ACTIVATION OF PLATELETS IN BRONCHIAL-ASTHMA

Study objectives: To investigate whether platelets are activated in as thmatics with increased release of preformed mediators and to investig ate the influence of oral administration of theophylline on them. Desi gn: Comparison of the intracellular free calcium concentration ([Ca2+] (i)) in platelets as an indicator of platelet activation, CD62P expres sion on platelets, and the chemokine regulated upon activation in norm al T cells expressed and presumably secreted (RANTES) level in platele t-rich buffer supernatants between asthmatics and normal subjects. Set ting: The respiratory outpatient clinics, Hiroshima University, Japan. Participants: Twenty-five normal volunteers, 19 asthmatics taking no oral drugs associated with asthma treatment (group A), and 1S asthmati cs taking oral theophylline (group B). Measurements and results: While the restling [Ca2+](i)s in platelets were similar among the three gro ups, the [Ca2+](i)s in group A were significantly higher than those in normal subjects (p<0.05) and group B (p<0.01) after thrombin or 9,11- epithia-11,12-methano-thromboxane A(2) (STA(2)) stimulation in the abs ence of external Ca2+. The CD62P expression level and RANTES level in group A after STA(2) stimulation were significantly higher than those in normal subjects and group B (p<0.05). Conclusions: We conclude that agonist-mediated activation of platelets is augmented in asthmatics r esulting in enhanced release of chemokine such as RANTES, which could be suppressed by oral administration of theophylline.