Proton pump inhibitors omeprazole, lansoprazole and pantoprazole induce relaxation in the rat lower oesophageal sphincter

Objectives We aimed to investigate effects of the proton pump inhibitors (PPIs) omeprazole, lansoprazole and pantoprazole, which are currently used for the treatment of hyperacidity and gastro‐oesophageal reflux, on the reactivity of the isolated rat lower oesophageal sphincter. Methods Omeprazole, lansoprazole and pantoprazole (all 10^–9–10^–3m , cumulatively) were tested on carbachol‐induced (10^–6m ) contraction. In addition, the effects of PPI preincubation (all 10^–3m ) on the contractions induced by cumulative carbachol (10^?9–10^?5m ), angiotensin‐2 (10^?9–10^–5m ) or electrical field stimulation (EFS; 40 V, 32 Hz, 1 ms, 10 s) were assessed. Finally, the effects of PPI on the spontaneous contractile activity of the tissue were also evaluated. Key findings PPI relaxed precontracted lower oesophageal sphincter in a concentration‐dependent manner and suppressed carbachol‐, angiotensin‐ and EFS‐induced contractions. Furthermore, PPI attenuated spontaneous contractile activity of the tissue. Conclusions Omeprazole, lansoprazole and pantoprazole had a suppressor effect on lower oesophageal sphincter contractions.     

Myogenic nitric oxide synthase activity in canine lower oesophageal sphincter: morphological and functional evidence

1. Studies on canine lower oesophageal sphincter (LOS) evaluated the existence and function of a myogenic, nitric oxide synthase (NOS) by use of immunocytochemistry for NOS isozymes, NADPH-d histochemistry, [³H]-L-arginine to [³H]-L-citrulline transformation. In addition, functional studies in the muscle bath were performed.
2. Smooth muscle bundles or freshly isolated smooth muscle cells of LOS were NADPH-d reactive but did not recognize some antibodies against neural, endothelial or inducible NOS. NADPH-d reactivity and immunoreactivity to a neural NOS antibody were colocalized in LOS enteric nerves. Muscle plasma membrane-enriched fractions from fresh and cultured LOS cells converted [³H]-L-arginine to [³H]-L-citrulline; activity was mostly Ca²⁺/calmodulin-dependent.
3. N-Nitro-L-arginine (L-NOARG) persistently increased tone (blocked by L-arginine) in muscle strips despite blockade of nerve function. Nifedipine prevented or abolished L-NOARG-induced, but not carbachol-induced, contraction showing that tone increase by L-NOARG required functional L-Ca channels.
4. Membrane-bound, myogenic NOS in canine LOS may release NO continuously when Ca²⁺ entry through L-Ca channels occurs under physiological conditions and thereby modulate tone in LOS.

     

Effect of propranolol on the lower oesophageal sphincter in man

Summary

The effect of an intravenous dose (2?mg) of propranolol on the lower oesophageal sphincter was studied in 10 human volunteers. A hydraulic-capillary infusion manometric technique was used to measure the lower oesophageal sphincter pressure. A significant increase in sphincter pressure was recorded, together with increased amplitude and duration of oesophageal peristaltic activity. This study confirms the presence of specific beta-receptors in the lower oesophageal sphincter.     

Regulation of basal tone, relaxation and contraction of the lower oesophageal sphincter. Relevance to drug discovery for oesophageal disorders

The lower oesophageal sphincter (LOS) is a specialized region of the oesophageal circular smooth muscle that allows the passage of a swallowed bolus to the stomach and prevents the reflux of gastric contents into the oesophagus. The anatomical arrangement of the LOS includes semicircular clasp fibres adjacent to the lesser gastric curvature and sling fibres following the greater gastric curvature. Such anatomical arrangement together with an asymmetric intrinsic innervation and distinct proportion of neurotransmitters in both regions produces an asymmetric pressure profile. The LOS tone is myogenic in origin and depends on smooth muscle properties that lead to opening of L-type Ca(2+) channels; however it can be modulated by enteric motor neurons, the parasympathetic and sympathetic extrinsic nervous system and several neurohumoral substances. Nitric oxide synthesized by neuronal NOS is the main inhibitory neurotransmitter involved in LOS relaxation. Different putative neurotransmitters have been proposed to play a role together with NO. So far, only ATP or related purines have shown to be co-transmitters with NO. Acetylcholine and tachykinins are involved in the LOS contraction acting through acetylcholine M(3) and tachykinin NK(2) receptors. Nitric oxide can also be involved in the regulation of LOS contraction. The understanding of the mechanisms that originate and modulate LOS tone, relaxation and contraction and the characterization of neurotransmitters and receptors involved in LOS function are important to develop new pharmacological tools to treat primary oesophageal motor disorders and gastro-oesophageal reflux disease.     

Effects of various prostaglandin synthesis inhibitors on the tone of the lower oesophageal sphincter in man

Summary The role of endogenous prostaglandins in the modulation of lower oesophageal sphincter (LES) function has been assessed by giving three structurally unrelated cyclooxygenase inhibitors and monitoring their acute effects on LES tonus and platelet thromboxane (TX) B₂ production in 20 healthy volunteers. In a double-blind, placebo-controlled, cross-over study, IV injection of soluble salts of acetylsalicylic acid and indomethacin elicited a transient increase in LES tonus of approximately 50% over baseline. A similar pattern was observed after the rectal administration of indomethacin. In contrast, indoprofen had no measurable effect on LES tones, despite comparable inhibition of platelet cyclooxygenase activity. This may have been due to the markedly different tissue distribution of the drug. The results suggest that endogenous prostaglandins physiologically exert an inhibitory influence on LES function.     

肠易激综合征患者血清血管活性肠肽,一氧化氮浓度变化及意义

目的：探讨血管活性肠肽（ＶＩＰ）和一氧化氮（ＮＯ）在肠易激综合征（ＩＢＳ）发病中的变化及意义，方法：分别采用酶标法和放射免疫分析法对３２例ＩＢＳ（便秘型１２型，腹泻型２０例）和１６例健康对照者血浆ＶＩＰ和ＮＯ浓度进行测定，观察正常时和不同类型的ＩＢＳ患者血ＶＩＰ和ＮＯ水平的变化。结果：ＩＢＳ组血ＮＯ水平较健康对照组显著增高（Ｐ〈０．０５），且以便秘型ＩＢＳ增调理我明显（Ｐ〈０．０１），ＶＩＰ水平在     

Effect of hydrogen peroxide on VIP-induced relaxation of the cat lower esophageal sphincter

We investigated the effects of hydrogen peroxide (H2O2) on relaxation of the cat lower esophageal sphincter (LES). Vasoactive intestinal peptide (VIP) caused dose-dependent relaxation of LES, and H2O2 reduced VIP-induced relaxation. Relaxation was also attenuated by pertussis toxin (PTX), indicating a Gi/o component. VIP treatment increased [35S]GTPgammaS binding to Gs and Gi3 protein, but not to Go, Gq, Gil or Gi2. This increase in Gs or Gi3 binding was reduced by H2O2. However, the relaxation induced by sodium nitroprusside (SNP), 3-morpholino sydnomine (SIN-1), 8-br cGMP (cGMP analog), forskolin (adenylate cyclase activator), and dibutyryl-cAMP (a stable cAMP analog) was not reduced by H2O2. These data suggest that H202 inhibits VIP-induced relaxation via a Gi-dependent pathway, perhaps by inhibiting the activation of G(i3) or Gs downstream of the VIP receptor and independent of cAMP or NO-cGMP signaling.     

Different in vitro and in vivo profiles of substituted 3-aminopropylphosphinate and 3-aminopropyl(methyl)phosphinate GABA(B) receptor agonists as inhibitors of transient lower oesophageal sphincter relaxation

BACKGROUND AND PURPOSE

Gastro-oesophageal reflux is predominantly caused by transient lower oesophageal sphincter relaxation (TLOSR) and GABA_B receptor stimulation inhibits TLOSR. Lesogaberan produces fewer CNS side effects than baclofen, which has been attributed to its affinity for the GABA transporter (GAT), the action of which limits stimulation of central GABA_B receptors. To understand the structure–activity relationship for analogues of lesogaberan (3-aminopropylphosphinic acids), and corresponding 3-aminopropyl(methyl)phosphinic acids, we have compared representatives of these classes in different in vitro and in vivo models.

EXPERIMENTAL APPROACH

The compounds were characterized in terms of GABA_B agonism in vitro. Binding to GATs and cellular uptake was done using rat brain membranes and slices respectively. TLOSR was measured in dogs, and CNS side effects were evaluated as hypothermia in mice and rats.

KEY RESULTS

3-Aminopropylphosphinic acids inhibited TLOSR with a superior therapeutic index compared to 3-aminopropyl(methyl)phosphinic acids. This difference was most likely due to differential GAT-mediated uptake into brain cells of the former but not latter. In agreement, 3-aminopropyl(methyl)phosphinic acids were much more potent in producing hypothermia in rats even when administered i.c.v.

CONCLUSIONS AND IMPLICATIONS

An enhanced therapeutic window for 3-aminopropylphosphinic acids compared with 3-aminopropyl(methyl)phosphinic acids with respect to inhibition of TLOSR was observed and is probably mechanistically linked to neural cell uptake of the former but not latter group of compounds. These findings offer a platform for discovery of new GABA_B receptor agonists for the treatment of reflux disease and other conditions where selective peripheral GABA_B receptor agonism may afford therapeutic effects.     

Inhibitory effect of hypochlorous acid on lower esophageal sphincter tone relaxation by vasoactive intestinal peptide

Under physiological conditions, hypochlorous acid (HOCl) is the major product of myeloperoxidase, a ferric heme enzyme released in inflammatory diseases. In the present study, we investigated the effect of HOCl compared to hydrogen peroxide (H₂O₂) on the vasoactive intestinal polypeptide (VIP)-induced relaxation of feline lower esophageal sphincter (LES) strips. Isometric tension on LES strips was measured using a force transducer. VIP induced the relaxation of basal LES tone in a concentration-dependent manner. Pretreatment with HOCl (10⁻⁴ M) significantly reduced the VIP-induced relaxation at smaller concentrations than H₂O₂ (10⁻³ M). VIP-induced relaxation is mediated via the Gi/o protein, since pretreatment with Pertussis Toxin (PTX) showed an inhibitory effect on the relaxation. HOCl showed an additional inhibitory effect on the reduced relaxation by PTX, indicating that HOCl might affect another G protein as well as Gi/o. However, HOCl did not affect SNP-, SIN-1-, and 8-br-cGMP-induced relaxation. Nor did HOCl modify the relaxation induced by either forskolin or db-cAMP in LES muscle strips. These results suggest that during short-term treatment, HOCl may damage the upstream events including G protein level, and result in alteration of LES tone in the feline esophagus, similar to the inhibitory effects of H₂O₂..     

The role of the L-arginine-nitric oxide pathway in relaxation of the opossum lower oesophageal sphincter.

1. The role of the L-arginine-nitric oxide pathway in lower oesophageal sphincter (LOS) relaxation and oesophageal peristalsis was investigated. 2. Twenty four adult opossums were anaesthetized and the right vagus nerve was isolated in the neck and sectioned. Electrical stimulation, applied to the peripheral end of the nerve, resulted in a frequency-dependent relaxation of the LOS, and peristaltic and non-peristaltic contractions in the oesophageal body. 3. N omega-nitro-L-arginine (L-NNA, 10(-8)-10(-5) mol kg-1), an inhibitor of the L-arginine-nitric oxide pathway, inhibited LOS relaxation in a dose-dependent manner, but did not affect resting LOS pressure. At the highest dose of L-NNA no relaxation of the LOS was elicited in response to vagal stimulation. The effect of L-NNA, (10(-5) mol kg-1) was fully reversed by infusion of 10(-4) mol kg-1 L-arginine. Peristaltic velocity and amplitude of contractions in the oesophageal body were unaffected by L-NNA. 4. Infusion of sodium nitroprusside reduced LOS pressure to zero, and the drug was equally potent in control animals (-log ED50:8.1 +/- 0.2 mol kg-1) and in animals pretreated with L-NNA (-log ED50:8.2 +/- 0.3 mol kg-1). This suggests that the effect of L-NNA was not directly on guanylate cyclase. 5. A significant elevation of blood pressure was recorded after administration of L-NNA (10(-5) mol kg-1).(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional differences in nitrergic innervation of the smooth muscle of murine lower oesophageal sphincter

BACKGROUND AND PURPOSE: Anatomical and pharmacological studies have demonstrated that the lower oesophageal sphincter (LES) is not a simple homogenous circular muscle with uniform innervation. Regional differences have been demonstrated in several species including humans. We investigated, for the first time in mice LES, regionally distinct physiological and pharmacological characteristics of the neuromusculature. EXPERIMENTAL APPROACH: Conventional intracellular recordings and pharmacological techniques were employed to evaluate electrical properties and functional innervation of smooth muscle cells. Results from CD1 (control), nNOS((-/-)) and eNOS((-/-)) genetic knockout mice were compared. KEY RESULTS: Smooth muscle of sling and clasp LES displayed unitary membrane potentials of 1- 4 mV. Transmural nerve stimulation produced a monophasic inhibitory junction potential (IJP) in the sling, whereas in the clasp a biphasic IJP, consisting of a brief IJP followed by a long-lasting slow IJP (lsIJP), was induced. Pharmacological interventions and genetically modified mice were used to demonstrate a monophasic apamin-sensitive (purinergic) component in both LES regions. However, the nitrergic IJP was monophasic in the sling and biphasic in the clasp. Unitary membrane potentials and IJPs were not different in CD1 and eNOS((-/-)) mice, suggesting no involvement of myogenic NOS. CONCLUSION AND IMPLICATIONS: These data in mouse LES indicate that there are previously unreported regional differences in the IJP and that both the apamin-resistant monophasic and biphasic IJPs are mediated primarily by nitrergic innervation.     

Nicotine administration stimulates the in vivo N-methyl-D-aspartate receptor/nitric oxide/cyclic GMP pathway in rat hippocampus through glutamate release

1. The in vivo effects of nicotine on the nitric oxide (NO) synthase/cyclic GMP pathway of the adult rat hippocampus have been investigated by monitoring the levels of extracellular cyclic GMP during microdialysis in conscious unrestrained animals.
2. Intraperitoneal (i.p.) administration of nicotine caused elevation of cyclic GMP levels which was prevented by mecamylamine. The effect of nicotine was abolished by local infusion of the NO synthase inhibitor N^G-nitro-L-arginine (L-NOARG) or by the soluble guanylyl cyclase blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ).
3. Local administration of the NMDA receptor antagonists cis-4-(phosphonomethyl)-2-piperidinecarboxylic acid ({"type":"entrez-protein","attrs":{"text":"CGS19755","term_id":"875773122","term_text":"CGS19755"}}CGS19755) and dizocilpine (MK-801) inhibited by about 60% the nicotine-induced elevation of cyclic GMP. Nicotine was able to stimulate cyclic GMP outflow also when administered directly into the hippocampus; the effect was sensitive to mecamylamine, L-NOARG, ODQ or MK-801.
4. Nicotine, either administered i.p. or infused locally, produced augmentation of glutamate and aspartate extracellular levels, whereas the outflows of γ-aminobutyric acid (GABA) and glycine remained unaffected. Following local administration of high concentrations of nicotine, animals displayed symptoms of mild excitation (sniffing, increased motor and exploratory activity) during the first 20–40 min of infusion, followed by wet dog shake episodes; these behavioural effects were prevented by mecamylamine or MK-801, but not by L-NOARG or by ODQ.
5. It is concluded that (a) nicotine stimulates the production of NO and cyclic GMP in the hippocampus; (b) this occurs, at least in part, through release of glutamate/aspartate and activation of NMDA receptors. Modulation of the NMDA receptor/NO synthase/cyclic GMP pathway may be involved in the cognitive activities of nicotine.

     

NO-cGMP信号通路舒张甲亢性高血压大鼠胸主动脉的特性

目的探讨NO-cGMP信号通路舒张甲亢性高血压大鼠胸主动脉的特性。方法大鼠皮下每天注射甲状腺素(T4)0.5 mg.kg-1的剂量或等体积的生理盐水连续16 d,制备甲亢性高血压大鼠模型组和对照组。采用两组大鼠的离体胸主动脉环标本,观察NO供体SNAP对胸主动脉环的影响;利用可溶性鸟苷酸环化酶(sGC)激活剂BAY 41-2272(BAY)、sGC阻断剂ODQ和能透过细胞膜进入胞内而激活蛋白激酶G(PKG)的8-Br-cGMP,观察NO-cGMP信号通路对甲亢性高血压大鼠胸主动脉的舒张作用的影响。结果与对照组相比,甲亢性高血压大鼠体重明显下降而心率、脉压差和收缩压明显升高;SNAP对两组大鼠的胸主动脉环均有明显的舒张作用,但在甲亢性高血压大鼠中的舒张作用明显弱于对照大鼠;用ODQ预处理后,SNAP对两组大鼠胸主动脉环的舒张作用均被阻断;BAY和8-Br-cGMP对两组大鼠的血管环均有明显的舒张作用,但在甲亢性高血压大鼠中的舒张作用明显弱于对照大鼠。结论甲亢性高血压的病理状态下,NO-cGMP信号通路对胸主动脉的舒张作用减弱,且此效应可能与sGC和PKG功能下调有着密切关系。     

Cross tolerance between nitroglycerin and neural relaxation of the rabbit sphincter of Oddi

We studied whether non-adrenergic, non-cholinergic (NANC) relaxation of the rabbit sphincter of Oddi was influenced by tolerance to nitroglycerin (NG)in vitro. Sphincter of Oddi (SO) muscle rings precontracted with EC₅₀concentrations of cholecystokinin octapeptide (CCK8) were exposed to cumulative increases in NG concentrations and tested for relaxation by measurement of isometric tension. A separate group of six rings was subjected to a preceding exposure to 275 μmnitroglycerin over 60 min to inducein vitrotolerance to nitroglycerin. The rings (both tolerant and non-tolerant) were subjected to electrical field stimulation (FS: 50 V, 0.1 ms, 20 Hz, 3 and 10 stimuli). The rings were then preincubated with NANC solution: phentolamine, oxprenolol and atropine (all 1 μm) for 20 min and FS was applied again. FS was repeated after additional incubation withN^G-nitro-l-arginine methyl ester (l-NAME), an inhibitor of NO synthase (30 μm) and after a successive incubation with 3 mml-arginine (20 min). Maximum contractions produced by CCK8 in `tolerant' and ‘non-tolerant’ sphincters were 29.9±5.8 and 28.3±5.2 mN, respectively. The sensitivity to CCK8 also was not different between the two groups with EC<sub>50</sub>(−log M) values of 8.5±0.2 and 8.3±0.1, respectively. FS evoked twitchlike contraction followed by relaxation in the ampullary SO in both `tolerant' and `non-tolerant' preparations. Incubation in NANC solution resulted in monophasic relaxations in response to FS in non-tolerant sphincters but not in tolerant ones.l-NAME (30 μm) reversed NANC relaxation in non-tolerant muscle rings whereas it failed to modify NANC contractions in the tolerant preparations.l-arginine (3 mm) reversed the inhibitory effect ofl-NAME on NANC relaxation in the `non-tolerant' rings and it was without effect on FS-induced contractions in the `tolerant' SO. As measured by radioimmunoassay, tolerance to NG was without any significant effect on tissue content of both cyclic adenosine 3′:5′ monophosphate (cAMP) and cyclic guanosine 3′:5′ monophosphate (cGMP). FS significantly increased tissue cAMP and cGMP content in ‘non-tolerant’ preparations. FS failed to increase the level of either cyclic nucleotide in `tolerant' tissue. We conclude that NANC relaxation of the ampullary part of the rabbit SO is significantly impaired in the state of tolerance to NG`in vitro'.     

Involvement of protein kinase C in reduced relaxant responses to the NO/cyclic GMP pathway in piglet pulmonary arteries contracted by the thromboxane A2-mimetic U46619

1. Impairment of nitric oxide (NO)/cyclic GMP production and/or increased activities of thromboxane A₂ (TXA₂) and endothelin-1 (ET-1) have been associated with pulmonary hypertension. We have analysed the interactions of noradrenaline (NA), the TXA₂-mimetic U46619 and ET-1 with the relaxation induced via cyclic GMP in isolated piglet intrapulmonary arteries.
2. The contractions induced by NA were augmented by endothelium removal or by methylene blue and pre-contracted rings were fully relaxed by acetylcholine, sodium nitroprusside (SNP), atrial natriuretic peptide and 8-bromo-cyclic GMP. In contrast, U46619- and ET-1 induced contractions were endothelium-independent and only partially relaxed by the latter vasodilators. Whereas the reduced responses to SNP in arteries contracted by U46619 were independent of the U46619-induced tone, a higher concentration of ET-1 (tone higher than that induced by NA) was required to reduce the vasodilator responses to SNP. NA, U46619 and ET-1 had no effect on the SNP-induced increases in cyclic GMP.
3. The reduced relaxant responses to SNP in arteries pre-contracted by U46619 were specific for piglet pulmonary arteries since they were not observed in piglet mesenteric or coronary arteries or in rat pulmonary arteries. Furthermore, there were no differences in the relaxant response to the adenylate cyclase activator forskolin in piglet pulmonary arteries pre-contracted by either NA, U46619 or ET-1.
4. SNP-induced relaxation was inhibited by thapsigargin (but not by inhibition of the membrane Na⁺/K⁺ ATPase nor K⁺ channels) indicating a role for Ca²⁺ sequestration by the Ca²⁺ ATPase in the effects of SNP.
5. The phorbol ester 12-myristate, 13-acetate inhibited the relaxant response to SNP. The inhibitory effect of U46619 on SNP-induced relaxation was abolished by the protein kinase C inhibitor (PKC) staurosporine suggesting that PKC may be a part of the signal transduction mechanism.
6. In summary, piglet pulmonary arteries when activated by a TXA₂-mimetic show abnormally reduced relaxant responses to the NO/cyclicGMP pathway. This effect appears to be mediated by activation of PKC.

     

Role of the NO/cGMP/K(ATP) pathway in the protective effects of sildenafil against ethanol-induced gastric damage in rats

BACKGROUND AND PURPOSE: Sildenafil is a selective inhibitor of cGMP-specific phosphodiesterase. Sildenafil, acting via NO-dependent mechanisms, prevents indomethacin-induced gastropathy. Activation of ATP-sensitive potassium channels (K(ATP)) is involved in gastric defence. Our objective was to evaluate the role of the NO/cGMP/K(ATP) pathway in the protective effects of sildenafil against ethanol-induced gastric damage. EXPERIMENTAL APPROACH: Rats were treated with L-NAME (1 or 3 mg kg(-1), i.p.) or with L-arginine (200 mg kg(-1), i.p.) + L-NAME (3 mg kg(-1), i.p.), the guanylate cyclase inhibitor, ODQ (10 mg kg(-1), i.p.), glibenclamide (0.1, 0.3, 1 or 3 mg kg(-1), i.p.) or with glibenclamide (1 mg kg(-1), i.p.) + diazoxide (3 mg kg(-1), i.p.). After thirty minutes, the rats received sildenafil (1 mg kg(-1), by gavage), followed by intragastric instillation of absolute ethanol (4 ml kg(-1)) to induce gastric damage. One hour later, gastric damage (haemorrhagic or ulcerative lesions) was measured with a planimetry programme. Samples of stomach were also taken for histopathological assessment and for assays of tissue glutathione and haemoglobin.KEY RESULTS: Sildenafil significantly reduced ethanol-induced gastric damage in rats. L-NAME alone, without L-arginine, significantly reversed the protection afforded by sildenafil. Inhibition of guanylate cyclase by ODQ completely abolished the gastric protective effect of sildenafil against ethanol-induced gastric damage. Glibenclamide alone reversed sildenafil's gastric protective effect. However, glibenclamide plus diazoxide did not alter the effects of sildenafil.CONCLUSIONS: Sildenafil had a protective effect against ethanol-induced gastric damage through the activation of the NO/cGMP/K(ATP) pathway.     

Sildenafil augments the beneficial hemodynamic and histopathological effects of amlodipine in nitric oxide-deficient hypertensive rats: Role of nitric oxide–cyclic GMP pathway

The association of erectile dysfunction (ED) with cardiovascular diseases is so common. This study was carried out to investigate possible impact of sildenafil; the prototype phosphodiesterase 5 inhibitor used for treatment of ED, on the beneficial hemodynamic and histopathological effects of the prototype third generation calcium antagonist, amlodipine, in nitric oxide (NO)-deficient hypertensive rats. Hypertension was induced by 4-weeks treatment with N(omega)-nitro-l-arginine-methyl ester (l-NAME). Animals were allocated into five groups: normal control, hypertensive control, amlodipine-treated group, sildenafil-treated group and combined treatment group. Drug treatment was started 2 weeks after l-NAME and continued together with l-NAME to the end of the treatment period. Systolic blood pressure (SBP), plasma nitrate/nitrite (NO(x)) and plasma cGMP levels were evaluated at the end of the treatment period. Aortic and renal structural alterations were also investigated. l-NAME treatment caused elevation of SBP, reduction in plasma NO(x) and cGMP levels as well as adverse histological alterations in the tissues studied. Amlodipine normalized SBP, restored plasma NO(x) and cGMP levels and ameliorated the adverse histological changes seen in NO-deficient rats. When combined with sildenafil, both hemodynamic and histopathological effects of amlodipine were augmented with an underlying enhanced elevation of both plasma NO(x) and cGMP levels to statistically higher values than amlodipine alone. These results show that sildenafil augments the beneficial hemodynamic and histopathological effects of amlodipine in NO-deficient hypertensive rats with a pivotal role being played by NO-cGMP pathway. Whether this pharmacodynamic interaction could exist in other models of hypertension that do not share such biochemical derangement warrants further investigations.     

硫化氢下调大鼠主动脉L-精氨酸/一氧化氮合酶/一氧化氮通路

目的观察H2S对血管L-精氨酸/一氧化氮(L-Arg/NO)通路的影响以探讨H2S和NO这两种气体信号分子间的相互作用。方法离体孵育大鼠主动脉薄片,加入H2S供体NaHS(10-7~10-4mol.L-1)孵育4 h,及50μmol.L-1NaHS分别孵育2、4和6 h。采用G re iss法测定血管亚硝酸盐含量;同位素示踪法检测血管组织一氧化氮合酶(NOS)活性及L-Arg转运,RT-PCR检测eNOS、CAT1基因表达。结果一次性给予50μmol.L-1NaHS,孵育2 h,孵育液中NO2-含量比对照组低62%,血管NOS活性下降48%,L-Arg转运减少50%(P<0.01);孵育6 h,NO2-含量比对照组低19%(P<0.05),而NOS活性和L-Arg转运已基本恢复(P>0.05)。NaHS(10-7~10-4mol.L-1),呈浓度依赖的抑制了L-Arg/NOS/NO通路,IC50分别为0.499、3.198及3.927μmol.L-1(P<0.01);而给予50μmol.L-1NaHS后,eNOS和CAT-1A的mRNA表达分别减少34.3%和55.1%(P<0.01)。结论H2S通过抑制血管组织L-Arg转运和NOS活性和基因表达,下调L-Arg/NOS/NO通路,从而减少血管NO生成。     

Involvement of vasoactive intestinal polypeptide in nicotine-induced relaxation of the rat gastric fundus

1. Nicotine-induced relaxation and release of vasoactive intestinal polypeptide (VIP)- and peptide histidine isoleucine (PHI)-like immunoreactivity (LI) were measured in longitudinal muscle strips from the rat gastric fundus.
2. Under non-cholinergic conditions (0.3 μM atropine), nicotine (3–300 μM) produced concentration-dependent relaxations of the 5-hydroxytryptamine (3 μM)-precontracted strips. Under non-adrenergic non-cholinergic (NANC) conditions (0.3 μM atropine+1 μM phentolamine+1 μM nadolol), relaxations induced by sub-maximal nicotine concentrations (10 and 30 μM) were significantly smaller, while that produced by the highest concentration used (300 μM) was similar to that seen under non-cholinergic conditions.
3. Re-exposure to the same nicotine concentration 1 h later induced smaller relaxations, indicating desensitization. The reductions seen in the second responses were proportional to the concentration used.
4. Under non-cholinergic conditions, the relaxant response to 30 μM nicotine was abolished by hexamethonium (100 μM) and significantly reduced by tetrodotoxin (TTX, 3 μM). The TTX-resistant component was not observed under NANC conditions.
5. NANC relaxation induced by 30 μM nicotine was significantly reduced by a specific anti-VIP serum (approximately 35% less than that seen with normal rabbit serum).
6. Nicotine (30–300 μM) caused significant, concentration-dependent increases in the outflow of VIP- and PHI-LI from the strips; these effects were also diminished with re-exposure. The increases in both types of immunoreactivity evoked by nicotine (300 μM) were abolished by hexamethonium (300 μM), TTX (3 μM) and a calcium-free medium.
7. These findings indicate that VIP and possibly PHI are involved in NANC relaxation of the rat gastric fundus induced by nicotine.

     

The induction of nitric oxide-mediated relaxation of human isolated pulmonary arteries by PACAP

1. The effects of pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) were analysed in human isolated circular segments of pulmonary arteries. Guinea-pig pulmonary arteries were used for comparison. The responses obtained were analysed in relation to the vascular endothelium and the nitric oxide (NO) synthase inhibitor N^G-monomethyl L-arginine (L-NMMA).
2. PACAP and VIP induced concentration-dependent relaxations of precontracted pulmonary arteries. The maximal dilator response (I_max,%) and the potency (pEC₅₀ value) were the same for both peptides, and there were no differences in the effects obtained on human and guinea-pig segments. PACAP and VIP were both more potent that acetylcholine (ACh).
3. Removal of the vascular endothelium abolished the PACAP induced dilator response in pulmonary arteries from both species. The VIP induced dilatation was unaffected, whereas the response to ACh was abolished. L-NMMA given before PACAP inhibited the dilatation. Furthermore, L-NMMA also reversed the dilatation already induced by PACAP and excess concentrations of L-arginine restored the dilator response of the L-NMMA treated arteries.
4. PACAP is a potent dilator of human pulmonary arteries. Although the dilator effect seems to be similar in amplitude to the one induced by VIP, the present results suggest differences in the underlying mechanisms of action (endothelium-dependency) between the two peptides.