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Abstract

Objectives

To determine whether mucosal permeability is altered during the prodromal stages of alimentary laminitis.

Animals

15 healthy adult ponies.

Procedures

Intestinal permeability was evaluated for control ponies (n = 5) and for ponies 4 to 12 (n = 5) and 20 to 28 (n = 5) hours after administration of carbohydrate overload. Mucosal permeability was determined by measuring the percentage of orally administered technetium Tc99m diethylenetriaminopentaacetate (99mTc-DTPA) excreted in urine during an 8-hour period, then measuring blood radioactivity at hourly intervals. Plasma endotoxin-like activity was measured by use of a chromogenic Limulus amebocyte assay.

Results

Urinary excretion of 99mTc-DTPA was 2.45% of administered dose for control ponies, and was 16.67% of administered dose 4 to 12 hours and 3.57% of administered dose 20 to 28 hours after administration of carbohydrate.

Conclusions

A marked but transient increase in intestinal permeability was observed early in the prodromal stages of alimentary laminitis.

Clinical Relevance

Absorption of substances from the intestine may be an initiating event in alimentary laminitis. (Am J Vet Res 1998;59:1431–1434)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To determine whether platelets become activated and form platelet-platelet or platelet-neutrophil aggregates, or both, when subjected to shear.

Sample Population

Blood obtained from 3 Thoroughbreds.

Procedures

Blood, with PCV adjusted to 32 (low hematocrit) or 60 (high hematocrit)%, was subjected to shear rates of 11.25, 22.5, 45, 90, 225, and 750/s for 3 minutes by use of a cone-plate viscometer. Flow cytometric techniques were used to identify activated platelets, platelet-platelet aggregates, and platelet-neutrophil aggregates.

Results

Shear resulted in decreased platelet count, increased mean platelet volume, platelet activation, and formation of platelet-platelet and platelet-neutrophil aggregates. These changes occurred at lower shear rates in blood with high hematocrit. Platelet-neutrophil aggregate formation was inhibited by blocking P-selectin, but not CD11/CD18 receptors.

Conclusions

Shear-induced platelet activation and aggregate formation occur at physiologic shear rates.

Clinical Relevance

Shear-induced platelet activation may explain the exercise-associated platelet-neutrophil aggregates observed in Thoroughbreds undergoing treadmill exercise. (Am J Vet Res 1998;59:1243-1246)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To determine whether synthetic peptides containing the arginine-glycine-aspartate (RGD) sequence inhibit equine platelet function.

Animals

For in vitro studies of blood, 3 healthy Thoroughbreds; for in vivo and ex vivo studies of administration of RGD-containing peptides, 4 young adult pony mares.

Procedure

Blood was incubated with and without addition of aspirin or RGD-containing peptides (RGDS, RPR 110885) and platelet aggregation responses and platelet adhesion to subendothelial collagen were determined. RPR 110885 was administered IV, and platelet function was evaluated. Platelet aggregation was determined by a turbidimetric method, and platelet adhesion was evaluated by the Baumgartner perfusion method. RPR110885 was administered IV at dosages of 30 and 60 μg/kg of body weight, and bleeding time, platelet aggregation responses, and platelet count were determined at hourly intervals for 4 hours.

Results

Both RGDS and RPR 110885 inhibited platelet aggregation in vitro in dose-dependent manner and inhibited platelet adhesion to subendothelial collagen. The concentration of RGDS that inhibited platelet aggregation by 50% (IC50) was 100 to 142 μM for the various agonists tested, whereas the concentration of RPR 110885 that inhibited platelet aggregation by 50% was 0.03 to 0.05 μM. When administered to ponies at 30 or 60 g/kg, RPR 110885 almost completely inhibited ADP-induced platelet aggregation.

Conclusions

RGDS and RPR 110885 inhibited equine platelet function; however, RPR 110885 was several thousand times more potent than RGDS.

Clinical Relevance

RGD-containing peptides may be useful for treatment of thrombotic diseases of horses. (Am J Vet Res 1997;58:457–460)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the role of tissue factor (TF) in the coagulation events leading to intra-alveolar fibrin deposition and intravascular thrombosis associated with pneumonic pasteurellosis in cattle.

Animals

Healthy 2- to 4-week-old male Holstein calves.

Procedures

Blood and bronchoalveolar lavage samples were collected before and at 1, 2, 4, and 6 hours after inoculation of saline solution or Pasteurella haemolytica. Total leukocyte count, platelet count, plasma total protein concentration, prothrombin time, and partial thromboplastin time were measured in blood samples. Total nucleated cell count, total protein concentration, and procoagulant activity were measured in bronchoalveolar lavage samples. Additionally, platelet survival in blood, platelet accumulation in affected lung tissue, and gross and microscopic lung lesions were determined.

Results

Administration of TF monoclonal antibodies (MAB) TF1-1F7 prevented the decrease in platelet survival and the increase in bronchoalveolar lavage fluid TF-dependent procoagulant activity observed in calves not treated with MAB TF1-1F7 antibody, but did not attenuate the increase in lavage fluid neutrophil numbers and total protein concentration. MAB TF1-1F7 administration reduced the percentage of lung affected by pneumonic lesions from 51.81 % to 10.40% and attenuated intra-alveolar deposition of fibrin, neutrophils, and erythrocytes.

Conclusion

Intra-alveolar fibrin deposition and activation of coagulation in cattle with pneumonic pasteurellosis is, at least in part, mediated by TF.

Clinical Relevance

Treatments that neutralize TF activity may attenuate lung injury in cattle with pneumonic pasteurellosis (Am J Vet Res 1997;58:28–33)

Free access
in American Journal of Veterinary Research

SUMMARY

Echinocytes have been incriminated in the pathogenesis of exertional diseases in horses. To evaluate the hypothesis that echinocytes are dehydrated erythrocytes, we decreased blood sodium and potassium concentrations in 4 horses by administering furosemide (1.0 mg/kg of body weight, q 12 h) for 2 days and we monitored cbc, serum and erythrocyte sodium and potassium concentrations, and echinocyte numbers. Serum sodium concentration decreased progressively over the 48 hours of furosemide administration, then returned to near baseline concentration at 168 hours. A statistically significant decrease (P < 0.05) in serum potassium concentration was observed at 24, 48, and 72 hours after initial furosemide administration, and remained less than the baseline value at the end of the study. Mean erythrocyte potassium concentration decreased rapidly and remained low at the end of the study. Minimal changes were observed in erythrocyte sodium concentration during the first 72 hours after furosemide administration, but the value was significantly (P < 0.05) increased at 168 hours. Type-I and type-II echinocyte numbers increased by 4 hours after furosemide administration and persisted throughout the study. Type-III echinocytes were not seen in baseline samples, but numbers increased only modestly after furosemide administration. Administration of epinephrine to well-hydrated horses increased echinocyte numbers only minimally, indicating that splenic contraction was not the likely cause for the furosemide-associated increase.

To determine whether the decrease in erythrocyte potassium concentration and increase in sodium concentration was caused by furosemide acting directly on the erythrocyte membrane, we quantified erythrocyte potassium and sodium concentrations before and after incubation with furosemide in vitro. Incubation of erythrocytes with furosemide failed to induce depletion of erythrocyte potassium concentration or to increase erythrocyte sodium concentration.

These data support the hypothesis that echinocytes are dehydrated cells and that these changes are induced by total body cation depletion.

Free access
in American Journal of Veterinary Research

Summary

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.

Free access
in American Journal of Veterinary Research

Summary

A flow cytometric platelet immunofluorescence assay (fc-pifa) was compared with a previously developed microscopic platelet immunofluorescence assay (mi-pifa) for detection of circulating platelet antibody. Both assays were performed on serum from 10 healthy dogs with normal platelet count, and on serum from 27 thrombocytopenic dogs—18 had primary immune-mediated thrombocytopenia (imt), and 9 had imt in addition to other immune-mediated disease (secondary imt). Both assays yielded negative results for all control dogs. The mi-pifa and fc-pifa results were in agreement in 23 dogs with imt (14 positive and 9 negative). There was linear correlation between mi-pifa scores and fc-pifa results (r = 0.873). Positive results were obtained for 55.5% of the dogs with suspected imt, using the mi-pifa, compared with 67%, using the fc-pifa; however, the difference was not statistically significant. Use of fresh or frozen fixed donor platelets as the antigen source yielded similar results in the fc-pifa.

Free access
in American Journal of Veterinary Research

SUMMARY

Objectives

To determining whether inhibition of platelet aggregation prevents development of carbohydrate overload-induced alimentary laminitis.

Animals

22 healthy adult ponies.

Procedures

Acute laminitis was induced by oral administration of corn starch/wood flour to 16 ponies, 8 of which were treated with a synthetic analogue of the platelet fibrinogen receptor antagonist peptide (RPR) RGDS (arginine-glycine-aspartic acid-serine) 110885; 6 ponies served as negative controls. Blood was collected before and at 4, 8, 12, 24, 28, and 32 hours after administration of carbohydrate overload, and PCV, total plasma protein concentration, platelet count, activated clotting time, whole blood recalcification time, spontaneous platelet aggregation, ex vivo platelet aggregation responses, in vivo platelet activation, and platelet-neutrophil aggregates were evaluated.

Results

Of 16 ponies given carbohydrate, 6 of 8 untreated ponies developed laminitis and 0 of 8 ponies treated with RPR 110885 developed laminitis. The RPR 110885 treatment attenuated the increase in platelet-neutrophil aggregates observed in untreated ponies.

Conclusions

Platelets are involved in the pathogenesis of equine alimentary laminitis.

Clinical Relevance

Platelet aggregation inhibitors may be useful for prevention or treatment of laminitis, or both. (Am J Vet Res 1998;59:814–817)

Free access
in American Journal of Veterinary Research

Objective

To compare the clinical and clinicopathologic findings in and prognosis for cats with lymphocytic portal hepatitis (LPH) versus cats with acute or chronic cholangiohepatitis (CH).

Design

Retrospective study.

Animals

25 cats with LPH; 16 cats with CH (7 acute, 9 chronic).

Procedure

Cats with LPH and CH were selected by evaluating records from liver biopsy specimens submitted to the University of Minnesota Veterinary Teaching Hospital during a 10-year period. Clinical and clinicopathologic data were retrieved.

Results

Cats with CH had higher segmented and band neutrophil counts, alanine aminotransferase activities, and total bilirubin concentrations than did cats with LPH. Cats with acute CH had higher segmented and band neutrophil counts and lower serum alkaline phosphatase activities and total bilirubin concentrations than did cats with chronic CH. Twelve of 14 cats with LPH or CH had coarse or nodular texture to the liver on ultrasonography, with loss of portal vein wall clarity noticed in 4 of 8 cats with LPH. Sixteen of 23 cats with LPH and 8 of 15 cats with CH survived > 1 year. Of those cats living < 1 year, all cats with LPH and 5 of 7 cats with CH had a serious concurrent illness that may have been responsible for their deaths.

Clinical Implications

LPH and CH can be detected and tentatively differentiated through evaluation of clinical laboratory test results, but histologic evaluation of liver specimens is necessary for definitive differentiation. Survival time was good regardless of the type of inflammatory liver disease. (J Am Vet Med Assoc 1999:214:513–516)

Free access
in Journal of the American Veterinary Medical Association

SUMMARY

Pneumonic pasteurellosis was experimentally induced in calves by inoculation of 5 × 108 Pasteurella haemolytica organisms into the right diaphragmatic lung lobe. Blood and bronchoalveolar lavage fluid samples were obtained prior to inoculation and at postinoculation hour (pih) 2, 4, and 6. Calves developed acute lung injury, characteristic of pneumonic pasteurellosis. Lesions were found only in the right diaphragmatic lobe. By pih 4, significant (P < 0.01) increases were detected in lavage fluid total cell count, neutrophil count, total protein and albumin concentrations, and alkaline phosphatase (alp) and lactic dehydrogenase (ld) activities. Myeloperoxidase and elastase activities did not increase. Neutrophil depletion ameliorated the lung lesions and prevented the increase in lavage fluid cell count, total protein, and albumin concentrations and alp and ld activities. Treatment with the iron chelator, deferoxamine mesylate-hydroxyethyl starch, attenuated the increase in total protein and albumin concentrations and alp and ld activities at pid 4, but not pih 6. Treatment with a neutrophil function inhibitor, pentoxifylline, prevented the increase in lavage fluid neutrophil numbers, but accentuated the increase in total protein and albumin concentrations, and alp, ld, myeloperoxidase, and elastase activities.

Free access
in American Journal of Veterinary Research