2017 ACVIM Forum Research Abstract Program

It was concluded that insulin expression did not differ between IR and IS groups and there was no evidence that insulin resistance increases insulin secretion within pancreatic islets. Lower glucagon expression in IR horses may be a result of compensatory downregulation of hormone secretion in response to hyperinsulinemia or hyperglycemia. Insulin dysregulation (ID), specifically hyperinsulinemia, has been identified as a cause of laminitis. Certain breeds are seemingly more susceptible. Understanding breed differences in insulin responses and measures of lipid metabolism/adipokines may be critical for identifying truly "at risk" individuals. Insulin-modified frequently sampled intravenous glucose tolerance tests (FSIGTT) (N = 90) and oral sugar tests (OST) (N = 82) were performed along with assessment of markers for lipid metabolism/adipokines (N = 90) in 5 breeds (Quarter Horses (QH), Arabians, Morgans, Welsh Ponies (WP), and Thoroughbreds). Minimal model analyses of the FSIGTT for insulin sensitivity (SI), the acute insulin response to glucose (AIRg), disposition index (DI), glucose mediated glucose disposal (Sg), the lowest glucose value (Gmin), and the deflection of glucose below baseline (dGB) were assessed. OST insulin thresholds, trajectories, and area under the curve (AUC) were assessed. Statistics included: multilevel regression analysis, regression modeling of time trajectories, one-way ANOVA, Kruskal-Wallis test, ROC curve analysis (significant at P < 0.05). QH had higher SI than all other breeds, lower AIRg than WP and Arabians, and higher DI than Morgans. Arabians had higher AIRg than Morgans, and lower Sg than WP. Morgans had lower AIRg than WPs. Arabians, Morgans, and WP had lower Gmins than Thoroughbreds. Morgans had a greater dGB than QHs. Different OST insulin thresholds for ID existed between breeds. OST glucose and insulin trajectories and AUC were lowest in QH. Significant breed differences existed in nonesterified fatty acids, high molecular weight adiponectin, leptin, and triglycerides. Breed specific differences are important to consider when evaluating metabolic health. Insulin dysregulation, specifically hyperinsulinemia, has been identified as a cause of laminitis. Muscle and adipose tissue have large roles in insulin regulation and in the pathology of human metabolic syndrome, but these roles have not been well interrogated in horses. Tailhead adipose tissue (N = 76) and middle gluteal muscle (N = 28) biopsies were performed (4 equine breeds: Quarter Horses (QH); Arabians, Morgans, Welsh Ponies (WP)) to relate adipocyte area (AA) and muscle fiber type percent area and proportions to body condition score (BCS), total body fat mass (TBFM) (using the deuterium dilution technique) and minimal model parameters from a frequently sampled intravenous glucose tolerance test (FSIGTT). Statistics included: Kolmogorov-Smirnov analysis, MANOVA, and Spearman correlation. Significance was set at P < 0.05. Overall BCS was weakly to moderately correlated to insulin sensitivity (SI), the acute insulin response to glucose (AIRg), and AA. TBFM was not correlated to SI and weakly correlated to AIRg and AA overall, but moderately correlated to AA in QH. QH had a significantly smaller AA than Arabians and WP but not Morgans. AA was weakly related to SI and moderately to AIRg. Baseline insulin concentrations were moderately correlated to Type 1 muscle fiber percent area and proportion. No breed differences existed between muscle fi