Cyclic GMP-independent relaxation of rat pulmonary artery by spermine NONOate, a diazeniumdiolate nitric oxide donor

Role of Endothelial Kinin B1 Receptor on the Membrane Potential of Transgenic Rat Aorta

The kinin receptors are classically involved in inflammation, pain and sepsis. The effects of the kinin B1 receptor agonist des-Arg9-bradykinin (DBK) and lipopolysaccharide (LPS) were investigated by comparing the membrane potential responses of aortic rings from transgenic rats overexpressing the kinin B1 receptor (B1R) in the endothelium (TGR(Tie2B1)) and Sprague Dawley (SD) rats. No difference in the resting membrane potential in the aorta’s smooth muscle from the transgenic and SD rats was observed. The aorta rings from SD rats hyperpolarized only to LPS but not to DBK, whereas the aorta rings from TGR(Tie2B1) responded by the administration of both drugs. DBK and LPS responses were inhibited by the B1 receptor antagonist R715 and by iberiotoxin in both cases. Thapsigargin induced a hyperpolarization in the smooth muscle of SD rats that was not reversed by R715, but was reversed by iberiotoxin and this hyperpolarization was further augmented by DBK administration. These results show that the model of overexpression of vascular B1 receptors in the TGR(Tie2B1) rats represent a good model to study the role of functional B1 receptors in the absence of any pathological stimulus. The data also show that KCa channels are the final mediators of the hyperpolarizing responses to DBK and LPS. In addition, we suggest an interaction between the B1R and TLR4, since the hyperpolarization induced by LPS could be abolished in the presence of R715.

Recent Developments in Pharmacological Effect, Mechanism and Application Prospect of Diazeniumdiolates

Nitric oxide (NO) is a simple structured and unstable free radical molecule, which participates in the regulation of many pathophysiological processes. It functions both as a second messenger and as an endogenous neurotransmitter. Diazeniumdiolates (NONOates) are a series of compounds containing the functional parent nuclear structure of [N(O)NO]-, which are the most widely studied NO donors. NONOates are unstable and easy to release NO in physiological conditions. The biomedical applications and drug development of NO donor have attracted the scientists' attention in recent years. In this review, recent advances in NONOates research are highlighted in terms of chemical structures, molecular characteristics, pharmacological effects, and biomedical application prospects.

Resistance training and caloric restriction prevent systolic blood pressure rise by improving the nitric oxide effect on smooth muscle and morphological changes in the aorta of ovariectomized rats

In this study, we investigated the effects of resistance training (RT), caloric restriction (CR), and the association of both interventions in aortic vascular reactivity and morphological alterations, matrix metalloproteinase-2 (MMP-2) activity, insulin resistance and systolic blood pressure (SBP) in ovariectomized rats. Fifty female Holtzman rats were subjected to ovariectomy and Sham surgery and distributed into the following groups: Sham-sedentary, ovariectomized-sedentary, ovariectomized-resistance training, ovariectomized-caloric restriction, and ovariectomized-resistance training and caloric restriction groups. RT and 30% CR protocols were performed for 13 weeks. Analyses were conducted to evaluate the following: acetylcholine and sodium nitroprusside-induced relaxation of aortic rings, MMP-2 activity, insulin tolerance test, highlighting of the aorta wall cross-sectional area by hematoxylin-eosin stain, aorta vessel remodeling and SBP. We observed that ovariectomy decreased the potency of dependent and independent endothelium relaxation and MMP-2 activity, prevented insulin resistance, promoted aorta vessel remodeling in the cross-sectional area, and promoted the media-to-lumen ratio, the collagen content, and the alteration of the structure and elastic fibers of the vessel. The effects of the ovariectomy could contribute to SBP increases. However, the association of exercise and diet improved the relaxation potency in dependent and independent endothelium relaxation, elevated MMP-2 activity, ameliorate insulin sensitivity, increased the aorta cross-sectional area and media-to-lumen ratio, decreased collagen content and promoted histological parameters of the aorta vessel wall, preventing the increase of SBP.

CONCLUSION

Our study revealed that the RT and CR separately, and even associatively, improved vascular function, activated MMP-2, and produced a beneficial hypertrophic remodeling, preventing the elevation of SBP in ovariectomized rats.

Pharmacological characterization of the vasodilating effect induced by the ruthenium complex cis-[Ru(NO)(NO2)(bpy)2].(PF6)2

Nitric oxide (NO) can be found in different species and is a potent vasodilator. The ruthenium compound cis-[Ru(NO)(NO2)(bpy)2].(PF6)2 (BPY) can generate NO. This study aimed to investigate the BPY stability at physiological pH, the cellular mechanisms involved in BPY effect, NO species originating from BPY, and to verify how BPY affects blood pressure. Our results has shown that at pH 7.4 and 9.4, the NO coordinated to ruthenium (Ru-NO) is converted to nitrite (Ru-NO2) and remains stable. In aortic rings, the stable configuration of BPY (Ru-NO2) induces vascular relaxation in a concentration-dependent manner. Thus, further experiments were made with stable configuration of BPY (Ru-NO2). The relaxation induced by BPY was abolished in the presence of guanylyl cyclase inhibitor and decreased in the presence of potassium channel blocker. By using radicalar (NO) and nitroxyl (NO) scavenger, our results suggest that the BPY mainly release the radicalar species. By using fluorescence probes to detect intracellular NO concentration ([NO]i) and cytosolic Ca concentration ([Ca]c), we verified that in smooth muscle cells, BPY induces an increase in [NO]i and a decrease in [Ca]c. The intravenous bolus injection of 1.25, 2.5, and 5.0 mg/kg from stable configuration of BPY results in a decrease on basal blood pressure values. Taken together, our results indicated that the stable configuration of the compound BPY induces vascular relaxation in aorta because of NO release and decrease of [Ca]c in vascular smooth muscle cells. Also, the stable configuration is able to reduce the blood pressure in a dose-dependent manner.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Gold nanoparticle modifies nitric oxide release and vasodilation in rat aorta

Nitric oxide (NO) plays an important role on several biological functions. Recently, it has been reported the possibility of modifying the NO release profile from the NO donors through its coupling to gold nanoparticles (AuNPs). Thus, AuNPs were synthesized and they were exposed to the NO donor ruthenium complex Cis-[Ru(bpy)2(NO)(4PySH)].(PF6)3 termed (Ru-4PySH)-forming AuNPs-{Ru-4PySH}n cluster. Our results indicate that AuNPs do not modify the maximum effect (ME) and potency (pD2) in the vasodilation induced by Ru-4PySH. Both complexes induce similar vascular relaxation in concentration-dependent way. However, the NO released from the complex AuNPs-{Ru-4PySH}n is lower than Ru-4PySH. Both complexes release only NO(0) specie, but AuNPs-{Ru-4PySH}n releases NO in constant way and exclusively in the extracellular medium. In time-course, Ru-4Py-SH was faster than AuNPs-{Ru-4PySH}n in inducing the maximum vasodilation. Inhibition of soluble guanylyl cyclase (sGC) abolished the vasodilation induced by Ru-4PYSH, but not by AuNPs-{Ru-4PySH}n. Non-selective potassium (K(+)) channel blocker TEA had no effect on the vasodilation induced by AuNPs-{Ru-4PySH}n, but it reduced the potency to Ru-4PySH. In conclusion, our results suggest that AuNPs can reduce the permeability of NO donor Ru-4PySH due to AuNPs-{Ru-4PySH}n cluster formation. AuNPs reduce NO release, but they do not impair the vasodilator effect induced by the NO donor. Ru-4PySH induces vasodilation by sGC and K(+) channels activation, while AuNPs-{Ru-4PySH}n activates mainly sGC. Taken together, these findings represent a new pharmacological strategy to control the NO release which could activate selective biological targets.

A comparative study of NONOate based NO donors: spermine NONOate is the best suited NO donor for angiogenesis

Nitric oxide (NO) is a known modulator of angiogenesis. The NONOate subfamily of NO donors has long been used in experimental and clinical studies to promote angiogenesis. However, no studies have been conducted yet to compare the angiogenesis potential of these NO donors in respect to their pattern of NO release. We hypothesize that having different pattern of NO release, each of the NO donors in NONOate subfamily can promote key stages of angiogenesis in differential manner. To verify our hypothesis, NO donors with half life ranging from seconds to several hours and having very different pattern of NO release were selected to evaluate their efficacy in modulating angiogenesis. Endothelial tube formation using EAhy926 cells was maximally increased by Spermine NONOate (SP) treatment. SP treatment maximally induced both ex vivo and in vivo angiogenesis using egg yolk and cotton plug angiogenesis models respectively. Experiment using chick embryo partial ischemia model revealed SP as the best suited NO donor to recover ischemia driven hampered angiogenesis. The present study elaborated that differential release pattern of NO by different NO donors can modulate angiogenesis differentially and also suggested that SP have a unique pattern of NO release that best fits for angiogenesis.

Novel β-galactosidase-specific O2-glycosylated diazeniumdiolate probes

Three β-galactosidase-specific nitric-oxide-releasing diazeniumdiolate conjugated probes were prepared as a prelude to studies of new potential molecular MRI imaging agents. A glycosylated derivative, 2e, designed to be trafficked across cell membranes, was also prepared. We report, in detail, the synthesis and characterization of these probes. In addition, the release of diazeniumdiolate from the probes by β-galactosidase-catalyzed hydrolysis was used to estimate their efficacy as serum-stable, specific NO donors.

Sustained release nitric oxide from long-lived circulating nanoparticles

The current limitations of nitric oxide (NO) delivery systems have stimulated an extraordinary interest in the development of compounds that generate NO in a controlled and sustained manner with a heavy emphasis on the treatment of cardiovascular disease states. This work describes the positive physiological response to the infusion of NO-releasing nanoparticles prepared using a new platform based on hydrogel/glass hybrid nanoparticles. When exposed to moisture, these nanoparticles slowly release therapeutic levels of NO, previously generated through thermal reduction of nitrite to NO trapped within the dry particles. The controlled and sustained release of NO observed from these nanoparticles (NO-np) is regulated by its hydration over extended periods of time. In a dose-dependent manner, circulating NO-np both decreased mean arterial blood pressure and increased exhaled concentrations of NO over a period of several hours. Circulating NO-np induced vasodilatation and increased microvascular perfusion during their several hour circulation lifetime. Control nanoparticles (control-np; without nitrite) did not induce changes in arterial pressure, although a decrease in the number of capillaries perfused and an increase in leukocyte rolling and immobilization in the microcirculation were observed. The NO released by the NO-np prevents the inflammatory response observed after infusion of control-np. These data suggest that NO release from NO-np is advantageous relative to other NO-releasing compounds, because it does not depend on chemical decomposition or enzymatic catalysis; it is only determined by the rate of hydration. Based on the observed physiological properties, NO-np has clear potential as a therapeutic agent and as a research tool to increase our understanding of NO signaling mechanisms within the vasculature.

Nitric oxide suppresses cerebral vasomotion by sGC-independent effects on ryanodine receptors and voltage-gated calcium channels

BACKGROUND/AIMS

In cerebral arteries, nitric oxide (NO) release plays a key role in suppressing vasomotion. Our aim was to establish the pathways affected by NO in rat middle cerebral arteries.

METHODS

In isolated segments of artery, isometric tension and simultaneous measurements of either smooth muscle membrane potential or intracellular [Ca(2+)] ([Ca(2+)](SMC)) changes were recorded.

RESULTS

In the absence of L-NAME, asynchronous propagating Ca(2+) waves were recorded that were sensitive to block with ryanodine, but not nifedipine. L-NAME stimulated pronounced vasomotion and synchronous Ca(2+) oscillations with close temporal coupling between membrane potential, tone and [Ca(2+)](SMC). If nifedipine was applied together with L-NAME, [Ca(2+)](SMC) decreased and synchronous Ca(2+) oscillations were lost, but asynchronous propagating Ca(2+) waves persisted. Vasomotion was similarly evoked by either iberiotoxin, or by ryanodine, and to a lesser extent by ODQ. Exogenous application of NONOate stimulated endothelium-independent hyperpolarization and relaxation of either L-NAME-induced or spontaneous arterial tone. NO-evoked hyperpolarization involved activation of BK(Ca) channels via ryanodine receptors (RYRs), with little involvement of sGC. Further, in whole cell mode, NO inhibited current through L-type voltage-gated Ca(2+) channels (VGCC), which was independent of both voltage and sGC.

CONCLUSION

NO exerts sGC-independent actions at RYRs and at VGCC, both of which normally suppress cerebral artery myogenic tone.

ADMA injures the glomerular filtration barrier: role of nitric oxide and superoxide

Chronic kidney disease (CKD) is associated with decreased renal nitric oxide (NO) production and increased plasma levels of methylarginines. The naturally occurring guanidino-methylated arginines N-monomethyl-l-arginine (l-NMMA) and asymmetric dimethyl-l-arginine (ADMA) inhibit NO synthase activity. We hypothesized that ADMA and l-NMMA compromise the integrity of the glomerular filtration barrier via NO depletion. We studied the effect of ADMA on albumin permeability (P(alb)) in isolated glomeruli and examined whether this effect involves NO- and superoxide (O(2)(*-))-dependent mechanisms. ADMA at concentrations found in circulation of patients with CKD decreased cGMP and increased P(alb) in a dose-dependent manner. A similar increase in P(alb) was caused by l-NMMA but at a concentration two orders of magnitude higher than that of ADMA. NO donor DETA-NONOate or cGMP analog abrogated the effect of ADMA on P(alb). The SOD mimetic tempol or the NAD(P)H oxidase inhibitor apocynin also prevented the ADMA-induced increase in P(alb). The NO-independent soluble guanylyl cyclase (sGC) activator BAY 41-2272, at concentrations that increased glomerular cGMP production, attenuated the ADMA-induced increase in P(alb). Furthermore, sGC incapacitation by the heme site-selective inhibitor ODQ increased P(alb). We conclude that ADMA compromises the integrity of the filtration barrier by altering the bioavailability of NO and O(2)(*-) and that NO-independent activation of sGC preserves the integrity of this barrier under conditions of NO depletion. NO-independent activation of sGS may be a useful pharmacotherapeutic approach for preservation of glomerular function in CKD thereby reducing the risk for cardiovascular events.

Role of the soluble guanylyl cyclase alpha1-subunit in mice corpus cavernosum smooth muscle relaxation

Soluble guanylyl cyclase (sGC) is the major effector molecule for nitric oxide (NO) and as such an interesting therapeutic target for the treatment of erectile dysfunction. To assess the functional importance of the sGCalpha(1)beta(1) isoform in corpus cavernosum (CC) relaxation, CC from male sGCalpha(1)(-/-) and wild-type mice were mounted in organ baths for isometric tension recording. The relaxation to endogenous NO (from acetylcholine, bradykinin and electrical field stimulation) was nearly abolished in the sGCalpha(1)(-/-) CC. In the sGCalpha(1)(-/-) mice, the relaxing influence of exogenous NO (from sodium nitroprusside and NO gas), BAY 41-2272 (NO-independent sGC stimulator) and T-1032 (phosphodiesterase type 5 inhibitor) were also significantly decreased. The remaining exogenous NO-induced relaxation seen in the sGCalpha(1)(-/-) mice was significantly decreased by the sGC-inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The specificity of the impairment of the sGC-related responses was demonstrated by the unaltered relaxations seen with forskolin (adenylyl cyclase activator) and 8-pCPT-cGMP (cGMP analog). In conclusion, the sGCalpha(1)beta(1) isoform is involved in corporal smooth muscle relaxation in response to NO and NO-independent sGC stimulators. The fact that there is still some effect of exogenous NO in the sGCalpha(1)(-/- mice suggests the contribution of (an) additional pathway(s).

Caveolae Dysfunction Contributes to Impaired Relaxation Induced by Nitric Oxide Donor in Aorta from Renal Hypertensive Rats

Relaxation induced by nitric oxide (NO) donors is impaired in renal hypertensive two kidney-one clip (2K-1C) rat aortas. It has been proposed that caveolae are important in signal transduction and Ca2+ homeostasis. Therefore, in the present study we investigate the integrity of caveolae in vascular smooth muscle cells (VSMCs), as well as their influence on the effects produced by NO released from both the new NO donor [Ru(NH.NHq) (terpy)NO+]3+ (TERPY) and sodium nitroprusside (SNP) on 2K-1C rat aorta. The potency of both TERPY and SNP was lower in the 2K-1C aorta that in the normotensive aorta [two kidney (2K)], whereas the maximal relaxant effect (ME) was similar in both 2K-1C and 2K aortas. In the 2K aorta, methyl-beta-cyclodextrin (CD) reduced both the potency of TERPY and SNP, and their ME compared with the control, but it had no effect on the potency and ME of these NO donors in 2K-1C aortas. The decrease in cytosolic Ca2+ concentration ([Ca2+]c) induced by TERPY was larger in 2K than in 2K-1C cells, and this effect was inhibited by CD in 2K cells only. Aortic VSMCs from 2K rats presented a larger number of caveolae than those from 2K-1C rats. Treatment with CD reduced the number of caveolae in both 2K and 2K-1C aortic VSMCs. Our results support the idea that caveolae play a critical role in the relaxant effect and in the decrease in [Ca2+]c induced by NO, and they could be responsible for impaired aorta relaxation by NO in renal hypertensive rats.

Modulation of gap-junction-dependent arterial relaxation by ascorbic acid

AIMS

To investigate whether ascorbic acid (AA) can influence endothelium-dependent relaxation by modulating the spread of endothelial hyperpolarization through the arterial wall via gap junctions.

METHODS

Force development and membrane potential were monitored by myography and sharp electrode techniques in isolated rabbit iliac arteries.

RESULTS

AA prevented the ability of the gap junction blocker 2-aminoethoxydiphenyl borate to inhibit endothelium-dependent relaxations and subintimal smooth muscle hyperpolarizations evoked by cyclopiazonic acid in the presence of nitric oxide (NO) synthase and cyclooxygenase blockade. AA also prevented the ability of a connexin-mimetic peptide targeted against Cx37 and Cx40 (37,40Gap 26) to attenuate the transmission of endothelial hyperpolarization to subintimal smooth muscle, and a peptide targeted against Cx43 (43Gap 26) to attenuate the spread of subintimal hyperpolarization to subadventitial smooth muscle and the associated mechanical relaxation. Parallel studies with endothelium-denuded preparations demonstrated that AA and cyclopiazonic acid both depressed relaxation evoked by the NO donor MAHMA NONOate.

CONCLUSIONS

The data suggest that AA can modulate arterial function through a previously unrecognized ability to preserve electrotonic signalling via myoendothelial and homocellular smooth muscle gap junctions under conditions where cell coupling is depressed. Underlying mechanisms do not involve amplification of 'residual' NO activity by AA.

Characterization of the mechanisms of action and nitric oxide species involved in the relaxation induced by the ruthenium complex

Nitric oxide (NO) plays an important role in the control of vascular tone. NO donors have therapeutic use and the most used NO donors, nitroglycerin and sodium nitroprusside have problems in their use. Thus, new NO donors have been synthesized to minimize these undesirable effects. Nytrosil ruthenium complexes have been studied as a new class of NO donors. trans-[RuCl([15]aneN(4))NO](2+), induces vasorelaxation only in presence of reducing agent. In this study, we characterized the mechanisms of vasorelaxation of trans-[RuCl([15]aneN(4))NO](2+) in denuded rat aorta and identified which NO forms are involved in this relaxation. We also evaluated the effect of this NO donor in decreasing the cytosolic Ca(2+) concentration ([Ca(2+)]c) of the vascular smooth muscle cells. Vasorelaxation to trans-[RuCl([15]aneN(4))NO](2+) (E(max): 101.8 +/- 2.3%, pEC(50): 5.03 +/- 0.15) was almost abolished in the presence of the NO* scavenger hydroxocobalamin (E(max): 4.0 +/- 0.4%; P < 0.001) and it was partially inhibited by the NO(-) scavenger L-cysteine (E(max): 79.9 +/- 6.9%, pEC(50): 4.41 +/- 0.06; P < 0.05). The guanylyl cyclase inhibitor ODQ reduced the E(max) (57.7 +/- 4.0%, P < 0.001) and pEC(50) (4.21 +/- 0.42, P < 0.01) and the combination of ODQ and TEA abolished the response to trans-[RuCl([15]aneN(4))NO](2+). The blockade of voltage-dependent (K(v)), ATP-sensitive (K(ATP)), and Ca(2+)-activated (K(Ca) K(+) channels reduced the vasorelaxation induced by trans-[RuCl([15]aneN(4))NO](2+). This compound significantly reduced [Ca(2+)]c (from 100% to 85.9 +/- 3.5%, n = 4). In conclusion, our data demonstrate that this NO donor induces vascular relaxation involving NO* and NO(-) species, that is associated to a decrease in [Ca(2+)]c. The mechanisms of vasorelaxation involve guanylyl cyclase activation, cGMP production and K(+) channels activation.

Topics on the Na+/Ca2+ exchanger: involvement of Na+/Ca2+ exchanger in the vasodilator-induced vasorelaxation

Many kinds of vasodilators induce relaxation of the vascular smooth muscle cells (VSMCs) through the production of cyclic AMP (cAMP) or cyclic GMP (cGMP). The relaxant effects mediated by these second messengers are thought to be mainly due to the decrease in intracellular Ca(2+) concentration ([Ca(2+)](i)), as well as the decrease in Ca(2+) sensitivity of the contractile apparatus of VSMCs. To explain the cAMP- or cGMP-mediated decrease in [Ca(2+)](i), several mechanisms have been proposed, including the inhibition of Ca(2+) influx due to a hyperpolarization, a stimulation of Ca(2+) uptake into the intracellular store, and an increase in Ca(2+) extrusion from VSMCs by stimulation of sarcolemmal Ca(2+)-pump. VSMCs have two major systems for Ca(2+) extrusion, namely, sarcolemmal Ca(2+)-pump and Na(+)/Ca(2+) exchanger (NCX). However, the involvement of NCX in the vasodilator-induced relaxation of VSMCs has not been well established. In this article, the possible involvement of NCX in the vasodilator-induced relaxation of VSMCs will be reviewed.

Cytosolic calcium concentration is reduced by photolysis of a nitrosyl ruthenium complex in vascular smooth muscle cells

The effect of the NO donors cis-[RuCl(bpy)(2)(NO)](PF(6)) (RUNOCL) and sodium nitroprusside (SNP) on the cytosolic Ca(2+) concentration ([Ca(2+)](c)) was studied in cells isolated from the rat aorta smooth muscle of cells isolated from the rat aorta smooth muscle. SNP is a metal nitrosyl complex made up of iron, cyanide groups, and a nitro moiety; the RUNOCL complex is made up of ruthenium and bipyridine ligands, with chloride and nitrosyl groups in the ruthenium axial positions. Rat aorta smooth muscle cells were loaded with fluo-3 acetoxymethyl ester (Fluo-3 AM) and imaged by a confocal scanning laser microscope excited with the 488 nm line of the argon ion laser. Fluorescence emission was measured at 510 nm. One of the NO donors, RUNOCL (100 micromol/L) or SNP (100 micromol/L), was then added to the cell chamber and the fluorescent intensity percentage (%IF) was measured after 240 s. RUNOCL reduced the %IF to 60.0+/-10.0% of the initial value. After treatment with the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) (10 micromol/L), the measurement of %IF was 81.0+/-5.0% (n=4). In the presence of tetraethylammonium (TEA) (1 mmol/L) the %IF was 79.0+/-6.4% (n=4). A combination of ODQ and TEA increased the %IF to 97.0+/-3.5% (n=4). As for SNP, it reduced the %IF to 81.4+/-4.7% (n=4), but this effect was inhibited by ODQ (%IF 94.0+/-3.6%; n=4) and TEA (%IF 88.0+/-2.1%; n=4). The combination of ODQ and TEA increased (%IF 92.0+/-2.8%; n=4). Taken together, these results indicate that both the new NO donor RUNOCL and SNP reduce [Ca(2+)](c). Our data also give evidence that soluble guanylyl cyclase and K(+) channels sensitive to TEA are involved in the mechanisms responsible for the reduction in [Ca(2+)](c) of the rat aorta smooth muscle cells.

Comparison of the mechanisms underlying the relaxation induced by two nitric oxide donors: sodium nitroprusside and a new ruthenium complex

We studied the mechanisms involved in the relaxation induced by nitric oxide (NO) donors, ruthenium complex ([Ru(terpy)(bdq)NO(+)](3+)-TERPY) and sodium nitroprusside (SNP) in denuded rat aorta. Both NO donors induced vascular relaxation independent of the agonist used in the pre-contraction. [Ru(terpy)(bdq)NO(+)](3+) and SNP activated guanylyl cyclase (GC) and K(+) channels. The production of cGMP induced by [Ru(terpy)(bdq)NO(+)](3+) - was higher than that obtained with SNP. The combination of GC inhibitor with K(+)channels blocker almost abolished the relaxation induced by the NO donors. The extracellular NO scavenger oxyhemoglobin reduced the potency without changing the maximum effect (Emax) of both NO donors. By using specific NO species scavengers, hydroxocobalamin and l-cysteine, we have identified the contribution of free radical NO (NO()) and nytroxil anion (NO(-)), respectively, to the rat aorta relaxation induced by both NO donors. The selective scavengers for NO() and NO(-) reduced the potency but not the Emax of [Ru(terpy)(bdq)NO(+)](3+). However, the NO(-) scavenger had no effect on the relaxation induced by SNP and NO() scavenger reduced only the potency to SNP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduced only the potency of SNP without effect on the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+). Our results demonstrate that both NO donors induce relaxation by activating the GC and K(+) channels. The NO() is the unique NO specie involved in the SNP-relaxation. On the other hand, the relaxant effect of [Ru(terpy)(bdq)NO(+)](3+) involves both NO() and NO(-), that produce higher concentration of cGMP. The inhibition of sarcoplasmic reticulum Ca(2+)-ATPase reduces the relaxation induced by SNP but it did not alter the relaxation induced by [Ru(terpy)(bdq)NO(+)](3+).

The biological chemistry of nitric oxide as it pertains to the extrapulmonary effects of inhaled nitric oxide

The chemical properties of nitric oxide (NO) have been studied for over 200 years. However, it is only within the last 20 years that the biological implications of this chemistry have been considered. The classical model of NO action within the vasculature centers on production in the endothelium, diffusion to the smooth muscle, and subsequent activation of guanylate cyclase via binding to its heme iron. In the context of this model, it is difficult to conceptualize extrapulmonary effects of inhaled NO. However, NO possesses complex redox chemistry and is capable of forming a range of nitrogen oxide species and is therefore capable of interacting with a variety of biomolecules. Of particular interest is its reaction with reduced cysteine to form an S-nitrosothiol (SNO). SNOs are formed throughout NO biology and are a post-translational modification that has been shown to regulate many proteins under physiologic conditions. Hemoglobin, which was considered to be solely a consumer of NO, can form SNO in a conformationally dependent manner, which allows for the transport of inhaled NO beyond the realm of the lung. Higher oxides of nitrogen are capable of modifying proteins via nitration of tyrosines, which has been shown to occur under pathologic conditions. By virtue of its redox reactivity, one can appreciate that inhaled NO has a variety of routes by which it can act and that these routes may lead to extrapulmonary effects.

Segmental heterogeneity in the mechanism of sodium nitroprusside-induced relaxation in ovine pulmonary artery

Segmental heterogeneity in relaxation response to nitric oxide (NO) was examined using NO donor sodium nitroprusside (SNP) in second- (medium) and fourth-generation (small) ovine isolated intralobar pulmonary arteries. In vessels precontracted with serotonin, NO donors SNP and S-nitroso-N-acetylpenicillamine (SNAP) were more potent in relaxing medium, in comparison to the small, arteries. Soluble guanylyl cyclase (sGC) inhibitor [1,2,4]oxadiazolo-[4,3-a]quinoxaline-1-one (ODQ 3 microM) caused a profound inhibition of SNP relaxation in small as compared with medium-sized arteries. However, both basal and SNP (10 microM)-stimulated intracellular cyclic guanosine monophosphate (cGMP) content was identical in these 2 arterial segments. The Na,K-ATPase inhibitor ouabain (1 microM) had a marked inhibitory effect on SNP-mediated relaxation in both segments. There was no segmental difference in SNP (10 microM)-stimulated plasma membrane Na,K-ATPase activity and ouabain-sensitive Rb-uptake. 4-AP (1 mM), a relatively selective inhibitor of Kv channels, decreased the potency of SNP relaxation by about 10-fold in the medium-sized vessels. On the other hand, 4-AP was without effect on the vasodilator potency of SNP in small vessels. Interestingly, in the presence of 4-AP, SNP was equipotent in dilating both medium (pD2 = 5.80 +/- 0.07; Emax = 84 +/- 1.6%, n = 7) and small (pD2 = 5.74 +/- 0.15; Emax = 83 +/- 2.5%, n = 7) pulmonary arteries. In conclusion, the results of the present study suggest that Kv channels determine the segmental heterogeneity of NO-mediated relaxation in ovine pulmonary artery.

BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine]-induced dilation in ovine pulmonary artery: role of sodium pump

The mechanisms of relaxation to nitric oxide (NO)-independent soluble guanylyl cyclase (sGC) activator BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine] were investigated in isolated ovine pulmonary artery. BAY 41-2272 (1 nM-10 microM) produced concentration-dependent relaxation of endothelium-denuded pulmonary artery rings (pD2 = 6.82 +/- 0.16; Emax = 92.30 +/- 2.31%; n = 8), precontracted with 1 microM 5-hydroxytryptamine (serotonin). 1-H-[1,2,4]Oxadiazole[4,3-a]quinoxalin-1-one (ODQ; 10 microM), an inhibitor of sGC, partially inhibited (Emax = 57.10 +/- 3.10%; n = 6) the relaxation response of BAY 41-2272. In comparison with ODQ, sodium pump inhibitor ouabain (1 microM) produced a greater decrease in the vasodilator response of BAY 41-2272 (Emax = 20.17 +/- 4.55%; n = 6). K+-free solution also attenuated (Emax = 39.97 +/- 3.52%; n = 6) BAY 41-2272-induced relaxation. ODQ (10 microM) plus 1 microM ouabain abolished the relaxant response of BAY 41-2272 (Emax = 12.09 +/- 3.76%, n = 6 versus vehicle control dimethyl sulfoxide; Emax = 15.83 +/- 1.72%, n = 6). KT-5823 [1-oxo-9.12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-I][1,6]benzodiazocine-10-carboxylic acid methyl ester (2 microM), a specific inhibitor of protein kinase G had no effect on 10 microM ODQ-insensitive relaxation evoked by BAY 41-2272. BAY 41-2272 (10 microM) inhibited Ca2+-induced contractions in K+-depolarized preparations. BAY 41-2272 (10 microM) caused about a 14-fold increase in the intracellular cGMP over the basal level, which was completely inhibited by 10 microM ODQ. BAY 41-2272 (0.1, 1.0, and 10 microM) significantly (P < 0.05) increased ouabain-sensitive 86Rb uptake in a concentration-dependent manner. BAY 41-2272 (10 microM) also stimulated sarcolemmal Na+-K+-ATPase activity. However, 10 microM ODQ had no significant effect on either basal or BAY 41-2272-stimulated 86Rb uptake/Na+-K+-ATPase activities. In conclusion, this study provides the first evidence of sodium pump stimulation by BAY 41-2272 independent of cGMP as an additional mechanism to sGC activation in relaxation of ovine pulmonary artery.

NO-donors, part 9 : diazeniumdiolates inhibit human platelet aggregation and induce a transient vasodilatation of porcine pulmonary arteries in accordance with the NO-releasing rates

Diazeniumdiolates (NONOates), among them a ciprofloxacin-diazeniumdiolate hybrid compound, were synthesized and the pH-, temperature- and structure-dependent liberation of nitric oxide (NO) was monitored by laser magnetic resonance spectroscopy (LMRS). The compounds induced a transient and reversible relaxation (EC(50) 8.3-150 nM) of pulmonary arteries independently from intact endothelium by stimulation of guanylyl cyclase (sGC). Increase in vascular cGMP was observed and blocking sGC with ODQ, an inhibitor of the NO-sensitive guanylyl cyclase, induced a rightward shift of the concentration-response curves. Repeated exposure did not show homologous desensitization. ADP-induced platelet aggregation (IC(50) = 0.15-3 microM, IC(50) for SNP: 2 microM) and collagen-induced aggregation were potently inhibited. Preincubation with ODQ also diminished these inhibitory effects.

Extracellular nitric oxide release mediates soluble guanylate cyclase-independent vasodilator action of spermine NONOate: comparison with other nitric oxide donors in isolated rat femoral arteries

Nitric oxide (NO) and NO donors exhibit actions that are not entirely mediated by soluble guanylate cyclase (sGC). The site of NO release may influence the involvement of sGC-independent effects. Here we use spermine NONOate (SPER/NO) to release NO extracellularly, compared with other NO donors. Isolated rat femoral arteries were perfused luminally and perfusion pressure monitored. Vessels were contracted with phenylephrine (2-14 microM) in the presence of an NO synthase inhibitor (N(omega)-nitro-L-arginine methyl ester; 20 microM). Vasodilator responses to NO donors were assessed before and after perfusion of an sGC inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; ODQ; 20 microM), NO scavengers (hemoglobin; Hb & hydroquinone; HQ), and a superoxide generator (duroquinone; DQ). ODQ (20 microM) abolished the vasodilator responses to glyceryl trinitrate (10(-8) - 10(-3) M), and sodium nitroprusside (10(-8) - 10(-4) M), which release NO intracellularly. ODQ (20 microM) attenuated, but failed to abolish, the vasodilator responses to SPER/NO (10(-6) - 10(-3) M). ODQ abolished responses to S-nitrosoglutathione and S-nitroso-N-valeryl-D-penicillamine (10(-8) - 10(-4) M), but a small residual vasodilatation remained in response to 10(-3) M. In the presence of ODQ, the remaining vasodilatation to SPER/NO was all but abolished by scavengers of extracellular NO (Hb; 10 microM, HQ; 100 microM). Superoxide generation (DQ; 100 microM) also attenuated ODQ-resistant vasodilatation. The data suggest that, in rat femoral arteries, NO donors that are capable of releasing extracellular NO cause vasodilatation that is only partially mediated by sGC. Lack of augmentation of sGC-independent effects by superoxide suggests that they are not mediated by peroxynitrite.

Modulating effects of L-arginine on cytokine-stimulated lymphocyte migration in vitro

Elective microsurgical transplants have become routine. Yet there remains a 1-5% rate of complete flap necrosis among these surgical reconstructions. This rate is much higher in emergent replantations. Despite technically accurate surgery, perfusion fails in this group. This lack of perfusion, or no-reflow, has been attributed to ischemic-reperfusion injury. The exact nature of this phenomenon remains poorly characterized, though it is clear that significant changes occur in such situations at the endothelial vascular interface. In an effort to understand the biomolecular events involved in ischemic-reperfusion injury we investigated the modulation of leukocyte transendothelial migration. Using a chemotactic chamber model with a cytokine stimulate mono-layer of umbilical vein endothelium, we evaluated the migration rate of peripheral blood mononuclear cells in the presence of exogenous L-arginine and/or the nitric oxide synthase inhibitor L-NAME. Levels of INF-gamma and TNF-alpha production were also determined. It was found that in the face of cytokine pre-stimulation and L-arginine, mononuclear cell trans-endothelial migration increased dramatically. There were also parallel increases in inflammatory cytokine output. These responses were sharply decreased by L-NAME. The results of this study suggest that in vitro nitric oxide augments transendothelial migration of inflammatory cells. Modulation of this response may provide a clinically useful method of minimizing ischemic-reperfusion injury.

Inhibition of nitric oxide synthase (NOS) conversion of L-arginine to nitric oxide (NO) decreases low density mononuclear cell (LD MNC) trans-endothelial migration and cytokine output

BACKGROUND

Biochemical, molecular, and cellular events at the micro-vascular endothelial interface determine the integrity of the vascular system. Disruption of these events has been described to occur in accordance with ischemic/reperfusion injury leading to inflammation, cell adhesion, and endothelial permeability changes. It has also been suggested that nitric oxide (NO) participates in these events. However, the manner in which it does is debated. The purpose of this study was to investigate the effects of exogenous L-arginine, an NO precursor, and L-N (G) nitroarginine methyl ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, upon inflammatory events at the endothelial interface.

MATERIAL AND METHODS

Fresh cultures of human umbilical vein endothelial cells were established and used to seed Transwell chemotaxic chambers, and then grown to confluence. Whole blood was obtained from the same healthy volunteer and processed for light density mononuclear cells. Following per-stimulation of the endothelial monolayer with IL-1beta or antigen-antibody complex, known numbers of mononuclear cells were seeded to the endothelium. Incubation with and without exogenous L-arginine or L-NAME for 48 h was done. Lower chamber supernatant was then collected, cell numbers and viability determined and levels of inflammatory cytokines TNF-alpha and INF-lambda determined via ELISA assay.

RESULTS

Tran-endothelial cellular migration was nil lacking pre-stimulation, regardless of the addition of exogenous L-arginine. With pre-stimulation trans-endothelial migration increased significantly, a response that was greatly enhanced by L-arginine. With the further addition of L-NAME cellular migration decreased substantially. Pro-inflammatory cytokine levels of TNF-alpha and INF-lambda followed levels of cellular migration.

CONCLUSIONS

In vitro there was little to no trans-endothelial migration of inflammatory cells across an unstimulated monolayer of vascular endothelium. Pre-stimulation of the same endothelial monolayer with either a cytokine or antigen-antibody complex resulted in a significant trans-endothelial migration of inflammatory cells. This latter response was associated with a concurrent increase in the secretion of the pro-inflammatory cytokines TNF-alpha and INF-gamma. The presence of the NO precursor L-arginine greatly enhanced the observed inflammatory response. Conversely, L-NAME, an inhibitor of NOS, depressed the inflammatory response.

Hyperosmolar solution effects in guinea pig airways. III. Studies on the identity of epithelium-derived relaxing factor in isolated perfused trachea using pharmacological agents

Hyperosmolar challenge of airway epithelium stimulates the release of epithelium-derived relaxing factor (EpDRF), but the identity of EpDRF is not known. We examined the effects of pharmacological agents on relaxant responses of methacholine (3 x 10(-7) M)-contracted guinea pig perfused trachea to mucosal hyperosmolar challenge using D-mannitol. Responses were inhibited by gossypol (5 x 10(-6) M), an agent with diverse actions, by the carbon monoxide (CO) scavenger hemoglobin (10(-6) M), and by the heme oxygenase (HO) inhibitor zinc (II) protoporphyrin IX (10(-4) M). The HO inhibitor chromium (III) mesoporphyrin IX (10(-4) M) was not inhibitory, and the HO activator heme-L-lysinate (3 x 10(-4) M) did not evoke relaxant responses. The CO donor tricarbonyldichlororuthenium (II) dimer (2.2 x 10(-4) M) elicited small relaxation responses. Other agents without an effect on responses included: apyrase, adenosine, 6-anilino-5,8-quinolinequinone (LY83583), proadifen, (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), diphenhydramine, glibenclamide, HgCl2, tetrodotoxin, nystatin, alpha-hemolysin, 8-bromoguanosine 3',5'-cyclic monophosphothioate, Rp-isomer, 12-O-tetradecanoylphorbol-13-acetate, cholera toxin, pertussis toxin, thapsigargin, nifedipine, Ca(2+)-free mucosal solution, hydrocortisone, and epidermal growth factor. Cytoskeleton inhibitors, includingerythro-9-(2-hydroxyl-3-nonyl)adenine, colchicine, nocodazole, latrunculin B, and cytochalasins B and D, had no effect on relaxation responses. The results suggest provisionally that a portion of EpDRF activity may be due to CO and that the release of EpDRF does not involve cytoskeletal reorganization.

S-nitrosocaptopril: in vitro characterization of pulmonary vascular effects in rats

(1) On rat isolated pulmonary arteries, vasorelaxation by S-nitrosocaptopril (SNOcap) was compared with S-nitrosoglutathione (GSNO) and nitroprusside, and inhibition by SNOcap of contractions to angiotensin I was compared with the angiotensin converting enzyme (ACE) inhibitor, captopril. (2) SNOcap was equipotent as a vasorelaxant on main (i.d. 2-3 mm) and intralobar (i.d. 600 micro m) pulmonary arteries (pIC(50) values: 5.00 and 4.85, respectively). Vasorelaxant responses reached equilibrium rapidly (2-3 min). (3) Pulmonary vasorelaxant responses to SNOcap, like GSNO, were (i) partially inhibited by the soluble guanylate cyclase inhibitor, ODQ (1H-(1,2,4) oxadiazolo(4,3-a)-quinoxalin-1-one; 3 micro M) whereas responses to nitroprusside were abolished and (ii) potentiated by hydroxocobalamin (HCOB; NO. free radical scavenger; 100 micro M) whereas responses to nitroprusside were inhibited. (4) The relative potencies for pulmonary vasorelaxation compared with inhibition of platelet aggregation were: SNOcap 7 : 1; GSNO 25 : 1; nitroprusside >2000 : 1. (5) SNOcap, like captopril, concentration-dependently and time-dependently increased the EC(50) for angiotensin I but not angiotensin II. The dependence on incubation time was independent of the presence of tissue but differed for SNOcap and captopril. This difference reflected the slow dissociation of SNOcap and instability of captopril, and precluded a valid comparison of the potency of the two drugs. After prolonged incubation (>/=5.6 h) SNOcap was more effective than captopril. (6) Thus, in pulmonary arteries SNOcap (i) possesses NO donor properties characteristic of S-nitrosothiols but different from nitroprusside and (ii) inhibits ACE at least as effectively as captopril. These properties suggest that SNOcap could be valuable in the treatment of pulmonary hypertension.

Smooth muscle membrane potential modulates endothelium-dependent relaxation of rat basilar artery via myo-endothelial gap junctions

The release of endothelium-derived relaxing factors, such as nitric oxide (NO), is dependent on an increase in intracellular calcium levels ([Ca(2+)](i)) within endothelial cells. Endothelial cell membrane potential plays a critical role in the regulation of [Ca(2+)](i) in that calcium influx from the extracellular space is dependent on membrane hyperpolarization. In this study, the effect of inhibition of vascular smooth muscle delayed rectifier K(+) (K(DR)) channels by 4-aminopyridine (4-AP) on endothelium-dependent relaxation of rat basilar artery to acetylcholine (ACh) was assessed. ACh-evoked endothelium-dependent relaxations were inhibited by N-(Omega)-nitro-L-arginine (L-NNA) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), confirming a role for NO and guanylyl cyclase. 4-AP (300 microM) also suppressed ACh-induced relaxation, with the maximal response reduced from approximately 92 to approximately 33 % (n = 11; P < 0.01). However, relaxations in response to exogenous NO, applied in the form of authentic NO, sodium nitroprusside or diethylamineNONOate (DEANONOate), were not affected by 4-AP treatment (n = 3-11). These data are not consistent with the view that 4-AP-sensitive K(DR) channels are mediators of vascular hyperpolarization and relaxation in response to endothelium-derived NO. Inhibition of ACh-evoked relaxation by 4-AP was reversed by pinacidil (0.5-1 microM; n = 5) or 18beta-glycyrrhetinic acid (18betaGA; 5 microM; n = 5), indicating that depolarization and electrical coupling of the smooth muscle to the endothelium were involved. 4-AP caused depolarization of both endothelial and vascular smooth muscle cells of isolated segments of basilar artery (mean change 11 +/- 1 and 9 +/- 2 mV, respectively; n = 15). Significantly, 18betaGA almost completely prevented the depolarization of endothelial cells (n = 6), but not smooth muscle cells (n = 6) by 4-AP. ACh-induced hyperpolarization of endothelium and smooth muscle cells was also reduced by 4-AP, but this inhibition was not observed in the combined presence of 4-AP and 18betaGA. These data indicate that 4-AP can induce an indirect inhibition of endothelium-dependent relaxation in the rat basilar artery by electrical coupling of smooth muscle membrane depolarization to the endothelium via myo-endothelial gap junctions.

Inhibition of rat platelet aggregation by the diazeniumdiolate nitric oxide donor MAHMA NONOate

1. Inhibition of rat platelet aggregation by the nitric oxide (NO) donor MAHMA NONOate (Z-1-N-methyl-N-[6-(N-methylammoniohexyl)amino]diazen-1-ium-1,2-diolate) was investigated. The aims were to compare its anti-aggregatory effect with vasorelaxation, to determine the effects of the soluble guanylate cyclase inhibitor, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), and to investigate the possible role of activation of sarco-endoplasmic reticulum calcium-ATPase (SERCA), independent of soluble guanylate cyclase, using thapsigargin. 2 MAHMA NONOate concentration-dependently inhibited sub-maximal aggregation responses to collagen (2-10 micro g ml(-1)) and adenosine diphosphate (ADP; 2 micro M) in platelet rich plasma. It was (i). more effective at inhibiting aggregation induced by collagen than by ADP, and (ii). less potent at inhibiting platelet aggregation than relaxing rat pulmonary artery. 3. ODQ (10 micro M) caused only a small shift (approximately half a log unit) in the concentration-response curve to MAHMA NONOate irrespective of the aggregating agent. 4. The NO-independent activator of soluble guanylate cyclase, YC-1 (3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole; 1-100 micro M), did not inhibit aggregation. The cGMP analogue, 8-pCPT-cGMP (8-(4-chlorophenylthio)guanosine 3'5' cyclic monophosphate; 0.1-1 mM), caused minimal inhibition. 5. On collagen-aggregated platelets responses to MAHMA NONOate (ODQ 10 micro M present) were abolished by thapsigargin (200 nM). On ADP-aggregated platelets thapsigargin caused partial inhibition. 6. Results with S-nitrosoglutathione (GSNO) resembled those with MAHMA NONOate. Glyceryl trinitrate and sodium nitroprusside were poor inhibitors of aggregation. 7. Thus inhibition of rat platelet aggregation by MAHMA NONOate (like GSNO) is largely ODQ-resistant and, by implication, independent of soluble guanylate cyclase. A likely mechanism of inhibition is activation of SERCA.

P2Y(1) and P2Y(2) receptors are coupled to the NO/cGMP pathway to vasodilate the rat arterial mesenteric bed

1. To assess the role of nucleotide receptors in endothelial-smooth muscle signalling, changes in perfusion pressure of the rat arterial mesenteric bed, the luminal output of nitric oxide (NO) and guanosine 3',5' cyclic monophosphate (cGMP) accumulation were measured after the perfusion of nucleotides. 2. The rank order of potency of ATP and analogues in causing relaxation of precontracted mesenteries was: 2-MeSADP=2-MeSATP>ADP>ATP=UDP=UTP>adenosine. The vasodilatation was coupled to a concentration-dependent rise in NO and cGMP production. MRS 2179 selectively blocked the 2-MeSATP-induced vasodilatation, the NO surge and the cGMP accumulation, but not the UTP or ATP vasorelaxation. 3. mRNA encoding for P2Y(1), P2Y(2) and P2Y(6) receptors, but not the P2Y(4) receptor, was detected in intact mesenteries by RT-PCR. After endothelium removal, only P2Y(6) mRNA was found. 4. Endothelium removal or blockade of NO synthase obliterated the nucleotides-induced dilatation, the NO rise and cGMP accumulation. Furthermore, 2-MeSATP, ATP, UTP and UDP contracted endothelium-denuded mesenteries, revealing additional muscular P2Y and P2X receptors. 5. Blockade of soluble guanylyl cyclase reduced the 2-MeSATP and UTP-induced vasodilatation and the accumulation of cGMP without interfering with NO production. 6. Blockade of phosphodiesterases with IBMX increased 15-20 fold the 2-MeSATP and UTP-induced rise in cGMP; sildenafil only doubled the cGMP accumulation. A linear correlation between the rise in NO and cGMP was found. 7. Endothelial P2Y(1) and P2Y(2) receptors coupled to the NO/cGMP cascade suggest that extracellular nucleotides are involved in endothelial-smooth muscle signalling. Additional muscular P2Y and P2X receptors highlight the physiology of nucleotides in vascular regulation.

Pulmonary vasoconstriction by serotonin is inhibited by S-nitrosoglutathione

Nitric oxide (NO) functions as an endothelium-derived relaxing factor by activating guanylate cyclase to increase cGMP levels. However, NO and related species may also regulate vascular tone by cGMP-independent mechanisms. We hypothesized that naturally occurring NO donors could decrease the pulmonary vascular response to serotonin (5-HT) in the intact lung through chemical interactions with 5-HT(2) receptors. In isolated rabbit lung preparations and isolated pulmonary artery (PA) rings, 50-250 microM S-nitrosoglutathione (GSNO) inhibited the response to 0.01-10 microM 5-HT. The vasoconstrictor response to 5-HT was mediated by 5-HT(2) receptors in the lung, since it could be blocked completely by the selective inhibitor ketanserin (10 microM). GSNO inhibited the response to 5-HT by 77% in intact lung and 82% in PA rings. In PA rings, inhibition by GSNO could be reversed by treatment with the thiol reductant dithiothreitol (10 mM). 3-Morpholinosydnonimine (100-500 microM), which releases NO and O simultaneously, also blocked the response to 5-HT. Its chemical effects, however, were distinct from those of GSNO, because 5-HT-mediated vasoconstriction was not restored in isolated rings by dithiothreitol. In the intact lung, neither NO donor altered the vascular response to endothelin, which activates the same second-messenger vasoconstrictor system as 5-HT. These findings, which did not depend on guanylate cyclase, are consistent with chemical modification by NO of the 5-HT(2) G protein-coupled receptor system to inhibit vasoconstriction, possibly by S-nitrosylation of the receptor or a related protein. This study demonstrates that GSNO can regulate vascular tone in the intact lung by a reversible mechanism involving inhibition of the response to 5-HT.

Polyamine effects on human myometrial contractility

OBJECTIVE

This study was undertaken to investigate the effects of the polyamine spermine on human uterine contractility.

STUDY DESIGN

Under physiologic conditions, an isometric tension recording was performed in isolated myometrial strips from biopsy specimens obtained at elective cesarean delivery (n = 24 specimens) and from premenopausal hysterectomy specimens (n = 6 specimens). The effects of spermine (1 micromol/L-10 mmol/L in cumulative doses) on spontaneous, agonist-induced myometrial contractions were measured, and dose response curves were constructed. The pD(2) (-log EC(50)) values and the maximal inhibition values achieved were compared for spontaneous and agonist-induced contractions.

RESULTS

Spermine exerted a potent relaxant effect on all spontaneous and agonist-induced myometrial contractions, with mean maximal inhibition values between 62.8% +/- 4.3% and 91.4% +/- 1.8% and pD(2) values between 2.66 +/- 0.23 and 4.01 +/- 0.20. Its inhibitory effect varied significantly with different contraction types (pD(2), P <.05; mean maximal inhibition, P <.001), and it was least potent on BAY K 8644-elicited contractions (pD(2), P <.05; mean maximal inhibition, P <.01).

CONCLUSION

The polyamine spermine exerts a potent relaxant effect on human uterine tissue. This effect appears to be mediated, at least partially, by calcium antagonism. Polyamines may play a role in the maintenance of uterine quiescence during pregnancy.

Comparison of responses to novel nitric oxide donors in the feline pulmonary vascular bed

Pulmonary vascular responses to the novel diazeniumdiolate nitric oxide (NO) donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt, were investigated and compared in the intact-chest cat. Under conditions of controlled blood flow, when tone in the pulmonary vascular bed had been raised to a high steady level, intralobar injections of diethylamine/NO (0.3-10 microg), diethylenetriamine/NO (10-30 microg), spermine/NO (10-30 microg), sulfite/NO (10-30 microg), and angeli's salt (10-30 microg) caused dose-related decreases in lobar arterial pressure without changing left atrial pressure. In terms of relative vasodilator activity in the pulmonary vascular bed, the dose of the compounds that decreased lobar arterial pressure 4 mm Hg (ED(4) mm Hg) was significantly lower for diethylamine/NO compared to S-nitroso-N-acetylpenicillamine which was significantly less than diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt. The half-life of the vasodilator responses, as measured by 50% response recovery time, to diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt was similar for doses with similar magnitudes of vasodilation, while the half-life to S-nitroso-N-acetylpenicillamine was significantly less than the diazeniumdiolate NO donors. The present data demonstrate that the diazeniumdiolate NO donors diethylamine/NO, diethylenetriamine/NO, spermine/NO, sulfite/NO, and angeli's salt have potent but relatively short-lasting vasodilator activity in the pulmonary vascular bed of the cat.

Vascular smooth muscle relaxation mediated by nitric oxide donors: a comparison with acetylcholine, nitric oxide and nitroxyl ion

1. Vasorelaxant properties of three nitric oxide (NO) donor drugs (glyceryl trinitrate, sodium nitroprusside and spermine NONOate) in mouse aorta (phenylephrine pre-contracted) were compared with those of endothelium-derived NO (generated with acetylcholine), NO free radical (NO*; NO gas solution) and nitroxyl ion (NO(-); from Angeli's salt). 2. The soluble guanylate cyclase inhibitor, ODQ (1H-(1,2,4-)oxadiazolo(4,3-a)-quinoxalin-1-one; 0.3, 1 and 10 microM), concentration-dependently inhibited responses to all agents. 10 microM ODQ abolished responses to acetylcholine and glyceryl trinitrate, almost abolished responses to sodium nitroprusside but produced parallel shifts (to a higher concentration range; no depression in maxima) in the concentration-response curves for NO gas solution, Angeli's salt and spermine NONOate. 3. The NO* scavengers, carboxy-PTIO, (2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide; 100 microM) and hydroxocobalamin (100 microM), both inhibited responses to NO gas solution and to the three NO donor drugs, but not Angeli's salt. Hydroxocobalamin, but not carboxy-PTIO, also inhibited responses to acetylcholine. 4. The NO(-) inhibitor, L-cysteine (3 mM), inhibited responses to Angeli's salt, acetylcholine and the three NO donor drugs, but not NO gas solution. 5. The data suggest that, in mouse aorta, responses to all three NO donors involve (i) activation of soluble guanylate cyclase, but to differing degrees and (ii) generation of both NO* and NO(-). Glyceryl trinitrate and sodium nitroprusside, which generate NO following tissue bioactivation, have profiles resembling the profile of endothelium-derived NO more than that of exogenous NO. Spermine NONOate, which generates NO spontaneously outside the tissue, was the drug that most closely resembled (but was not identical to) exogenous NO.