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  • Author or Editor: K. H. McKeever x
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SUMMARY

The effect of premedication with phenylbutazone on systemic hemodynamic and diuretic effects of furosemide was examined in 6 healthy, conscious, mares. Mares were instrumented for measurement of systemic hemodynamics, including cardiac output and pulmonary arterial, systemic arterial, and intracardiac pressures, and urine flow. Each of 3 treatments was administered in a randomized, blinded study; furosemide (1 mg/kg of body weight, iv) only, phenylbutazone (8.8 mg/kg, po, at 24 hours and 4.4 mg/kg, iv, 30 minutes before furosemide) and furosemide, or 0.9% NaCl. Phenylbutazone administration significantly attenuated, but did not abolish, the diuretic effect of furosemide. Phenylbutazone completely inhibited the immediate effect of furosemide on cardiac output, stroke volume, total peripheral resistance, and right ventricular peak pressure. Premedication with phenylbutazone did not inhibit equally the diuretic and hemodynamic effects of furosemide, indicating that some of furosemide's hemodynamic effects are mediated by an extrarenal activity of furosemide.

Free access
in American Journal of Veterinary Research
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.

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in American Journal of Veterinary Research

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

Abstract

Objective—To determine components of the increase in oxygen consumption (O2) and evaluate determinants of hemoglobin saturation (SO2) during incremental treadmill exercise in unfit horses.

Animals—7 unfit adult mares.

Procedures—Horses performed 1 preliminary exercise test (EXT) and 2 experimental EXT. Arterial and mixed venous blood samples and hemodynamic measurements were taken during the last 30 seconds of each step of the GXT to measure PO2, hemoglobin concentration ([Hb]), SO2, and determinants of acidbase state (protein, electrolytes, and PCO2).

Results—Increased O2 during exercise was facilitated by significant increases in cardiac output (CO), [Hb], and widening of the arteriovenous difference in O2. Arterial and venous pH, PaO2, and PvO2 decreased during exercise. Arterial PCO2, bicarbonate ([HCO3])a, and [HCO3]v decreased significantly, whereas PvCO2 and increased. Arterial and venous sodium concentration, potassium concentration, strong ion difference, and venous lactate concentration all increased significantly during exercise.

Conclusions and Clinical Relevance—Increases in CO, [Hb], and O2 extraction contributed equally to increased O2 during exercise. Higher PCO2 did not provide an independent contribution to shift in the oxyhemoglobin dissociation curve (OCD) in venous blood. However, lower PaCO2 shifted the curve leftward, facilitating O2 loading. The shift of ODC resulted in minimal effect on O2 extraction because of convergence of the ODC at lower values of PO2. Decreased pH appeared responsible for the rightward shift of the ODC, which may be necessary to allow maximal O2 extraction at high blood flows achieved during exercise. (Am J Vet Res 2000;61:1325–1332)

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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

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