A comparison of the action of the endothelium-derived relaxant factor and the inhibitory factor from the bovine retractor penis on rabbit aortic smooth muscle

A gentle introduction to gasotransmitters with special reference to nitric oxide: biological and chemical implications

Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are gaseous molecules of major impact in biology. Despite their toxicity, these molecules have profound effects on mammalian physiology and major implications in therapeutics. At tiny concentrations in human biology, they play key signaling and regulatory functions and hence are now labeled as “gasotransmitters.” In this literature survey, an introduction to gasotransmitters in relevance with NO, CO and H2S has been primarily focused. A special attention has been given to the conjoint physiological, pathophysiological and therapeutic aspects of NO in this work. In addition to the aforementioned elements of the investigation being reported, this report gives a detailed account of some of the recent advancements covering the NO release from both the nitro as well as nitroso compounds. The importance of the metallic center on the eve of producing the reduction center on NO and to develop photolabile properties have been elaborated within the effect of a few examples of metallic centers. Also, theoretical investigations that have been reported in the recent past and some other current theories pertaining to NO chemistry have been enlightened in this review. From the overall study, it is eminent that a number of facts are yet to be explored in context with NO for deeper mechanistic insights, model design for these molecules, other key roles and the search to find the best fit formalism in theoretical chemistry.

The role of nitric oxide in penile erection

The functional state of the penis, flaccid or erect is governed by smooth muscle tone. Sympathetic contractile factors maintain flaccidity whilst parasympathetic factors induce smooth muscle relaxation and erection. It is generally accepted that nitric oxide (NO) is the principal agent responsible for relaxation of penile smooth muscle. NO is derived from two principal sources: directly from non-adrenergic non-cholinergic parasympathetic nerves and indirectly from the endothelium lining cavernosal sinusoids and blood vessels in response to cholinergic stimulation. The generation of NO from L-arginine is catalysed by nitric oxide synthase (NOS). There has been controversy over the relative prevalence of endothelial or neuronal NOS within the penis of different animal species. This review examines the role of NO in the penis in detail. Established and new treatments for erectile dysfunction whose effects are mediated via manipulation of the NO pathway are also described.

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.

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.

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.

Relaxant effects of alpha-human atrial natriuretic peptide on venous smooth muscle

1 The present study has examined the relaxant effects of alpha-human atrial natriuretic peptide (alpha-hANP) and sodium nitroprusside on dog saphenous vein ring preparations; responses were tested on a background of tone corresponding to 30% and 80% of maximal contraction. Also tested on the lower background of tone were the responses to carbachol, M&B 22,948, forskolin and 3-isobutyl-1-methylxanthine (IBMX). The vascular responses to alpha-hANP and carbachol were also examined in dog splenic artery ring preparations. 2 On a background of tone corresponding to 30% of maximal contraction, both alpha-hANP and sodium nitroprusside were found to relax venous ring preparations with IC50 values of 6 x 10(-8) and 2 x 10(-7) M, respectively. When the background of tone was raised to 80% of maximal contraction, the relaxant effect of sodium nitroprusside was significantly reduced and that of alpha-hANP became almost completely abolished; the IC50 value for sodium nitroprusside in these experimental conditions was 2 x 10(-6) M. 3 The cGMP phosphodiesterase inhibitor M&B 22,948 was found to produce a concentration-dependent relaxation, with an IC50 value of 2 x 10(-6)M in saphenous vein rings with a background of tone corresponding to 30% of maximal contraction. By contrast, saphenous vein rings were found to be insensitive to carbachol. Forskolin and IBMX were also found to produce concentration-dependent relaxing responses of venous preparations, with IC50 values of 2 x 10(-7) and 7 x 10(-7) M, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of methylene blue on the uptake, release and metabolism of noradrenaline in mesenteric arterial vessels

Methylene blue (3, 10 and 30 microM) increased the spontaneous outflow of endogenous dopamine and noradrenaline from sympathetic nerves supplying the dog mesenteric artery and drastically reduced the formation of endogenous dihydroxyphenylglycol (DOPEG). In addition, it decreased the accumulation of [3H]noradrenaline in the tissue, reduced the formation of [3H]DOPEG and [3H]normetanephrine, without altering the formation of [3H]dihydroxymandelic acid. In tissue homogenates of the same blood vessel, methylene blue 30 and 100 microM produced a significant reduction in the deamination of 5-hydroxytryptamine (5-HT), beta-phenylethylamine (beta-PEA) and tyramine. Methylene blue increased the accumulation of [3H]isoprenaline in the tissue, and markedly reduced the formation of [3H]O-methylisoprenaline ([3H]OMI). These results show that methylene blue alters the storage and disposition of the adrenergic transmitter.