ENDOTHELIUM-DERIVED HYPERPOLARIZING FACTOR - CHARACTERIZATION AS A CYTOCHROME-P450 1A-LINKED METABOLITE OF ARACHIDONIC-ACID IN PERFUSED RATMESENTERIC PREARTERIOLAR BED

The isolated perfused rat mesenteric bed releases endothelium-derived hyperpolarizing factor (EDHF) in response to acetylcholine (ACh) or hi stamine. I propose that EDHF released in the mesenteric vascular bed i s a cytochrome P450 (CYP)-linked, arachidonate metabolite, In the pres ence of nitro-L-arginine methyl ester (L-NAME) and indomethacin, injec tions of ACh (0.001 to 10 nmol) or histamine (0.1 to 1,000 nmol) elici ted transient, dose-dependent dilation of cirazoline (an alpha(1)-adre noceptor selective agonist) preconstricted mesenteric beds. The L-NAME -resistant responses to ACh or histamine were insensitive to tetrodoto xin (1 mu mol/L), thus negating its neuronal origin, but were profound ly attenuated by a K+ channel inhibitor tetrabutylammonium (0.5 mmol/L ). 7-Ethoxyresorufin (a selective and competitive blocker of CYP 1A is ozyme) blunted ACh and histamine mediated EDHF responses but did not a lter vasodilation initiated through K+ channel activation by either cr omakalim or NS-1619, or through the nitric oxide-cGMP pathway (sodium nitroprusside). Clotrimazole, an imidazole that inhibits CYP by bindin g to the heme moiety, attenuated ACh, histamine, and cromakalim but no t sodium nitroprusside-mediated vasodilator responses. Other CYP isozy me selective inhibitors, such as metyrapone (CYP 2B), 7-pentoxyresoruf in (CYP 2B1), sulfaphenazole (CYP 2C/3A), and 17-octadecynoic acid (4A -linked omega-hydroxylase inhibited, did not alter ACh or histamine-in duced 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 A(2) 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 respons e to ACh and histamine, an EDHF that causes vasodilation through K+ ch annel activation; 2) the EDHF is most likely a CYP-derived arachidonat e product; 3) CYP 1A is well suited as the isozyme responsible for EDH F production in this vascular bed; and 4) PLA(2) appears to mediate th e release of the precursor arachidonic acid. (C) 1997 American Journal of Hypertension, Ltd.