Inhibition of Nitric Oxide–Stimulated Vasorelaxation by Carbon Monoxide-Releasing Molecules (original) (raw)
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Carbon monoxide-induced vasorelaxation and the underlying mechanisms
British Journal of Pharmacology, 1997
Carbon monoxide (CO) induced a concentration-dependent relaxation of isolated rat tail artery tissues which were precontracted with phenylephrine or U-46619. This vasorelaxing effect of CO was independent of the presence of the intact endothelium.The CO-induced vasorelaxation was partially inhibited by the blockade of either the cyclicGMP pathway or big-conductance calcium-activated K (KCa) channels. When both the cyclicGMP pathway and KCa channels were blocked, the CO-induced vasorelaxation was completely abolished.Incubation of vascular tissues with hemin, in order to enhance the endogenous production of CO, suppressed the phenylephrine-induced vasocontraction in a time- and concentration-dependent manner. The hemin-induced suppression of the vascular contractile response to phenylephrine was abolished after the vascular tissues were co-incubated with either oxyhaemoglobin or zinc protoporphyrin-IX, suggesting an induced endogenous generation of CO from vascular tissues.The effect of hemin incubation on vascular contractility did not involve the endogenous generation of nitric oxide.Our results suggest that CO may activate both a cyclicGMP signalling pathway and KCa channels in the same vascular tissues, and that the endogenously generated CO may significantly affect the vascular contractile responses.Carbon monoxide (CO) induced a concentration-dependent relaxation of isolated rat tail artery tissues which were precontracted with phenylephrine or U-46619. This vasorelaxing effect of CO was independent of the presence of the intact endothelium.The CO-induced vasorelaxation was partially inhibited by the blockade of either the cyclicGMP pathway or big-conductance calcium-activated K (KCa) channels. When both the cyclicGMP pathway and KCa channels were blocked, the CO-induced vasorelaxation was completely abolished.Incubation of vascular tissues with hemin, in order to enhance the endogenous production of CO, suppressed the phenylephrine-induced vasocontraction in a time- and concentration-dependent manner. The hemin-induced suppression of the vascular contractile response to phenylephrine was abolished after the vascular tissues were co-incubated with either oxyhaemoglobin or zinc protoporphyrin-IX, suggesting an induced endogenous generation of CO from vascular tissues.The effect of hemin incubation on vascular contractility did not involve the endogenous generation of nitric oxide.Our results suggest that CO may activate both a cyclicGMP signalling pathway and KCa channels in the same vascular tissues, and that the endogenously generated CO may significantly affect the vascular contractile responses.
Carbon monoxide inhibits hypoxic pulmonary vasoconstriction in rats by a cGMP-independent mechanism
Pflugers Archiv-european Journal of Physiology, 1997
Hypoxia activates erythropoietin-producing cells, chemoreceptor cells of the carotid body and pulmonary artery smooth muscle cells (PSMC) with a comparable arterial PO2 threshold of some 70 mmHg. The inhibition by CO of the hypoxic responses in the two former cell types has led to the proposal that a haemoprotein is involved in the detection of the PO2 levels. Here, we report the effect of CO on the hypoxic pulmonary vasoconstriction (HPV). Pulmonary arterial pressure (PAP) was measured in an in situ, blood-perfused lung preparation. PAP in normoxia (20% O2, 5% CO2) was 15.2±1.8 mmHg, and hypoxia (2% O2, 5% CO2) produced a ΔPAP of 6.3±0.4 mmHg. Addition of 8% or 15% CO to the hypoxic gas mixture reduced the ΔPAP by 88.3±2.7% and 78.2±6.1% respectively. The same levels of CO did not affect normoxic PAP nor reduced the ΔPAP produced by angiotensin II. The effect of CO was studied after inhibition of the NO-cyclic guanosine monophosphate (cGMP) cascade with N-methyl-l-arginine (5·10–5 M) or methylene blue (1.4·10–4 M). It was found that both inhibitors more than doubled the hypoxic ΔPAP without altering the effectiveness of CO to inhibit the HPV. In in vitro experiments we verified the inhibition of guanylate cyclase by measuring the levels of cGMP in segments of the pulmonary artery. Cyclic GMP levels were 1.4±0.2 (normoxia), 2.5±0.3 (hypoxia) and 3.3±0.5 pmole/mg tissue (hypoxia plus 8% CO); sodium nitroprusside increased normoxic cGMP levels about fourfold. Methylene blue reduced cGMP levels to less than 10% in all cases, and abolished the differences among normoxic, hypoxic and hypoxic plus CO groups. It is concluded that CO inhibits HPV by a NO-cGMP independent mechanism and it is proposed that a haemoprotein could be involved in O2-sensing in PSMC.
Pharmacology & Toxicology, 1993
The present study was designed to assess the effect of LY83583 on H,OZ/O,-production from endothelial cells and neturophils, as determined by chemiluminiscence generation in vitro. We found that LY83583 increased H,02/0,production from endothelial cells, but inhibited the H20,/0,-production from phorbol myristate acetate-stimulated neutrophils. Furthermore, LY83583 consumed NADPH under certain conditions. Since neutrophils generate superoxide anion radicals via an NADPH-oxidase, we suggest that the reduction of chemiluminiscence, seen after addition of LY83583 to phorbol myristate acetate-stimulated neutrophils, is due to increased consumption of NADPH. In endothelial cells, NADPH is required as a co-factor in the generation of nitric oxide, which may interact with superoxide anion. A consumption in NAPDH would therefore be expected to decrease the production of nitric oxide and increase H,O,/ 0,-generation. The consumption of NADPH in endothelial cells could also cause reduced scavenger functions of the glutathion system, resulting in a further increase in H,02 release.
Frontiers in pharmacology, 2012
Nitric oxide (NO) is a potent dilator of vascular smooth muscle (VSM) by modulating intracellular cGMP ([cGMP] i ) through the binding and activation of receptor guanylyl cylases (sGC). The kinetic relationship of NO and sGC, as well as the subsequent regulation of [cGMP] i and its effects on blood vessel vasodilation, is largely unknown. In isolated VSM cells exposed to both pulsed and clamped NO we observed transient and sustained increases in [cGMP] i , with sub-nanomolar sensitivity to NO (EC 50 = 0.28 nM). Through the use of pharmacological inhibitors of sGC, PDE5, and PKG, a comprehensive VSM-specific modeling algorithm was constructed to elucidate the concerted activity profiles of sGC, PDE5, phosphorylated PDE5, and PDE1 in the maintenance of [cGMP] i . In small pressure-constricted arteries of the resistance vasculature we again observed both transient and sustained relaxations upon delivery of pulsed and clamped NO, while maintaining a similarly high sensitivity to NO (EC 50 = 0.42 nM). Our results propose an intricate dependency of the messengers and enzymes involved in cGMP homeostasis, and vasodilation in VSM. Particularly, the high sensitivity of sGC to NO in primary tissue indicates how small changes in the concentrations of NO, irrespective of the form of NO delivery, can have significant effects on the dynamic regulation of vascular tone. Citation: Held KF and Dostmann WR (2012) Sub-nanomolar sensitivity of nitric oxide mediated regulation of cGMP and vasomotor reactivity in vascular smooth muscle. Front. Pharmacol. 3:130.
Carotid body chemosensory excitation induced by nitric oxide: involvement of oxidative metabolism
Respiratory Physiology & Neurobiology, 2002
Nitric oxide (NO) produces a dual effect on carotid body (CB) oxygen chemoreception. At low concentration, NO inhibits chemosensory response to hypoxia, while in normoxia, medium and high [NO] increases the frequency of carotid chemosensory discharges (f x). Since NO and peroxynitrite inhibit mitochondrial respiration, it is plausible that the NO-induced excitation may depend on the mitochondrial oxidative metabolism. To test this hypothesis, we studied the effects of oligomycin, FCCP and antimycin A that produce selective blockade of hypoxic and NaCN-induced chemosensory responses, leaving nicotinic response less affected. CBs excised from pentobarbitoneanaesthetised cats were perfused in vitro with Tyrode (P O 2 : 125 Torr, pH 7.40 at 38°C). Hypoxia (P O 2 : 30 Torr), NaCN and nicotine (1-100 mg) and S-nitroso-N-acetylpenicillamide (SNAP, 300-600 mg) increased f x. Oligomycin (12.5-25 mg), antimycin A (10 mg) and FCCP (5 mM) transiently increased f x. Subsequently, chemosensory responses to hypoxia, NaCN and SNAP were reduced or abolished, while the response to nicotine was less affected. The electron donor system tetramethyl-p-phenylene diamide and ascorbate that bypasses the electron chain blockade produced by antimycin A, restores the excitatory responses to NaCN and SNAP. Present results suggest that the chemoexcitatory effect of NO depends on the integrity of mitochondrial metabolism.
Activation of soluble guanylate cyclase by carbon monoxide and inhibition by superoxide anion
European Journal of Biochemistry, 1990
Human platelet soluble guanylate cyclase activity was studied with respect to the function of its hemecontaining regulatory subunit. As an enzyme source, the 10000 x g supernatant was used and, since its specific activity proved to be too low for inhibition studies, also a partially purified preparation was employed. The partially purified enzyme was stimulated about 2.5-fold by carbon monoxide and this effect was abolished by illumination with visible light. Sodium nitroprusside also increased the basal activity about fourfold, which, however, is much less than the > 100-fold stimulation seen with the supernatant. Superoxide anions generated by the xanthine/xanthine-oxidase system were strongly inhibitory in the enriched preparation as well as in the COstimulated platelet supernatant (median effector concentration = 0.1 mUjml). Unlike CO and NO, the effect of superoxide cannot be mediated through the heme-containing regulatory subunit, since heme-free enzyme, which could not be activated by NO or CO, was inhibited to the same extent as the heme-containing enzyme. Superoxide dismutase did not influence the basal activity, but resulted in a synergistic stimulation in the presence of CO. When Mn2+ replaced MgZf as a cofactor, the basal activity was higher but superoxide could not inhibit the enzyme, possibly due to the superoxide-dismutase-like activity of Mn2+. Superoxide turned out to be a potent and reversible inhibitor of soluble guanylate cyclase which, together with endothelium-derived relaxing factor, recently identified as NO, could form a physiologically relevant regulatory effector system. Guanosine 3',5'-(cyc1ic)phosphate (cGMP) is emerging as an important cellular second messenger, although its mode of action and the regulation of soluble guanylate cyclase and particulate guanylate cyclase are only poorly understood (for a review see [l, 21). Soluble guanylate cyclase contains a heme regulatory subunit and represents the dominant enzyme in platelets and smooth muscle. Its activation is associated with inhibition of platelet aggregation [3] and with smooth muscle relaxation [4, 51. Hence its stimulation under conditions of coronary heart diseases is a preferred pharmacological target. Likewise, the potent vasodilatory properties of organic nitrates seem to be mediated by the release of nitric oxide [6, 71. Recently, the endothelium-derived relaxing factor (EDRF) was identified as NO which has therefore gained not only a pharmacological but also a physiological role in the relaxation of vascular tissue [8]. When studying platelet aggregation, we obtained evidence that carbon monoxide prevents aggregation of human platelets by stimulation of soluble guanylate cyclase [9]. From the reversibility of this effect by visible light, we concluded
Roberto MOTTERLINI, 2007
The well-known adverse effects of CO (carbon monoxide) intoxication are counterbalanced by its positive actions when small amounts are produced intracellularly by the cytoprotective enzyme HO-1 (haem oxygenase-1). As compelling scientific evidence accumulated to sustain that HO-1 plays a fundamental role in counteracting vascular and inflammatory disorders, we began to appreciate that a controlled delivery of CO to mammals may provide therapeutic benefits in a number of pathological states. This is the rationale for the recent development of CO-RMs (CO-releasing molecules), a group of compounds capable of carrying and liberating controlled quantities of CO in cellular systems, which offer a plausible tool for studying the pharmacological effects of this gas and identifying its mechanism(s) of action. The present review will highlight the encouraging results obtained so far on the vasodilatory, anti-ischaemic and anti-inflammatory effects elicited by CO-RMs in in vitro and in vivo models with an emphasis on the prospect of converting chemical CO carriers into CO-based pharmaceuticals.