Endothelium-derived hyperpolarizing factor: characterization as a cytochrome P450 1A-linked metabolite of arachidonic acid in perfused rat mesenteric prearteriolar bed.
The isolated perfused rat mesenteric bed releases endothelium-derived hyperpolarizing factor (EDHF) in response to acetylcholine (ACh) or histamine. I propose that EDHF released in the mesenteric vascular bed is a cytochrome P450 (CYP)-linked, arachidonate metabolite. In the presence of nitro-L-arginine methyl ester (L-NAME) and indomethacin, injections of ACh (0.001 to 10 nmol) or histamine (0.1 to 1,000 nmol) elicited transient, dose-dependent dilation of cirazoline (an alpha1-adrenoceptor selective agonist) preconstricted mesenteric beds. The L-NAME-resistant responses to ACh or histamine were insensitive to tetrodotoxin (1 micromol/L), thus negating its neuronal origin, but were profoundly attenuated by a K+ channel inhibitor tetrabutylammonium (0.5 mmol/L). 7-Ethoxyresorufin (a selective and competitive blocker of CYP 1A isozyme) blunted ACh and histamine mediated EDHF responses but did not alter vasodilation initiated through K+ channel activation by either cromakalim or NS-1619, or through the nitric oxide-cGMP pathway (sodium nitroprusside). Clotrimazole, an imidazole that inhibits CYP by binding to the heme moiety, attenuated ACh, histamine, and cromakalim but not sodium nitroprusside-mediated vasodilator responses. Other CYP isozyme selective inhibitors, such as metyrapone (CYP 2B), 7-pentoxyresorufin (CYP 2B1), sulfaphenazole (CYP 2C/3A), and 17-octadecynoic acid (4A-linked omega-hydroxylase inhibitor), did not alter ACh or histamine-induced EDHF response. The EDHF-mediated dilations initiated by ACh and histamine, as well as K(ATP) activation by cromakalim, were blocked by mepacrine, a nonselective phospholipase A2 inhibitor. Mepacrine did not alter K(Ca) activation by compound NS-1619. I conclude that 1) the isolated perfused rat mesenteric prearteriolar bed releases in response to ACh and histamine, an EDHF that causes vasodilation through K+ channel activation; 2) the EDHF is most likely a CYP-derived arachidonate product; 3) CYP 1A is well suited as the isozyme responsible for EDHF production in this vascular bed; and 4) PLA2 appears to mediate the release of the precursor arachidonic acid.
Adeagbo
A S
AS
Department of Physiology and Biophysics and the Center of Excellence in Applied Microcirculatory Research, University of Louisville, Kentucky 40292, USA. ASADEA01@ulkyvm.louisville.edu
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001685:Biological Factors / Q000378:metabolism*; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006632:Histamine / Q000494:pharmacology; D007213:Indomethacin / Q000494:pharmacology; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010477:Perfusion; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism; D054467:Phospholipases A2; D011796:Quinacrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects
D001685:Biological Factors; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; C067410:endothelium-dependent hyperpolarization factor; D016718:Arachidonic Acid; D006632:Histamine; D019001:Nitric Oxide Synthase; D019363:Cytochrome P-450 CYP1A1; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester; D007213:Indomethacin