Evidence that cyclic guanosine monophosphate (cGMP) mediates endothelium-dependent relaxation

The mechanism of action of endothelium-derived relaxant factor (EDRF) was studied using aortic strip preparations of the rabbit and a bioassay system of a rabbit coronary artery perfused in series with an intact aorta. Methylene blue (an inhibitor of guanylate cyclase) inhibited, and 2-O-propoxyphenyl-8-azapurine-6-one (MB22948, an inhibitor of cGMP phosphodiesterase) potentiated the vascular effects of EDRF whether these were due to its basal or to stimulated release. Infusion of these agents at different sites in the bioassay indicated that they act pharmacologically at the smooth muscle level and not on release of EDRF or by chemical interaction with EDRF. The data are consistent with the hypothesis that EDRF-induced relaxation is mediated by elevation of smooth muscle cGMP levels.     

Release of endothelial nitric oxide in coronary arteries by celiprolol, a beta(1)-adrenoceptor antagonist: possible clinical relevance

Mechanisms underlying celiprolol-induced vasodilatation were analyzed in isolated porcine coronary arteries. Celiprolol induced dose-related relaxation of the artery rings with endothelium, an effect which was suppressed by N(G)-nitro-L-arginine methylester (L-NAME), nitric oxide (NO) scavenger, guanylate cyclase inhibitor, endothelium denudation, and removal of Ca(2+). L-NAME contracted, and superoxide dismutase relaxed, the arteries only when the endothelium was preserved. Neither superoxide dismutase nor beta-adrenoceptor antagonists changed celiprolol-induced relaxations. Celiprolol increased the cyclic GMP content in the tissue. The release of NO from endothelium, estimated by the extracellular production of cyclic GMP in arteries incubated in medium containing guanylate cyclase and GTP, was augmented by celiprolol, and L-NAME abolished this action of celiprolol. It is concluded that celiprolol elicits relaxation by acting on sites other than beta-adrenoceptors in the endothelium and by releasing NO, which activates soluble guanylate cyclase in smooth muscle and produces cyclic GMP. Scavenging of superoxide anions from the endothelium does not seem to account for the induced relaxation.     

Developmental changes in the effect of atrial natriuretic peptide on tissue cyclic GMP content and particulate guanylate cyclase activity of aorta, kidney and lung of rats.

To investigate possible developmental changes in the physiological effect of atrial natriuretic peptide (ANP) after birth, we studied the effect of ANP on the slice cGMP content and the particulate guanylate cyclase activity of aorta, kidney and lung in neonate, 2-week-old and adult rats of both sexes. Incubation with human ANP(99-126) (hANP) increased significantly the slice cGMP content of aorta, kidney and lung in three ages of rats. The hANP-stimulated fraction of cGMP contents of kidney decreased, that of lung increased with development, whereas that of aorta showed no significant change. Consistently, the hANP-responsive particulate guanylate cyclase activity decreased in kidney, increased in lung during development, without significant developmental change in aorta. These results indicate a differential change in the effect of hANP on the slice cGMP content among tissues during development. The developmental change in the effect of hANP on slice cGMP content is probably caused by the ontogenetic change in activation of ANP receptor-linked guanylate cyclase.     

Role of cyclic AMP- and cyclic GMP-phosphodiesterases in the control of cyclic nucleotide levels and smooth muscle tone in rat isolated aorta. A study with selective inhibitors

Three isoforms of cyclic nucleotide phosphodiesterase (PDE) have been recently isolated from aortic tissue and two of them specifically hydrolyzed adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3':5'-cyclic monophosphate (cGMP), respectively (Lugnier et al., Biochem. Pharmac. 35, 1743, 1986). The role of these forms in controlling cyclic nucleotide levels and smooth muscle tone was investigated by the use of PDE inhibitors. The effects of selective inhibitors of the two forms specifically hydrolyzing cAMP or cGMP (cAMP-PDE and cGMP-PDE, respectively) were compared to those of non-selective inhibitors of the three aortic PDE forms, including the calmodulin-sensitive one (CaM-PDE). Relaxation responses and accumulation of tissue cAMP and cGMP induced by these drugs were studied in precontracted rat isolated aorta, and compared to the effects of isoprenaline and forskolin (stimulants of adenylate cyclase) or sodium nitroprusside (SNP) and sodium azide (stimulants of guanylate cyclase). The eight PDE inhibitors tested all relaxed aorta with potencies that correlated with their potencies as inhibitors of cAMP-PDE, but not of cGMP-PDE. At a concentration producing half-maximal relaxation, all PDE inhibitors induced a moderate but significant accumulation of cAMP, which was comparable to the accumulation of cAMP elicited by half-maximally relaxing concentrations of adenylate cyclase stimulating agents. At this concentration, some PDE inhibitors (M&B 22,948, dipyridamole and to a lesser extent, trequinsin) also induced a significant increase in cGMP levels, of the same order of magnitude as that caused by agents stimulating guanylate cyclase. However, the cGMP-increasing effect of these inhibitors was dissociated from their relaxing effect. In particular, the relaxing concentrations of M&B 22,948 (a selective inhibitor of cGMP-PDE) were clearly higher than the cGMP-increasing concentrations of the compound. At a concentration at which they elicited 10% relaxation by themselves, the selective cAMP-PDE inhibitor, rolipram, as well as the mixed inhibitor of cAMP- and cGMP-PDE, AAL 05 (a cilostamide analogue) enhanced both the cAMP-increasing and the relaxing effect of isoprenaline. Under the same conditions, no clear enhancement of the relaxation induced by SNP was observed. Only M&B 22,948 showed a slight potentiating effect on SNP-induced relaxation, but this effect was limited to low concentrations of SNP (less than 10 nM).(ABSTRACT TRUNCATED AT 400 WORDS)     

Age-associated decrease in histamine-induced vasodilation may be due to reduction of cyclic GMP formation.

1. The effects of aging on histamine-induced vasodilatation and cyclic GMP production in rat thoracic aorta were investigated. 2. This histamine-induced dilatation of the aorta was mediated by H1-receptors and was dependent on the endothelium. 3. Histamine induced the greatest dilatation of arteries of 3-4 week old rats, progressively less of those of rats of 8 to 56 weeks old, and scarcely detectable dilatation of those of 100 week old rats. 4. Histamine induced cyclic GMP production in aorta from rats of 4 weeks old, with no change in the cyclic AMP level. This increase in the cyclic GMP level induced by histamine also decreased with age, being about 70% as great at 8 weeks, 50% as great at 50-60 weeks, and 10% as great at 130 weeks of age. 5. Removal of the endothelium completely abolished the histamine-induced increase in cyclic GMP. 6. The dilator effect of nitroprusside, which enhances cyclic GMP production by stimulating guanylate cyclase directly (not indirectly via the endothelium derived relaxing factor, EDRF), also showed age-related attenuation. 7. The dilator effect of 8-bromo cyclic GMP, which stimulates cyclic GMP-dependent protein kinase, also decreased during aging. 8. These results suggest that aging reduces the ability of the endothelium to produce EDRF, which stimulates guanylate cyclase, and so decreases cyclic GMP production. Thus the decreased dilator response of the arteries to histamine during aging is probably due to both loss of endothelial function and reduction of guanylate cyclase activity. Alteration of cyclic GMP-dependent protein kinase activity may also participate in the age-related changes.     

The effect of tributyltin chloride on vascular responses to atrial natriuretic peptide.

The effects of tributylin chloride (TBT) on vascular smooth muscle responses to norepinephrine, nitroprusside (SNP) and atrial natriuretic peptide (ANP) were studied in isolated aortic rings of rats. TBT did not interfere with norepinephrine-induced contraction or SNP-induced vasorelaxation. However, TBT produced a dose-dependent inhibition of ANP-induced vasorelaxation. Inhibition was not observed with inorganic tin chloride, SnCl2. The inhibition of vasorelaxation was accompanied by a parallel inhibition of ANP-induced cGMP generation. SNP-induced generation of cGMP was not affected by TBT. TBT did not interfere with binding of ANP to its receptor in bovine adrenal glands suggesting that the effects of TBT were mediated by direct interaction with membrane-bound guanylate cyclase.     

Comparative study of the inhibitory effects of adrenomedullin on angiotensin II contraction in rat conductance and resistance arteries.

Adrenomedullin (ADM), a ubiquitous vasoactive peptide, has been the target of a multitude of studies concerning its effect on the vascular tone. The present work aims at clarifying a series of its interactions with the renin-angiotensin system. The study uses the rat aorta ring as a model of conductance vessels, with or without vascular endothelium, and the second order branch of rat mesenteric arteries as a model of resistance arteries. Interactions between various concentrations of ADM and angiotensin II (Ang II) were studied, in the presence of L-NAME (a nitric oxide [NO] synthase inhibitor) and methylene blue (MB; a soluble guanylate cyclase inhibitor). Results point out differences in the mechanism of the inhibitory action of ADM upon Ang II effects in the two vessel types studied. Inhibition of Ang II contraction by ADM involves guanylate cyclase in both cases. However, NO is involved in ADM-induced inhibition of angiotensinergic vasoconstriction only in the conductance arteries, not in the resistance ones.     

Role of endothelium in the contractions induced by norepinephrine and clonidine in rat aorta

The inhibitory effects of endothelium-derived relaxing factor (EDRF) on the contractions induced by norepinephrine and clonidine in rat aorta were examined. Carbachol induced a relaxation of norepinephrine-induced contraction in rat aorta with endothelium. Removal of endothelium inhibited the carbachol-induced relaxation and increased the magnitude of norepinephrine-induced contraction. Quinacrine, a phospholipase A2 inhibitor, methylene blue, a guanylate cyclase inhibitor and tetraethylammonium, a potassium permeability inhibitor, inhibited carbachol-induced relaxation and augmented the magnitude of norepinephrine-induced contraction only when endothelium was present. Clonidine induced a contraction when endothelium was removed or muscle was treated with methylene blue. The contractions induced by norepinephrine and clonidine were equally sensitive to prazosin and equally less sensitive to yohimbine. Clonidine inhibited the norepinephrine-induced contraction, whereas it potentiated the angiotensin 11- or 12 mM K-induced contractions in the aorta with endothelium. The inhibitory effect of clonidine on the norepinephrine-induced contraction was reduced by endothelium-removal and by methylene blue but not by yohimbine. These results suggest that norepinephrine has a strong direct stimulating action and clonidine has a weak one on vascular smooth muscle cells possibly mediated by alpha 1-adrenoceptors, and their contractile effects are inhibited by the spontaneously released EDRF.     

Modification by LY 83583 and methylene blue of relaxation induced by nitric oxide,glyceryl trinitrate,sodium nitroprusside and atriopeptin in aortae of the rat,guinea-pig and rabbit

• 1.1. The relaxation by nitroglycerin (GTN) and nitric oxide (NO) of aortic smooth muscles from rabbit and rat contracted by phenylephrine was inhibited by LY 83583 (LY) and methylene blue (MB) (the same applied to guinea-pig aorta), while the relaxation by SNP was not inhibited in rabbit. The relaxation by ANP was not inhibited.
• 2.2. All these agents produced concentration-dependent increases in cyclic GMP. While the increases by GTN and NO were inhibited by LY and MB, the increases by SNP were inhibited only in rat and those by ANP were not inhibited.
• 3.3. Thus, LY behaved essentially similar to MB, indicating that the substance is an inhibitor of activation of soluble guanylate cyclase by NO and NO-related vasodilators. It was assumed that, like MB, LY facilitated intracellular release of NO from SNP in rabbit.

     

Effect of calcium on endothelium-derived relaxing factor formation and cGMP levels in endothelial cells

Various stimulants of the release of EDRF (endothelium-derived relaxing factor) increased intracellular cGMP levels in bovine aortic endothelial cells. ATP was the most effective compound tested, increasing cGMP 7-fold, followed by the calcium ionophore, A23187 (4.8-fold), and bradykinin (4.0-fold). The EC₅₀ values were similar to those obtained when EDRF release was measured with the bioassay technique, which suggests a stimulation of endothelial guanylate cyclase by EDRF. The direct acting stimulants of soluble guanylate cyclase, sodium nitroprusside and SIN-1 (3-morpholino-sydnonimine), also increased the cGMP content of endothelial cells by 9.4 and 7.2 times, respectively. The effects of both groups of stimulants of cGMP levels were antagonized by the lipoxygenase inhibitor, nordihydroguaiaretic acid, and by the radical scavenger, phenylbutylnitrone, whereas gossypol or canavanine only antagonized the EDRF-induced effect on endothelial cGMP levels. Bradykinin, ATP and A23187 also increased the uptake of ⁴⁵CaCl₂ into endothelial cells but since the complete removal of extracellular Ca²⁺ or blockade of Ca²⁺ transport by LaCl₃ did not affect the ability of these compounds to elevate cGMP levels, the formation of EDRF appears not to be triggered by an influx of extracellular calcium. This study provides evidence that EDRF stimulators enhance cGMP levels in endothelial cells, probably due to a direct activation of guanylate cyclase by EDRF.     

High salt diet modulates cAMP- and nitric oxide-mediated relaxation responses to isoproterenol in the rat aorta

This study tested the hypothesis that nitric oxide (NO) production contributes to relaxation induced by 3',5'-cyclic adenylate monophosphate (cAMP)-elevating agents and that high salt diet impairs this mechanism of relaxation. Relaxation response to isoproterenol but not sodium nitroprusside, a NO donor, was reduced in the thoracic aorta from rats that were placed on a high salt diet (8% NaCl; 60+/-4%, P<0.001). 1H-[1,2,4]oxadiazolol [4,3,-alpha]quinoxalin-1-one (ODQ, 10 microM), a soluble guanylate cyclase inhibitor, but not N(omega)-nitro-L-arginine methyl ester (L-NAME, 100 microM), an inhibitor of NO synthase (NOS), attenuated the relaxation to isoproterenol (59+/-16%, P<0.01). High salt diet also impaired the relaxation responses to forskolin, an activator of adenylate cyclase, or 8-Bromo-cAMP (8-Br-cAMP). (N-[2-((p-bromocinnamyl)aminoethyl]-5-isoquinolinesulfonamide hydrochloride (H-89) (8 microM), an inhibitor of cAMP-dependent protein kinase, did not affect the relaxation produced by isoproterenol. These data suggest that high salt diet impairs relaxation response to isoproterenol by a dual mechanism involving diminished NO/NOS pathway linked to cGMP pathway and diminished cAMP pathway that is independent of protein kinase A.     

Simultaneous measurement of endothelium-derived relaxing factor by bioassay and guanylate cyclase stimulation.

1. Endothelium-derived relaxing factor (EDRF) released by cultured endothelial cells (EC) from bovine aortae was measured by bioassay using pre-contracted strips of rabbit aorta and by radioimmunoassay of guanosine 3':5'-cyclic monophosphate (cyclic GMP) produced by stimulation of bovine lung soluble guanylate cyclase. 2. Bradykinin (Bk, 3 and 30 pmol) injected through a column of EC caused release of EDRF as detected by bioassay and increased cyclic GMP concentrations. Superoxide dismutase (SOD, 15 u ml-1) increased the amount of EDRF detected by the activation of soluble guanylate cyclase. 3. In the absence of endothelial cells, nitric oxide (NO, 1-2 microM), arachidonic acid (AA, 3-30 microM) or sodium nitroprusside (SNP, 1-100 microM) stimulated guanylate cyclase. Superoxide dismutase strongly increased the stimulation of guanylate cyclase induced by NO, but had little effect on the stimulation induced by SNP and no effect on the stimulation induced by AA. 4. Oxyhaemoglobin (10-300 microM) abolished the stimulation of guanylate cyclase by EDRF, NO or SNP but was much less effective as an inhibitor of AA-induced stimulation of guanylate cyclase. 5. These results demonstrate that measurement of guanylate cyclase stimulation by radioimmunoassay is a viable method for detecting EDRF release, especially useful when the drugs used interfere with bioassay tissues.     

Atrial natriuretic peptide antagonists: biological evaluation and structural correlations

A collection of analogues of atrial natriuretic peptide (ANP) were screened for their ability to inhibit ANP-induced cGMP stimulation. The antagonists revealed through this screen are structurally related; almost all are substituted at either aspartate-13 or phenylalanine-26. This tendency is consistent throughout several families of small ANP analogues, suggesting that these two amino acid residues are involved in the process of ANP/cGMP signal transduction. One compound, A74186, was studied in some detail. A74186 is a potent inhibitor of the activation of guanylate cyclase by ANP; it acts with a pA2 of 7.12 in rat vascular smooth muscle cells and shifts the ANP/cGMP dose-response curve by 3 orders of magnitude at a 10 microM concentration. It also inhibits cGMP release in vivo, and at an infusion rate of 10 micrograms/kg-min it completely abolishes ANP-induced natriuresis and diuresis. A74186 does not, however, antagonize the hypotensive or vasorelaxant effects of ANP; in fact it acts as an agonist in these assays. It thus appears that cGMP, although it may mediate the renal responses to ANP, is not responsible for the vascular and hemodynamic effects that result from the action of the hormone.     

Vas deferens smooth muscle responses to the nitric oxide-independent soluble guanylate cyclase stimulator BAY 41-2272

The nitric oxide-cGMP signaling pathway modulates the ejaculatory functions. The nitric oxide (NO)-independent soluble guanylate cyclase haem-dependent stimulator BAY 41-2272 potently relaxes different types of smooth muscles. However, no study investigated its effects in vas deferens smooth muscle. Therefore, we designed experiments to evaluate the in vitro relaxing responses of vas deferens to BAY 41-2272. The effects of prolonged oral intake with BAY 41-2272 in vas deferens contractions of rats treated chronically with the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) were also investigated. BAY 41-2272 (0.001-100 μM) produced concentration-dependent relaxations in the prostatic and epididymal portions of vas deferens, an effect markedly reduced by the soluble guanylate cyclase inhibitor ODQ (100 μM). BAY 41-2272 significantly increased cGMP levels that were fully prevented by ODQ. In separate protocols, rats received L-NAME (20mg/rat/day) concomitantly with BAY 41-2272 (10mg/kg/day, 4 weeks), after which vas deferens contractions to electrical-field stimulation and noradrenaline were achieved. Electrical-field stimulation (1-32 Hz) evoked frequency-dependent contractions that were significantly enhanced in L-NAME-treated rats. Co-treatment with BAY 41-2272 fully reversed the increased contractile responses in L-NAME group. Noradrenaline (0.01-100 μM)-induced contractions were also greater in L-NAME-treated rats, and that was normalized by BAY 41-2272. In conclusion, BAY 41-2272 potently relaxes in vitro rat vas deferens smooth muscle and elevates the cGMP levels in an ODQ-sensitive manner. Moreover, prolonged oral intake with BAY 41-2272 restores the enhanced contractile vas deferens activity in rats treated with L-NAME. NO-independent soluble guanylate cyclase stimulators may be an alternative treatment for premature ejaculation.     

Involvement of nitric oxide pathway in the PAF-induced relaxation of rat thoracic aorta.

1. The mechanism of the vasorelaxant effect of platelet activating factor (PAF) on rat thoracic aorta and the effect of aging on the PAF-induced relaxation were investigated. 2. PAF at concentrations causing relaxation induced marked increases in guanosine 3':5'-cyclic monophosphate (cyclic GMP) production, but did not induce an increase in adenosine 3':5'-cyclic monophosphate (cyclic AMP). 3. Removal of the endothelium by mechanical rubbing, and treatment with the PAF antagonists CV-3988, CV-6209 and FR-900452, the nitric oxide biosynthesis inhibitor, NG-nitro L-arginine, the radical scavenger, haemoglobin, and the soluble guanylate cyclase inhibitor, methylene blue, inhibited PAF-induced relaxation and abolished or attenuated PAF-stimulated cyclic GMP production. 4. The relaxation was greatest in arteries from rats aged 4 weeks. With an increase in age, the response of the arteries to PAF was attenuated. 5. Endothelium-dependent cyclic GMP production also decreased with increase in age of the rats. 6. These results suggest that PAF stimulates production of nitric oxide from L-arginine by acting on the PAF receptors in the endothelium, which in turn stimulates soluble guanylate cyclase in the smooth muscle cells, and so increases production of cyclic GMP, thus relaxing the arteries. Age-associated decrease in PAF-induced relaxation may result from a reduction of cyclic GMP formation.     

Endothelin-3-induced relaxation of rat thoracic aorta: a role for nitric oxide formation.

1. Endothelin-3 (ET-3) at concentrations below those which caused contraction (30 nM) elicited endothelium-dependent relaxation followed by rebound contraction in rat isolated thoracic aorta. 2. Endothelin-1 also relaxed the rat aorta with a similar potency. 3. The nitric oxide (NO) synthase inhibitor, NG-nitro L-arginine, the radical scavenger, haemoglobin and the soluble guanylate cyclase inhibitor, methylene blue, each inhibited the ET-3-induced relaxation. 4. The calmodulin inhibitor, calmidazolium, considerably attenuated the relaxation caused by ET-3 without affecting that to nitroprusside. 5. Concentrations of ET-3 that were necessary to induce the relaxation also caused concentration-dependent elevation of guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels. 6. NG-nitro L-arginine, haemoglobin, methylene blue, calmidazolium and removal of the endothelium completely abolished ET-3-stimulated cyclic GMP production. 7. These results suggest that ET-3 triggers NO formation possibly via ETB receptors on the endothelium to activate soluble guanylate cyclase, which in turn stimulates cyclic GMP production and smooth muscle relaxation. The enzyme contributing to the NO formation may be of the calcium/calmodulin-dependent, constitutive type.     

Nitric oxide-dependent reduction in soluble guanylate cyclase functionality accounts for early lipopolysaccharide-induced changes in vascular reactivity

We investigated the role of soluble guanylate cyclase in lipopolysaccharide-induced hyporesponsiveness to phenylephrine. The effects of phenylephrine on the blood pressure of female Wistar rats were evaluated at 2, 8, and 24 h after lipopolysaccharide injection (12.5 mg/kg i.p.). Vasoconstrictive responses to phenylephrine were reduced 40 to 50% in all time periods. Methylene blue, a soluble guanylate cyclase inhibitor (15 micromol/kg i.v.) restored the reactivity to phenylephrine in animals injected with lipopolysaccharide 2 and 24 h earlier. However, it failed to do so in animals injected with lipopolysaccharide 8 h earlier. Incubation with sodium nitroprusside (SNP) increased lung and aorta cGMP levels in control animals and in tissues of rats treated with lipopolysaccharide 24 h earlier. However, SNP failed to increase tissue cGMP in rats injected 8 h earlier. Lipopolysaccharide reduced the vasodilatory response to NO donors 8 h after injection. This effect and the decreased lung cGMP accumulation in response to SNP were reversed by an NO synthase blocker. Guanylate cyclase protein levels were lower than controls in lungs harvested from rats injected 8 h earlier and were back to normal values in lungs of rats injected 24 h earlier with lipopolysaccharide. Thus, data indicate that there is a temporal window of 8 h after lipopolysaccharide injection in which soluble guanylate cyclase is not functional and that this loss of function is NO-dependent. Thus, the putative use of soluble guanylate cyclase inhibitors in the treatment of endotoxemia may be beneficial mainly at early stages of this condition.     

Action of atrial natriuretic peptide (ANP) on dog cerebral arteries: evidence that neurogenic relaxation is not mediated by release of ANP.

1. Atrial natriuretic peptide (ANP) (10(-9) to 10(-8) M) produced a concentration-related relaxation in helical strips of dog cerebral arteries partially contracted with prostaglandin F2 alpha. The relaxation was not affected by treatment with ouabain, quinidine, oxyhaemoglobin, methylene blue, or removal of endothelium. 2. Relaxations induced by nicotine or transmural electrical stimulation were not reduced in arteries in which tachyphylaxis to ANP had developed. 3. In arteries exposed to Ca2+-free media under severe hypoxia, contractions due to prostaglandin F2 alpha and Ca2+ were attenuated by treatment with ANP, whereas the reoxygenation-induced contraction was unaffected. 4. The results suggest that ANP does not mediate neurogenic relaxation of dog cerebral arteries. The ANP-induced relaxation is not associated with activation of the sodium pump but is due to an inhibitory action on the release and influx of Ca2+, probably as a result of stimulation of guanylate cyclase.     

Urocortin舒张自发性高血压大鼠胸主动脉与NO和K~+通道的关系

目的探讨Urocortin(Ucn)对自发性高血压大鼠(SHR)胸主动脉舒缩功能的作用及机制。方法采用体外血管灌流,观察Ucn对SHR胸主动脉的舒张作用,以及左旋硝基精氨酸甲酯(N(ω)n itro-L-argin ine methyl ester,L-NAME)、亚甲蓝(M ethylene B lue,MB)和格列本脲(G lybenc lam ide)对其舒张作用的影响。结果Ucn(1 nmol.L-1~1μmol.L-1)可明显舒张内皮完整和去内皮SHR胸主动脉(P<0.01),此作用具有剂量依赖性;一氧化氮(NO)合成酶抑制剂L-NAME(100μmol.L-1)和鸟苷酸环化酶(GC)抑制剂MB部分抑制Ucn舒张血管的作用,而且增强去甲肾上腺素(NE)产生的收缩反应。ATP敏感钾通道(KATP)阻断剂格列本脲(10μmol.L-1)可减弱Ucn的舒血管作用。结论Ucn对SHR血管具有内皮依赖性和非内皮依赖性舒张作用,此作用部分是Ucn增加血管内皮细胞NO水平实现的,并且与NO-cGMP通路和KATP通道有关。     

Effects of hydrazine derivatives on vascular smooth muscle contractility,blood pressure and cGMP production in rats: comparison with hydralazine

Hydralazine is a hydrazine derivative used clinically as a vasodilator and antihypertensive agent. Despite numerous studies with the drug, its mechanism of action has remained unknown; guanylate cyclase activation and release of endothelial relaxing factors are thought to be involved in its vasodilator effect. Other hydrazine derivatives are known to stimulate guanylate cyclase and could therefore share the vasodilator activity of hydralazine, although such possibility has not been assessed systematically. In the present study, hydralazine, hydrazine, phenylhydrazine, and isoniazid were evaluated for vascular smooth muscle relaxation in rat aortic rings with and without endothelium, as well as after incubation with the guanylate cyclase inhibitor methylene blue. They were also tested for enhancement of cyclic guanosine monophosphate (cGMP) production by cultured rat aortic smooth muscle cells and for hypotension in the anesthetized rat. All hydrazines relaxed aortic rings, an action unaffected by endothelium removal and, in all cases except hydralazine, antagonized by methylene blue. Only phenylhydrazine increased cGMP production and only hydralazine markedly lowered blood pressure. It was concluded that hydralazine vascular relaxation is independent of endothelium and is not related to guanylate cyclase activation. The other hydrazines studied also elicit endothelium-independent relaxation, but the effect is related to guanylate cyclase. The marked hypotensive effect of hydralazine contrasts with its modest relaxant activity and is not shared by the other hydrazines. The fact that hydrazine and isoniazid produce methylene blue-sensitive relaxation, yet do not enhance cGMP production suggests the need for activating factors present in aortic rings but not in isolated cells.