Glucose uptake in horses with polysaccharide storage myopathy

Objective-To determine whether excessive glycogen accumulation in skeletal muscle of Quarter Horses with polysaccharide storage myopathy (PSSM) is a r esult of enhanced cellular uptake of glucose. Animals-6 horses with PSSM and 10 healthy (control) horses. Procedure-Intravenous glucose tolerance tests (IVGTT), oral glucose toleran ce tests (OGTT), and modified insulin tolerance tests (MITT) were performed . Plasma glucose and insulin concentrations were measured in blood samples collected before and for up to 8 hours after glucose or insulin administrat ion. Results-Peak glucose concentrations during IVGTT were similar for both grou ps of horses, but rate of glucose clearance was 1.5 times faster in horses with PSSM than in controls. Moreover, circulating concentrations of insulin before and after glucose injection were lower in the PSSM group. Blood glu cose concentrations from minute 90 to minute 300 of the OGTT were lower in horses with PSSM than in controls. The MITT resulted in acute decreases in blood glucose concentrations in both groups of horses; however, horses with PSSM sustained tow blood glucose concentrations for more than 3 hours afte r insulin injection, whereas blood glucose concentrations in controls retur ned to baseline values within 2 hours. Conclusions-Quarter Horses with PSSM have enhanced cellular uptake of gluco se that may be, in part, caused by an increased sensitivity to insulin. Clinical Relevance-Horses with PSSM have an increased rate of glucose clear ance in response to insulin secretion. Thus, diets tow in soluble carbohydr ate may be the most effective way to decrease glycogen accumulation in skel etal muscle of these horses.