Hypoxic vasoconstriction of rat main pulmonary artery: role of endogenous nitric oxide, potassium channels, and phosphodiesterase inhibition

This study investigated the influence of NO, potassium (K+) channel blockade, and the phosphodiesterase inhibitors (PDEIs) theophylline (non-selective PDEI), siguazodan (PDE3I), rolipram (PDE4I), and zaprinast (PDE5I) on rat isolated main pulmonary artery hypoxic (95% N2 and 5% CO2) vasoconstriction. Hypoxic vasoconstriction increased by 27% (p < 0.01) in the presence of the NO synthase inhibitor L-NAME (10(-4) M), and by 15% (p < 0.05) in the presence of the K(ATP) channel blocker glibenclamide (10(-6) M), without potentiation by the combination of these two drugs. Hypoxic vasoconstriction decreased by 28% (p < 0.01) in presence of the Kv,-voltage-dependent channel blocker 4-aminopyridine (10(-3) M), whereas the other K+ channel blockers, charybdotoxin (BKCa, large-conductance Ca2+-sensitive K+ channels) and apamin (SKCa, small-conductance Ca2+-sensitive K+ channels) had no effect. The nonselective PDEI theophylline induced a concentration-dependent relaxation (pD2 = 4.05, Emax = 90% [expressed as a percentage of maximal relaxation induced by papaverine 10(-4) M]). Among the selective PDEIs, siguazodan was significantly (p < 0.01) more efficient than rolipram and zaprinast (Emax values were 84%, 67%, and 58%, respectively) and significantly (p < 0.05) more potent than zaprinast (pD2 values were 6.48, 6.34, and 6.16 for siguazodan, rolipram, and zaprinast). Glibenclamide and L-NAME significantly (p < 0.05) shifted the concentration-response curve (CRC) for zaprinast to the right, and L-NAME shifted the CRC significantly to the right for siguazodan. In the presence of L-NAME, glibenclamide had no effect on the CRC of zaprinast. We conclude that (a) NO exerts a permanent inhibitory effect against hypoxic vasoconstriction that might be mediated in part by an activation of K(ATP) channels; (b) a 4-aminopyridine-sensitive K+ channel is involved in vasoconstriction under hypoxic conditions; (c) PDEs 3 and 5 are the predominant PDE isoforms in rat pulmonary artery relaxation; and (d) NO and K(ATP), but neither BK(Ca), SK(Ca), nor Kv channels, are involved in the relaxant effect of PDEIs.     

Endogenous nitric oxide modulates adrenergic neural vasoconstriction in guinea-pig pulmonary artery.

1. Electrical field stimulation (EFS) of guinea-pig isolated pulmonary artery induced a frequency-dependent contraction. This was abolished by tetrodotoxin (1 microM) and prevented by phentolamine and prazosin (both 1 microM), indicating a role for alpha 1-adrenoceptors activated by noradrenaline (NA) released from perivascular adrenergic nerves. 2. L-NG-monomethyl arginine (L-NMMA, 0.3-100 microM) caused a concentration-dependent enhancement of the EFS-induced contraction with a 3.4 +/- 0.5 fold increase at 100 microM n = 6). The augmenting effect of 30 microM L-NMMA on the contraction to EFS was completely reversed by 100-300 microM L-arginine, but not by an identical concentration of D-arginine. 3. The contractile response to exogenous NA was similarly enhanced by 30 microM L-NMMA (2.9 +/- 0.6 fold increase, n = 5). 4. The contractile responses to exogenous phenylephrine and prostaglandin F2 alpha while matched the contraction to EFS (4 Hz) were equally augmented by 30 microM L-NMMA. 5. In vessel rings submaximally contracted with the thromboxane analogue U44069 (2 microM), the selective alpha 2-adrenoceptor agonist UK14304 induced concentration-dependent relaxation, which was abolished by removal of endothelium. NA had little relaxant effect on these precontracted vessel rings unless in the presence of prazosin (1 microM). 6. Indomethacin had no significant effect on the contractile response to EFS or NA, indicating that vasodilator cyclo-oxygenase products such as prostacyclin are not involved in modulating these responses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of acute inflammation by endogenous nitric oxide.

The role of endogenous nitric oxide (NO) in acute inflammation was investigated using two inhibitors of NO synthase (NG-nitro-L-arginine methyl ester(L-NAME) and NG-monomethyl-L-arginine (L-NMMA)) as well as L- or D-arginine. The effect of test compounds was studied on the carrageenin-induced increase in vascular permeability in rat skin and in dextran- and carrageenin-induced paw oedema. Both L-NAME and L-NMMA dose dependently inhibited the increase in vascular permeability and oedema formation. L- but not D-arginine increased these inflammatory responses and reversed the inhibitory effects of L-NAME and L-NMMA. In dexamethasone-treated rats L-arginine enhanced the dextran-induced oedema and the early phase of carrageenin-induced oedema but did not modify the inhibition by dexamethasone of the late phase of carrageenin-induced oedema. These results suggest that endogenous NO is released at the site of acute inflammation and modulates oedema formation. Depending on the time course or on the type of inflammation, NO may be predominantly generated by the constitutive or by the inducible NO synthase.     

Modulation of adjuvant arthritis by endogenous nitric oxide.

1. The role of endogenous nitric oxide (NO) in adjuvant arthritis in Lewis rats has been studied by use of L-arginine, the amino acid from which NO is synthesized, and NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Prolonged modulation (35 days) of the L-arginine: NO pathway in rats was achieved by dissolving test compounds in the drinking water (L-arginine: 3, 10 and 30 mg ml-1; L-NAME: 0.1, 1 and 10 mg ml-1). 2. Arthritis was exacerbated by L-arginine and suppressed by L-NAME in a dose-related fashion. Combined treatment with L-NAME (1 mg ml-1) and L-arginine (30 mg ml-1) did not modify the arthritis. 3. Reduced weight gain, which is a feature of adjuvant arthritis, was modified by these compounds so that L-arginine reduced weight gain whereas L-NAME increased weight gain compared with that in control animals. 4. D-Arginine (30 mg ml-1), NG-nitro-D-arginine methyl ester (D-NAME: 1 mg ml-1) and L-lysine (30 mg ml-1), an amino acid not involved in the generation of NO, were without effect on either arthritis or body weight gain. 5. Antigen-stimulated proliferation of T-lymphocytes as well as generation of nitrite (NO2-) and release of acid phosphatase from macrophages were all enhanced in L-arginine-treated arthritic rats and reduced in L-NAME-treated animals. 6. These results suggest that endogenous NO modulates adjuvant arthritis, possibly by interfering with the activation of T-lymphocytes and/or macrophages.     

The role of endogenous norepinephrine release in potassium-evoked vasoconstriction of the rat tail artery.

Potassium-containing solutions are often used to study the sequence of events leading from excitation to vasoconstriction. In densely innervated vessels, such as the rat tail artery, potassium-induced vasoconstriction may be mediated via smooth muscle depolarization and release of endogeneous norepinephrine. The relative contribution of these two mechanisms--a 'direct' depolarization of the vascular smooth muscle cell membrane, and an 'indirect' sympathomimetic action--to the vasoconstrictor response was studied in the present paper. Perfusion/superfusion of the rat tail artery in vitro with potassium-containing solutions had different effects depending on the concentration used. A change in potassium concentration from 4.7 to 20 mM had no effect on either perfusion pressure or norepinephrine overflow. From 30 to 70 mM, potassium produced increasing amounts of norepinephrine overflow. Experiments with phentolamine and reserpine showed that this norepinephrine overflow contributed for up to half of the vasoconstrictor response observed. A second norepinephrine-independent mechanism was also involved but the latter appeared to be incapable of producing sustained contraction. At concentrations of potassium above 50-70 mM, the results of experiments with (+/-)-propranolol suggest that the norepinephrine released by potassium has a beta-adrenoceptor-mediated vasorelaxant effect.     

Evidence that endogenous nitric oxide modulates plasma fibrinogen levels in the rat.

This study investigated the effect of prolonged inhibition of nitric oxide (NO) synthase on plasma fibrinogen levels and platelet count in the rats. NG-nitro-L-arginine methyl ester (L-NAME), when administered orally twice a day, at 10-100 mg kg-1, for 7 consecutive days, 14 times in all, significantly elevated fibrinogen levels and systolic blood pressure in a dose-dependent manner. The same dose range of L-NAME failed to alter platelet count and plasma protein concentrations. The increase in fibrinogen levels produced by chronic treatment with L-NAME at 30 mg kg-1 was reversed by L-arginine at 500-1500 mg kg-1 in a dose-dependent manner. These findings suggest that endogenous NO tonically acts to reduce plasma fibrinogen levels in rats under physiological conditions.     

Investigation of endogenous nitric oxide vascular function in the carotid artery of cholesterol-fed rabbits.

1. The function of endogenous nitric oxide (NO) at the level of vascular smooth muscle, was assessed in a popular experimental model of accelerated atherosclerosis, the cholesterol-fed rabbit. 2. Endothelium-dependent vasorelaxation in response to acetylcholine (ACh, 1 microM) was significantly impaired in the carotid artery from rabbits maintained on a 1% (W/W) cholesterol diet for 8-10 weeks. Furthermore, the ability of an inhibitor of nitric oxide synthase (NOS), NG-nitro-L-arginine methyl ester (L-NAME, 1-300 microM), to enhance the contractile reactivity to a submaximal concentration of noradrenaline (NA, 3 microM), was significantly attenuated in hypercholesterolaemia. 3. A significant linear correlation between the maximal contractile effect of L-NAME (300 microM) and maximal vasorelaxation to ACh (1 microM) was determined in the carotid artery from control rabbits. In contrast, no such linear correlation was found in the carotid artery from hypercholesterolaemic rabbits. 4. We conclude that there are lesions both in agonist-stimulated, endogenous NO-dependent vasorelaxation and in the regulation of vasoconstrictor reactivity by endogenous NO in the hypercholesterolaemic rabbit carotid artery. Furthermore, the normal linear relationship between the contractile effect of L-NAME and vasorelaxation to ACh is lost after cholesterol-feeding.     

糖尿病大鼠血中内源性一氧化氮合酶抑制物增高

目的：测定糖尿病大鼠血中内源性ＮＯ合酶抑制物二甲基精氨酸（ＤＭＡ）的含量，方法：在链佐星诱发的糖尿病大鼠测定血清ＤＭＡ的含量和乙酰胆碱（ＡＣｈ）诱导血管内皮依赖性舒张，结果：与对照组相比，糖尿病大鼠ＤＭＡ血清浓度显增加（５．４±１．０ｖｓ０．７±０．３μｍｏｌ．Ｌ＾－１，Ｐ〈０．０１）；丙二醛含量也高于对照组（２．５±０．３ｖｓ２１．５±０．１μｍｏｌ．Ｌ＾－１，Ｐ〈０．０１）；糖尿病大鼠ＡＣｈ     

Attenuation by prolonged nitric oxide synthase inhibition of the enhancement of fibrinolysis caused by environmental stress in the rat.

1. Nitric oxide (NO) suppresses platelet aggregation and plasminogen activator inhibitor (PAI) release from platelets, playing physiological and/or pathological roles in the haemostatic system. We investigated the effect of NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, on the disseminated intravascular coagulation (DIC)-like phenomena in rats under environmental stress, induced by prolonged fluctuation in air temperature, known as SART (specific alternation of rhythm in temperature) stress. 2. Exposure of rats to SART stress for 7 days caused mild DIC-like symptoms such as thrombocytopenia, hypofibrinogenemia, decreased factor VIII: coagulant activity and shortened euglobulin clot lysis time (ECLT). The enhanced fibrinolysis was accompanied by a marked decrease in the activity of plasma PAI. 3. L-NAME, but not its D-enantiomer, when administered orally at 0.3-10 mg kg-1, twice a day for 7-day exposure to stress, inhibited the stress-induced decrease in fibrinogen levels in a dose-dependent manner, whereas it failed to alter platelet count, factor VIII:coagulant activity and plasma protein levels in stressed rats. All these parameters in unstressed rats were resistant to L-NAME at 10 mg kg-1. 4. Repeated treatment with 10 mg kg-1 of L-NAME blocked the shortening of ECLT and the decrease in PAI activity following stress exposure, although it was without effect in unstressed rats. 5. The inhibitory effects of L-NAME at 10 mg kg-1 on the stress-induced alterations in fibrinogen levels and in ECLT were significantly reduced by coadministered L-arginine at 1000 mg kg-1. 6. These findings demonstrate that repeated administration of L-NAME attenuates the enhanced fibrinolysis, without aggravating thrombocytopenia, in SART-stressed rats. Endogenous NO appears to contribute to the stress-induced development of fibrinolysis by suppressing, plasma PAI activity, most probably as a result of inhibition of the PAI release from platelets.     

Modulation of morphine antinociception in the mouse by endogenous nitric oxide.

1. L-Arginine (100-1000 mg kg-1) administered orally (p.o.) or intraperitoneally (i.p.), but not intracerebroventricularly (i.c.v., 0.08 mg per mouse), reduced the antinociceptive effect of morphine (0.5-10 mg kg-1 s.c.) assessed in mice using three different tests: hot plate, tail-flick and acetic acid-induced writhing. D-Arginine (up to 1000 mg kg-1 p.o. or i.p.) was ineffective. 2. NG-Monomethyl-L-arginine (L-NMMA, 5-50 mg kg-1 i.p.) and NG-nitro-L-arginine methyl ester (L-NAME, 5- 30 mg kg-1 i.p.), but not NG-nitro-D-arginine methyl ester (D-NAME, 30 mg kg-1 i.p.), reversed in all assays the effect of L-arginine on morphine-induced antinociception. 3. Morphine (10 mg kg-1 s.c.), L-arginine (1000 mg kg-1 p.o.) or L-NAME (30 mg kg-1 i.p.), either alone or in combination, did not produce changes in locomotor activity or sensorimotor performance of animals. 4. These results suggest that the L-arginine-nitric oxide pathway plays a modulating role in the morphine-sensitive nociceptive processes.     

Attenuation of contractions to acetylcholine in canine bronchi by an endogenous nitric oxide-like substance.

1. The involvement was assessed of an endogenous nitric oxide-like substance in contractions of canine bronchi to acetylcholine. 2. Canine third order bronchial rings, in some of which the epithelium was removed mechanically, were suspended in organ chambers and isometric tension was recorded. In some experiments, the content of guanosine 3',5'-cyclic monophosphate (cyclic GMP) of the bronchi was also measured. 3. Acetylcholine induced concentration-dependent contractions. The contractions were potentiated by nitro-L-arginine (an inhibitor of the synthesis of nitric oxide), oxyhaemoglobin (a scavenger of nitric oxide), and methylene blue (an inhibitor of soluble guanylate cyclase). The magnitude of the potentiation to acetylcholine-induced contractions by these inhibitors were not significantly different between tissues with and without epithelium. 4. Acetylcholine induced a concentration-dependent increase in intracellular content of cyclic GMP, which was similar in bronchi with and without epithelium. These increases were abolished by nitro-L-arginine and methylene blue. 5. During contractions to acetylcholine, exogenous nitric oxide relaxed the canine bronchi. The relaxations were not affected by nitro-L-arginine, but were augmented by superoxide dismutase plus catalase, and were abolished by methylene blue. 6. These observations suggest that, during contraction evoked by acetylcholine, the production of an endogenous nitric oxide-like substance increases and in turn attenuates the response of the airways to the muscarinic agonist. However, the endogenous nitric oxide-like substance does not play a major role in the epithelium-dependent attenuation of the contraction to acetylcholine in canine bronchi.     

Endothelial nitric oxide attenuates Na+/Ca2+ exchanger-mediated vasoconstriction in rat aorta

BACKGROUND AND PURPOSE: The Na+/Ca2+ exchanger (NCX) may be an important modulator of Ca2+ entry and exit. The present study investigated whether NCX was affected by prostacyclin and nitric oxide (NO) released from the vascular endothelium, as NCX contains phosphorylation sites for PKA and PKG. EXPERIMENTAL APPROACH: Rat aortic rings were set up in organ baths. Tension was measured across the ring with a force transducer. KEY RESULTS: Lowering extracellular [Na+] ([Na+]o) to 1.18 mM induced vasoconstriction in rat endothelium-denuded aortic rings. This effect was blocked by the NCX inhibitor KB-R7943 (2-2-[4-(4-nitrobenzyloxy)phenyl] ethyl isothiourea methanesulphonate; 1 microM). In endothelium-intact aortic rings, decreasing [Na+]o did not constrict the aortic rings significantly, but after treatment with the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 1 microM) or the NOS inhibitor L-NAME (N(omega)-nitro-L-arginine methyl ester; 50 microM), a vasoconstriction that was similar in size to that in endothelium-denuded preparations was evident. The vasorelaxation induced by the NO donor sodium nitroprusside sodium nitroprusside dihydrate (30 nM) was the same in the endothelium-denuded aortic rings preconstricted with either low Na+ (1.18 mM), the thromboxane A2 agonist U46619 (9,11-dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F(2alpha); 0.1 microM) or high K+ (80 mM). CONCLUSIONS AND IMPLICATIONS: The results suggest that the endothelium inhibits NCX operation via guanylate cyclase/NO. This is stronger than for other constrictors such as phenylephrine and may relate to concomitant NCX-stimulated NO release from the endothelium. This finding may be important where NCX operates in reverse mode, such as during ischaemia, and highlights a new mechanism whereby the endothelium modulates Ca2+ homoeostasis in vascular smooth muscle.     

Role of endogenous nitric oxide in the nitric oxide donor-induced plasma extravasation of mouse skin.

The role of endogenous nitric oxide (NO) and prostanoids in the increase in microvascular permeability induced by NO donors was investigated in the mouse skin by a dye leakage method. Subcutaneous (s.c.) injection of 1-hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1-triazene (NOC 5), 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC 18) and sodium nitroprusside dose-dependently increased local dye leakage. While indomethacin inhibited the dye leakage elicited by these NO donors, N(G)-nitro-L-arginine methyl ester (L-NAME) inhibited the effect of NOC 5 and NOC 18 but not of sodium nitroprusside. These results suggest that endogenous NO, in addition to the prostanoid biosynthesis, is involved in the dermal microvascular permeability increase induced by the NOC series NO donors.     

Elevation of an endogenous inhibitor of nitric oxide synthase in diabetic rat serum

目的：测定糖尿病大鼠血中内源性ＮＯ合酶抑制物二甲基精氨酸（ＤＭＡ）的含量．方法：在链佐星诱发的糖尿病大鼠测定血清ＤＭＡ的含量和乙酰胆碱（ＡＣｈ）诱导血管内皮依赖性舒张．结果：与对照组相比，糖尿病大鼠ＤＭＡ血清浓度显著增加（５４±１０ｖｓ０７±０３μｍｏｌ·Ｌ－１，Ｐ＜００１）；丙二醛含量也高于对照组（２５±０３ｖｓ１５±０１μｍｏｌ·Ｌ－１，Ｐ＜００１）；糖尿病大鼠ＡＣｈ舒血管效应减弱，其作用可被左旋精氨酸所改善．结论：链佐星诱发糖尿病大鼠高血糖症引起内源性ＤＭＡ含量升高，同时血管内皮依赖性舒张功能被削弱．     

Reduced nitric oxide formation causes coronary vasoconstriction and impaired dilator responses to endogenous agonists and hypoxia in dogs

We investigated the relative contribution of basal and agonist stimulated EDRF/NO release to the adjustment of coronary tone and myocardial perfusion in conscious dogs by inhibiting coronary endothelial NO formation with N^G-nitro-l-arginine methyl ester (l-NAME). Chronically instrumented conscious dogs (n = 9) were prepared for measurement of mean arterial blood pressure (MAP), heart rate (HR), coronary blood flow (CF) and diameter of the left circumflex (CD_LC) and left anterior descending (CD_LAD) coronary artery, respectively. Intracoronary infusions of l-NAME (30.3 mM; 0.25 ml × min^–1) caused significant increases in MAP and decreases in HR. CD_LC decreased by 3.8% from 3.01 ± 0.04 to 2.90±0.04 mm and CF decreases by 30% from 12.9 ± 0.2 to 9.1 ± 0.2 (aU). Peak reactive hyperemia (CF_max) evoked by 20-s-lasting occlusions of the left circumflex coronary artery decreased from 29.9 ± 0.8 to 25.8 ± 1.0 aU and maximal flow-dependent coronary dilation were reduced from 2.04 ± 0.08 to 0.91±0.12% after inhibition of NO-synthesis. Intracoronary infusions of acetylcholine (ACh), Adenosinc (Ado), bradykinin (Bk), and papaverine (Pap) caused dose-dependent increases in CD_LC and CE Infusion of l-NAME nearly abolished the dilator effect of Ado on CD_LC and reduced those to ACh, Bk and Pap. Increases in CF to ACh, Ado and Bk but not to Pap were reduced by l-NAME. Subsequent intracoronary infusions of l-arginine (303 mM; 0.25 ml × min^–1) reduced l-NAME-induced CF-changes partly, but did not reverse coronary constriction. These results suggest that inhibition of the continuous release of nitric oxide markedly reduces myocardial perfusion in vivo. Endogenous dilator mechanisms are likewise impaired. Thus, in the heart, nitric oxide deficiency probably cannot be fully compensated for by counter-regulating mechanisms. Correspondence to: E. Bassenge at the above address     

Endothelium-independent vasorelaxation by ticlopidine and clopidogrel in rat caudal artery

Objectives Thienopyridines are prodrugs currently used as anti‐aggregating agents. The aim of this study was to determine if these compounds might have vascular activity independent of hepatic bioactivation. Methods The direct activity of thienopyridines was studied in rat caudal arterial rings and aortic smooth muscle cells in culture. Key findings Both compounds (0.01 µm –100 µm ) showed a concentration‐dependent vasorelaxation in arterial tissues precontracted with phenylephrine, 5‐hydroxytryptamine and KCl. The relaxation induced by 100 µm ticlopidine and clopidogrel was greater than 80%. The relaxation by ticlopidine was compared with the activity of acetylcholine. These two agents showed similar potency, although ticlopidine was slightly more active. Pretreatment with the nitric oxide synthase inhibitor L‐NAME inhibited the relaxation by acetylcholine but not that by ticlopidine. To further study vasorelaxation by ticlopidine, other pharmacological inhibitors including propranolol, nifedipine and suramin were used. These compounds lacked inhibitory effects on the vasorelaxation by ticlopidine. In vascular smooth muscle cells, 1 µm ticlopidine induced a decrease in cell proliferation, while incubation with both ticlopidine and ADP or 2‐methioADP led to an additive effect. Conclusions The data suggest that ticlopidine and clopidogrel cause relaxation of arterial tissues and influence vascular smooth muscle cell proliferation directly without hepatic biotransformation. Furthermore, the arterial relaxation induced in vitro by thienopyridines is endothelium independent, and β‐adrenergic and P2 receptors are not involved.     

Modulation by nitric oxide of prostaglandin biosynthesis in the rat.

1. Modulation of prostaglandin biosynthesis in vivo by either exogenous or endogenous nitric oxide (NO) has been studied in the rat using arachidonic acid (AA)-induced paw oedema and measuring both the foot volume and the amount of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), the stable metabolite of prostacyclin (PGI2), in the oedematous fluid recovered from inflamed paws. 2. Paw injections of 150 or 300 nmol of AA were virtually inactive whereas 600 nmol produced a moderate oedema which was greatly reduced by the NO synthase inhibitor L-NG-nitro arginine methyl ester (L-NAME, 100 nmol/paw) and the NO scavenger haemoglobin (Hb, 30 mumol/paw), but unaffected by the inhibitor of the soluble guanylate cyclase, methylene blue (Mb, 3 mumol/paw) and L-arginine (15 mumol/paw). 3. The NO-donors (10 mumol/paw) 3-morpholino-sydnonimine-hydrochloride (SIN-1), S-nitroso-N-acetyl-D, L-penicillamine (SNAP) and sodium nitroprusside (SNP) significantly potentiated the paw oedema induced by AA (300 nmol/paw). 4. SIN-1 (2.5, 5 and 10 mumol/paw) produced a significant dose-dependent increase of the oedema induced by AA which was correlated with increased amounts of 6-keto-PGF1 alpha in the fluid recovered from inflamed paws. 5. Both oedema and prostaglandin biosynthesis induced by the combination AA+SIN-1 were greatly suppressed by either Hb (30 mumol/paw) or indomethacin (3 mumol/paw or 5 mg kg-1 s.c.) but unaffected by Mb (3 mumol/paw).(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet aggregation responses are critically regulated in vivo by endogenous nitric oxide but not by endothelial nitric oxide synthase

Background and purpose:

Although exogenous nitric oxide (NO) clearly modifies platelet function, the role and the source of endogenous NO in vivo remain undefined. In addition, endothelial NO synthase (NOS-3) critically regulates vessel tone but its role in modulating platelet function is unclear. In this paper we have investigated the roles of endogenous NO and NOS-3 in regulating platelet function in vivo and determined the functional contribution made by platelet-derived NO.

Experimental approach:

We used a mouse model for directly assessing platelet functional responses in situ in the presence of an intact vascular endothelium with supporting in vitro and molecular studies.

Key results:

Acute NOS inhibition by N_ω-nitro-L-arginine methyl ester hydrochloride (L-NAME) enhanced platelet aggregatory responses to thrombin and platelets were shown to be regulated primarily by NO sources external to the platelet. Elevation of endogenous NOS inhibitors to mimic effects reported in patients with cardiovascular diseases did not enhance platelet responses. Platelet responsiveness following agonist stimulation was not modified in male or female NOS-3^−/− mice but responses in NOS-3^−/− mice were enhanced by L-NAME.

Conclusions and implications:

Platelets are regulated by endogenous NO in vivo, primarily by NO originating from the environment external to the platelet with a negligible or undetectable role of platelet-derived NO. Raised levels of endogenous NOS inhibitors, as reported in a range of diseases were not, in isolation, sufficient to enhance platelet activity and NOS-3 is not essential for normal platelet function in vivo due to the presence of bioactive NO following deletion of NOS-3.     

Regulation of gastric mucosal integrity by endogenous nitric oxide: interactions with prostanoids and sensory neuropeptides in the rat.

1. The interactions between nitric oxide (NO), prostacyclin and sensory neuropeptides in the maintenance of gastric mucosal integrity have been investigated in the anaesthetized rat. 2. Administration of either NG-monomethyl-L-arginine (L-NMMA) to inhibit endothelium-derived NO formation, indomethacin to inhibit prostanoid biosynthesis or chronic capsaicin pretreatment to deplete sensory neuropeptides, did not induce acute mucosal injury. 3. In capsaicin-pretreated rats, however, L-NMMA (12.5-100 mg kg-1 i.v.) dose-dependently induced acute mucosal damage, characterized as vasocongestion and haemorrhagic necrosis. The enatiomer D-NMMA (100 mg kg-1 i.v.) did not induce any detectable mucosal damage. 4. This mucosal injury induced by L-NMMA was inhibited by concurrent administration of L-arginine (300 mg kg-1 i.v.). 5. In indomethacin (5 mg kg-1 i.v.)-pretreated rats, L-NMMA also induced mucosal damage. Furthermore, following indomethacin administration in capsaicin-pretreated rats, L-NMMA induced widespread, severe haemorrhagic necrotic damage. 6. These findings suggest a role for endogenous NO formed from L-arginine, acting in concert with prostacyclin and sensory neuropeptides, in the modulation of gastric mucosal integrity.