Pharmacodynamic evaluation of the effects of oral melatonin on expression of the T-cell cytokines interleukin-2 and interferon gamma in the dog.

OBJECTIVE: To determine the effects of exogenous melatonin administration on activated whole blood expression of the T-cell cytokines interleukin-2 (IL-2) and interferon gamma (INF-γ) in dogs. ANIMALS: Ten healthy dogs. PROCEDURES: Heparinized whole blood was collected from 10 dogs for analysis of cytokine expression before administration of melatonin (baseline). Each dog was then administered melatonin at a dosage of approximately 1 mg/kg, PO, q 12 hr for 14 days. On day 14, whole blood was again collected from each dog at the time points of trough (0 hr) and 6 hr postmelatonin administration to evaluate the effects of melatonin on cytokine expression. At all evaluated time points, analysis of activated whole blood expression of mRNA coding for both IL-2 and IFN-γ was performed using quantitative reverse transcription polymerase chain reaction to determine whether a difference existed for any time point. Blood melatonin concentrations were also measured at comparable time points. RESULTS: A statistical difference in the expression of either cytokine was not appreciated at any time point, despite attainment of expected blood concentrations of the drug. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that melatonin therapy does not significantly affect IL-2 or IFN-γ expression in healthy dogs. While melatonin is thought to have an effect on the immune system in dogs, it does not appear this effect is through altering T-cell IL-2 or IFN-γ expression. Further studies investigating the effects of melatonin on the immune system of dogs are warranted.

Correlation of hematocrit, platelet concentration, and plasma coagulation factors with results of thromboelastometry in canine whole blood samples.

OBJECTIVE: To evaluate the components of canine whole blood samples that contribute to results of thromboelastometry (TEM). ANIMALS: 127 healthy dogs. PROCEDURES: For each dog, a blood sample was collected from a jugular vein into tubes containing no anticoagulant, EDTA, or citrate anticoagulant. Citrated whole blood samples underwent TEM with tissue factor and TEM with ellagic acid. Indicators of RBC mass and platelet concentration were evaluated, and plasma coagulation tests were performed; data obtained were compared with results of TEM. For technical reasons, samples were not available from all dogs for all tests. RESULTS: Coagulation time was correlated with concentrations of primarily extrinsic pathway coagulation factors for TEM with tissue factor and with most factors via TEM with ellagic acid. Clot formation time, α angle, and maximum clot firmness were highly correlated with fibrinogen and platelet concentrations and some individual factor concentrations. Sample Hct was strongly correlated with most measured variables; low Hct was associated with relative hypercoagulability, and high Hct was associated with relative hypocoagulability. CONCLUSIONS AND CLINICAL RELEVANCE: For TEM of canine blood samples, coagulation time was primarily a function of coagulation factor concentrations, whereas other variables were dependent on platelet and fibrinogen concentrations. Sample Hct strongly influenced the results of TEM, likely because RBCs act as a diluent for plasma coagulation factors. Thromboelastometry appeared to be affected by abnormalities of coagulation factors, platelet concentrations, and RBC mass. In samples from anemic patients, results of TEM indicative of hypercoagulability may be artifactual because of low RBC mass.

Evaluation of effects of low-dose aspirin administration on urinary thromboxane metabolites in healthy dogs.

OBJECTIVE: To evaluate markers of in vivo platelet function (urinary 11-dehydro-thromboxane B(2) [11-dehydroTXB(2)] and 2,3-dinorTXB(2)) and assess their response to administration of 2 commonly used dosages of aspirin in healthy dogs. ANIMALS: 20 healthy dogs. PROCEDURES: Urine was collected prior to aspirin administration and on the morning following the last evening administration. Twenty dogs received aspirin (1 mg/kg, PO, q 24 h) for 7 consecutive doses. After a washout period of 5 months, 10 dogs received a single dose of aspirin (10 mg/kg, PO). Concentrations of urinary thromboxane metabolites 11-dehydroTXB(2) and 2,3-dinorTXB(2) were measured via ELISA, and values were normalized to urine creatinine concentration. RESULTS: Median baseline 11-dehydroTXB(2) concentrations were 0.38 ng/mg of creatinine (range, 0.15 to 1.13 ng/mg). Mean ± SD baseline 2 at a 3-dinorTXB(2) concentrations were 6.75 ± 2.77 ng/mg of creatinine. Administration of aspirin at a dosage of 1 mg/kg, PO, every 24 hours for 7 days did not significantly decrease urinary 11-dehydroTXB(2) concentration, but administration of the single aspirin dose of 10 mg/kg did significantly decrease 11-dehydroTXB(2) concentration by a median of 45.5% (range, 28.2% to 671%). Administration of the 1 mg/kg aspirin dosage significantly decreased urinary 2,3-dinorTXB(2) concentration by a mean ± SD of 33.0 ± 23.7%. Administration of the single aspirin dose of 10 mg/kg also significantly decreased 2,3-dinorTXB(2) concentration by a mean ± SD of 46.7 ± 12.6%. CONCLUSIONS AND CLINICAL RELEVANCE: Aspirin administration (1 mg/kg/d) may be insufficient for reliable platelet inhibition in healthy dogs.

Clot formation in canine whole blood as measured by rotational thromboelastometry is influenced by sample handling and coagulation activator.

The objective of the present study was to systematically evaluate the impact of methodology on thromboelastometry with canine whole blood. Thromboelastometry was performed on citrated blood using a variety of combinations of clotting activators [ex-tem (tissue factor or TF), in-tem (ellagic acid), diluted TF from Innovin, or Ca (recalcification only)] and storage times. Thromboelastometry was also performed using diluted TF from Innovin on blood collected into a contact inhibitor. Ex-vivo contact activation was compared between canine and human blood. Clotting activator had a marked impact on coagulation time, a minor impact on alpha angle, and no impact on clot formation time or maximum clot firmness. When ex-tem or in-tem was the clotting activator, sample storage up to 30 min did not affect results. With diluted TF from Innovin or Ca, sample storage was associated with the development of increased coagulability (as indicated by shorter coagulation time and clot formation time and higher alpha angle) due to ex-vivo contact activation. Canine blood underwent markedly more ex-vivo contact activation than did human blood. Canine blood undergoes significant ex-vivo contact activation during and after collection, which influences thromboelastometry results when a weak clotting activator (such as low TF or recalcification) is used. Thromboelastometry with a strong activator (such as ex-tem or in-tem) is less influenced by ex-vivo changes, and, therefore, likely to be more reflective of in-vivo hemostatic capabilities and to provide consistently interpretable and comparable results.