Insulin sensitivity in Belgian horses with polysaccharide storage myopathy.
OBJECTIVE
To determine insulin sensitivity, proportions of muscle fiber types, and activities of glycogenolytic and glycolytic enzymes in Belgians with and without polysaccharide storage myopathy (PSSM).


METHODS
10 Quarter Horses (QHs) and 103 Belgians in which PSSM status had been determined.


METHODS
To determine insulin sensitivity, a hyperinsulinemic euglycemic clamp (HEC) technique was used in 5 Belgians with PSSM and 5 Belgians without PSSM. Insulin was infused i.v. at 3 mU/min/kg for 3 hours, and concentrations of blood glucose and plasma insulin were determined throughout. An i.v. infusion of glucose was administered to maintain blood glucose concentration at 100 mg/dL. Activities of glycogenolytic and glycolytic enzymes were assessed in snap-frozen biopsy specimens of gluteus medius muscle obtained from 4 Belgians with PSSM and 5 Belgians without PSSM. Percentages of type 1, 2a, and 2b muscle fibers were determined via evaluation of >or= 250 muscle fibers in biopsy specimens obtained from each Belgian used in the aforementioned studies and from 10 QHs (5 with PSSM and 5 without PSSM).


RESULTS
Belgians with and without PSSM were not significantly different with respect to whole-body insulin sensitivity, muscle activities of glycogenolytic and glycolytic enzymes, or proportions of muscle fiber types. However, Belgians had an increased proportion of type 2a and decreased proportion of type 2b muscle fibers, compared with proportions in QHs, regardless of PSSM status.


CONCLUSIONS
PSSM in Belgians may be attributable to excessive glycogen synthesis rather than decreased glycogen utilization or enhanced glucose uptake into muscle cells.
Firshman
Anna M
AM
Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR 97331, USA.
Valberg
Stephanie J
SJ
Baird
John D
JD
Hunt
Luanne
L
DiMauro
Salvatore
S
D000818:Animals; D001706:Biopsy / Q000662:veterinary; D001786:Blood Glucose / Q000378:metabolism; D005260:Female; D015309:Glucose Clamp Technique / Q000662:veterinary; D006008:Glycogen Storage Disease / Q000097:blood / Q000201:enzymology / Q000662:veterinary*; D006651:Histocytochemistry / Q000662:veterinary; D006734:Horse Diseases / Q000097:blood*; D006736:Horses; D007328:Insulin / Q000097:blood; D007333:Insulin Resistance / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism; D009140:Musculoskeletal Diseases / Q000097:blood / Q000201:enzymology / Q000662:veterinary*; D025203:Phosphofructokinase-1, Muscle Type / Q000378:metabolism; D010733:Phosphoglucomutase / Q000378:metabolism; D010736:Phosphoglycerate Mutase / Q000378:metabolism; D010762:Phosphorylase a / Q000378:metabolism
D001786:Blood Glucose; D007328:Insulin; D007770:L-Lactate Dehydrogenase; D010762:Phosphorylase a; D025203:Phosphofructokinase-1, Muscle Type; D010736:Phosphoglycerate Mutase; D010733:Phosphoglucomutase