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
Animals—4 adult Quarter Horses with PSSM.
Procedure—A 2 × 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 and Clinical Relevance—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.
(Am J Vet Res 2005;66:1718–1723)