Effects of exercise on canine skeletal muscle proteolysis: an investigation of the ubiquitin-proteasome pathway and other metabolic markers.

215 n ABSTRACT The effects of long-term athletic training are associated with excessive skeletal muscle turnover attributable to increased rates of myofibrillar protein synthesis and proteolysis, which are mechanisms poorly understood in the athletic dog. A physiologic field study using 44 English pointers and Labrador retrievers that had been purposely bred for bird hunting and retrieving was conducted to examine changes in the ubiquitin-proteasome (UP) pathway, which has been implicated in exercise-induced proteolysis. Muscle biopsy samples were collected from all dogs in September (preseason, pretraining) and February (peak season, peak activity). Western blot analysis was used to assess changes in expression of various components of the UP pathway in the biopsy samples. Citrate synthase and glycogen levels were also measured in a subset of these samples. Results across the population indicated pronounced up-regulation of ubiquitinated conjugates and the p31 regulatory capping subunit during the peak hunting period compared with the preseason period. In contrast, the catalytic core of the proteasome (β−subunits) showed no apparent up-regulation in response to increased physical activity. Increased Effects of Exercise on Canine Skeletal Muscle Proteolysis: An Investigation of the UbiquitinProteasome Pathway and Other Metabolic Markers*