Relationship Between β-cell Response and Insulin Sensitivity in Horses based on the Oral Sugar Test and the Euglycemic Hyperinsulinemic Clamp

Abstract

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.

Keywords: Equine metabolic syndrome; Hyperbolic relationship; Insulin dysregulation; Insulin resistance.