Serum creatine kinase response to exercise during dexamethasone-induced insulin resistance in Quarter Horses with polysaccharide storage myopathy.
OBJECTIVE
To determine effects of dexamethasone on insulin sensitivity, serum creatine kinase (CK) activity 4 hours after exercise, and muscle glycogen concentration in Quarter Horses with polysaccharide storage myopathy (PSSM).


METHODS
4 adult Quarter Horses with PSSM.


METHODS
A 2 x 2 crossover design was used with dexamethasone (0.08 mg/kg) or saline (0.9% NaCl) solution administered IV every 48 hours. Horses were exercised on a treadmill daily for 3 wk/treatment with a 2-week washout period between treatments. Serum CK activity was measured daily 4 hours after exercise. At the end of each treatment period, serum cortisol concentrations were measured, a hyperinsulinemic euglycemic clamp (HEC) technique was performed, and muscle glycogen content was determined.


RESULTS
Mean +/- SEM serum cortisol concentration was significantly lower after 48 hours for the dexamethasone treatment (0.38 +/- 0.08 mg/dL), compared with the saline treatment (4.15 +/- 0.40 mg/dL). Dexamethasone significantly decreased the rate of glucose infusion necessary to maintain euglycemia during the HEC technique, compared with the saline treatment. Muscle glycogen concentrations and mean CK activity after exercise were not altered by dexamethasone treatment, compared with the saline treatment.


CONCLUSIONS
Dexamethasone significantly reduced whole-body insulin-stimulated glucose uptake in Quarter Horses with PSSM after a 3-week period but did not diminish serum CK response to exercise or muscle glycogen concentrations in these 4 horses. Therefore, a decrease in glucose uptake for 3 weeks did not appear to alleviate exertional rhabdomyolysis in these horses. It is possible that long-term treatment may yield other results.
Firshman
Anna M
AM
Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331, USA.
Valberg
Stephanie J
SJ
Karges
Tami L
TL
Benedict
Luke E
LE
Annandale
Erin J
EJ
Seaquist
Elizabeth R
ER
D000704:Analysis of Variance; D000818:Animals; D003402:Creatine Kinase / Q000097:blood*; D018592:Cross-Over Studies; D003907:Dexamethasone / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism; D006008:Glycogen Storage Disease / Q000378:metabolism / Q000662:veterinary*; D006734:Horse Diseases / Q000378:metabolism*; D006736:Horses; D007333:Insulin Resistance; D018482:Muscle, Skeletal / Q000378:metabolism; D005082:Physical Exertion
D003907:Dexamethasone; D006003:Glycogen; D003402:Creatine Kinase; D005947:Glucose