Abstract
The role of calcium-independent phospholipase A2(iPLA2)-produced arachidonic acid (AA) in acetylcholine (ACh)-mediated, endothelium-dependent vascular relaxation was investigated. ACh-induced relaxation of phenylephrine-constricted isolated rat mesenteric resistance arteries was attenuated following pretreatment with (E)-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one (BEL; 1 μM; p < 0.01), a highly selective suicide substrate inhibitor of iPLA2. Following BEL, the ACh relaxation could be completely restored following pretreatment with picomolar quantities of the cell-permeant methyl ester analog of AA (arachidonic acid methyl ester, AA-Me). Higher amounts of AA-Me (1 μM) had a direct endothelium-dependent relaxing action, which was inhibited by the nitric-oxide synthase inhibitor (Nω-nitro-l-arginine; 100 μM), independent of ACh, and unaffected by BEL. Neither the ACh relaxation restoring action nor the direct relaxing action of AA-Me was affected by preincubation with inhibitors of the lipoxygenase (esculetin, 10 μM) or cytochrome P450 monooxygenase (17-octadecynoic acid; 10 μM) pathways; and both actions of AA-Me were enhanced following preincubation with the cyclooxygenase inhibitor indomethacin (10 μM;p < 0.05). The results of the present study indicate that iPLA2-produced AA plays an essential role in ACh-mediated endothelium-dependent relaxation in rat mesenteric resistance arteries.
Footnotes
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This research was supported by National Institutes of Health Grant 2R01HL4125-10.
- Abbreviations:
- NO
- nitric oxide
- NOS
- nitric-oxide synthase
- eNOS
- endothelial NOS
- PLA2
- phospholipase A2
- cPLA2
- Ca2+-dependent PLA2
- iPLA2
- Ca2+-independent PLA2
- AA
- arachidonic acid
- AA-Me
- AA methyl ester
- PE
- phenylephrine
- BEL
- (E)-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one
- 17-ODYA
- 17-octadecynoic acid
- AACOCF3
- arachidonyl trifluoromethyl ketone
- l-nna,Nω-nitro-l-arginine
- ACh, acetylcholine
- [Ca2+]i
- intracellular calcium concentration
- Received December 26, 2001.
- Accepted May 7, 2002.
- The American Society for Pharmacology and Experimental Therapeutics
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