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Keywords:

  • horse;
  • exercise;
  • equine;
  • insulin sensitivity;
  • somatostatin;
  • C-peptide

Summary

Reasons for performing study: There is limited information about factors regulating glucose utilisation post exercise in horses.

Objectives: To determine the effects of a single bout of moderate intensity exercise on measures of insulin-mediated (IMGU) and noninsulin-mediated (NIMGU) glucose uptake during a hyperglycaemic clamp (HC).

Methods: Hyperglycaemic clamps were administered in random order to 8 Standardbreds under 4 conditions: 1) rest, insulinopenia (R-L); 2) rest, hyperinsulinaemia (R-H); 3) post exercise (45 min at ∼50% VO2peak), insulinopenia (Ex-L) and 4) post exercise, hyperinsulinaemia (Ex-H). In the R-L and Ex-L trials, somatostatin was infused to suppress insulin secretion and induce insulinopenia. After 30 min, a 2 h HC was initiated with plasma glucose concentrations maintained at ∼10 mmol/l by variable glucose infusion. In R-H and Ex-H, regular insulin (1.0 mu/kg bwt/min) was also administered to induce physiological hyperinsulinaemia. Serum insulin and C-peptide concentrations were measured in samples obtained at 10 min intervals. Glucose uptake was calculated from mean glucose infusion rate (GIR) during the last 60 min of the HC.

Results: In all HCs C-peptide remained below baseline concentrations, evidence of suppression of insulin secretion by somatostatin. Overall, mean ± s.e. insulin concentrations during the final 60 min of the HC in R-L and Ex-L were 5.7 ± 1.1 and 6.9 ± 1.9 mu/l respectively, and corresponding values in R-H and Ex-H were 64.1 ± 11.1 and 61.2 ± 10.9 mu/l. Prior exercise affected IMGU but not NIMGU. Over the final 60 min of the HC, mean GIR was higher (P<0.001) in Ex-H (5.6 ± 1.1 mg/kg bwt/min) than in R-H (3.3 ± 0.9 mg/kg bwt/min), whereas mean GIR did not differ (P = 0.26) between R-L (1.2 ± 0.3 mg/kg bwt/min) and Ex-L (1.8 ± 0.5 mg/kg bwt/min).

Conclusions: A single bout of moderate intensity exercise increased glucose uptake during a hyperglycaemic clamp under hyperinsulinaemic conditions but not under somatostatin-induced insulinopenia.