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

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.