Effects of prior exercise on components of insulin signalling in equine skeletal muscle.

This study explores the impact of exercise on elements of insulin regulation in horse muscle. It suggests that high levels of insulin and previous exercise activity boost certain biochemical processes in muscle tissue, bringing about improved glucose use.

Objective and Hypothesis

The main objective was to investigate the role that exercise plays in enhancing glucose utilisation in muscle tissue. The scientists focused on the signalling components Akt and glycogen synthase kinase-3 (GSK3). These two components are involved in insulin’s regulation of glycogen synthase (GS) activity – the process that converts glucose into glycogen for storage. The researchers hypothesised that high levels of insulin (hyperinsulinaemia) and prior exercise would cause an increase in Akt phosphorylation and GSK3beta deactivation, thus increasing the insulin stimulation of GS activity in skeletal muscle.

Methods

• Eight Standardbred horses were used for the study.
• A euglycaemic-hyperinsulinaemic clamp (EHC) was performed either without prior exercise (NonEX), or 0.5 hours, 4 hours or 24 hours post exercise.
• Samples were collected before and at the end of each EHC to measure Akt and GSK3 serine phosphorylation, and GS fractional velocity (GSFV, a measure of GS activity).
• Protein separation was conducted using SDS-PAGE on polyacrylamide gels, and blots were probed with antibodies against phospho-Akt and GSK3alpha/beta.

Results

• GSFV increased two-fold at 0.5, 4 and 24 hours post-exercise compared to NonEX in Pre-INS and increased by 33% and 28% in NonEX and at 24 PostEX, respectively, when compared to Pre-INS in these trials.
• Phospho-Akt increased only at 0.5 PostEX in Pre-INS but increased in all trials in Post-INS.
• Phospho-GSK3alpha was also greater at 0.5 PostEX in Pre-INS than in NonEX and 24 PostEX, and in Post-INS it increased in NonEX and at 24 PostEX but not at 0.5 PostEX or 4 PostEX post exercise.
• There was no effect of time or treatment on GSK3, phosphorylation or on total GSK3.

Conclusions

Increased levels of plasma insulin and prior exercise were linked with Akt activation and GSK3alpha deactivation, particularly during the early post-exercise period. This indicates that the physiological effects of exercise on insulin mechanisms begin soon after activity has ended. The changes were consistent with insulin signalling downstream from these molecules, suggesting that they could play a critical role in insulin regulation in muscle tissues.