Thirty healthy male horses were allotted to 3 groups and treated blindly during 4 days. Group-1 horses received unfractioned calcium heparin (100 IU/kg of body weight, SC, q 12 h). Group-2 horses received a single dose of a low-molecular-weight heparin (50 anti-Xa IU/kg, SC) every morning, and a similar volume of saline solution every evening. Group-3 horses received the vehicle (saline solution), SC, every 12 hours. Citrated and EDTA-anticoagulated blood samples were collected before starting the medication (T-0) and once daily 3 hours after each morning injection (T-3, T-27, T-51, and T-75). The PCV, hemoglobin concentration, RBC and platelet counts, and clotting times (activated partial thromboplastin time and thrombin time) were determined, and a microscopic examination to detect hemagglutination was performed. Plasma concentration of heparin was measured by use of the antifactor Xa activity assay. Bleeding time was determined on the first and fourth days, using a double-template method. The horses given unfractioned heparin had marked agglutination of erythrocytes after the first injection that became more pronounced as treatment progressed. Also, significant decrease in PCV, hemoglobin concentration, and RBC count was observed during treatment. Platelet count was significantly decreased after the first day, and clotting times were significantly prolonged. In contrast to the horses given unfractioned heparin, those given low-molecular-weight heparin did not have any agglutination of erythrocytes during the 4 days of treatment, and there were no significant changes in PCV, hemoglobin concentration, or RBC and platelet counts. Activated partial thromboplastin time increased slightly in the horses given low-molecular-weight heparin, although the values remained within reference range. Both groups of horses achieved adequate concentrations of heparin in plasma for prophylactic purposes, but those given low-molecular-weight heparin achieved those values after the first injection. Bleeding times were not significantly different between heparin-treated horses and horses given saline solution during treatment. We conclude that low-molecular-weight heparin may be used more safely and conveniently in horses, because it does not affect equine erythrocytes, platelets, or clotting and bleeding times.

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.

We evaluated the effect of anticoagulant (lithium heparin, sodium heparin, or none) and type of autoanalyzer on selected blood biochemical values of the loggerhead sea turtle (Caretta caretta). More differences were observed between the analytes in serum and those in the 2 types of plasma than were observed between the 2 types of plasma. Differences in electrolyte concentrations were not significant when plasma from sodium-heparinized blood was compared with plasma from lithium-heparinized blood. Serum is not recommended for reptilian studies because clot formation is unpredictable and because the time required for clotting may allow substantial changes in the chemical composition of the sample. For most determinants, values varied more between the 2 types of autoanalyzers than among the 3 anticoagulant treatments. These sources of variation must be considered when performing comparative studies.

Ticlopidine hydrochloride was evaluated for its effectiveness in inhibiting platelet aggregation and serotonin release in 5 laboratory Beagles before and after heartworm implantation with 7 adult Dirofilaria immitis, and after embolization with 7 dead heartworms to mimic what happens after heartworm adulticide treatment. Five other laboratory Beagles, similarly implanted and embolized with heartworms, were used as nonmedicated controls. During the heartworm-negative stage, the dosage of ticlopidine that inhibited adenosine diphosphate (ADP)-induced platelet aggregation in 5 dogs by at least 50% after 5 days of treatment was 62 mg/kg of body weight once a day. In the same dogs implanted with 7 adult heartworms 21 days previously, mean (+/- SD) ticlopidine dosage required to obtain similar results was 71 (+/- 13) mg/kg given once daily. During the 21 days after dead heartworms were implanted in heartworm-infected dogs, mean ticlopidine dosage was 108 (+/- 35) mg/kg (range, 62 to 150 mg/kg). Ticlopidine treatment was associated with increased platelet numbers in all 5 dogs during the heartworm-negative stage and in 4 of 5 dogs during the heartworm implantation and heartworm embolization stages. Mean platelet volume tended to decrease as platelet numbers increased. At necropsy, gross and histologic pulmonary lesions were less severe in ticlopidine-treated dogs than in nonmedicated control dogs.

Platelet aggregation and release, platelet number, mean platelet volume, antithrombin-III activity, and fibrinogen concentration were evaluated in heartworm-negative and heartworm-infected dogs at baseline and on days 3, 10, and 21 after treatment with thiacetarsamide. Platelet reactivity was enhanced in a group of dogs naturally infected with Dirofilaria immitis, compared with 2 groups of heartworm-negative dogs, but platelet reactivity was not further enhanced after treatment with thiacetarsamide. A significant decrease in antithrombin-III activity was detected 21 days after treatment. The platelets from a group of laboratory Beagles implanted with 50 adult D immitis displayed enhanced reactivity 6 months after implantation, but by 18 months, platelet reactivity had returned to near, or less than, baseline. Platelet reactivity was enhanced after thiacetarsamide treatment in this group. Thiacetarsamide-associated changes were not observed in platelet number or size; antithrombin-III activity decreased, but the change was not significant. Fibrinogen concentration was increased significantly (P < 0.05) on day 10. Enhanced adenosine diphosphate (ADP)-induced platelet aggregation was observed on days 3, 10, and 21 after treatment in heartworm-negative dogs. This change was not observed in 6 control Beagles not treated with thiacetarsamide. Although antithrombin-III activity was decreased on day 3 and fibrinogen concentration was increased on day 10, paralleling changes observed in the heartworm-infected dogs, the changes were not statistically significant. In this study, thiacetarsamide was procoagulatory in heartworm-negative dogs and may be an important contributing factor to the thromboembolism observed with adulticidal therapy.

Administration of vitamin K1, SC, to anticoagulant-poisonsed (diphenadione) dogs provided diagnostic information within 4 hours, when vitamin K1 and its epoxide were measured in canine sera. Twelve dogs (2 groups of 6) were given 2.5 mg of diphenadione/kg of body weight for 3 days. Dogs were treated with vitamin K1, 2.5 (n = 6) or 5 mg/kg/day (n = 6) SC for 21 days, and their responses were compared. Four nonexposed control dogs were given 5 mg of vitamin K1/kg/day. Serum concentration of vitamin K epoxide was significantly (P less than 0.02) higher in diphenadione-exposed dogs than in control dogs 1 to 4 hours after the initial vitamin K1 treatment on day 4. Vitamin K epoxide/vitamin K1 ratios were similarly higher and became more distinct. Cessation of vitamin K1 therapy on day 24 resulted in prolongation of one-stage prothrombin times in diphenadione-exposed dogs, becoming clearly evident on day 27. Serum vitamin K1 concentrations were not detectable on day 27 in diphenadione-exposed dogs, whereas serum vitamin K1 concentrations were readily detectable in control dogs. One stage prothrombin time changes, during days 24 to 32, indicated 5 mg of vitamin K1/kg provided better protection than did 2.5 mg of vitamin K1/kg. Coagulopathy in the dogs was resolved by day 32.