Glucose uptake in horses with polysaccharide storage myopathy

Abstract

Abstract Objective To determine whether excessive glycogen accumulation in skeletal muscle of Quarter Horses with polysaccharide storage myopathy (PSSM) is a result of enhanced cellular uptake of glucose. Animals 6 horses with PSSM and 10 healthy (control) horses. Procedure Intravenous glucose tolerance tests (IVGTT), oral glucose tolerance 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 administration. Results Peak glucose concentrations during IVGTT were similar for both groups 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 glucose 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 low blood glucose concentrations for more than 3 hours after insulin injection, whereas blood glucose concentrations in controls returned to baseline values within 2 hours. Conclusions Quarter Horses with PSSM have enhanced cellular uptake of glucose that may be, in part, caused by an increased sensitivity to insulin. Clinical Relevance Horses with PSSM have an increased rate of glucose clearance in response to insulin secretion. Thus, diets low in soluble carbohydrate may be the most effective way to decrease glycogen accumulation in skeletal muscle of these horses. (Am J Vet Res 1999;60:458-462)