Determination of reference range values indicative of glucose metabolism and insulin resistance by use of glucose clamp techniques in horses and ponies

OBJECTIVES: To acquire reference range values indicative of glucose metabolism by use of the hyperglycemic clamp technique in healthy horses and evaluate the usefulness of the euglycemic hyperinsulinemic clamp technique in healthy horses and ponies. ANIMALS: Dutch Warmblood horses and 4 Shetland ponies. PROCEDURE: The hyperglycemic clamp technique was used for quantification of the sensitivity of beta cells to exogenous glucose infusion in horses. The euglycemic hyperinsulinemic clamp technique was used to determine the sensitivity and responsiveness of tissues to exogenous insulin in horses and ponies. RESULTS: During the hyperglycemic clamp technique, the mean amount of glucose metabolized (M) in horses was 0.011 +/- 0.0045 mmol/kg x min(-1) (95% confidence interval CI, 0.0018 to 0.020 mmol/kg x min(-1); range, 0.000035 to 0.021 mmol/kg x min(-1)) and the mean M value-to-plasma insulin concentration (I) ratio (ie, mmol of glucose/kg x min(-1) per pmol of insulin/L x 100) was 0.017 +/- 0.016 (95% CI, -0.014 to 0.049; range, 0.000025 to 0.055). During the euglycemic hyperinsulinemic clamp technique, the mean M value was 0.014 +/- 0.0055 mmol/kg x min(-1) (95% CI, 0.0026 to 0.025 mmol/kg x min(-1); range, 0.0042 to 0.023 mmol/kg x min(-1)) in horses and 0.0073 +/- 0.0020 mmol/kg x min(-1) (95% CI, 0.0034 to 0.011 mmol/kg x min(-1); range, 0.0049 to 0.011 mmol/kg x min(-1)) in ponies. The M value was significantly lower in ponies than in horses, whereas the M:I ratios were not significantly different between horses and ponies. CONCLUSION AND CLINICAL RELEVANCE: Glucose clamp techniques offer good methods to investigate glucose metabolism in horses and ponies. A higher degree of insulin resistance was found in ponies, compared with Dutch Warmblood horses.