Effects of furosemide, exercise, and atropine on tracheal mucus transport rate (TMTR) in horses were investigated. Atropine (0.02 mg/kg of body weight) administered IV or by aerosolization significantly (P < 0.05) decreased TMTR at 60, but not at 30 minutes after its administration in standing horses. Furosemide (1.0 mg/kg, IV) did not have any significant effect on TMTR when measured at 2 or 4 hours after its administration in standing horses. Exercise alone or furosemide (1.0 mg/kg, IV) administration followed 4 hours later by exercise did not alter TMTR, compared with values for standing control or exercised horses administered saline solution. Atropine (0.02 mg/kg, IV) administered after exercise significantly (P < 0.05) decreased TMTR, compared with values for no exercise standing controls, for exercise after administration of saline solution, and for furosemide and exercise.

Objective--To study whether end products of 2 pathways of anaerobic energy metabolism, lactate and purines, that accumulate in the blood after intense exercise indicate any relation to exercise performance. Design--Venous blood samples were taken within 1 and 15 minutes after a trotting race of 2,100 m. Animals--16 Clinically healthy Standardbred trotters. Procedure--Blood and plasma lactate concentrations were measured by enzymatic analyzer, and purines, uric acid and allantoin, were determined by high-performance liquid chromatography. The concentrations of metabolites were then correlated to racing time and individual performance indexes that are annually calculated from the percentage of winnings, placings, and starts rejected, average earnings per start, and the racing record. Results--Blood lactate concentration immediately and calculated cell lactate concentration immediately and 15 minutes after the race correlated positively (P < 0.05 to P < 0.01 ) with the individual performance indexes. Plasma lactate concentration was not correlated to the individual performance indexes. Uric acid concentration, immediately and 15 minutes after the race, was negatively correlated (P < 0.05) to the individual performance indexes, and a positive relation (P < 0.05) was found between the highest concentration of uric acid and the racing time. Concentration of allantoin immediately or 15 minutes after the race did not have any significant correlation to the individual performance indexes. Conclusions--Accumulation of lactate in the blood, which was greater in the superior performing horses, may prove to be an useful predictor of anaerobic capacity. The results also indicate that the loss of purine nucleotides was less in the superior performing horses, although further studies are needed to confirm this.

Using catheter mounted microtip manometers, right atrial, pulmonary artery, and pulmonary artery wedge pressures were studied in 8 horses while they were standing quietly (rest), and during galloping at treadmill speeds of 8, 10, and 13 m/s. At rest, mean (+/- SEM) heart rate, mean right atrial pressure, mean pulmonary artery pressure, and mean pulmonary artery wedge pressure were 37 (+/- 2) beats/min, 8 (+/- 2) mm of Hg, 31 (+/- 2) mm of Hg, and 18 (+/- 2) mm of Hg, respectively. Exercise at treadmill belt speed of 8 m/s resulted in significant (P < 0.05) increments in heart rate, right atrial pressure, pulmonary artery systolic, mean, diastolic and pulse pressures, and pulmonary artery wedge pressure. All these variables registered further significant (P < 0.05) increments as work intensity increased to 10 m/s, and then to 13 m/s. Pulmonary artery diastolic pressure was, however, not different among the 3 work intensities. During exercise at belt speed of 13 m/s, heart rate, mean right atrial pressure, mean pulmonary artery pressure, pulmonary artery pulse pressure, and mean pulmonary artery wedge pressure were 213 (+/- 5) beats/min, 44 (+/- 4) mm of Hg, 89 (+/- 5) mm of Hg, 69 (+/- 4) mm of Hg, and 56 (+/- 4) mm of Hg, respectively. Assuming mean intravascular pulmonary capillary pressure to be halfway between the mean pulmonary arterial and venous pressures, its value during exercise at 13 m/s may have approached 72.5 mm of Hg. Transmural pressure (intravascular minus alveolar pressure) across pulmonary capillaries may be even higher because of the large negative pleural pressure swings in galloping horses. High transmural pressures may cause stress failure of pulmonary capillaries, resulting in exercise-induced pulmonary hemorrhage.

In this preliminary investigation, various hematologic variables potentially influential in determining the degree of blood viscosity were evaluated in 10 Thoroughbred horses subjected to competitive acute running exercise. Following completion of sprints over a distance of 1.25 miles, mean percent (+/- SD) increases in PCV (38.3 +/- 12.9%), RBC (47.8 +/- 15.3%), and rouleaux index (232.7 +/- 176.8%) were recognized. Simultaneous increases in total plasma protein (28.3 +/- 5.31%), serum albumin (26.7 +/- 6.80%), alpha 1-globulin (60.0 +/- 49.0%), alpha 2-globulin(25.5 +/- 27.9%), beta 1-globulin (46.7 +/- 21.1%), beta 2-globulin (35.0 +/- 50.6%), gamma 1- and 2-globulins (38.7 +/- 29.6%), and plasma fibrinogen (12.5 +/- 10.4%) concentrations increased simultaneously. Horses also had consistent decreases in albumin:globulin ratio (- 10.0 +/- 7.43%). Alterations in these hematologic values after acute running exercise in Thoroughbred horses accompanied increases in serum (69.3 +/- 39.7%), plasma (39.7 +/- 11.9%), and blood (134.7 +/- 55.3%) viscosity.

Blood ionized calcium (Ca2+) and pH; plasma lactate concentrations; and total protein, total calcium (CaT), albumin, and phosphorus concentrations in serum were determined in 40 healthy horses before (T1), at the finish line (T2), and 10 minutes after the finish (T3) of the cross-country phase of a 3-dayevent competition. Mean ( +/- SEM) Ca2+ concentrations decreased from 6.22 +/- 0.04 mg/dl at T1 to 5.04 +/- 0.07 mg/dl at T2 (P less than or equal to 0.05). This decrease was accompanied by a nonsignificant increase in CaT between T1 and T2. The mean (+/- SEM) percent ionization of calcium decreased significantly (P less than or equal to 0.05), from 50.9 +/- 2.75% at T1 to 40.3 +/- 3.58% at T2. Significant increases in mean albumin, total protein, phosphorus, and lactate concentrations and a significant decrease in mean pH were observed at T2 (P less than or equal to 0.05). At T3, mean Ca2+ and percent ionization had increased, but remained significantly less than resting values. Mean CaT was significantly decreased at T3, compared with values at T1 and T2. Correlation of mean Ca2+ concentration with all other measured variables at each time was evaluated; correlation coefficients between mean Ca2+ and all other variables were low (r2 less than or equal to 0.38), indicating low biological significance.

Right atrial, pulmonary artery, pulmonary capillary, pulmonary artery wedge, and systemic blood pressures of strenuously exercising horses increase markedly. As a consequence, myocardial metabolic O2 demand in exercising horses must be high. Experiments were, therefore, carried out on 9 healthy, exercise-conditioned horses (2.5 to 8 years old; 481 +/- 16 kg) to ascertain the regional distribution of myocardial blood supply in the atria and ventricles at rest and during exercise. Blood flow was measured, using 15-micrometer-diameter radionuclide-labeled microspheres that were injected into the left ventricle while reference blood samples were being withdrawn at a constant rate from the thoracic aorta. Myocardial blood flow was determined at rest and during 2 exercise bouts performed on a high-speed treadmill at 8 and 13 m/s (0% grade). The sequence of exercise bouts was randomized among horses, and a 60-minute rest period was permitted between exercise bouts. There was considerable heterogeneity in the distribution of myocardial perfusion in the atria and the ventricles at rest; the right atrial myocardium received significantly (P < 0.05) less perfusion than did the left atrium, and these values were significantly (P < 0.05) less than those for the respective ventricular myocardium. The right ventricular myocardial blood flow also was significantly less than that in the left ventricle. With exercise, myocardial blood flow in all regions increased progressively with increasing work intensity and marked coronary vasodilation was observed in all cardiac regions. During exercise at 8 or 13 m/s, right and left atrial myocardial blood flows (per unit weight basis) were not different from each other. Although at treadmill speed of 8 m/s, left ventricular myocardial blood flow exceeded that in the right ventricle, this was not the case at 13 m/s, when perfusion values (per unit weight basis) became similar.

Hematologic and rheologic changes were examined in 49 Thoroughbreds before and after competitive racing. Mean postrace values for RBC count, hemoglobin concentration, and PCV increased by 58 to 61%, whereas blood viscosity increased 2 to 3 times. Postrace echinocyte numbers were 162% greater than prerace values. Smaller, but statistically significant, changes were found for mean corpuscular hemoglobin concentration, red cell distribution width, plasma total protein concentration, total WBC count, neutrophil count, and lymphocyte count. Variables measured did not predict whether a horse was a bleeder not treated with furosemide, a bleeder treated with furosemide, or a nonbleeder.