Effect of naloxone on platelet aggregation in rats

The effect of naloxone on aggregation of blood platelets was investigated. Naloxone in millimolar concentrations dose-dependently inhibited collagen (20 mu g/ml)-induced platelet aggregation in rats PRP. For comparison with IC50 values on a molar basis, the ability of naloxone against platelet aggregation is similar to aspirin, but about 7-8 fold smaller than verapamil. In anesthetized spontaneously hypertensive rats (SHR), naloxone did not significantly alter the pressure response whereas administration of prazosin caused diminution of mean arterial pressure (MAP) related to dose. Naloxone did not interfere with the hematological parameters (i.e., WBC, RBC, PLT, HGB, HCT ... etc.) in Sprague-Dawley (SD) rats. The present study shows naloxone to be effective in obviating platelet aggregation, and seems to be reasonable in prevention of pulmonary platelet trapping (PPT), which is thought to play an important role in the pathogenesis of adult respiratory distress syndrome (ARDS).