INSULIN SENSITIVITY, HORMONAL LEVELS AND SKELETAL-MUSCLE PROTEIN-METABOLISM IN TUMOR-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 wi th a euglycaemic hyperinsulinaemic clamp revealed a normalised glucose disposal rate in tumour-bearing exercising (TBE) versus sedentary (TB S) 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 corticosteron e during the damp. Serum levels of insulin during tumour progression w ere unaffected by exercise, but the insulin : glucagon ratio increased and the progressive decrease in rT(3) was attenuated. The concentrati on of glucagon decreased in both tumour-bearing groups during the expe riment, while TBE animals showed a relative reduction in corticosteron e. 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 C-14-phenylal anine into skeletal muscle protein was increased in the TBE group in v itro and in vivo. In the postexercise period, protein degradation eval uated by tyrosine release in vitro was increased, but decreased over t ime. This study has confirmed a positive skeletal muscle protein balan ce in exercising tumour-bearing animals, partly explained by the incre ased insulin sensitivity. This conclusion was further supported by the less catabolic pattern indicated by hormonal levels.