PLATELET 12-HYDROXY-5,8,10, HEPTADECATRIENOIC ACID (HHT) INCREASES PROSTACYCLIN PRODUCTION BY AN EFFECT ON VASCULAR CYCLOOXYGENASE

Abstract

No definite function has been attributed to HHT, a plt. arachidonic acid (AA) product produced in equivalent amounts to the plt. proaggregatory metabolite thromboxane (Tx.) We report that HHT stimulates prostacyclin production by endothelial cells, and have identified the mechanism for this effect. In human umbilical venous endothelial cells, HHT (0.5 and 1μM) stimulated prostacyclin (RIA for 6KPGF_1α) by 32 ± 10% (1SE) and 42±13% (p<0.05 and 0.01). Similar changes were observed when the effect of HHT on exogenous ¹⁴C-AA metabolism in fetal bovine aortic endothelial cells (FBAECs) was studied. 6KPGF_1α was stimulated by 25±9% and 30±6% at HHT cones, of 0.5 and 1μM (p<0.05 and 0.01). While prelabelling experiments with ¹⁴C-AA revealed that HHT (1μM) had no effect on AA release from FBAEC membrane lipids (6481±232cpm/well control vs 6928±339 in HHT treated cells), kinetic analyses revealed that HHT affected vascular cyclooxygenase. HHT (IpM) increased Vmax in test microsomes (706±49pmol/mg/min) when compared to controls (524±47; p<0.02). No effect on Km was observed (6.16±0.64μM control vs 7.19±1.02 in test microsomes). The effect of HHT on plt. AA metabolism was next evaluated. Preincubation of washed plts, with HHT (1μM) did not enhance thrombin (0.2U/ml) induced plt TXB₂ (2.27±1.34pmol/10⁶ pits, control vs 2.28±1.62 in HHT treated plts). No effect was also seen when AA (20μM) was the agonist. Further studies in plts prelabeled with ¹⁴C-AA did not reveal an effect of HHT on plt. AA release. HHT stimulates vascular prostacyclin production without a concomitant effect on pit. AA metabolism. HHT may be an important local modulator of plt. plug formation.

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