Specificity of different organic nitrates to elicit NO formation in rabbit vascular tissues and organs in vivo

Abstract

1 In the present study we assessed the formation of nitric oxide (NO) from classical and thiolcontaining organic nitrates in vascular tissues and organs of anaesthetized rabbits, and established a relationship between the relaxant response elicited by nitroglycerin (NTG) and NO formation in the rabbit isolated aorta. Furthermore, the effect of isolated cytochrome P450 on NO formation from organic nitrates was investigated. the animals were killed, blood vessels and organs were removed, and subsequently analyzed for spintrapped NO by cryogenic electron spin resonance (e.s.r.) spectroscopy. 3 In the saline-treated control group, NO remained below the detection limit in all vessels and organs. In contrast, all of the nitrates tested elicited measurable NO formation, which was higher in organs (liver, kidney, heart, lung, spleen) (up to 4.8 nmol g-' 20 min-') than in blood vessels (vena cava, mesenteric bed, femoral artery, aorta) (up to 0.7 nmol ge' 20 min'). Classical organic nitrates (NTG, ISDN) formed NO preferentially in the mesenteric bed and the vena cava, while the SPM compounds elicited comparable NO formation in veins and arteries. 4 Using a similar spin trapping technique, NO formation was assessed in vitro in phenylephrineprecontracted rabbit aortic rings. The maximal relaxation elicited by a first exposure (10 min) to NTG (0.3 to 10 juM) was positively correlated (r = 0.8) with the net increase (NTG minus basal) of NO spintrapped during a second exposure to the same concentration of NTG in the presence of DETC. 5 Cytochrome P450 purified from rabbit liver enhanced NO formation in a NADPH-dependent fashion from NTG, but not from the other nitrates, as assessed by activation of purified soluble guanylyl cyclase. 6 We conclude that the vessel selective action of different organic nitrates in vivo reflects differences in vascular NO formation. Thus, efficient preload reduction by classical organic nitrates can be accounted for by higher NO formation in venous capacitance as compared to arterial conductance and resistance vessels. In contrast, NO is released from cysteine-containing nitrates (SPMs) to a similar extent in arteries and veins, presumably independently of an organic nitrate-specific biotransformation. Limited tissue bioavailability of NTG and ISDN might account for low NO formation in the aorta, while true differences in biotransformation seem to account for differences in NO formation in the other vascular tissues.

Cardiorenal and Humoral Properties of a Novel Direct Soluble Guanylate Cyclase Stimulator BAY 41-2272 in Experimental Congestive Heart Failure

“…A possible explanation for the differential actions is that sGC activation by NTG depends on the biotransformation of NTG, which has been reported to be higher on the venous side. 8 Furthermore, cGMP-independent actions of NO may account for the differences. Importantly, in addition to concerns regarding mitochondrial toxicity associated with nitrate bioactivation, 3 there is controversy about some poten- tially adverse consequences of cGMP-independent actions of NO such as peroxynitrite generation, nitrosation, and apoptosis.…”

Complex I Dysfunction and Tolerance to Nitroglycerin

“…Umbilical cords obtained from the Department of Gynaecology (Faculty of Medicine of Valencia) were cut into rings (5 mm) and placed in Krebs solution ([in ϫ10 Ϫ3 mol/L] NaCl 118, KCl 4.75, CaCl 2 1.9, MgSO 4 1.2, KH 2 PO 4 1.2, NaHCO 3 25, and glucose 10.1). Human umbilical vein cells (HUVECs) and human umbilical arterial endothelial cells (HUAECs) were cultured in medium 199 (Cambrex, Walkersville, Md) as previously described.…”

“…have generally been attributed to its bioconversion into the relaxant agent nitric oxide (NO), which acts on the enzyme soluble guanylate cyclase (sGC). [1][2][3] However, most studies that support the existence of such a pathway have demonstrated increases of NO only when GTN concentrations considerably exceeded the plasma levels reached during clinical dosing. 4 Moreover, the involvement of other NO-related species in the actions of GTN when used at clinically relevant concentrations is also under debate.…”

Effects of Cyanamide, an Aldehyde Dehydrogenase Type 2 Inhibitor, on Glyceryl Trinitrate- and Isosorbide Dinitrate-Induced Vasodilation in Rabbit Excised Aorta and in Anesthetized Whole Animal

“…Although the details of GTN metabolism are not fully understood, possible pathways yielding 1,2-glyceryl dinitrate and NO 2 − have been suggested 3) and those yielding 1,2-glyceryl dinitrate and NO, part of the latter may be the source of NO 2 − , have also been reported. 4) Increases in NO and NO 2 − by ISDN have been reported not only in vitro, 7,15,25,29,30) but also in vivo, 29,30) although the possible metabolic pathways, including whether NO 2 − is a direct or indirect product, are not fully elucidated. Nevertheless, the dose-dependent increase in plasma NO 2 − with concomitant decrease in blood pressure by ISDN is in good agreement with previous studies.…”

“…The weak inhibitory effect of cyanamide on GTN-induced hypotension with concurrent small increase in plasma NO 2 − indicate that, in whole animal, cyanamide-insensitive bioactivation mechanism(s) could be largely operative in organs other than vascular smooth muscle. Indeed, it is reported that the formation of NO by GTN is quite larger in liver, lung and kidney than vascular tissues in rabbits 31,30) and that high doses of GTN are metabolized by several other enzymes (low affinity pathway), including glutathione-S-transferases, xanthine oxidoreductase, and cytochrome P450. 5) These possible mechanisms might release at least small amounts of NO 2 − or NO into the plasma where the latter is easily affected by oxidation to yield NO 2 − .…”