Platelet aggregation induced in the hamster cheek pouch by a photochemical process with excited fluorescein...

Excitation of intravascular fluorescein isothiocyanate (FITC)-dextran by light induces platelet aggregation in arterioles of the hamster cheek pouch. Time to aggregate appearance (TAA) was found to be 45 +/- 5.6 sec in vessels of 10-14 micron diameter. The interindividual differences of TAA are low (coefficient of variance = 12.5%) and the TAA in individual animals can be reproduced for several hours with a coefficient of variance of 14.5%. TAA decreased at higher concentrations of intravascular FITC-dextran (r = 0.98) and with increased energy of the exciting beam. Scavengers of singlet oxygen, sodium azide, and trans-beta-carotene, delayed TAA. A scavenger of hydroxyl radicals, dimethyl sulfoxide, did not influence TAA. Acetylsalicylic acid showed a dose-dependent inhibitory effect from 1 (P less than 0.01) to 100 mg/kg body weight ia. The time-dependent increase of TAA after administration of 100 mg/kg acetylsalicylic acid is demonstrated; the dosage finally delayed TAA to longer than 360 seconds. The findings suggest that platelet formation, initiated by exciting FITC-dextran may involve local production of singlet oxygen. The consequently observed damaging process and the primary role of the endothelial cell damage are described. It is postulated that the described procedure provides a new model of intravascular platelet aggregation, characterized by a good reproducibility. A new damaging mechanism is proposed to study platelet aggregation in vivo.