Possible role of P-450-derived metabolites in endothelium-dependent relaxation of rat small mesenteric arteries

Abstract

We reported previously that acetylcholine (ACh)-induced endothelium-dependent relaxation of rat mesenteric microvessels depended both on nitric oxide (NO) and on a charybdotoxin (CTX)-sensitive endothelium-derived hyperpolarizing vasodilator. Cytochrome P450 (CYP)-dependent arachidonic acid metabolites act in some systems as hyperpolarizing vasodilators. We sought to quantitate contributions of such metabolites to the CTX-sensitive component of ACh-induced vasodilation in isolated rat mesenteric resistance arteries. ACh relaxed these vessels nearly completely (93.3 ± 1.2%, n = 71); cyclooxygenase inhibition with indomethacin did not diminish this response (94.3 ± 11.4%, n = 9). NO synthase inhibition with Nitro-L-arginine (NNLA) reduced relaxation by 30% (n = 54, p < 0.05). Pretreatment of vessels with CYP inhibitors, either clotrimazole (CTM) or 17-octadecynoic acid (17-ODYA), or with selective K + channel inhibitors, either tetraethyammonium acetate (TEA) or CTX, each led to similar small reductions in maximal relaxation (17%, 22%, 16%, and 9% respectively, n = 3–6). Combined pretreatment with NNLA + either (CTM or 17-ODYA) or (TEA or CTX) each led to similar maximal relaxations (52.2 ± 4.8%, 50.6 ± 9.2, 37.6 ± 8.6%, and 44.1 ± 11.5%, respectively, n = 6–35; p < 0.05 for NNLA + [CTM or TEA or CTX]vs NNLA alone). Combined pretreatment with NNLA + CTM + (CTX or TEA) led to similar maximal relaxations (43.0 ± 7.3%, 43.7 ± 15%, n = 6–11) that did not differ from values in vessels pretreated with either NNLA + CTM or NNLA + (CTX or TEA). We conclude that the ACh-induced vasodilation was insensitive to cyclooxygenase inhibition, partially sensitive to NO synthase inhibition, and that the K + channel blockers TEA and CTX identified the same minor component of ACh relaxation as did the CYP inhibitor CTM.