Platelet aggregation and dense granule secretion in a colony of dogs with spontaneous hypertension.

AIM: Since canine hereditary essential hypertension has been previously reported in a colony of Siberian husky dogs, we tested the suitability of this model for use in studies on the platelet defect identified in humans with essential hypertension. METHODS: Platelet aggregation and dense granule ATP secretion were measured in dogs with essential hypertension and normotensive control dogs. RESULTS: The platelets from the hypertensive group showed significantly increased aggregation and secretion in response to stimulation with ADP. There was no significant increase in aggregation or secretion when platelets from hypertensive dogs were stimulated by platelet-activating factor, thrombin, calcium ionophore A23187 or phorbol myristate acetate. CONCLUSION: The increased aggregation and secretion responses in platelets from the hypertensive dogs suggest that a defect similar to that reported in humans with essential hypertension exists and that further investigation is warranted.

Monocrotaline pyrrole-induced pulmonary hypertension in fawn-hooded rats with platelet storage pool deficiency: 5-hydroxytryptamine uptake by isolated, perfused lungs.

Platelets are believed to be involved in the development of monocrotaline pyrrole (MCTP)-induced pulmonary hypertension. To help identify the role of the platelet, the cardiopulmonary toxicity of MCTP was examined in fawn-hooded (FH) rats, a strain with a platelet function defect. Both Sprague-Dawley (SD) and FH rats developed right ventricular hypertrophy and increased lung weights and exhibited decreased biogenic amine removal by isolated, perfused lung preparations after MCTP treatment. The responses of the FH rats were not significantly different from those of the SD rats, suggesting that platelet uptake and release of 5-hydroxytryptamine (5HT) are not the platelet functions involved in MCTP-induced pulmonary hypertension. The FH rats had an interesting strain-related difference from SD rats; isolated lungs from FH rats removed and metabolized a greater proportion of perfused 5HT than the SD rats.

Absent platelet aggregation with normal fibrinogen binding in basset hound hereditary thrombopathy.

Platelets from dogs with Basset Hound Hereditary Thrombopathy (BHT) initially displayed a thrombasthenia-like aggregation defect but have been shown to have normal amounts of platelet membrane glycoproteins IIb and IIIa (GPIIb-IIIa), and therefore are more accurately described as thrombopathic. The presence of normal quantities of GPIIb-IIIa, however, did not rule out the possibility of a functionally abnormal glycoprotein complex which would be unable to bind radio-labeled fibrinogen. Therefore, fibrinogen binding in BHT platelets was evaluated. Platelets from BHT and normal dogs were activated with 1 x 10(-5) M ADP in the presence of 125I-fibrinogen and the surface-bound radioactivity was quantitated. The amount of fibrinogen bound by BHT dog platelets was not significantly different than that bound by normal dog platelets. Platelets from dogs with BHT bound 30,282 +/- 3,133 and normal dog platelets bound 31,664 +/- 2,772 molecules of fibrinogen per platelet. The quantitatively normal GPIIb-IIIa complex binds fibrinogen in normal amounts and does not seem to represent the abnormality responsible for the aggregation defect in BHT platelets. Therefore, other factors central to normal platelet function and related to platelet aggregation must be considered.

Abnormal release of storage pool adenine nucleotides from platelets of dogs affected with basset hound hereditary thrombopathy.

Platelets from dogs affected with Basset Hound Hereditary Thrombopathy (BHT), have a thrombasthenia-like aggregation defect but release storage pool ATP in quantities not significantly different from normal controls or BHT heterozygotes when stimulated with 1 X 10(-5)M ADP and 0.22 U/ml thrombin. However, the release occurs so rapidly in the BHT platelets stimulated with ADP that it is complete in approximately one-sixth of the time required for release from normal control and heterozygote platelets. Sequential electron micrographs reveal early release of BHT dense body constituents 30 seconds after stimulation with 1 X 10(-5)M ADP while resting BHT morphology is indistinguishable from normal control animals.

Two-dimensional electrophoretic studies of platelets from dogs affected with basset hound hereditary thrombopathy: a thrombasthenia-like aggregation defect.

Because of a thrombasthenia-like platelet aggregation defect, platelets from dogs affected with Basset Hound Hereditary Thrombopathy were compared to normal control dog platelets by three different techniques in order to assess platelet membrane glycoprotein content. Crossed immunoelectrophoresis (CIE), two-dimensional nonreduced-reduced electrophoresis (NR-R), and O'Farrell two-dimensional electrophoresis were used for the assays. CIE and NR-R gels detected no differences between affected Basset Hound and control dog platelets. Gels run by the O'Farrell technique detected no differences in glycoprotein/protein content, however, there appear to be several constituents missing from BHT affected dog platelet samples. The missing components appear to be either lipids or sialoglycoproteins as they were detectable by silver staining but not by Coomassie Blue staining.

A primary platelet disorder of consanguineous simmental cattle.

A severe hereditary hemorrhagic diathesis in Simmental cattle has been identified in North America. Platelet numbers and coagulation profiles of affected cattle are normal. We have further characterized the severe dysfunction of platelet aggregation. All agonists tested elicited normal shape change. Aggregations in response to ADP, A23187, and collagen were absent. Aggregations were decreased or required more time for completion in response to PAF and thrombin. No ultrastructural abnormalities were observed in transmission electron micrographs. Dense granule release of ATP in response to PAF was normal. Thrombin-induced aggregation was dependent upon external calcium concentration in normal but not affected animals. Clot retraction in the blood from affected animals was abnormal. The data implicate a defect of Ca++ mobilization or utilization.

Defective contact activation of platelets from dogs with basset hound hereditary thrombopathy.

Basset Hound Hereditary Thrombopathy (BHT) is an autosomally inherited disorder of platelet function characterized by a thrombasthenia-like defect in aggregation but normal clot retraction. Glycoprotein IIb-IIIa (GP IIb-IIIa) is detectable in BHT platelets but may be functionally defective. In order to further characterize this potential model for human Glanzmann's thrombasthenia, contact reactivity of BHT platelets was studied by whole mount electron microscopy. Gel filtered BHT platelets, after 30 minutes of contact activation, attached poorly to a formvar substrate. There was an 8 fold difference in the number of adherent BHT platelets and normal platelets. In addition, contact induced shape change was inhibited when compared to control dogs. Almost 95% of control platelets reached fully dendritic or spread forms after 30 minutes of contact; in contrast only 63.7% of BHT platelets reached this degree of activation. The addition of 8.2 uM ADP to BHT platelets induced nearly a 4 fold increase in the number of spread forms and a 5 fold increase in the number of adherent BHT platelets, but did not cause aggregate formation. Both the defect in adhesion and shape change and the ability of ADP to stimulate both adhesion and contact-induced shape change in BHT platelets are similar to recent observations in our laboratory in patient's with type II Glanzmann's thrombasthenia.

Aggregation of platelets from monocrotaline pyrrole-treated rats.

Aggregation responses of platelet-rich plasma (PRP) from monocrotaline pyrrole (MCTP)-treated rats were examined to help elucidate the role of platelets in MCTP-induced pulmonary hypertension. PRP from rats treated one or four days earlier with MCTP (5 mg/kg, i.v.) or vehicle exhibited the same slope and maximum aggregation to ADP (1 X 10(-5) M, 2 X 10(-6) M, 1 X 10(-6) M), 74 micrograms/ml dog collagen, or 500 micrograms/ml arachidonic acid. PRP collected 7 days after MCTP treatment had a 15% decrease in both slope and maximum aggregation to 1 X 10(-5) M ADP and a 25% decrease in response to 2 X 10(-6) M ADP relative to the control group. Fourteen days after MCTP treatment, the responses to all of the aggregating agents were decreased 18-71% from control values. These results indicate that MCTP treatment alters the responses of PRP to aggregating agents.

Biologic interaction of prostaglandin, thromboxane and prostacyclin: potential clinical applications.

Prostaglandins are vasoactive agents which have potent and varied effects depending on the species, conditions and organs tested. The clinician wishing to gain a significant overview of the field from current research literature has a demanding task for himself. A review of biologic interactions is exactly what is needed in a consideration of possible clinical applications of prostaglandins. Thus, it is necessary first to recount the last five years' advances in prostaglandin research. Only then will the listing and discussion of some diseases soon to benefit from the application of research be meaningful.

Hemorrhagic diathesis associated with a hereditary platelet disorder in Simmental cattle.

A severe bleeding disorder in Simmental cattle has been described in widespread locations in the USA and Canada. The clinical findings are consistent with a hemophilia-like disease or, more precisely, a hereditary hemorrhagic diathesis and include spontaneous epistaxis, hematuria, and excessive bleeding associated with trauma or standard management procedures such as tattooing, ear tagging, and castration. A preliminary investigation of this defect showed that blood-platelet numbers and coagulation profiles of affected cattle were normal. Affected animals have a marked dysfunction of platelets (thrombopathy), termed Simmental hereditary thrombopathy. The defect is very similar or identical to that described in the same breed by 2 other laboratories.

Experimental model of type II bovine viral diarrhea virus-induced thrombocytopenia in neonatal calves.

Thrombocytopenia has been associated with type II bovine viral diarrhea virus (BVDV) infection in immunocompetent cattle, but the mechanism is unknown. The purpose of the present study was to develop and characterize a model of type II BVDV-induced thrombocytopenia. Colostrum-deprived Holstein calves were obtained immediately after birth, given a BVDV-negative and BVDV antibody-negative plasma transfusion, housed in an isolation facility, and randomly assigned to either control (n = 4) or infected (n = 5) groups. Infected calves were inoculated by intranasal instillation on day 3 of age with 10(7) TCID50 of the prototype type II isolate, BVDV 890, whereas control calves were sham inoculated. Blood counts and virus isolations from serum, white blood cells, and platelets were performed daily until day 12 after infection, at which time all experimental calves were euthanatized, and pathologic, virologic, and immunohistochemical examinations were performed. On physical examination, the control calves remained normal, but the infected calves developed pyrexia and diarrhea characteristic of type II BVDV infection. The platelet count decreased in all infected calves, and a statistically significant difference in the platelet count between control and infected calves was observed on days 7-12 after infection. In addition, the mean platelet volume and white blood cell counts also decreased. Examination of the bone marrow from the infected calves revealed immunohistochemical staining for BVDV antigen in megakaryocytes and evidence of concurrent megakaryocyte necrosis and hyperplasia.

Platelet aggregation responses and virus isolation from platelets in calves experimentally infected with type I or type II bovine viral diarrhea virus.

Altered platelet function has been reported in calves experimentally infected with type II bovine viral diarrhea virus (BVDV). The purpose of the present study was to further evaluate the ability of BVDV isolates to alter platelet function and to examine for the presence of a virus-platelet interaction during BVDV infection. Colostrum-deprived Holstein calves were obtained immediately after birth, housed in isolation, and assigned to 1 of 4 groups (1 control and 3 treatment groups). Control calves (n = 4) were sham inoculated, while calves in the infected groups (n = 4 for each group) were inoculated by intranasal instillation with 10(7) TCID50 of either BVDV 890 (type II), BVDV 7937 (type II), or BVDV TGAN (type I). Whole blood was collected prior to inoculation (day 0) and on days 4, 6, 8, 10, and 12 after inoculation for platelet function testing by optical aggregometry by using adenosine diphosphate and platelet activating factor. The maximum percentage aggregation and the slope of the aggregation curve decreased over time in BVDV-infected calves; however, statistically significant differences (Freidman repeated measures ANOVA on ranks, P < 0.05) were only observed in calves infected with the type II BVDV isolates. Bovine viral diarrhea virus was not isolated from control calves, but was isolated from all calves infected with both type II BVDV isolates from days 4 through 12 after inoculation. In calves infected with type I BVDV, virus was isolated from 1 of 4 calves on days 4 and 12 after inoculation and from all calves on days 6 and 8 after inoculation. Altered platelet function was observed in calves infected with both type II BVDV isolates, but was not observed in calves infected with type I BVDV. Altered platelet function may be important as a difference in virulence between type I and type II BVDV infection.

Effect of arsenical drugs on in vitro vascular responses of pulmonary artery from heartworm-infected dogs.

OBJECTIVE: To test the effect of thiacetarsamide and melarsomine on vascular responses in isolated rings of pulmonary artery from heartworm-infected dogs. ANIMALS: 18 heartworm-infected dogs. PROCEDURE: Isolated rings of pulmonary artery from heartworm-infected dogs were randomly treated with thiacetarsamide (30 micrograms/ml) or melarsomine dihydrochloride (30 micrograms/ml) for 30 minutes; untreated rings from the same dog served as control. Cumulative dose-response relations to norepinephrine, nitroglycerin, and methacholine were determined. RESULTS: Norepinephrine-induced constriction was not altered by treatment with either thiacetarsamide or melarsomine. Treatment with thiacetarsamide depressed nitroglycerin-induced relaxation, compared with values for untreated control rings and rings treated with melarsomine. Treatment of rings with thiacetarsamide or melarsomine depressed methacholine-induced relaxation, compared with values for untreated rings. Histologic examination of rings indicated that treatment with thiacetarsamide or melarsomine resulted in loss of endothelial cells. CONCLUSION: Endothelial cell loss as a direct drug effect may be responsible for impaired endothelium-dependent relaxation in pulmonary artery from heartworm-infected dogs. Thiacetarsamide appears to have additional effects on vascular smooth muscle, which may explain why fewer complications are observed in dogs treated with melarsomine. CLINICAL RELEVANCE: Melarsomine may be a safer drug than thiacetarsamide and could be a better treatment for dogs with heartworm infection.

Streptokinase treatment of cats with experimentally induced aortic thrombosis.

An investigation was initiated to determine the dosage of streptokinase (given IV) that would consistently produce systemic fibrinolysis, as determined by laboratory evaluation, and to determine the relative safety of this drug in the cat. Results indicated that a loading dose of 90,000 IU of streptokinase (given by continuous infusion over 20 to 30 minutes) and a maintenance dosage (IV) of 45,000 IU of streptokinase/hr predictably produced systemic fibrinolysis in the cat. There were no detectable adverse affects seen on physical examination, necropsy, or histopathologic examination. Using the foregoing dosage regimen, investigation was begun to evaluate the use of streptokinase for treatment of feline thromboembolism. Aortic thrombosis was created experimentally in 15 cats. There was no clearly predictable improvement in nonspecific venous angiograms or thermal circulatory indices for the cats given streptokinase, compared with the values for the control cats. After a total of 180 minutes of treatment, the mean weight of remaining clot removed at necropsy from the aortic trifurcation was 7.3 mg in the streptokinase-treated cats, compared with 13.4 mg in the control cats.

Effect of experimentally induced type II bovine viral diarrhea virus infection on platelet function in calves.

OBJECTIVE: To evaluate platelet aggregation responses in calves experimentally infected with a thrombocytopenia-inducing type II bovine viral diarrhea virus (BVDV) isolate (BVDV 890). ANIMALS: 9 neonatal male Holstein calves. PROCEDURE: 5 calves were inoculated with BVDV 890, and 4 were used as controls. Platelet aggregation studies and attempts to isolate BVDV from platelets were performed 2 days before, the day of, and every 2 days for 12 days after inoculation. Platelet function was assessed by means of optical aggregometry, using adenosine diphosphate and platelet-activating factor as agonists. Bovine viral diarrhea virus was isolated from purified platelet preparations by use of an immunoperoxidase monolayer assay. RESULTS: Maximum percentage aggregation and slope of the aggregation curve decreased over time in calves infected with BVDV. Bovine viral diarrhea virus was not isolated from platelets from control calves, but it was isolated from infected calves from 4 through 12 days after inoculation. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that platelet function may be depressed in calves infected with type II BVDV. Although the mechanism for altered platelet function was not determined, it likely involved an increase in the percentage of aged platelets in the circulation, a direct virus-platelet interaction, or an indirect virus-platelet interaction. Platelet dysfunction, in addition to thrombocytopenia, may contribute to the hemorrhagic syndrome associated with acute type II BVDV infection in calves.

Prolonged bleeding time in Aleutian mink associated with a cyclo-oxygenase-independent aggregation defect and nucleotide deficit in blood platelets.

A prolonged mean template bleeding time of 13 minutes was present in nine Aleutian mink affected with Chediak-Higashi syndrome (CHS) compared with 4 minutes in dark control mink. The concentrations of blood platelets in normal and affected animals did not differ significantly. However, in mink with CHS, a marked disturbance of platelet response to collagen was present. Administration of aspirin and indomethacin completely blocked CH platelet response to collagen. Blood platelet adenosine triphosphate and adenosine diphosphate values from mink with CHS were significantly less than those of normal mink, and the platelet adenosine triphosphate/adenosine diphosphate ratios were 10.31 in affected mink and 2.74 in normal mink. These findings are consistent with our previous investigations in affectd cattle and persons and indicate that a "storage pool disease" of platelets exist in the mink with CHS.

Relationship between degree of viremia and disease manifestation in calves with experimentally induced bovine viral diarrhea virus infection.

OBJECTIVE: To compare degree of viremia and disease manifestations in calves with type-I and -II bovine viral diarrhea virus (BVDV) infection. ANIMALS: 16 calves. PROCEDURE: Colostrum-deprived calves obtained immediately after birth were assigned to 1 control and 3 treatment groups (4 calves/group). Calves in treatment groups were inoculated (day 0) by intranasal instillation of 10(7) median tissue culture infective dose BVDV 890 (type II), BVDV 7937 (type II), or BVDV TGAN (type I). Blood cell counts and virus isolation from serum and leukocytes were performed daily, whereas degree of viremia was determined immediately before and 4, 6, 8, and 12 days after inoculation. Calves were euthanatized on day 12, and pathologic, virologic, and immunohistochemical examinations were performed. RESULTS: Type-II BVDV 890 induced the highest degree of viremia, and type-I BVDV TGAN induced the lowest. Virus was isolated more frequently and for a longer duration in calves inoculated with BVDV 890. A parallel relationship between degree of viremia and rectal temperature and an inverse relationship between degree of viremia and blood cell counts was observed. Pathologic and immunohistochemical examinations revealed more pronounced lesions and more extensive distribution of viral antigen in calves inoculated with type-II BVDV. CONCLUSIONS AND CLINICAL RELEVANCE: Degree of viremia induced during BVDV infection is associated with severity of clinical disease. Isolates of BVDV that induce a high degree of viremia may be more capable of inducing clinical signs of disease. Strategies (eg, vaccination) that reduce viremia may control clinical signs of acute infection with BVDV.

Primary malignant pulmonary neoplasia in two horses.

Although primary malignant pulmonary neoplasia of horses is rarely encountered, this diagnosis was confirmed in 2 horses on the basis of necropsy and histopathologic findings. One horse, with cystic mucinous adenocarcinoma, had respiratory tract and neurologic signs directly attributable to the neoplasm, and a tentative antemortem diagnosis of pulmonary neoplasia was made. The other horse, with anaplastic bronchogenic carcinoma, did not have clinical signs of pulmonary neoplasia.

Ataxia, depression, and dermatitis associated with the use of dichlorvos-impregnated collars in the laboratory cat.

Ataxia and depression developed in 21 of 50 (42%) laboratory cats wearing flea collars impregnated with 2,2-dichlorovinyl dimethyl phosphate (dichlorvos or DDVP) in a warm dry environment. Five (10%) of the cats died. Whole blood cholinesterase (ChE) activity was significantly (P smaller than 0.001) reduced in all cats and cervical dermatitis occurred in 37 (74%) of them.

Genetic disorders affecting reproduction and periparturient care.

There are numerous genetic diseases influencing reproduction and periparturient care in dogs including such disorders as anasarca, cleft palate, swimmers, congenital heart disease, and the various conditions that cause excessive bleeding. It is probable that all breeds of dogs are at risk for these or other traits that influence whelping and neonatal care. Therefore, genetic counseling should be considered as an important aspect of prenatal and pediatric veterinary medicine.