A comparison of haemoglobin and erythrocytes as inhibitors of smooth muscle relaxation by the NANC transmitter in the BRP and rat anococcygeus and by EDRF in the rabbit aortic strip

Nitric oxide (NO) produced by the endothelium diffuses both into the lumen and to the smooth muscle cells according to the concentration gradient in each direction. The extremely high reaction rate between NO and hemoglobin (Hb), k Hb ‫؍‬ 3-5 ؋ 10 7 M ؊1 ⅐s ؊1 , suggests that most of the NO produced would be consumed by Hb in the red blood cells (RBCs), which then would block the biological effect of NO. Therefore, specific mechanisms must exist under physiological conditions to reduce the NO consumption by RBCs, in which the Hb concentration is very high (24 mM heme). By using isolated microvessels as a bioassay, here we show that physiological concentrations of RBCs in the presence of intravascular f low does not inhibit NO-mediated vessel dilation, suggesting that RBCs under this condition are not an NO scavenger. On the other hand, RBCs (50% hematocrit) without intravascular f low reduce NO-mediated dilation to serotonin by 30%. In contrast, free Hb (10 M) completely inhibits NO-mediated dilation with or without intravascular f low. The effect of f low on NO consumption by RBCs may be attributed to the formation of an RBC-free zone near the vessel wall, which is caused by hydrodynamic forces on particles. Intravascular f low does not affect the reaction rate between NO and free Hb in the lumen, because the latter forms a homogeneous solution and is not subject to the hydrodynamic separation. However, intravascular f low only partially contributes to the reduced consumption of NO by RBCs, because without the f low, the NO consumption by RBCs is already about 3 orders of magnitude slower than free Hb.Nitric oxide (NO) is a biological messenger that participates in neurotransmission, vascular regulation, and immunological responses. It is produced in many cell types such as neurons, endothelial cells vascular smooth muscle cells, and macrophages. Since the discovery of its biological activity, the roles of NO in physiological and pathophysiological processes have been seen as increasingly important. In the cardiovascular system, NO has been documented to participate in the regulation of vascular tone and permeability (1, 2), platelet adhesion and aggregation (3, 4), smooth muscle proliferation (5, 6), and endothelial cell-leukocyte interactions (1, 7). The functions of NO in vivo have been clearly demonstrated by administration of L-arginine analogs that block NO production. For example, the administration of N G -monomethyl-L-arginine (L-NMMA) has been shown to cause hypertension in vivo (8) and abolish shear-induced, NO-mediated vessel dilation both in vivo (9) and in isolated intact vessel preparation (10).Despite the well-documented importance of NO, the transfer of NO from the producing cell to the target is poorly understood, because NO, as a free radical, can be degraded in a variety of reactions. In particular, NO reacts with deoxy-and oxy-hemoglobin (Hb) at a very high rate to form nitrosyl-Hb (HbNO), and metHb, respectively. The bimolecular reaction rate constants for these reactions are on th...

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“…3). This difference also has been observed previously under conditions without the RBC-free zone (20,(30)(31)(32). Fig.…”

Section: Discussionsupporting

confidence: 89%

Intravascular flow decreases erythrocyte consumption of nitric oxide

Liao

Hein

Vaughn

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

286

200

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“…These results provide strong evidence that NANC relaxations in this tissue, as in several others (Rand, 1992), involve the L-arginine: nitric oxide (NO) pathway, and that the neurotransmission system resembles that responsible for the production and release of the endothelium-derived relaxing factor (EDRF; Moncada et al, 1991). However, in both the endothelial (McCall & Vallance, 1992) and NANC (Gillespie & Sheng, 1989) systems there is still considerable debate over the nature of the substance actually released from the synthesizing cell, since several observations are difficult to reconcile with the release of free NO. Indeed, in the mouse anococcygeus we have demonstrated that hydroquinone, acting as a free radical scavenger, greatly reduces relaxations induced by NO, but has no effect on those to NANC nerve stimulation or several other nitrovasodilators (Hobbs et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

An investigation of some S‐nitrosothiols, and of hydroxy‐arginine, on the mouse anococcygeus

Gibson

Babbedge

Brave

et al. 1992

British J Pharmacology

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1 The effect of five S-nitrosothiols, and of the stereoisomers of N0-hydroxy-arginine (HOARG), were investigated on the mouse anococcygeus. 2 All five S-nitrosothiols produced concentration-related (0.1-100IM) relaxations of carbachol (50 LM)-induced tone; the order of potency was S-nitroso-L-cysteine (CYSNO)> S-nitroso-N-acetyl-D,Lpenicillamine (SNAP)>S-nitrosoglutathione (GSNO)> S-nitrosocoenzyme A (CoASNO)> S-nitroso-N-acetyl-L-cysteine (NACNO). The relaxations were unaffected by the nitric oxide synthase (NOS) inhibitor, L-NG-nitro-arginine (10 JIM) (L-NOARG).3 Cold-storage of the tissue for 72 h resulted in loss of sympathetic and non-adrenergic, noncholinergic (NANC) nerve function. NOS activity in the tissue was reduced by 97%. Despite this, relaxations induced by the S-nitrosothiols were unaffected. 4 Haemoglobin (50 jM) attenuated relaxations induced by NO and the S-nitrosothiols, although responses to 3-isobutyl-1-methyl-xanthine were unaffected. N-methyl-hydroxylamine (2 mM) which has been shown previously to produce selective inhibition of NANC and nitrovasodilator responses in this tissue, also reduced responses to all S-nitrosothiols.5 Hydroquinone (100 gM) greatly reduced relaxations to CYSNO (by 88%) but had no effect on those to SNAP, GSNO, CoASNO or NACNO. Since hydroquinone does not reduce responses to NANC stimulation, CYSNO is unlikely to be the NANC transmitter. 6 L-HOARG by itself (up to 100 piM) had no significant effect on carbachol-induced tone or on NANC (10 Hz; 10 s train every 100 s) relaxations. However, it produced reversal of the inhibitory effects of L-NOARG (10;pM), being only slightly less potent than L-arginine. D-HOARG was without effect. L-HOARG had no effect on relaxations induced by 1.51iM NO. 7 The results show that S-nitrosothiols are potent relaxants of the mouse anococcygeus; they act directly on the smooth muscle with a mechanism similar to NO and other nitrovasodilators. In addition, the results are consistent with L-HOARG being an intermediate in the biosynthesis of NO from L-arginine, although there is no evidence for it acting to stabilize NO extracellularly.

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“…However, some differences between the vascular and NANC endogenous nitrate systems have been reported (Gillespie & Sheng, 1989;Gibson et al, 1990;Toda & Okamura, 1990). If the two systems are the same, then drugs known to influence EDRF/NO function should show parallel effects on the Author for correspondence.…”

Section: Introductionmentioning

confidence: 99%

Differentiation by hydroquinone of relaxations induced by exogenous and endogenous nitrates in non‐vascular smooth muscle: role of superoxide anions

Hobbs

Tucker

Gibson

1991

British J Pharmacology

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1 The influence of hydroquinone on relaxations induced by nitric oxide (NO), nitrovasodilator drugs, and non-adrenergic, non-cholinergic (NANC) field stimulation has been investigated in three tissues in which endogenous nitrates have been implicated in the NANC response; the mechanism of action of hydroquinone was also studied. 2 In mouse anococcygeus, hydroquinone (10-1OOpM) produced a concentration-dependent inhibition of relaxations induced by 1S5UM NO. Hydroquinone, 100pMm, which reduced responses to NO by 85%, had no effect on relaxations induced by NANC field stimulation (1OHz; 20s trains), hydroxylamine (1OpM), sodium nitroprusside (1 gM) or sodium azide (20juM).3 In guinea-pig trachea, 100pM hydroquinone reduced relaxations to 150pM NO by 75%, but had no effect on those to NANC stimulation (1OHz; 30s trains) or sodium azide (5 pM).4 In rat gastric fundus, 100pUM hydroquinone reduced relaxations to 1 ,M NO by 85%, but had no effect on those to NANC stimulation (0.5 Hz; 15 s trains) or sodium azide (2pM). 5 Superoxide dismutase (SOD; 50uml-1) had no effect on relaxations of the mouse anococcygeus in response to 15,UM NO or 10Hz NANC stimulation. Further, the inhibition of responses to NO by hydroquinone was unaffected in the presence of SOD. 6 Hydroquinone (10-1OOuM) failed to generate superoxide anions, as detected by a chemiluminescent assay. However, 100piM hydroquinone, like SOD (50uml-1), produced almost complete inhibition of superoxide anion chemiluminescence induced by xanthine (500pgM): xanthine oxidase (0.07 u ml-1). 7 It is concluded that, in our system, hydroquinone inhibits NO by acting as a free radical scavenger rather than by generating superoxide anions. The ability of hydroquinone to block relaxations to NO, but not NANC stimulation, may suggest that the endogenous nitrate substance released by these NANC nerves may not be free NO, but may be an NO-containing, or NO-generating, molecule.

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A comparison of haemoglobin and erythrocytes as inhibitors of smooth muscle relaxation by the NANC transmitter in the BRP and rat anococcygeus and by EDRF in the rabbit aortic strip

Cited by 35 publications

References 12 publications

Intravascular flow decreases erythrocyte consumption of nitric oxide

Intravascular flow decreases erythrocyte consumption of nitric oxide

An investigation of some S‐nitrosothiols, and of hydroxy‐arginine, on the mouse anococcygeus

Differentiation by hydroquinone of relaxations induced by exogenous and endogenous nitrates in non‐vascular smooth muscle: role of superoxide anions

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