An acetylenic fatty acid: 9,12,15-octadecatrien-6-ynoic acid (dicranin) was extracted from and preincubated with platelets which were then stimulated by exogenous arachidonic acid (20:4 n-6). This molecule at 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 10−5 M and with 10−5 M of dicranin but to a lesser extent. Platelet hydroxylated dicranin metabolites were also found and the structure of the main compound determined by GC-MS was a 13-hydroxy derivative. Its origin has not yet been elucidated. Platelet aggregation induced by 1 μg/ml of U46619, a structural PGH2 analogue was completely abolished in the presence of dicranin. Platelet aggregation induced either by thrombin or by arachidonic acid was inhibited by 10−4 M of dicranin only after preincubation. This observation indicates that the formation of metabolites of dicranin are necessary to effect this inhibition. Dicranin is thus a new inhibitor of platelet aggregation and may prove to be useful for elucidating the effects of 12-HETE in biological systems. |