Serum creatine kinase response to exercise during dexamethasone-induced insulin resistance in Quarter Horses with polysaccharide storage myopathy.

This study is about how dexamethasone influences insulin sensitivity, muscle glycogen concentration, and the serum creatine kinase (CK) activity after exercise in Quarter Horses with polysaccharide storage myopathy (PSSM). The researchers have found that while dexamethasone decreases the rate of glucose infusion necessary to maintain normal blood glucose levels during the HEC technique and reduces the insulin-stimulated glucose uptake, it does not alter muscle glycogen concentrations or serum CK response to exercise.

Methodology

• A crossover design was used, involving 4 adult Quarter Horses diagnosed with PSSM. They were given either dexamethasone (0.08 mg/kg) or saline (0.9% NaCl) intravenously, every 48 hours.
• These horses underwent daily exercises on a treadmill for three weeks per treatment, with a two-week break between the two treatments.
• Serum CK activity was measured daily, 4 hours after each exercise session. At the end of each treatment period, serum cortisol concentrations were taken, a hyperinsulinemic euglycemic clamp (HEC) technique was performed and muscle glycogen content was determined.

Findings

• The mean serum cortisol concentration was significantly lower 48 hours after the dexamethasone treatment compared to the saline treatment.
• Dexamethasone significantly decreased the glucose infusion rate necessary to maintain euglycemia during the HEC technique in comparison to the saline treatment.
• No significant differences were found in muscle glycogen concentrations and mean CK activity after exercise between dexamethasone and saline treatment.

Conclusions

• Dexamethasone significantly reduced the glucose uptake stimulated by insulin in Quarter Horses with PSSM after a 3-week period.
• No differences were observed in the serum CK response to exercise or muscle glycogen concentrations in these 4 horses despite the dexamethasone treatment.
• The decrease in glucose uptake for 3 weeks did not seem to mitigate the effects of exertional rhabdomyolysis in these horses, leading the researchers to hypothesize that long-term treatment may yield differing results.