Responses to sprint exercise in the greyhound: effects on haematology, serum biochemistry and muscle metabolites

To investigate the haematological, biochemical and metabolic response of greyhounds to sprint exercise, five greyhound dogs with previously placed carotid arterial catheters were sprinted over a distance of 400 m, chasing a lure. The time to complete the 400 m ranged from 25 to 27 seconds. Before exercise and at intervals for up to one hour after exercise, arterial blood samples were collected for haematology, serum biochemistry, plasma lactate and arterial blood gas measurements. Muscle samples for metabolite measurements were collected by needle biopsy of the vastus lateralis muscle. Red cell indices were increased for up to 20 minutes after exercise and there was a transient leucocytosis and neutrophilia. Serum biochemical changes reflected some fluid movement from the vascular compartment, there being increases in osmolality and total protein. Other changes included significant increases over resting control values for serum glucose, creatinine and potassium. The tension of oxygen in arterial blood was increased after exercise, while that of carbon dioxide fell, and there was a decrease in arterial pH. These changes were no longer significant by 30 minutes after exercise. The mean rectal temperature increased to 41 degrees C after exercise and remained elevated up to and including the 30 minutes after exercise measurement. No changes were found in muscle ATP or glycogen from before to after exercise. However, concentrations of muscle glucose and glucose-6-phosphate were increased immediately after exercise. Muscle and plasma lactate concentrations showed a similar time course for disappearance and after peaking at 27 mmol litre-1, five minutes after exercise, the plasma lactate returned towards pre-exercise values by 30 minutes after exercise.     

Effects of oral administration of sodium citrate or acetate to pigs on blood parameters, postmortem glycolysis, muscle pH decline, and quality attributes of pork

The objective of this study was to determine the effects of oral administration of sodium citrate (CIT) or acetate (ACE) to pigs on blood parameters, postmortem glycolysis, pH decline, and quality attributes of pork. Previous studies have shown that CIT has the potential to inhibit phosphofructokinase (PFK), a key enzyme in postmortem muscle glycolysis. In Exp. 1, CIT, ACE, or water was orally administered (0.75 g/kg of BW) to 24 pigs. After a 30-min rest, pigs were exercised, and blood samples were taken at 45 and 75 min after oral treatment. Citrate and ACE tended (P = 0.08) to increase blood pH and increased (P = 0.02) bicarbonate levels immediately after exercise. After a 30-min rest, blood pH of pigs administered ACE tended (P = 0.09) to remain higher, whereas blood pH of CIT-treated pigs was similar to that of control pigs. Bicarbonate levels in ACE- and CIT-treated pigs were still greater (P < 0.05) than those of control pigs at 75 min after oral treatment. In Exp. 2, 30 pigs were administered CIT, ACE, or water 45 min before stunning (electric plus captive bolt). Antemortem treatments had no effect (P > 0.10) on muscle pH or postmortem concentrations of the glycolytic metabolites of glucose-6 phosphate, fructose-6 phosphate, fructose-1,6 bisphosphate, glyceraldehyde-3 phosphate, dihydroxyacetone phosphate, or lactate. Minor, but inconsistent, differences in quality attributes were found in LM chops, and no differences in quality attributes were found between control and CIT- or ACE-treated pigs for inside and outside semimembranosus muscles (P > 0.10). There was no significant inhibition of the PFK enzyme by orally administered CIT or ACE; however, the PFK glycolytic metabolite data analysis indicated that PFK was a main regulatory enzyme in postmortem muscle.     

Effects of exercise on skeletal muscle and serum enzyme activities in pigs

In order to determine skeletal muscle and serum enzyme activities following exercise, six adult Landrace pigs were submitted to 10 min running on a treadmill (0.5 m/s, on a 12% gradient) and compared to six controls. Blood samples were obtained just before the exercise, immediately after, and 24 h, 48 h and 144 h after exercise. Muscle biopsies were taken from the longissimus dorsi and biceps femoris 24 h after exercise. Total lactic dehydrogenase (LDH) and LDH isoenzymes in muscle and serum were unchanged. In muscle homogenates, there was no difference in total creatine phosphokinase (CK) activity between the two groups. Total CK activity in the biceps femoris muscle represented only 59% of that observed in the longissimus dorsi muscle. A mean CK-MB value of 2.5% was found in the control group for both muscles but after exercise it was 9.5% (p<0.05) for the biceps femoris and 12.2% (p<0.01) of the longissimus dorsi muscle. In serum, the total CK (p<0.05), CK-MM (p<0.05) and CK-BB (p<0.05) increased immediately after the exercise, followed by a progressive decrease.     

Free Radical Formation after Intensive Exercise in Thoroughbred Skeletal Muscles

Although high oxygen consumption in skeletal muscle may result in severe oxidative stress, there are no direct studies that have documented free radical production in horse muscles after intensive exercise. To find a new parameter indicating the muscle adaptation state for the training of Thoroughbred horses, we examined free radical formation in the muscle by using electron paramagnetic resonance (EPR). Ten male Thoroughbred horses received conventional training for 18 weeks. Before and after the training period, all horses performed an exhaustive incremental load exercise on a 6% incline treadmill. Muscle samples of the middle gluteal muscle were taken pre-exercise and 1 min, 1 hr, and 1 day after exercise. Muscle fiber type composition was also determined in the pre-exercise samples by immunohistochemical staining with monoclonal antibody to myosin heavy chain. We measured the free radical in the muscle homogenate using EPR at room temperature, and the amount was expressed as relative EPR signal intensity. There was a significant increase in Type IIA muscle fiber composition and a decrease in Type IIX fiber composition after the training period. Before the training period, the mean value of the relative EPR signal intensity showed a significant increase over the pre-exercise value at 1 min after the exercise and an incomplete recovery at 24 hr after the exercise. While no significant changes were found in the relative EPR signal intensity after the training period. There was a significant relationship between percentages of Type IIA fiber and change rates in EPR signal intensity at 1 min after exercise. The measurement of free radicals may be useful for determining the muscle adaptation state in the training of Thoroughbred horses.     

Effect of creatine supplementation on muscle metabolic response to a maximal treadmill exercise test in Standardbred horses

The aim of the present study was to investigate the effect of creatine (Cr) supplementation on muscle metabolic response in connection with a maximal treadmill exercise test, known to cause a marked anaerobic metabolic response and adenine nucleotide degradation. First, 6 Standardbred trotters performed a standardised maximal exercise test until fatigue (baseline test). The test used was an inclined incremental treadmill test in which the speed was increased by 1 m/s, starting at 7 m/s, every 60 s until the horse could no longer keep pace with the treadmill. After this baseline test, the horses were separated into 2 equal groups. One half received a dose of 25 g creatine monohydrate twice daily, and the other group were given the same dose of lactose (placebo). The supplementation period was 6.5 days, after which the maximal treadmill exercise test was performed again. A washout period of 14 days was allowed before treatments were switched between groups and a new supplementation period started. After this second supplementation period a new maximal exercise test was performed. After supplementation with creatine or placebo, horses were stopped after performing the same number of speed steps and duration of exercise as they had in the baseline test. Blood samples for analysis of plasma lactate, creatine (Cr), creatinine, hypoxanthine, xanthine and uric acid concentrations were collected at rest, during each speed step and during recovery. The total blood volume (TBV) was also determined. Muscle biopsies for analysis of muscle metabolites (adenosine triphosphate [ATP], adenosine diphosphate [ADP], adenosine monophosphate [AMP], inosine monophosphate [IMP], creatine phosphate [CP], lactate [La] and glycogen) were taken at rest, immediately post exercise and after 15 min recovery. The results showed no significant increase in plasma Cr or muscle total creatine concentration (TCr) after supplementation with Cr. At the end of exercise ATP and CP concentrations had decreased and IMP and lactate concentrations increased in muscle in all groups. Plasma lactate concentration increased during exercise and recovery and plasma uric acid concentration increased during recovery in all groups. No influence could be found in TBV after supplementation with creatine. These results show that creatine supplementation in the dosage used in this study had no influence on muscle metabolic response or TBV.     

Effects of nandrolone treatment on recovery in horses after strenuous physical exercise

To test the effect of nandrolone on their recovery, six adult half-bred riding horses performed a competition exercise test (CET) and a standardized exercise test (SET) on consecutive days before and after a 2-week treatment with the anabolic steroid nandrolone laurate. Blood samples were collected during and between these tests for the determination of red cell volume and concentrations of blood lactate, plasma glucose, non-esterified fatty acids, glycerol, triglycrides, erythropoietin, cortisol, insulin, and glucagon. Muscle biopsy specimens were taken immediately after the CET and before the SET for analysis of glycogen content, citrate synthase, and 3-hydroxyacyl CoA dehvdrogenase activity. Nandrolone administration increased the rate of muscle glycogen repletion after exercise, an increase that may be explained by increased glucose output by the liver, higher plasma insulin concentration, and increased insulin-independent glucose transport, but not by better availability of lipid fuels during recovery.     

Dietary sodium bicarbonate as a treatment for exertional rhabdomyolysis in a horse

A 3-year-old mare repeatedly had clinical signs of rhabdomyolysis on mild exertion. Serum creatine kinase and aspartate transaminase activities were high at rest. Responses to dietary sodium bicarbonate were tested through 7 alternating periods of supplementation of a basal ration of timothy hay and oats. Physical signs; venous blood pH and gases; blood glucose and lactate; serum electrolytes, enzymes, and creatinine; and urine pH were monitored before and after exercise. Dietary sodium bicarbonate raised resting venous blood pH and bicarbonate slightly and significantly increased urine pH from pH 7.46 to 8.2 (P less than 0.001). An exercise test included 5 minutes at the walk followed by 20 minutes at the trot. The exercise induced gait stiffness, muscle fasciculations, and muscle induration when the diet was not supplemented, but not when it was supplemented with sodium bicarbonate. Myoglobin was present in 16 of 21 urine samples after exercise during nonsupplemented periods, but only in 3 of 28 urine samples during supplemented periods (P less than 0.0001). Bicarbonate supplementation significantly decreased the responses of blood lactic acid, serum creatine kinase, and aspartate transaminase to exercise. Supplementation of the diet was associated with higher venous blood pH and bicarbonate ion concentrations throughout exercise. Dietary sodium bicarbonate apparently mitigated or prevented physical, chemical, and enzymatic characteristics of exertional rhabdomyolysis in this mare, possibly through its enhancement of buffering capacity in muscle tissue fluids.     

Effects of a submaximal treadmill training programme on histochemical properties, enzyme activities and glycogen utilisation of skeletal muscle in the horse

The effects of training on skeletal muscle composition were studied in four Standardbred geldings given a seven week submaximal treadmill training programme. Before the start of training, muscle biopsies were collected from the left middle gluteal muscle for the determination of muscle fibre types, oxidative capacity and capillary numbers using histochemical techniques. The concentrations of citrate synthase, 3-hydroxyacyl-CoA dehydrogenase (HAD), lactate dehydrogenase and total muscle glycogen were measured using fluorometric methods. Muscle biopsy samples were repeated after one, three, five and seven weeks of training and the same measurements performed. No significant changes were found in muscle fibre types or capillary numbers as a result of training, although there was an increase in the oxidative capacity of the Type IIB fibres after seven weeks training. After seven weeks of training there were also increases in the concentrations of citrate synthase and HAD and a decrease in lactate dehydrogenase. Before commencement of training the horses underwent a standardised submaximal exercise test and muscle glycogen concentrations were measured before and immediately after the exercise. This procedure was repeated after one, three, five and seven weeks of training. A progressive decrease in the rate of glycogen utilisation occurred throughout the period of training, which by seven weeks was 36 per cent lower than that before training.     

The effect of skeletal muscle needle biopsy on blood constituents, muscle glycogen and heart rate of cattle

Muscle samples from Friesian bulls were obtained using the Bergstr?m percutaneous biopsy needle. The samples (100 to 200 mg) were suitable for metabolite and enzymic analyses and histological examination in relation to meat quality. The physiological response to biopsy was assessed by measuring serum free fatty acid and blood glucose concentrations, plasma creatine kinase activity and heart rate. Muscle glycogen concentration was also measured. These parameters were unchanged by the experimental procedure, with the exception of blood glucose and heart rate which showed significant increases. The experimental animals showed no adverse effects after repeated biopsy and it is concluded that the technique is suitable for investigating beef muscle metabolism in vivo, and does not cause an unacceptable degree of stress.     

Effects of hypothyroidism on the skeletal muscle blood flow response to contractions

Hypothyroidism is associated with impaired blood flow to skeletal muscle under whole body exercise conditions. It is unclear whether poor cardiac and/or vascular function account for blunted muscle blood flow. Our experiment isolated a small group of hindlimb muscles and simulated exercise via tetanic contractions. We hypothesized that muscle blood flow would be attenuated in hypothyroid rats (HYPO) compared with euthyroid rats (EUT). Rats were made hypothyroid by mixing propylthiouracil in their drinking water (2.35 x 10-3 mol/l). Treatment efficacy was evidenced by lower serum T3 concentrations and resting heart rates in HYPO (both P<0.05). In the experimental preparation, isometric contractions of the lower right hindlimb muscles at a rate of 30 tetani/min were induced via sciatic nerve stimulation. Regional blood flows were determined by the radiolabelled microsphere method at three time points: rest, 2 min of contractions and 10 min of contractions. Muscle blood flow generally increased from rest ( approximately 5-10 ml/min per 100 g) through contractions for both groups. Further, blood flow during contractions did not differ between groups for any muscle (eg. red section of gastrocnemius muscle; EUT, 59.9 +/- 14.1; HYPO, 61.1 +/- 15.0; NS between groups). These findings indicate that hypothyroidism does not significantly impair skeletal muscle blood flow when only a small muscle mass is contracting. Our findings suggest that impaired blood flow under whole body exercise is accounted for by inadequate cardiac function rather than abnormal vascular function.     

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

OBJECTIVE: To determine whether disruption of adenine triphosphate (ATP) regeneration and subsequent adenine nucleotide degradation are potential mechanisms for rhabdomyolysis in horses with polysaccharide storage myopathy (PSSM) performing submaximal exercise. ANIMALS: 7 horses with PSSM and 4 control horses. PROCEDURES: Horses with PSSM performed 2-minute intervals of a walk and trot exercise on a treadmill until muscle cramping developed. Control horses exercised similarly for 20 minutes. Serum creatine kinase (CK) activity was measured 4 hours after exercise. Citrate synthase (CS), 3-OH-acylCoA dehydrogenase, and lactate dehydrogenase activities prior to exercise and glucose-6-phosphate (G-6-P) and lactate concentrations before and after exercise were measured in gluteal muscle specimens. Adenine triphosphate, diphosphate (ADP), monophosphate (AMP), and inosine monophosphate (IMP) concentrations were measured before and after exercise in whole muscle, single muscle fibers, and pooled single muscle fibers. RESULTS: Serum CK activity ranged from 255 to 22,265 U/L in horses with PSSM and 133 to 278 U/L in control horses. Muscle CS activity was lower in horses with PSSM, compared with control horses. Muscle G-6-P lactate, ATP, ADP, and AMP concentrations in whole muscle did not change with exercise in any horses. Concentration of IMP increased with exercise in whole muscle, pooled muscle fibers, and single muscle fibers in horses with PSSM. Large variations in ATP and IMP concentrations were observed within single muscle fibers. CONCLUSIONS AND CLINICAL RELEVANCE: Increased IMP concentration without depletion of ATP in individual muscle fibers of horses with PSSM during submaximal exercise indicates an energy imbalance that may contribute to the development of exercise intolerance and rhabdomyolysis.     

ATP loss with exercise in muscle fibres of the gluteus medius of the thoroughbred horse

Muscle ATP loss with exercise has implications both to the causes of fatigue and muscle damage. To study this at the single muscle fibre level, five trained thoroughbred horses performed consecutive 90 second gallops on an inclined treadmill followed by a final gallop to fatigue. Biopsies of the m. gluteus medius were taken at rest, post-exercise and during 24 hour recovery. Blood lactate was 20·0 mmol litre⁻¹ or more, and plasma NH₃ 300–800 μmol litre⁻¹, following the final gallop. Minimal changes occurred in the plasma markers, and . ATP loss with exercise was 32·2 ( 12·2) per cent. Following exercise single fibre contents showed a much broader distribution than at rest, with contents in some close to zero. Following five and 24 hour recovery, however, frequency distribution curves were close to those seen at rest. There was no difference in the ATP contents of types I, IIa and IIb at rest of with exercise or recovery. The results pointed to marked heterogeneity between individual fibres in their biochemical response with exercise, independent of fibre type.     

Changes in salivary and plasma cortisol levels in Purebred Arabian horses during race training session

Physical activity and stress both cause an increase in cortisol release ratio. The aim of this study was to evaluate the use of saliva samples for the determination of cortisol concentrations indicating the work‐load level in horses during race training. Twelve Purebred Arabian horses aged 3–5 years were studied during the routine training session. After the warm‐up, the horses galloped on the 800 m sand track at a speed of 12.8 m/s. Three saliva samples, and three blood samples were collected from each horse. Both types of samples were taken at rest, immediately after return from the track and after 30 min restitution. The concentrations of blood lactic acid (LA), and cortisol in saliva and plasma samples were measured and analyzed. Blood LA, plasma and salivary cortisol levels increased significantly after exercise (P < 0.05). Salivary cortisol concentration determined 30 min after the exercise correlated significantly with plasma cortisol level obtained immediately after exercise (P < 0.05) as well as measured 30 min after the end of exercise (P < 0.05). The determination of cortisol concentration in saliva samples taken from racehorses 30 min after the end of exercise can be recommended to use in field conditions to estimate the work‐load in racehorses.     

Storage and mobilization of muscle glycogen in exercising horses fed a fat-supplemented diet

In a switchback experiment, six mature mares were fed a control and a fat-supplemented diet while being exercised in a galloping regimen. After three weeks adaptation to each diet, horses performed an exercise test (ET) consisting of four, 600-m gallops. Muscle biopsies were obtained before and after the ET, and blood samples were taken before, during and throughout recovery from the ET. Resting glycogen concentration in the biceps femoris muscle increased (P<.05) from 15.77 mg/g wet tissue when the horses were fed the control diet to 22.89 mg/g when they were fed the fats-supplemented diet. During the ET, the amount of glycogen mobilized by the muscle increased (P<.05) from 6.99 mg/g when the horses were fed the control diet to 13.09 mg/g when they were fed the fat-supplemented diet. When the horses were fed the fat-supplemented diet, they galloped faster (P<.09), at a constant heart rate, during the last two gallops of the ET. Thus, adapting exercising horses to a fat-supplemented diet increased muscle glycogen concentrations, which appeared to enhance their performance past the anaerobic threshold.     

Titrimetric determination of muscle buffering capacity (beta mtitr) in biopsy samples

In vitro titration of muscle homogenates has been used to assess muscle buffering capacity (beta mtitr) in a variety of species. In the present study, factors likely to affect the estimation of beta mtitr were investigated. Also, values of beta mtitr from normal Thoroughbred horses are presented. A non-linear titration curve was obtained with addition of HCl to muscle homogenates. As a result, beta mtitr is expressed as the mumol H+ required to change the pH of 1g of dry muscle or wet muscle from 7.1 to 6.5. An effect of dilution on the initial pH was found below 40 mg wet muscle per ml homogenising reagent (10 mg dry muscle per ml) and on beta mtitr below 10 mg wet muscle. As a result, 40 mg wet muscle or 10 mg dry muscle per ml was chosen as the minimum concentration for determination of beta mtitr. Incubation of homogenates up to 60 mins did not affect beta mtitr significantly. As a mean, beta mtitr in wet muscle was approximately 25 per cent higher compared to dry muscle. The beta mtitr of dry muscle was increased by approximately 18 per cent when HCO3- was added in an amount equivalent to the calculated HCO3- content of wet muscle at rest. The homogenisation process resulted in complete loss of adenosine triphosphate and phosphocreatine with only small changes in adenosine diphosphate and adenosine monophosphate. It was concluded that the estimates of beta mtitr did not include any contribution from 'dynamic' buffering via rephosphorylation of adenosine diphosphate by phosphocreatine, and in dry muscle it was accounted for mainly through physico-chemical buffering by phosphates, proteins and dipeptides. beta mtitr determined in biopsy samples of muscle from 20 Thoroughbred horses ranged from 100.8 to 131.8 mumol H+/g dry muscle pH 7.1 to 6.5 (mean 121.2, sd +/- 7.4).     

Effect of hypophosphatemia on muscle metabolism after exercise in pigs.

Five Swedish Landrace pigs with a mean weight of 51 +/- 5 kg performed an exercise test on a treadmill at a speed of 1.8 m/s and a duration of 10 min. Hypophosphatemia was then induced in these pigs by addition of aluminium hydroxide (liquid antacid) to the normal feed. After 3 weeks, the exercise test was repeated when the mean weight of the pigs was 65 +/- 9 kg. Five other Swedish Landrace pigs with a mean weight of 72 +/- 4 kg performed a similar exercise test. Muscle biopsies from M. biceps and blood samples were taken from all pigs 3-5 days before and immediately after each exercise test. Hypophosphatemic pigs had significantly lower serum phosphate and higher aluminium levels than normophosphatemic pigs. In all pigs, glycogen content in muscle decreased significantly (-108 to -135 mmol/kg muscle) with exercise while no changes were seen in adenosine triphosphate, creatine phosphate or inorganic phosphate concentrations. In normophosphatemic pigs, glucose-6-phosphate and lactate concentrations increased significantly during exercise by 2-4 mmol/kg and 12.8-14.4 mmol/kg, respectively. However, in hypophosphatemic pigs, glucose-6-phosphate concentrations decreased significantly during exercise by 4.4 mmol/kg and lactate levels were unchanged. These results indicate that low serum inorganic phosphate levels influence muscle metabolism and glycolysis in connection with physical exercise.     

Salivary Cortisol Concentration in Exercised Thoroughbred Horses

Both physical activity and stress result in an increase in plasma cortisol level. The measurement of cortisol in plasma requires taking blood samples, which is stressful itself. Therefore, the aim of this study was to evaluate the use of saliva sampling for the determination of cortisol concentrations, indicating the intensity of exercise in horses during race training. Twelve Thoroughbred horses aged 2-3 years were examined during their speed training sessions. The horses galloped on the 1,200-m sand track at a speed of 14.4-15.3 m/s. Three saliva samples and three blood samples were collected from each horse. Both types of samples were taken when the horse was at rest, immediately after returning from the track and 30 minutes after the end of exercise. Blood lactic acid (LA) concentration was determined using the enzymatic cuvette test. The concentrations of cortisol in saliva and plasma samples were measured by enzyme immunoassay methods. Statistically significant correlations were found between salivary cortisol level determined 30 minutes after the end of exercise and blood LA concentration obtained immediately after exercise (P = .003) and between salivary and plasma cortisol levels measured 30 minutes after the end of training session (P = .015). The measurement of cortisol concentration in saliva samples taken from race horses 30 minutes after the end of exercise can be recommended for use in practice under field conditions to estimate the level of relative intensity of exercise in race horses.     

Effects of feeding meals with various soluble-carbohydrate content on muscle glycogen synthesis after exercise in horses

OBJECTIVES: To determine effects of feeding diets with various soluble-carbohydrate (CHO) content on rates of muscle glycogen synthesis after exercise in horses. ANIMALS: 7 fit horses. PROCEDURES: In a 3-way crossover study, horses received each of 3 isocaloric diets (a high soluble CHO [HC] diet, a low soluble CHO [LC] diet, or a mixed soluble CHO [MC] diet). For each diet, horses were subjected to glycogen-depleting exercise, followed by feeding of the HC, LC, or MC diet at 8-hour intervals for 72 hours. RESULTS: Feeding the HC diet resulted in a significantly higher glycemic response for 72 hours and significantly greater muscle glycogen concentration at 48 and 72 hours after exercise, compared with results after feeding the MC and LC diets. Muscle glycogen concentrations similar to baseline concentrations were detected in samples obtained 72 hours after exercise in horses when fed the HC diet. Rate of glycogen synthesis was significantly higher when horses were fed the HC diet, compared with values when horses were fed the MC and LC diets. Glycogen synthase activity was inversely related to glycogen content. Protein content of glucose transporter-4 was the lowest at 72 hours after exercise when horses were fed the HC diet. CONCLUSIONS AND CLINICAL RELEVANCE: Muscle glycogen synthesis was slower after glycogen-depleting exercise in horses, compared with synthesis in humans. Feeding HC meals after strenuous exercise hastened replenishment of muscle glycogen content, compared with results for feeding of LC and MC diets, by increasing availability of blood glucose to skeletal muscles.     

Muscle metabolic changes associated with long-term inhalation anaesthesia in the horse analysed by muscle biopsy and microdialysis techniques

During anaesthesia in the horse, muscle blood flow has been found to be reduced, possibly leading to hypoxia or ischaemia in the muscle. The aim of this study was to use the muscle biopsy and microdialysis techniques to determine whether long-term inhalation anaesthesia in laterally recumbent horses induces metabolic changes in gluteal muscle indicative of anaerobic metabolism. Muscle biopsies and plasma samples were taken from seven horses at the start and end of halothane anaesthesia. In six isoflurane-anaesthetised horses, given three pharmacological provocations (dobutamine, detomidine, acepromazine), repeated blood samples and microdialysis was performed during anaesthesia and muscle biopsies were taken before and at the end of anaesthesia. Adenosine triphosphate (ATP), adenosine diphosphate, adenosine monophosphate, inosine monophosphate (IMP) creatine phosphate and lactate concentrations did not differ between dependent and non-dependent muscles at either sampling time. Creatine phosphate decreased in both the halothane (-38%) and isoflurane (-28%) group. In the halothane group, ATP was decreased (-15%) at the end of anaesthesia, while IMP was increased (+32%). Lactate in muscle and plasma increased in both groups. Lactate in dialysate increased after induction and remained elevated above plasma concentrations. These results show that long-term inhalation anaesthesia in horses is associated with an anaerobic metabolic response within the muscle and that microdialysis can be used to detect metabolic changes within the muscle during equine anaesthesia.     

Sarcoplasmic Reticulum Ca2+-ATPase Activity and Glycogen Content in Various Fiber Types after Intensive Exercise in Thoroughbred Horses

To find a new parameter indicating muscle fitness in Thoroughbred horses, we examined time-dependent recovery of glycogen content and sarcoplasmic reticulum (SR) Ca²⁺-ATPase activity of skeletal muscle after intensive treadmill running. Two repeated 50-sec running sessions (13 m/sec) were performed on a flat treadmill (approximately 90%VO₂max). Muscle samples of the middle gluteal muscle were taken before exercise (pre) and 1 min, 20 min, 60 min, and 24 hr after exercise. Muscle fiber type composition was determined in the pre muscle samples by immunohistochemical staining with monoclonal antibody to myosin heavy chain. SR Ca²⁺-ATPase activity of the muscle and glycogen content of each muscle fiber type were determined with biochemical analysis and quantitative histochemical staining, respectively. As compared to the pre value, the glycogen content of each muscle fiber type was reduced by 15–27% at 1 min, 20 min, and 60 min after the exercise and recovered to the pre value at 24 hr after exercise test. These results indicate that 24 hr is enough time to recover glycogen content after short-term intensive exercise. The mean value of the SR Ca²⁺-ATPase activity showed a slight decrease (not significant) immediately after exercise, and complete recovery at 60 min after exercise. There were no significant relationship between the changes in glycogen content of each muscle fiber type and SR Ca²⁺-ATPase. Although further studies are needed, SR Ca²⁺-ATPase is not a useful parameter to detect muscle fitness, at least in Thoroughbred horses.