Altered arachidonic acid metabolism and platelet size in atopic subjects

The release and metabolism of endogenous arachidonic acid (AA) in physiologically activated platelets obtained from 11 atopic patients with allergic rhinitis and/or asthma was compared to that of sex- and age-matched nonatopic controls. Prelabeled [3H]AA platelets were stimulated with thrombin or collagen and the amount of free [3H]AA and radiolabeled metabolites released were measured by high-performance liquid chromatography. The results obtained indicate that although the incorporation of [3H]AA into platelet phospholipids and total release of 3H-radioactivity upon stimulation were comparable in the two groups, the percentage of 3H-radioactivity released from platelets as free AA was significantly lower (P less than 0.01) in the atopic group. The reduction in free [3H]AA was accompanied by an increase (P less than 0.01) in the percentage of 3H-radioactivity released as cyclooxygenase products in atopic platelets (compared to nonatopic cells) after stimulation with 10 and 25 micrograms/ml collagen. The amount of platelet lipoxygenase product released was comparable between the two groups. Although the blood platelet counts were similar, the mean platelet volume was statistically higher (P less than 0.01) in the atopic group. These results indicate that arachidonic acid metabolism in atopic platelets is altered, the pathophysiological significance of which remains to be clarified.