Insulin sensitivity, hormonal levels and skeletal muscle protein metabolism in tumour-bearing exercising rats.

We have previously shown that spontaneous physical exercise can delay onset of experimental anorexia and cachexia, and retard tumour growth; we now report the effects on insulin sensitivity, hormonal levels and skeletal muscle protein metabolism. Insulin sensitivity determined with a euglycaemic hyperinsulinaemic clamp revealed a normalised glucose disposal rate in tumour-bearing exercising (TBE) versus sedentary (TBS) animals (TBE 15.55 +/- 2.71 versus TBS 2.47 +/- 2.12 mg/kg/min; P < 0.05). Both TBE and TBS animals had decreased levels of corticosterone during the clamp. Serum levels of insulin during tumour progression were unaffected by exercise, but the insulin: glucagon ratio increased and the progressive decrease in rT3 was attenuated. The concentration of glucagon decreased in both tumour-bearing groups during the experiment, while TBE animals showed a relative reduction in corticosterone. Capacity for skeletal muscle protein synthesis, expressed as RNA: protein ratio, was normalised in TBE animals in two tumour protocols (TBE 5.9 +/- 0.6 versus TBS 4.7 +/- 0.3; TBE 2.9 +/- 0.4 versus TBS 1.8 +/- 0.2; P < 0.05, respectively). Incorporation rate of 14C-phenylalanine into skeletal muscle protein was increased in the TBE group in vitro and in vivo. In the postexercise period, protein degradation evaluated by tyrosine release in vitro was increased, but decreased over time. This study has confirmed a positive skeletal muscle protein balance in exercising tumour-bearing animals, partly explained by the increased insulin sensitivity. This conclusion was further supported by the less catabolic pattern indicated by hormonal levels.