Relationship Between β-cell Response and Insulin Sensitivity in Horses based on the Oral Sugar Test and the Euglycemic Hyperinsulinemic Clamp
Background A hyperbolic relationship between β-cell response and insulin sensitivity (IS) has been described in several species including rodents, dogs, and humans. This relationship has not been elucidated in the horse. Hypothesis/Objectives To determine whether the hyperbolic relationship between β-cell response and IS exists in horses by using indices of β-cell response from the oral sugar test (OST) and IS measurements from the euglycemic hyperinsulinemic clamp (EHC). A second aim was to compare how well IS estimates from the OST and EHC correlate. Animals Forty-nine horses with different degrees of insulin regulation (normal-to-severe insulin dysregulation). Methods Cross-sectional study. Horses were examined with an OST and an EHC. Results Decreased IS was associated with increased β-cell response in the horses. Nine of 12 comparisons between indices of β-cell response and IS measures fulfilled the criteria for a hyperbolic relationship. Indices of IS calculated from the OST correlated highly with the insulin-dependent glucose disposal rate (M) and the insulin-dependent glucose disposal rate per unit of insulin (M/I) determined from the EHC (r = 0.81–0.87). Conclusions and Clinical Importance A hyperbolic relationship between β-cell response and IS exists in horses, which suggest that horses with insulin dysregulation respond not only with postprandial hyperinsulinemia but are also insulin resistant. The OST is primarily a test for β-cell response rather than a test for IS, but calculated indices of IS from the OST may be useful to estimate IS in horses, especially when the horse is insulin resistant.