Effects of submaximal exercise on adenine nucleotide concentrations in skeletal muscle fibers of horses with polysaccharide storage myopathy.

The study investigates how submaximal exercise impacts adenine nucleotide concentrations in horses stricken with polysaccharide storage myopathy (PSSM), aiming to analyze if the breakdown of ATP and the consequential degradation of adenine nucleotides potentially lead to rhabdomyolysis in these horses.

Study Methodology

• The study involved seven horses diagnosed with PSSM and four control horses.
• The horses with PSSM were directed to perform intervals of walk and trot exercises on a treadmill until visible signs of muscular cramping appeared.
• The control horses were subjected to a similar exercise routine for a period of 20 minutes.
• Four hours post-exercise, the researchers measured and documented serum creatine kinase (CK) activity in these horses.
• They collected specimens from the gluteal muscle and measured the activities of citrate synthase (CS), 3-OH-acylCoA dehydrogenase, and lactate dehydrogenase before the commencement of the exercise.
• Similarly, the concentrations of glucose-6-phosphate (G-6-P) and lactate were measured in these muscle specimens before and after the exercise.
• The concentrations of ATP, ADP, AMP, and inosine monophosphate (IMP) were documented before and after exercise from samples drawn from whole muscle, pooled single muscle fibers, and individual muscle fibers.

Study Findings

• The study recorded a range of 255 to 22,265 U/L in serum CK activity in PSSM horses and 133 to 278 U/L in control horses.
• Compared to the control group, the muscle CS activity was recorded lower in PSSM horses.
• Changes in concentrations of lactate, ATP, ADP, and AMP in the whole muscle remained unaffected by exercise in all horses.
• An increase in concentration of IMP in whole muscle, pooled muscle fibers, and individual muscle fibers was observed in PSSM horses following exercise.
• Within individual muscle fibers, researchers documented significant variations in ATP and IMP concentrations.

Conclusion

• The research concludes that horses suffering from PSSM experienced an increase in IMP concentration without a corresponding depletion of ATP within individual muscle fibers during submaximal exercise.
• This phenomenon of energy imbalance, as suggested by the study, may contribute to exercise intolerance and the onset of rhabdomyolysis in horses with PSSM.