Tissue Nitric Oxide Concentration Research Articles

Dapsone Protects Against Lithium-Pilocarpine-Induced Status Epilepticus in Rats through Targeting Tumor Necrosis Factor-α and Nitrergic Pathway.

Status epilepticus (SE) results in permanent neuronal brain damage in the central nervous system. One of the complex etiologies underlying SE pathogenesis is neuroinflammation. Dapsone has been recently considered as a potential neuroprotective agent in neuroinflammatory conditions. Therefore, the present study aims to investigate effects of dapsone on lithium-pilocarpine-induced SE in rats and assess whether tumor necrosis factor-alpha (TNF-α) and nitric oxide (NO) pathway participate in this effect. SE was established by injecting lithium chloride (127 mg/kg, intraperitoneally [i.p.]) and pilocarpine (60 mg/kg, i.p.). The animals received pre-treatment dapsone (2, 5, 10, and 20 mg/kg, oral gavage) and post-treatment dapsone (10 mg/kg). Subsequently, seizure score and mortality rate were documented. To assess the underlying signaling pathway, L-Nω-Nitro-L-arginine methyl ester hydrochloride (a non-specific NO synthase [NOS] inhibitor), 7-nitroindazole (a specific neuronal NOS inhibitor), and aminoguanidine (a specific inducible NOS inhibitor) were administered 15 minutes before dapsone (10 mg/kg) pre- or post-treatment. Hippocampal tissue TNF-α and NO concentrations were quantified using the enzyme-linked immunosorbent assay method. Dapsone (10 mg/kg) pre-and post-treatment significantly attenuated the increased seizure score and mortality rate due to lithium-pilocarpine-induced SE. The development of SE in animals was associated with higher TNF-α and NO metabolites levels, which notably decreased in the dapsone-treated rats. Moreover, co-administration of NOS inhibitors with dapsone markedly reversed the anti-epileptic effects of dapsone and caused an escalation in TNF-α level but a significant reduction in NO concentration level. It seems that dapsone may exert an anti-epileptic effect on lithium-pilocarpine-induced SE through TNF-α inhibition and modulation of the nitrergic pathway.

Nitric oxide mediated effects on reproductive toxicity caused by carbon disulfide in male rats

This study investigated nitric oxide (NO) mediation of carbon disulfide (CS2) toxicity that compromised male rat spermatogenesis and endocrine function. Rats were exposed to multiple levels of CS2 concentration (0, 50, 250, 1250mg/m3). A 1250mg/m3 CS2+sodium nitroprusside (SNP) group and a 1250mg/m3 CS2+NG-monomethyl-l-arginine (l-NMMA) group were established to explore the role of NO in mediating CS2 toxicity. NO concentrations, NO synthase (NOS) activity, and sex hormone levels were measured, and sperm characteristics were observed and analyzed. Our data show that CS2 exposure decreased: NOS activity; tissue NO concentrations; serum levels of gonadotropin-releasing hormones, luteinizing hormones, and testosterone; and sperm count and activity. In contrast, increased serum follicle-stimulating hormone concentrations and teratospermia were observed with CS2 exposure. SNP reduced some of the toxic effects of CS2, while l-NMMA treatment showed no effect. The results suggests that NO mediates compromised reproductive system function caused by CS2 exposure.

The protective potential of Yucca schidigera (Sarsaponin 30®) against nitrite-induced oxidative stress in rats

The present study was designed to determine the protective effects of Yucca schidigera (Ys) against oxidative damage induced by acute nitrite intoxication as well as the histopathological evaluation of Ys in rats. The rats were divided into three groups each containing 12 rats: control (C); nitrite intoxication (N); Ys + nitrite intoxication (NY). C and N groups were fed standard rat feed (SRF). The NY group was fed SRF + 100 ppm Ys powder for 4 weeks. Acute nitrite intoxication was induced by subcutaneous (s.c.) administration of sodium nitrite (60 mg/kg) 1 day after the feeding period. Fifty minutes after sodium nitrite administration, blood samples and tissues including lung, liver, and kidney were collected for clinical biochemistry and histopathological investigations. Ys treatment was found to decrease methemoglobin, blood and tissue malondialdehyde, and tissue nitric oxide concentrations, and to increase the glutathione in blood and various tissues. However, plasma nitric oxide, total antioxidant activity, beta-carotene, and vitamin A did not differ between N and NY groups. While the N group rats showed distinct pathology in various tissues (compared with controls), the NY group had similar lung and liver pathology to the control. Only moderate or mild hemorrhage and hyperemia were seen in kidneys of NY group rats. Consequently, the natural compounds found in Ys, such as polyphenols, steroidal saponins, and other phytonutrients, could be used to substantially protect the organism from nitrite-induced oxidative damage and its complications.

Pitavastatin prevents intestinal ischemia/reperfusion–induced bacterial translocation and lung injury in atherosclerotic rats with hypoadiponectinemia

Atherosclerosis with hypoadiponectinemia can be further aggravated by intestinal ischemia/reperfusion (II/R)-induced injuries, such as bacterial translocation and lung injury. We investigated the effect of statin administration on the risk of II/R-induced injury in atherosclerotic rats with hypoadiponectinemia. Wistar rats were divided into 4 groups: (1) the Normal group (normal diet), (2) the Chol group (2% high cholesterol diet), (3) the St-1w group, and (4) the St-2w group (Chol group plus pitavastatin administration for 1 or 2 weeks, respectively). The serum concentrations of lipids and adiponectin were measured preoperatively. After midline laparotomy (time, T0), the superior mesenteric artery was occluded with a microvascular clamp for 30 min, followed by 360 min of reperfusion (T1). Intestinal and lung nitric oxide (NO) concentrations were measured. Intestinal injury was assessed by microcirculatory flow, histology, and permeability. Bacterial translocation was assessed by analysis of serum peptidoglycan concentration. Lung injury was assessed by histologic examination, pulmonary permeability index, and wet/dry lung weight ratio. The 2-week administration of statins with high-cholesterol feeding (St-2w group) improved hypoadiponectinemia to levels similar to those of the Normal group. Intestinal and lung NO concentrations were significantly lower at T1 in the Normal and St-2w groups than in the Chol group. Statin administration improved poor recovery of intestinal microcirculatory flow in the Chol group. At T1, intestinal and lung injuries were significantly aggravated and serum peptidoglycan concentration was significantly elevated in the Chol group compared with the Normal and St-2w groups. The 1-week administration of statins had no significant influence on serum adiponectin levels, tissue NO concentration, or tissue injury. Administration of pitavastatin reduces the risk of II/R-induced injury in atherosclerotic rats with hypoadiponectinemia by improving hypoadiponectinemia and inhibiting inducible NO synthase-produced NO. Furthermore, preoperative improvement of hypoadiponectinemia may be important as an index of the protective effect of pitavastatin for II/R-induced injury in atherosclerotic rats with hypoadiponectinemia.

A Comparative ESR Study on Blood and Tissue Nitric Oxide Concentration during Renal Ischemia-Reperfusion Injury

Electron paramagnetic resonance (EPR) spin trapping technology is a sensitive and unambiguous method for detection of nitric oxide (NO). Due to the short lifetime, NO must be trapped before EPR measurement. There are two EPR spin trapping techniques used currently, including the detections of EPR signals of diethyldithiocarbamate-iron-nitric oxide (DETC2-Fe2+-NO) and nitrosyl hemoglobin (HbNO). In this study, we firstly investigated the kinetics of the EPR signal of DETC2-Fe2+-NO in normal and ischemia-reperfused kidneys. In normal rat kidneys, the signal of DETC2-Fe2+-NO was found at 5 min after the spin trappers Fe2+/DETC were administrated, the peak concentration was at 15 min and the period with relatively stable signal intensity was at the time range from 15 to 70 min. In the ischemia-reperfused rat kidneys, the signal of DETC2-Fe2+-NO was increased at 30 min of ischemia and decreased at 60 min of ischemia after the occlusion of renal artery (corresponding to the time course of 60 and 90 min after Fe2+/DETC injection respectively). We then investigated the EPR signal of HbNO in blood. No characteristic HbNO signal was found in the rats of the sham control and 30 min of ischemia. An HbNO signal occurred in the rats exposed to 60 min of ischemia and it became pronounced with increased duration of reperfusion. The signal intensity reached a plateau at 150 min of reperfusion. The results suggest that the DETC2-Fe2+-NO signal can be only suitable for the NO measurement in the short-term ischemia-reperfusion model, whereas the HbNO signal can be applied to represent NO in the relatively long-term ischemia-reperfusion model. In addition, NG-nitro-L-arginine (L-NAME) and allopurinol were used to identify the source of NO. By detecting the HbNO signal, we demonstrated that the activation of xanthine oxidase is an important source of NO formation at the long-term period of ischemia and reperfusion.

Neuroprotection with Erythropoietin Administration Following Controlled Cortical Impact Injury in Rats

This study was designed to determine the effect of erythropoietin (Epo) on cerebral blood flow (CBF), nitric oxide (NO) concentration, and neurological outcome after traumatic brain injury. In one experiment, the hemodynamic effects of Epo were determined after controlled cortical impact injury (CCII) by measuring mean arterial pressure, intracranial pressure, CBF using laser Doppler flowmetry, and brain tissue NO concentrations using an NO electrode. In total, 41 rats were given either Epo (5000 U/kg) or saline s.c. 3 days before injury. In animals pretreated with saline, L-arginine but not D-arginine administration resulted in a significant increase in tissue NO concentrations and an improvement in CBF at the impact site. Likewise, in animals pretreated with Epo, L-arginine but not D-arginine given postinjury increased brain tissue NO concentrations and increased CBF. In another experiment, 74 rats underwent CCII (3-mm deformation, velocity 5 m/s), and they were given saline or Epo 5000 U/kg s.c. at 5 min, 1 h, 3 h, 6 h, 9 h, or 12 h postinjury. The contusion volume and cell counts of viable neurons in the CA1 and CA3 regions of the hippocampus were assessed at 2 weeks postinjury. The contusion volume was significantly reduced at 5 min, 1 h, 3 h, and 6 h postinjury Epo administration. The neuron density in the CA1 and CA3 region of the hippocampus was increased at 1, 3, and 6 h after injury. These data demonstrate the neuroprotective effects of Epo in traumatic injury, and the effects are optimal when Epo is given within 6 h of injury.

Effect of smoking on exhaled nitric oxide and flow-independent nitric oxide exchange parameters

It is a well-known fact that smoking is associated with a reduction in exhaled nitric oxide (NO) levels. There is, however, limited knowledge relating to the smoking-induced changes in production or exchange of NO in different compartments of the airways. This study comprised 221 adult subjects from the European Community Respiratory Health Survey II, who were investigated in terms of their exhaled NO, lung function, immunoglobulin E sensitisation and smoking habits. The following parameters were determined using extended NO analysis: airway tissue nitric oxide concentration (Caw,NO), airway transfer factor (or diffusing capacity) for nitric oxide (Daw,NO), alveolar nitric oxide concentration (CA,NO) and fractional exhaled nitric oxide concentration at a flow rate of 50 mL x s(-1) (FeNO,0.05). Maximum total airway nitric oxide flux (J'aw,NO) was calculated from Daw,NO(Caw,NO-CA,NO). Current smokers (n = 35) exhibited lower (geometric mean) FeNO,0.05 (14.0 versus 22.8 ppb), Caw,NO (79.0 ;versus 126 ppb) and J'aw,NO (688 versus 1,153 pL x s(-1)) than never-smokers (n = 111). Ex-smokers (n = 75) were characterised by lower FeNO,0.05 (17.7 versus 22.8 ppb) and Jaw,NO (858 versus 1,153 pL x s(-1)) than never-smokers. These relationships were maintained after adjusting for potential confounders (sex, age, height, immunoglobulin E sensitisation and forced expiratory volume in one second), and, in this analysis, a negative association was found between current smoking and CA,NO. Snus (oral moist snuff) consumption (n = 21) in ex-smokers was associated with an increase in Daw,NO and a reduction in Caw,NO, after adjusting for potential confounders. Passive smoking was associated with a higher CA,NO. Using extended nitric oxide analysis, it was possible to attribute the reduction in exhaled nitric oxide levels seen in ex- and current smokers to a lower total airway nitric oxide flux in ex-smokers and reduced airway and alveolar nitric oxide concentrations in current smokers. The association between snus (oral tobacco) use and reduced nitric oxide concentrations in the airways and increased nitric oxide transfer from the airways warrants further studies.

Nitric Oxide as an Independent Regulatory Factor in Regenerating Rat Liver

Nitric oxide production and lipid peroxidation modulate the proliferating activity of liver cells, but the relationship between enhanced nitric oxide production, lipid peroxidation, and liver regeneration remains unclear. We examined the role of nitric oxide and lipid peroxidation on experimental liver regeneration. Thirty-five male Wistar albino rats underwent a sham operation (I), partial hepatectomy alone (II, IV), partial hepatectomy and daily N-nitro-L-argi-nine methyl ester (L-NAME) treatment for 24-hrs (III) or 48-hrs (V). Liver tissue concentrations of catalase, nitrite and nitrate, glutathione, and serum levels of alaninaminotransferase and bilirubin were measured. CD34, Ki-67 and proliferating cell nuclear antigen were evaluated in liver samples. Compared with other groups, both of the L-NAME groups had decreased tissue nitric oxide concentrations. Nitrate and nitrite (nitric oxide) concentrations were higher in partial hepatectomy-alone groups, as were CD34 counts and proliferation indexes. Partial hepatectomy elevated catalase, and glutathione levels in all groups compared to the sham-operated controls.In conclusion, nitric oxide inhibition impaired hepatic regeneration following partial hepatectomy. An obvious effect of nitric oxide on lipid peroxidation in the context of hepatocyte and endothelial cell proliferation could not be demonstrated. Thus, while lipid peroxidation could influence some steps in liver regeneration, nitric oxide poses as an independent regulatory factor in regenerating rat liver.

Protective effect of leptin against ischemia-reperfusion injury in the rat small intestine

BackgroundThe small intestine is extremely sensitive to ischemia-reperfusion (I/R) injury and a range of microcirculatory disturbances which contribute to tissue damage. Previous studies have shown that leptin plays an important physiological role in the microvasculature. The aim of this study was to evaluate the protective effects of leptin in I/R – induced mucosal injury in the small intestine.MethodsForty rats were divided into 5 groups (n = 8). Group I was subjected to a sham operation. Following mesenteric ischemia in group II (control); physiologic saline 1 cm3, in group III; leptin 100 μg/kg, and physiologic saline 1 cm3, in group IV; NG-L-arginine methyl ester (L-NAME) 20 mg/kg, and physiologic saline 1 cm3, in group V; leptin 100 μg/kg, L-NAME 20 mg/kg, and physiologic saline 1 cm3 were given intra-peritoneally. In these groups, an I/R procedure was performed by occlusion of the superior mesenteric artery for 45 min followed by 120 min reperfusion. After reperfusion, the small intestines were resected for malondialdehyde (MDA) and nitric oxide (NO) concentration and histopathologic properties. Mucosal lesions were scored between 0 and 5. Tissue MDA and NO concentration and histopathologic grades were compared statistically.ResultsTissue MDA level significantly increased (P < 0.05), tissue NO level significantly decreased in group V animals, compared to group III animals respectively (P < 0.001). Histopathologically, intestinal injury significantly decreased in the leptin treated ischemic group.ConclusionLeptin can be used safely in mesenteric occlusive diseases, since it induces NO formation and release in mesenteric vessels.

Release and hemodynamic influence of nitro-glycerine-derived nitric oxide in endotoxemic rats

Background and aim Nitric oxide released from nitro-glycerine (NG) has been considered to improve the microcirculation. Septic conditions are, however, associated with excessive formation of nitric oxide (NO), which is formed from l-arginine by the inducible NO synthase (iNOS) activity. Since the characteristics and influence of NG-derived NO in sepsis remains unclear, the major aims of the present study were to quantify the release and to determine the effects of NO formed from NG on systemic blood pressure under endotoxemic conditions. Material and methods Four hours following endotoxin challenge (10 mg/kg intraperitoneally), rats received an infusion of NG (0.5 or 5.0 μmol/kg/h) over 45 min. We determined the changes in blood pressure and the NO concentrations generated in brain, heart, intestine, kidney, liver, and lung by means of NO trapping and EPR technique. Results NG infusion in control rats and endotoxin challenge decreased systemic blood pressure to the same extent. However, in rats subjected to endotoxin challenge NG infusion did not affect the blood pressure. The endotoxin-induced increase in tissue NO concentrations were found to be 15-folds higher than tissue levels of NO following NG infusion. Conclusion Our results suggest that under endotoxic shock conditions in rats NG may not additionally affect the systemic blood pressure. This may relate to the excessive tissue NO levels induced by endotoxin that are not further increased by NG.

Renal ischemia induces an increase in nitric oxide levels from tissue stores

Tissue nitric oxide (NO) levels increase dramatically during ischemia, an effect that has been shown to be partially independent from NO synthases. Because NO is stored in tissues as S-nitrosothiols and because these compounds could release NO during ischemia, we evaluated the effects of buthionine sulfoximine (BSO; an intracellular glutathione depletor), light stimulation (which releases NO, decomposing S-nitrosothiols), and N-acetyl-L-cysteine (a sulfhydryl group donor that repletes S-nitrosothiols stores) on the changes in outer medullary NO concentration produced during 45 min of renal artery occlusion in anesthetized rats. Renal ischemia increased renal tissue NO concentration (+223%), and this effect was maintained along 45 min of renal arterial blockade. After reperfusion, NO concentration fell below preischemic values and remained stable for the remainder of the experiment. Pretreatment with 10 mg/kg nitro-L-arginine methyl ester (L-NAME) decreased significantly basal NO concentration before ischemia, but it did not modify the rise in NO levels observed during ischemia. In rats pretreated with 4 mmol/kg BSO and L-NAME, ischemia was followed by a transient increase in renal NO concentration that fell to preischemic values 20 min before reperfusion. A similar response was observed when the kidney was illuminated 40 min before the ischemia. The coadministration of 10 mg/kg iv N-acetyl-L-cysteine with BSO + L-NAME restored the increase in NO levels observed during renal ischemia and prevented the depletion of renal thiol groups. These results demonstrate that the increase in renal NO concentration observed during ischemia originates from thiol-dependent tissue stores.

Elevated plasma viscosity in extreme hemodilution increases perivascular nitric oxide concentration and microvascular perfusion

We tested the hypothesis that high-viscosity (HV) plasma in extreme hemodilution causes wall shear stress to be greater than low-viscosity (LV) plasma, leading to enhanced production of nitric oxide (NO). The perivascular concentration of NO was measured in arterioles and venules and the tissue of the hamster chamber window model, subjected to acute extreme hemodilution, with a hematocrit (Hct) of 11% using Dextran 500 (n = 6) or Dextran 70 (n = 5) with final plasma viscosities of 1.99 +/- 0.11 and 1.33 +/- 0.04 cp, respectively. HV plasma significantly increased the periarteriolar, perivenular, and tissue NO concentration by 2.0, 1.9, and 1.4 times the control (n = 7). The NO concentration with LV plasma was not statistically different from control. Arteriolar shear stress was significantly increased in HV plasma relative to LV plasma in arterioles but not in venules. Aortic endothelial NO synthase (eNOS) protein expression was increased with HV plasma but not with LV plasma. There was a weak correlation between perivascular NO concentration and the locally calculated shear stress induced by the procedures, when blood viscosity was corrected according to Hct values previously determined in studies of microvascular Hct distribution. The finding that the periarteriolar and venular NO concentration in HV plasma was the same although arteriolar shear stress was significantly greater than venular shear stress maybe be due to differences in vessel wall metabolism between arterioles and venules and the presence of NO transport through the blood stream in the microcirculation. Results support the concept that in extreme hemodilution HV plasma maintains functional capillary density through a NO-mediated vasodilatation.

Effect of exogenous angiotensin II on renal tissue nitric oxide and intrarenal circulation in anaesthetized rats

The renal medullary circulation is protected against depressor action of angiotensin II (Ang II) because of the opposed action of a vasodilator agent, possibly nitric oxide (NO). This possibility was evaluated by a simultaneous determination of the effect of exogenous Ang II on renal cortical and medullary tissue NO and on intrarenal circulation. In anaesthetized rats effects were determined of pressor and subpressor Ang II doses on tissue NO concentration in the renal cortex and inner medulla (selective NO electrodes), total renal blood flow (RBF, Transonic renal artery probe) and inner medullary blood flow (IMBF, laser Doppler flux). The measurements were repeated in rats treated with tempol, a scavenger of superoxide. Moderately pressor Ang II infusion significantly decreased tissue NO signal from 5.7 +/- 0.2 to 5.3 +/- 0.2 nA in the cortex and from 10.7 +/- 0.6 to 10.1 +/- 0.6 nA in the medulla. The RBF, a measure of cortical perfusion, decreased, and IMBF did not change. Subpressor doses of Ang II did not change medullary or cortical tissue NO. Tempol prevented an Ang II dependent decrease in medullary (but not cortical) NO without affecting RBF or IMBF responses. An absence of an increase in renal cortical or medullary tissue NO after infusion of subpressor or pressor doses of Ang II speaks against the role of this agent in buffering the intrarenal vasoconstrictor action of the hormone. Elimination of the post-Ang II decrease in medullary NO in animals pre-treated with tempol suggests that tissue superoxide generation stimulated by the hormone might reduce local bioavailability of NO.

Comparison of Tetrahydrobiopterin and L-Arginine on Cerebral Blood Flow after Controlled Cortical Impact Injury in Rats

The purpose of this study was to compare the effects of L-arginine and tetrahydrobiopterin administration on post-traumatic cerebral blood flow (CBF) and tissue levels of NO in injured brain tissue. Rats were anesthetized with isoflurane. Mean blood pressure, intracranial pressure, cerebral blood flow using laser Doppler flowmetry (LDF) and brain tissue nitric oxide (NO) concentrations were measured prior to, and for 2 h after a controlled cortical impact injury. L-Arginine, 300 mg/kg, tetrahydrobiopterin, 10 mg/kg, or equal volume of saline was given at 5 min after injury. In the saline-treated animals, LDF decreased to 34 ± 4% of baseline values after injury. NO concentration also decreased by approximately 20 pmol/ml from baseline values. L-Arginine and tetrahydrobiopterin administration both resulted in a significant preservation of tissue NO concentrations and an improvement in LDF, compared to control animals given saline. These studies demonstrate that tetrahydrobiopterin administration has a beneficial effect on cerebral blood flow that is similar to L-arginine administration, and may suggest that depletion of tetrahydrobiopterin plays a role in the post-traumatic hypoperfusion of the brain.

Effects of pneumoperitoneum with or without colostomy on rat colonic anastomotic healing.

Elevated intra-abdominal pressure and colostomy have adverse effects on colonic anastomoses. The aim of the present study was to investigate the effects of laparoscopic colon surgery with and without diverting colostomy on healing of colonic anastomoses in an experimental model. Thirty-six male rats were divided into three equal groups: group 1, control (colonic anastomosis and anaesthesia for 180 min only); group 2, 180 min pneumoperitoneum and colonic anastomosis; and group 3, similar to group 2 with a proximal colostomy. On day 7, bursting pressures, tissue hydroxyproline and nitric oxide concentrations and histopathological inflammation scores were determined and compared. Mean bursting pressures were higher in the control group than the two pneumoperitoneum groups (P=0.0003). Mean tissue hydroxyproline concentrations showed no difference (P>0.05). Mean tissue nitric oxide concentrations were significantly increased in the control group (P=0.0013). Histopathological scores demonstrated increased inflammatory response in group 3 compared to the controls (P=0.0009). Pneumoperitoneum delays collagen maturation and impairs anastomotic strength in the colon. Following pneumoperitoneum, performance of a diverting loop colostomy to protect the anastomosis will not have additional detrimental effects on anastomotic healing.

Responses to acute changes in arterial pressure on renal medullary nitric oxide activity in dogs.

A direct relationship between renal arterial pressure (RAP) and cortical tissue nitric oxide (NO) activity in the canine kidney was reported earlier. We have conducted further experiments to evaluate medullary NO responses to alterations in RAP with the use of a NO-selective microelectrode inserted into the renal medulla of 6 anesthetized, sodium-replete dogs. Graded reductions in RAP (from 140 to 80 mm Hg) elicited decreases in medullary tissue NO concentration, with a slope of 10.2+/-4.5 nmol x L(-1) x mm Hg(-1). These changes in NO levels were associated with decreases in urinary excretion rate of nitrate and nitrite (U(NOx)V; control value, 1.7+/-0.03 nmol x min(-1) x g(-1); slope, 0.02+/-0.004 nmol x min(-1) x g(-1) x mm Hg(-1)) and sodium excretion (U(Na)V; control, 3.2+/-0.7 micromol x min(-1) x g(-1); slope, 0.06+/-0.02 micromol x min(-1) x g(-1) x mm Hg(-1)) without changes in glomerular filtration rate control (0.84+/-0.06 mL x min(-1) x g(-1)). Intra-arterial administration of the NO synthase inhibitor N(omega)-nitro-L-arginine (NLA; 50 microg x kg(-1) x min(-1)) decreased medullary NO concentration by 218+/-55 nmol x L(-1) (n=5) and attenuated the relationship between RAP and NO concentration (slope, 2.7+/-2.2 nmol x L(-1) x mm Hg(-1)). NLA infusion decreased U(NOx)V (0.8+/-0.06 nmol x min(-1) x g(-1)) and U(Na)V (1.1+/-0.2 micromol x min(-1) x g(-1)) without changes in glomerular filtration rate and attenuated RAP versus U(Nox)V and U(Na)V relationships. Total and regional blood flows, as measured by electromagnetic and laser Doppler needle flow probes, respectively, remained autoregulated both before and during NLA infusion. These data support the hypothesis that acute changes in RAP elicit changes in intrarenal NO production, which may participate in the mediation of pressure natriuresis.

Intrarenal Nitric Oxide Activity and Pressure Natriuresis in Anesthetized Dogs

Recent studies have indicated that changes in intrarenal nitric oxide (NO) production participate in mediating arterial pressure-induced changes in urinary sodium excretion. Until recently, however, the means to measure changes in intrarenal NO activity in vivo have not been available. For the present study, changes in renal tissue NO activities were assessed directly using an NO-selective microelectrode inserted into the cortical tissue of anesthetized dogs. Control studies demonstrated that the electrode was responsive to intrarenal bolus injections of acetylcholine and to the NO donor S-nitroso-acetylpenicillamine (SNAP). Intrarenal nitro-L-arginine (50 microg x kg(-1) x min(-1)) decreased renal tissue NO concentration by 593+/-127 nmol/L (P<0.05; n=7). Infusions of SNAP (1, 2, and 3 microg x kg(-1) x min(-1) for 25 minutes) in nitro-L-arginine-treated dogs (n=5) resulted in dose-dependent increases in renal tissue NO activity, which showed a positive correlation with changes in urinary excretion rates of NO metabolites, nitrates and nitrites, (r=0.62, P<0.05) and sodium (r=0.78, P<0.01). During graded reductions of renal arterial pressure within the autoregulatory range (144+/-3 to 73+/-2 mm Hg; n=10), there were decreases in tissue NO activity that were positively correlated with changes in renal arterial pressure (r=0.45; P<0.05), urinary nitrate/nitrite excretion (r=0.64, P<0.005), and urinary sodium excretion (r=0.46; P<0.05). These data support the hypothesis that acute changes in renal arterial pressure result in alterations in intrarenal NO activity, which may be responsible for the associated changes in sodium excretion.

Protective effect of angiotensin II-induced increase in nitric oxide in the renal medullary circulation.

This study examined the effect of intravenous infusion of subpressor doses of angiotensin (Ang II) on renal medullary blood flow (MBF), medullary partial oxygen pressure (PO2), and nitric oxide (NO) concentration under normal conditions and during reduction of the medullary nitric oxide synthase (NOS) activity in anesthetized rats. With laser Doppler flowmetry and polarographic measurement of PO2 with microelectrodes, Ang II (5 ng/kg per minute) did not alter renal cortical and medullary blood flows or medullary PO2. N(omega)-nitro-L-arginine methyl ester (L-NAME) was infused into the renal medullary interstitial space at a dose of 1.4 microg/kg per minute, a dose that did not significantly alter basal levels of MBF or PO2. Intravenous infusion of Ang II at the same dose in the presence of L-NAME decreased MBF by 23% and medullary PO2 by 28%, but it had no effect on cortical blood flow or arterial blood pressure. An in vivo microdialysis-oxyhemoglobin NO trapping technique was used in other rats to determine tissue NO concentrations using the same protocol. Ang II infusion increased tissue NO concentrations by 85% in the renal cortex and 150% in the renal medulla. Renal medullary interstitial infusion of L-NAME (1.4 microg/kg per minute) reduced medullary NO concentrations and substantially blocked Ang II-induced increases in NO concentrations in the renal medulla, but not in the renal cortex. Tissue slices of the renal cortex and medulla were studied to determine the effects of Ang II and L-NAME on the nitrite/nitrate production. Ang II stimulated the nitrite/nitrate production predominately in the renal medulla, which was significantly attenuated by L-NAME. We conclude that small elevations of circulating Ang II levels increase medullary NO production and concentrations, which plays an important role in buffering the vasoconstrictor effects of this peptide and in maintaining a constancy of MBF.

Nitric oxide in renal cortex and medulla. An in vivo microdialysis study.

This study examined the production of nitric oxide (NO) in the renal cortex and medulla through the use of an in vivo microdialysis technique. Oxyhemoglobin (OxyHb) at a concentration of 3 mumol/L was perfused through the dialysis system to trap tissue NO. Methemoglobin (MetHb), which was formed by NO oxidation of OxyHb in the dialysate, was spectrophotometrically assayed at 401 nm. Because the oxidation of OxyHb to produce MetHb is stoichiometric with NO, the production of NO can be determined by the rate of MetHb formation. We found that NO concentration was significantly higher (P < .05) in the medulla (57.1 +/- 5.57 nmol/L, n = 10) than in the cortex (31.2 +/- 5.7 nmol/L, n = 9). The minimal detectable NO level of this assay is approximately 10 nmol/L. Intravenous infusion of L-arginine (3 mg/kg per minute) for 30 minutes produced a twofold to three fold increase in cortical and medullary NO; NG-nitro-L-arginine methyl ester (L-NAME) (10 micrograms/kg per minute) decreased NO by 33% in the renal cortex and by 46.5% in the renal medulla. We have also compared under the same conditions the degradation products of NO, nitrite, and nitrate in the renal cortex and medulla using in vivo microdialysis combined with microtiter plate colorimetry. Nitrite/nitrate concentration was significantly higher (P < .05) in the medulla (2.7 +/- 0.6 mumol/L, n = 4) than in the cortex (2.1 +/- 0.2 mumol/L, n = 4). Infusion of L-arginine increased cortical and medullary nitrite/nitrate by 65% and 39%, respectively. L-NAME reduced cortical and medullary nitrite/nitrate by 18% and 23%, respectively. The results indicate that the OxyHb-NO microdialysis trapping technique is a highly sensitive in situ method for detecting regional tissue NO concentration and changes in the NO synthase activity in the kidney. These studies have shown that NO concentration is higher in medullary tissue than in the cortex.