Effect of supplemental L-arginine in a chemical-induced model of colorectal cancer.

L-Arginine inhibits the development of spontaneous, transplantable solid tumors and chemically induced mammary tumors. The aim of the present study was to investigate the effect of l-arginine on chemically induced colorectal cancer in male Wistar rats. Colorectal cancer was induced in all animals by weekly subcutaneous injections of the colonic procarcinogen 1,2-dimethylhydrazine (DMH) at a dosage of 20 mg/kg body weight. Arginine was given in a 1% solution of drinking water. Group I was the DMH control; group II, arginine for 22 weeks; group III, arginine for the first 10 weeks only. Lymphocyte function was evaluated by measuring the thymic lymphocyte proliferative response to the T cell mitogen phytohemagglutinin. The results show that tumor incidence and tumor burden (tumors/rat and tumors/tumor-bearing rat) were significantly reduced in both groups of animals receiving arginine compared to DMH controls (p < 0.05). The tumor areas and volumes were also reduced in both arginine groups (p < 0.05). Thymic lymphocyte stimulation indices were significantly increased by arginine supplementation (p < 0.05). These results would be in keeping with the reduction in colorectal tumor production due to a "nonspecific" stimulation of the host immune system by L-arginine.