Platelet cyclooxygenase expression in normal dogs.

Area of Science:

• Veterinary Medicine
• Pharmacology
• Biochemistry

Background:

• Human platelets express cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2).
• Variations in COX-2 expression may explain differing responses to aspirin therapy.

Purpose of the Study:

• To determine if circulating canine platelets express COX-1 and COX-2.
• To investigate how aspirin administration affects COX expression and platelet function in dogs.

Main Methods:

• Eight intact female hounds were studied using a repeated measures design.
• Platelet COX-1 and COX-2 expression were measured by flow cytometry before and after 10 days of aspirin (10 mg/kg Q12h).
• Platelet function was assessed using PFA-100(®) (collagen/epinephrine), and urine 11-dehydro-thromboxane B(2) (11-dTXB(2)) to creatinine ratio was measured.

Main Results:

• Both COX-1 and COX-2 were detected in canine platelets.
• Aspirin administration led to a 250% increase in COX-1 expression in all dogs.
• COX-2 expression showed significant inter-individual variation and did not change significantly after aspirin; platelet function was impaired, and urine 11-dTXB(2) decreased in all dogs.

Conclusions:

• Canine platelets express both COX-1 and COX-2 isoforms.
• Aspirin increases COX-1 expression and impairs platelet function, but COX-2 expression varies considerably among dogs.
• Inter-individual variability in platelet COX-2 expression warrants further investigation as a potential marker for variable aspirin responsiveness.