Blood glucose and insulin concentrations after alpha-2-agonists administration in horses with and without insulin dysregulation.

BACKGROUND: In metabolically stable horses, alpha-2-agonists suppress insulin secretion with transient hyperglycemia and rebound hyperinsulinemia. In horses with insulin dysregulation (ID), the effect of alpha-2-agonists has not been investigated; however, both the alpha-2-agonist-induced suppression of insulin secretion and rebound hyperinsulinemia could have clinical relevance. HYPOTHESIS/OBJECTIVES: In horses with ID, alpha-2-agonists will alter insulin and glucose dynamics. ANIMALS: Seven horses with ID and 7 control horses. METHODS: In this randomized crossover study, xylazine hydrochloride (1.1 mg/kg) or detomidine hydrochloride (30 µg/kg) were administered IV, and blood was collected for glucose and insulin concentrations at 0, 15, 30, 45, 60, 90, 120, 150, 180, and 300 minutes after administration. Horses received each drug in a random order with a 24-hour washout period between drugs. Percent change in glucose and insulin concentrations was compared between groups, drugs, and over time with P < .05 considered significant. RESULTS: A significant time-dependent effect of both alpha-2-agonists on glucose and insulin concentrations in control and ID horses was identified (P = .01 for all comparisons). There was no significant effect of sedative selection and endocrine status on blood glucose concentration in either group; however, in ID horses, xylazine administration resulted in severe rebound hyperinsulinemia whereas detomidine administration did not (P = .02). CONCLUSIONS AND CLINICAL IMPORTANCE: Alpha-2-agonists have a significant effect on glucose and insulin concentrations in horses. In ID horses, detomidine could minimize hyperinsulinemia when compared to xylazine.

Immunoreactive insulin stability in horses at risk of insulin dysregulation.

BACKGROUND: Diseases associated with insulin dysregulation (ID), such as equine metabolic syndrome and pituitary pars intermedia dysfunction, are of interest to practitioners because of their association with laminitis. Accurate insulin concentration assessment is critical in diagnosing and managing these diseases. HYPOTHESIS/OBJECTIVES: To determine the effect of time, temperature, and collection tube type on insulin concentrations in horses at risk of ID. ANIMALS: Eight adult horses with body condition score >6/9. METHODS: In this prospective study, subjects underwent an infeed oral glucose test 2 hours before blood collection. Blood samples were divided into ethylenediaminetetraacetic acid, heparinized, or serum tubes and stored at 4 or 20°C. Tubes were centrifuged and analyzed for insulin by a chemiluminescent assay over 8 days. Changes in insulin concentrations were compared with a linear mixed effects model. RESULTS: An overall effect of time, tube type and temperature was identified (P = .01, P = 0.001, and P = 0.001, respectively). Serum and heparinized samples had similar concentrations for 3 days at 20°C and 8 days at 4°C; however, after 3 days at 20°C, heparinized samples had significantly higher insulin concentrations (P = .004, P = .03, and P = .03 on consecutive days). Ethylenediaminetetraacetic acid samples had significantly lower insulin concentrations regardless of time and temperature (P = .001 for all comparisons). CONCLUSIONS AND CLINICAL IMPORTANCE: These results suggest an ideal protocol to determine insulin concentrations involves using serum or heparinized samples with analysis occurring within 3 days at 20°C or 8 days at 4°C.