L-NG-nitro-arginine and its methyl ester are potent inhibitors of non-adrenergic, non-cholinergic transmission in the rat anococcygeus

Effect of biliary cirrhosis on neurogenic relaxation of rat gastric fundus and anococcygeus muscle: role of nitric oxide pathway

BACKGROUND

Cirrhosis, associated with a host of hemodynamic abnormalities, could affect the gastrointestinal (GI) tract motility. On the other hand, the nonadrenergic noncholinergic (NANC) neurotransmission has been shown to play a pivotal role in GI tract motility and has been linked with release of nitric oxide (NO) on electrical stimulation. In this study, we investigated the effect of biliary cirrhosis on the neurogenic relaxation of rat gastric fundus and anococcygeus muscle and also the possible role of nitric oxide system in this manner.

METHODS

Isolated gastric fundus and anococcygeus strips of sham-operated and biliary cirrhotic (4 weeks after bile duct ligation) rats were mounted under tension in a standard organ bath. Electrical stimulation was applied to obtain NANC-mediated relaxations in precontracted gastric fundus and anococcygeus muscle. The neurogenic relaxations were examined in the presence of different doses of NO synthase inhibitor, N (w)-Nitro-L-Arginine Methyl Ester (L-NAME). The concentration-dependent relaxant responses to the NO donor sodium nitroprusside were also evaluated.

RESULTS

The neurogenic relaxation of both gastric fundus and anococcygeus muscle was significantly (P < 0.001) increased in cirrhotic animals. L-NAME (0.03-1,000 µM) inhibited relaxations in both groups in a dose-dependent manner (P < 0.001), but cirrhotic groups were more resistant to the inhibitory effects of L-NAME (P < 0.01). Sodium nitroprusside-mediated relaxations were similar in two groups.

CONCLUSIONS

This study for the first time demonstrated that cirrhosis increases the NO-mediated neurogenic relaxation of both rat gastric fundus and anococcygeus muscle, suggesting a crucial role for the neurogenic NO in the pathophysiology of disturbed GI motility in cirrhosis.

Apelin elevates blood pressure in ICR mice with L‑NAME‑induced endothelial dysfunction

Apelin is the endogenous ligand of APJ, which belongs to the family of G protein-coupled receptors. Apelin and APJ are highly expressed in various cardiovascular tissues, including the heart, kidney and vascular endothelial and smooth muscle cells. Although apelin exerts hypotensive effects via activation of endothelial nitric oxide synthase (eNOS), the ability of apelin to regulate blood pressure under pathological conditions is poorly understood. In the current study, N^G-nitro-L-arginine methyl ester (L-NAME), a potent NOS inhibitor, was administered chronically, to induce peripheral vascular damage in mice. L-NAME-treated mice exhibited hypertension, increased vascular cell adhesion molecule-1 and plasminogen activator inhibitor-1 mRNA levels in the aorta and impaired vasodilatation associated with decreased aortic eNOS expression, consistent with endothelial damage. Three days following withdrawal of L-NAME treatment, the blood pressure response to apelin stimulation was assessed. Although apelin reduced blood pressure in non-treated mice, it was found to transiently elevate blood pressure in L-NAME-treated mice. These results indicate that apelin functions as a vasopressor peptide under pathological conditions, including vascular endothelial dysfunction in mice.

Characterization of agonist-induced endothelium-dependent vasodilatory responses in the vascular bed of the equine digit

The role of endothelium-derived relaxing factors was studied in the regulation of vascular responses in the Krebs perfused equine isolated digit. Perfusion pressure was recorded in response to bolus doses of 5-hydroxytryptamine (6 nmol) alone or co-administered with carbachol (CCh; 0.2 micromol), bradykinin (BK; 0.2 nmol), substance P (SP; 0.2 nmol) or sodium nitroprusside (SNP; 0.2 micromol). N(omega)-Nitro-L-Arginine methyl ester hydrochloride (L-NAME; 300 microm) caused partial but significant inhibition of CCh-induced vasodilatory response, whereas BK and SP-induced responses were resistant to L-NAME. High potassium (K(+), 30 mm) and the cytochrome P-450 (CYP) epoxygenase inhibitor, clotrimazole (10 microm) plus L-NAME (100 microm), completely abolished the CCh, BK and SP-induced vasodilatory responses, whereas the response to SNP was unaffected. In contrast, the L-NAME-resistant proportion of CCh, BK and SP-induced vasodilatory response was not inhibited by the highly selective CYP2C9 inhibitor, sulphaphenazole (10 microm). The cyclo-oxygenase inhibitor, ibuprofen (10 microm) did not affect the CCh, BK and SP-induced responses. These data demonstrate that CCh, BK and SP-induced relaxation in the equine digit involve a combination of the NO and endothelium-derived hyperpolarizing factor (EDHF) pathways. These results do not support the evidence for the involvement of CYP-derived epoxyeicosatrienoic acids and the exact nature of EDHF in the equine digit remains to be established.

Biphasic neurogenic vasodilatation in the bovine intraocular long posterior ciliary artery: involvement of nitric oxide and an additional unidentified neurotransmitter

We have investigated the neurogenic factors inducing relaxation in the intraocular segment of the bovine long posterior ciliary artery. In precontracted vessels, electrical field stimulation (EFS, 0.5-128 Hz, 10 s trains) in the presence of guanethidine (30 microM) evoked biphasic relaxation: optimal relaxation for the first and second components occurred at 10 and 50 s, respectively. The first component, but not the second, was abolished by L-NAME (100 microM) or ODQ (3 microM). Relaxation to exogenous CGRP (0.1-300 nM) was inhibited by the CGRP antagonist, CGRP(8-37) (1-5 microM), but neither component of neurogenic relaxation was affected. Preincubation with the sensory nerve excitotoxin, capsaicin (1 microM), had no effect on either the first or second components of neurogenic relaxation. Substance P (0.1 nM-0.1 microM) induced relaxation, but rapid and complete desensitisation occurred within minutes. Neither desensitisation to substance P (0.1 microM) nor incubation with the NK(1) antagonist, L-733,060 (0.3 microM), had any effect on the first or second components of neurogenic relaxation.VIP (0.1 nM-0.3 microM) induced relaxation and this was followed by substantial desensitisation. Neither desensitisation to VIP (0.6 microM) nor treatment with the protease, alpha-chymotrypsin (10 U ml(-1)), had any effect on the first or second components of neurogenic relaxation. The results indicate that nitric oxide mediates the first component of neurogenic relaxation in the bovine intraocular ciliary artery. The neurotransmitter mediating the second component remains to be determined but is unlikely to be CGRP, substance P or VIP.

Inhibition of L-arginine transport by reactive oxygen species in rat anococcygeus muscle

The effect of L-arginine on nitrergic transmission and its alteration with reactive oxygen species (ROS) were investigated. L-arginine potentiated the relaxation response induced by electrical field stimulation in rat anococygeus muscle. This effect was inhibited by L-lysine, a cationic amino acid using y+ L and y+ transport systems in a similar way with L-arginine. The neutral amino acid L-leucine, which uses only y+ L system as a transport mechanism, inhibited this potentiation at only low frequency stimulation. Electrolysis of the physiological solution did not change the responses to electrical field stimulation, but inhibited the potentiation elicited by L-arginine that was prevented in the presence of mannitol and N-acetyl-L-cysteine. In conclusion, L-arginine is transported via y+ system predominantly to potentiate the relaxation response to nitrergic nerve stimulation in rat anococcygeus muscle. ROS, primarily hydroxyl radicals inhibited L-arginine-induced potentiation probably by interacting with the y+ amino acid transport system.

Purines and pyrimidines are not involved in NANC relaxant responses in the rabbit vaginal wall

1. Non-adrenergic non-cholinergic (NANC) relaxant responses were elicited by electrical field stimulation (EFS) in rabbit vaginal wall strips after treatment with guanethidine and scopolamine and raising smooth muscle tone with phenylephrine. Under these conditions treatment with NOS inhibitors revealed a non-nitrergic NANC relaxant response. The possible role of purines and pyrimidines in these non-nitrergic NANC responses was investigated. 2. Exogenous application of ATP, ADP, adenosine, UTP, or UDP (all at 0.03-10 mM) induced concentration-dependent relaxant responses. 3. Responses to exogenous application of ATP were reduced by the general P2 antagonist cibacron blue (500 micro M), but not by suramin (100 micro M) and were unaffected by L-NAME (500 micro M), omega-conotoxin GVIA (omega-CTX, 500 nM) or tetrodotoxin (TTX, 1 micro M). 4. Responses to exogenous application of adenosine were reduced by the A(2A) antagonist ZM-241385 (30 micro M). 5. ATP- and ADP-induced responses were unaffected by the G-protein inhibitor pertussis toxin (100 ng ml(-1)), whilst ADP- but not ATP-induced responses were reduced by GDPbetaS (100 micro M), which stabilizes G-proteins in their inactive state. 6. EFS-induced non-nitrergic NANC relaxant responses were unaffected by suramin, cibacron blue, ZM-241385, pertussis toxin or GDPbetaS, but were completely inhibited by TTX. 7. Exogenous application of ATP (10 mM) and adenosine (10 mM) increased intracellular cyclic adenosine-3', 5'-monophosphate (cAMP). However, non-nitrergic NANC responses were not associated with increased cAMP. Neither non-nitrergic NANC responses nor responses to ATP or adenosine were associated with increased intracellular cyclic guanosine-3', 5'-monophosphate (cGMP) concentrations. 8. These results suggest that adenosine A(2A) receptors and P2 receptors are present in the rabbit vaginal wall, but that they are not involved in non-nitrergic NANC relaxant responses.

The nonadrenergic noncholinergic relaxation of anococcygeus muscles of bile duct-ligated rats

Previous studies have shown the naloxone-induced withdrawal syndrome and the development of tolerance in the tissues of cholestatic animals. Increased neuronal nitric oxide synthase (nNOS) expression is reported to exist in morphine-tolerant animals. This, together with evidence for nitric oxide (NO) overproduction in cholestasis, suggested the possibility of an alteration of nonadrenergic noncholinergic (NANC) relaxation of anococcygeus muscles of cholestatic rats. To study this, we used three main groups of animals: unoperated, sham-operated and bile duct-ligated. Electrical field stimulation, in the presence of atropine and guanethidine, caused NANC relaxation in the anococcygeus muscle which was enhanced in bile duct-ligated animals. N(G)-nitro-L-arginine methyl ester (L-NAME), a NOS blocker, caused a dose-dependent inhibition of the NANC relaxation. The IC(50)'s of L-NAME in 7-day (7.30+/-0.87 microM), 14-day (6.98+/-0.70 microM) and 21-day (8.25+/-1.40 microM) bile duct-ligated groups were significantly different from those of unoperated (1.69+/-0.30 microM) and sham-operated groups (1.90+/-0.27 microM). L-NAME (100 microM) completely inhibited the NANC relaxation response, suggesting that NANC relaxation in the rat anococcygeus muscle is mediated mainly via NO. The contraction response of the intact muscle to phenylephrine, an alpha(1)-adrenoceptor agonist, and the relaxation response of the phenylephrine-contracted muscle to sodium nitroprusside, an NO donor, were not different in unoperated, sham-operated and 7-day bile duct-ligated groups. These results showed that the smooth muscle component of NANC relaxation is not altered in anococcygeus muscles of bile duct-ligated rats. It can thus be concluded that the NANC relaxation in the anococcygeus of cholestatic rats is more resistant to a NOS blocker, providing evidence for increased nitrergic neurotransmission in the anococcygeus muscles of cholestatic rats.

Nitric oxide does not inhibit cerebral cytochrome oxidase in vivo or in the reactive hyperemic phase after brief anoxia in the adult rat

In this study, near-infrared spectroscopy was applied to examine whether cytochrome oxidase in the rat brain is inhibited by nitric oxide in vivo. During normoxia, intravenous N(G)-nitro-L-arginine methyl ester (L-NAME) administration significantly decreased the cerebral saturation of hemoglobin with oxygen but did not alter the cytochrome oxidase redox state. Anoxia significantly reduced the cytochrome oxidase. The time course of the recovery of the redox state during reoxygenation was not altered by L-NAME. The results suggest that in adult rats, cytochrome oxidase is not inhibited by nitric oxide, either in physiologic conditions or during reoxygenation after a brief anoxic period.

Characterization of the non-nitrergic NANC relaxation responses in the rabbit vaginal wall

Electrical field stimulation (EFS)-induced non-adrenergic non-cholinergic (NANC) relaxation responses in the rabbit vaginal wall were investigated. These NANC responses were partially inhibited with the nitric oxide synthase (NOS) inhibitors N(G)-nitro-L-arginine methyl ester (L-NAME; 500 microM), N(G)-nitro-L-arginine (300 microM) or N-iminoethyl-L-ornithine (500 microM) or the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 10 microM). Application of L-NAME and ODQ concomitantly did not increase the degree of inhibition. L-NAME or ODQ were observed to be more effective at low frequencies. The resistant part of the responses was more pronounced at higher frequencies and was completely inhibited by tetrodotoxin (1 microM). Exogenous application of the peptides vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptide (PACAP-27 and PACAP-38), peptide histidine methionine (PHM), peptide histidine valine (PHV), helospectin-I or -II induced a relaxation response. Calcitonin gene-related peptide or substance P did not cause any relaxation. The peptidase alpha-chymotrypsin (type II; 2 units ml(-1)) did not affect non-nitrergic NANC responses, although it did inhibit relaxation responses elicited by exogenous VIP, PACAP-27, PACAP-38, PHM, PHV, helospectin-I or -II. K(+) channel inhibitors apamin (1 microM) or charybdotoxin (100 nM) when used alone or in conjunction did not affect non-nitrergic NANC responses. The non-nitrergic NANC responses were not associated with any increase in intracellular cyclic adenosine-3', 5'-monophosphate (cyclic AMP) or cyclic guanosine-3', 5'-monophosphate (cyclic GMP) concentrations. The peptide-induced relaxations were all associated with increases in cyclic AMP concentrations. These results suggest that a neuronal factor elicits non-nitrergic NANC responses in the rabbit vaginal wall. The identity of this factor remains to be established.

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.

Apamin- and nitric oxide-sensitive biphasic non-adrenergic non-cholinergic inhibitory junction potentials in the rat anococcygeus muscle

1. Changes in membrane potential following electrical field stimulation (EFS; 1, 2 and 5 pulses at 5 Hz, 0.5 ms duration, 60-80 V) of non-adrenergic non-cholinergic (NANC) inhibitory nerves in the rat isolated anococcygeus muscle were measured using standard intracellular recording techniques. Resting membrane potential ranged between -60 and -70 mV. 2. In the presence of guanethidine (30 microM), atropine (1 microM), propranolol (1 microM) and phentolamine (0.05 microM) to establish NANC conditions, the membrane potential depolarized to between -40 and -50 mV. Under these conditions, EFS caused pulse-dependent, tetrodotoxin (1 microM)-sensitive biphasic inhibitory junction potentials (IJPs) comprising a fast onset and time-to-peak phase followed by a second, slower phase that delayed repolarization. The duration of NANC IJPs ranged between 10 and 20 s. 3. Inhibition of small-conductance Ca2+-activated K+ channels with apamin (0.1 microM) selectively blocked the first fast phase of the NANC IJP, whereas inhibitors of large-conductance Ca2+-activated K+ channels (charybdotoxin and iberiotoxin) and ATP-sensitive K+ channels (glibenclamide) all had no effect on NANC IJPs. 4. Both the nitric oxide synthase inhibitor N G-nitro-L-arginine (L-NOARG; 100 microM) and the inhibitor of soluble guanylate cyclase 1-H-oxodiazol-[1,2,4]-[4,3-a] quinoxaline-1-one (ODQ; 10 microM) had no effect on the first fast phase of the NANC IJP. Each treatment, however, markedly inhibited the slow phase with the duration of the IJP reduced to between 1 and 3 s. The L-NOARG-resistant fast phase of the NANC IJP was almost abolished by the subsequent addition of apamin (0.1 microM). 5. In conclusion, the present study demonstrates unequivocal NANC nerve-mediated biphasic IJPs in the rat isolated anococcygeus. We propose that nitric oxide (NO), via activation of cGMP-dependent K+ channels, and a non-NO inhibitory factor which activates apamin-sensitive K+ channels contribute to NANC nerve-evoked IJPs in the rat anococcygeus.

Antagonist of nitric oxide synthesis inhibits nerve-mediated relaxation of isolated strips of rumen and reticulum

The present study investigated the possibility that nitric oxide is a nonadrenergic, noncholinergic neurotransmitter of nerves that are intrinsic to the forestomach. Tunica muscularis, myenteric plexus preparations of bovine reticulum and rumen were maintained in vitro in a physiological solution of buffer that contained scopolamine. Trains of electric field stimulation transiently reduced (relaxed) the tone induced by BaCl2. NG-Nitro-L-arginine methyl ester, a nitric oxide synthase competitive antagonist, inhibited relaxation of the rumen and reticulum preparations that had been induced by the electrical field. The actions of NG-nitro-L-arginine methyl ester were partially reversed by L-arginine. These data suggest that nitric oxide, or a related substance, is an inhibitory neurotransmitter of nerves that are intrinsic to tunica muscularis, myenteric plexus preparations of the bovine forestomach.

The effect of Ba2+ on the nitrergic mechanism in the isolated frog lung preparation

1. The present study was undertaken to investigate effects of Ba2+ on the isolated frog lung strips depolarized by 20 mM K+ in Ca2+ free Ringer solution. 2. Ba2+ produced monophasic relaxant response, whereas Ca2+ induced biphasic response consisting of a transient relaxation and a marked contraction. Both kinds of relaxation were inhibited completely by L-NOARG. L-arginine reversed the action of L-NOARG. 3. Ferrous sulfate, pyrogallol, hydroquinone, and vanadate reduced the Ba(2+)-induced relaxation in a concentration-dependent manner. 4. These findings suggest that Ba(+)-induced relaxation may fully be mediated by the nitrergic mechanism and the effect of Ba2+ on the nitric oxide synthase may be more selective than Ca2+.

Evidence that NO acts as a redundant NANC inhibitory neurotransmitter in the guinea-pig isolated taenia coli

1. The relative contribution of the putative transmitters, nitric oxide (NO) and an apamin-sensitive factor, possibly ATP, to inhibitory responses evoked by electrical field stimulation (EFS; 0.2-5 Hz, 0.2 ms duration, supra-maximal voltage for 10 s) of non-adrenergic, non-cholinergic (NANC) nerves was investigated in the guinea-pig isolated taenia coli contracted with histamine (1 microM). 2. Peak relaxations to EFS (0.2-5 Hz) were tetrodotoxin (1 microM)-sensitive, maximal at 0.2 Hz and completely resistant to the nitric oxide synthase inhibitor, NG-nitro-L-arginine (L-NOARG; 100 microM) in either the presence or absence of atropine (1 microM). Furthermore, the specific inhibitor of soluble guanylyl cyclase, 1H-[1,2,4] oxadiazolo [4,3-a] quinoxaline-1-one (ODQ; 10 microM), the cytochrome P450 inhibitor and free radical generator, 7-ethoxyresorufin (7-ER; 10 microM) and the NO scavenger, oxyhaemoglobin (HbO; 30 microM) had no effect on EFS-induced relaxations alone and in combination with L-NOARG (100 microM). 3. Maximum relaxation to the NO donor, sodium nitroprusside (SNP; 1 microM) was significantly reduced by HbO (30 microM), abolished by 7-ER (10 microM) and ODQ (10 microM) but was unaffected by apamin (0.1 microM), an inhibitor of small conductance Ca(2+)-activated K+ channels. 4. The relaxation to EFS at 0.2 Hz was resistant to apamin but those to 0.5 and 5 Hz were significantly reduced. EFS (0.2-5 Hz)-evoked relaxations that persisted in the presence of apamin were further significantly inhibited by L-NOARG (100 microM) or ODQ (10 microM), but not by HbO (30 microM) or 7-ER (10 microM). 5. ATP (1-30 microM) produced concentration-dependent relaxations that were abolished by apamin (0.1 microM), unaffected by ODQ (10 microM) but only significantly reduced by L-NOARG (100 microM) at the lowest concentration of ATP (1 microM) used. 6. Nifedipine (0.3 microM), abolished contractions to 67 mM KCl, histamine (10 microM), endothelin-1 (0.03 microM), 5-hydroxytryptamine (5-HT; 10 microM) and the thromboxane-mimetic, 9-11-dideoxy-9 alpha, 11 alpha-methano-epoxy-prostaglandin F2 alpha (U46619; 0.1 microM). 7. The findings of the present study suggest that NO is released during NANC nerve stimulation, but plays no role in NANC relaxations in the guinea-pig taenia coli unless the effects of another apamin-sensitive, nerve-derived hyperpolarizing factor (NDHF) are blocked. Thus, we propose that in this tissue, NO acts as a 'backup' or redundant NANC nerve inhibitory transmitter and like NDHF mediates relaxation via hyperpolarization.

Evidence that both nitric oxide (NO) and a non-NO hyperpolarizing factor elicit NANC nerve-mediated relaxation in the rat isolated anocococcygeus

1. Responses to electrical field stimulation (EFS; 0.5-10 Hz, 0.2 ms duration, supramaximal voltage for 20 s) of non-adrenergic, non-cholinergic, (NANC) nerves were obtained in preparations of rat anococcygeus pre-contracted with titrated concentrations of phenylephrine (0.1-1 microM) to approximately 40% of their maximum contraction to phenylephrine (Fmax) regardless of drug treatment. 2. With this set level of active force, NANC nerve stimulation resulted in relaxations that were maximal (peak relaxation) at 0.5-1 Hz, abolished by tetrodotoxin (1 microM) but only minimally blocked by the nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine, (L-NOARG; 100 microM). Furthermore, the nitric oxide (NO) scavenger, oxyhaemoglobin (HbO; 30 microM) gave no further block alone or in combination with L-NOARG (100 microM). By comparison, in preparations contracted with phenylephrine to approximately 70% Fmax, relaxations to NANC nerve stimulation were markedly reduced or abolished by combined treatment with L-NOARG (100 microM) and HbO (30 microM). 3. Nifedipine (0.3 microM) significantly inhibited NANC nerve-mediated relaxations, which became frequency-dependent and abolished those resistant to L-NOARG (100 microM) and HbO (30 microM). 4. These data suggest that a non-NO, hyperpolarizing factor and NO both contribute to NANC nerve-mediated inhibitory responses in the rat anococcygeus. However, responses to the non-NO factor were observed only in preparations contracted sub-maximally by a nifedipine-sensitive mechanism.

Increase in hepatic tissue blood flow by teprenone

The major objective of the present study was to evaluate mechanisms by which teprenone, a gastric mucosal protecting agent, increases hepatic mucosal blood flow using male Sprague-Dawley rats. Hepatic and gastric blood flow was measured using a laser blood flow meter after administration of teprenone, dissolved in Tween 80, into the inferior vena cava. Teprenone itself increased hepatic and gastric blood flow. It also increased hepatic and gastric blood flow in rats with acute hepatic disorders due to carbon tetrachloride (CCL4) and improved histological changes, such as inflammatory cell infiltration and fatty changes in the liver. The fact that blood endothelin (ET) concentrations increased after administration of teprenone suggest that teprenone has great affinity for ET beta receptors and shows ET beta-receptor antagonist-like effects. Hepatic blood flow decreased after administration of N-nitro-L-arginine methyl ester, a nitric oxide (NO) synthetase inhibitor, suggesting that teprenone increase NO activity. Teprenone was thought to increase hepatic and gastric blood flow by different mechanisms, because it increased gastric mucosal prostaglandin E2 concentrations.

Nitric oxide-dependent and -independent modulation of sympathetic vasoconstriction in the human saphenous vein

The possible modulation by the endothelium of the contractile responses to sympathetic nerve stimulation was examined in isolated superfused human saphenous vein. Contractile response curves for transmural nerve stimulation and noradrenaline were higher in endothelium-denuded than in intact human saphenous vein rings. In vessels with endothelium, transmural nerve stimulation- and noradrenaline-induced contractions were unaffected by the cyclooxygenase inhibitor, indomethacin (10 microM), but were potentiated by the nitric oxide (NO) synthase inhibitor, L-N omega-nitro-L-arginine (L-NNA, 3 microM) even when combined with D-arginine (0.3 mM), but not with L-arginine (0.3 mM). As in the case of noradrenaline, contractile responses to 5-HT, but not to KCI, were enhanced by endothelium removal, L-NNA or L-NNA plus D-arginine, but were unaffected by L-NNA plus L-arginine. The guanylyl cyclase inhibitor, methylene blue (10 microM), potentiated both transmural nerve stimulation- and noradrenaline-induced contractions in endothelium intact rings, whereas it enhanced, although to a lesser degree, only the neurally evoked contractions in endothelium-denuded human saphenous vein. In the vessels without endothelium L-NNA failed to affect the vasoconstriction induced by both transmural nerve stimulation and noradrenaline. Our results suggest that at least two inhibitory factors are involved in modulating the sympathetic vasoconstriction in the human saphenous vein: (1) at a postjunctional level, NO, the release of which from endothelial cells is probably stimulated by the activation of specific receptors, and (2) at a prejunctional level, an unidentified vasodilator agent, which is unmasked by the removal of the endothelium layer and which is probably co-released along with noradrenaline, and which acts through the guanylyl cyclase pathway.

Cholinergic-nitrergic interactions in the guinea-pig gastric fundus

The influence of nitric oxide (NO) on the spontaneous tone and on the contractile responses to electrical field stimulation or to exogenous acetylcholine (ACh) was studied. Circular strips from the guinea-pig gastric fundus were used. The NO-releasing compound sodium nitroprusside reduced the spontaneous tone while the NO-synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) increased it. The L-NAME-induced increase of the tone was antagonized by atropine or indomethacin, suggesting the involvement of cholinergic and prostaglandinergic pathways in this effect. L-NAME significantly potentiated the ACh (10(-8) to 10(-5) M)-induced contractions. L-NAME concentration-dependently potentiated the cholinergic contractions evoked by electrical field stimulation without affecting [3H]ACh overflow from [3H]choline-treated tissues. It is concluded that electrical field stimulation of gastric fundus muscle induces the release of endogenous nitrate which, in turn, functionally antagonizes cholinergic neurotransmission.

Interaction between neurotransmitters and exogenous norepinephrine in isolated rat anococcygeus muscle

Continuous electrical field stimulation (EFS) elicited a sustained contraction and significantly increased the EC50 value of norepinephrine (NE), shifting the concentration-response curve for NE to the right. Tetrodotoxin significantly reduced the continuous EFS-evoked increases in basal tone and produced further dextral shift in the concentration-response curve for NE. N-methylhydroxylamine and NG-monomethyl-L-arginine (L-NMMA) attenuated the "dual" effects of continuous EFS on NE-induced contractions. L-Arginine partially reversed the inhibitory effect of L-NMMA. The results of the present study suggest that continuous EFS causes simultaneous release of both excitatory and inhibitory neurotransmitters, and the interaction (or functional antagonism) between the inhibitory neurotransmitter (endogenous nitric oxide, NO) and the excitatory neurotransmitter (endogenous NE), as well as exogenous NE, may occur at postjunctional site(s).

Nitric oxide control of lower genitourinary tract functions: a review

It is apparent that evolving concepts of the regulatory basis for functions in the pelvis must take into account the role exerted by nitric oxide. A recently characterized messenger molecule, nitric oxide has been associated with numerous physiologic processes. Intense investigations of this molecule have extended its importance to several genitourinary functions. Penile erection, micturition, peristalsis of the male excurrent duct system, contractile properties of the prostate, and lumbosacral spinal cord neurotransmission are all functions that may transpire under some degree of control by nitric oxide. Impotence, urinary obstruction, or ejaculatory problems, in turn, may represent alterations of nitric oxide production or action. The strategic manipulation of nitric oxide or its mechanism of action, possibly by pharmacologic means, may restore or produce desired functional effects. These possibilities, therefore, suggest that the advancing knowledge of nitric oxide in the genitourinary tract may be of enormous clinical value in the future.

Comparison of effects of chronic and acute administration of NG-nitro-L-arginine methyl ester to the rat on inhibition of nitric oxide-mediated responses

1. Vascular responses to acetylcholine and sodium nitroprusside in vivo and in vitro, in the isolated perfused kidney and in rings of rat thoracic aorta, were measured in rats treated chronically with NG-nitro-L-arginine methyl ester (L-NAME; approx, 70 mg kg-1) and compared to responses in age-matched control animals, and age-matched animals after the acute administration of L-NAME (3-100 mumol kg-1). Parallel experiments examined alterations in responsiveness in rings of trachea and anococcygeus muscles taken from the same animals. 2. Chronic oral administration of L-NAME elevated the blood pressure in anaesthetized animals from 114 +/- 5 mmHg to 153 +/- 11 mmHg (n = 5). The hypotensive responses to both acetylcholine (1 nmol kg-1) and sodium nitroprusside (10 nmol kg-1) were enhanced by chronic L-NAME treatment (n = 5-7) whereas acute L-NAME administration enhanced only the response to sodium nitroprusside (n = 5). 3. After chronic treatment with L-NAME, the basal perfusion pressure in the isolated perfused kidney was elevated. However, vasodilator responses to either acetylcholine (1 nmol) or sodium nitroprusside (3 nmol) were unaltered (n = 5-7). The vasodilatation induced by acetylcholine was inhibited in a concentration-dependent manner by the administration of acute L-NAME (0.1 - 100 microM; n = 5), such that significant inhibition was seen at 10 microM L-NAME. The response to sodium nitroprusside was unaffected by L-NAME. 4. The relaxations of isolated rings of rat thoracic aorta induced by acetylcholine were inhibited in tissues prepared from rats treated chronically with L-NAME (n = 5-7). Acute administration of L-NAME (0.1-100 microM) concentration-dependently inhibited the relaxations induced by acetylcholine in this preparation, with significant inhibition occurring at 1 microM L-NAME (n = 5). Responses to sodium nitroprusside were unaffected by either chronic or acute exposure to L-NAME (n = 5-7).5. Relaxations of precontracted anococcygeus muscles induced by electrical field stimulation, or contractions of rings of trachea induced by carbachol or endothelin-1, were unaffected by chronic oral administration of L-NAME (n = 4-6). Acute addition of L-NAME (0.1-100 microM) to the organ baths inhibited in a concentration-dependent manner the relaxations of anococcygeus muscles taken from control animals, with a significant effect being seen at a concentration of 10 micro.M (n = 4-6).6. Our cardiovascular data are consistent with chronic oral administration of L-NAME inhibiting the production of nitric oxide (NO) within the vasculature, although the pattern of inhibition is not uniform between different tissues. Despite the inhibition of endothelial NO production, chronic L-NAME does not alter the vasodepressor activity of acetylcholine in vivo or in the isolated perfused kidney. This maybe explained by an enhanced responsiveness of guanylyl cyclase pathways, the increased release of vasodilators other than nitric oxide or a decreased importance of nitric oxide in resistance vessels compared with conductance vessels. The resistance of peripheral neuronal NO responses to chronic treatment with L-NAME indicates that selective inhibition of different isoforms of NOS may be achieved in vivo.

Nitric oxide formation is involved in vagal inhibition of the stomach of the trout (Salmo gairdneri)

Stimulation of the vagus nerves to isolated stomach preparations from trout (Salmo gairdneri) caused both excitation and inhibition of smooth muscle activity. Excitatory responses were partly reduced by atropine, suggesting that cholinergic neurons are involved. The atropine-resistant excitation could not readily be ascribed to a 'rebound' from preceding inhibition, to the production of prostaglandins, or to the activation of either adrenergic or capsaicin-sensitive fibres. Inhibitory responses were reduced by the nicotinic antagonist d-tubocurarine and more profoundly reduced by an inhibitor of nitric oxide synthase, NG-nitro-L-arginine. The latter effect was reversed by excess L-arginine. The nitric oxide donors sodium nitroprusside and nitroglycerine caused inhibition of the muscle. It is concluded that the vagal inhibitory postganglionic neurons are nitergic in this tissue.

Involvement of endogenous nitric oxide in non-adrenergic, non-cholinergic contraction elicited by [Met5]-enkephalin in rat isolated duodenum

To investigate the possible neuromodulatory role of nitric oxide (NO) in the gastrointestinal tract, an examination was made of the effects of NG-nitro-L-arginine (L-NOARG), an inhibitor of NO synthase, on the intestinal response to [Met5]-enkephalin (ENK) by recording the mechanical activity of the isolated duodenum from rats. [Met5]-enkephalin elicited a biphasic response of the duodenum, i.e. transient relaxation followed by contraction. The relaxation induced by ENK was blocked by naloxone, an opioid receptor antagonist, but not by tetrodotoxin (TTX). The contractile response of the duodenum to ENK was blocked by TTX but not by naloxone. The contractile response was not affected by hyoscine, a muscarinic antagonist, or guanethidine, an adrenergic neuron blocking agent, indicating mediation by non-adrenergic, non-cholinergic (NANC) nerves. The contractile but not the relaxant response to ENK was blocked by L- but not D-NOARG. The contractile response was also inhibited by methylene blue, an inhibitor of both NO synthase and guanylate cyclase, and by indomethacin, a cyclooxygenase inhibitor. Thus, endogenous NO and prostaglandins are involved in the contractile response to ENK. Endogenous NO may modulate the release of excitatory NANC transmitters via a prejunctional mechanism.

Photon pharmacology of an iron-sulphur cluster nitrosyl compound acting on smooth muscle

1. The mechanisms of action on smooth muscle of the iron-sulphur cluster nitrosyl compound, heptanitrosyl-tri-mu 3-thioxotetraferrate (1-), (RBS), a photosensitive nitric oxide donor, have been investigated in the guinea-pig taenia caeci (coli) in vitro. 2. After exposure to RBS (50 microM) for 30 min, and subsequent washout, a sustained contraction was recorded in the absence of light to either the agonist carbachol (50 microM) or a depolarizing concentration of KCl (23.5 mM). Photon irradiation (> 400 nm) caused a prompt relaxation of precontracted RBS-treated muscle, the magnitude of which depended upon the intensity (1.1 x 10(3) to 1.1 x 10(5) lux), duration (30 s to 20 min) and wavelength (400 to 800 nm), of the incident illumination. 3. Repeated periods of illumination at 1.1 x 10(4) lux produced a reversible relaxation of both carbachol and KCl-evoked tone in muscle pretreated with RBS (50 microM). These photorelaxations were reproducible at 10 min intervals for several hours with a maximal relaxation amounting to 80 to 90% that of the tone produced by carbachol (50 microM). 4. The nitric oxide synthase inhibitor, NG-nitro-L-arginine (60 microM), caused no inhibition of the photon-induced relaxation of RBS-treated muscle. In contrast, N-methylhydroxylamine (2 mM), L-cysteine (10 mM), DL-dithiothreitol (2 mM), methylene blue (30 microM), and haemoglobin (20 microM), all reversibly but significantly inhibited (P < 0.001) the photorelaxation response. However, neither the aminothiol N-acetyl-L-cysteine (10 mM) nor the tripeptide glutathione (10 mM) blocked the RBS-induced photorelaxation. 5 The photolytic cleavage of RBS depended on the intensity and duration of illumination; it was accompanied by a corresponding decrease in absorbance and by the liberation of NO as measured by the Griess diazo reaction with sulphanilic acid. L-Cysteine (10 mM) prevented the decrease in absorbance and the photolytic liberation of NO.6 It is concluded that (i) sequestered or bound RBS, when photon-activated, liberates NO by a process which can be controlled by the wavelength, intensity and duration of the incident light, (ii) the photon-released NO rapidly relaxes the smooth muscle cells of the taenia coli primarily via cyclic GMP-dependent pathways which can be blocked by use of appropriate inhibitors, and (iii) the RBS-induced photorelaxation effect does not involve the activation of NO synthase. RBS is therefore a valuable photosensitive NO donor for establishing the functional and pharmacological significance of NO.

Nitrergic stimulation does not inhibit carbachol-induced inositol phosphate generation in the rat anococcygeus

Carbachol (50 microM) produced a rapid, transient increase in inositol-1,4,5-trisphosphate (IP3) levels in the rat anococcygeus; the peak increase observed at 10 s (3-fold above controls) was greatly reduced in the presence of atropine (100 nM), but was unaffected by nitrergic stimulation (10 Hz), sodium nitroprusside (10 microM) or 8-Br-cyclic GMP (200 microM). Following loading of muscles with [3H]myo-inositol, subsequent exposure to carbachol for 30 min resulted in a 6-fold increase in the accumulation of [3H]inositol-1-monophosphate; again, this action of carbachol was greatly attenuated by atropine, but unaffected by nitrergic stimulation, sodium nitroprusside or 8-Br-cyclic GMP. It is concluded that inhibition of agonist-induced generation of inositol phosphates cannot explain the ability of nitrergic activation to relax (by 54-62%) carbachol-induced tone in this tissue.

Effects of omega-conotoxin GVIA on electrical field stimulation- and agonist-induced changes in cytosolic Ca2+ and tension in isolated rat anococcygeus muscle

1. It has been reported that omega-conotoxin GVIA (omega-CgTx) blocks L- and N-type voltage-sensitive Ca2+ channels (VSCCs) in neurones and inhibits neurotransmitter release in various tissues. The present study investigates the effects of omega-CgTx on electrical field stimulation (EFS)- and agonist-induced changes in free cytosolic Ca2+ ([Ca2+]cyt) levels and tension in isolated fura-2 loaded rat anococcygeus muscle. 2. EFS produced frequency-dependent increases in [Ca+]cyt levels and contractions. Phentolamine (1 microM) and omega-CgTx (0.1 microM) significantly inhibited EFS-induced responses and shifted the frequency-response curves to the right. 3. alpha-adrenoceptor agonists (noradrenaline and clonidine) and carbachol (in the presence of phentolamine) produced concentration-dependent increases in [Ca2+]cyt levels and contractions. Though omega-CgTx (0.1 microM) significantly inhibited the increases in [Ca2+]cyt levels induced by low doses of noradrenaline, the overall concentration-response curves of [Ca2+]cyt and contractions for noradrenaline, clonidine, and carbachol were not affected by omega-CgTx. 4. When the tone of rat anococcygeus muscle was raised with either clonidine (0.1 microM) or carbachol (30 microM, in the presence of 3 microM phentolamine), EFS (2 Hz) produced reproducible decreases in [Ca2+]cyt levels and relaxations. These responses were significantly inhibited by omega-CgTx when the tissue was precontracted with clonidine, but not when it was precontracted with carbachol. 5. The results of the present study suggest that in rat anococcygeus muscle, omega-CgTx inhibits the EFS-induced release of both excitatory and inhibitory neurotransmitters, probably by blocking Ca2+ channels on nerve terminals. Furthermore, the Ca2+ channels present on the smooth muscle cell membrane, which are involved in the agonist-induced Ca2+ influx and contractions, may not be sensitive to omega-CgTx.

The role of enteric inhibitory motoneurons in peristalsis in the isolated guinea-pig small intestine

1. Peristalsis is a co-ordinated motor behaviour in which an anally propagated contraction of the circular muscle propels intraluminal contents. The role of excitatory motoneurons in peristalsis is well established; however the role of enteric inhibitory motoneurons is unknown. 2. A combination of a nitric oxide synthase inhibitor and apamin, which blocks relaxation of the circular muscle of guinea-pig small intestine mediated by enteric inhibitory motoneurons, was used to investigate the role of inhibitory motoneurons in peristalsis in isolated segments of guinea-pig small intestine. 3. N omega-nitro-L-arginine methyl ester (L-NAME, 400 microM) and N omega-nitro-L-arginine (L-NOArg, 100 microM) significantly reduced the threshold volume required to trigger emptying of the intestine. This effect was reversed by L-arginine (4 mM) and L-arginine alone increased the threshold volume for initiation of peristalsis. Sodium nitroprusside (0.1-10 microM), which generates nitric oxide, also increased the threshold volume. L-NAME, L-NOArg, L-arginine and sodium nitroprusside did not alter the maximal intraluminal pressure generated during emptying. Contraction of the longitudinal muscle during the initial phase of fluid infusion was significantly increased by L-NAME and L-NOArg and reduced by sodium nitroprusside (1 nM to 10 microM). 4. Apamin (0.5 microM) did not significantly alter the threshold volume necessary to initiate peristalsis or contraction of the longitudinal muscle. However, the maximal pressure generated when the intestine was emptying was significantly increased. Furthermore, short segments of circular muscle contracted apparently randomly, before peristaltic emptying was triggered. 5. A combination of L-NAME and apamin completely disrupted peristalsis. Contractions of the circular muscle did not always start at the oral end. Stationary contractions as well as contractions propagating orally and anally were observed. 6. It is concluded that enteric inhibitory motoneurons are crucial for peristalsis to occur. They are important in setting the threshold at which peristaltic emptying is triggered, via nitric oxide. They are essential for the propagation of the circular muscle contraction, via an apamin-sensitive mechanism of transmission. Contraction of the longitudinal muscle during peristalsis is partly inhibited by a nitric oxide-mediated mechanism.

Noradrenergic-nitrergic interactions in the rat anococcygeus muscle: evidence for postjunctional modulation by nitric oxide

1. The distribution of NADPH-diaphorase positive and catecholamine-containing nerve structures, and functional noradrenergic-nitrergic interactions, were studied in the rat anococcygeus muscle. 2. The morphological findings demonstrated NADPH-diaphorase positive neurons mostly as aggregates in intramural ganglia, nerve tracts and few single nerve fibres forming plexus-like structures. 3. The nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NOARG) inhibited concentration-dependently the nitrergic relaxation, an effect reversed by L-arginine. The drug had dual effects on noradrenergic contractile responses: at lower concentrations (0.1-10 microM) it decreased the amplitude of contractions and this was not affected by L-arginine; higher concentrations (50-500 microM) potentiated the contractions, an effect that was prevented by L-arginine. 4. The electron acceptor, nitro blue tetrazolium (NBT) produced a rapid inhibition of the noradrenergic contractile responses (EC50 0.178 +/- 0.041 microM). The drug decreased the tone of the preparations. However, it potentiated concentration-dependently the nitrergic relaxations. 5. NBT (1 microM) had no significant effect on the relaxations induced by exogenously applied nitric oxide (NO)-donor sodium nitroprusside (SNP, 0.01-50 microM). However, the effect of NBT (0.1-10 microM) on the electrically induced relaxation was significantly decreased by L-NOARG (10 and 50 microM). The inhibition was of a non-competitive type. 6. Neither L-NOARG (100 microM) nor NBT (1 microM) had any effect on the spontaneous or electrically-induced release of 3H-radioactivity from the tissues preincubated in [3H]-noradrenaline. 7. It is concluded that L-arginine-NO pathway can modulate noradrenergic transmission in the rat anococcygeus muscle at postjunctional, but not prejunctional site(s).

Ethanol inhibits nonadrenergic, noncholinergic neurotransmission in the anococcygeus muscle of the rat

The anococcygeus muscle of the rat is innervated by both excitatory adrenergic and inhibitory nonadrenergic, noncholinergic (NANC) neurons. The transmitter released from NANC neurons appears to be nitric oxide or a related molecule. In vitro, acute administration of ethanol inhibited, in a dose-dependent manner, NANC-induced relaxation of anococcygeus muscle obtained from ethanol-naive animals. Two days of in vivo ethanol administration resulted in an increase in the maximal relaxation induced by stimulation of NANC neurons and in a significant shift to the right of the acute ethanol dose-response curve for inhibition of NANC relaxation. The sensitivity of the anococcygeus muscle to relaxation induced by the nitric oxide donors, acidified sodium nitrite or sodium nitroprusside, was not altered significantly by acute in vitro or chronic ethanol treatment 2 days in vivo. These data suggest that acutely administered in vitro ethanol inhibits the production of nitric oxide induced by stimulation of NANC neurons. Data further suggest that 2 days of ethanol administration in vivo produce an enhanced responsiveness of the NANC neurons to transmural stimulation and that this enhanced responsiveness accounts for the tolerance to the inhibition induced by the acutely administered ethanol in vitro.

Non-adrenergic, non-cholinergic relaxation of the bovine retractor penis muscle: role of S-nitrosothiols

1. This study examined the possibility that an S-nitrosothiol, rather than nitric oxide, functions as the non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the bovine retractor penis (BRP) muscle. 2. Treatment of BRP muscle with either of two sulphydryl inactivating agents, diamide (1 mM) and N-ethylmaleimide (0.3 mM), inhibited NANC relaxation and this was prevented by pretreating tissues with L-cysteine (3 mM), L-glutathione (3 mM) or dithiothreitol (3 mM). Inhibition was not specific, however, since the inactivating agents also inhibited the relaxant actions of authentic nitric oxide (0.3 microM), glyceryl trinitrate (0.001-1 microM) and isoprenaline (0.01-1 microM). 3. Reacting nitric oxide with L-cysteine in nominally oxygen-free solution at pH 3, followed by purging to remove free nitric oxide and neutralisation, produced greater and more prolonged relaxant activity when assayed on rabbit aortic rings than could be attributed to nitric oxide alone. H.p.l.c. analysis of the mixture identified a new peak distinct from either L-cysteine or nitric oxide which was responsible for the relaxant activity. The spectral absorption of this new compound had two bands with peaks at 218 and 335 nm. 4. Using a series of structural analogues of L-cysteine (all at 15 mM) it was found that removal of the carboxyl group (L-cysteamine), replacement of the carboxyl with an ester function (L-cysteine methyl ester) or substitution at the amino group (N-acetyl-L-cysteine) had no effect on the ability to generate relaxant activity upon reaction with nitric oxide (0.1 mM). In contrast, substitution at the sulphydryl group (S-methyl-L-cysteine, L-cysteinesulfinic acid and L-cysteic acid), or formation of disulphides(L-cystine and L-cystamine) led to a complete loss of ability to generate relaxant activity. L-Glutathione was also able to react with nitric oxide to produce relaxant activity, and this too was blocked upon substitution of the free sulphydryl group (S-methyl-L-glutathione). A free sulphydryl group was therefore required to generate relaxant activity following reaction with nitric oxide.5. Reacting L-cysteine (10 mM) with nitric oxide (~ 3 mM) under more stringent oxygen-free conditions followed by purging to remove free nitric oxide resulted in the generation of low relaxant activity and small absorption peaks at 218 and 335 nm and these were unaffected upon exposure to the air. In contrast, admitting air to the reaction chamber before purging enhanced both relaxant activity and the absorption peaks at 218 and 335 nm by some 40 fold and the solution turned pink due to the appearance of another absorption peak at 543 nm. This enhanced relaxant activity was not due to nitrogen dioxide being the reactive species, since at 0.1 mM this gas failed to react with L-cysteine to generate relaxant activity, and at 1 mM generated less activity than the equivalent concentration of nitricoxide.6. The relaxant activity generated by reacting nitric oxide with L-cysteine or L-glutathione was abolished following treatment with haemoglobin (3 MicroM), methylene blue (10 MicroM) or Nmethylhydroxylamine(100 MicroM), but was unaffected by N0-nitro-L-arginine (30 MicroM). Furthermore, two agents that generate superoxide anion, pyrogallol (0.1 mM) and hydroquinone (0.1 mM), also inhibited this relaxant activity as well as that induced by authentic nitric oxide (0.3 MicroM) but as previously reported, had no effect on relaxation induced by NANC nerve stimulation. Superoxide dismutase(100 u ml1) reversed the actions of pyrogallol and hydroquinone but had no effect on NANC relaxation.7. In conclusion, the reaction of nitric oxide with L-cysteine or L-glutathione generates relaxant activity which exceeds that of nitric oxide alone and probably results from formation of S-nitrosocysteine and S-nitrosoglutathione, respectively. The effects of pyrogallol and hydroquinone suggest that the NANCneurotransmitter is a superoxide anion-resistant, nitric oxide-releasing molecule and that neither S-nitrocysteine nor S-nitrosoglutathione is a suitable candidate for this.

NG-nitro-L-arginine methyl ester inhibits the effect of an H3-histaminergic receptor agonist on NANC contraction in guinea-pig perfused bronchioles

A role for nitric oxide in the H3-histaminergic agonist-induced inhibition of the non-adrenergic, non-cholinergic (NANC) contraction has been studied in guinea-pig perfused bronchioles. (R)-alpha-Methylhistamine ((R)-alpha-MeHA), an agonist for H3 receptors, inhibited the NANC contraction induced by electrical field stimulation. NG-Nitro-L-arginine methyl ester (L-NAME) (50 microM), an inhibitor of nitric oxide synthesis, blocked the effect of (R)-alpha-MeHA. The effect of L-NAME was reversed by L-arginine (50 microM). L-NAME, L-arginine or (R)-alpha-MeHA were without effect on exogenous substance P- or neurokinin A-induced contractile responses of the perfused bronchioles. These results show that an H3-agonist inhibited the release of neurotransmitters in NANC nerve endings of guinea-pig perfused bronchioles presumably by production of nitric oxide.

Analysis of bradykinin-induced relaxations in the rat isolated anococcygeus muscle

The present study investigates the mechanism(s) of action of relaxations induced by bradykinin and by electrical field stimulation (EFS) in isolated rat anococcygeus muscle, where contractile tone has been elevated with clonidine. Bradykinin, EFS, and the bradykinin B1 receptor agonist, des-Arg9-bradykinin, produced quantitatively and qualitatively similar relaxations. Bradykinin B1 receptor antagonist, [des-Arg9,Leu8]-bradykinin (1 microM), attenuated the relaxation responses of bradykinin B1 receptor agonist and inhibited bradykinin and EFS-induced relaxation responses. Bradykinin B2 receptor antagonist, [beta-(2-thienyl)-Ala5,8,D-Phe7]-bradykinin (1 microM), significantly inhibited the relaxation responses of bradykinin, EFS, and bradykinin B1 receptor agonist. Methylene blue (30 microM) and N-methylhydroxylamine (1 mM) significantly inhibited the bradykinin- and EFS-induced relaxation responses. The relaxation responses of bradykinin and EFS were not affected by captopril (5 microM), superoxide dismutase (100 U/ml), and catalase (100 U/ml). Nitric oxide synthase inhibitor, L-NG-nitro-arginine (L-NOARG, 30 microM), significantly inhibited the EFS- and bradykinin-induced relaxation responses. L-arginine (100 microM) reversed the inhibitory effect of L-NOARG on the relaxation responses of EFS and bradykinin. In addition, L-arginine potentiated the relaxation responses of EFS and bradykinin. The data of the present study suggests that bradykinin, similar to EFS, generates an endogenous nitrate, probably nitric oxide, which subsequently activates guanylate cyclase and relaxes the rat anococcygeus muscle.

Differential effects of nifedipine on nerve-mediated and noradrenaline-evoked contractions of rat anococcygeus muscle

In rat anococcygeus muscle the inhibitory effect of nifedipine (0.01, 0.1, 1.0 and 10 microM) was determined on adrenergic twitches in response to electrical field stimulation (trains of 4 pulses, 0.1 ms pulse duration, 10 Hz) and on twitch-matching contractions evoked by noradrenaline. Nifedipine concentration-dependently reduced the neurogenic twitch with an IC50 of 0.083 microM. Nifedipine reduced the noradrenaline-evoked contraction to a markedly lesser degree (IC50 > 10 microM). The difference in the magnitude of inhibition of electrically evoked twitch and twitch-matching noradrenaline-evoked contraction was statistically significant at every concentration of nifedipine. It is concluded that inhibition of the twitch by nifedipine involves some other mechanism(s) in addition to its Ca2+ channel blocking property in smooth muscle.

Selective inhibition of basal but not agonist-stimulated activity of nitric oxide in rat aorta by NG-monomethyl-L-arginine

1. Two inhibitors of nitric oxide synthase, NG-monomethyl-L-arginine (L-NMMA, 1-100 microM) and NG-nitro-L-arginine (L-NOARG, 3-300 microM), each produced a concentration-dependent augmentation of phenylephrine-induced tone in endothelium-containing but not endothelium-denuded rings of rat aorta. Pretreatment with L-arginine (10 mM) prevented the augmentation of tone induced by L-NOARG and L-NMMA. 2. Following induction of sub-maximal tone with phenylephrine in endothelium-containing rings, acetylcholine (1 nM-3 microM) induced relaxations which were inhibited in a concentration-dependent manner by L-NOARG (10-100 microM). 3. In contrast to the action of L-NOARG, L-NMMA (100-1000 microM) had no effect on acetylcholine-induced relaxations. L-NMMA (100-300 microM) also had no effect on the endothelium-dependent relaxant actions of ATP (0.1-100 microM), whereas L-NOARG (100 microM) produced powerful blockade. 4. Unexpectedly, pretreatment with L-NMMA (30-300 microM), as with the endogenous substrate L-arginine (10 microM-10 mM), inhibited in a concentration-dependent manner the ability of L-NOARG (30 microM) to block acetylcholine-induced relaxation. 5. The ability of L-NOARG to augment phenylephrine-induced tone and inhibit relaxation by acetylcholine and ATP in endothelium-containing rings is consistent with blockade of basal and agonist-stimulated production of nitric oxide, respectively. 6. The ability of L-NMMA to augment phenylephrine-induced tone without affecting relaxation to acetylcholine or ATP in endothelium-containing rings suggests a selective ability to block basal but not agonist-stimulated production of nitric oxide in rat aorta.

Localisation of nitric oxide synthase within non-adrenergic, non-cholinergic nerves in the mouse anococcygeus

Immunocytochemical staining of whole mount preparations of the mouse anococcygeus muscle, using antibodies to rat brain nitric oxide synthase (NOS), revealed a dense network of NOS-immunoreactive nerve fibres running through the tissue. These fibres were resistant to the sympathetic neurotoxin 6-hydroxydopamine and are therefore likely to be the non-adrenergic nerves which mediate relaxation of this smooth muscle. Further, NOS-immunoreactive fibres were absent following denervation by cold-storage (4 degrees C; 72 h), which has been shown to abolish non-adrenergic, non-cholinergic (NANC) relaxations. The results provide strong support for the hypothesis that the L-arginine:NO pathway is responsible for the generation of the NANC transmitter in the anococcygeus.

The effect of nitric oxide on the efficacy of synaptic transmission through the chick ciliary ganglion

1. The effect of nitric oxide on the efficacy of synaptic transmission in the chick ciliary ganglion of post-hatched birds has been determined by use of the size of the postganglionic compound action potential resulting from chemical transmission through the ganglion as a measure of synaptic efficacy. 2. Sodium nitroprusside (100 microM) increased the synaptic efficacy by an average 26%. This is likely to be due to its ability to release nitric oxide, as potassium ferricyanide (100 microM) did not cause a potentiation. Sodium azide (100 microM), shown in sympathetic ganglia to stimulate production of cyclic GMP, did not modulate synaptic efficacy significantly. 3. 8-Br-cyclic-GMP (100 microM) increased synaptic efficacy by an average 61%. The addition of 8-Br-cyclic-AMP (100 microM) had less effect, increasing transmission by on average 46%. 4. The nitric oxide synthase blocker, NG-nitro-L-arginine methyl ester (L-NAME, 100 microM) was added prior to the tetanic stimulation of the preganglionic nerves at 30 Hz for 20 s, a procedure known to produce both post-tetanic potentiation and long-term potentiation of synaptic transmission through the ganglion. L-NAME reduced the long-term potentiation by an average of 47% but did not significantly change the post-tetanic potentiation. 5. Following the brief application of 8-Br-cyclic AMP, 8-Br-cyclic GMP and sodium nitroprusside there was an enhancement of the efficacy of synaptic transmission that persisted after the withdrawal of the drugs. The maximum increase in synaptic efficacy following the brief addition of 8-Br-cyclic GMP was 116%, sodium nitroprusside was 110% and 8-Br-cyclic AMP was 126%.6. These results suggest that nitric oxide modulates synaptic transmission through the ganglion by acting on an endogenous guanylate cyclase that produces cyclic GMP.

NADPH diaphorase innervation of the rat anococcygeus and retractor penis muscles

NADPH diaphorase histochemistry was used to determine whether the rat anoocccygeus (AC) and retractor penis (RP) muscles are innervated by nerves capable of synthesizing nitric oxide. In both tissues, muscle fascicles were enclosed by a varicose plexus of NADPH diaphorase positive (ND+) fibers. Perikarya of neurons on the surface of the AC muscle were also intensely stained for NADPH diaphorase. Many AC-RP ganglion cells in the pelvic plexus, located by the retrograde tracer Fluorogold, also stained for the enzyme. However, a significant population of AC-RP neurons in this location remained unstained. These results provide further evidence that nitric oxide may be an important neurotransmitter in these tissues.

Evidence for nitric oxide as an inhibitory neurotransmitter in rabbit isolated anococcygeus

The role of nitric oxide (NO) and ATP as putative inhibitory non-adrenergic, non-cholinergic (NANC) neurotransmitters was investigated in rabbit isolated anococcygeus after block of adrenergic and cholinergic responses, and raising tone with histamine. NANC nerve stimulation produced rapid relaxations which were completely abolished by tetrodotoxin. The magnitude of the NANC inhibitory responses was significantly reduced by the nitric oxide synthase inhibitors NG-nitro-L-arginine (NO-Arg) and NG-nitro-L-arginine methyl ester (L-NAME). This effect could be partially reversed by L-arginine but not by D-arginine. Oxyhaemoglobin inhibited NANC nerve responses and sodium nitroprusside mimicked the effects of NANC nerve stimulation. NO-Arg also reduced the magnitude of the inhibitory junction potentials recorded from the smooth muscle cells during NANC nerve stimulation. Exogenously applied ATP and adenosine each produced concentration dependent relaxations which were unaffected by the NO-synthase inhibitor NO-Arg. Relaxations to adenosine were virtually abolished by the P1 purinoceptor antagonist 8-(p-sulphophenyl)theophylline. Relaxations to ATP were also significantly reduced, indicating that part of the response to exogenous ATP is due to its breakdown to adenosine and subsequent action on P1 purinoceptors. Relaxations of the tissue to ATP and adenosine were unaffected by the P2 purinoceptor antagonist suramin. NANC nerve mediated responses were not significantly changed by either 8-(p-sulphophenyl)theophylline or suramin. These results suggest that NO is involved in inhibitory NANC neurotransmission in the rabbit isolated anococcygeus, but do not support a role for ATP as a NANC neurotransmitter in this tissue.

Multiple inhibitory mechanisms mediate non-adrenergic non-cholinergic relaxation in the circular muscle of the guinea-pig colon

The mechanisms responsible for nerve-mediated, non-adrenergic, non-cholinergic (NANC) relaxation in mucosa-free circular muscle strips from the proximal colon of the guinea-pig were investigated. Electrical field stimulation (EFS, 1-20 Hz, trains of 5 s duration, 100 V, 0.25 ms pulse width) in the presence of atropine (1 mumol/l) and guanethidine (3 mumol/l) evoked a triphasic motor response consisting of: (a) a primary relaxation, (b) a rebound contraction and (c) a secondary relaxation. These three responses were abolished by tetrodotoxin (1 mumol/l). B oth apamin (0.01-0.3 mumol/l), a known blocker of low conductance, calcium-activated potassium channels in smooth muscles, and L-nitro-arginine (L-NOARG) (1-100 mumol/l), a known blocker of nitric oxide (NO) synthase, increased the tone of the strips. Maximum effects on tone were observed with 0.1 mumol/l apamin (21 +/- 3% of KCl-induced contraction) and 30 mumol/l L-NOARG (26 +/- 4% of KCl response). The combined administration of 0.1 mumol/l apamin and 30 mumol/l L-NOARG produced an increase in tone (47 +/- 5% of KCl response) that was larger than that produced by either compound alone. Neither apamin (0.1 mumol/l) nor L-NOARG (30 mumol/l) affected the isoprenaline-induced relaxation. Apamin (0.1 mumol/l) depressed, but did not abolish, the primary relaxation to EFS at all frequencies without affecting the secondary relaxation.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of L-NG-nitro-arginine on sympathetic nerve induced contraction and noradrenaline release in the rat isolated anococcygeus muscle

1. The possibility of an interaction between the motor sympathetic and inhibitory non-adrenergic, non-cholinergic (NANC) nerves in the rat anococcygeus was investigated using L-NG-nitro-arginine (L-NOARG), an inhibitor of L-arginine: NO synthase. 2. L-NOARG (50 microM) increased contractions induced by field stimulation (20 s trains; 0.5-40 Hz); overall, the frequency-response curve was displaced six-fold to the left. D-NOARG (50 microM) was without effect. 3. The potentiation produced by L-NOARG was reversed by 200 microM L-, but not D-, arginine. 4. L-NOARG had no effect on contractions induced by exogenous noradrenaline (NA) or on field stimulation-induced overflow of tritium from muscles previously loaded with [3H]-NA. 5. It is concluded that the endogenous nitrate NANC transmitter does not influence release of NA from the sympathetic nerves and the potentiation of contractions induced by field stimulation in the presence of L-NOARG most probably results from removal of the opposing relaxing influence of concomitantly released NANC transmitter.

The role of nitric oxide in the regulation of cerebral blood flow

The role of nitric oxide in the cerebral circulation under basal conditions and when exposed to hypoxic, hypercapnic and hypotensive stimuli, was studied in mechanically ventilated rats using a venous outflow technique, by examining the effects of inhibition of nitric oxide synthase with N-nitro-L-arginine methyl ester (L-NAME). L-NAME (10 or 30 mg/kg injected intravenously) raised mean arterial blood pressure by 14% and 24%, and increased cerebrovascular resistance (CVR) by 20% and 24%, respectively. Cerebral blood flow (CBF) was unaltered, as were blood gases and pH. The increases in MABP and CVR were attenuated by L-arginine (300 mg/kg). Following the administration of L-NAME, the increases in CBF elicited by ventilation with 8% oxygen for 25 s were unaltered, in comparison to control responses. L-NAME attenuated the increases in CBF and reduced the time for recovery to basal flow rates evoked by ventilation with 10% carbon dioxide. These effects were reversed by L-, but not by D-, arginine. Autoregulation by CBF during hypotensive episodes, as measured by comparisons of CVR values, was unaffected by L-NAME. The results suggest that endogenous nitric oxide is involved in the responses of the cerebral vasculature to elevated levels of CO2 in the arterial blood. Nitric oxide does not appear to play a major role in autoregulation to increases or decreases in MABP, or in hypoxia-evoked vasodilation.

Involvement of nitric oxide and peptides in the inhibitory non-adrenergic, non-cholinergic (NANC) response in bovine mesenteric artery

The cyclic GMP mediated non-adrenergic non-cholinergic (NANC) relaxation in field stimulated bovine mesenteric artery and its modulation by various factors was studied. Electrical field stimulation of precontracted (Phe 2.5 microM or histamine 5 microM) bovine mesenteric arteries resulted in relaxations varying between 10-70% in different preparations. Tetrodotoxin (3 microM) completely blocked the inhibitory NANC response. Preincubation with high concentrations (100 microM-1 mM) of NG-nitro-L-arginine for 15 min. significantly reduced the relaxation induced by electrical field stimulation. Blockade of cyclooxygenases and prostaglandin synthesis by indomethacin had no effect on the relaxatory response to electrical field stimulation. Neither the alpha 2-adrenoceptor selective antagonist yohimbine (1 microM) nor the alpha 2-adrenoceptor selective agonist UK 14,304 (1 microM) had any significant effect on the electrical field stimulation-induced relaxation. Pertussis toxin (100 ng/ml) was without effect on relaxations elicited by electrical field stimulation. GTP in the concentration range 10 microM-1 mM slightly potentiated the relaxant response. N-carboxymethyl-Phe-Leu (an inhibitor of enkephalinase) or aprotinin (an inhibitor of several proteases) had no significant effect on the electrical field stimulation response. Addition of trypsin (100 U/ml) in combination with chymotrypsin (20 U/ml) significantly reduced the electrical field stimulation-induced relaxation. In the present study we have found indications for the involvement of nitric oxide and possibly also peptides in mediating the inhibitory NANC response (relaxation) in bovine mesenteric arteries.

Mediators of nonadrenergic, noncholinergic inhibition in the proximal, middle and distal regions of rat colon

1. The mediators of non-adrenergic non-cholinergic (NANC) relaxation of the longitudinal muscle of rat proximal, middle and distal colon were examined in vitro. 2. Electrical transmural stimulation (TMS) of proximal, middle and distal segments of rat colon induced NANC relaxations which were inhibited by tetrodotoxin (1 microM), but not by atropine (1 microM) or guanethidine (4 microM). 3. In the proximal colon, L-nitro-arginine (N5-nitroamidino-L-2,5-diaminopentanoic acid) inhibited the TMS-induced NANC relaxation and L-arginine (1 mM) reversed this inhibition. Nitric oxide (0.3-10 microM) induced relaxation of the proximal segment. 4. NANC relaxation of the proximal segments was still evident after desensitization to vasoactive intestinal peptide (VIP). A VIP antagonist (VIP 10-28, 10 microM) had no effect on the TMS-induced NANC relaxation, which was also resistant to alpha-chymotrypsin (2 units ml-1) and a substance P antagonist ([D-Pro2, D-Trp7,9]substance P, 1 microM). 5. In the middle colon, L-nitro-arginine did not inhibit the TMS-induced NANC relaxation in 6 of 9 preparations tested and partially inhibited the relaxation in the other 3 preparations. L-Arginine did not reverse the partial inhibition. 6. Complete desensitization to VIP was not achieved in the middle colon. The VIP antagonist had no effect on the TMS-induced NANC relaxation. After alpha-chymotrypsin treatment of the segment, desensitization of the segments to substance P, or in the presence of the substance P antagonist, the TMS-induced NANC relaxation was augmented. 7. In the distal colon, L-nitro-arginine did not have any significant effect on the TMS-induced relaxation and nitric oxide did not induce relaxation. The VIP antagonist significantly inhibited TMS-induced NANC relaxation. Alpa-Chymotrypsin-treatment of the distal segments resulted in significant inhibition of NANC relaxation. No desensitization to substance P was achieved. Treatment with the substance P antagonist had no effect. 8. These results suggest that nitric oxide is the mediator of the NANC inhibitory response in the proximal region of rat colon; in the middle colon, substance P acts as an excitatory neurotransmitter, antagonizing the NANC relaxation caused by the mediator of the response, which is still uncertain. Our results suggest that that VIP is the most likely candidate as a NANC transmitter in the distal colon.

Distribution of NADPH-diaphorase activity in rat paravertebral, prevertebral and pelvic sympathetic ganglia

Paravertebral (superior cervical and stellate), prevertebral (coeliac-superior mesenteric, inferior mesenteric) and pelvic (hypogastric) sympathetic ganglia of the rat were investigated by enzyme histochemistry to ascertain the distribution of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-diaphorase) activity. In the paravertebral ganglia the majority of the sympathetic neuronal perikarya contained lightly and homogeneously distributed formazan reaction product but there was a range of staining intensities amongst the neuron population. In contrast, in the prevertebral ganglia, intense NADPH-diaphorase staining was present in certain neurons. Firstly, a population of neurons of the coeliac-superior mesenteric ganglion complex were surrounded by densely NADPH-diaphorase-positive 'baskets' of fibres and other stained fibres were seen in interstitial nerve bundles and in nerve trunks connected to the ganglion complex. Secondly, in both the inferior mesenteric ganglion and hypogastric ganglion there were many very intensely NADPH-diaphorase positive neurons. Stained dendritic and axonal processes emerged from these cell bodies. In both ganglia this population of neurons was smaller in size than the lightly stained ganglionic neurons and commonly had only one long (presumably axonal) process. The similarity of these highly NADPH-diaphorase-positive neurons with previously described postganglionic parasympathetic neurons in the hypogastric ganglion is discussed.

Actions and interactions of NG-substituted analogues of L-arginine on NANC neurotransmission in the bovine retractor penis and rat anococcygeus muscles

1. The effects and interactions of a series of NG-substituted analogues of L-arginine known to inhibit nitric oxide synthase were examined on non-adrenergic, non-cholinergic (NANC) neurotransmission in the bovine retractor penis (BRP) and rat anococcygeus muscles. 2. Treatment of BRP muscle strips with either NG-nitro L-arginine (L-NOARG: 0.1-10 microM) or NG-nitro L-arginine methyl ester (L-NAME; 0.1-100 microM) produced a concentration-dependent blockade of NANC relaxation: blockade was complete at the highest concentration of each. 3. Pretreatment with L-arginine (1-10 mM) had no effect on NANC relaxation by itself, but inhibited, in a concentration-dependent manner, the subsequent ability of both L-NOARG (0.1-300 microM) and L-NAME (0.1-1 mM) to produce blockade. L-Arginine (1-10 mM) reversed established submaximal blockade of NANC relaxation induced by L-NOARG (1 microM) or L-NAME (1 microM), but had little effect on maximal blockade induced by these agents. 4. In contrast to L-NOARG and L-NAME, NG-monomethyl L-arginine (L-NMMA; 1 microM-1 mM) had no effect by itself on NANC relaxation of the BRP. L-NMMA (0.1-1 mM) did, however, like L-arginine, inhibit, in a concentration-dependent manner, the subsequent ability of both L-NOARG (0.1-1 mM) and L-NAME (0.1-3 mM) to produce blockade, but was more potent. As with L-arginine, L-NMMA (0.1-1 mM) reversed established submaximal blockade of NANC relaxation induced by L-NOARG (1 microM) or L-NAME (1 microM), but had little effect on maximal blockade induced by these agents. 7. These findings suggest a complex series of interactions between L-arginine and certain of its NG-substituted analogues that are commonly used to inhibit nitric oxide synthase. The most striking new finding is that L-NMMA does not block NANC relaxation in the BRP, but acts with greater potency than the endogenous substrate, L-arginine, to inhibit the blockade induced by L-NOARG or L-NAME.Even on rat anococcygeus where L-NMMA acts as a partial blocker of NANC relaxation, further blockade by L-NOARG is inhibited.