Open access publications in the SLU publication database

Abstract

The first aim of the present thesis was to establish a method for determination of proglycogen (PG) and macroglycogen (MG) in equine skeletal muscle. The measurement technique for determination of PG and MG was accurate and gave reproducible results. There was an excellent correlation for total glycogen determined in muscle biopsy specimens between the new PG and MG technique and the traditional acid hydrolysis method. A further aim was to examine the degradation of PG and MG in Standardbreds during a maximal exercise test. Horses performed an incremental maximal treadmill exercise test in one-minute steps until they no longer could keep pace with the treadmill. The exercise test induced an anaerobic metabolic response as demonstrated by decreased glycogen, ATP and creatine phosphate and increased lactate in muscle after exercise. The two fractions of glycogen contributed equally to glycogenolysis, 48% and 52% of total glycogen degradation for PG and MG respectively. A study was also performed to determine the degradation and resynthesis of PG and MG in skeletal muscle after intermittent exercise on a slope. At a training camp well trained Standardbreds performed a training session comprising a warm up period, seven repeated 500 m bouts of uphill exercise and a recovery period. Muscle biopsies were taken at rest, at the end of exercise and 1, 4, 8, 24, 48 and 78 hours post exercise. The exercise caused degradation in MG that was twice as large as for PG. The rate of glycogen resynthesis during 1 to 24 hours post exercise was higher for MG than PG. The rate of muscle glycogen synthesis thereafter was slower and did not differ between MG and PG up to 72 hours. The last study was conducted in order to determine PG, MG, glucose and glucose-6-phosphate (G-6-P) in skeletal muscle of horses with polysaccharide storage myopathy (PSSM) before and after light exercise. Horses with PSSM completed repeated intervals of 2 minutes of walking followed by 2 minutes of trotting until muscle cramping developed. Untrained control horses performed a similar exercise test for up to 20 minutes. Before exercise muscle glycogen concentrations were 1.5, 2.2 and 1.7 times higher for PG, MG and total glycogen respectively in PSSM horses compared to control horses. No changes in total glycogen, PG, MG, G-6-P and lactate were found after exercise. However, free glucose concentration increased in skeletal muscle in PSSM horses after exercise indicating that glucose uptake in skeletal muscle is augumented after light exercise.