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Abstract

Objective

To determine the potential usefulness of tests for detection of platelet activation and platelet-leukocyte aggregates in horses.

Samples

Blood from 3 healthy Thoroughbreds.

Procedures

Microscopic and flow cytometric assays were used to evaluate spontaneous platelet aggregation, platelet activation, and platelet-leukocyte aggregates. Platelet activation was detected by evaluation of binding of anti-human fibrinogen to unactivated and ADP-, thrombin-, thrombin agonist receptor peptide-, and platelet activating factor-activated platelets. Platelet-leukocyte aggregates were evaluated microscopically and by flow cytometric determination of leukocyte fluorescence that resulted from binding of fluorescently labeled platelets to leukocytes.

Results

Equine platelets readily aggregated spontaneously when blood was stirred at low, medium, and high speeds. Compared with unactivated platelets, activated platelets had a marked increase in the percentage of cells with increased fluorescence intensity and in mean fluorescence intensity. Unactivated platelets formed aggregates with neutrophils and monocytes, but not with lymphocytes. Activation of platelets resulted in a calcium-dependent increase in platelet-leukocyte aggregates.

Conclusions

Flow cytometric techniques can be used to detect in vitro platelet activation and platelet-leukocyte aggregates in horses.

Clinical Relevance

Flow cytometric techniques may be useful for detection of prothrombotic disorders in horses. (Am J Vet Res 1997;58:823–827)

Free access
in American Journal of Veterinary Research

Summary

Records of 8 dogs with drug-associated aplastic anemia were reviewed. Drugs suspected as being causative included estradiol cyclopentylpropionate (3 dogs), phenylbutazone (2 dogs), meclofenamic acid (1 dog), trimethoprim-sulfadiazine and fenbendazole (1 dog), and quinidine (1 dog). Five of the dogs died or were euthanatized. One dog with estrogen-associated aplasia recovered after prolonged treatment. The dogs with trimethoprim-sulfadiazine and quinidine-associated marrow aplasia recovered promptly after treatment was discontinued.

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objectives

To determine whether pentoxifylline treatment altered hematologic, rheologic, electrolyte, or blood gas test results of Thoroughbreds during submaximal treadmill exercise.

Animals

5 healthy Thoroughbreds that had raced within the past year and had no history of exercise-induced pulmonary hemorrhage.

Procedure

Mixed venous blood samples were obtained before exercise, at treadmill speeds of 9 and 13 m/s, and 20 minutes after exercise; hematologic, rheologic, electrolyte, and blood gas test results were determined.

Results

Pentoxifylline treatment resulted in a 45% reduction in RBC filtration pressures for horses at rest. The improved RBC filterability persisted during treadmill exercise. Horses treated with pentoxifylline had a greater decrease in Po2 values and a lesser increase in plasma lactate concentration during treadmill exercise.

Conclusion

Administration of pentoxifylline improved RBC deformability of horses at rest and during treadmill exercise.

Clinical Relevance

Improved RBC deformability resulting from pentoxifylline treatment may reduce exercise-associated shear stress in pulmonary capillaries, thereby attenuating exercise-induced pulmonary hemorrhage. (Am J Vet Res 1996;57:1364-1368)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine whether furosemide treatment altered the blood flow properties and serum and RBC electrolyte concentrations of Thoroughbreds during submaximal treadmill exercise.

Design

Thoroughbreds were subjected to submaximal treadmill exercise with and without treatment with furosemide (1 mg/kg of body weight, IV).

Animals

5 healthy Thoroughbreds that had raced within the past year and had no history of exercise-induced pulmonary hemorrhage.

Procedure

Venous blood samples were obtained before exercise, at treadmill speeds of 9 and 13 m/s, and 10 minutes after exercise, and hemorheologic and electrolyte test results were determined.

Results

Hemorheologic changes 60 minutes after furosemide administration included increased PCV, plasma total protein concentration, whole blood viscosity, mean RBC volume, and RBC potassium concentration, and decreased serum potassium concentration, serum chloride concentration, and RBC chloride concentration. Furosemide treatment attenuated the exercise-associated changes in RBC size, serum sodium concentration, serum potassium concentration, RBC potassium and chloride concentrations, and RBC density; exacerbated exercise-associated increases in whole blood viscosity; and had no effect on RBC filterability.

Conclusions

The hemorheologic effects of furosemide probably occurred secondary to total body and transmembrane fluid and electrolyte fluxes and would not improve blood flow properties.

Clinical Relevance

The beneficial effects of furosemide treatment in reducing the severity of bleeding in horses with exercise-induced pulmonary hemorrhage cannot be explained by improved blood flow properties. (Am J Vet Res 1996;57:891–895)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate platelet surface-associated P-selectin, mean platelet component concentration (MPC), mean platelet component distribution width (MPCDW), mean platelet volume (MPV), and platelet distribution width (PDW) for detection of activated platelets in dogs with septic and nonseptic inflammatory disease.

Animals—20 healthy dogs and 20 dogs with septic and nonseptic inflammatory disease.

Procedures—Platelet surface-associated P-selectin (expressed as the median fluorescence intensity [MFI] of the platelet population), MPC, MPCDW, MPV, and PDW were determined in 20 healthy adult dogs, and reference ranges were calculated. These parameters were also determined in 11 dogs with nonseptic and 9 dogs with septic inflammatory disease and evaluated to determine which parameters were useful for detection of activated platelets.

Results—12 dogs with inflammatory disease had Pselectin greater than the upper limit of the reference range, whereas 16 dogs with inflammatory disease had MPC lower than the lower limit of the reference range. All dogs in which P-selectin was greater than the upper limit of the reference range had MPC lower than the lower limit of the reference range. The correlation coefficient for P-selectin and MPC was 0.62. Differences in the MPCDW, MPV, and PDW in most dogs with inflammatory disease (compared with healthy dogs) were found; however, the correlation coefficients for P-selectin and MPCDW, MPV, and PDW were low.

Conclusions and Clinical Relevance—Platelet surface- associated P-selectin and MPC appeared to be useful to detect activated platelets in most dogs with septic and nonseptic inflammatory disease. (Am J Vet Res 2005;66:325–329)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine functional characteristics of monocytes obtained from cows with subclinical infection with Mycobacterium avium subsp paratuberculosis (MAP) that may have predisposed those cows to becoming infected with MAP.

Sample Population—Monocytes obtained from 5 uninfected cows and 5 cows subclinically infected with MAP in a herd with a high prevalence of paratuberculosis (ie, Johne's disease).

Procedures—Monocytes from uninfected and subclinically infected cows were incubated with MAP for 2, 6, 24, 72, or 96 hours. Variables measured included expression of tumor necrosis factor-α (TNF-α), interleukin (IL)-10, IL-12, transforming growth factor-β, and suppressor of cytokine signaling-3 (SOCS-3); apoptosis of monocytes; acidification of phagosomes; and killing of MAP.

Results—Monocytes from infected cows had greater expression of IL-10 and SOCS-3 at 2 hours of coincubation with MAP and lower expression of TNF-α and IL-12 when results for all incubation times were combined. Monocytes from infected cows had a greater capacity to acidify phagosomes. No differences were observed in the rate of apoptosis or capacity of monocytes to kill MAP organisms.

Conclusions and Clinical Relevance—Monocytes obtained from cows with subclinical infection with MAP had upregulated expression of IL-10 and SOCS-3 within the first 2 hours after exposure to MAP organisms. Although this did not inhibit acidification of phagosomes, apoptosis of monocytes, or attenuation of the capacity to kill MAP organisms, it may have attenuated the capacity of mononuclear phagocytes to initiate inflammatory and adaptive immune responses. (Am J Vet Res 2005;66:1114–1120)

Full access
in American Journal of Veterinary Research

SUMMARY

Prothrombotic changes occurring in the prodromal stages of carbohydrate-induced laminitis were investigated. Hemostatic alterations were evaluated by determining platelet counts, platelet survival, activated partial thromboplastin time, one-stage prothrombin time, and monocyte procoagulant activity. Thrombosis of vessels in the hoof wall was evaluated by contrast arteriography and histologic examination. Of 5 horses, 4 became lame between 28 and 52 hours after carbohydrate administration. Mean platelet count in laminitis-affected horses was lower throughout the prodromal stages of laminitis, compared with that in control horses, but differences were not statistically significant. However, survival of indium-111-labeled platelets was less than the value in control horses by 6 hours after carbohydrate administration. Arteriography of disarticulated feet revealed marked reduction in blood supply to hooves in laminitis-affected horses. Histologic examination of the laminar dermis disclosed microthrombi in venules of the laminar dermis in 2 of 4 affected horses. Statistically significant changes in prothrombin time were not observed, and changes in activated partial thromboplastin time were slight and occurred only at the onset of lameness. Statistically significant changes in monocyte procoagulant activity were not observed. Plasma endotoxin-like activity was not detected in laminitis-affected horses. These data indicate that platelet survival was decreased within the first 6 hours after induction of carbohydrate-induced laminitis, but systemic activation of the coagulation system was not detected.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To evaluate the contribution of hematocrit and RBC deformability to pulmonary vascular pressures of racehorses.

Design

Pony lungs were isolated and right and left lungs were perfused separately with blood. The effects of changing hematocrit and of pentoxifylline treatment were evaluated.

Animals

11 healthy mixed-breed ponies.

Procedure

Ponies were anesthesized, blood was collected, and lungs were removed and perfused with blood at constant flow rate.

Results

Increasing the hematocrit from 35% to 65% resulted in increases in pulmonary arterial pressure (53%, 45%), capillary shear stress (45%, 32%), and total vascular resistance (92%, 143%) at low (352 ± 33 ml/min) and high (1,442 ± 48 ml/min) flow rates, respectively. Pulmonary artery pressures were lower (10%, 11%) when lungs were perfused with blood from pentoxifylline-treated ponies, compared with blood from control ponies with low hematocrit (PCV, 30%) and low-flow rate and with high hematocrit (PCV, 45%) and high flow rate, respectively. Decreases in capillary shear stress and total vascular resistance were also observed for pentoxifylline-treated blood.

Conclusions

Increases in hematocrit equivalent to those occurring during competitive racing activity contribute substantially to pulmonary vascular pressures in horse lungs. Administration of pentoxifylline to ponies reduced RBC deformability and attenuated increases in pulmonary vascular pressures.

Clinical Relevance

Treatment of racehorses with pentoxifylline may reduce exercise-associated increases in pulmonary vacular pressure, thereby attenuating exercise-induced pulmonary hemorrhage.(Am J Vet Res 1996;57:346-350)

Free access
in American Journal of Veterinary Research

Summary

Cat foods containing propylene glycol (pg) induce Heinz body formation in feline erythrocytes. To further study the hematologic importance of dietary pg, 21 adult cats were allotted to 3 groups of 7 each and fed diets containing 0,6, or 12% pg on a dry-weight basis. Cats fed pg had a dose-related increase in Heinz bodies within 2 weeks, and the increase persisted throughout the study. Although only slight changes occurred in pcv, hemoglobin concentration, and rbc count, punctate reticulocytes were significantly increased in the group fed 12% pg. Mean rbc survival was decreased in the groups fed 6 or 12% pg by 30 and 55%, respectively, compared with the control group. These data indicate that pg-containing diets cause a dose-dependent erythrocyte destruction, even when fed at concentrations as low as 6%.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether platelet-activating factor (PAF) is involved in acute lung microvascular injury associated with pneumonic pasteurellosis in calves.

Animals—15 healthy 2- to 4-week-old male Holstein calves.

Procedure—Calves were anesthetized and inoculated intrabronchially with saline (0.9% NaCl) solution (n = 5) or 1 × 109 Pasteurella haemolytica organisms (n = 10). Of the 10 calves inoculated with P haemolytica, 5 also were treated with WEB 2086, a potent inhibitor of PAF, and 5 were treated with vehicle. Blood and bronchoalveolar lavage samples were collected before and 1, 2, 4, and 6 hours after inoculation of P haemolytica. Blood samples were analyzed to evaluate total number and differential counts of leukocytes, dilute whole-blood leukocyte deformability, size of neutrophils, and neutrophil CD11b expression. Bronchoalveolar lavage samples were analyzed for total number and differential counts of nucleated cells, total protein concentration, and hemoglobin concentration. Size and gross and histologic appearance of lung lesions also was determined.

Results—Treatment of calves with WEB 2086 reduced size of lung lesions, attenuated the increase in microvascular permeability, and reduced neutrophil infiltration in the first 4 hours after inoculation. Treatment with WEB 2086 also attenuated a decrease in leukocyte deformability, increase in size of neutrophils, and CD11b expression by circulating neutrophils.

Conclusions and Clinical Relevance—It appears that PAF is a major mediator for altered lung microvascular permeability and activation of circulating neutrophils in the first 4 hours after onset of pneumonic pasteurellosis in calves. (Am J Vet Res 2000;61: 248–254)

Full access
in American Journal of Veterinary Research