EXERCISE TRAINING AND MOUSE MAMMARY-TUMOR METASTASIS

The present study was designed to address whether exercise influences the experimental metastasis of a mouse mammary tumour; a related issue was the impact of timing of exercise onset relative to tumour exposur e on NK and LAK mediated cytotoxicity. After 8 weeks of forced treadmi ll exercise or voluntary wheel running or remaining sedentary, female BALB/c mice received an intravenous (i. v.) injection of MMT line 66 t umour cells. Mice were then randomized into continuation of activity ( TT, WW), cessation of activity (TS, WS), initiation of activity (ST, S W) and maintenance of sedentary condition (SS) for three weeks. Tumour control (TC) mice, who were matched to the SS mice for age, received an i.v. injection of heat-killed MMT 66 tumour cells. In total there w ere 8 groups including the tumour control. The average number of lung tumours did not differ by activity condition; however, the mice in the continuous treadmill group (TT) tended to have a higher tumour multip licity (162 +/- 22) and those in the treadmill x sedentary condition ( TS) tended to have lower tumour multiplicity (109 +/- 16) compared wit h the other groups except the SW group (95 +/- 15). The lymphokine act ivated killer activity in the spleen was significantly elevated in the TS (49 +/- 3%) and WS (44 +/- 3%) mice compared with the sedentary an imals'(30 +/- 3%) (p<0.003 and 0.05, respectively). NK activity was lo wer in the mice that had stopped exercising (TS and WS) after injectio n of tumour compared with sedentary animals. These data suggest that a lthough exercise training influences natural immune cytotoxic mechanis ms in vitro, this may not translate into clinically significant change s in tumour burden. The dissociation between natural immunity and tumo ur outcome may reflect the relative resistance of the tumour line to l ysis by natural killer cells. It remains to be tested if infusion of I L-2 (to induce LAK activity), in exercise trained animals results in f ewer tumour metastases.