capacities of liver from rats of both sexes were studied in a bacterial mutation test containing an in-vitro metabolic activation system. Livers of male Wistar rats had higher metabolic activity than those of females for the oesophageal carcinogens, N-nitrosomethylbenzylamine and N-nitrosomethylamylamine. Castration of and/or injection of oestradiol to male rats decreased the metabolic activation capacity of their livers towards these oesophageal carcinogens to the level seen in females. Neither castration nor injection of testosterone to female rats had a significant effect on the metabolic activation capacity of their livers; however, injection of testosterone to castrated females increased the metabolic activation capacity to that of male liver. Liver from male rats also had higher in-vitro metabolic activation capacities for N-nitrosodimethylamine and N-nitrosodiethylamine than that of females.