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Abstract

Objective

To determine effects of walking or standing on hepatic blood flow of horses after brief, intense exercise.

Animals

6 adult Thoroughbreds (4 mares, 2 geldings).

Procedure

Horses were preconditioned on a treadmill to establish uniform level of fitness. Once fit, treadmill speed causing each horse to exercise at 120% of maximal oxygen consumption was determined and used in simulated races at 14-day intervals. In a three-way crossover study, horses were exercised at a speed inducing 120% of maximal oxygen consumption until fatigued or for a maximum of 2 minutes. Three interventions were studied: resting on the treadmill (REST), exercised then standing on the treadmill for 30 minutes (MS), and exercised then walking at 2 m/s for 30 minutes (MW). At 60 seconds after completion of exercise, bromsulphalein (BSP) was infused IV, and blood samples were collected every 2 minutes for 30 minutes for analysis of BSP concentration. Hematocrit and plasma total solids concentration were measured. Pharmacokinetic parameters were derived, using nonlinear regression, and were compared, using Friedman’s repeated measures analysis on ranks.

Results

Plasma BSP concentration was higher after exercise. Median hepatic blood flow (BSP clearance) decreased significantly from 23.8 (REST) to 20.7 (MS) and 18.7 (MW) ml/min/kg. Median steady-state volume of distribution of BSP decreased from 47.6 (REST) to 42.7 (MW) and 40.2 (MS) ml/kg. Differences among trials were not significant when horses walked or stood after exercise.

Conclusions

Hepatic blood flow and pharmacokinetics of BSP are markedly altered immediately after exercise. Limiting movement of horses during this period did not affect hepatic blood flow. (Am J Vet Res 1998;59:1476–1480)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To describe changes in blood constituents of horses after oral and IV administration of sodium bicarbonate (NaHCO3), and to determine whether the changes are dose dependent.

Animals

6 adult Standardbred mares.

Procedure

3 oral doses (1,500, 1,000, and 250 mg/kg of body weight) or 1 intravenous dose (250 mg/kg, 5% solution) of NaHCO3 in 3 L of water, or water (3 L orally), were given to the mares; then changes in blood constituents were measured. Access to food and water was denied during the experiment. Blood samples were collected immediately before treatment and at hourly intervals for 12 hours after treatment, and were analyzed for blood gas tensions; serum osmolality; serum sodium, potassium, chloride, and creatinine concentrations; PCV; and total solids concentration in plasma.

Results

All NaHCO3 treatments induced significant (P < 0.05) metabolic alkalosis, hypernatremia, hypokalemia, and hyperosmolality for at least 8 hours. In mares given the 1,500- and 1,000-mg doses of NaHCO3 orally, hypercapnia persisted for at least 12 hours, whereas hypercapnia lasted 2 hours in mares given the 250-mg dose orally or IV (P < 0.05). A tendency for reduction in PCV, proteins in plasma concentration, and serum concentration of chloride was observed 1 hour after IV administered doses of NaHCO3.

Conclusions

Oral or IV administration of NaHCO3 (≥ 250 mg/kg) to resting horses without ad libitum access to water induces significant and persistent acidbase and electrolyte changes. (Am J Vet Res 1997;58:658–663)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To describe changes in renal function of horses after oral and IV administration of sodium bicarbonate (NaHCO3) and to determine whether changes are dose dependent.

Animals

6 Standardbred mares.

Procedure

Blood and urine samples for determination of renal function were collected immediately before and at hourly intervals for 12 hours after administration of each of 3 oral doses (1,500, 1,000, and 250 mg/kg of body weight, in 3 L of water) and 1 IV dose (250 mg/kg, 5% solution) of NaHCO3, or water (3 L orally).

Results

NaHCO3 induced increases in urine flow; electrolyte-free water reabsorption; urine concentrations of sodium and bicarbonate; fractional excretion of sodium, potassium, chloride, and bicarbonate; urinary excretion and clearance of sodium and bicarbonate; urine pH and anion gap; and mean plasma concentration of antidiuretic hormone. NaHCO3 induced attenuation in reduction with time of urine excretion and clearance of potassium, chloride, and osmoles, and induced reduction in urine osmolality. Plasma aldosterone and atrial natriuretic peptide concentrations and glomerular filtration rate were not modified.

Conclusions

Renal responses to NaHCO3 load emphasize conservation of plasma volume and re-establishment of acid-base balance over control of hyperosmolality by means of diuresis, natriuresis, and increased bicarbonaturia. These responses imply a large fluid shift from the extravascular space to the vascular compartment, which was eliminated via diuresis, thus preventing hypervolemia. (Am J Vet Res 1997;58:664–671)

Free access
in American Journal of Veterinary Research