In an effort to find new inhibitors of platelet aggregation,
crude methanol extracts of 261 marine invertebrate sam-
ples, consisting of sponges and tunicates, collected in Baler,
Aurora, Davao Oriental, and Davao Gulf, Davao, Philip-
pines, were screened rapidly in a new microplate assay
using Giemsa dye to detect platelet aggregates. Twenty-five
extracts inhibited Ca2+-induced platelet aggregation at 2
mg/ml. The method detected an all-or-none response at a
set concentration selecting for potent inhibitors. Inhibition
was indicated by absence of Giemsa-stained violet gels or
platelet aggregates on the microplate wells (Figure 1).
Among the active samples, 2 samples identified as PI96
1-14 and PDZ198 1-35 were pursued.