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Summary

The effect of furosemide-induced weight loss on the energetic responses of horses to running was examined in a 3-way crossover study. Eight 2- to 3-year-old Standardbred mares received, in random order, 10 ml of saline solution 4 hours before running on a treadmill (control trial, C); or, during 2 trials, 1 mg of furosemide/kg of body weight, iv, 4 hours before running. During one of the trials when the horses received furosemide, they carried weight equal to that lost over the 3.75 hours after furosemide administration while running (furosemide-loaded, fl), and during the other trial they did not carry weight equal to that lost after furosemide administration (furosemide-unloaded, fu). Horses performed an incremental exercise test on a treadmill during which rates of oxygen consumption (Vco2) and carbon dioxide production (Vco2) were measured, respiratory exchange ratio was calculated, and blood samples were collected for determination of mixed venous plasma lactate concentration and arterial and mixed venous oxygen saturation. Furosemide treatment caused significantly (P < 0.001) greater weight loss than did saline administration; mean ± sem weight loss (exclusive of fecal loss) was 1.6, 8.8, and 10.2 kg (sem = 2.0) for C, fl, and fu trials, respectively. The speed at which peak Vo2 was achieved was 9.31, 9.56, and 9.50 (sem = 0.16) m/s, respectively, time to fatigue was 547, 544, and 553 (sem = 26) seconds, respectively, and the highest speed attained was 10.3, 10.2, and 10.2 (sem = 0.2) m/s, respectively. Mean peak rate of oxygen consumption was 130.7, 129.6, and 129.6 (sem = 1.9) ml/min/kg, respectively. There was a significant (P = 0.070) group × speed interaction for Vco2; during trial fu, horses had significantly (P < 0.05) lower rate of CO2 production at speed of 9 m/s and at the speed that caused peak Vo2, than during trial C. The respiratory exchange ratio during the fu trial was significantly (P < 0.05) less than that during the C trial at the speed that caused peak Vo2. Plasma lactate concentration at speed of 9 m/s for C, fl, and fu trials was 15.4, 16.5, and 13.3 (sem = 0.8) mmol/L, respectively; values for the fl and C trials were not significantly different, whereas the mean value for the fu trial was significantly (P < 0.05) less than that for the C trial. Thus, administration of furosemide to horses altered the energetic response to exertion. Replacement of the furosemide-induced weight loss resulted in Vco2, plasma lactate, and respiratory exchange values indistinguishable from those during the control trial.

Free access
in American Journal of Veterinary Research

Summary

Plasma insulin concentration of many species has a characteristic early or acute-phase response in the minutes after IV administration of glucose. However, the plasma insulin response of horses soon after the IV administration of glucose has not been examined, whereas the more prolonged response has been evaluated. We examined the plasma insulin and glucose concentration responses of adult mares during the 30 minutes after rapid IV administration of glucose (0.33 g/kg of body weight). Plasma glucose concentration peaked at 664 ± 54 mg/dl within 1 minute of cessation of glucose administration, whereas insulin concentration peaked at 326 ± 24 pmol/L at 2 minutes after the end of glucose administration. Thus, these mares had an acute insulin response, consistent with that observed in other species, including dogs, human beings, and cattle.

Free access
in American Journal of Veterinary Research

SUMMARY

Objective

To compare the accuracy of anion gap (AG) and strong ion gap (SIG) for predicting unmeasured strong ion concentration in plasma and serum from horses.

Animals

6 well-trained Standardbred horses undergoing high-intensity exercise (experimental study) and 78 horses and ponies that underwent IV administration of lactic acid or endotoxin, and endurance, submaximal, or high-intensity exercise.

Procedure

Anion gap was calculated as AG = (Na+ + K+) − (Cl- + HCO 3), and SIG was calculated, using the simplified strong ion model, whereby SIG (mEq/L) = 2.24 × total protein (g/dl)/(1 + 106.65−pH) − AG. The relation between AG or SIG and plasma lactate concentration was evaluated, using linear regression analysis.

Results

Linear relations between plasma lactate concentration and AG and SIG were strong for the experimental study (r2 = 0.960 and 0.966, respectively) and the published studies (r2 = 0.914 and 0.925, respectively). The following relations were derived: AG = 1.00 × plasma lactate + 10.5; SIG = 0.99 × plasma lactate + 2.8. An AG > 15 mEq/L indicated an increased unmeasured anion concentration, whereas a SIG < −2 mEq/L indicated an increased unmeasured strong anion concentration.

Conclusions and Clinical Relevence

Anion gap and SIG can be used to predict plasma lactate concentration in horses. AG is accurate and clinically useful for estimating unmeasured strong ion concentration in horses with total protein concentrations within or slightly outside reference range, whereas SIG is more accurate in horses with markedly abnormal total protein concentrations and those of various ages and with various concentrations of albumin, globulin, and phosphate. (Am J Vet Res 1998;59:881–887)

Free access
in American Journal of Veterinary Research

Summary

Effects of furosemide administration on exertion-induced changes in plasma renin activity and plasma concentrations of atrial natriuretic peptide and aldosterone in horses during sustained submaximal exertion were examined. Furosemide (1 mg/kg of body weight) or heparinized saline solution was administered iv to each of 6 mares not conditioned to exercise, either 4 hours or 2 minutes before 60 minutes of sustained submaximal running on a treadmill. Horses ran at a speed that induced heart rate approximately 65% of maximal after saline treatment. After 15 minutes of running, furosemide suppressed the exertion-induced increase in plasma concentrations of atrial natriuretic peptide (mean [95% confidence interval] values of 63.9 [9.9 to 421] pg/ml vs 100 [15.4 to 652] pg/ml after furosemide or saline treatment, respectively), and enhanced the response of plasma renin activity to exertion (18.6 [5.7 to 60.4] ng/ml/h vs 6.0 [1.8 to 19.4] ng/ml/h, respectively). An effect of furosemide on the exertion-induced increase in plasma aldosterone concentration was not detected.

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

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 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