NANC neurotransmission in the bovine retractor penis muscle is blocked by superoxide anion following inhibition of superoxide dismutase with diethyldithiocarbamate

Sustained Maternal Smoking Triggers Endothelial-Mediated Oxidative Stress in the Umbilical Cord Vessels, Resulting in Vascular Dysfunction

Nitric oxide (NO) bioavailability is fundamental in the regulation of redox balance and functionality of the endothelium, especially in the case of the umbilical cord (UC), which has no innervation. The analysis of UC vessel-related complications could serve as a useful tool in the understanding of the pathophysiological mechanisms leading to neonatal cardiovascular disorders. Therefore, the aim of this study was to characterize the mechanisms that rule the severity of prenatal endothelial dysfunction, induced by the long-term effect of maternal smoking. Our analysis describes the initiation and the consequences of endothelial nitric oxide synthase (NOS3) deactivation, along with the up-regulation of possible compensatory pathways, using structural, molecular and biochemical approaches. This study was carried out on both the UC arteries and veins originated from neonates born to non-smoking and heavy-smoking mothers. The alterations stimulated by maternal smoking are vessel-specific and proportional to the level of exposure to harmful materials passed through the placenta. Typically, in the primarily exposed veins, an increased formation of reactive oxygen species and an up-regulation of the highly-efficient NOS2-NO producing pathway were detected. Despite all the extensive structural and functional damages, the ex vivo heat and cadmium ion-treated UC vein pieces still support the potential for stress response.

Protective effect of quercetin, a polyphenolic compound, on mouse corpus cavernosum

Flavonoids are plant-based phenolic compounds, and quercetin is the most abundant dietary member of this family. One of the most important characteristics of quercetin is its antioxidant property. The aim of this study was to investigate antioxidant effects of quercetin on corpora cavernosa of mice. Corpora cavernosa were isolated in organ baths, precontracted with phenylephrine (0.5 microm) and relaxant responses were mediated by acetylcholine (0.1-1 microm), electrical field stimulation (EFS, 1-16 Hz, 0.5 ms, 30 V) or acidified sodium nitrite (a NaNO(2), 0.5 mm). Superoxide anion generators; pyrogallol (50 microm), hydroquinone (100 microm), LY 83583 (6-Anilinoquinolin-5,8-quinone, 10 microm) and superoxide dismutase (SOD) inhibitor; diethyldithiocarbamic acid (DETCA, 8 mm) were used in order to expose corpus cavernosa to oxidant stress. Acetylcholine (0.1-1 microm) induced relaxant responses were significantly inhibited in LY 83583 (10 microm) and DETCA + LY 83583 applicated trials. EFS-induced relaxant responses were significantly inhibited in DETCA (8 mm) and DETCA + LY 83583 administrated trials. On the other hand, acidified sodium nitrite-induced responses were inhibited by all of the superoxide anion generators tested. Quercetin (10 microm) failed to improve the inhibitions on endothelium and electrically stimulated responses. Acidified sodium nitrite (0.5 mm) mediated relaxant responses were significantly restored by quercetin except the groups in which LY 83583 were used. The data suggest that quercetin acts as a protective agent in mouse corpus cavernosum, increasing the bioavailability of exogenous nitric oxide by protecting it from superoxide anion (O(2)(-)).

Investigation of a possible interaction between the heme oxygenase/biliverdin reductase and nitric oxide synthase pathway in murine gastric fundus and jejunum

This study investigated the possible interaction between the heme oxygenase (HO)/biliverdin reductase (BVR) and nitric oxide synthase (NOS) pathway in murine gastric fundus and jejunum, since previous studies have shown that both HO-2 and BVR are expressed in interstitial cells of Cajal (ICCs) and co-localized with neuronal NOS in a large proportion of myenteric neurons along the gastrointestinal tract. Neither HO inhibition by chromium mesoporphyrin (CrMP) nor co-incubation with CO or biliverdin/bilirubin affected nitrergic neurotransmission - i.e. relaxations induced by non-adrenergic non-cholinergic (NANC) nerve stimulation or exogenous NO - under normal physiological conditions. However, biliverdin/bilirubin reversed the inhibitory effect of the superoxide generator LY83583 on exogenous NO-induced relaxations in both tissues. When gastric fundus muscle strips were depleted of the endogenous antioxidant Cu/Zn superoxide dismutase (SOD) by the Cu-chelator DETCA, electrically induced NANC relaxations were also affected by LY82583; however, biliverdin/bilirubin could not substitute for the loss of Cu/Zn SOD when this specific antioxidant enzyme was depleted. In jejunal muscle strips, the combination DETCA plus LY83583 nearly abolished contractile phasic activity and, hence, did not allow studying nitrergic relaxation in these experimental conditions. In conclusion, this study does not establish a role for HO/CO in inhibitory NANC neurotransmission in murine gastric fundus and jejunum under normal physiological conditions. However, the antioxidants biliverdin/bilirubin might play an important role in the protection of the nitrergic neurotransmitter against oxidative stress.

Role of superoxide dismutase enzymes and ascorbate in protection of nitrergic relaxation against superoxide anions in mouse duodenum

AIM

The aim of this study was to investigate whether superoxide dismutase (SOD) enzymes and ascorbate play a role in the protection of the nitrergic relaxation against superoxide anion inhibition in the mouse duodenum.

METHODS

The effects of exogenous SOD, N,No-bis(salicylidene) ethylenediamine chloride (EUK-8; a synthetic cell-permeable mimetic of the manganese SOD [Mn-SOD] and ascorbate on relaxant responses induced by nitrergic nerve stimulation), exogenous nitric oxide (NO), and nitroglycerin were investigated in isolated mouse duodenum tissues.

RESULTS

Diethyldithiocarbamate (DETCA) inhibited the relaxation to exogenous NO and nitroglycerin, but not relaxation to electrical field stimulation (EFS). SOD and ascorbate partially prevented the inhibitory effect of DETCA on relaxation to NO, abut not to nitroglycerin. The DETCA-induced inhibition on nitroglycerin was prevented by EUK-8. Hemoglobin, 2- (4-carboxyphenyl)-4,4,5,5-tetramethylimidazolinel-oxyl-3-oxide, and hydroxocobalamin inhibited the relaxation to NO, but not to EFS and nitroglycerin in the presence of DETCA. Pyrogallol and hydroquinone inhibited the relaxation to NO, but not to EFS and nitroglycerin. This inhibition was prevented by exogenous SOD and ascorbate, but was not prevented by EUK-8. Pyrogallol and hydroquinone did not inhibit the EFS-induced relaxation in the presence of DETCA. Duroquinone and 6-anilino-5.8-quinolinedione inhibited the relaxation to EFS, NO, and nitroglycerin, and this inhibition was prevented by EUK-8.

CONCLUSION

These results suggest that the nitrergic neurotransmission in the mouse duodenum is protected by endogenous tissue antioxidants against superoxide anions, and Mn SOD, in addition to copper/zinc SOD, can protect NO from attack from superoxide anion generators intracellularly. Also, the possibility that the endogenous neurotransmitter may not be the free NO but a NO-containing or NO-generating molecule in the mouse duodenum remains open.

Torsion/detorsion of the testis does not modify responses to nitric oxide in rat isolated penile bulb

Ischaemia-reperfusion damage induced by torsion/detorsion of the testicles may be a causative factor leading to erectile dysfunction through oxidative stress-dependent changes in the responses of the penile bulb, an erectile tissue of the penis. We aimed at investigating the effects of unilateral testicular torsion/detorsion (2 or 24 hr) treatment on relaxations induced by electrical field stimulation and sodium nitroprusside in rat isolated penile bulb. Male Sprague-Dawley rats used in the study were divided into two groups. The treatment group was subjected to unilateral torsion followed by detorsion for 2 or 24 hr, while the control group underwent only sham operation. For in vitro organ bath experiments, penile bulbs were isolated and responses to relaxant agents and electrical field stimulation (70 V, 1 msec., 0.5-8 Hz, 5 sec.) were recorded on a computer-based data acquisition system via a force displacement transducer. In tissues precontracted with phenylephrine (3 x 10(-6 )M), relaxations induced by electrical field stimulation were not significantly different before and after 2 or 24 hr of detorsion. Similarly sodium nitroprusside- (10(-8)-3 x 10(-6 )M) and papaverine-induced (10(-7)-10(-4 )M) relaxations were also found unchanged in the detorsion group compared to control. In conclusion, spermatic cord torsion did not lead to impairment in nitric oxide-mediated relaxant responses of the rat isolated penile bulb.

Reactive oxygen species and erectile dysfunction: possible role of NADPH oxidase

Erectile dysfunction (ED) is a widespread condition, the incidence of which is increasing globally. ED is also indicative of underlying vasculopathy and represents a predictor of more serious cardiovascular disorders. Understanding the aetiology of ED may therefore provide invaluable pointers to the pathobiology of other cardiovascular diseases (CVDs) and syndromes. It follows, too, that therapeutic interventions that are successful in treating ED may, ipso facto, be effective in treating the early stages of conditions that include atherosclerosis, angina, plaque rupture and diabetic angiopathy. One common pathological denominator in both CVD and ED is oxidative stress, that is, the overproduction of reactive oxygen species (ROS), in particular, superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)). In this review, therefore, we consider the aetiology and pathobiology of O(2)(*-) in promoting ED and focus on NADPH oxidase as an inducible source of O(2)(*-) and H(2)O(2). Therapeutic strategies aimed at reducing oxidative stress to improve erectile function are also discussed.

The location of photodegradable nitric oxide store in the mouse stomach fundus

The aim of this study was to investigate the location of photodegradable nitric oxide (NO) store using a pharmacological approach in mouse gastric fundus. The ultraviolet light irradiation (UV; 360 nm, 60 s), electrical field stimulation (EFS; 4 Hz, 25 V, 1 ms, 15s-train), exogenous nitric oxide (NO; 10 microM), nitroglycerin (100 microM) and isoproterenol (5 nM) induced relaxation in mouse gastric fundus preparations in the absence or presence of an intact mucosa. The NO scavenger, haemoglobin (20 microM), significantly inhibited the relaxation of intact and denuded mucosa stomach fundus to UV light irradiation, EFS and NO, but not to nitroglycerin and isoproterenol. The superoxide anion generator, pyrogallol (50 microM), inhibited relaxation of intact and denuded mucosa stomach fundus induced by UV light irradiation, EFS, NO, but not to nitroglycerin and isoproterenol. The inhibition observed with pyrogallol was prevented by exogenous Cu/Zn superoxide dismutase (SOD; 100 U/ml), a membrane impermeable antioxidant. The Cu/Zn SOD inhibitor, diethyldithiocarbamic acid (DETCA; 8 mM), inhibited the relaxation of intact and denuded mucosa stomach fundus to UV light irradiation, EFS, NO and nitroglycerin but not those to isoproterenol. Exogenous SOD (100 U/ml) partially prevented the inhibitory effect of DETCA on relaxation to UV light irradiation, EFS, NO but not to nitroglycerin. DETCA-induced inhibition of the nitroglycerin-induced relaxation was partially prevented by the cell-permeable polyethylene-glycol-superoxide dismutase (100 U/ml). These results indicate that photodegradable NO store is, at least in part, unlikely to be within smooth muscle cells, and furthermore, that UV light-induced relaxation is not dependent on gastric mucosal layer.

Superoxide anion production in the rat penis impairs erectile function in diabetes: influence of in vivo extracellular superoxide dismutase gene therapy

INTRODUCTION

Superoxide anion may contribute to erectile dysfunction (ED) in diabetes mellitus by reducing cavernosal nitric oxide (NO) bioavailability. The purpose of this study was to determine if gene transfer of extracellular superoxide dismutase (EC-SOD) can reduce superoxide anion formation and determine if this reactive oxygen species may contribute to diabetes-related ED in an experimental model of diabetes.

METHODS

Three groups of animals were utilized: (1) control; (2) streptozotocin (STZ)-diabetic rats [60 mg/kg intraperitoneally (ip)] intracavernosally injected with AdCMVbetagal (negative control); and (3) STZ-rats intracavernosally injected with AdCMVEC-SOD. Two months after ip injection of STZ, groups 2 and 3 were transfected with the adenoviruses and 2 days after transfection, all animals underwent cavernosal nerve stimulation (CNS) to assess erectile function. Confocal microscopy for superoxide anion and von Willebrand Factor (vWF) was performed in the STZ-diabetic rat. Superoxide anion production, total SOD activity, and cyclic guanosine monophosphate (cGMP) levels were measured in each experimental group of rats.

RESULTS

Confocal microscopy demonstrated superoxide in smooth muscle and endothelial cells of the STZ-rat cavernosum and colocalized with vWF in the endothelium. Higher superoxide anion levels and decreased cGMP levels were found in the penis of STZ-rats at a time when erectile function was reduced. Two days after administration of AdCMVEC-SOD, superoxide anion levels were significantly lower in the penis of STZ-rats. Total SOD activity and cavernosal cGMP was increased in the penis of EC-SOD-transfected rats. STZ-rats transfected with AdCMVEC-SOD had a peak intracavernosal pressure (ICP) and total ICP to CNS that was similar to control rats.

CONCLUSIONS

These data demonstrate that in vivo adenoviral gene transfer of EC-SOD can reduce corporal superoxide anion levels and raise cavernosal cGMP levels by increasing NO bioavailability thus restoring erectile function in the STZ-diabetic rat.

Peripheral N-methyl-D-aspartate receptors modulate nonadrenergic noncholinergic lower esophageal sphincter relaxation in rabbits

We investigated the role of peripheral N-methyl-D-aspartate (NMDA) receptors in the myenteric plexus in mediating nonadrenergic noncholinergic (NANC) nitrergic relaxation of the lower esophageal sphincter (LES). Isometric contraction of LES strips from Japanese White rabbits was measured. NANC relaxation was induced by KCl (30 mM) in the presence of atropine and guanethidine. The concentration of 3',5'-cyclic guanosine monophosphate (cGMP) was measured using a radioimmunoassay. The muscle strips were exposed to diethyldithiocarbamic acid (DETCA; 3 mM) to inactivate Cu/Zn superoxide dismutase. MK801 (5-methyl-10,11-dihydroxy-5H-dibenzo(a,d)cyclohepten-5,10-imine) inhibited NANC relaxation in a concentration-dependent manner (EC50 = 1.5 x 10(-5) M), accompanied by a decrease in cGMP production. NMDA induced a concentration-dependent relaxation, which was antagonized by MK801. NMDA stimulated cGMP production, which was inhibited by N(G)-nitro-L-arginine. Superoxide dismutase (100 U/mL) shifted the concentration-response relationship of MK801-mediated inhibition of NANC relaxation to the right (EC50 = 3.4 x 10(-5) M), whereas catalase did not. Treatment with DETCA shifted the concentration-response relationships of pyrogallol-, ketamine- and MK801-mediated inhibition of NANC relaxation to the left. These findings suggest that the peripheral NMDA receptors mediate NANC smooth muscle relaxation, and modulate it, in part, through extracellular production of superoxide anions, thus eliminating the relaxant effect of endogenous nitric oxide.

The effects of superoxide anion generators on responses to exogenous nitric oxide and non-adrenergic, non-cholinergic nerve stimulation in rat isolated penile bulb

The effects of the superoxide anion generators, pyrogallol and hydroquinone on relaxations induced by electrical field stimulation (70 V, 0.7 msec., 0.5-8 Hz for 5 sec.) and exogenous nitric oxide donor sodium nitroprusside, were investigated in rat penile bulb precontracted with phenylephrine (10(-4) M). Pyrogallol (10(-4) M, 3 x 10(-4) M) and hydroquinone (3 x 10(-4) M) reduced the relaxations induced by sodium nitroprusside, but had no effect on relaxations elicited by nitrergic nerve stimulation. After treatment with diethyldithiocarbamate (3 x 10(-3) M), an inhibitor of Cu/Zn superoxide dismutase, both agents reduced the relaxations induced by electrical field stimulation. Superoxide dismutase, at 300 U/ml, significantly reversed the inhibitory action of pyrogallol and hydroquinone on responses to sodium nitroprusside. This concentration of superoxide dismutase failed to reverse the inhibitory action of pyrogallol on responses to electrical field stimulation observed in the presence of diethyldithiocarbamate, while at 600 U/ml it significantly prevented the reduction in relaxations. However, even at 600 U/ml, superoxide dismutase did not alter the decrease in responses to electrical field stimulation evoked by hydroquinone in tissues pretreated with diethyldithiocarbamate. These results suggest that the nitrergic transmitter in rat penile bulb is protected against superoxide anions by endogenous Cu/Zn superoxide dismutase in a manner similar to gastric fundus and anococcygeus muscles.

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

Gastrointestinal (GI) smooth muscle responses to stimulation of the nonadrenergic noncholinergic inhibitory nerves have been suggested to be mediated by polypeptides, ATP, or another unidentified neurotransmitter. The discovery of nitric-oxide (NO) synthase inhibitors greatly contributed to our understanding of mechanisms involved in these responses, leading to the novel hypothesis that NO, an inorganic, gaseous molecule, acts as an inhibitory neurotransmitter. The nerves whose transmitter function depends on the NO release are called "nitrergic", and such nerves are recognized to play major roles in the control of smooth muscle tone and motility and of fluid secretion in the GI tract. Endothelium-derived relaxing factor, discovered by Furchgott and Zawadzki, has been identified to be NO that is biosynthesized from l-arginine by the constitutive NO synthase in endothelial cells and neurons. NO as a mediator or transmitter activates soluble guanylyl cyclase and produces cyclic GMP in smooth muscle cells, resulting in relaxation of the vasculature. On the other hand, NO-induced GI smooth muscle relaxation is mediated, not only by cyclic GMP directly or indirectly via hyperpolarization, but also by cyclic GMP-independent mechanisms. Numerous cotransmitters and cross talk of autonomic efferent nerves make the neural control of GI functions complicated. However, the findingsrelated to the nitrergic innervation may provide us a new way of understanding GI tract physiology and pathophysiology and might result in the development of new therapies of GI diseases. This review article covers the discovery of nitrergic nerves, their functional roles, and pathological implications in the GI tract.

Influence of polyethylene-glycol-superoxide dismutase and combined depletion and repletion of antioxidants on nitrergic relaxation in the pig gastric fundus

In circular smooth muscle strips of porcine gastric fundus, polyethylene-glycol-superoxide dismutase, a membrane-permeable analogue of endogenous copper/zinc (Cu/Zn) superoxide dismutase, reversed the inhibitory effect of the superoxide anion generator 6-anilino-5,8-quinolinedione (LY83583) on electrically induced nitrergic relaxations of fundic tissues which are depleted of the endogenous antioxidant Cu/Zn superoxide dismutase by diethyldithiocarbamate, to the same extent as exogenously added Cu/Zn superoxide dismutase. Addition of a second antioxidant together with Cu/Zn superoxide dismutase does not result in a higher degree of reversal of the inhibitory effect of LY83583. Depletion of either tissue glutathione or tissue catalase in combination with diethyldithiocarbamate does not increase the inhibitory action of LY83583 or the nitric oxide (NO)-scavenger hydroxocobalamin upon nitrergic relaxations (electrically induced or by exogenous NO) when compared to their action in the presence of diethyldithiocarbamate alone. In conclusion, these results demonstrate that endogenous Cu/Zn superoxide dismutase is the essential antioxidant responsible for safeguarding peripheral nitrergic neurotransmission, whereby extracellular protection of endogenous NO is most important.

Catalase has negligible inhibitory effects on endothelium-dependent relaxations in mouse isolated aorta and small mesenteric artery

1. The current study examined the hypothesis that endothelial production of hydrogen peroxide (H2O2) mediates relaxations to acetylcholine (ACh) in aorta and small mesenteric arteries (SMA) from mice. 2. Relaxations to ACh (0.01-10 microM) and H2O2 (0.1-1000 microM) were produced in aorta and SMA isolated from wild-type C57BL/6 mice and type II diabetic mice (db/db). In SMA, relaxations to ACh were produced in the presence of N omega-nitro-L-arginine methyl ester (100 microM) and indomethacin (Indo, 10 microM). 3. 1-H[1,2,4]oxadiazolo[4,3-]quinoxalin-1-one (10 microM) significantly reduced ACh-induced relaxations in SMA, abolished responses in aorta, but had no effect on relaxations induced by H2O2. Catalase (2500 U ml-1) abolished responses to H2O2, but did not alter relaxations to ACh in the SMA and only caused a small rightward shift in responses to ACh in the aorta. 4. ACh-, but not H2O2-, mediated relaxations were significantly reduced by tetraethylammonium (10 mM), the combination of apamin (1 microM) and charybdotoxin (100 nM), and 25 mm potassium chloride (KCl). Higher KCl (60 mM) abolished relaxations to both ACh and H2O2. Polyethylene glycolated superoxide dismutase (100 U ml-1), the catalase inhibitor 3-amino-1,2,4-triazole (3-AT, 50 mM) and treatment with the copper chelator diethyldithiolcarbamate (3 mM) did not affect relaxations to ACh. 5. H2O2-induced relaxations were endothelium-independent and were not affected by ethylene diamine tetraacetic acid (EDTA 0.067 mM), 4-aminopyridine (1 mM), ouabain (100 microM) and barium (30 microM), 3-AT or Indo. 6. Although the data from this study show that H2O2 dilates vessels, they do not support the notion that H2O2 mediates endothelium-dependent relaxations to ACh in either aorta or SMA from mice.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Oxygen free radicals and the penis

Penile erection is dependent upon vascular smooth muscle relaxation in erectile tissue and penile arteries, the principal mediator of relaxation being nitric oxide (NO). Evidence from basic scientific studies indicates that oxidative stress mediated through the superoxide radical (superoxide) and other reactive oxygen species (ROS) may be central to impaired cavernosal function in erectile dysfunction (ED). Increased inactivation of NO by superoxide results in impaired penile NO transmission and smooth muscle relaxation. Furthermore, propagation of endothelial dysfunction by ROS may result in chronic impairment of penile vascular function, a process analogous to early atherogenesis. Indeed, ED and atherosclerosis are closely linked through shared risk factors. Given our current understanding of ED pathophysiology, antioxidants may be of benefit in both the short- and long-term. Evidence supporting the paradigm of antioxidant therapy for the prevention or treatment of ED is presented herein.

Influence of antioxidant depletion on nitrergic relaxation in the pig gastric fundus

1. The hypothesis that endogenous tissue antioxidants might explain the inability of the superoxide generators 6-anilino-5,8-quinolinedione (LY83583) and hydroquinone (HQ) and of the NO-scavengers hydroxocobalamin (HC) and 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) to affect nitrergic neurotransmission in the porcine gastric fundus was tested by selective pharmacological depletion of respectively Cu/Zn superoxide dismutase (Cu/Zn SOD) and reduced glutathione (GSH) in circular smooth muscle preparations. 2. Diethyldithiocarbamate (DETCA; 3x10(-3) M), which almost completely abolished tissue Cu/Zn SOD activity, had no effect per se on nitrergic relaxations induced by either electrical field stimulation (EFS; 4 Hz, 10 s) or exogenous nitric oxide (NO; 10(-5) M). In these DETCA-treated tissues however, electrically-induced nitrergic relaxations became sensitive to inhibition by LY83583 (10(-5) M) or HC (10(-4) M), but not by HQ (10(-4) M) or c-PTIO (10(-4) M); only for the combination of DETCA plus LY83583, this inhibition was partially reversed by exogenous Cu/Zn SOD (1000 u ml(-1)). 3. Immunohistochemical analysis of porcine gastric fundus revealed a 100% colocalization of Cu/Zn SOD and neuronal nitric oxide synthase (nNOS) in the intrinsic neurons of the myenteric plexus. 4. Buthionine sulphoximine (BSO; 10(-3) M) in the absence or presence of LY83583 (10(-5) M) or HC (10(-4) M) did not alter nitrergic relaxations, although it reduced per se the tissue GSH content to 62% of control. 5. Pharmacological depletion studies, corroborated by immunohistochemical data, thus suggest a role for Cu/Zn SOD but not for GSH in nitrergic neurotransmission in the porcine gastric fundus.

Biology of the anococcygeus muscle

The anococcygeus is a smooth muscle tissue of the urogenital tract which, in the male, runs on to form the retractor penis. The motor innervation is classically sympathetic with noradrenaline as transmitter, but the relaxant parasympathetic transmitter has only recently been identified as nitric oxide. Indeed, the anococcygeus has provided an extremely useful model with which to probe the mechanisms underlying this novel nitrergic system, including the importance of physiological antioxidants in maintaining the potency of nitric oxide as a neurotransmitter. The cellular mechanisms of contraction and relaxation are slowly being clarified, with particular interest in the contribution of capacitative calcium entry and the guanylyl cyclase/cyclic GMP system. Many questions remain unanswered, however, including the precise physiological role of the muscle, the identity of substances released from subcellular vesicles of nitrergic nerves, the unusual sensitivity of the tissue to certain peptides (oxytocin and urotensin II), and the nature of store-operated channels through which calcium enters the cell to maintain contraction.

Corpus cavernosum dysfunction in diabetic rats: effects of combined alpha-lipoic acid and gamma-linolenic acid treatment

BACKGROUND

The effects of streptozotocin-induced diabetes on nitric oxide (NO)-mediated relaxation of rat corpus cavernosum smooth muscle to neurogenic and endothelial stimulation was examined. The aim was to assess the effects of treatment with low doses of the antioxidant, alpha-lipoic acid, and the omega-6 essential fatty acid, gamma-linolenic acid, either separately or in combination.

METHODS

Treatment was preventive from diabetes induction or corrective over 4 weeks after 4 weeks of untreated diabetes. Corpus cavernosum responses were examined in vitro.

RESULTS

Neither diabetes nor treatment affected contractile responses to transmural electrical field stimulation of noradrenergic nerves. Stimulation of phenylephrine precontracted cavernosa in the presence of guanethidine and atropine caused relaxation via the nitrergic innervation. Maximum relaxation responses were 40% and 46% decreased after 4 and 8 weeks of diabetes, respectively. alpha-Lipoic acid, gamma-linolenic acid combination treatment fully prevented this deficit, and partially (52%) corrected the effect of 4 weeks of untreated diabetes. Neither alpha-lipoic acid nor gamma-linolenic components alone had significant effects, which suggests that there were synergistic interactions between the drugs. Both 4 and 8 weeks of untreated diabetes reduced maximum endothelium-dependent relaxation of phenylephrine precontracted cavernosa to acetylcholine by approximately 40%. While alpha-lipoic acid or gamma-linolenic acid were ineffective, joint treatment fully prevented and corrected this diabetic endothelial deficit. Neither diabetes nor treatment affected endothelium-independent relaxation to the NO donor, sodium nitroprusside.

CONCLUSION

The data show that alpha-lipoic acid and gamma-linolenic acid interact synergistically to improve NO-mediated neurogenic and endothelium-dependent relaxation of corpus cavernosum in experimental diabetes.

Pre- and postjunctional protective effect of neocuproine on the nitrergic neurotransmitter in the mouse gastric fundus

1. Electrical field stimulation (EFS) of non-adrenergic non-cholinergic nerves of the mouse gastric fundus induced frequency-dependent transient relaxations which were mimicked by nitric oxide (NO), added as acidified NaNO(2). The NO donors S-nitrosocysteine, S-nitrosoglutathione, SIN-1 and hydroxylamine induced sustained concentration-dependent relaxations. The NO synthase blocker L-nitro arginine (L-NOARG; 300 microM) abolished the relaxations to EFS without affecting the relaxations to NO. 2. The copper(I) chelator neocuproine (10 microM) enhanced the relaxations to EFS and NO but inhibited those to S-nitrosocysteine and S-nitrosoglutathione. Neocuproine potentiated the relaxations to SIN-1, which releases NO extracellularly, without affecting the relaxations to hydroxylamine, which releases NO intracellularly. 3. The potentiating effect of neocuproine on the relaxations to EFS was more pronounced after inhibition of catalase with 3-amino-1,2,4-triazole (1 mM) but not after inhibition of Cu/Zn superoxide dismutase (SOD) with diethyl dithiocarbamic acid (DETCA, 1 mM). The potentiating effect of neocuproine on relaxations to NO was not altered by 3-amino-1,2,4-triazole or DETCA treatment. 4. The relaxations to EFS were significantly inhibited by the oxidants hydrogen peroxide (70 microM) and duroquinone (10 microM) but only after inhibition of catalase with 3-amino-1,2,4-triazole or after inhibition of Cu/ZnSOD with DETCA respectively. 5. Our results suggest that neocuproine can act as an antioxidant in the mouse gastric fundus and that both catalase and Cu/ZnSOD protect the nitrergic neurotransmitter from oxidative breakdown. Since inhibition of catalase but not inhibition of Cu/ZnSOD potentiated the effect of neocuproine on relaxations to EFS without affecting the relaxations to NO, catalase may protect the nitrergic neurotransmitter mainly at a prejunctional site whereas Cu/ZnSOD protects at a postjunctional site.

Effect of neocuproine, a selective Cu(I) chelator, on nitrergic relaxations in the mouse corpus cavernosum

The effects of neocuproine and bathocuproine, Cu(I) and Cu(II) chelators, respectively, were studied on relaxations in response to electrical field stimulation, acetylcholine, S-nitrosoglutathione, acidified sodium nitrite and sodium nitroprusside in the mouse corpus cavernosum precontracted with phenylephrine. Neocuproine significantly inhibited relaxations induced by electrical field stimulation, acetylcholine and S-nitrosoglutathione, but not by acidified sodium nitrite and sodium nitroprusside. The pre-prepared neocuproine-Cu(I) complex was ineffective on the responses. The discrepancy between the shape of relaxations in response to electrical field stimulation or to acetylcholine and S-nitrosoglutathione was abolished by adding CuCl(2) into the bathing medium. The copper action was blocked by neocuproine but not by bathocuproine. However, the pre-prepared bathocuproine-Cu(II) complex did not accelerate the relaxations affected by CuCl(2). These findings suggest that a Cu(I)-dependent mechanism may play a role in the relaxation induced by the endogenous relaxant factor as well as by S-nitrosoglutathione in mouse cavernosal tissue.

Interaction of hypoxanthine/xanthine oxidase with nitrergic relaxation in the porcine gastric fundus

The influence of hypoxanthine (HX)/xanthine oxidase (XO) on short-term [electrical field stimulation (EFS; 4 Hz) for 10 s and 3 min; bolus of exogenous NO (10(-5) M)] and long-term [EFS (4 Hz) and continuous NO-infusion for 20 min] nitrergic relaxations was investigated in circular muscle strips of the pig gastric fundus. HX (3x10(-4) M) / XO (64 mu ml(-1)) did not affect EFS for 10 s and 3 min; the short-lasting relaxation in response to a bolus of exogenous NO (10(-5) M) was changed into a biphasic relaxation with a small and short first phase followed by a larger and prolonged second phase. Cu/Zn superoxide dismutase (Cu/Zn SOD; 1000 u ml(-1)) and uricase (100 mu ml(-1)) respectively enhanced the amplitude of the first phase and diminished the amplitude of the second phase. Ascorbate (5x10(-4) M) and bilirubin (2x10(-4) M) prevented the prolonged component. Exposure to HX/XO during long-term EFS elicited a complete, stable reversal of relaxation starting after a delay. During continuous NO-infusion, HX/XO induced an immediate, complete but transient reversal. The antioxidants bilirubin, ascorbate, alpha-tocopherol, urate, glutathione and Cu/Zn SOD, the hydrogen peroxide degrading enzyme catalase, the hydroxyl radical scavengers dimethylsulphoxide and mannitol, and the cofactor flavin adenine dinucleotide did not influence the reversal induced by HX/XO during either EFS or NO-infusion. The cell-permeable manganese SOD mimetic EUK-8 modified the stable reversal during long-term EFS into a transient one. The results suggest that a nitrated uric acid derivative is responsible for the prolonged second phase in the relaxation to a bolus of exogenous NO in the presence of HX/XO. The exact underlying mechanism of the reversal induced by HX/XO during sustained relaxation remains unclear.

Influence of bilirubin and other antioxidants on nitrergic relaxation in the pig gastric fundus

1. The influence of several antioxidants (bilirubin, urate, ascorbate, alpha-tocopherol, glutathione (GSH), Cu/Zn superoxide dismutase (SOD) and the manganese SOD mimic EUK-8) on nitrergic relaxations induced by either exogenous nitric oxide (NO; 10(-5) M) or electrical field stimulation (4 Hz; 10 s and 3 min) was studied in the pig gastric fundus. 2. Ascorbate (5x10(-4) M), alpha-tocopherol (4x10(-4) M), SOD (300 - 1000 u ml(-1)) and EUK-8 (3x10(-4) M) did not influence the relaxations to exogenous NO. In the presence of GSH (5x10(-4) M), the short-lasting relaxation to NO became biphasic, potentiated and prolonged. Urate (4x10(-4) M) and bilirubin (2x10(-4) M) also potentiated the relaxant effect of NO. None of the antioxidants influenced the electrically evoked relaxations. 3. 6-Anilino-5,8-quinolinedione (LY83583; 10(-5) M) had no influence on nitrergic nerve stimulation but nearly abolished the relaxant response to exogenous NO. Urate and GSH completely prevented this inhibitory effect, while it was partially reversed by SOD and bilirubin. Ascorbate, alpha-tocopherol and EUK-8 were without effect. 4. Hydroquinone (10(-4) M) did not affect the electrically induced nitrergic relaxations, but markedly reduced NO-induced relaxations. The inhibition of exogenous NO by hydroquinone was completely prevented by urate and GSH. SOD and ascorbate afforded partial protection, while bilirubin, EUK-8 and alpha-tocopherol were ineffective. 5. Hydroxocobalamin (10(-4) M) inhibited relaxations to NO by 50%, but not the electrically induced responses. Full protection versus this inhibitory effect was obtained with urate, GSH and alpha-tocopherol. 6. These results strengthen the hypothesis that several endogenous antioxidant defense mechanisms, enzymatic as well as non-enzymatic, might play a role in the nitrergic neurotransmission process.

Effects of superoxide generating systems on muscle tone, cholinergic and NANC responses in cat airway

To study the possible role of reactive oxygen species in airway hyperreactivity, we examined the effects of the superoxide anion radical (O(2)(-)) generating systems, pyrogallol and xanthine with xanthine oxidase, on muscle tone, excitatory and inhibitory neurotransmission in the cat airway. Smooth muscle contraction or non-adrenergic non-cholinergic (NANC) relaxation evoked by electrical field stimulation (EFS) were measured before or after O(2)(-) generating systems with or without diethydithiocarbamic acid (DEDTCA), an inhibitor of endogenous superoxide dismutase (SOD). Resting membrane potential or excitatory junction potential (EJP) were also measured in vitro. Both pyrogallol and xanthine/xanthine oxidase produced biphasic changes in basal and elevated (by 5-HT) muscle tone. After SOD pretreatment, both systems consistently produced a prolonged contraction, thereby indicating that O(2)(-) was converted to H(2)O(2) by the action of SOD and as a result the actions of O(2)(-) were lost but those of H(2)O(2) introduced. The O(2)(-) showed no significant effect on smooth muscle contraction or EJP evoked by EFS, however after DEDTCA pretreatment, it evoked initial enhancement followed by suppression of the contraction and EJP. DEDTCA pretreatment ameliorated the inhibitory action of pyrogallol and xanthine/xanthine oxidase on the NANC relaxation, probably because O(2)(-) could combine with endogenous NO to form peroxynitrite. These results indicate that the O(2)(-) generating systems have multiple actions, presumably due to the presence and simultaneous action of at least two different reactive oxygen species (O(2)(-) and H(2)O(2)). While H(2)O(2) seems to be responsible for elevation of muscle tone and augmentation of smooth muscle contraction by EFS, O(2)(-) inhibits muscle tone, cholinergic and NANC neurotransmission.

Spontaneous photo-relaxation of urethral smooth muscle from sheep, pig and rat and its relationship with nitrergic neurotransmission

1. In the present work we have characterized the relaxant response induced by light stimulation (LS) in the lower urinary tract from sheep, pig and rat, establishing its relationship with nitrergic neurotransmission. 2. Urethral, but not detrusor, preparations showed pronounced photo-relaxation (PR) which declined progressively following repetitive LS. Sheep urethral PR was again restored either spontaneously or (to a greater extent) by exogenous nitric oxide (NO) addition and by electrical field stimulation (EFS) of intrinsic nitrergic nerves. 3. Greater NO generation was detected from sheep urethral than from detrusor homogenates following illumination. 4. Sheep urethral PR was inhibited by oxyhaemoglobin, but not by methaemoglobin, carboxy-PTIO, extracellular superoxide anion generators or superoxide dismutase. Guanylyl cyclase but not adenylyl cyclase activation mediates urethral relaxation to LS. 5. Urethral PR was more resistant to inhibition by L-thiocitrulline than EFS-induced responses, although this agent prevented PR restoration by high-frequency EFS. 6. Urethral PR was TTX insensitive and partially modified in high-K+ solutions. Cold storage for 24 h greatly impaired urethral PR, although it was restored by high-frequency EFS. 7. Repetitive exposure to LS, EFS or exogenous NO induced changes in the shape of the EFS-induced nitrergic relaxation, possibly by pre-synaptic mechanisms. 8. In conclusion, we suggest the presence of an endogenous, photo-labile, nitro-compound store in the urethra, which seems to be replenished by neural nitric oxide synthase activity, indicating a close functional relationship with the nitrergic neurotransmitter.

Effects of superoxide anion generators and thiol modulators on nitrergic transmission and relaxation to exogenous nitric oxide in the sheep urethra

The effects of superoxide anion generators, the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoine-1-oxyl 3-oxide (carboxy-PTIO), the specific guanylate cyclase inhibitor 1H-[1,2,4]-oxadiazole-[4,3-a]-quinoxalin-1-one (ODQ), and thiol modulating agents were investigated on relaxations induced by nitrergic stimulation and exogenous NO addition in the sheep urethra. Methylene blue (MB, 10 microM), pyrogallol (0.1 mM) and xanthine (X, 0.1 mM)/xanthine oxidase (XO, 0.1 u ml(-1)) inhibited NO-mediated relaxations, without affecting those induced by nitrergic stimulation. This resistance was not diminished following inhibition of endogenous Cu/Zn superoxide dismutase (Cu/Zn SOD) with diethyldithiocarbamic acid (DETCA, 3 mM), which almost abolished tissue SOD activity. Carboxy-PTIO (0.1 - 0.5 mM) inhibited NO-mediated relaxations but had no effect on responses to nitrergic stimulation, which were not changed by treatment with ascorbate oxidase (2 u ml(-1)). Relaxations to NO were reduced, but not abolished, by ODQ (10 microM), while nitrergic responses were completely blocked. The thiol modulators, ethacrynic acid (0.1 mM), diamide (1.5 mM), or 5,5'-dithio-bis (2-nitrobenzoic acid) (DTNB, 0. 5 mM), and subsequent treatment with dithiothreitol (DTT, 2 mM) had no effect on responses to nitrergic stimulation or NO. In contrast, N-ethylmaleimide (NEM, 0.2 mM) markedly inhibited both relaxations. L-cysteine (L-cys, 0.1 mM) had no effect on responses to NO, while it inhibited those to nitrergic stimulation, in a Cu/Zn SOD-independent manner. Our results do not support the view that the urethral nitrergic transmitter is free NO, and the possibility that another compound is acting as mediator still remains open. British Journal of Pharmacology (2000) 129, 53 - 62

Neocuproine potentiates the activity of the nitrergic neurotransmitter but inhibits that of S-nitrosothiols

In the present study, we investigated the cellular components that are involved in the release of nitric oxide (NO) from S-nitrosothiols and whether these components also modulate the activity of the nitrergic neurotransmitter in the rat gastric fundus. Electrical stimulation of nitrergic nerves induced frequency-dependent transient relaxations which were mimicked by exogenous NO. The S-nitrosothiols S-nitrosocysteine, S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine induced concentration-dependent relaxations which were generally more sustained as compared to those to nitrergic nerve stimulation or NO. The relaxations to nitrergic nerve stimulation and those to NO were significantly enhanced by the copper(I) chelator neocuproine but not affected by the copper(II) chelator cuprizone. The relaxations to the S-nitrosothiols were significantly inhibited by neocuproine but not by cuprizone. The antioxidant ascorbate did not affect the tension of the muscle strip. However, in the presence of an S-nitrosothiol, ascorbate induced an immediate, sharp and transient relaxation that was significantly inhibited by a low concentration of neocuproine but not by cuprizone. Ascorbate did not induce a relaxation during short-train or prolonged nerve stimulation of the muscle strip. These results suggest that ascorbate interacts with copper to modulate the biological activity of S-nitrosothiols but not that of the nitrergic neurotransmitter. The differential effect of neocuproine indicates that S-nitrosothiols do not mediate the nitrergic neurotransmission of the rat gastric fundus. As neocuproine is to date the only compound that exerts an opposite effect on the biological activity of the nitrergic neurotransmitter and on that of S-nitrosothiols, it may be useful to elucidate the nature of the nitrergic neurotransmitter in the peripheral nervous system.

The role of antioxidant enzymes in the control of opossum gallbladder motility

BACKGROUND

Superoxide rapidly oxidizes nitric oxide (NO) to form peroxynitrite, thus terminating the biological activity of NO. The aims of our study were to determine if superoxide alters the motor function of the gallbladder and to localize the antioxidant enzymes in the gallbladder.

MATERIALS AND METHODS

Immunostaining and immunoblots were performed and enzyme activities were measured in the gallbladder. In physiologic experiments, force-displacement transducers recorded tension in gallbladder muscle strips. Superoxide was generated by the addition of xanthine with xanthine oxidase, while superoxide radicals were scavenged by the addition of superoxide dismutase (SOD) and catalase. SOD was inhibited by deithyldithiocarbamate.

RESULTS

Immunostaining demonstrated superoxide dismutase and catalase immunoreactivity in ganglia situated throughout the smooth muscle. Total superoxide dismutase activity was 115 +/- 12 U/mg. Western blots detected expression of proteins of 19.4 kDa for copper/zinc SOD and 25.0 kDa for manganese SOD. Generation of superoxide increased isometric tension, while pretreatment with SOD prevented the increase in isometric tension induced by superoxide. Inhibition of SOD diminished the EFS-induced off response.

CONCLUSIONS

We conclude that superoxide alters gallbladder motor function, and the presence of superoxide scavenging enzymes in enteric plexuses suggests that they may regulate gallbladder neuromuscular function by clearing endogenous superoxide.

Effects of chelator treatment on aorta and corpus cavernosum from diabetic rats

Transition-metal catalyzed reactions contribute to oxidative stress, which has been implicated in the pathogenesis of diabetic complications. The aim was to evaluate the effects of treatment with the transition metal chelator trientine on endothelium-dependent relaxation of aorta and corpus cavernosum from streptozotocin-induced diabetes of 8 weeks duration in rats. Effects on cavernosum autonomic innervation were also examined. Diabetes caused a 30.1 +/- 3.8% reduction in maximum aorta endothelium-dependent relaxation to acetylcholine (ACh), which was markedly attenuated (72.7 +/- 10.6%) by trientine treatment. Reversal treatment (4 weeks untreated diabetes, 4 weeks trientine) did not effect endothelium-dependent relaxation compared with aortas from rats with 4 weeks of diabetes, however, there was a 22.5 +/- 6.2% improvement compared with 8 weeks of diabetes. Eight weeks of diabetes caused a 41.5 +/- 6.6% reduction in corpus cavernosum endothelium-dependent maximum relaxation to ACh that was 70.1 +/- 16.9% prevented by trientine. Cavernosum nonadrenergic, noncholinergic (NANC) nerve stimulation caused frequency-dependent relaxation to a maximum of 40.9 +/- 2.4%, which was reduced by diabetes to 24.2 +/- 2.1%. Trientine partially prevented this deficit, maximum relaxation being 31.9 +/- 2.3%. Thus, metal chelator treatment has beneficial effects on aorta and cavernosum endothelium-dependent relaxation and on cavernosum NANC innervation.

Effects of superoxide dismutase mimetics on the activity of nitric oxide in rat aorta

A number of structurally distinct superoxide dismutase (SOD) mimetics were examined to determine if they shared the ability of authentic Cu/Zn SOD to produce endothelium-dependent relaxation of rings of rat aorta by protecting basal nitric oxide from destruction by endogenously produced superoxide anion. MnCl2 (10 nM-100 microM), CuSO4 (100 nM-1 mM) and CuDIPS (Cu [II]-[diisopropylsalicylate]2; 100 nM-30 microM) each mimicked the ability of Cu/Zn SOD (0.1-300 u ml(-1)) to produce relaxation of phenylephrine-precontracted aortic rings in a manner inhibited by endothelial removal or treatment with N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM). In contrast, MnTMPyP (Mn [III] tetrakis [1-methyl-4-pyridyl] porphyrin; 10 nM-30 microM) augmented phenylephrine-induced contraction and this was blocked by endothelial removal or treatment with L-NAME (100 microM), consistent with destruction rather than protection of basal nitric oxide activity. Pretreatment with Cu/Zn SOD (250 u ml(-1)) blocked this augmentation suggesting that it arose paradoxically through destruction of nitric oxide by superoxide anion. The spin trap agents tiron (100 nM-1 mM), tempol (100 nM-1 mM) and PTIYO (4-phenyl-2,2,5,5-tetramethyl imidazolin-1-yloxy-5-oxide; 100 nM-300 microM) all failed to promote endothelium-dependent relaxation. In fact, the last two augmented phenylephrine-induced tone and this was blocked by endothelial removal or treatment with L-NAME (100 microM), consistent with destruction of basal nitric oxide activity. This destruction was unaffected by pretreatment with Cu/Zn SOD (250 u ml(-1)) and probably reflected the direct ability of tempol and PTIYO to destroy nitric oxide. Thus, the ideal SOD mimetic for protection of nitric oxide activity in conditions of oxidant stress still awaits development.

Comparison of the redox forms of nitrogen monoxide with the nitrergic transmitter in the rat anococcygeus muscle

1. A sustained tone was produced in rat isolated anococcygeus muscles with guanethidine and clonidine and relaxant responses were elicited by electrical stimulation of its nitrergic nerves and by the three redox forms of nitrogen monoxide. 2. The nitroxyl anion (NO ) was donated by dissociation of Angeli's salt; the free radical (NO*) was from an aqueous solution of nitric oxide gas; the nitrosonium cation (NO+) was donated by dissociation of nitrosonium tetrafluoroborate. 3. The concentrations producing approximately 50% relaxations of the anococcygeus muscle were 0.3 microM for Angeli's salt (nitroxyl), 0.5 microM for NO* and 100 microM for nitrosonium tetrafluoroborate. Nitrergic nerve stimulation at 1 Hz for 10 s produced equivalent relaxant responses. 4. The superoxide generator pyrogallol (100 microM) had no effect on responses to nitrergic nerve stimulation or Angeli's salt but significantly reduced responses to NO* and nitrosonium tetrafluoroborate. 5. The NO* scavenger carboxy-PTIO (100 microM) had no effect on responses to nitrergic nerve stimulation or Angeli's salt but significantly reduced responses to NO* and nitrosonium tetrafluoroborate. 6. Hydroxocobalamin (30 microM) had no significant effect on responses to the nitrergic transmitter, enhanced the response to Angeli's salt, and significantly reduced responses to NO* and nitrosonium tetrafluoroborate. 7. The findings suggest that the nitroxyl anion donated by Angeli's salt is a better candidate than NO* to serve as the nitrergic transmitter in the rat anococcygeus muscle, although it still does not behave exactly like the transmitter.

Pharmacological comparison between the nitrergic responses produced by intramural nerve stimulation and exogenous NO-donors in rat gastric fundus

To investigate whether the nitrergic nerve-mediated smooth muscle relaxation is caused by authentic nitric oxide (NO) and is mediated via guanosine 3':5'-cyclic monophosphate (cyclic GMP), we compared the response to electrical field stimulation of nitrergic nerve (EFS) with other NO-related responses in rat gastric fundus strips. EFS, sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), and acidified NaNO2 and inducible NO synthase (iNOS)-mediated NO all produced relaxation and elevated cyclic GMP level in rat fundus strips. However, the basal and stimulated cyclic GMP levels were significantly lower than the basal level in aorta (40+/-4 pmol/g wet tissue). Methylene blue and 6-anilino-5,8-quinolinedione (LY83583), both known as soluble guanylyl cyclase inhibitors and O2- generators that scavenge NO, reduced the elevation of cyclic GMP level by all stimuli and inhibited the relaxations only in response to NaNO2 and iNOS-mediated NO but not to the other stimuli. These results suggest that in the rat gastric fundus strips the relaxations induced by not only nitrergic nerve but also SNP and SNAP are not associated with cyclic GMP production, in contrast to the relaxations mediated by authentic NO.

Effects of hydroxocobalamin and carboxy-PTIO on nitrergic transmission in porcine anococcygeus and retractor penis muscles

The effects of carboxy-PTIO and hydroxocobalamin were studied on nitrergic transmission in anococcygeus and retractor penis muscles taken during post mortem examination from young male pigs. In both muscles under resting conditions, electrical field stimulation (EFS) caused contractions that were sensitive to tetrodotoxin (1 microM) and were greatly inhibited by prazosin (1 microM) and guanethidine (10-30 microM), but were not significantly affected by atropine (1 microM). In the anococcygeus muscle, but not in the retractor penis muscle, guanethidine produced a prolonged contraction. After tone was raised by guanethidine in the anococcygeus or by phenylephrine (1 microM) in the presence of guanethidine in the retractor penis, EFS caused tetrodotoxin-sensitive relaxations. The EFS-induced relaxations were abolished by the NO synthase inhibitor N(G)-L-nitro-arginine methyl ester (L-NAME; 100 microM) and its effect was partly overcome by L-arginine (1 mM), indicating it was mediated by nitrergic nerves. Carboxy-PTIO (0.1-1 mM) had no significant effect in reducing stimulation-induced nitrergic relaxations in either muscle. However, hydroxocobalamin (0.1-1 mM) caused concentration-dependent reductions of nitrergic relaxations in both muscles. Relaxations to exogenous nitric oxide (1 microM) in both muscles were abolished by carboxy-PTIO (0.3 mM) and hydroxocobalamin (0.1 mM). There were no differences in reactivity to carboxy-PTIO or hydroxocobalamin between anococcygeus and retractor penis muscles from the same species (pig). The finding also confirms earlier observations that the nitrergic transmitter is generally resistant to the NO-scavenger carboxy-PTIO.

Effects of pyrogallol, hydroquinone and duroquinone on responses to nitrergic nerve stimulation and NO in the rat anococcygeus muscle

1. The hypothesis that endogenous superoxide dismutase (SOD) protects the nitrergic transmitter from inactivation by superoxide and that this explains the lack of sensitivity of the transmitter to superoxide generators was tested in the rat isolated anococcygeus muscle. 2. Responses to nitrergic nerve stimulation or to NO were not significantly affected by exogenous SOD or by the Cu/Zn SOD inhibitor diethyldithiocarbamic acid (DETCA). 3. Hydroquinone produced a concentration-dependent reduction of responses to NO with an IC50 of 27 microM, and higher concentrations reduced relaxant responses to nitrergic nerve stimulation with an IC50 of 612 microM. The effects of hydroquinone were only slightly reversed by SOD, so it does not appear to be acting as a superoxide generator. 4. Pyrogallol produced a concentration-dependent reduction in responses to NO with an IC50 value of 39 microM and this effect was reversed by SOD (100-1000 u ml(-1)). Pyrogallol did not affect responses to nitrergic nerve stimulation. Treatment with DETCA did not alter the differentiating action of pyrogallol. 5. Duroquinone produced a concentration-dependent reduction of relaxations to NO with an IC50 value of 240 microM and 100 microM slightly decreased nitrergic relaxations. After treatment with DETCA, duroquinone produced greater reductions of relaxant responses to NO and to nitrergic stimulation, the IC50 values being 8.5 microM for NO and 40 microM for nitrergic nerve stimulation: these reductions were reversed by SOD. 6. The findings do not support the hypothesis that the presence of Cu/Zn SOD explains the greater susceptibility of NO than the nitrergic transmitter to the superoxide generator pyrogallol, but suggest that it may play a role in the effects of duroquinone.

Neurogenic vasodilation mediated by nitric oxide in porcine cerebral arteries

Mechanisms of neurogenic vasodilatation and its modification by superoxide, acetylcholine, and vasoactive intestinal peptide (VIP) in porcine cerebral arteries were investigated. Relaxant responses to transmural electrical stimulation and nicotine of cerebral artery strips without endothelium were abolished by tetrodotoxin and hexamethonium, respectively. N(G)-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, abolished or markedly reduced the neurogenic response but did not affect the relaxation by exogenous NO. The inhibitory effect was reversed by L-arginine. Duroquinone, a superoxide-generating agent, did not alter the relaxations induced by electrical stimulation and nicotine. However, in the strips treated with diethyldithiocarbamate, an inhibitor of copper/zinc superoxide dismutase (SOD), the responses were significantly inhibited by duroquinone. The inhibition was partially reversed by SOD. Physostigmine inhibited, but atropine potentiated, the neurogenic response. The relaxation was attenuated by acetylcholine but not by VIP. There were nerve fibers and bundles containing NADPH diaphorase in the adventitia of cerebral arteries. It appears that porcine cerebral arteries are innervated by NO synthase-containing nerves that liberate NO on excitation as a neurotransmitter to produce muscular relaxation, and the nerve function is protected by endogenous SOD from degradation of NO by superoxide anions. The neurogenic relaxation is inhibited by acetylcholine released from cholinergic nerves, possibly because of an impaired production or release of NO.

Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways

In a guinea pig model of allergic asthma, we have recently established that a deficiency of nitric oxide (NO) contributes to the increased ex vivo responsiveness of isolated perfused tracheae to methacholine after the early asthmatic reaction at 6 h after inhalational challenge of the animals with ovalbumin aerosol. Because this deficiency could be caused by a reaction of NO with enhanced levels of inflammation-induced superoxide anion (O-2), we examined the effect of endogenous O-2 on the regulation of methacholine-induced constriction by NO of intact perfused tracheal tube preparations from unchallenged (control) guinea pigs and from animals 6 h after ovalbumin challenge. In the presence of the NO synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 100 microM), tracheae obtained from unchallenged guinea pigs showed a 1.7-fold increase in the maximal response to intraluminally applied methacholine (p < 0.05). By contrast, the maximal airway response to methacholine was significantly decreased in the presence of the O-2 scavenger superoxide dismutase (SOD; 100 U/ml), by approximately 45% (p < 0.01). The SOD-induced decrease in responsiveness to methacholine was reversed by L-NAME. Tracheal preparations obtained at 6 h after allergen challenge showed a 1. 8-fold increased responsiveness to intraluminally applied methacholine compared with controls (p < 0.001), which was not further enhanced in the presence of L-NAME. SOD had neither an effect on the increased responsiveness nor did it restore the potentiating effect of L-NAME. These results indicate that (1) in normoreactive tracheal preparations, the regulatory role of NO is partially counteracted by endogenous O-2, and ( 2) the deficiency of NO in hyperreactive tracheae obtained at 6 h after ovalbumin challenge is not caused by its reaction with O-2, but rather to decreased cNOS activity. De Boer J, Pouw FMH, Zaagsma J, Meurs H. Effects of endogenous superoxide anion and nitric oxide on cholinergic constriction of normal and hyperreactive guinea pig airways.

A possible role of S-nitrosothiols at the nitrergic relaxations in the mouse corpus cavernosum

Relaxations induced by electrical field stimulation and acetylcholine were compared with those induced by acidified sodium nitrite, sodium nitroprusside, S-nitrosoglutathione and S-nitroso-N-acetyl-D,L-penicillamine in the mouse corpus cavernosum precontracted with phenylephrine. NG-nitro-L-arginine inhibited electrical field stimulation- or acetylcholine-induced relaxation, but was ineffective on relaxations caused by the other stimuli. Hydroquinone and pyrogallol had no inhibitory action on the relaxations caused by any stimulus except acidified sodium nitrite. Incubation of the tissue with diethyldithiocarbamic acid significantly inhibited the relaxations induced by all stimuli except papaverine. In the tissues pre-treated with diethyldithiocarbamic acid, superoxide dismutase, hydroquinone and pyrogallol failed to yield restore or further inhibit the relaxations in response to electrical field stimulation or acetylcholine. LY 83583 (6-anilino-5,8-quinolinedione) and hydroxocobalamin clearly inhibited the relaxant responses to electrical field stimulation, acetylcholine, S-nitrosoglutathione and acidified sodium nitrite whereas there was significant enhancement of the relaxation produced by S-nitroso-N-acetyl-D,L-penicillamine. These findings suggest that the relaxant factor released from non-adrenergic non-cholinergic nerves or endothelial cells in mouse cavernosal tissue may be a superoxide anion-resistant nitric oxide-containing molecule and that S-nitrosoglutathione rather than S-nitroso-N-acetyl-D,L-penicillamine could be a suitable candidate for this.

Non-adrenergic non-cholinergic relaxation of the rat stomach

1. Receptive and adaptive relaxations of the proximal third of the stomach are reflex responses that enable the stomach to accommodate large volumes with minimal increases in intraluminal pressure. The smooth muscle relaxations are termed non-adrenergic non-cholinergic (NANC). 2. Nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) are considered to be the principal neurotransmitters of NANC relaxation of the rat stomach. NO appears to be mainly responsible for the speed of the relaxation and VIP appears to be responsible for the duration. 3. Studies indicate that inhibitory neurons may also release other neurotransmitters, such as adenosine triphosphate (ATP) and peptide histidine isoleucine (PHI). 4. NANC relaxation of the rat stomach is a complex phenomenon that appears to involve many neurotransmitters, each with a specific role.

Recovery by ascorbate of impaired nitric oxide-dependent relaxation resulting from oxidant stress in rat aorta

1. In this study we investigated the ability of ascorbate to protect nitric oxide from destruction by superoxide anion. 2. Ascorbate produced concentration-dependent relaxation of rings of rat aorta, comprising two components: the first, seen at 1-300 microM, reached a maximum of 45.3+/-2.8%, and was abolished by endothelial removal or treatment with L-NAME (100 microM), demonstrating involvement of nitric oxide. The second occurred at concentrations of 1 mM and above and was associated with falls in the pH of the bathing fluid. 3. Pretreatment with ascorbate at concentrations up to 3 mM had no effect on the relaxation to acetylcholine (10 nM-10 microM) on endothelium-containing rings or adenosine (0.1 microM-3 mM) on endothelium-denuded rings. 4. An oxidant stress was applied to aortic rings, comprising inhibition of endogenous Cu/Zn superoxide dismutase by diethyldithiocarbamate (0.1 mM) followed by generation of superoxide anion by hypoxanthine (0.1 mM/xanthine oxidase (16 u ml(-1)). This reduced maximal acetylcholine-induced relaxation from 96.7+/-1.3% to 42.4+/-3.5% (P<0.001). Treatment with ascorbate (30 microM-3 mM) reversed this blockade in a concentration-dependent manner. 5. Our findings show that ascorbate has the ability to protect nitric oxide from destruction by superoxide anion. This action is seen with ascorbate at levels normally present in plasma, suggesting that this antioxidant may exert a tonic protective effect on nitric oxide within the vasculature.

Comparison between endothelial and neuronal nitric oxide pathways in rat aorta and gastric fundus

This study examines the ability of different nitric oxide synthase (NOS) inhibitors and NO donors to inhibit the endothelium-dependent relaxation of the rat aorta and the NANC relaxation of the rat gastric fundus. NG-Nitro-L-arginine, N-monomethyl-L-arginine, and S-methyl-L-thiocitrulline elicite comparable potency in the aorta and in the fundus. However, 1-(2-trifluoromethyl)imidazole (TRIM), unlike 7-nitroindazole, is more potent on the fundus than on the aorta, showing that TRIM elicits a selective functional inhibition of the neural NOS isoform. (1H)-(1,2,4)Oxadiazole(4,3-a)quinoxalin-1-one, a selective inhibitor of soluble guanylyl cyclase, inhibits the dilator response in both tissues and the cyclic GMP mimetic, 8-Br-cGMP, is 16 times more potent for inducing relaxation in the gastric fundus than in the aorta. However, methylene blue and LY-83583, two other inhibitors of soluble guanylyl cyclase and superoxide anion-generating agents, are at least 100 times less potent on fundus strips than on aortic rings. The data suggest that once released into the extracellular space, NO is more susceptible to inactivation by superoxide anions in the vascular tissue than in the gastric fundus. Thus, the study shows that selective inhibition of NO in a target tissue may be reached not only at the NOS isoform level but also by the manipulation of the NO pathway.

Effect of xanthine oxidase inhibition on endothelium-dependent and nitrergic relaxations

The effects of inhibition of xanthine oxidase on responses mediated by nitric oxide (NO) were examined using the selective xanthine oxidase inhibitors allopurinol and 4-amino-6-hydroxypyrazolo[3,4-d]pyrimidine (AHPP). In rat aortic rings precontracted with phenylephrine (1 microM), allopurinol (300 microM) and AHPP (100, 300 microM) significantly reduced tone, an effect not seen after inhibition of NO synthase with Nomega-nitro-L-arginine (NOLA 100 microM). Relaxations produced by acetylcholine (0.01-10 microM) were significantly enhanced by AHPP (100, 300 microM) but not by allopurinol. Nitrergic relaxations in the rat anococcygeus muscle (field stimulation 1 ms pulses; 1 Hz: 10 s) were not affected by either allopurinol or AHPP. However, relaxations produced by exogenous NO (0.25 microM) were significantly enhanced by AHPP, allopurinol (100 microM) and superoxide dismutase (100 U/ml). Xanthine (500 microM) partially, but significantly, reversed the enhancement produced by AHPP. These findings suggest that superoxide generated by xanthine oxidase modulates the activity of basal and stimulated NO derived from the rat aortic endothelium, but does not affect the activity of the nitrergic transmitter in the rat anococcygeus muscle, despite its ability to modulate responses to exogenous NO.

Physiological features of visceral smooth muscle cells, with special reference to receptors and ion channels

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

No evidence for a significant non-nitrergic, hyperpolarising factor contribution to field stimulation-induced relaxation of the mouse anococcygeus

1. The aim of the study was to determine whether a nerve-derived hyperpolarizing factor (NDHF) might contribute to non-adrenergic, non-cholinergic (NANC) relaxations of the mouse anococcygeus when low concentrations of contractile agent are used to raise tone and low frequencies of field stimulation applied; such a non-nitrergic NDHF has been proposed to contribute to NANC relaxations of the rat anococcygeus and guinea-pig taenia coli. 2. Phenylephrine (0.1-100 microM) produced concentration-related contractions of the mouse isolated anococcygeus muscle; 0.2 microM phenylephrine (EC26) was used to raise tone in subsequent experiments. 3. Field stimulation (0.5, 1.0 and 5.0 Hz) produced frequency-dependent relaxations of phenylephrine-induced tone. In the presence of the nitric oxide synthase inhibitor L-NG-nitro-arginine (L-NOARG; 100 microM), the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-1-one (ODQ; 5 microM), or a combination of these two drugs, relaxations to field stimulation were abolished at all frequencies studied. Relaxations to sodium nitroprusside (0.01-5 microM) were unaffected by L-NOARG but strongly inhibited by ODQ; neither enzyme inhibitor affected relaxations to 8-Br-cyclic GMP (10 microM). 4. Nifedipine (1 microM) reduced the contractile response to 0.2 microM phenylephrine by 38%; however, it had no effect on NANC relaxations. 5. It is concluded that NANC relaxations of the mouse anococcygeus are purely nitrergic and that there is no significant contribution from a putative NDHF.

In vitro and in vivo effects of nitric oxide synthase inhibitors and nitric oxide inactivators on the South American opossum ileocolonic junction

The potential role of nitrergic nerves in the regulation of the South American (SA) opossum ileocolonic junction (ICJ) function was investigated. In vitro, the effects of nitric oxide (NO) synthase inhibitors and NO inactivators on the non-adrenergic non-cholinergic (NANC) nerve-mediated relaxations of the circular muscle of the SA opossum ICJ were determined by employing isolated strips. Electrical field stimulation (0.2-8.0 Hz) caused frequency-dependent NANC relaxations. Nicotine and ATP also induced concentration dependent NANC relaxations that were abolished by tetrodotoxin (TTX). The relaxation response induced by NANC nerve activation was reduced in a dose dependent manner by NO synthase inhibitors while vasoactive intestinal peptide (VIP) and sodium nitroprusside (SNP) induced relaxations were uninfluenced by these drugs. In vivo, the NO synthase inhibitor, L-NAME, administered into the local artery caused a raise in intraluminal pressure of the ICJ in anaesthetized SA opossums in a L-arginine-preventable manner. Hydroquinone and pyrogallol, while being able to reduce, in a superoxide dimutase (SOD) reversible manner, the relaxations induced by exogenous NO failed to affect the NANC nerve-induced relaxations. Finally, neurones and nerve fibres in the myenteric plexus as well as varicose nerve fibres on the circular smooth layer were positive for NADPH-diaphorase activity. These findings indicate that nitrergic nerves inhibit ICJ circular smooth muscle in vitro and in vivo but cast doubts on the neuromediator being the NO radical.

Inhibition of nitrergic neurotransmission in the bovine retractor penis muscle by an oxidant stress: effects of superoxide dismutase mimetics

1. A number of superoxide dismutase (SOD) mimetics were examined both biochemically for their ability to inhibit the superoxide-catalyzed reduction of cytochrome c and nitro blue tetrazolium, and functionally for their ability to mimic authentic Cu/Zn SOD in restoring nitrergic neurotransmission in bovine retractor penis (BRP) muscle following its inhibition by oxidant stress. 2. The SOD mimetics investigated were CuSO4, MnCl2, CuDIPS (copper [II] [diisopropylsalicylate]2), MnTBAP (manganese [III] tetrakis 4-benzoic acid porphyrin), MnTMPyP (manganese [III] tetrakis 1-methyl-4-pyridyl porphyrin pentachloride), tiron (4,5-dihydroxy-1,3-benzene disulphonic acid), PTIYO (4-phenyl,2,2,5,5,-tetramethyl-3-imidazolin-1-yloxy-3-oxide) and tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl). 3. The rank order of potency in inhibiting the reduction of cytochrome c was: CuSO4 > or = MnCl2 > or = CuDIPS > or = MnTMPyP > MnTBAP > tempol > or = tiron > PTIYO. 4. The requirement for EDTA (0.1 mM) prevented assessment of the activity of CuSO4, MnCl2 and CuDIPS in the assay involving inhibition of reduction of nitro blue tetrazolium. However, the rank order of potency for those agents which could be examined (MnTMPyP > MnTBAP > tiron > or = tempol > PTIYO) was essentially similar to that seen in the cytochrome c assay. 5. Inhibition of endogenous Cu/Zn SOD with diethyldithiocarbamate (DETCA, 3 mM, 120 min) in BRP muscle strips, followed by addition of the superoxide anion generator, LY 83583 (1 microM), resulted in almost complete abolition of nitrergic relaxation (4 Hz, 10 s). 6. Authentic Cu/Zn SOD (1-300 u ml(-1)), CuSO4 (0.1-300 microM), MnCl2 (0.1-100 microM) and MnTMPyP (10-300 microM) each restored nitrergic transmission by around 50%. However, CuDIPS (0.1-30 microM), MnTBAP (0.1-100 microM), tempol (10 microM - 3 mM), PTIYO (1-300 microM) and tiron (10 microM - 10 mM) all failed to restore nitrergic transmission. 7. The ability of MnTMPyP to restore nitrergic neurotransmission may therefore provide a lead in the development of SOD mimetics as therapeutic agents in the treatment of neuropathies associated with oxidant stress.

S-nitrosothiols and the nitrergic neurotransmitter in the rat gastric fundus: effect of antioxidants and metal chelation

1. The effects of the antioxidants ascorbic acid and alpha-tocopherol and of the metal chelator ethylenediaminetetraacetic acid (EDTA) were studied on relaxations in response to S-nitrosothiols, authentic nitric oxide (NO) and nitrergic non-adrenergic non-cholinergic stimulation of the rat gastric fundus. 2. The S-nitrosothiols S-nitrosocysteine (1-100 nM), S-nitrosoglutathione (0.01-3 microM) and S-nitroso-N-acetylpenicillamine (0.01-3 microM) induced concentration-dependent relaxations of the rat gastric fundus muscle strips, which were precontracted with prostaglandin F2alpha. The relaxations to all S-nitrosothiols were concentration-dependently enhanced by the antioxidants ascorbic acid (0.1-3 microM) and alpha-tocopherol (3-30 microM) and inhibited by the metal chelator EDTA (26 microM). 3. Ascorbic acid and alpha-tocopherol alone did not induce a relaxation of the precontracted rat gastric fundus muscle strip. However, when ascorbic acid (1 microM) or alpha-tocopherol (1 microM) were injected in the organ bath 1 minute after S-nitrosoglutathione (0.1 microM) or after S-nitroso-N-acetylpenicillamine (0.1 microM), they induced an immediate, sharp and transient relaxation. This relaxation was inhibited by the superoxide generator pyrogallol (2 microM). Such a relaxation to ascorbic acid or alpha-tocopherol was not observed in the presence of S-nitrosocysteine (10 nM). 4. Electrical field stimulation (0.5-4 Hz) of the precontracted rat gastric fundus strips induced frequency-dependent nitrergic relaxations which were mimicked by authentic NO (3-300 nM) and by acidified sodium nitrite NaNO2 (0.3-10 microM). Ascorbic acid (0.33-3 microM), alpha-tocopherol (3-30 microM) or EDTA (26 microM) did not affect the relaxations to nitrergic stimulation, NO or NaNO2. 5. In summary, relaxations to S-nitrosothiols in the rat gastric fundus are enhanced by the antioxidants ascorbic acid and alpha-tocopherol and inhibited by the metal chelator EDTA. However, relaxations to nitrergic stimulation of the rat gastric fundus or those to authentic NO were not affected by the antioxidants or by the metal chelator. These results indicate that antioxidants and metal chelators have a different effect on the biological activity of S-nitrosothiols and on that of the nitrergic neurotransmitter. Therefore, our results suggest that S-nitrosothiols do not act as intermediate compounds in nitrergic neurotransmission in the rat gastric fundus.