Plasma chemistry before and after two consecutive days of racing in sled dogs: Associations between muscle damage and electrolyte status

Exercising long distance endurance sled dogs display plasma biochemistry changes characterised by elevations in creatine kinase (CK) and aspartate aminotransferase (AST), hypoproteinemia, hypoglobulinemia and decreases in sodium and potassium. The aim of this study was to compare resting to day 2 racing plasma biochemistry and associations between electrolytes and markers of muscle damage in well-conditioned sled dogs during a stage-stop race. Blood samples were obtained from 23 dogs prior to the start and on day 2, immediately after racing. Results showed significant decreases in potassium (day 0 - 4.7±0.3 and day 2 - 4.2±0.3 mEq/l), total protein (day 0 - 6.0±0.3 and day 2 - 5.5±0.4 g/dl) and albumin concentrations (day 0 - 3.9±0.2 and day 2 - 3.6±0.3 g/dl). Increases in AST (day 0 - 24±7 and day 2 - 137±97 U/l) and CK activities (day 0 - 129±39 and day 2 - 2,047±2,021 U/l) were also observed. Plasma sodium concentrations were not significantly different after day 2 of racing (day 0 - 153±5.2 and day 2 - 151±4.1). Alterations in plasma electrolytes, and increases in AST, CK, alanine aminotransferase and urea nitrogen were similar to those observed in long distance endurance sled dogs. A strong negative association was observed between plasma potassium and increases in plasma CK activity on day 2 (R²=0.69). The maintenance of sodium concentrations with a concurrent potassium decline, suggests sodium conservation via the renin-angiotensinaldosterone pathway as previously shown in endurance sled dogs. The negative correlation between muscle damage and plasma potassium warrants further investigation regarding its relationship to rhabdomyolysis.