5-Hydroxytryptamine and the metabolism of arachidonic acid by the lipoxygenase and cyclooxygenase of washed human platelets.
During secondary aggregation, platelets release 5-hydroxytryptamine (5-HT) from their dense granule stores concurrent with arachidonic acid (AA) metabolism. To examine the hypothesis that released 5-HT has a modulatory effect on the metabolism of AA by platelets, we incubated nonaggregating washed human platelets with 5-HT in the presence of [3H]AA. Stimulation with 10(-4) M 5-HT, followed by incubation with 3 microM AA and 1 microCi [3H]AA for 5 min, resulted in a decrease in the formation of thromboxane B2 (TxB2) and 12-hydroxyheptadecatrienoic acid (HHT, P less than 0.05). The same treatment conditions and stimulation with 10(-7) to 10(-4) M 5-HT resulted in an elevation of 12-hydroxyeicosatetraenoic acid (12-HETE) formation (P less than 0.05). Treatment with the monoamine uptake inhibitor imipramine (20 microM) further increased the stimulation of 12-HETE formation observed in the presence of 10(-4) M 5-HT, suggesting that 5-HT may act at the platelet surface. A 5-HT1A receptor agonist, 8-hydroxy-dipropylaminotetralin (DPAT, 10(-6) to 10(-4) M) stimulated the formation of platelet cyclooxygenase (CO) products, whereas (+/-)1-(2,5-dimethoxy-4-iodo phenyl)-amino propane hydrochloride (DOI, 10(-6) to 10(-4) M), a 5-HT2 receptor agonist, had no significant effect on CO product formation. In addition, the 5-HT2 receptor antagonist ketanserin (10(-7) M) did not block the changes in CO or lipoxygenase metabolism induced by 5-HT. Since both DOI and DPAT stimulated 12-HETE formation whereas ketanserin was unable to reverse the 5-HT-enhanced 12-HETE formation, it seems unlikely that the stimulation of a 5-HT2 receptor is responsible for this action of 5-HT on platelets. We conclude that 5-HT depresses CO product formation while increasing 12-HETE formation through interaction with a platelet serotonergic binding site other than the 5-HT2 receptor.
Dragan
Y P
YP
Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond 23298.
Ellis
E F
EF
D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D000328:Adult; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism*; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D006893:Hydroxyeicosatetraenoic Acids / Q000378:metabolism; D007099:Imipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D008084:Lipoxygenase / Q000502:physiology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000502:physiology*; D011985:Receptors, Serotonin / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology
D001095:Arachidonic Acids; D006893:Hydroxyeicosatetraenoic Acids; D011985:Receptors, Serotonin; D013764:Tetrahydronaphthalenes; D016718:Arachidonic Acid; D012701:Serotonin; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D008084:Lipoxygenase; D011451:Prostaglandin-Endoperoxide Synthases; D007099:Imipramine