Effects of 9,12,15-octadecatrien-6-ynoic acid on the metabolism of arachidonic acid in platelets and on the platelet aggregation.

An acetylenic fatty acid: 9,12,15-octadecatrien-6-ynoic acid (dicranin), extracted from Dicranum Scoparium was preincubated with platelets stimulated by exogenous arachidonic acid (20:4 n-6). Dicranin (10(-4) M) weakly inhibited the cyclooxygenase activity as assessed by measurement of 12-hydroxy-heptadecatrienoic acid (HHT) In contrast, the 12-hydroxy-eicosatetraenoic acid (12-HETE) synthesized by the 12-lipoxygenase was strongly increased by about 650%. The same effects were observed with 10(-6) M of dicranin but to a lesser extent. The main platelet hydroxylated dicranin metabolite determined by GC-MS was a 13-hydroxy derivative Platelet aggregation induced either by thrombin or by arachidonic acid or by U46619, an structural PGH2 analogue was inhibited by 10(-4) M of dicranin.