The Effects of an Oral Glucose Polymer on Muscle Glycogen Resynthesis in Standardbred Horses

Abstract

In the horse there have been various studies inves tigating muscle adaptations to exercise (EssA©n et al. 1980, Hodgson and Rose 1987, Hodgson et al. 1985, Lindholm 1974, Lindholm and Piehl 1974, Snow et al. 1981), but the area of postexercise muscle glycogen resynthesis has received little attention. In humans, provision of a glucose supplement immediately postexercise increases the rate of muscle glycogen repletion (Ivy et al. 1988). However, in horses low-, moderateand high-carbohydrate diets had similar effects on muscle glycogen resynthesis when studied at 12 and 24 h after exercise (Snow et al. 1987). The aim of the current investigation was to examine the effect of the postexercise administration of an oral glucose polymer on the rate of skeletal muscle gly cogen resynthesis in the horse. In particular, we sought to determine whether glycogen resynthesis could be enhanced in the first 12 h after submaximal and max imal exercise. Materials and Methods. Four Standardbred geld ings aged 5.5 ±2.9 y (mean ±SEM)and 512 ±29 kg body weight were randomly allocated to treatments in a crossover design. Testing was carried out on con secutive weeks with all horses being tested at the same time and on the same day each week. The research protocal was approved by The University of Sydney Animal Ethics committee. Each horse was exercised on an inclined treadmill for 45 min at 30% VO2maxand 15 min at 50% VO2max, after which they were rested for 30 min. This was fol lowed by six 1-min sprints at 100% VO2maxwith 5min rest periods between sprints. Muscle biopsies were taken using the needle biopsy technique as described in Lindholm and Piehl (1974). Biopsies were taken from the m. gluteus mA©dius at a depth of 8 cm using the same locations in each horse. Samples were taken at rest, at the end of the exercise period and at 3, 6, 9, 12 and 24 h after treatment. Blood samples were collected every 30 min for 6 h after the treatment. Samples for glucose analysis were collected into chilled 5-ml evacuated tubes containing potassium oxalate and sodium fluoride, whereas those for insulin were collected into chilled 5-ml evacuated tubes containing lithium heparin. The blood was centrifuged for 15 min at 3000 rpm and plasma stored at -20°Cuntil assays were conducted.