Presence of cytochrome P-450-dependent monooxygenase in intimal cells of the hog aorta.

107

1 Inhibition of nitric oxide generation with Nw-nitro-L-arginine (nitroarginine) reduced vasodilator responses to bradykinin and acetylcholine and enhanced those to nitroprusside in the rat isolated perfused kidney, preconstricted with phenylephrine. 2 Inhibition of cyclo-oxygenase with indomethacin, decreased the vasodilator responses to bradykinin by -25% without affecting those to acetylcholine or nitroprusside. 3 BW755c, a dual inhibitor of cyclo-oxygenase and lipoxygenase, reduced renal vasodilator responses to bradykinin, comparable to the effect of indomethacin suggesting an effect related to inhibition of cyclo-oxygenase rather than lipoxygenase. 4 ETYA, an inhibitor of all arachidonic acid metabolic pathways, markedly reduced vasodilator responses to bradykinin but was without effect on the renal vasodilatation induced by acetylcholine or nitroprusside. 5 Clotrimazole and 7-ethoxyresorufin, inhibitors of cytochrome P450, greatly attenuated vasodilator responses to bradykinin without affecting those to acetylcholine or nitroprusside. 6 These data suggest that the renal vasodilator response to bradykinin is subserved by arachidonic acid metabolites as well as nitric oxide, the former accounting for up to 70% of the vasodilator effect of bradykinin.

Section: Discussionsupporting

confidence: 90%

Contribution of NO and cytochrome P450 to the vasodilator effect of bradykinin in the rat kidney

Fulton

McGiff

Quilley

1992

107

“…A role for the cytochrome P4sO enzyme system in the metabolism of GTN to NO has also been found in the LLC-PKI pig kidney epithelial cells (Schr6der & Schr6r, 1992). A cytochrome P4S, system has also been described in blood vessels (Juchau et al, 1976) and is present both in SMC (Serabjit-Singh et al, 1988;Bornfeldt & Axelsson, 1987) and in EC (Abraham et al, 1985;Pinto et al, 1986). Here, the cytochrome P450 TR b enzyme system metabolizes fatty acids such as arachidonic acid (AA) into products which relax smooth muscle such as a 5,6 epoxide of AA (Carroll et al, 1987).…”

Section: Discussionmentioning

confidence: 99%

Conversion of glyceryl trinitrate to nitric oxide in tolerant and non‐tolerant smooth muscle and endothelial cells

Salvemini

Pistelli

Vane

1993

Exposure of smooth muscle cells (SMC) to glyceryl trinitrate (GTN, 75–600 μm) for 30 min led to a concentration‐dependent increase in nitrite (NO2−), one of the breakdown products of nitric oxide (NO). This was not affected by 30 min pretreatment of the cells with 0.5 mm of sulphobromophthalein (SBP) an inhibitor of glutathione‐S‐transferase (GST), by metyrapone or SKF‐525A inhibitors of cytochrome P450. These experiments were confirmed by organ bath studies using rabbit aortic strips denuded of endothelium and contracted with phenylephrine. Thus, a 30 min incubation of the strips with 0.5 mm SPB, metyrapone or SKF‐525A did not affect the relaxations in response to GTN (10−10−10−6 m). Potentiation of the anti‐platelet effect of GTN (44 μm) by endothelial cells (EC, 40 × 103 cells) was not affected by prior incubation of EC with SBP, metyrapone or SKF‐525A (all at 0.5 mm). Potentiation of the antiplatelet activity of GTN (11–352 μm) by small numbers of SMC (24 × 103 cells) or EC (40 × 103 cells) treated with indomethacin (10 μm) was attenuated when the SMC or EC were treated in culture with a high concentration of GTN (600 μm) for 18 h beforehand (referred to as ‘tolerant’ cells). In addition, tolerant SMC produced far less NO2− than non‐tolerant SMC. Exposure of non‐tolerant SMC or EC (105 cells) to GTN (200 μm) for 3 min increased (3–4 fold) the levels of guanosine 3′:5′‐cyclic monophosphate (cyclic GMP). This increase was much less (≤ 1 fold) in the tolerant SMC or EC (105 cells). The basal levels of cyclic GMP were similar in normal or tolerant SMC or EC. Sodium nitroprusside (80 μm) or atrial natriuretic factor (ANF, 10−7 m) increased the levels of cyclic GMP in normal or tolerant SMC or EC to the same extent. The anti‐platelet effects of GTN (44 μm) were potentiated by the sulphydryl donor N‐acetylcysteine (NAC, 0.5 mm). Incubation of GTN (150–1200 μm) for 30 min with NAC (0.1–1 mm) led to a concentration‐dependent increase in NO2− formation. The reduced ability of tolerant SMC or EC to potentiate the anti‐platelet activity of GTN was restored by NAC (0.5 mm). These anti‐aggregatory effects were abolished by concurrent co‐incubation with oxyhaemoglobin (10 μm) indicating that they were due to NO release. Thus, in SMC or EC, metabolism of GTN to NO does not depend on glutathione‐S‐transferase or the cytochrome P450 system. Furthermore, when compared to normal cells, tolerant SMC or EC metabolize GTN to NO less effectively as assessed by the reduced capacity to potentiate the antiplatelet effects of GTN, to release NO2− and to increase the level of cyclic GMP. This decrease in NO formation shows that tolerance to GTN is mainly due to impaired biotransformation of GTN to NO. NAC, by directly forming NO from GTN, compensates for this failing mechanism.

“…& Kim, 1993). The mono-oxygenases themselves seem to be located primarily within the endothelium (Abraham et al, 1985) and endothelial cells are capable of synthesizing EETs (see Harder et al, 1995). These findings, together with the ability of cytochrome P450 inhibitors, such as proadifen and clotrimazole, to attenuate EDHF-mediated vasodilatation, support the view that EDHF is an arachidonic acid metabolite derived via a cytochrome P450-dependent mono-oxygenase (Fulton et al, 1992;Bauersachs et al, 1994;Hecker et al, 1994;Lischke et al, 1995).…”

Section: Introductionmentioning

confidence: 85%

Effects of cytochrome P450 inhibitors on EDHF‐mediated relaxation in the rat hepatic artery

Zygmunt

Edwards

Weston

et al. 1996

1 The possibility that the endothelium-derived hyperpolarising factor (EDHF) in the rat hepatic artery is a cytochrome P450 mono-oxygenase metabolite of arachidonic acid was examined in the present study. In this preparation, acetylcholine elicits EDHF-mediated relaxations in the presence of the nitric oxide (NO) synthase and cyclo-oxygenase inhibitors No-nitro-L-arginine (L-NOARG) and indomethacin, respectively.2 17-Octadecynoic acid (17-ODYA, 50 gM), a suicide-substrate inhibitor of the cytochrome P450 mono-oxygenases responsible for the production of 5, 8, 11,[12][13][14], had no effect on acetylcholine-induced relaxations in the presence of L-NOARG (0.3 mM) plus indomethacin (10 gM). Furthermore, 5, 8, 11, Clotrimazole (3 gM) was without effect on these responses. The relaxant actions of the NO donor, 3-morpholino-sydnonimine, were unaffected by proadifen (10 gM). 5 The relaxant effects of the opener of ATP-sensitive potassium channels, levcromakalim, were abolished by proadifen (10 gM) and strongly attenuated by clotrimazole (3 gM). Proadifen (10 gM) also abolished the hyperpolarization induced by levcromakalim (1 gM). 6 The lack of effect of 17-ODYA on relaxations mediated by EDHF, together with the failure of extracellularly-applied EETs to produce relaxation, collectively suggest that EDHF is not an EET in the rat hepatic artery. It seems likely that inhibition of ion channels in the smooth muscle rather than reduced EDHF formation in the endothelium offers a better explanation for the actions of the cytochrome P450 inhibitors proadifen and clotrimazole.