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Abstract

Objective

To measure renal clearance of antipyrine and urinary excretion of antipyrine (AP) metabolites in horses by use of validated high-performance liquid chromatography (HPLC) methods.

Animals

8 Standardbred mares.

Procedure

HPLC methods for measurement of AP in equine plasma and AP and its metabolites in equine urine were validated. Antipyrine (20 mg/kg of body weight) was administered IV, and blood samples and urine specimens were collected over 24 hours.

Results

Median plasma clearance of AP in horses was 6.2 ml/min/kg, of which < 2% could be attributed to renal clearance. Urinary excretion of AP and its metabolites over 24 hours accounted for < 22% of the AP dose administered. The major metabolite of AP in urine was 4-hydroxyantipyrine.

Conclusions and Clinical Relevance

Use of the proven validated methods for measuring AP and its metabolites indicated that AP has minimal renal clearance in horses, suggesting that plasma clearance of AP reflects hepatic clearance. Combined with AP metabolite data, the pharmacokinetics of AP may be useful for assessment of hepatic cytochrome P450 activity in horses. (Am J Vet Res 1998;59:280–285)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the effects of acute exercise on hepatic blood flow by studying hepatic clearance of bromsulphalein for several submaximal exercise intensities.

Animals

8 adult Standardbred mares.

Procedure

Horses were subjected to 4 submaximal exercise intensities (resting and 40, 60, and 80% maximal oxygen consumption). After horses had been running at the required treadmill speed for 1 minute, bromsulphalein (BSP; 5 mg/kg of body weight, IV) was administered during a 45- to 60-second period, and horses continued at the desired speed for an additional 15 minutes. Blood samples were collected at 2-minute intervals for 30 minutes, and plasma concentration of BSP was determined by spectrophotometry. Estimates of pharmacokinetic variables were compared among the 4 exercise intensities, using a Friedman repeated-measures analysis on ranks and linear regression.

Results

Median values for clearance of BSP from blood and plasma decreased significantly with exercise and was linearly related to exercise intensity. Exercise-induced differences were not detected in the volume of distribution of BSP. Elimination half-life of BSP increased significantly with increasing exercise intensity and was linearly related to exercise intensity.

Conclusions

Acute submaximal exercise has a dramatic effect on clearance of BSP in horses. Presumably, exercise-induced decreases in splanchnic blood flow limit blood flow to the liver, decreasing hepatic clearance of BSP and leading to persistence of plasma concentrations of BSP.

Clinical Implications

Drugs that are efficiently extracted by the liver may have decreased hepatic clearance when horses exercise at submaximal intensities. (Am J Vet Res 1998;59:1481–1487)

Free access
in American Journal of Veterinary Research

SUMMARY

Exertion has an effect on plasma, serum, and/or urine prostanoid concentrations in many species. We investigated the effect of exercise intensity on plasma prostaglandin concentrations during and after exercise in horses. Six Thoroughbreds completed 4 trials: 3 exercise trials (low-, medium-, and high-speed) and 1 nonexercise (control) trial on a high-speed treadmill. Blood samples were collected from a jugular catheter before, during, and after exercise. The pcv and blood lactate, plasma protein, plasma prostacyclin (6-keto-pgf ), thromboxane B2 (txb 2), and prostaglandin E2 (pge 2) concentrations were measured before, during, and after exercise. Exercise significantly (P = 0.001) increased plasma txb 2 concentration during and after exercise in the low-, medium-, and high-speed trials, although effect of exercise intensity was not detected. Exercise was associated with an increase in pcv and blood lactate and plasma protein concentrations. There was no effect of exercise on plasma 6-keto-pgf concentrations; pge 2 was not detected in plasma from any horse in any trial.

Free access
in American Journal of Veterinary Research

Summary:

Fifty-five blood samples were collected from 28 dogs competing in the 1991 Yukon Quest International Sled-Dog Race to examine race-induced changes in serum biochemical values. Blood was collected after a 36-hour mandatory rest at the midpoint of the race, and again at 2 subsequent checkpoints. The mean speed of dogs between checkpoints was approximately 4.5 mph. There were no significant increases in PCV, or in serum total protein, sodium, or creatinine concentrations during the race. Mean serum potassium concentration decreased significantly (P < 0.05) from 4.8 ± 0.4 to 4.4 ± 0.3 to 3.9 ± 0.3 mEq/L, as did the serum triglyceride concentration (138 ± 52, 88 ± 25, 81 ± 16 mg/dl). Plasma cortisol concentration did not change significantly. Increases in the mean serum activity of creatine kinase (167, 420, 344 U/L), and aspartate aminotransferase (55, 79, 62 U/L) during the race were significant (P < 0.05). Participation in a long-distance sled race was associated with mild changes in routinely measured serum biochemical values in dogs.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To determine the effects of walking, standing, or standing with a splint on 1 forelimb on rate of recuperation of horses after a brief, intense bout of exercise.

Animals

6 adult Thoroughbreds (435 to 542 kg).

Procedure

Horses were preconditioned by exercise on a treadmill to establish a uniform level of fitness. Once fit, the treadmill speed causing each horse to exercise at 120% of its maximal oxygen consumption was determined and was used in simulated races at 14-day intervals. Horses were instrumented for collection of arterial and mixed venous blood samples for measurement of acid-base status, concentrations of metabolites, and cardiopulmonary indices. The horses were exercised at a speed inducing 120% of their maximal oxygen consumption until fatigued or for a maximum of 2 minutes. Three recuperative interventions were evaluated: walking at 1.8 m/s for 30 minutes, then standing for the remainder of the 90-minute trial; standing stationary for 90 minutes; and standing stationary for 90 minutes with a splint on the right forelimb.

Results

Walking significantly increased cardiac output during the recuperative phase and hastened recovery of normal acid-base status and return of blood lactate concentration to baseline values.

Conclusion

Limiting movement of horses during the recuperative period delays recovery from maximal exercise. Most measured indices returned to baseline by 60 minutes after exercise. All measured cardiopulmonary indices returned to baseline values by 90 minutes after exercise.

Clinical Relevance

Horses that are not allowed to walk during recuperation from exercise may have a prolonged recovery period. (Am J Vet Res 1997;58:1003–1009)

Free access
in American Journal of Veterinary Research

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.

Full access
in American Journal of Veterinary Research

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.

Full access
in Journal of the American Veterinary Medical Association

Objective

To determine the effect of furosemide on performance of Thoroughbreds racing on dirt surfaces at tracks in the United States and Canada.

Design

Cross-sectional study.

Animals

All Thoroughbreds (n = 22,589) that finished a race on dirt surfaces at tracks in the United States and Canada between June 28 and July 13, 1997 in jurisdictions that allowed the use of furosemide.

Procedure

Race records were analyzed by use of multivariable ANOVA procedures and logistic regression analyses to determine the effect of furosemide on estimated 6-furlong race time, estimated racing speed, race earnings, and finish position. Principal component analysis was used to create orthogonal scores from multiple collinear variables for inclusion in the models.

Results

Furosemide was administered to 16,761 (74.2%) horses. Horses that received furosemide raced faster, earned more money, and were more likely to win or finish in the top 3 positions than horses that did not. The magnitude of the effect of furosemide on estimated 6-furlong race time varied with sex, with the greatest effect in males. When comparing horses of the same sex, horses receiving furosemide had an estimated 6-furlong race time that ranged from 0.56 ± 0.04 seconds (least-squares mean ± SE) to 1.09 ± 0.07 seconds less than that for horses not receiving furosemide, a difference equivalent to 3 to 5.5 lengths.

Conclusions and Clinical Relevance

Because of the pervasive use of furosemide and its apparent association with superior performance in Thoroughbred racehorses, further consideration of the use of furosemide and investigation of its effects in horses is warranted. (J Am Vet Med Assoc 1999;215:670–675)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine whether prolonged exercise by conditioned sled dogs affects urine concentrations of homovanillic acid (a metabolite of dopamine), vanillylmandelic acid (a metabolite of norepinephrine and epinephrine), and cortisol.

Animals—24 conditioned Alaskan sled dogs (2 to 8.5 years old) that were in training for a multiday endurance race.

Procedures—Voided urine samples were collected from 4 groups of dogs (randomly selected from 54 dogs) after no exercise (control group; n = 6 dogs), completion of a 160km run (group A; 3), completion of a 420-km run (group B; 7), and completion of a 560-km run (group C; 6). Urine cortisol concentrations were determined by use of an immunoassay technique; urine vanillylmandelic acid and homovanillic acid concentrations were measured via high-performance liquid chromatography.

Results—Compared with the control group, urine cortisol concentration in groups A, B, and C was significantly different (5.33 × 10−4 ± 2.62 × 10−4 μg/dL vs 1.04 × 10−4 ± 2.31 × 10−5 μg/dL, 8.88 × 10−4 ± 5.49 × 10−4 μg/dL, and 6.31 × 10−4 ± 5.09 × 10−4 μg/dL, respectively). Urine homovanillic acid concentration did not differ among the 4 groups. Vanillylmandelic acid was not detected in any urine samples.

Conclusions and Clinical Relevance—Results indicated that prolonged exercise by sled dogs did not affect urine homovanillic acid concentration but did increase urinary cortisol secretion, which is indicative of adrenocortical stimulation. The apparent lack of vanillylmandelic acid in voided urine samples requires further investigation.

Full access
in American Journal of Veterinary Research