EFFECT OF METHIONINE-DEPRIVED TOTAL PARENTERAL-NUTRITION ON TUMOR PROTEIN-TURNOVER IN RATS

Background. Previous studies have shown that a methionine-lacking diet inhibited tumor growth in rats. The aim of this study was to determin e how methionine free total parenteral nutrition (MTPN) can result in the inhibition of tumor growth on tumor protein metabolism in rats. Me thods. On day 0, AH109A rat ascites hepatoma cells were implanted subc utaneously into male Donryu rats (n = 68, body weight, 200-225 gm). On day 10, a catheter for total parenteral nutrition (TPN) was placed an d either MTPN or standard TPN solution was given for 5 days. On day 15 , 1-C-14-leucine was infused continuously to measure tumor protein syn thesis. Tumor proteolysis was calculated from tumor regional blood flo w, using the Sr-85-microsphere injection method. Results. 1) Tumor wei ght was reduced with MTPN. 2) MTPN did not affect tumor protein synthe sis, probably because endogenous methionine production was increased w ith MTPN (87.3 +/- 13.5 mu mole methionine/kg/hour vs. 218.6 +/- 29.5, P < 0.01); however, MTPN caused an increase of tumor proteolysis (2.6 8 +/- 0.53 mu mole leucine/g/hour vs. 3.79 +/- 0.73, P < 0.05). Conclu sion. The enhanced tumor protein breakdown contributed to the inhibiti on of tumor growth that was found with the rats given the methionine f ree diet.