METABOLIC RESPONSE IN SKELETAL-MUSCLE FIBERS OF STANDARD-BRED TROTTERS AFTER RACING

Histochemical and biochemical analyses were performed on muscle biopsi es obtained after racing from the gluteus muscle of 18 standardbred tr otters. Fibre type composition and enzyme activities varied among the horses. The percentage of type IIB fibres showed a positive correlatio n to the lactate dehydrogenase activity and a negative correlation to the citrate synthase activity. ATP concentrations in whole muscle afte r racing showed a negative correlation to both lactate and IMP concent rations. Within individual fibres, ATP concentrations varied markedly, with some type II fibres having Values as low as 1-5 mmol/kg d.w. and some fibres having values as high as 40-58 mmol/kg d.w., whereas mean ATP concentration for whole muscle was 18.3 +/- 7.7 mmol/kg d.w. Some fibres with low ATP concentrations revealed high IMP concentrations. Blood samples taken after racing showed high values for lactate, ammon ia, and uric acid in plasma. Muscle AMP and ADP concentrations after r acing were related to the horses placing in a race, with higher concen trations giving a lower placing. The results of this study show that a denine nucleotide breakdown in muscle is of great importance for energ y release during racing, and that ATP and IMP concentrations may vary markedly among individual fibres. Thus, metabolite analyses on whole m uscle must be evaluated with caution, as this only represents a mean v alue for metabolic responses in different fibres during racing. (C) 19 97 Elsevier Science Inc.