Difference in effects of vinblastine and vincristine on the dog platelet aggregation

The present study was attempted to determine difference in effects of vinblastine and vincristine on ADP-induced aggregation of dog platelets. Vinblastine manifested biphasic influence depending upon concentrations, i.e., in low concentrations (0.2-20 micrograms/ml) it promoted the aggregation, and in a high concentration (100 micrograms/ml) it inhibited the aggregation with increasing incubation time. Vincristine in any concentrations, however, neither promoted nor inhibited the aggregation. In scanning electron micrographs, platelets were gradually damaged as revealed by their surface appearances with increasing incubation time in the presence of vinblastine (100 micrograms/ml). There existed a parallel relationship between the inhibition of the aggregation by vinblastine and the increase in number of severely damaged platelets. However, there was no such a parallel relationship between them in the presence of vincristine.