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

Abstract

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-angiotensin-aldosterone 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.

Serum myoglobin, creatine kinase, and cell‐free DNA in endurance sled dogs and sled dogs with clinical rhabdomyolysis

“…Myoglobin values increased from prerace value to the midrace point in the winning team, but reduced to near baseline values by the finish. This suggests peak muscle damage occurs at or before midrace in endurance canine athletes, consistent with previous studies of CK values peaking between days 2–4 of racing or simulated racing . Myoglobin and CK values were highly correlated in dogs in this study.…”

“…Endurance racing necessitates a 10,000–12,000 kcal/d expenditure, but this intake cannot be effectively delivered . Reduced intestinal digestive capacity may result from changes in intestinal permeability and rapid transit time, and both may contribute to the weight loss identified . Glycogenolysis during repeated exercise and increasing reliance on catabolism of endogenous nitrogen sources (proteins and nucleotide precursors) may lead to the decreases in cfDNA observed in these dogs over the course of the race.…”

“…Myoglobin and CK values were highly correlated in dogs in this study. In the dog, myoglobin has a very short half‐life compared to CK (<10 minutes and 6 hours, respectively) . This suggests that the rhabdomyolysis was identified early in course of disease.…”

“…As such, it may be less suitable for detecting early rhabdomyolysis in the field especially during endurance dog distance racing. To date, the most reliable biochemical marker for ER and its severity is the increase in blood creatine phosphokinase activity (CK) . Modest increases in serum and plasma CK within 4–5 times the high end of the reference interval are considered normal in exercised animals .…”

“…To date, the most reliable biochemical marker for ER and its severity is the increase in blood creatine phosphokinase activity (CK) . Modest increases in serum and plasma CK within 4–5 times the high end of the reference interval are considered normal in exercised animals . The extent of increases in CK activity consistent with musculoskeletal damage leading to ER is yet to be defined in dogs.…”