Insulin sensitivity in Belgian horses with polysaccharide storage myopathy.

This research studied insulin sensitivity, muscle fiber types, and the activity of certain enzymes in Belgian horses with and without a condition called polysaccharide storage myopathy (PSSM). The researchers found that the presence of PSSM in these horses did not significantly affect these variables, but all Belgian horses had a higher proportion of certain muscle fiber types compared to Quarter Horses. It was suggested that PSSM in Belgian horses might be due to excess glycogen production rather than issues with glycogen use or glucose uptake into muscle cells.

Insulin Sensitivity and PSSM

• The study aimed to find out if PSSM, a muscle disorder common in some breeds of horses, had an effect on insulin sensitivity, muscle fibers, and the activity of enzymes involved in the breakdown of glycogen (glycogenolytic) and glucose (glycolytic).
• The researchers used a method known as the hyperinsulinemic euglycemic clamp (HEC) technique to assess insulin sensitivity in 5 Belgians with PSSM and 5 without the condition. Insulin and glucose were administered intravenously and the levels of glucose and insulin in the blood were monitored throughout the process.
• The insulin sensitivity of horses with PSSM was compared with those without PSSM. The results showed that the disease did not significantly affect the whole-body insulin sensitivity of Belgian horses.

Enzyme Activity and Muscle Fibers

• The activity of glycogenolytic and glycolytic enzymes was also assessed in muscle biopsy samples from Belgians with and without PSSM. These enzymes are responsible for the breakdown of stored glycogen and glucose respectively in the body.
• Just like insulin sensitivity, the activities of these enzymes were also found to be similar in both groups of horses. This implies that PSSM does not affect their functioning.
• Further, the study went on to analyze the proportions of type 1, 2a, and 2b muscle fiber types in Belgians and compared them with those of 10 Quarter Horses. The results showed that Belgians, irrespective of their PSSM status, had a higher proportion of type 2a and a lower proportion of type 2b muscle fibers when compared to Quarter Horses.

Conclusion in Relation to PSSM

• Despite the variations in muscle fiber types, the study could not find any significant differences in insulin sensitivity or enzyme activities between Belgians with and without PSSM.
• The researchers concluded that PSSM in Belgians may not be due to impaired glycogen utilization or enhanced glucose uptake into muscle cells as previously thought. Rather, it may be attributable to excessive glycogen synthesis. This implies that the body might be making more glycogen than necessary which gets accumulated in the muscles leading to PSSM.