Platelet Aggregation and Thromboxane A2 Production after Adrenergic Stimulation in Young Healthy Humans

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Abstract
The effects of adrenergic stimulation on platelet aggregation (platelet aggregation ratio; PAR), β-thromboglobulin (β -TG) release and plasma thromboxane B2 (T×B2) levels were investigated in 25 healthy young volunteers. Adrenergic stimulation induced by cold application was checked by evaluating the changes in the calculated vascular resistance in the forearm. A prompt increase in platelet aggregates and plasma β -TG and T×B2 concentrations was observed after adrenergic stimulation. PAR changed from resting values of 0.97 ± 0.05 to 0.75 ± 0.08 (p < 0.001) at the end of cold application. At the same time, β -TG plasma concentration increased from 32.09 ± 19.64 to 135.48 ± 37.97 ng/ml (p < 0.001) and T×B2 plasma levels changed from 0.49 ± 0.24 to 0.99 ± 0.39 pmol/ml (p < 0.001). TxB2 levels, but not PAR and β -TG concentration came back to the resting values at the end of the observation period (10 min). Aspirin, as the lysine acetylsalicylate equivalent to 5 mg/kg i.v. of acetylsalicylic acid, although able to completely inhibit platelet cyclooxygenase failed to inhibit the plasma T×B2 increase induced by adrenergic stimulation. This strongly suggests that the increase in plasma T×B2 following adrenergic stimulation is of extraplatelet origin. Also β-TG and PAR changes were not affected by aspirin administration.