Obligatory role of nitric oxide in platelet-activating factor-induced microvascular leakage

We examined the independent and interdependent effects of platelet-activating factor (PAF) and nitric oxide (NO) on microvascular leakage of fluorescein isothiocyanate (FITC)-dextran in the cheek pouch microcirculation of anesthetized hamsters. Superfusing the cheek pouch microcirculation with 100-nM PAF elicited rapid leakage of FITC-dextran that was markedly inhibited by prior treatment with a nitric oxide synthase (NOS) inhibitor, N(omega)-nitro-L-arginine (L-NA; 1 microM). This inhibition by L-NA was completely reversed by application of a NO donor (S-nitroso-N-acetylpenicillamine, SNAP; 10 microM) at the same time PAF was applied. SNAP alone, however, did not cause leakage of FITC-dextran; neither did it enhance PAF-induced leakage. PAF-induced leakage was completely inhibited by prior treatment with the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxalin-1-one (ODQ, 10 microM). 8-bromoguanosine 3',5'-cyclic monophosphate (8-br-cGMP) did not reverse this inhibition by ODQ although this cell permeable cGMP analog was able to completely reverse arteriolar vasoconstriction produced by ODQ. These results indicate that PAF-induced leakage of FITC-dextran in the hamster cheek pouch microcirculation requires an intact NO/cGMP pathway, although NO production does not cause PAF-induced leakage. This supports the hypothesis that NO plays an obligatory role in PAF-induced leakage.     

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)     

Involvement of nitric oxide and eicosanoids in platelet-activating factor-induced haemodynamic and haematological effects in dogs.

1. Platelet-activating factor (PAF) is a phospholipid mediator with potent cardiovascular and haematological actions. But its mechanisms of action in vivo have not been fully elucidated, probably due to difficulties arising from previous findings that the effects of PAF are largely mediated by the release of a variety of other autacoids. In the present study, the roles of nitric oxide and eicosanoids in the effects of PAF (0.01-0.25 microgram kg-1 i.v.) on systemic and pulmonary vasculatures and circulating blood cell count were pharmacologically evaluated in anaesthetized dogs. 2. Higher doses of PAF (> 0.1 microgram kg-1) produced a biphasic systemic hypotension. The first hypotension seen 30 s after the injection was accompanied by a decrease in systemic vascular resistance, thrombocytopenia and leukopenia, while the second hypotension seen 1-2 min after PAF was accompanied by a marked rise in pulmonary vascular resistance and decreases in aortic blood flow and cardiac contractility. Lower doses of PAF (0.01 - 0.05 microgram kg-1) caused only the first responses in a dose dependent manner. 3. Pretreatment with indomethacin inhibited the second responses to PAF without affecting the first responses. The thromboxane A2/prostaglandin H2 (TP)-receptor antagonist vapiprost blocked the PAF-induced rise in pulmonary vascular resistance. AA-861, a 5-lipoxygenase inhibitor, attenuated the PAF-induced cardiac depression. The nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester inhibited the PAF-induced early decrease in systemic vascular resistance. 4. All observed changes in haemodynamics and blood cell count after PAF were almost abolished by TCV-309, a PAF-receptor antagonist. 5. Reproducible hypotension and thrombocytopenia produced by a lower dose of PAF (0.05 microgram kg-1) were respectively attenuated and potentiated by pretreatment with NG-nitro-L-arginine, another nitric oxide synthase inhibitor. Administration of L-arginine reversed the effects of the nitric oxide synthase inhibitor. 6. These results indicate that PAF-receptor-mediated production of not only eicosanoids but also nitric oxide may contribute to the cardiovascular and haematological responses to PAF in the dog.     

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.     

Modulation by nitric oxide of spontaneous mechanical activity in rat proximal colon

1 In order to examine the role of nitric oxide (NO) in the tonic neural inhibition in rat proximal colon, the effects of N_ω-nitro- l -arginine methyl ester (L-NAME) were studied on the spontaneous contractions of circular muscle (monitored as intraluminal pressure changes) and of longitudinal muscle (detected as isometric tension changes). 2 L-NAME (3 × 10^??6–3 × 10^??4 m ) caused a concentration-dependent increase in the amplitude of circular contractions, without affecting those of longitudinal muscle. This effect was prevented by l -arginine (1–5 × 10^??3 m ), but not d -arginine. 3 In the presence of tetrodotoxin (10^??6 m ), which per se induced increase of the pressure waves, L-NAME (10^??4 m ) caused no further effects on the amplitude of the spontaneous contractions. 4 The response to L-NAME (10^??4 m ) was unaffected by atropine (10^??6 m ), guanethidine (10^??6 m ), hexamethonium (up to 3 × 10^??4 m ) or α-chymotrypsin (up to 5 U ml^??1). 5 NK₂ receptor antagonists, SR 48968 (3 × 10^??6 m ) or MEN 10627 (10^??6 m ), produced a reduction of the amplitude of the pressure waves but failed to affect the contractile response to L-NAME (10^??4 m ). 6 These findings suggest that tonic production of NO from inhibitory neurones influences the degree of contractions of circular muscle. An involvement of an inhibitory peptide as well as disinhibition of cholinergic or NK₂-tachykinergic excitatory neurotransmission in the mechanism of NO action can be ruled out.     

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.     

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.     

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 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.     

Vascular responses to endothelin-1 following inhibition of nitric oxide synthesis in the conscious rat.

1. The objectives of the present experiments were to assess the role of endogenous nitric oxide (NO) in mediating and/or modulating the effects of endothelin-1 (ET-1) on blood pressure and microvascular permeability in conscious rats. 2. Intravenous administration of the NO synthesis inhibitors, NG-monomethyl-L-arginine (L-NMMA) or NG-nitro-L-arginine methyl ester (L-NAME) at a dose (25 mg kg-1 or 2 mg kg-1, respectively) which evoked maximum increase in mean arterial blood pressure (MABP) significantly attenuated (by about 40%) the vasodepressor response and potentiated (by 100-180%) the pressor response to ET-1 (1 nmol kg-1, i.v.) compared to the effects of ET-1 in animals where the peripheral vasoconstrictor effects of L-arginine analogues were mimicked by an infusion of noradrenaline (620-820 ng kg-1 min-1). Similar inhibition of the depressor and potentiation of the pressor actions of ET-1 were observed when the MABP which had been elevated by L-NMMA or L-NAME was titrated to normotensive levels with hydralazine or diazoxide before injection of ET-1. 3. L-NAME (2 mg kg-1) increased the vascular permeability of the large airways, stomach, duodenum, pancreas, liver, kidney and spleen (up to 280%) as measured by the extravasation of Evans blue dye. The permeability of pulmonary parenchyma, skeletal muscle and skin was not affected significantly by L-NAME treatment. Elevation of MABP by noradrenaline infusion did not evoke protein extravasation in the vascular beds studied with the exception of the lung.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of angiotensin-converting enzyme by nitric oxide

1. The aim of the present study was to determine the effect of nitric oxide (NO) on angiotensin-converting enzyme (ACE) activity.
2. A biochemical study was performed in order to analyse the effect of the NO-donors, SIN-1 and diethylamine/NO (DEA/NO), and of an aqueous solution of nitric oxide on the ACE activity in plasma from 3-month old male Sprague-Dawley rats and on ACE purified from rabbit lung. SIN-1 significantly inhibited the activity of both enzymes in a concentration-dependent way between 1 and 100 μM. DEA/NO inhibited the activity of purified ACE from 0.1 μM to 10 μM and plasma ACE, with a lower potency, between 1 and 100 μM. An aqueous solution of NO (100 and 150 μM) also inhibited significantly the activity of both enzymes. Lineweaver-Burk plots indicated an apparent competitive inhibition of Hip-His-Leu hydrolysis by NO-donors.
3. Modulation of ACE activity by NO was also assessed in the rat carotid artery by comparing contractions elicited by angiotensin I (AI) and AII. Concentration-response curves to both peptides were performed in arteries with endothelium in the presence of the guanylyl cyclase inhibitor, ODQ (10 μM), and the inhibitor of NO formation, L-NAME (0.1 mM). NO, which is still released from endothelium in the presence of 10 μM ODQ, elicited a significant inhibition of AI contractions at low concentrations (1 and 5 nM). In the absence of endothelium, 1 μM SIN-1 plus 10 μM ODQ, as well as 10 μM DEA/NO plus 10 μM ODQ induced a significant inhibition on AI-induced contractions at 1 and 5 nM and at 1–100 nM, respectively.
4. In conclusion, we demonstrated that (i) NO and NO-releasing compounds inhibit ACE activity in a concentration-dependent and competitive way and that (ii) NO release from endothelium physiologically reduces conversion of AI to AII.

     

Modulation by nitric oxide of spontaneous motility of the rat isolated duodenum: role of tachykinins.

1. Incubation of proximal segments of the rat isolated duodenum with NG-nitro-L-arginine (L-NOARG; 3-100 microM) produced a concentration-dependent increase in both resting tone and the amplitude of the spontaneous contractions. These effects were attenuated by concurrent incubation with L-arginine (1 mM) but not D-arginine (1 mM). 2. These changes in resting tone and motility induced by L-NOARG (30 microM) were substantially reduced by concurrent incubation with tetrodotoxin (1 microM) or hexamethonium (10 microM), implicating the involvement of a local neuronal response. 3. The L-NOARG-induced increase in duodenal motility was not, however, inhibited by atropine (1 microM), guanethidine (6.4 microM) phentolamine (1 microM), or indomethacin (10 microM), indicating a non-cholinergic, non-adrenergic and non-prostanoid-mediated contractile response. 4. The NK1/NK2 tachykinin receptor antagonist, (D-Pro2, D-Trp7.9 substance P, 1-10 microM), and the NK2-receptor antagonists, MEN 10,207 and MEN 10,376 (1-5 microM), concentration-dependently reduced the effect of L-NOARG (30 microM) on spontaneous duodenal motility. 5. The resting tone and amplitude of the spontaneous contractions was likewise increased by incubation with NG-monomethyl-L-arginine (L-NMMA; 100-1000 microM). However, incubation with L-NMMA (100 microM) attenuated the actions of more potent L-NOARG (30 microM) on resting motility. 6. Administration of E.coli endotoxin (3 mg kg-1, i.v.) to the rat 5 h prior to tissue removal, at a time of known induction of NO synthase, reduced the amplitude of spontaneous contractions of the isolated duodenum, an effect inhibited by pretreatment of the rats with dexamethasone (1 mg kg-1) 2 h prior to endotoxin challenge. 7. These findings indicate a role of endogenous NO in the modulation of spontaneous tone and motility in the rat duodenum. Induction of NO synthase may result in a reduction in spontaneous motility of the tissue. By contrast, inhibition of constitutive NO biosynthesis unmasks a contractile response that is neuronally mediated and involves tachykinin NK2 receptors.     

Mediation by nitric oxide formation in the preoptic area of endotoxin and tumour necrosis factor-induced inhibition of water intake in the rat.

1. Contractions in human bronchial rings evoked by methacholine (10(-6) M) were reversed by single contractions of alpha-human atrial natriuretic peptide (10(-6) M), salbutamol (10(-6) M), sodium nitroprusside (10(-6) M) or isosorbide dinitrate (4.2 x 10(-5) M) and the extent of the relaxations compared. The activity of combinations of ANP with salbutamol, sodium nitroprusside and isosorbide dinitrate were compared with those for each agonist alone. 2. ANP and salbutamol were equipotent in reversing methacholine-evoked contraction and, in combination these agonists evoked an additive response. ANP and sodium nitroprusside also evoked similar degrees of relaxation and were additive, as were ANP and isosorbide dinitrate; however, with isosorbide dinitrate a higher concentration was required to evoke the same degree of relaxation as ANP, sodium nitroprusside or salbutamol. 3. Cumulative concentration-response curves to methacholine (10(-9)-3 x 10(-4) M) were examined in the presence and absence of the above bronchodilator substances, alone and in combination allowing their abilities to protect against contraction to be compared. ANP (10(-6) M) and salbutamol (10(-6) M) each attenuated subsequent contractions evoked by methacholine, an ability not shared with sodium nitroprusside (10(-6) M) or isosorbide dinitrate (4.2 x 10(-5) M). Indeed at lower concentrations of methacholine (< 3 x 10(-7) M), sodium nitroprusside evoked a paradoxical enhancement of methacholine-evoked contractions. 4. In combination, ANP and salbutamol attenuated contractions evoked by methacholine to a significantly greater degree than that seen with either agonist alone, whilst a combination of ANP and sodium nitroprusside evoked no greater effect than that seen with ANP alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between nitric oxide and platelet-activating factor in castor-oil induced mucosal injury in the rat duodenum

The modualtion of platelet activating factor (PAF) formation in duodenal tissue by nitric oxide (NO) released in response to castor oil was studied in rats pretreated with N^G-nitro-L-arginine methyl ester (L-NAME, 6.25-25 mg/kg, i.p.), an inhibitor of NO synthase, N^G-nitro-D-arginine methyl ester (D-NAME, 25 mg/kg, i.p.), the inactive enantiomer of L-NAME or isosorbide-5-mononitrate (IMN, 30–90 mg/kg, p.o.), a NO donating compound. Castor oil (2 ml/rat orally) increased PAF production in the rat duodenum 3 h after challenge. L-NAME, but not D-NAME, enhanced the amount of PAF formed by duodenal tissue, while IMN (30–90 mg/kg) counteracted the effects of L-NAME (12.5 mg/kg) and also reduced PAF release in the tissue of rats treated with castor oil. L-NAME 12.5 mg/kg, but not D-NAME, enhanced both macroscopic damage and acid phosphatase release induced by castor oil. These effects were reduced by a PAF antagonist BN 52021 (3-t-Butyl-hexahydro-4, 7b, 11-trihydroxy-[8]-methyl-9H-1, 7a-epoxymethano-1H, 6aH-cyclopenta [c] furo [2,3b] furo [32:3,4] cyclopenta [1,2-d]furan-5,9,12(4H)trione) 10 and 20 mg/kg i.p. Such findings suggest that endogenous nitric oxide could reduce PAF biosynthesis in castor oil-treated rats.     

Modulation of stress-induced neurobehavioral changes by nitric oxide in rats

The involvement of nitric oxide (NO) in stress-induced neurobehavioral changes in rats was evaluated using the elevated plus maze and open field tests. Restraint stress (1 h) reduced both the number of entries and time spent in open arms, with both expressed as percent of controls (no restraint stress), and these changes were reversed with diazepam (1 mg/kg) and the NO precursor, L-arginine (500 and 1000 mg/kg) pretreatment. The nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) (50 mg/kg), aggravated restraint stress effects in the elevated plus maze test, whereas the lower dose (10 mg/kg) of the drug attenuated the same. In the open field test, the restraint stress-induced (a) increased entry latency and (b) decreased ambulation and rearing were reversed by diazepam and L-arginine and L-NAME (10 mg/kg), whereas L-NAME (50 mg/kg) aggravated restraint stress effects. The neuronal nitric oxide synthase inhibitor, 7-nitroindazole (10 and 50 mg/kg), did not influence these restraint stress-induced behavioral changes to any significant extent. Biochemical data showed that L-NAME (10 and 50 mg/kg.) induced opposite effects on the total brain nitrate/nitrite content during restraint stress. The results indicate a possible involvement of NO in stress-induced neurobehavioral effects.     

Platelet-activating factor: the effector of protein-rich plasma extravasation and nitric oxide synthase induction in rat immune complex peritonitis.

1. The involvement of platelet-activating factor (PAF) in immune complex-induced/polymorphonuclear-mediated tissue injury was studied by use of a reverse passive Arthus (RPA) model in the peritoneal cavity of rats. 2. Extravasation of protein-rich plasma, accumulation of polymorphonuclear leukocytes (PMN), and the production of nitric oxide (NO) by resident peritoneal mononuclear phagocytes were assayed. 3. Treatment of rats with either UR-12460 or BB-823, two compounds which possess different chemical structures, but elicit the same antagonistic effect on the PAF receptor, abrogated protein-rich plasma extravasation. In contrast, they did not show any effect on the accumulation of PMN. 4. Inhibition of NO production with both NG-mono methyl-L-arginine and NG-nitro-L-arginine failed to prevent protein-rich plasma extravasation. 5. The production of NO by peritoneal adherent cells following RPA was measured in cells maintained for 2 to 28 h in culture, and it was significantly increased in cells removed as early as 15 min after RPA induction, as compared to controls. 6. Addition of 10 nM PAF to the culture medium reduced the generation of NO by peritoneal cells from RPA rats, whereas this mediator enhanced NO production in cells from naive control animals. 7. Treatment with either UR-12460 or BB-823 prior to the induction of RPA produced an almost complete inhibition of NO production. 8. Assay of nitric oxide synthase activity in cell homogenates from peritoneal cells showed that the activity was due to the inducible form of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rosiglitazone increases extravasation of macromolecules and endothelial nitric oxide synthase in skeletal muscles of the fructose-fed rat model

Reduced extravasation of macromolecules in skeletal muscle has recently been documented in the fructose-fed rat model, corroborating a hypothesis that a functional obliteration of muscle regional microcirculation might lead to hypertension and restrict access of nutrients and hormones to their target cells. The goal of this study was to assess the impact of a treatment with rosiglitazone on the reduced muscle vasopermeability observed previously in the fructose-fed rat model. Fructose-fed Sprague-Dawley rats were gavaged with rosiglitazone (10 micromol kg(-1) per day; n = 21) or the vehicle only (n = 19) for 3 consecutive weeks before assessing the extravasation of Evans Blue (EB) dye in vivo in distinct muscle groups. Relative to control group, rosiglitazone reduced mean arterial blood pressure (Delta = -16.7%, P < 0.001), plasma insulin (Delta= -39.1%, P < 0.05) and plasma triglyceride (Delta= -32.8 %, P < 0.01) concentrations in a significant manner. Plasma VEGF concentrations were significantly lower in the rosiglitazone-treated animals compared to the control animals (32.7 +/- 0.8 pg ml(-1) versus 46.1 +/- 1.2 pg ml(-1), P < 0.001). While no changes were observed in the lungs or the kidneys, fructose-fed rats treated with rosiglitazone had a 30-50% increase (P < 0.005) in the extravasation of EB regardless of the skeletal muscle group studied (rectus femoris, soleus, gastrocnemius lateralis, vastus lateralis and tibialis cranalis). In homogenates of skeletal muscles (vastus lateralis) of fructose-fed rats, rosiglitazone resulted in a significant increase in NO synthase (NOS) activity (Delta = +41.9 %, P < 0.003) as well as endothelial NOS immunoreactive mass (Delta = +37.8 %, P < 0.01) compared to the control animals. There was no change in the immunoreactive level of the nNOS isoform, the most abundant muscle isoform, or in the immunoreactive levels of VEGF. In conclusion, rosiglitazone appears to restore a vascular dysfunction previously documented in the skeletal muscle microcirculation, as evidenced by improved skeletal muscle vasopermeability and upregulation of the muscle endothelium-NO system in the fructose-fed rat model. These effects on muscle per se might also result in a partial improvement of the insulin resistance phenomenon by improving the distribution of nutrients and insulin to skeletal muscle. This effect appears to be independent of circulating levels of VEGF since changes in plasma concentrations of this permeability factor were lower in the rosiglitazone-treated group.     

Modulation of cholinergic and substance P-like neurotransmission by nitric oxide in the guinea-pig ileum.

1. The role of endogenous nitric oxide (NO) as a modulator of enteric neurotransmission was investigated in longitudinal muscle myenteric plexus (LMMP) preparations of guinea-pig isolated ileum. 2. In tissues previously incubated with [3H]-choline, exogenous NO inhibited electrically-evoked [3H]-choline overflow as well as responses to exogenous agonists, indicating that NO has the potential of neuromodulation both pre- and postjunctionally. 3. A series of NO synthase inhibitors enhanced contractile responses to nerve stimulation indicating inhibitory neuromodulation by endogenous NO. 4. The potency order of the NO synthase inhibitors and their consistent effects after dexamethasone, on responses to nerve stimulation, indicate action on a constitutive NO synthase. 5. Responses enhanced by NO synthase inhibitors were inhibited by the substance P receptor antagonist, spantide, suggesting a neuromodulatory influence on substance P-like neurotransmission by the endogenous NO. 6. NO synthase inhibition did not modify contractile responses to application of acetylcholine or substance P, or [3H]-choline overflow, indicating that endogenous NO mainly has a prejunctional inhibitory action on substance P-like neurotransmission. Nor did it modify responses to direct electrical muscle stimulation in the presence of tetrodotoxin. This suggests a prejunctional enhancing effect by NO synthesis inhibition. 7. Evidence for endogenous NO modulation of acetylcholine release was obtained when NO synthase inhibition modified atropine-sensitive, nerve-mediated contractile responses. However, [3H]-choline overflow was unaltered by NO synthase inhibition. 8. NO synthase inhibition did not modify responses to inhibitory neurotransmission. 9. The findings suggest that endogenous NO inhibits substance P-like motor neurotransmission, probably via prejunctional mechanisms. Cholinergic transmission may also be reduced by endogenous NO, acting prejunctionally.     

Endrin-induced production of nitric oxide by rat peritoneal macrophages.

The effect of oral endrin administration to rats on the production of nitric oxide (NO) by peritoneal macrophages was investigated. Nitric oxide formation was measured as nitrite. Endrin (4.5 mg/kg) enhanced the secretion of NO by approx. 300%. The effect of endrin on NO formation was both dose- and time-dependent. Ellagic acid, which has been shown to be a potent antioxidant, inhibited the elevation of NO production induced by endrin. These results suggest that the toxicity of endrin may at least in part be due to the production of an oxidative stress.