Platelet Function, Size and Yield in Whole Blood and in Platelet-Rich Plasma Prepared Using Differing Centrifugation Force and Time in Domestic and Food-Producing Animals

The effects of centrifugation force and time upon platelets function, mean platelet volume and platelet yield were compared with whole blood platelet counts and size in citrated blood samples from the bovine, canine, caprine, equine, feline, ovine and porcine species. The results were similar, for a given species, irregardless of sample volume. Bovine, caprine, feline and ovine platelet yields and mean platelet volumes were maximal when platelet-rich plasma was prepared using longer centrifugation times and lower gravitational forces. Canine, equine and porcine platelet yields and mean platelet volumes were maximal when platelet-rich plasma was prepared using shorter centrifugation times and higher gravitational forces. Platelet aggregation to adenosine diphosphate or arachidonic add was not effected by the method of platelet-rich plasma preparation in bovine, caprine, feline, ovine or pordne platelets. Equine platelet aggregation was maximal when platelet-rich plasma was prepared using longer centrifugation times and lower gravitational forces. Canine platelet aggregation, particularly arachidonic add-induced aggregation, was maximal when platelet-rich plasma was prepared using short centrifugation times and higher gravitational forces. It appeared that the effects of centrifugation parameters upon platelet yield depended upon the relative difference between platelet and red blood cell volumes.

Prolonged Bleeding Time of Chediak-Higashi Cats Corrected by Platelet Transfusion

Cats with the Chediak-Higashi syndrome (CHS) have a platelet storage pool deficiency (SPD). Ten CHS cats were transfused with a concentrate of 51Cr-labeled platelets prepared from normal donor cats. Gne hour after transfusion, the donor platelet count in CHS recipient cats was 40,000-60,000/μl. Bleeding time before transfusion was 9.1 ± 3.0 min. When donor platelet count in CHS cats was 50,000/μl, bleeding time was 1.7 ± 0.2 min. Bleeding time of normal cats was 1.4 ± 0.3 min. Bleeding time increased to 3.3 ± 0.2 min and to 5.3 ± 0.2 min when the platelet count was 30,000/μl, and 15,000/μl, respectively. The close inverse relationship between bleeding time and number of donor platelets in CHS cats (r = —0.92), suggests that prolonged bleeding time is due to a platelet abnormality, that platelet transfusion can effectively correct prolonged bleeding time in an animal model of platelet SPD and that CHS cats may be an appropriate animal model to evaluate hemostatic capabilities of transfused platelets.

Evaluation of binding of fibrinogen and annexin V to equine platelets in response to supramaximal treadmill exercise

There is evidence that equine platelet reactivity is altered by strenuous exercise. Changes in platelet reactivity could impact haemostasis following exercise-induced injury and may play a role in the pathophysiology of exercise-induced pulmonary haemorrhage. Interpretation of results of previous studies is hindered by potential in vitro-induced changes in platelet activity through the choice of anticoagulant and the use of platelet inhibitors. The present study was undertaken to re-evaluate the effect of exercise on equine platelets using methodologies that minimise in vitro-induced changes in platelet activation. The percentage of platelet-neutrophil aggregates increased significantly (P = 0.01) from mean +/- s.e. 3.5 +/- 0.6% at rest to 7.2 +/- 13% during exercise. There were no significant changes in binding of anti-fibrinogen antibody or annexin V to platelets in response to exercise. An inability to detect increased binding of fibrinogen or annexin V may be a result of poor test sensitivity or low statistical power. Alternatively, activated platelets may be quickly removed from the circulation and miss detection. The significance of increased numbers of platelet-neutrophil aggregates in association with exercise is currently unknown and warrants further investigation.

Effects of sodium citrate, low molecular weight heparin, and prostaglandin E1 on aggregation, fibrinogen binding, and enumeration of equine platelets

OBJECTIVE

To investigate the effects of sodium citrate, low molecular weight heparin (LMWH), and prostaglandin E1 (PGE1) on aggregation, fibrinogen binding, and enumeration of equine platelets.

SAMPLE POPULATION

Blood samples obtained from 4 Thoroughbreds.

PROCEDURE

Blood was collected into syringes in the ratio of 9 parts blood:1 part anticoagulant. Anticoagulants used were sodium citrate, LMWH, sodium citrate and LMWH, or 300 nM PGE1/ml of anticoagulant. Platelet aggregation in response to ADP, collagen, and PGE1 was assessed, using optical aggregometry. Platelet activation was evaluated, using flow cytometry, to detect binding of fluorescein-conjugated anti-human fibrinogen antibody. Plasma concentration of ionized calcium was measured, using an ion-selective electrode.

RESULTS

Number of platelets (mean +/- SEM) in samples containing LMWH (109.5+/-11.3 x 10(3) cells/microl) was significantly less than the number in samples containing sodium citrate (187.3+/-30.3 x 10(3) cells/microl). Increasing concentrations of sodium citrate resulted in reductions in platelet aggregation and plasma concentration of ionized calcium. Addition of PGE1 prior to addition of an agonist inhibited platelet aggregation in a concentration-dependent manner, whereas addition of PGE1 4 minutes after addition of ADP resulted in partial reversal of aggregation and fibrinogen binding.

CONCLUSIONS AND CLINICAL RELEVANCE

A high concentration of sodium citrate in blood samples decreases plasma concentration of ionized calcium, resulting in reduced platelet aggregation and fibrinogen binding. Platelets tend to clump in samples collected into LMWH, precluding its use as an anticoagulant. Platelet aggregation and fibrinogen binding can be reversed by PGE1, which may result in underestimation of platelet activation.

Use of a prestorage leukoreduction filter effectively removes leukocytes from canine whole blood while preserving red blood cell viability

Leukoreduction of blood products is a technique used to prevent leukocyte-induced transfusion reactions. Filters currently used for human blood products achieve at least a 99.9% reduction in leukocyte numbers per unit (450 mL) of blood. Goals of this study were to determine if a prestorage leukoreduction filter could effectively achieve leukoreduction of canine blood and to determine if viability of the leukoreduced red blood cell (RBC) product could be maintained after 35 days of storage. Blood collected from each dog was filtered through a leukoreduction filter at either room temperature or after cooling (4 degrees C) for 4 hours. Filtration efficacy was determined by measurement of pre- and postfiltration leukocyte counts. In vitro viability of RBCs was determined by comparing RBC adenosine triphosphate concentration and percent hemolysis before and after the storage period. In vivo viability of stored cells was determined using a biotin-streptavidin-phycoerythrin labeling technique and flow cytometry. Blood filtered within 30 minutes of collection versus blood filtered after cooling had mean reductions in leukocyte numbers of 88.90 and 99.99%, respectively. The mean ATP and hemoglobin concentrations from the in vitro analysis were comparable to those obtained in previously for canine RBC adequately stored for 35 days. The mean in vivo 24-hour survival of the stored RBC was 84.7%. The leukoreduction filter used did not adversely affect in vitro or in vivo viability of canine RBCs. The filter effectively removed leukocytes from blood, with maximal efficiency of filtration achieved with use of cooled blood.

The effect of supramaximal exercise on equine platelet function

When blood is collected into sodium citrate in the proportion of 9 parts blood:1 part sodium citrate, the concentration of plasma sodium citrate in the sample will depend on the packed cell volume (PCV) of the blood sample. This difference in plasma sodium citrate concentration secondary to alterations in PCV significantly affects human platelet aggregation responses. Since horses attain a high PCV in response to high-intensity exercise we investigated the effect of differences in sample plasma sodium citrate concentration on equine platelet aggregability. In addition, low molecular weight heparin (LMWH) was evaluated as an alternative anticoagulant for assessment of platelet aggregability during strenuous exercise in horses. Blood samples were collected pre-exercise and at fatigue after supramaximal treadmill exercise into either 3.8% sodium citrate (9 parts blood:1 part sodium citrate) or 20 u LMWH/ml of blood. Platelet aggregation responses to 1.25 mumol/l adenosine diphosphate (ADP) were measured via optical aggregometry. For samples collected into sodium citrate, aggregability was significantly less than pre-exercise values in samples collected at fatigue and in pre-exercise samples in which sodium citrate concentrations were adjusted to equal those in fatigue samples. However, samples collected into LMWH showed significantly increased platelet aggregability in samples collected at fatigue when compared to pre-exercise samples. In conclusion, higher plasma sodium citrate concentration had a marked inhibitory effect on equine platelet aggregation responses. Low molecular weight heparin was a good alternative anticoagulant for assessment of equine platelet function and results indicate that equine platelet aggregability was enhanced in response to supramaximal exercise.

Plasma von Willebrand factor changes during various reproductive cycle stages in mixed-breed dogs with normal von Willebrand factor and in Doberman pinschers with type-I von Willebrand's disease

OBJECTIVE

To determine whether plasma von Willebrand factor (vWf) concentration changes during the estrous cycle and pregnancy in Doberman Pinschers with type-I von Willebrand's disease (vWd) and in mixed-breed dogs with normal vWf, and if so, whether alterations in vWf concentration are associated with changes in serum concentrations of reproductive hormones.

ANIMALS

5 sexually intact female Doberman Pinschers with type-I vWf and 8 sexually intact female mixed-breed dogs with normal vWf.

PROCEDURE

Concentrations of plasma vWf and serum progesterone and estradiol-17 beta were measured during the estrous cycle of nonpregnant dogs and during pregnancy, parturition, and lactation. Serum concentrations of total triiodothyronine, total thyroxin, and free thyroxin were measured during pregnancy, parturition, and lactation.

RESULTS

Von Willebrand factor concentration did not change during the estrous cycle, but during pregnancy, vWf concentration gradually increased. Peak concentrations were obtained at parturition and were 103 and 92% higher in mixed-breed dogs and dogs with type-I vWd, respectively, than were mean prepregnancy (anestrus) values. At parturition, total triiodothyronine concentration decreased from the prepregnancy value. The increase in vWf concentration during pregnancy was positively associated with changes in concentration of estradiol-17 beta and was negatively associated with changes in concentration of progesterone.

CONCLUSIONS

The increase in vWf concentration in pregnant bitches may be associated with changes in concentrations of reproductive hormones. However, the increase in vWf concentration during pregnancy may involve other factors because vWf concentration did not change during the estrous cycle of nonpregnant dogs despite increases in concentrations of estradiol-17 beta and progesterone.

Plasma von Willebrand factor in thoroughbreds in response to high-intensity treadmill exercise

OBJECTIVE

To determine whether plasma von Willebrand factor (vWf) concentration changes in horses during and after treadmill exercise.

ANIMALS

5 mature, fit Thoroughbreds.

PROCEDURE

A blood sampling catheter was placed in the right jugular vein. A warm-up period was followed by a 3-minute rest period. Horses were galloped at racing pace until fatigued (about 2 minutes). Blood samples were collected prior to warm-up, during the postwarm-up rest period, 1 minute into the run, at cessation of the run, and 5 to 120 minutes after cessation of the run. vWf activity was measured by ELISA and corrected for plasma volume changes (measured by changes in plasma albumin concentration). Platelet-poor plasma from 10 clinically normal, resting horses was pooled, assigned a value of 100 U/dl, and served as a control for all assays.

RESULTS

vWf activity began increasing 1 minute after horses reached full speed. At 5 minutes after cessation of exercise, vWf values had increased by mean of 92% (P < 0.05) from baseline. vWf activity returned baseline by 15 minutes after exercise, and remained there until 90 minutes after exercise, when it began to increase.

CONCLUSION AND CLINICAL RELEVANCE

The spontaneous decrease in vWf values after completion of exercise was unexpected because vWf has a long half-life in circulation. This unexpected finding is compatible with increased vWf consumption and suggests that microvascular trauma may occur in horses during strenuous exercise.

A primary production deficit in the thrombocytopenia of equine infectious anemia

The purpose of this study was to identify the mechanisms responsible for the thrombocytopenia that develops following infection of horses by the lentivirus equine infectious anemia virus (EIAV). Immunocompetent Arabian foals and Arabian foals with severe combined immunodeficiency (SCID), which lack functional B and T lymphocytes, were experimentally infected with EIAV. Levels of viremia and a number of clinical and hematologic parameters were examined prior to and following infection. Thrombocytopenia was not dependent on the immune response: SCID foals were affected as severely as immunocompetent foals. Production of platelets, measured by metabolic incorporation of radioactive label, was significantly reduced. The decrease ranged from 35 to 89% in three SCID and two immunocompetent foals examined. Platelet survival, measured by 51Cr labeling, also declined following infection in both SCID and immunocompetent foals: 51 and 68%, respectively, relative to the preinfection life spans. The difference between immunocompetent and immunodeficient foals was not statistically significant. The number of megakaryocytes (MK) per square millimeter of bone marrow, determined by digitizing morphometry, was not significantly altered in either SCID or immunocompetent thrombocytopenic foals. Numbers of denuded MK nuclei per unit area increased, but the elevation was not statistically significant. No evidence for viral replication in MK was found. Three different parameters of intravascular coagulation (activated prothombin time, fibrin degradation products, and one-step prothombin time) remained normal until after platelet numbers had declined significantly, arguing against an important role for disseminated intravascular coagulation. The findings indicate that EIAV induces thrombocytopenia principally through an indirect, noncytocidal suppressive effect on platelet production, the mechanism of which is unknown. A shortening of platelet life span apparently contributes moderately to the platelet deficit as well. The shortening of platelet life span is multifactorial in origin, including both mechanisms that depend on an active immune response and those that do not.

Inheritance of von Willebrand factor deficiency in Doberman pinschers

OBJECTIVE

To determine the inheritance of von Willebrand factor (vWF) deficiency in Doberman Pinschers.

DESIGN

Prospective, observational study.

ANIMALS

26 adult Doberman Pinschers or mixed-breed dogs and 101 pups produced from 18 matings between adult dogs.

PROCEDURE

Measurement of plasma vWF concentrations in parents and progeny. On the basis of plasma vWF concentrations, dogs were grouped as normal (75 to 160 U of vWF/dl), midrange (> or = 30 and < 75 U of vWF/dl), or low (< 30 U of vWF/dl).

RESULTS

The percentile distribution of vWF concentrations was trimodal. Distribution between dogs with low and midrange plasma vWF concentrations changed sharply, whereas the change between dogs with midrange and normal plasma vWF concentrations was gradual. Three matings between dogs with low vWF concentrations produced 13 offspring, all with low vWF concentrations. Two matings between dogs with normal plasma vWF concentrations produced 14 offspring, all with normal vWF concentrations. Eight matings between dogs with normal and low plasma vWF concentrations produced 54 offspring 40 with midrange, 13 with normal, and 1 with low vWF concentrations. There were 5 matings of dogs with midrange plasma vWF concentrations to dogs with low, midrange, or high vWF concentrations. The results of all matings were consistent with a single gene defect where each normal allele produced half the total amount of vWF when both alleles are normal and each defective allele produced < 15 U of vWF/dl.

CLINICAL IMPLICATIONS

Dogs with low plasma vWF concentrations may be homozygous for the defective allele, whereas dogs with midrange plasma vWF concentrations may be heterozygous. It can be difficult to distinguish normal homozygotes from heterozygotes if evaluation is based only on plasma vWF concentration.

Temporal variation and factors affecting measurement of canine von Willebrand factor

OBJECTIVE

To determine whether canine plasma von Willebrand factor (vWf) varies between and within individuals over time and with different blood sample collection and processing procedures.

ANIMALS

26 adult dogs and 6 pups.

PROCEDURE

Blood was obtained from the jugular or cephalic vein daily for 8 to 19 days and weekly for 9 to 23 weeks in adult dogs and periodically up to 180 days of age in pups. Temporal variation in vWf concentration and the effect of vascular occlusion, venipuncture site, lipemia, hemolysis, anticoagulant, storage time, freeze-thawing, and centrifugation speed on plasma vWf concentration, measured by ELISA, were determined.

RESULTS

Plasma vWf concentration varied over time. In dogs with mean vWf concentration > or = 79 U/dl, the largest intraindividual range in vWf spanned 64 U/dl with daily and 53 U/dl with weekly sample collection. In dogs with mean vWf concentration < or = 24 U/dl, the largest individual variation was 12 U/dl with daily and weekly sample collection. In dogs with mean vWf concentration > or = 53 and < or = 74 U/dl, the largest intraindividual range spanned 35 U/ dl. Mean vWf concentration of pups from 3 to 180 days of age did not change. Sample hemolysis decreased mean vWf by 37%. Mean vWf concentration was 9% higher in cephalic than jugular vein samples (P = 0.056). Other sample collection/preparation procedures did not affect vWf concentration.

CONCLUSION

There was substantial temporal variation in vWf concentration within individual dogs.

CLINICAL RELEVANCE

Multiple tests may be necessary to obtain a reliable estimate of vWf concentration in dogs.

Fibrinolytic activity in dogs after surgically induced trauma

OBJECTIVE

To determine whether alterations in the fibrinolytic pathway analytes, plasminogen (PLG), tissue plasminogen activator, and alpha 2-antiplasmin are significant in dogs subjected to minor and major surgical trauma.

ANIMALS

18 dogs in 3 groups of 6 each.

PROCEDURE

Plasma fibrinolytic pathway analytes were measured in dogs with trauma of ovariohysterectomy (minor trauma) or orthopedic surgery (major trauma) and halothane anesthesia (control group). A commercial procedure adapted to a microtitration plate was used to measure the analytes. Blood was obtained 24 hours before anesthesia, at extubation (0 hours), and again at 2, 24, and 48 hours after extubation. An analyte quality-control strategy was maintained.

RESULTS

In the major trauma group, there was a significant, transient, postsurgical decrease in PLG activity at 0 and 24 hours and a return to presurgical values by 48 hours. The minor trauma group had a similar trend without significant changes, including an increase in PLG values at 48 hours that exceeded the reference range. Antiplasmin values changed significantly in the major trauma group only. Tissue plasminogen activator values remained within the reference range.

CONCLUSIONS

Tissue plasminogen activator was not considered a clinical marker of interest for detection of alterations in fibrinolysis after trauma. In contrast, plasma PLG and alpha 2-antiplasmin values may be useful in the evaluation of hemostatic complications of surgery.

CLINICAL RELEVANCE

Identification of altered fibrinolysis in dogs undergoing traumatic surgery may provide a baseline for preventive pre-and postsurgical hemostatic care.

Evaluation of chromogenic substrate assays for fibrinolytic analytes in dogs

OBJECTIVE

To evaluate the ability of commercial, chromogenic kits designed to measure human fibrinolytic pathway components to measure the canine plasma fibrinolytic pathway enzymes, tissue plasminogen activator (tPA) and plasminogen (PLG), and their respective inhibitors, plasminogen activator inhibitor 1 (PAI) and alpha 2-antiplasmin (AP).

ANIMALS

20 healthy dogs of various ages and breeds.

PROCEDURE

The commercial procedure was adapted to a microtitration plate. Standard curves were generated by use of a canine plasma pool.

RESULTS

Modifications of the commercial kit consisted of change in incubation periods and the substitution of urokinase for the streptokinase. Plasminogen and AP procedures yielded intra- and interassay coefficients of variation (CV) ranging from 2 to 6.4%. The tPA activity gave an acceptable intra-assay CV of 4.2%, but an equivocal interassay CV of 18%. The PAI assay gave unacceptable intra-assay and interassay CV of 59 and 66%, respectively.

CONCLUSIONS

Modifications of the commercial PLG and AP procedures were appropriate for use with fresh and frozen canine plasma. However, equivocal results were obtained for canine plasma tPA. Although the PAI assay was able to detect the inhibitor, it gave unacceptable quantifiable results. Human and canine plasma contained similar amounts of PLG and AP, but 25% more tPA was found in canine plasma than human plasma.

CLINICAL RELEVANCE

With modifications, the commercial human PLG and AP chromogenic kits may serve to elucidate such canine fibrinolytic disorders as disseminated coagulopathy. The high cost of the chromogenic substrate limits its application.

Canine idiopathic thrombocytopenic purpura

Canine idiopathic thrombocytopenic purpura (ITP) is a disease in which antibodies bound to the surface of platelets mediate premature platelet destruction by macrophages. ITP in dogs and chronic ITP in humans are analogous diseases. This article draws on information from the literature on ITP in dogs and in humans, and reviews the pathogenesis, diagnosis, and treatment of ITP in dogs.

Studies of platelet-bound and serum platelet-bindable immunoglobulins in dogs with idiopathic thrombocytopenic purpura

Canine idiopathic thrombocytopenic purpura (ITP) is clinically analogous to chronic ITP in human beings. The objective of this study was to investigate the pathogenesis of canine ITP by determining whether immunoglobulins bound to the surface of platelets from dogs with ITP (platelet-bound immunoglobulins) were directed against host platelet antigen and whether platelet glycoproteins (GP) IIb and IIIa were target antigens in dogs with ITP. Thirty-two dogs with ITP were studied. Increased platelet-bound immunoglobulin concentrations were detected in 30 cases (94%), and increased concentrations of serum platelet-bindable immunoglobulins were detected in 11 cases (34%). Immunoglobulins eluted from the surface of platelets from dogs with ITP bound to homologous normal canine platelets in 11 of 19 cases (58%). Immunoglobulins against platelet membrane GP IIb and/or IIIa were detected in serum from four of 17 affected dogs. This study provides evidence that immunoglobulins bound to surface of platelets from some dogs with ITP are directed against host platelet antigens and that platelet target antigens are, in some cases, GP IIb and IIIa. This supports the hypothesis that canine ITP is an autoimmune disease, similar to the pathogenesis of chronic ITP in human beings.

Differential distribution of von Willebrand factor in canine vascular endothelium

OBJECTIVE

To determine whether endothelial cell (EC) von Willebrand factor (vWf) is uniformly distributed in canine blood vessels.

DESIGN

Contents of EC vWf from vascular segments was evaluated in Haütchen preparations, using immuno-histochemistry. EC from femoral arteries and veins and jugular veins were grown in culture, and the intracellular content and constitutive release of vWf from these cells were measured. The amount of vWf mRNA in the cultured EC was determined.

ANIMALS

Vascular segments for Häutchen preparations and EC for culture were obtained from 5 and 10 clinically normal, mixed-breed dogs, respectively.

PROCEDURES

Appropriate vascular segments were removed, fixed; processed for immunohistochemistry, using a monospecific polyclonal antibody to canine vWf, and Haütchen preparations were made. Intracellular and constitutive released vWf was measured, using an ELISA, and vWf mRNA was measured by Northern blot analysis.

RESULTS

Intact endothelial linings from femoral veins, jugular veins, vena cava, and pulmonary veins stained more intensely than femoral arteries, carotid arteries, aorta, and pulmonary veins. Constitutive release and intracellular content of vWf in cultured EC from femoral veins was about 30 times higher than that from femoral arterial EC, which was barely detectable. Similar differences were seen in amounts of mRNA.

CONCLUSIONS

There is marked diversity in EC vWf in canine vasculature that may result from differences in vWf mRNA.

CLINICAL RELEVANCE

Low amounts of vWf in canine systemic arterial EC may contribute to thromboresistance of canine arteries.

Measurement of von Willebrand factor-specific mRNA and release and storage of von Willebrand factor from endothelial cells of dogs with type-I von Willebrand's disease

OBJECTIVE

To characterize the cellular basis of the plasma von Willebrand factor (vWf) deficiency in Doberman Pinschers with type-1 von Willebrand's disease (vWd).

ANIMALS

Five Doberman Pinschers with type-I vWd and 5 clinically normal dogs used as controls.

PROCEDURE

Vascular endothelial cell cultures were used to measure constitutive vWf release, thrombin-stimulated vWf release, baseline intracellular vWf concentration, and vWf mRNA expression.

RESULTS

Cells cultured from vWd-affected dogs were morphologically indistinguishable from cells cultured from control dogs, but had reductions in constitutive vWf release (6.5-fold) and vWf mRNA content (fivefold) that correlated to the reduction in plasma vWf concentration (sixfold) in these dogs. The 9.0-kb, canine vWf message was identified, using a polymerase chain reaction-amplified segment of the canine vWf gene and was similar in size to the human vWf message. The vWd cells also had reductions in baseline intracellular vWf concentration (15.6-fold) and thrombin-stimulated vWf release (14.5-fold). Additionally, it was observed that normal canine endothelial cells from different anatomic locations were heterogeneous with respect to vWf expression.

CONCLUSIONS

These findings suggest that the plasma vWf deficit in dogs with type-I vWd results from decreased endothelial cell production of vWf resulting from either decreased transcription of the vWf gene or abnormalities in mRNA processing/stability. This is similar to findings in human beings with type-I vWd.

Detection of platelet-bound and serum platelet-bindable antibodies for diagnosis of idiopathic thrombocytopenic purpura in dogs

The sensitivity and specificity of 2 antibody tests for diagnosis of idiopathic thrombocytopenic purpura (ITP) in dogs were investigated prospectively. An ELISA to detect antibodies bound to the surface of platelets from affected dogs (direct test) was performed in 34 dogs with a clinical diagnosis of ITP and in 21 dogs with thrombocytopenia attributable to other causes. An ELISA to detect platelet-bindable antibodies in serum from affected dogs (indirect test) was performed in 32 dogs with ITP and in 15 dogs with other causes of thrombocytopenia. The direct test was positive in 32 of 34 dogs with ITP (sensitivity, 94%) and negative in 13 of 21 dogs with other causes of thrombocytopenia (specificity, 62%). Positive direct test results were obtained in 2 dogs with systemic lupus erythematosus, and in 1 dog each with concurrent Ehrlichia canis and Babesia canis infections, dirofilariasis, myelodysplasia, disseminated intravascular coagulation (of unknown cause), and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine, as well as in 1 dog with thrombocytopenia 14 days after a whole blood transfusion. The indirect test had positive results in 11 of 32 dogs with ITP (sensitivity, 34%) and negative results in 12 of 15 dogs with other causes of thrombocytopenia (specificity, 80%). Positive indirect test results were obtained in 1 dog each with systemic lupus erythematosus, concurrent E canis and B canis infections, and thrombocytopenia subsequent to administration of trimethoprim/sulfadiazine. Detection of platelet-bound antibodies was more sensitive than detection of serum-platelet bindable antibodies in confirming a diagnosis of ITP in dogs.(ABSTRACT TRUNCATED AT 250 WORDS)

von Willebrand factor is not altered in azotemic dogs with prolonged bleeding time

The effects of azotemia on von Willebrand factor (vWf) plasma concentration, structure, and function were studied by utilizing canine models for both uremic bleeding and type I vWf deficiency (vWd). Seventy-five percent to 80% renal mass reduction in eight mixed-breed dogs induced marked azotemia (blood urea nitrogen [BUN] 103 +/- 7 mg/dl [mean +/- SEM]; creatinine 5.8 +/- 1 mg/dl) and prolonged mean buccal mucosal bleeding time (BMBT) from 1.8 +/- 0.2 minutes to 7.0 +/- 0.4 minutes. The mean vWf plasma concentration increased from 0.88 +/- 0.11 U/ml to 1.26 +/- 0.14 U/ml. The pre- and postsurgical sodium dodecyl sulfate-agarose gel electrophoresis multimeric patterns were similar in all dogs. Administration of cryoprecipitate from pooled azotemic mixed-breed dog plasma to five Doberman pinschers with type I vWd increased the mean plasma vWf from 0.14 +/- 0.01 U/ml to 0.48 +/- 0.04 U/ml and decreased the BMBT from 7.1 +/- 0.6 minutes to 3.14 +/- 0.09 minutes. After renal mass reduction, five type I vWd Dobermans developed marked azotemia (BUN 79 +/- 8.6 mg/dl; creatinine 3.7 +/- 0.6 mg/dl) and prolonged BMBT (16.1 +/- 3.6 minutes). Findings in the eight azotemic mixed-breed dogs indicated that (1) vWf plasma levels were normal to increased in azotemic dogs; (2) vWf structure and multimeric distribution were not altered in canine azotemia; and (3) vWf was functional when placed in a non-azotemic environment. The prolongation of the BMBT in azotemic vWd dogs indicated that factors other than alteration of vWf function were responsible for the prolonged BMBT in canine azotemia.

Experimentally induced renal failure in the dog as an animal model of uremic bleeding

Experimental canine renal failure was studied as a potential animal model for human uremic bleeding. Renal failure accompanied by hemostatic alterations was induced in eight dogs by means of two surgical techniques of renal mass reduction. The hemostatic deficits consisted of immediate and marked reduction of the platelet glass bead retention (PR) to less than 10% of normal and gradual prolongation of the buccal mucosal bleeding time (BMBT) to approximately four times the normal value. Platelet count, volume, aggregation responses, and coagulation were normal. A packed cell volume (PCV) of less than 30% was observed in three dogs. Elevation of the PCV normalized the BMBT in two dogs, but because the PR was unchanged and the BMBT effect was temporary, anemia was not considered the primary cause of the prolonged bleeding time. There was a significant, positive correlation between BMBT and BUN, suggesting that the altered hemostasis may be related to the accumulation of urea or other uremic toxins of protein origin. The finding of a defect in PR and BMBT--tests that require normal platelet adhesion and aggregation--in azotemic dogs were platelet numbers and aggregation are normal indirectly implicates platelet adhesion as the primary hemostatic defect.

Evaluation of an additive solution for preservation of canine red blood cells

The effect of an additive preservative solution on canine red blood cell posttransfusion viability (PTV) and on selected canine red blood cell biochemical parameters was studied. One unit (450 mL) of blood was collected from 6 clinically normal dogs into the anticoagulant citrate phosphate dextrose, centrifuged, and the plasma removed. The red blood cells were then suspended in 100 mL of a saline, adenine, dextrose, and mannitol solution and stored at 4 degrees C. Aliquots were removed for study at 1, 10, 20, 30, 37, and 44 days. The 24-hour PTV of autologous red blood cells was determined using a sodium chromate (51Cr) label. Red blood cell concentrations of 2,3-diphosphoglycerate (2,3-DPG), adenosine-5'-triphosphate (ATP), and pH were also determined. Canine red blood cell PTV, pH, ATP, and 2,3-DPG concentrations decreased during storage (P < .05). The PTV decreased from 94% using day 1 red blood cells to 80% and 75% using day 37 and day 44 red blood cells, respectively (P < .05). Although the mean PTV of the day 44 stored units equaled the Food and Drug Administration (FDA) minimum standard for human red blood cells, the PTV was substandard in 75% of the day 44 units. The FDA standard was exceeded in 83% of the day 37 units. It was concluded that 37-day-old canine red blood cells preserved with a saline, adenine, dextrose, and mannitol solution are of acceptable quality for transfusion.

Effect of anticoagulant and blood storage time on platelet-bound antibody concentrations in clinically normal dogs

A solid-phase ELISA to detect antibodies bound to the surface of canine platelets (platelet-bound antibodies) is described. Using this assay, the effect of anticoagulant and storage time of anticoagulant blood on the concentration of antibodies bound to the surface of platelets from clinically normal dogs was investigated. Blood from 3 clinically normal dogs was anticoagulated with acid citrate dextrose, Na3 citrate, and aqueous K3 EDTA and stored on ice for up to 48 hours. Platelet-bound antibody concentration was measured on platelets isolated from anticoagulated blood immediately after venipuncture and subsequent to storage of blood for 24 and 48 hours. Differences in platelet-bound antibody concentrations were investigated among dogs, anticoagulants, and storage times by ANOVA and Bonferroni pair-wise comparison of means. There was no effect of dog on platelet-bound antibody concentration. The effect of time was significant (P < 0.0001), with higher concentration of platelet-bound antibodies detected with increasing storage time. Effect of anticoagulant on platelet-bound antibody concentration was not statistically significant; however, there was a trend to increasing concentration of antibodies bound to platelets isolated from Na3 citrate- and K3 EDTA-anticoagulated blood. Moreover, there was significant (P = 0.02) interaction between anticoagulant and time. Platelet-bound antibody concentration increased with storage of anticoagulated blood prior to platelet isolation and with use of Na3 citrate and K3 EDTA anticoagulants. The preferred anticoagulant for platelet-bound antibody measurement is acid citrate dextrose. Platelet-bound antibody concentration should be determined not longer than 24 hours after blood collection.

Effect of cryoprecipitate and plasma on plasma von Willebrand factor multimeters and bleeding time in Doberman Pinschers with type-I von Willebrand's disease

We determined whether administration of cryoprecipitate or fresh-frozen plasma (FFP) would enhance glass bead platelet retention and shorten the bleeding time in von Willebrand factor (vWf)-deficient Doberman Pinschers. Plasma concentration of vWf was < 15% of the reference value in these dogs and, on the basis of multimeric analysis of vWf, these dogs had type-I von Willebrand's disease (vWd). Concentration of vWf in cryoprecipitate (prepared from FFP of clinically normal dogs) was enriched almost 20 times, and the preparation was a concentrate of the largest and most physiologically active multimers. Administration of a dose of cryoprecipitate calculated to increase plasma vWf concentration of recipient dogs to 50 U/dl increased plasma vWf concentration in recipient dogs to about 40 U/dl. Mean buccal mucosal bleeding time (BMBT) shortened from 6.7 minutes before treatment to 3.8 minutes at 2 hours after treatment. Cryoprecipitate from donor dogs treated with deamino-8-D-arginine vasopressin (1 micrograms/kg of body weight) effectively shortened mean BMBT from 6.4 minutes to 3.1 minutes. Administration of cryoprecipitate from vWf-deficient dogs prolonged, rather than shortened, the BMBT. After FFP (450 ml) infusion, plasma vWf concentration increased in recipient dogs, but the BMBT did not shorten. Glass bead platelet retention did not change after administration of cryoprecipitate or FFP.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged bleeding time of Chediak-Higashi cats corrected by platelet transfusion

Cats with the Chediak-Higashi syndrome (CHS) have a platelet storage pool deficiency (SPD). Ten CHS cats were transfused with a concentrate of 51Cr-labeled platelets prepared from normal donor cats. One hour after transfusion, the donor platelet count in CHS recipient cats was 40,000-60,000/microliters. Bleeding time before transfusion was 9.1 +/- 3.0 min. When donor platelet count in CHS cats was 50,000/microliters, bleeding time was 1.7 +/- 0.2 min. Bleeding time of normal cats was 1.4 +/- 0.3 min. Bleeding time increased to 3.3 +/- 0.2 min and to 5.3 +/- 0.2 min when the platelet count was 30,000/microliters, and 15,000/microliters, respectively. The close inverse relationship between bleeding time and number of donor platelets in CHS cats (r = -0.92), suggests that prolonged bleeding time is due to a platelet abnormality, that platelet transfusion can effectively correct prolonged bleeding time in an animal model of platelet SPD and that CHS cats may be an appropriate animal model to evaluate hemostatic capabilities of transfused platelets.

Evaluation of the buccal bleeding time and platelet glass bead retention as assays of hemostasis in the dog: the effects of acetylsalicylic acid, warfarin and von Willebrand factor deficiency

The study evaluated two hemostatic assays in the dog, a modified version of the buccal mucosal bleeding time (BMBT) and the platelet glass bead retention (PR), to describe the aspects of hemostasis measured by these assays. Von Willebrand factor (vWf)-deficient Doberman pinscher dogs were used in evaluating the effects of altered platelet adhesion. Normal dogs were treated with either acetylsalicylic acid (ASA) or warfarin to evaluate the effects of altered platelet aggregation and coagulation. There was significant prolongation of the BMBT and reduction of the PR in vWf-deficient dogs as compared to normal dogs. In ASA treated dogs the BMBT was slightly prolonged; the PR was significantly reduced. The change in ASA-induced BMBT did not correlate with the sensitivity of the dog platelets to arachidonic acid. In warfarin treated dogs there was no change in the BMBT; however, the PR was significantly reduced. The BMBT is a test of hemostasis that is sensitive to platelet adhesion and aggregation deficits. The PR is useful in detecting general abnormalities in hemostasis including platelet adhesion defects due to reduced vWf.

Primary and secondary lysosomes in megakaryocytes and platelets from cattle with the Chediak-Higashi syndrome

The ultrastructure of lysosomes from megakaryocytes (MK) and platelets of cattle with the Chediak-Higashi syndrome (CHS) was characterized using acid phosphatase histochemistry with beta-glycerophosphate as substrate and cerium as a capturing agent. Acid phosphatase was localized in the trans aspect of the Golgi complex and/or granules in MK at all stages of maturation. Morphometric analysis of the diameter of each lysosome was performed on MK from CHS cattle and compared to MK from normal cattle. Lysosomes in CHS MK were neither enlarged nor different with respect to classification as secondary lysosomes, which composed 35% of the lysosomes in CHS MK. Lysosomes were demonstrated in 22% of the CHS platelet sections and appeared similar to those from normal cattle, 56% of them being classified as secondary lysosomes. Why lysosomes are not enlarged in bovine CHS MK and platelets, whereas they are enlarged in most other cell types, remains unknown.

Compartmentation of 4,6-difluoro-5HT studied by nuclear magnetic resonance in normal and CHS bovine platelets

A platelet storage pool deficiency (SPD) is present in platelets from cattle with the Chediak-Higashi syndrome (CHS). The most plausible hypothesis for the SPD is that dense granule precursors are simply not formed in CHS megakaryocytes. There is, however, evidence that some recently acquired 5-hydroxytryptamine (5HT) is located in granules and that the granules have an acidic interior. To obtain a greater understanding of the processing of 5HT by SPD platelets, normal and CHS platelets were incubated with 4,6-difluoro-5HT and studied by 19F NMR at 188 mHz. Normal platelets contained 2 compartments for 4,6-difluoro-5HT as indicated by 2 well-developed resonances for each 19F. The resonances were unequal in magnitude. The predominant resonance broadened with lower temperatures and was absent in CHS bovine platelets; it was, therefore, the dense granule compartment. There was only 1 resonance for each 19F in CHS platelets. The chemical shift was identical to the minor resonance, or non-dense granule resonance, found in normal bovine platelets but the resonance width was increased, indicating that some non-dense granule 4,6-difluoro-5HT was in a more restricted environment within CHS platelets than it was in normal platelets.

Demonstration of secondary lysosomes in bovine megakaryocytes and platelets using acid phosphatase cytochemistry with cerium as a trapping agent

The ultrastructure of lysosomes from bovine megakaryocytes (MK) and platelets was characterized using acid phosphatase cytochemistry with beta-glycerophosphate as substrate and cerium as a trapping agent. The technique was easily reproducible; cerium-phosphate precipitates were uniform, readily visualized, and there was a virtual absence of nonspecific reaction product. Acid phosphatase was localized in the trans aspect of the Golgi complex and/or granules of less than 50 nm to 650 nm diameters in MK at all stages of maturation. Forty percent of the MK lysosomes contained inclusions of variable shapes, sizes and electron-density and were classified as secondary lysosomes. Twenty-four percent of the platelet sections contained acid phosphatase-positive granules. Fifty-four percent of these were secondary lysosomes. This is the initial report demonstrating secondary lysosomes in either resting MK or platelets using acid phosphatase cytochemistry. These findings suggest that MK and platelet lysosomes have an intracellular function in resting MK and platelets.

Effect of exercise, DDAVP, and epinephrine on the factor VIII:C/von Willebrand factor complex in normal dogs and von Willebrand factor deficient Doberman pinscher dogs

Endothelial cells in biopsied blood vessels from von Willebrand factor (vWf)-deficient Doberman pinscher dogs contain immunologically detectable vWf. These dogs and normal dogs were treated with DDAVP (0.6 microgram/kg) and epinephrine (0.5 microgram/kg/min for 30 minutes) and were exercised, using 5 different exercise protocols, (3-4 m/s for 5-40 minutes at 0-5% grade) to determine if treatments reported to increase plasma factor VIII:C/vWf complex in humans would elevate canine plasma vWf. Following the two most strenuous exercise conditions--30 and 40 minutes--plasma von Willebrand factor antigen (vWf:Ag) increased in normal dogs by 30% and 70%, respectively. Factor VIII:C was increased 47% by the most strenuous exercise conditions. The vWf-deficient dogs would not exercise beyond 30 minutes and neither vWf:Ag nor factor VIII:C activity increased. Following DDAVP, plasma vWf:Ag increased in the normal dogs by 47% and factor VIII:C activity was increased by 48%. Factor VIII:C activity increased by 30% in the vWf-deficient dogs, but there was only a slight change in vWf:Ag. Bleeding time decreased in 5 of 6 vWf-deficient dogs. In the normal dogs vWf:Ag increased by 14% after epinephrine infusion, but factor VIII:C activity did not change; neither parameter was altered in the vWf-deficient dogs. While the factor VIII:C/vWf:Ag complex was increased in the normal dog by exercise and DDAVP, the increase is not as pronounced as has been reported for humans. It is not known whether the poor response of the vWf-deficient dog is due to low levels of vWf in their endothelium or to a release defect.

von Willebrand factor is present in the vascular endothelium from normal dogs and from Doberman pinscher dogs with a plasma von Willebrand factor deficiency

An immunohistochemical study was undertaken to determine the presence and distribution of von Willebrand factor antigen (vWf:Ag) in blood vessels from normal dogs and from Doberman pinscher dogs with a marked plasma deficiency of vWf. vWf:Ag could not be detected in plasma from the Doberman pinscher dogs by ristocetin- and botrocetin-induced platelet agglutination or by EIA. An ELISA assay revealed vWf:Ag levels that were between 2-4% of that in normal canine plasma. Factor VIII:C activity was 30-46% of normal. The activated partial thromboplastin time (APTT) was increased but not the one-stage prothrombin time (OSPT). Four different antibody preparations were used in this study to detect vWf--a monoclonal and a polyclonal antibody prepared against human vWf and 2 polyclonal antibodies against canine vWf. vWf:Ag was detected with monospecific antibody in endothelial cells in veins, venules, and arterioles from normal dogs and vWf-deficient dogs. The histofluorescence observed in vessels of vWf-deficient dogs was indistinguishable from that observed in vessels from normal dogs.

Storage pool deficiency in cattle with the Chédiak-Higashi syndrome results from an absence of dense granule precursors in their megakaryocytes

Platelets from cattle with the Chédiak-Higashi syndrome (CHS) have a storage pool deficiency and virtual absence of platelet dense granules. Megakaryocytes (MKs) from five control (n = 135) and five CHS (n = 133) cattle were evaluated using standard transmission electron microscopy. Osmiophilic dense granules were not observed in control or CHS MKs. In MKs from normal cattle, clear vesicles of 200- to 650-nm diameter bounded by a sharp membrane were observed. They were easily differentiated from the demarcation membrane system, endoplasmic reticulum, and alpha granules. The clear vesicles were virtually absent in MKs from CHS cattle at all stages of maturation. MKs in bone marrow samples from two control (n = 91) and two CHS (n = 61) cattle that had been processed for the uranaffin reaction were also evaluated. The clear vesicles were replaced by uranaffin-positive granules in MKs from control cattle, but positive uranaffin granules were not observed in CHS MKs. These findings indicate that the platelet dense granule storage pool deficiency in CHS cattle results from an anatomic absence of dense granule precursors in maturing and mature CHS MKs.

Interaction of a vasopressin antagonist with vasopressin receptors in the septum of the rat brain

The ability of d(CH2)5-Tyr(Me)-arginine-8-vasopressin, an antagonist of peripheral pressoric (V1-type) vasopressin receptors, to label vasopressin binding sites in the septum of the rat brain was evaluated. Using crude membrane preparations from the septum, 3H-arginine-8-vasopressin (AVP) specifically labels a single class of binding sites with a Kd of 2.9 nM and maximum binding site concentration of 19.8 fmole/mg protein. 3H-Antag also labels a single class of membrane sites but with higher affinity (Kd = 0.47 nM) and lower capacity (10.1 fmole/mg protein) than 3H-AVP. The rank order of potency of various competitor peptides for 3H-AVP and 3H-Antag binding was similar. Oxytocin was 100-1,000 fold less potent than AVP in competing for binding with both ligands. 3H-AVP and 3H-Antag showed similar labeling patterns when incubated with septal tissue slices. Unlabeled Antag also effectively antagonized vasopressin-stimulated phosphatidylinositol hydrolysis in septal tissue slices.

Equine hemostasis. Description, evaluation, and alteration

This is a review of equine hemostasis and is divided into three sections. The initial portion describes the normal hemostatic system and includes platelet function, coagulation, fibrinolysis and control processes. The second phase is devoted to laboratory tests of hemostasis, and the last section provides information on specific alterations.

Evaluation of hepatic and renal function in cats with chediak-higashi syndrome

Cats with the Chediak-Higashi Syndrome (CHS) have partial oculocutaneous albinism, a bleeding tendency, and enlarged cytoplasmic granules in many cell types including those in the liver and kidney. Hepatic and renal function was evaluated in six CHS and six age-matched control cats to determine if the functions of these organs were compromised by the CHS trait. Serum concentrations of alanine aminotransferase, alkaline phosphatase, and total bilirubin were determined to assess the status of the liver. Sulfobromophthalein retention tests were also performed. Renal function was evaluated by determination of (14)C-inulin clearance; blood urea nitrogen and serum creatinine concentrations; 24-hour protein/creatinine ratios, percent clearance ratios of calcium, phosphorus, sodium, potassium and chloride; and urinalysis values. The CHS cats were not significantly (P > 0.05) different from the control cats in any of the above tests. Use of a non-parametric statistical test did reveal a mild difference (P = 0.047) in 24-hour protein excretion between CHS and control cats. Complete blood counts were performed, and the packed cell volume and hemoglobin concentrations were significantly lower (P< 0.05) in the CHS cats than in the control cats.

Anesthetics and anticoagulants used in the preparation of rat platelet-rich-plasma alter rat platelet aggregation

Aggregation of platelets in heparin- and citrate-anticoagulated platelet-rich-plasma (PRP) from rats anesthetized with methoxyflurane (M), diethyl ether (E), acepromazine/ketamine (A/K), or sodium pentobarbital (P) is described, as are platelet counts. Platelet counts were highest in heparin- or citrate-PRP from E and A/K anesthetized rats. Collagen and arachidonic acid (AA) induced aggregation in heparin-PRP only, and ADP induced greater aggregation in heparin-PRP than in citrate-PRP. Differences between citrate-PRP and heparin-PRP are probably due to citrate inhibition of platelet aggregation, since addition of citrate to heparin-PRP decreased aggregation, while addition of heparin to citrate-PRP did not alter aggregation. Aggregation of hirudin-PRP was slightly less than heparin-PRP. Anesthetics affected rat platelet aggregation: the rank order of the maximal extent of ADP-induced aggregation in citrate-PRP was M greater than E = A/K greater than P, and that for AA and collagen in heparin-PRP was E = A/K greater than M = P. The correlation between the effect of the anesthetics and activation of the sympathoadrenal system is discussed. It appeared that of the commonly used anticoagulants and anesthetics, heparin and methoxyflurane had the least influence on rat platelet aggregation.

Rat platelet aggregation: strain and stock variations

Platelet aggregation induced by ADP, arachidonic acid, and collagen was monitored in rats from two stocks, WSU-SD and CD, and from three strains, Lewis, Holtzman, and NBR. ADP-induced aggregation did not vary between the WSU-SD, CD, Lewis, Holtzman, and NBR rats. In contrast, the response to AA and collagen depended upon the stock or strain of rat. Platelets from the Holtzman and especially the NBR were much more sensitive to AA than were those from the other strains. At 0.25 mM AA, 7 of 8 NBR rats and 5 of 8 Holtzman rats aggregated irreversibly, while only 1 in 8 WSU-SD, CD, and Lewis rats aggregated irreversibly at that concentration. Collagen-induced aggregation reflected that to AA. The possible relationship between the variation in platelet aggregation and sympathoadrenal activity is discussed.

Diadenosine 5',5'''-p1,p4-tetraphosphate deficiency in blood platelets of the Chédiak-Higashi syndrome

Diadenosine tetraphosphate (AP4A) is an unusual nucleotide found in a variety of cells, including platelets. It has been suggested that platelet AP4A is stored in the dense granules and is metabolically inactive. We have studied the AP4A content of blood platelets in two patients and three cattle with Chédiak-Higashi syndrome (CHS), a hereditary platelet defect with dense granule deficiency. Acid-soluble extractions of whole blood and platelets were neutralized. The adenosine triphosphate (ATP) level was measured by luminescence technique. To measure the AP4A content, the neutralized extract was treated with phosphomonoesterase for removal of ATP. The AP4A content was then measured by coupling the phosphodiesterase and luciferase reaction. The AP4A content was 0.43 nmol/mg protein for normal human platelets and 0.004 nmol/mg protein for CHS platelets. The ATP/AP4A ratio was 67 for normal and 3,023 for CHS platelets. The whole blood AP4A was reduced by 89% in CHS patients who had only a slight decrease in ATP level (26% reduction). Similarly, bovine platelets with CHS showed a marked decrease of AP4A content and a moderate reduction of the ATP level. The platelet ATP/AP4A ratio was 351 and 3,133 for normal and CHS cattle, respectively. Results demonstrate a marked reduction of AP4A in CHS platelets and suggest that AP4A may be a useful marker for the measurement of dense granule content in platelets.

Alterations in coagulation and hemograms of horses given endotoxins for 24 hours via hepatic portal infusions

This experiment was designed to establish a model for the study of gastrointestinal disturbances as a result of prolonged endotoxin uptake in the horse. The hepatic portal vein of 7 horses was catheterized (through flank incisions) to give chronic hepatic portal infusions of lipopolysaccharide (LPS, endotoxin). Lipopolysaccharide was infused at a rate of 1 microgram/kg of body weight/hr for 24 hours. Two of the horses were infused with saline solution for 12 hours before LPS infusions were given. Lipopolysaccharide was shown to affect behavior and hematologic and coagulation values. The 1st hour was critical for the LPS-infused horses; yet by 4 hours, the horses had apparently become refractory to continued infusion of LPS. During the 1st hour, all horses collapsed without an accompanying hypotension. A decrease in polymorphonuclear leukocytes (neutrophils) was seen during this time and was accompanied by a shortening of the recalcification tests, 1-stage prothrombin time, and activated partial thromboplastin time. There was an increased concentration of circulating fibrinogen/fibrin degradatory products. All of the LPS-infused horses showed signs of hoof discomfort and either stood with the 4 feet together beneath the body or continually shifted their weight from one front foot to the other. Hoof temperature decreased approximately 3 degrees (C) during this time and remained decreased for the duration of the experiment.

Genetics of the fawn-hooded rat strain. The coat color dilution and platelet storage pool deficiency are pleiotropic effects of the autosomal recessive red-eyed dilution gene

The inheritance of coat color, hooded-coat pattern, and platelet storage pool deficiency of fawn-hooded rats was studied by crossing fawn-hooded rats with rats of other strains. It was determined that the tan coat color and the platelet storage pool deficiency were pleiotropic effects of the autosomal recessive red-eyed dilution (r) gene. The hooded-coat pattern was determined to be the effect of a different autosomal recessive gene. It also was demonstrated that the tan coat color of fawn-hooded rats is a dilution and that the shade of the tan coat color expressed varied with the underlying coat color genes.

Secondary amyloidosis in a bull with Chediak-Higashi syndrome

A ten year old Hereford bull with Chediak-Higashi syndrome was examined at necropsy after a lifelong history of recurrent bacterial infections. Amyloidosis, which has not been previously reported in Chediak-Higashi, was identified in liver, spleen and kidney.

Acquisition and aggregation of canine blood platelets: basic mechanisms of function and differences because of breed origin

A method for obtaining reliable blood platelet yields in canine platelet-rich plasma, using increased sodium citrate concentration, is presented. Maintaining a quiet environment or anesthetizing the animals with thiamylal sodium aids in collection of platelets. Aggregation of platelets from 60 dogs of various breeds in response to arachidonic acid, collagen, adenosine diphosphate, epinephrine, and serotonin was monitored. Canine platelets reversibly or irreversibly aggregated to arachidonic acid. The percentage of arachidonate-irreversible platelets varied from 0% to 100% depending upon the breed of dogs examined. Arachidonate-irreversible platelets also aggregated irreversibly at lower concentrations of collagen and exhibited biphasic irreversible aggregation to adenosine diphosphate and serotonin. Serotonin-induced irreversible aggregation was dependent upon receptor activation and upon arachidonic acid metabolism. Irreversible aggregation to serotonin was associated with release of 3H-serotonin and thromboxane B2 formation, indicating that a couple between the serotonergic receptor and arachidonic acid metabolism may exist.

Platelet function, size and yield in whole blood and in platelet-rich plasma prepared using differing centrifugation force and time in domestic and food-producing animals

The effects of centrifugation force and time upon platelets function, mean platelet volume and platelet yield were compared with whole blood platelet counts and size in citrated blood samples from the bovine, canine, caprine, equine, feline, ovine and porcine species. The results were similar, for a given species, irregardless of sample volume. Bovine, caprine, feline and ovine platelet yields and mean platelet volumes were maximal when platelet-rich plasma was prepared using longer centrifugation times and lower gravitational forces. Canine, equine and porcine platelet yields and mean platelet volumes were maximal when platelet-rich plasma was prepared using shorter centrifugation times and higher gravitational forces. Platelet aggregation to adenosine diphosphate or arachidonic acid was not effected by the method of platelet-rich plasma preparation in bovine, caprine, feline, ovine or porcine platelets. Equine platelet aggregation was maximal when platelet-rich plasma was prepared using longer centrifugation times and lower gravitational forces. Canine platelet aggregation, particularly arachidonic acid-induced aggregation, was maximal when platelet-rich plasma was prepared using short centrifugation times and higher gravitational forces. It appeared that the effects of centrifugation parameters upon platelet yield depended upon the relative difference between platelet and red blood cell volumes.

Reduction of the red blood cell mass of horses: toxic effect of heparin anticoagulant therapy

This study was designed to test the efficacy of heparin anticoagulant therapy in the horse and its effect on the formed elements of blood. Nine clinically normal, nontraumatized adult horses were subjected to 4 different heparin maintenance regimens (dosages of 320, 240, 160, and 40 U/kg of body weight). Porcine intestinal mucosa heparin (20,000 U/ml) was injected subcutaneously every 12 hours for 96 hours (total 9 times). A loading dose of one-third the maintenance dose was given IV just before the first heparin injection. Three control horses were given an equivalent volume of 0.9% saline solution. The 2 large doses of heparin (320, 240 U/kg) resulted in an extension of the therapeutic range for heparin anticoagulant therapy (1.5 to 2.5 X data base-line prolongation of the activated partial thromboplastin time [APTT]). The 160-U/kg dose maintained the APTT in the therapeutic range, and the 40-U/kg dose had no effect on the APTT. Heparin was shown to exert a profound influence on the RBC mass of the horse. Three of the heparin regimens (320, 240, and 160 U/kg) resulted in a significant decrease in RBC numbers, PCV, and total hemoglobin content. Platelet count also was reduced in the horses when given the 320 and 240 U/kg doses. The observed increase in the mean corpuscular volume was associated with decreasing RBC numbers. Plasma proteins, serum bilirubin, free hemoglobin (plasma), haptoglobin (plasma), and urine and fecal hemoglobin values remained unchanged in all groups. Heparin anticoagulation therapy with the smallest dose (40 U/kg) had no detectable effects on the measured values, nor did the saline solution.

Serotonin accumulation in granules of storage pool-deficient platelets of Chediak-Higashi cattle

Platelets from cattle with the Chediak-Higashi (CH) syndrome are virtually devoid of dense granules, serotonin (5-HT), and stored ATP and ADP. The present study determined how the handling of 5-HT in normal cattle platelets differed from that in CH cattle platelets. Normal and CH platelets accumulated 5-[14C]HT to the same extent. After normal and CH platelets were incubated with 5-HT for 12 h most 5-HT is still intact, indicating that it was protected from metabolism. Part of the newly acquired 5-HT in normal and CH platelets was in a pool that was rapidly released by 5 U/ml of thrombin, suggesting that 5-HT was, in part, within granules. Subcellular fractionation studies showed that, whereas most of the newly acquired 5-HT in normal platelets was located in the dense granule fractions, about one fourth was found in the lighter granule fraction that was enriched in alpha-granules. The dense granule fraction was virtually absent in CH platelets, and most of the granule 5-HT was associated with the lighter granule fraction. The mixed granule fraction from CH platelets accumulated 5-HT but the uptake was about 10% of that from normal platelets. Unlike normal granules the uptake of 5-HT by CH granules was only slightly inhibited by reserpine but was reversed by NH4Cl and nigericin treatment.

Regulation of canine platelet function II. Catecholamines

The action of epinephrine (E) on canine platelet aggregation is described. Although E did not induce a change in platelet shape or aggregation, potentiation of aggregation induced by the following agents was observed at physiological E concentrations (that is, less than 10 nM/1): arachidonic acid; the dense granule agonists, ADP and serotonin (5-HT); and collagen. Epinephrine-induced potentiation was in part independent of formation of arachidonic acid metabolites, and E potentiated the aggregating action of the bivalent cationophore A23187. Potentiation was inhibited by alpha-adrenergic receptor antagonists phenoxybenzamine, phentolamine, and ergotamine, and mimicked by alpha-adrenergic receptor agonists norepinephrine, clonidine, and in some cases, phenylephrine. The beta-adrenergic receptor agonists isoproterenol and dobutamine inhibited ADP-induced aggregation, and this action was presented by pretreating the platelets with propranolol and dichloroisoproterenol. An augmentation of the aggregation response of platelets to arachidonic acid was observed in blood samples withdrawn when circulating catecholamines were elevated. The physiological implication of epinephrine acting as a gain controller that alters the relationship between actuating signal and the platelet response to an agonist is discussed.

[3H]-imipramine binding sites in fawn-hooded rats

The existence of high-affinity [3H]-imipramine recognition sites was demonstrated in membranes prepared from the cerebral cortex, hypothalamus and platelets obtained from fawn-hooded rats. The Bmax and Kd values for [3H]-imipramine binding to cerebral cortical membranes were virtually identical to those obtained with cortical membrane preparations of Sprague-Dawley rats. An NBR strain of rats, genetically related to fawn-hooded rats, was found to have significantly higher levels of [3H]-imipramine binding sites in cerebral cortical membranes when compared to fawn-hooded and Sprague-Dawley rats. All four strains of rats examined possessed extremely high densities of [3H]-imipramine binding sites in a purified platelet membrane fraction. These results do not support the finding of others that the cerebral cortex and platelets of fawn-hooded rats are virtually devoid of [3H]-imipramine binding sites.

Binding of 125I-labeled endotoxin to bovine, canine, and equine platelets and endotoxin-induced agglutination of canine platelets

Endotoxin from Escherichia coli O127:B8, Salmonella abortus-equi and S minnesota induced clumping of some canine platelets (PLT) at a final endotoxin concentration of 1 microgram/ml. Endotoxin-induced clumping of canine PLT was independent of PLT energy-requiring processes, because clumping was observed with canine PLT incubated with 2-deoxy-D-glucose and antimycin A. The PLT responded to adenosine diphosphate before, but not after, incubation with the metabolic inhibitors. Endotoxin induced a slight and inconsistant clumping of bovine and equine PLT at high (mg/ml) endotoxin concentration. High-affinity binding sites could not be demonstrated on canine, bovine, and equine PLT, using 125I-labeled E coli O127:B8 endotoxin. Nonspecific binding was observed and appeared to be due primarily to an extraneous coat on the PLT surface that was removed by gel filtration. The endotoxin that was bound to PLT did not appear to modify PLT function. An attempt to identify plasma proteins that bound physiologically relevant amounts of endotoxin was not successful. The significance of the endotoxin-induced clumping or lack of it on the pathophysiology of endotoxemia is discussed.

Comparative study of platelet dense granule constituents

Cat, cattle, dog, horse, human, mink, pig, and rabbit platelets were separated from plasma by gel filtration. The gel-filtered platelets (GFP) were treated with thrombin to induce maximal granule secretion and the potential dense granule constituents ATP, ADP, serotonin (5-HT), Ca2+, and Mg2+ were measured in GFP and in the control and thrombin-treated platelets and in the respective supernatants. The amount of Ca2+, Mg2+, 5-HT, ATP, and ADP within the nonreleasable pool for all species varied between 3.1 and 10.0 mumol/10(11) platelets for Ca2+ and Mg2+ was less than 1.5 mumol/10(11) platelets for ADP and 5-HT and was between 2.0 and 5.0 mumol/10(11) platelets for ATP. Marked differences were observed in the releasable fraction. Human platelets were characterized by the largest releasable Ca2+ pool (greater than 10 mumol/10(11) platelets), the smallest secretable 5-HT and Mg2+ pool (less than 0.5 mumol/10(11) platelets), and the lowest ATP-to-ADP ratio (greater than 1.0). Pig platelets had the highest amount of releasable Mg2+ (approximately 8.0 mumol/10(11) platelets). Rabbits platelets released the most 5-HT (greater than 3.0 mumol/10(11)) and had the highest ATP/ADP (greater than 5.0). The releasable pool of Ca2+, Mg2+, ATP, and ADP in the remaining species varied in mumol/10(11) platelets from approximately 1.5-4.0, approximately 1.0-3.0, 0.5-3.5, and approximately 0.5-1.5, respectively.

Ultrastructure of resting and activated storage pool deficient platelets from animals with the Chédiak-Higashi syndrome

The ultrastructural of platelets from Chédiak-Higashi (CH) and normal cattle, mink, and cats at rest was studied. Platelets from CH animals had a virtual absence of platelet dense granules. Alpha granules, amorphous membrane-surrounded structures, mitochondria, and microtubules of CH bovine platelets were similar in number and appearance to those in normal bovine platelets. Giant CH granules, present in other cells and considered diagnostic of the syndrome, could not be identified in platelets from CH animals. The open canalicular system and dense tubule system were not readily identifiable in resting bovine platelets. The ultrastructure of normal and CH cattle platelets was evaluated at various stages of ADP-induced aggregation. After platelets changed shape during the first phase of aggregation, the ultrastructural appearance of CH platelets was similar to that of normal platelets. The CH platelets composing the aggregates during irreversible aggregation did not appear as activated as did normal platelets, even though the aggregation tracings were similar. Normal and CH cattle platelets treated with thrombin appeared morphologically similar and were characterized by centrifugal movement of granules.

Evaluation of the platelet storage pool deficiency in the feline counterpart of the Chediak-Higashi syndrome

Cats with the Chediak-Higashi (CH) syndrome have abnormal hemostasis with prolonged bleeding times and normal coagulation times. Platelet aggregation induced by serotonin, ADP, and collagen was impaired. Platelets from normal and CH cats were incubated with 14C-adenine and then gel-filtered. Gel-filtered platelets (GFP) from CH cats contained 63% of the ATP, 38% of the ADP, 100% of the Ca2+, and 75% of the Mg25 of normal platelets. Serotonin could not be detected in CH platelets. Acid hydrolase and total platelet protein of CH platelets was similar to normal platelets. Gel-filtered platelets were treated with thrombin to induce maximal secretion. Secretion of ATP, Ca2+, and Mg2+ was 1.9%, 12.4%, and 16% respectively of normal platelets. ADP secretion by CH platelets was not detectable. The ATP/ADP ratio in the 14C-labeled metabolic pool of normal platelets was similar to that of total measured nucleotide pool of CH platelets. These findings suggest that in feline CH platelets, as in platelets from CH mink and cattle, there is storage pool deficiency that is virtually complete, and the virtual absence of ADP and 5HT may in part account for the abnormal hemostasis. Aggregation of platelets from CH cats was impaired, but these platelets did aggregate to arachidonate, serotonin-induced biphasic aggregation, and the aggregation response to ADP and collagen varied according to the amount of serotonin-induced TxB2 formed. These findings support a major role for arachidonate in platelet activation.