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- Author or Editor: Kenneth W. Hinchcliff x
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Abstract
Objective—To determine the effects of IV administration of enalaprilat on cardiorespiratory and hematologic variables as well as inhibition of angiotensin converting enzyme (ACE) activity in exercising horses.
Animals—6 adult horses.
Procedure—Horses were trained by running on a treadmill for 5 weeks. Training was continued throughout the study period, and each horse also ran 2 simulated races at 120% of maximum oxygen consumption. Three horses were randomly selected to receive treatment 1 (saline [0.9% NaCl] solution), and the remaining 3 horses received treatment 2 (enalaprilat; 0.5 mg/kg of body weight, IV) before each simulated race. Treatment groups were reversed for the second simulated race. Cardiorespiratory and hematologic data were obtained before, during, and throughout the 1-hour period after each simulated race. Inhibition of ACE activity was determined during and after each race in each horse.
Results—Exercise resulted in significant increases in all hemodynamic variables and respiratory rate. The pH and PO2 of arterial blood decreased during simulated races, whereas PCO2 remained unchanged. Systemic and pulmonary blood pressure measurements and arterial pH, PO2, and PCO2 returned to baseline values by 60 minutes after simulated races. Enalaprilat inhibited ACE activity to < 25% of baseline activity without changing cardiorespiratory or blood gas values, compared with horses administered saline solution.
Conclusions and Clinical Relevance—Enalaprilat administration almost completely inhibited ACE activity in horses without changing the hemodynamic responses to intense exercise and is unlikely to be of value in preventing exercise-induced pulmonary hemorrhage. (Am J Vet Res 2001;62:1008–1013)
Abstract
Objective—To evaluate the diagnostic value of serum concentrations of total magnesium (tMg) and ionized magnesium (iMg), concentrations of magnesium (Mg) in muscle, intracellular Mg (icMg) concentrations, urinary Mg excretion (EMg), Mg clearance (CMg), and fractional clearance of Mg (FCMg) in horses fed diets with Mg content above and below National Research Council recommendations.
Animals—9 young female horses.
Procedures—6 horses were fed a reduced-Mg diet for 29 days followed by an Mg-supplemented diet for 24 days. Control horses (n = 3) were fed grass hay exclusively. Blood, urine, and tissue samples were collected, and an Mg retention test was performed before and after restriction and supplementation of Mg intake. Serum tMg, serum iMg, muscle Mg, icMg, and urine Mg concentrations were measured, and 24-hour EMg, CMg, and FCMg were calculated.
Results—Reductions in urinary 24-hour EMg, CMg, and FCMg were evident after 13 days of feeding a reduced-Mg diet. Serum tMg and iMg concentrations, muscle Mg content, and results of the Mg retention test were not affected by feeding the Mg-deficient diet. Spot urine sample FCMg accurately reflected FCMg calculated from 6- and 24-hour pooled urine samples. Mean ± SD FCtMg of horses eating grass hay was 29 ± 8%, whereas mean FCtMg for horses fed a reduced-Mg diet for 29 days was 6 ± 3%.
Conclusions and Clinical Relevance—The 24-hour EMg was the most sensitive indicator of reduced Mg intake in horses. Spot sample FCMg can be conveniently used to identify horses consuming a diet deficient in Mg. (Am J Vet Res 2004;65:422–430)
Abstract
Objective—To determine the effect of a single bout of exercise and increased substrate availability after exercise on gene expression and content of the glucose transporter-4 (GLUT-4) protein in equine skeletal muscle.
Animals—6 healthy adult Thoroughbreds.
Procedure—The study was designed in a balanced, randomized, 3-way crossover fashion. During 2 trials, horses were exercised at 45% of their maximal rate of oxygen consumption for 60 minutes after which 1 group received water (10 mL/kg), and the other group received glucose (2 g/kg, 20% solution) by nasogastric intubation. During 1 trial, horses stood on the treadmill (sham exercise) and then received water (10 mL/kg) by nasogastric intubation. Muscle glycogen concentration and muscle GLUT-4 protein and mRNA content were determined before exercise and at 5 minutes and 4, 8, and 24 hours after exercise.
Results—Although exercise resulted in a 30% reduction in muscle glycogen concentration, no significant difference was detected in muscle GLUT-4 protein or mRNA content before and after exercise. Glycogen replenishment was similar in both exercised groups and was not complete at 24 hours after exercise. Horses that received glucose had significantly higher plasma glucose and insulin concentrations for 3 hours after exercise, but no effect of hyperglycemia was detected on muscle GLUT-4 protein or mRNA content.
Conclusions and Clinical Relevance—Under the conditions of this study, neither exercise nor the combination of exercise followed by hyperglycemia induced translation or transcription of the GLUT-4 protein in horses. (Am J Vet Res 2003;64:1401–1408)
Abstract
Objective—To determine the anesthetic, cardiorespiratory, and metabolic effects of 4 IV anesthetic regimens in Thoroughbred horses recuperating from a brief period of maximal exercise.
Animals—6 adult Thoroughbreds.
Procedure—Horses were preconditioned by exercising them on a treadmill. Each horse ran 4 simulated races, with a minimum of 14 days between races. Races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until fatigued or for a maximum of 2 minutes. Two minutes after exercise, horses received a combination of xylazine hydrochloride (2.2 mg/kg of body weight) and acepromazine maleate (0.04 mg/kg) IV. Five minutes after exercise, horses received 1 of the following 4 IV anesthetic regimens: ketamine hydrochloride (2.2 mg/kg); ketamine (2.2 mg/kg) and diazepam (0.1 mg/kg); tiletamine hydrochloride-zolazepam hydrochloride (1 mg/kg); and guaifenesin (50 mg/kg) and thiopental sodium (5 mg/kg). Treatments were randomized. Cardiopulmonary indices were measured, and samples of blood were collected before and at specific times for 90 minutes after each race.
Results—Each regimen induced lateral recumbency. The quality of induction and anesthesia after ketamine administration was significantly worse than after other regimens, and the duration of anesthesia was significantly shorter. Time to lateral recumbency was significantly longer after ketamine or guaifenesinthiopental administration than after ketaminediazepam or tiletamine-zolazepam administration. Arterial blood pressures after guaifenesin-thiopental administration were significantly lower than after the other regimens.
Conclusions and Clinical Relevance—Anesthesia can be safely induced in sedated horses immediately after maximal exercise. Ketamine-diazepam and tiletamine- zolazepam induced good quality anesthesia with acceptable perturbations in cardiopulmonary and metabolic indices. Ketamine alone and guaifenesinthiopental regimens are not recommended. (Am J Vet Res 2000;61:1545–1552)
Abstract
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. (Am J Vet Res 2004;65:916–923)
Abstract
Objective—To determine whether repetitive endurance exercise in sled dogs was associated with substantial lipid peroxidation, decreases in antioxidant capacity of the serum, and skeletal muscle damage.
Animals—24 lightly trained sled dogs.
Procedure—16 dogs completed a 58-km run on each of 3 consecutive days; the other 8 dogs (control) did not exercise during the study. Blood samples were collected before the first exercise run and after the first and third exercise runs. Plasma isoprostane and serum vitamin E concentrations, total antioxidant status of plasma, and serum creatine kinase activity were measured.
Results—Plasma isoprostane concentrations in dogs in the exercise group were significantly increased after the first exercise run and further significantly increased after the third exercise run. Serum vitamin E concentration was significantly decreased after the first exercise run in dogs in the exercise group, and this change persisted after the third exercise run. There was a significant linear relationship between plasma isoprostane concentration and the logarithm of serum creatine kinase activity (adjusted r 2 = 0.84).
Conclusions and Clinical Relevance—Results demonstrate that repetitive endurance exercise in dogs is associated with lipid peroxidation and a reduction in plasma antioxidant concentrations. We interpret these results as indicating that the antioxidant mechanisms of minimally trained dogs may, in some instances, be inadequate to meet the antioxidant requirements of repetitive endurance exercise. (Am J Vet Res 2000;61:512–517)
Abstract
Objective—To clone and sequence cDNA for equine insulin-responsive glucose transporter (glucose transporter type 4 [GLUT-4]) and determine effects of glycogen-depleting exercise and meal type after exercise on GLUT-4 gene expression in skeletal muscle of horses.
Animals—Muscle biopsy specimens from 7 healthy adult horses.
Procedure—Total RNA was extracted from specimens, and GLUT-4 cDNA was synthesized and sequenced. Horses were exercised on 3 consecutive days. On the third day of exercise, for 8 hours after exercise, horses were either not fed, fed half of daily energy requirements as hay, or fed an isocaloric amount of corn. The GLUT-4 mRNA was determined by use of realtime reverse transcriptase-polymerase chain reaction in muscle biopsy specimens obtained before 3 consecutive days of exercise and within 10 minutes and 4, 8, and 24 hours after the third exercise bout.
Results—A 1,629-bp segment was sequenced, of which 1,530 bp corresponded to the coding region and encoded a protein of 509 amino acids. Expression of GLUT-4 gene increased by 2.3, 4.3, 3.3, and 2.6 times 10 minutes and 4, 8, and 24 hours after exercise, respectively, compared with that prior to exercise. No differences were observed in GLUT-4 gene expression among conditions of feed withholding, corn feeding, and hay feeding during the 8 hours postexercise.
Conclusions and Clinical Relevance—Lack of increase of GLUT-4 gene expression after grain feeding and exercise may explain the apparently slower rate of glycogen synthesis after exercise in horses relative to that of other species. (Am J Vet Res 2005;66:379–385)
Abstract
Objective—To assess changes in muscle glycogen (MG) and triglyceride (MT) concentrations in aerobically conditioned sled dogs during prolonged exercise.
Animals—54 Alaskan sled dogs fed a high-fat diet.
Procedures—48 dogs ran 140-km distances on 4 consecutive days (cumulative distance, up to 560 km); 6 dogs remained as nonexercising control animals. Muscle biopsies were performed immediately after running 140, 420, or 560 km (6 dogs each) and subsequently after feeding and 7 hours of rest. Single muscle biopsies were performed during recovery at 28 hours in 7 dogs that completed 560 km and at 50 and 98 hours in 7 and 6 dogs that completed 510 km, respectively. Tissue samples were analyzed for MG and MT concentrations.
Results—In control dogs, mean ± SD MG and MT concentrations were 375 ± 37 mmol/kg of dry weight (kgDW) and 25.9 ± 10.3 mmol/kgDW, respectively. Compared with control values, MG concentration was lower after dogs completed 140 and 420 km (137 ± 36 mmol/kgDW and 203 ± 30 mmol/kgDW, respectively); MT concentration was lower after dogs completed 140, 420, and 560 km (7.4 ± 5.4 mmol/kgDW; 9.6 ± 6.9 mmol/kgDW, and 6.3 ± 4.9 mmol/kgDW, respectively). Depletion rates during the first run exceeded rates during the final run. Replenishment rates during recovery periods were not different, regardless of distance; only MG concentration at 50 hours was significantly greater than the control value.
Conclusions and Clinical Relevance—Concentration of MG progressively increased in sled dogs undergoing prolonged exercise as a result of attenuated depletion.
Abstract
Objective—To determine the effects of training and sustained submaximal exercise on hematologic values in racing sled dogs.
Design—Cohort study.
Animals—39 Alaskan sled dogs bred for endurance racing.
Procedures—Blood samples were collected prior to initiation of a 7-month training regimen (n = 39), after completion of the training regimen (19), and after completion of an 1,100-mile race (9), and a CBC, differential cell count, and flow cytometry for leukocyte surface antigens were performed.
Results—Both training and exercise caused significant decreases in PCV and hemoglobin concentration and significant increases in total WBC count. In contrast, training and exercise were not found to have significant effects on absolute numbers or fractions of CD4+ or CD8+ lymphocytes, other than a significant increase in the fraction of CD8+ lymphocytes associated with training.
Conclusions and Clinical Relevance—Results suggested that training and exercise induced changes in several hematologic values in racing sled dogs. Extracellular fluid volume expansion was the likely explanation for the training-induced decrease in PCV, and acute blood loss secondary to gastrointestinal tract bleeding was likely responsible for the decrease in PCV associated with acute exercise.
