Mammalian platelets are rich in lipoxygenase activity and capable of enzymatically producing a number of n-6 and n-3 hydroxy fatty acids. Submicromolar levels of the n-3 hydroxy fatty acids specifically antagonize both the contractile effects of a thromboxane mimetic, U46619, and its platelet aggregating effect. It is proposed that these hydroxy fatty acids may specifically interact with the thromboxane receptor in both platelet and smooth muscle. Analysis of binding parameters indicated that in presence of 14-OH-22:6n3 a marked decrease in the affinity of the receptor for thromboxane occurred with no change in the number of receptor sites. A direct relationship exists between the inhibition of 3H-U46619 specific binding and U46619 platelet aggregation by 14-OH-22:6n3. Both rat aortic ring contractility and human platelet aggregation to U46619 and arachidonic acid were reduced by all of the hydroxy fatty acids tested. In general, the rank order of their potency was 14-OH-22:6n3=14-OH- 22:5n3>11-OH-22:6n3=17-OH-22:6n3>14-OH22:5n6=12-OH-20:4n6>13-OH-18:2n6. In addition, OH-22:6 dose-dependently stimulates the production of lipoxygenase products from airway tissue, neutrophils and monocytes. It is proposed that a direct correlation may exist between n-3 hydroxy fatty acid-induced changes in cell function and endogenously produced lipoxygenase products. Hydroxy fatty acids production from exogenous substrate was depressed in platelets obtained from chronic ethanol-exposed rats (14-56 days). Production of the n-3 hydroxy fatty acids was elevated following short-term ethanol exposure (1-7 days). Vasculature and platelets obtained from the ethanol-treated rats were less responsive to the thromboxane mimetic, U46619. However, the reduction in platelet aggregation was greatest following short-term ethanol exposure.
