Nitric oxide synthase mediates delta opioid receptor-induced hypothermia in rats

The role of nitric oxide (NO) production in delta opioid receptor-induced hypothermia has not been reported. The present study investigated the effect of nitric oxide synthase (NOS) inhibitors on the hypothermic effect of (+)-4-[(aR)-a-((2S,5R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC-80), a nonpeptide delta opioid agonist. SNC-80 (35 mg/kg, i.p.) administered to rats caused a significant hypothermia. N-nitro-L-arginine methyl ester (L-NAME) (10, 25 and 50 mg/kg, i.p.), a NOS inhibitor, and 7-nitroindazole (7-NI) (5 and 10 mg/kg, i.p.), a neuronal NOS inhibitor, were ineffective. For combined administration, L-NAME (50 mg/kg, i.p.) or 7-NI (10 mg/kg, i.p.) attenuated SNC-80-evoked hypothermia. To determine the involvement of central NOS, L-NAME (0.25, 0.5 and 1 mg/rat) was administered i.c.v. 30 min prior to SNC-80 (35 mg/kg, i.p.). Experiments revealed that L-NAME (1 mg/rat, i.c.v.) attenuated SNC-80-induced hypothermia. The present data demonstrate that central NO production is necessary for delta opioid receptor-induced hypothermia.     

Endogenous nitric oxide and sensory neuropeptides interact in the modulation of the rat gastric microcirculation.

1. The effects of depletion of sensory neuropeptides from primary afferent neurones by capsaicin pretreatment, on the changes in resting gastric mucosal blood flow following administration of inhibitors of nitric oxide biosynthesis have been investigated in the pentobarbitone-anaesthetized rat. 2. Bolus administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 0.8-12.5 mg kg-1 i.v.), induced a dose-dependent increase in systemic arterial blood pressure (BP) and a reduction in resting mucosal blood flow, as determined by laser Doppler flowmetry. 3. Concurrent administration of L-arginine (300 mg kg-1 i.v.) attenuated the effects of L-NAME (6.25 mg kg-1) on resting mucosal blood flow and BP. The enantiomer, D-NAME (50 mg kg-1 i.v.), which does not inhibit NO biosynthesis, had no effect on either parameter. 4. The fall in mucosal blood flow induced by submaximal doses of L-NAME (0.8-3.2 mg kg-1) was substantially augmented in rats pretreated 2 weeks earlier with capsaicin. 5. The fall in resting mucosal blood flow induced by the less potent NO-synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA; 1.6-25 mg kg-1 i.v.) was likewise significantly augmented in capsaicin-pretreated rats. 6. Pretreatment (15 min) with indomethacin (5 mg kg-1 i.v.) did not augment further the microvascular actions of L-NAME or L-NMMA in capsaicin-pretreated rats, suggesting the lack of interaction of endogenous prostanoids with these other mediators in regulating local blood flow. The effects of L-NAME on BP were not altered by capsaicin and indomethacin administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Icilin-induced wet-dog shakes in rats are dependent on NMDA receptor activation and nitric oxide production

Icilin is a cold channel agonist that produces vigorous wet-dog shaking in rats. The shaking is accompanied by an increase in the level of extracellular glutamate in the brain. Hence, we hypothesized that icilin-induced wet-dog shakes are dependent on increased glutamatergic transmission and nitric oxide (NO) production. Rats injected with icilin (0.5, 1, 2.5, 5 mg/kg, i.p.) displayed a dose-related increase in wet-dog shakes. Pretreatment with LY 235959 (1, 2 mg/kg, i.p.), a NMDA receptor antagonist, or L-NAME (50 mg/kg, i.p.), a NO synthase (NOS) inhibitor, attenuated icilin-induced wet-dog shakes. The shaking was also reduced by intracerebroventricular L-NAME (1 mg/rat, i.c.v.) administration, indicating that the stimulant effect of icilin is dependent on central NO production. Pretreatment with 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX) (10, 20 mg/kg, i.p.), an AMPA receptor antagonist, or ceftriaxone (200 mg/kg, i.p. for 5 days), a beta-lactam antibiotic and glutamate transporter subtype 1 (GLT-1) activator, did not alter the incidence of icilin-induced shaking. The present data reveal that icilin produces behavioral stimulation by a mechanism requiring NMDA receptor activation and nitric oxide production and suggest that glutamate and NO signaling play important roles in cold channel pharmacology.     

Effects of nitric oxide synthase inhibitors and melatonin on the hyperglycemic response to streptozotocin in rats

Recent studies evidence that peroxynitrite is spontaneously formed when nitric oxide (NO) and superoxide coexist and suggest that it is likely to be involved in the destruction of the pancreatic beta cells. We examined whether drugs that inhibit nitric oxide synthase (NOS) or scavenge peroxynitrite could abrogate STZ-induced hyperglycemia in rats. Blood glucose levels were measured before (0 h) and 24, 48, and 72 h following intraperitoneal administration of 60 mg/kg streptozotocin (STZ). The levels of blood sugar in STZ-treated control animals were significantly elevated at all time points of observation with a peak increase at 48 h. The hyperglycemic response of STZ was found to be significantly reduced in animals pretreated with aminoguanidine (50 mg/kg i.p.), an inducible isoform-selective NOS (iNOS) inhibitor with antioxidant property, and by melatonin (6 mg/kg i.p.), an antioxidant that also prevents peroxynitrite formation but not by Nw-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.p.), and 7-nitroindazole (7-NI, 50 mg/kg i.p.), the constitutive inhibitors of endothelial and neuronal NOS, respectively. These findings indicate the possible participation of iNOS-derived NO as well as oxygen free radicals in STZ-induced pancreatic beta cell destruction and compounds that act as scavengers of peroxynitrite may offer protection against such a damage.     

L-arginine dilates rat pial arterioles by nitric oxide-dependent mechanisms and increases blood flow during focal cerebral ischaemia.

L-Arginine (> or = 30 mg kg-1, i.v.), but not D-arginine (300 mg kg-1) administered 5 min after unilateral common carotid/middle cerebral artery occlusion increased regional cerebral blood flow (rCBF) within the dorsolateral ischaemic cortex in spontaneously hypertensive rats. L-Arginine (300 mg kg-1) increased rCBF from 22 +/- 2.7 to 33 +/- 4% of baseline as measured by laser-Doppler flowmetry. This increase may explain the ability of L-arginine to reduce infarct size following focal cerebral ischaemia, as reported previously. The mechanism appears to be mediated by nitric oxide since topical L-NAME (1 microM), a nitric oxide synthase inhibitor, decreased pial arteriole calibre from 115 +/- 2.2 to 106 +/- 0.9% of baseline following L-arginine infusion (300 mg kg-1).     

The effects of nitric oxide on the acquisition and expression of nicotine-induced conditioned place preference in mice

In the present study, the possible role of nitric oxide on the conditioned place preference (CPP) induced by nicotine in mice was investigated. Intraperitoneal (i.p.) injections of nicotine (1 mg/kg) and the nitric oxide (NO) precursor, L-arginine (200 and 500 mg/kg), produced significant place preference. However, injection of mecamylamine (0.05 and 0.1 mg/kg; i.p.) or the NO synthase (NOS) inhibitor, L-Nitro-amino-methyl-ester, L-NAME (5-20 mg/kg; i.p.), had no effect. Ineffective doses of nicotine in combination with ineffective doses of L-arginine produced significant place preference. Administration of L-arginine (50, 100 and 150 mg/kg; i.p.) on the test day reduced the expression of nicotine-induced place preference. Nicotine injection (0.25, 0.5 and 0.75 mg/kg) on the test day reduced the expression of place preference induced by L-arginine, while both mecamylamine (0.05 and 0.1 mg/kg) and L-NAME (5, 10 and 20 mg/kg) inhibited the acquisition of place preference induced by nicotine (1 mg/kg) and L-arginine (200 mg/kg). Moreover, neither of the antagonists reduced the expression of nicotine- or L-arginine-induced place preference. It is suggested that nitric oxide may play an important role in nicotine-induced place preference.     

Involvement of nitric oxide in the modulation of dural arterial blood flow in the rat

1. Nitric oxide (NO) has been proposed to be a key molecule in the pathogenesis of migraine pain and other headaches that are linked to vascular disorders. Several lines of evidence indicate that the meningeal vascularization is crucially involved in the generation of these headaches. In an experimental model in the rat a dominating role of calcitonin gene-related peptide (CGRP) in causing neurogenic vasodilatation and increased blood flow has been shown. The aim of the present study was to clarify the role of NO in this model with regard to the meningeal blood flow. 2. The blood flow in and around the medial meningeal artery (dural arterial flow) was recorded in the exposed parietal dura mater encephali of barbiturate anaesthetized rats using laser Doppler flowmetry. Local electrical stimulation of the dura mater (pulses of 0.5 ms delivered at 7.5 - 17.5 V and 5 or 10 Hz for 30 s) caused temporary increases in dural arterial flow for about 1 min that reached peaks of 1.6 - 2.6 times the basal flow. The effects of NO synthase (NOS) inhibitors on the basal flow and the electrically evoked increases in flow were examined. 3. Systemic (i. v.) administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) at cumulative doses of 10 and 50 mg kg(-1) lowered the basal flow to 87 and 72%, respectively, of the control and reduced the evoked increases in blood flow to 82 and 44% on an average. Both these effects could partly be reversed by 300 mg kg(-1) L-arginine. The systemic arterial pressure was increased by L-NAME at both doses. Injection of the stereoisomer D-NAME at same doses did not change basal flow and evoked increases in flow. 4. 4. Topical application of L-NAME (10(-4) - 10(-2) M) was effective only at the highest concentration, which caused lowering of the basal blood flow to 78% of the control; the evoked increases in flow were not changed. Topical application of 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), a specific inhibitor of the inducible NOS, at concentrations of 10(-4) - 10(-2) M lowered the basal flow to 89, 87.5 and 85%, respectively, but did not significantly change the evoked flow increases. Same concentrations of 7-nitroindazole monosodium salt (7-NINA), a specific inhibitor of the neuronal NOS, had no significant effects on basal flow and evoked increases in flow. 5. It is concluded that NO is involved in the maintenance of the basal level of dural arterial blood flow as well as in the electrically evoked flow increases, which have been shown to be mainly mediated by CGRP released from dural afferent fibres. The most important source of NO is probably the endothelium of dural arterial vessels. The synergistic effect of NO and CGRP on the stimulated blood flow may be in part due to a NO mediated facilitation of the CGRP release.     

Role of nitric oxide in the gastric cytoprotection induced by central vagal stimulation

The role of nitric oxide (NO) in the vagal cholinergic-mediated cytoprotective effect of intracisternal (i.c.) injection of the stable thyrotropin-releasing hormone (TRH) analog, RX 77368, was investigated in conscious rats. RX 77368 (1.5 ng i.c.) reduced by 88% gastric hemorrhagic lesions induced by oral administration of ethanol (60%). L-N^G-Nitro-arginine methyl ester (L-NAME, 3 mg/kg i.v.), an inhibitor of NO synthase, abolished the cytoprotection provided by i.c. RX 77368. The effect of L-NAME was reversed by L- but not D-arginine. These results suggest that the L-arginine-nitric oxide pathway is involved in the cytoprotective effect of i.c. TRH analog, probably through the modulation of gastric mucosal blood flow.     

Role of nitric oxide in gastric injury induced by hemorrhagic shock in rats

The aim of this study was to investigate the effect of nitric oxide (NO) on the gastric injury induced by hemorrhagic shock. Hemorrhagic shock was created by withdrawing 3 ml blood/200 g body weight of the rats. Before the hemorrhage, N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg i.v. bolus), D-NAME (10 mg/kg i.v. bolus), or L-arginine (100 mg/kg i.v. bolus and 10 mg/kg/min infusion) + L-NAME were administered. At the end of the 1-hour hypovolemic shock period, histological analysis, gastric ulcer index, gastric myeloperoxidase (MPO) activity, and gastric protein oxidation (PO) levels were determined. In histological analysis a destructive effect of L-NAME (NO synthase inhibitor) was demonstrated. L-NAME treatment increased gastric MPO activity, L-arginine reversed this effect and D-NAME had no effect. Tissue PO activity was found to be increased in L-NAME-treated rats; L-arginine treatment reversed this activity. It is concluded that gastric barrier function is altered after hemorrhagic shock, and L-arginine (NO precursor) can prevent mucosal injury in the stomach. This effect of NO may be on gastric blood flow and can be mediated by tissue neutrophils.     

Role of nitric oxide synthase inhibitors and NMDA receptor antagonist in nicotine-induced behavioral sensitization in the rat

Repeated injections of nicotine are well known to produce progressively larger increases in locomotor activity, an effect defined as behavioral sensitization. This study was carried out to investigate the role of nitric oxide (NO) and N-methyl-D-aspartate (NMDA) receptors in nicotine-induced behavioral sensitization. Rats were given repeated injections of nicotine (0.4 mg/kg, s.c., twice daily for 7 days) followed by one challenge injection on the fourth day after the last daily injection. Systemic challenge with nicotine produced a much larger increase in locomotor activity in nicotine-pretreated rats. Rats were pretreated with the nonselective nitric oxide synthase (NOS) inhibitor, N(G)-nitro-arginine-methyl-ester (L-NAME; 75 mg/kg, i.p.), the selective constitutive NOS inhibitor, N-nitro-L-arginine (L-NNA; 15 mg/kg, i.p.), the prototypical selective inducible NOS inhibitor, aminoguanidine (100 mg/kg, i.p.) or NMDA receptor antagonist, MK-801 ((5R,10S)-(+)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine; 0.3 mg/kg, i.p.), 30 min before injections of nicotine during a 7-day development or a 3-day withdrawal phase after which challenged with nicotine on day 11. Pretreatment with L-NAME, L-NNA and MK-801, but not aminoguanidine, blocked the development of nicotine-induced sensitization to subsequent nicotine challenge. Injections of MK-801 twice daily during 3-day withdrawal periods after a 7-day induction period of nicotine attenuated nicotine-induced behavioral sensitization, whereas injections of L-NAME, L-NNA or aminoguanidine had no effects on the expression of sensitization produced by repeated nicotine. This study demonstrates that NMDA receptors can play a major role in the expression as well as development of nicotine-induced behavioral sensitization, and that NO is also involved in the development, but not critically involved in the expression of behavioral sensitization to nicotine.     

The role of nitric oxide in systemic and hepatic haemodynamics in the rat in vivo

The physiological role of nitric oxide (NO) in portal venous and hepatic arterial haemodynamics in the rat in vivo during healthy and diseased conditions remains unclear. The present study determined the physiological role of nitric oxide in hepatic haemodynamics in the rat in vivo during healthy conditions as a basis for future pharmacological work. Male Wistar rats (300–350 g) were anaesthetised with fentany/fluanisone (0.3 mg/kg s.c.) and midazolam (0.3 mg/kg s.c.) and heparinised (30 U/100 g i.v.) via a cannulated left carotid artery for measurement of heart rate, mean arterial pressure, and the difference between systolic and diastolic blood pressures (P_S-D). Following laparotomy, two distal ileocolic veins were cannulated, one catheter introduced to a distance of 1 cm and used for intraportal drug injections and the other to the main trunk of the portal vein for continuous measurement of portal venous pressure. The portal venous trunk and hepatic artery were carefully isolated and electromagnetic probes placed around each of them for measurement of portal venous flow and hepatic arterial flow. Augmentation of NO production was achieved by intraportal injection of 0.2, 0.4, 0.6 and 0.8 g/kg L-arginine and the NO donor, 3-morpholinosydnonimine (SIN-1), was injected intraportally at 0.2, 0.4, 0.6 and 0.8 mg/kg. L-NAME, the non-selective NOS inhibitor, was injected intraportally in increasing doses of 5, 10, 15 and 20 mg/kg in the absence or presence of L-arginine in doses of 0.2 and 0.5 g/kg. L-arginine increased portal blood flow by 25% without significant changes in systemic haemodynamics. SIN-1 decreased mean arterial pressure by 33% with no effect on portal blood flow. Both L-arginine and SIN-1 reduced portal venous pressure by 25% in a dose-dependent manner. L-NAME had no effect on portal haemodynamics despite a significant increase in systemic arterial pressure of 60% that was reduced dose-dependently by L-arginine. Hepatic arterial flow increased by 88% and 49% at the second and third doses of L-arginine and by 68% and 27% at the first two doses of L-NAME. No significant changes in hepatic arterial flow were found when L-NAME and L-arginine were given together. It is concluded that augmented endogenous NO production increased portal flow. Inhibition of endogenous NO had no effect on portal haemodynamics. Endogenous NO may not play a major role in regulation of portal haemodynamics in the rat in vivo.     

Nitric oxide signaling pathway in the anti-convulsant effect of adenosine against pentylenetetrazol-induced seizure threshold in mice

The present study was performed to examine the involvement of nitric oxide (NO) signaling pathway in the anti-convulsant effect of adenosine against pentylenetetrazol seizure threshold in mice. Minimal dose of pentylenetetrazol (i.v., mg/kg) needed to induce different phases (myoclonic jerks, generalized clonus and tonic extension) of convulsions was recorded as an index of seizure threshold. Adenosine (100 or 200 mg/kg i.p.) produced a significant increase in the seizure threshold for convulsions induced by pentylenetetrazol i.v. infusion. The anti-convulsant effect of adenosine (100 mg/kg i.p.) was prevented by either L-arginine (50 mg/kg i.p.) [substrate for nitric oxide synthase (NOS)] or sodium nitroprusside (3 mg/kg i.p.) [a NO donor]. On the other hand, N(G)-nitro-L-arginine methyl ester (L-NAME, 2.5 mg/kg i.p.) [a non-selective NOS inhibitor] or 7-nitroindazole (7-NI) (25 mg/kg i.p.) [a specific neuronal nitric oxide synthase (nNOS) inhibitor] potentiated the anti-convulsant action of sub-effective dose of adenosine (50 mg/kg i.p.). Aminoguanidine (100 mg/kg i.p.) [a specific inducible NOS (iNOS) inhibitor] pre-treatment was not effective in inducing anti-convulsant effect with sub-effective dose of adenosine (50 mg/kg i.p.). Furthermore, the increase in seizure threshold elicited by adenosine (100 mg/kg i.p.) was also inhibited by concomitant administration with sildenafil (5 mg/kg i.p.) [phosphodiesterase 5 inhibitor]. In contrast, treatment of mice with methylene blue (1 mg/kg i.p.) [a direct inhibitor of both nitric oxide synthase (NOS) and soluble guanylate cyclase (sGC)] failed to induce anti-convulsant action with adenosine (50 mg/kg i.p.) against pentylenetetrazol i.v. infusion. The results demonstrated that the anti-convulsant action of adenosine in the pentylenetetrazol i.v. seizure threshold paradigm may possibly involve an interaction with the L-arginine-NO-cGMP pathway which may be secondary to the activation of adenosine receptors.     

Nitric oxide mediates rat mucosal vasodilatation induced by intragastric capsaicin.

The role of endogenous nitric oxide (NO) in the gastric mucosal vasodilatation induced by acute intragastric perfusion with capsaicin or close-arterial infusion of rat alpha-calcitonin gene-related peptide (CGRP) was evaluated in the pentobarbitone-anaesthetised rat using laser Doppler flowmetry (LDF). The mucosal vasodilatation induced by intraluminal capsaicin (160 microM) was dose dependently reduced by the inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (L-NAME; 1-5 mg kg-1 i.v.), effects reversed by concurrent administration of L-arginine (100 mg kg-1 i.v.). L-NAME (2 mg kg-1) induced a small reduction in the mucosal vasodilatation induced by close-arterial infusion of rat alpha-CGRP (50 pmol kg-1 min-1). These findings indicate a role of NO in the gastric vasodilatation induced by stimulation of sensory neurones with intragastric capsaicin.     

Evidence for a role of nitric oxide in hypovolemic hemorrhagic shock.

Hypovolemic hemorrhagic shock was induced in rats by intermittently withdrawing blood from an iliac catheter for 20 min until mean arterial blood pressure (MAP) decreased to 30 mm Hg. Survival rate, survival time, plasma myocardial depressant factor (MDF) activity, MAP, and microscopic gastric alterations were then evaluated. NG-nitro-L-arginine methyl-ester (L-NAME), a selective inhibitor of nitric oxide (NO) production from L-arginine, was injected intravenously (i.v.) after the bleeding was discontinued. Untreated hemorrhagic shocked rats died in 27 +/- 3.3 min, had enhanced plasma activity of MDF, and exhibited hemorrhagic infiltrates in gastric fundus mucosa. L-NAME (5 and 10 mg/kg) significantly increased survival rate and time, blunted the increase in plasma MDF activity, and protected against the gastric lesions induced by hemorrhagic hypovolemic shock. All these protective effects were reversed by a bolus of L-arginine (30 mg/kg/i.v.), given 2 min after administration of L-NAME. Our findings suggest that NO production plays an important role in the pathophysiology of hemorrhagic shock.     

The role of nitric oxide in the reversal of hemorrhagic shock by oxotremorine.

In the present study, the effect of the nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methylester (L-NAME), on the antishock actions of oxotremorine was investigated in rats subjected to hemorrhagic shock under urethane anesthesia. L-citrulline production in the AV3V region, as an indicator of nitric oxide (NO) synthesis, was assayed by high-performance liquid chromatography (HPLC) with fluorescent detection throughout the experiment. The rats were pretreated with either intravenous (i.v.) physiological saline or L-NAME (2.5 mg/kg) before bleeding. L-NAME potentiated the reversal of hypotension by oxotremorine (25 microg/kg, i.v.). However, oxotremorine either alone or in combination with L-NAME did not produce any significant change in 60-min survival rate at this low dose. Analysis of microdialysis samples collected from the AV3V region showed that L-citrulline concentration increased during bleeding and that this increase was abolished by L-NAME pretreatment. These results may suggest that nitric oxide production contributes to hypotension in rats bled to shock since nitric oxide levels in the AV3V region increased in response to bleeding and nitric oxide synthase (NOS) inhibition abolished this increase and potentiated the oxotremorine-induced reversal of hypotension.     

Raloxifene lowers ischaemia susceptibility by increasing nitric oxide generation in the heart of ovariectomized rats in vivo

We studied the effects of a 2-week period of oral raloxifene therapy on the cardiac level of nitric oxide (NO) and on the susceptibility to angina in ovariectomized rats. Ovariectomy decreased the activity of Ca2+-dependent nitric oxide synthase (NOS) in the left ventricle, an effect restored by raloxifene (0.2-5 mg kg(-1) day(-1)) or 17beta-oestradiol (0.3 mg kg(-1) day(-1)). Ovariectomy led to a significant ST segment depression after the injection of (1) ornithine-vasopressin (0.5 IU kg(-1), i.v.) or (2) epinephrine (10 microg kg(-1), i.v.), followed 30 s later by phentolamine (15 mg kg(-1), i.v.); both effects were reversed by raloxifene or 17beta-oestradiol treatment. Inhibition of nitric oxide synthase (with NG-nitro-L-arginine methyl ester [L-NAME]; 5 mg kg(-1), s.c.) augmented the ST segment depression in the ovariectomized rat and abolished the anti-ischaemic effect of 17beta-oestradiol or raloxifene. Thus, an oestrogen deficiency down-regulates the cardiac constitutive nitric oxide synthase, which increases the susceptibility of the heart to ishaemia because both actions can be blocked by exogenous administration of the natural oestrogen 17beta-oestradiol or the selective oestrogen-receptor modulator (SERM) raloxifene. In the present in vivo system, raloxifene exerts oestrogen-agonist properties.     

Low endotoxemia prevents the reduction of gastric blood flow induced by NSAIDs: role of nitric oxide

1 The role of nitric oxide (NO) in the effects of low endotoxemia on gastric damage and blood flow has been evaluated in indomethacin-treated rats. 2 Pretreatment (-1 h) with endotoxin (40 micro g kg(-1)) reduced gastric damage induced by indomethacin (20 mg kg(-1)) in conscious rats. 3 Endotoxin prevented the reduction in gastric blood flow (laser Doppler flowmetry) induced by indomethacin in pentobarbital-anaesthetised rats. 4 Pretreatment with an NO-synthase (NOS) inhibitor (L-NAME, 1 mg kg(-1)) reversed the protective effect of endotoxin on gastric blood perfusion. 5 Endotoxin did not modify the expression of mRNA for endothelial NOS or inducible NOS in the gastric corpus when evaluated 1 h postinjection. However, a 3.8-fold increase in inducible NOS mRNA and a 61% reduction in endothelial NOS mRNA were observed in the gastric corpus 4 h after endotoxin administration. 6 Evaluation of both total and Ca(2+)-dependent NOS activity by analysing the rate of conversion of L-arginine to L-citrulline in gastric corpus homogenates showed no differences between animals treated with endotoxin and those treated with saline 1 or 4 h beforehand. Ca(2+)-independent NOS activity was almost non-apparent in control as well as in endotoxin-treated rats at all the time points analysed. 7 Low endotoxemia preserves blood perfusion and protects the gastric mucosa against the deleterious effects of indomethacin through the endogenous NO release. NO synthesis in response to endotoxin does not involve the inducible NOS, but probably depends on the post-translational/biochemical regulation in vivo of a Ca(2+)-dependent NOS, most probably endothelial NOS.     

The effect of NG-nitro-L-arginine methyl ester upon basal blood flow and endothelium-dependent vasodilatation in the dog hindlimb.

1. The role played by the endothelium-derived relaxing factor (EDRF), nitric oxide (NO) in the regulation of blood flow to the skeletal muscle vasculature of the dog skinned hindlimb has been determined by examining the effects of the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) upon (i) basal iliac artery blood flow, (ii) vasodilator responses to endothelium-dependent and -independent agonists and (iii) reactive hyperaemic responses to arterial occlusion. 2. L-NAME (0.1-3 mg min-1) infused directly into the iliac artery dose-dependently reduced basal iliac artery blood flow by a maximum of 48.6 +/- 6.9% (n = 4) and also increased mean systemic arterial blood pressure by 25.6 +/- 5.0 mmHg (n = 4) (at 3 mg min-1 L-NAME). 3. Over the same dose range, L-NAME also inhibited the peak vasodilator responses to intra-arterially administered, submaximal bolus doses of the endothelium-dependent agonists, bradykinin (3-300 ng) and acetylcholine (30-300 ng) by approximately 40%. In contrast, peak vasodilator responses to the endothelium-independent agonists, sodium azide (3-30 micrograms) and adenosine (0.3-1 mg), and peak reactive hyperaemic responses to arterial occlusion (60 s) were largely unaffected by L-NAME. 4. The dose-related effects of L-NAME on basal iliac artery blood flow, mean systemic arterial blood pressure and endothelium-dependent vasodilator responses were significantly attenuated by pretreatment with L-arginine (100 mg min-1) followed by co-infusion of L-arginine (100 mg min-1) with L-NAME.(ABSTRACT TRUNCATED AT 250 WORDS)     

Altered vasodilator role of nitric oxide synthase in the pancreas, heart and brain of rats with spontaneous type 2 diabetes

Type 2 diabetes is associated with altered regional blood flow and expression of nitric oxide synthase (NOS). We examined the functional role of constitutive and inducible NOS synthase (cNOS and iNOS, respectively) on regional blood flow in thiobutabarbital-anesthetized Zucker diabetic fatty (ZDF) and control rats via the radioactive microspheres technique. Blood flow was measured at baseline (1 h after surgery), after i.v. administration of 1400W (N-3-aminomethyl-benzyl-acetamidine, selective iNOS inhibitor, 3 mg/kg), and again after i.v. N(G)-nitro-l-arginine methyl ester (L-NAME, non-selective NOS inhibitor, 8 mg/kg). Both groups had similar baseline mean arterial pressure, cardiac output and total peripheral resistance, but the ZDF rats had lower heart rate relative to the control rats (272 versus 305 beats/min). Whereas 1400W did not alter mean arterial pressure or blood flow in either group, L-NAME markedly increased mean arterial pressure and total peripheral resistance, and reduced cardiac output, heart rate, blood flow and arterial conductance in all organs/tissues of both the control and ZDF rats. L-NAME caused greater vasoconstriction in the heart (1.5-times the constriction in control rats) and brain (1.5-times) of the ZDF rats, but less in the pancreas (0.6-times). Thus, cNOS had greater vasodilator control of the heart and brain, but less in the pancreas of the ZDF than control rats. iNOS has negligible influence on blood flow in both groups of rats.