Study objectives: To investigate whether platelets are activated in asthmatics with increased release of preformed mediators and to investigate the influence of oral administration of theophylline on them.
Design: Comparison of the intracellular free calcium concentration ([Ca2+]i) in platelets as an indicator of platelet activation, CD62P expression on platelets, and the chemokine regulated upon activation in normal T cells expressed and presumably secreted (RANTES) level in platelet-rich buffer supernatants between asthmatics and normal subjects.
Setting: 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 18 asthmatics taking oral theophylline (group B).
Measurements and results: While the resting [Ca2+]is in platelets were similar among the three groups, the [Ca2+]is 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 A2 (STA2) stimulation in the absence of external Ca2+. The CD62P expression level and RANTES level in group A after STA2 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 resulting in enhanced release of chemokine such as RANTES, which could be suppressed by oral administration of theophylline.