INHIBITION OF RAT MONONUCLEAR CELL LEUKEMIA BY CORN-OIL GAVAGE - IN-VIVO, IN-SITU AND IMMUNE COMPETENCE STUDIES

Corn oil administered by oral gavage decreases the spontaneous inciden ce of mononuclear cell leukemia (MNCL) in male Fischer rats used as ve hicle controls in long-term carcinogenesis experiments. We used an MNC L transplant model, an in situ MNCL cell proliferation assay and immun e competence assays to explore mechanism(s) underlying the effects of corn oil gavage on MNCL development in male rats. Relative to non-gava ged or water-gavaged rats, corn oil-gavaged rats had similar to 25% lo wer MNCL incidence as well as longer MNCL latency and increased surviv al. There were no differences in body weight or caloric intake between treatment groups, as corn oil-gavaged rats compensated for calories s upplied by the gavaged oil by consuming less food. These data indicate that transplanted MNCL cells grew slower in corn oil-gavaged rats tha n in non-gavaged or water-gavaged rats and suggest that corn oil gavag e may exert its effects through a decrease in protein or other nutrien ts. Five-day proliferation rates of cultured MNCL cells in diffusion c hambers implanted in male corn oil-gavaged rats were 40% less than in water-gavaged rats, suggesting nutrition-sensitive endogenous factors mediate the suppression of MNCL cell proliferation in corn oil-gavaged rats. Corn oil-gavaged rats had 54% lower serum growth hormone (GH) l evels, and replacement of GH into corn oil-gavaged rats by osmotic min ipump infusion increased in situ MNCL cell proliferation to rates obse rved in water-gavaged animals. Corn oil-gavaged rats also showed enhan ced cellular immune competence as measured by mitogen stimulation, nat ural cytotoxicity and immunofluorescence assays. Taken together, these findings suggest corn oil administered by oral gavage may decrease MN CL development by slowing MNCL cell proliferation, mediated at least i n part by altered levels of diffusible factors such as GH, and/or by e nhancing immune competence.