The impact of prolonged hyperinsulinaemia on glucose transport in equine skeletal muscle and digital lamellae.

The research investigates the effect of prolonged high insulin levels on glucose transport in horses’ skeletal muscle and digital lamellae (tissues in the hooves), focusing on their relationship with laminitis, a painful condition in equines. The study compares the protein expression of glucose transporters in healthy horses and during periods of increased insulin levels.

Objective and Hypothesis

• The study was designed to compare the protein expression of major glucose transporter (GLUT) isoforms in the muscle and digital lamellae in healthy horses and during periods of high insulin levels.
• The hypothesis was that prolonged high insulin levels alter the regulation of glucose transport in insulin-sensitive tissue and digital lamellae, potentially contributing to laminitis.

Methodology

• The research was a randomized, controlled study. The prolonged hyperinsulinemia and lamellar damage in horses were induced either by a prolonged euglycaemic-hyperinsulinaemic clamp (a method that maintains blood glucose and insulin at constant, elevated levels) or a prolonged glucose infusion.
• The results were then compared with the control group – horses treated with electrolytes.
• Protein expression of GLUTs in the skeletal muscle and lamellae was examined with immunoblotting, a technique used to detect specific proteins.

Results

• Lamellae tissue showed more GLUT1 protein than skeletal muscle and less GLUT4 than the heart.
• During periods of high insulin and acute laminitis, the GLUT1 protein expression decreased in skeletal muscle but remained unchanged in the lamellae, while the expression of new GLUTs (8 and 12) increased in the lamellae but not in skeletal muscle.
• However, moderate hyperinsulinemia and subclinical laminitis did not result in differential GLUT protein expression in the lamellae compared to control horses.

Conclusions

• The findings suggest that lamellar tissue operates independently of insulin, leading to the conclusion that insulin resistance may not be a necessary element in the development of laminitis.
• Significant differences in GLUT expression were found between insulin-sensitive and insulin-independent tissues during metabolic dysfunction in horses. These different expression profiles of novel GLUTs during acute and subclinical laminitis could be critical to understanding the pathology of the disease and warrant further research.