Immunohistochemical analysis of MCT1 and CD147 in equine skeletal muscle fibres.

Monocarboxylate transporter 1 (MCT1) and its ancillary protein CD147 facilitate efflux of lactate from the muscle. Expression of MCT1 and CD147 were studied with immunohistochemistry in type I, IIA, IIAB and IIB fibres of equine gluteal muscle. Staining intensity of MCT1 in the cytoplasm as well as in the membranes of fibre types decreased in the order I=IIA>IIAB>IIB and correlated with the oxidative capacity. Capillaries were pronounced in the MCT1 staining. CD147 antibody stained plasma membranes of all fibre types evenly, whereas the staining in the cytoplasm followed that of MCT1. In the middle gluteal muscle the expression of MCT1 follows the oxidative capacity of muscle fibres, but the expression of CD147 in sarcolemma does not vary among fibre types. The use of horse specific MCT1 and CD147 antibodies can in future studies help to evaluate lactate efflux from different muscle fibre types.

Altered homeostasis of extracellular matrix proteins in joints of standardbred trotters during a long-term training programme.

This study evaluates how strenuous training, age and lameness influence the release of cartilage oligomeric matrix protein (sf-COMP), aggrecan and collagen type II into synovial fluid in 28 (19.5-40 months) Standardbred trotters (STB), during a long-term training programme (24 months). All the horses were trained by the same trainer and were healthy on entering the training programme. Synovial fluid (sf) from the left middle carpal joint in each subject was sampled every third month. Enzyme-linked immunosorbent assay was used to determine the concentrations of sf-COMP, sf-aggrecan and sf-collagen type II. Concentration of sf-COMP decreased with increasing age and total days of training. The concentration of sf-COMP was found similarly related to both age and total days of training, so they could not be differentiated. It was also shown that the concentration of collagen type II degradation products increased with total days of training. The study shows that extensive and long-term training programme induces metabolic changes in articular cartilage exemplified by reduced release and synthesis of COMP. This is most likely due to strenuous training leading to inappropriate load on the articular cartilage.

Muscle characteristics and plasma lactate and ammonia response after racing in Standardbred trotters: relation to performance.

Blood samples from the jugular vein and muscle biopsies (gluteus medius) in 25 Standardbred trotters were obtained 5-10 min after racing. The biopsies were analysed for fibre type composition and enzymatic profile and blood samples for plasma lactate and ammonia concentrations. Muscle characteristics, plasma lactate and ammonia concentrations after racing were compared with each horse's individual performance index (IPI). The IPI is calculated annually from the individual horse's racing performance (% placing 1, 2 or 3, total annual earnings, average earning per start, and best racing record), respectively, converted to and expressed as a percentage deviation from the average record of the same sex and age group. The IPI values were 100-116. Plasma lactate concentrations were 15.0-42.7 mmol/l (mean 31.3 mmol/l) and ammonia concentrations 65-210 micromol/l (mean 141 micromol/l) after racing. Fibre type composition varied among horses (range 9-27% for Type I, 32-54% for Type IIA, and 27-46% for Type IIB). Fibre type composition, enzyme activities, plasma lactate and ammonia responses to racing were not correlated to IPI. Ten of the horses also performed a submaximal test on the track, consisting of 5 incremental 1000 m heats at approximate speeds of 9.1, 9.5, 10.0, 10.5, and 11.1 m/s. Immediately after each heat a blood sample was drawn from the jugular vein for plasma lactate analysis. Plasma lactate response to exercise differed between horses, but no correlation was seen with IPI. Muscle characteristics, plasma lactate and ammonia concentrations after racing and lactate response to a submaximal track test did not correlate with current race performance expressed as IPI in a group of horses with average or better performance capacity at the time of testing. Analysis of lactate and ammonia in blood after racing is not a valuable tool to predict an individual performance index.

Metabolic response in skeletal muscle fibres of standardbred trotters after racing.

Histochemical and biochemical analyses were performed on muscle biopsies obtained after racing from the gluteus muscle of 18 standardbred trotters. Fibre type composition and enzyme activities varied among the horses. The percentage of type IIB fibres showed a positive correlation to the lactate dehydrogenase activity and a negative correlation to the citrate synthase activity. ATP concentrations in whole muscle after racing showed a negative correlation to both lactate and IMP concentrations. 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, ammonia, and uric acid in plasma. Muscle AMP and ADP concentrations after racing were related to the horses placing in a race, with higher concentrations giving a lower placing. The results of this study show that adenine nucleotide breakdown in muscle is of great importance for energy release during racing, and that ATP and IMP concentrations may very markedly among individual fibres. Thus, metabolite analyses on whole muscle must be evaluated with caution, as this only represents a mean value for metabolic responses in different fibres during racing.

Skeletal muscle characteristics and metabolic response to exercise in young standardbreds.

OBJECTIVE: To determine whether performance capacity in a group of young trained Standardbreds is related to skeletal muscle characteristics and metabolic response to exercise. ANIMALS: 13 clinically normal 2-year-old Standardbreds. PROCEDURE: Venous blood and middle gluteal muscle biopsy samples were obtained from each horse within 1 to 2 minutes after trotting at high speed for 1,600 m. RESULTS: There was a positive correlation between plasma lactate and muscle glucose-6-phosphate (G-6-P) concentrations and trotting speed. There was a negative correlation between muscle adenosine triphosphate concentration and trotting speed, plasma lactate concentration, and muscle lactate and G-6-P concentrations. Muscle concentration of G-6-P was positively correlated with muscle lactate and plasma lactate concentrations. Percentage of type-1, -2A, and -2B fibers in skeletal muscle and muscle enzyme activities of hexokinase, 3-OH-acyl-CoA dehydrogenase, lactate dehydrogenase, and citrate synthase were not correlated with trotting speed. CONCLUSION: Speed of trotting at a distance of 1,600 m in young trained Standardbreds is related to the ability of muscle to produce energy by use of anaerobic glycolysis.

Plasma lactate response to submaximal and maximal exercise tests with training, and its relationship to performance and muscle characteristics in standardbred trotters.

Seven young Standardbred trotters, born, raised and trained at the same camp, performed submaximal and maximal work tests on a track. The submaximal test consisted of four 1,000 m runs at the trot, with increasing speed at each run. Each horse performed this test when 24, 26, 29 and 40 months old. The maximal test consisted of trotting 1,600 m and was performed at 24 and 29 months of age. Blood samples for plasma lactate analyses were obtained after each run, during the submaximal test and after the maximal test. Muscle biopsy samples were obtained at 24 and 29 months of age. The results showed marked individual differences in lactate response to submaximal effort. Early training only appeared to influence plasma lactate response in some horses. After 40 months of age the lactate response to the final submaximal test was significantly lower (7.2 mmol/l) than at 29 months (14.5 mmol/l). A negative correlation was found between lactate concentration after all runs in the submaximal test, and the horses speed over 1,600 m. No correlations were found between lactate concentration after the maximal test and the horses' speed. The activity of citrate synthase, a marker for muscle oxidative capacity, increased from 24 to 29 months of age. The proportion of Type IIB fibres decreased, whereas that of Type I fibres increased. It is concluded that lactate response to a submaximal work test on a track can be an important tool for evaluating performance capacity of an individual horse.