Effects of glaucocalyxin A on aggregation and cAMP levels of rabbit platelets in vitro.

Glaucocalyxin A (Gla A) is a new diterpenoid isolated from ethereal extract of the leaves of Rabdosia japonica (Burm f) Hara var glaucocalyx (Maxim) Hara (Labiatae) collected in Northeastern China. When incubated with washed rabbit platelets, Gla A inhibited ADP-, AA-, and PAF-induced aggregation of rabbit platelets with IC50 values of 3.44, 13.32, and 7.74 mumol.L-1, respectively. Gla A 10 and 100 mumol.L-1 increased the cAMP levels in platelets. In combination with imazodan hydrochloride, Gla A (1-100 mumol.L-1) caused a marked increase of platelet cAMP levels, while no effect with PGE1.