SECRETION OF BETA-THROMBOGLOBULIN AND SEROTONIN FROM HUMAN PLATELETS INDUCED BY MICROBUBBLES DIFFERS FROM SECRETION INDUCED BY COLLAGEN ANDPOLYSTYRENE MICROSPHERES

The effect of nitrogen (N2)-microbubbles on human platelets resembles that of common agonists in terms of aggregation, but displays one unus ual feature in that cyclooxygenase-inhibitors (e.g. aspirin) poorly in hibit the reaction. In the present study, we have investigated the cyc looxygenase-dependence of microbubble-induced platelet secretion of be ta-thromboglobulin (beta-TG) and C-14-serotonin. The effect of microbu bbles in stirred platelet-rich plasma (PRP) was compared with that of collagen and of polystyrene microspheres. The reduction in the number of single platelets induced by microbubbles was continuous with time a nd reached 60% after 30 min and was accompanied by secretion of C-14-s erotonin and beta-TG. While 50% of the secretion of beta-TG persisted in spite of aspirin treatment, secretion of C-14-serotonin was complet ely abolished. The enhancing effect of epinephrine on microbubble-indu ced platelet secretion appeared to be prostanoid dependent. Platelet s ecretion of beta-TG and C-14-serotonin induced by a high dose of colla gen was significantly reduced by aspirin, while a low dose of collagen induced a cyclooxygenase-independent secretion of beta-TG and C-14-se rotonin. The reduction in single platelets when PRP was stirred with m icrospheres reached a mean value of 27% after 10 min but did not incre ase further with time. Microspheres caused a small but significant sec retion of beta-TG but no secretion of C-14-serotonin. Aspirin did not reduce the loss in single platelets nor the secretion of beta-TG. The present study suggests that cyclooxygenase independent alpha-granule s ecretion may facilitate and, at least in part, sustain the reaction be tween microbubbles and platelets. The difference in agonistic effect o f polystyrene microspheres on platelets shows that polystyrene spheres are not suitable substitutes for microbubbles in in vitro or in vivo experiments.