Impact of surgery on nitric oxide in rats: evidence for activation of inducible nitric oxide synthase

Decreased nitric oxide serum level after pituitary adenoma resection

BACKGROUND

Nitric oxide (NO) is synthesized by the conversion of Arginine (Arg) into the NO and Citrulline (Cit). Although the NO is involved into the pathogenesis of several physiological and pathological processes, the role of NO in pituitary adenomas (PA) progression is not determined. Our purpose was to evaluate the relationship between NO and PA as well as the effect of tumor resection on NO metabolites level in serum.

METHODS

The study group consisted of 21 patients with PA, 18 patients with macroadenomas and 3 with microadenomas. Venous blood samples were collected at two time-points; 1) before the surgery and 2) 3-5 days after PA resection. Arg and Cit levels were determined by the automated ion-exchange chromatography with usage of Amino Acids Analyser (AAA 400). Commercially available kit for the evaluation of nitrate/nitrite serum levels was applied for indirect assessment of serum NO level.

RESULTS

Significant decrease in NO concentration after the surgery was observed in comparison with the time-point 1. Arg level did not significantly change during the study period. Cit level was ranged below the detection limit of applied method.

CONCLUSIONS

The decrease of NO level after the pituitary adenoma resection indicates the relationship between NO synthesis and PA occurrence.

Impaired blood flow in acute kidney injury: pathophysiology and potential efficacy of intrarenal vasodilator therapy

PURPOSE OF REVIEW

Acute kidney injury (AKI) is a common complication of hospitalized patients and associated with significant morbidity and mortality. Numerous studies have documented that acute reductions in glomerular filtration rates are associated with significant in-hospital mortality. Moreover, patients progressing to dialysis-dependent AKI can have mortality rates that exceed 60%. The pathophysiology of AKI is unknown, but marked reductions in corticomedullary blood flow leads to significant reductions in glomerular filtration rate during early phases of the disease. The recognition that hypoperfusion of the outer medulla is common to many forms of AKI and contributes to tubular ischemia has led many investigators to re-examine the use of vasodilators to restore blood flow and stabilize renal function.

RECENT FINDINGS

Numerous prospective trials have studied the efficacy of various vasoactive compounds with primarily negative results. However, trial designs that failed to fully examine the dose response of many investigational agents contributed to the development of systemic hypotension, thus offsetting potential benefits of the treatment. Emerging devices that allow for intrarenal administration of drugs have led to the concept of 'targeted renal' prophylaxis and treatment. The rationale is that local renal administration can improve the safety profile of many vasoactive agents. Recent studies confirm that higher doses of fenoldopam or other vasodilators can be administered intrarenally without the development of systemic hypotension.

SUMMARY

Previous trials utilizing vasodilator therapy to stabilize renal function in AKI have given conflicting results. This study will critically review trial design and dose selection used in previous studies of vasodilator therapy in AKI. Lastly, the potential for high-dose therapy using intrarenal drug delivery systems will be discussed.

Cardiovascular and pulmonary effects of NOS inhibition in endotoxemic conscious rats subjected to swimming training

Sepsis is characterized by systemic hypotension, hyporeactiveness to vasoconstrictors, impaired tissue perfusion, and multiple organ failure. During exercise training (ET), dynamic cardiovascular adjustments take place to maintain proper blood pressure and adjust blood supply to different vascular beds. The aim of this study was to investigate whether ET protects against the cardiovascular abnormalities induced by LPS, a model of experimental endotoxemia, and to evaluate the role of nitric oxide (NO) in pulmonary edema. Wistar rats were subjected to swimming training (up to 1 h/day, 5 days/week for 4 weeks) after which their femoral artery and vein were catheterized. LPS (5 mg/kg, i.v.), injected in control (C) and trained animals (ET), promoted 3 distinct phases in mean arterial pressure (MAP) and heart rate (HR). After ET the alterations in MAP were attenuated. The ET animals showed a lower pulmonary edema index (PEI) after LPS (C=0.65+/-0.01; ET=0.60+/-0.02), which was attenuated after treatment with aminoguanidine in both groups (C=0.53+/-0.02; ET=0.53+/-0.02, p<0.05). After l-NAME, PEI was enhanced numerically in the C and was statistically higher in the ET group (C=0.73+/-0.05; ET=1.30+/-0.3, p<0.05). 7-nitroindazole did not promote any alteration in either group. The adaptations promoted by ET seem to be beneficial, counteracting the cardiovascular abnormalities and pulmonary edema seen in septicemia induced by LPS. The results suggest that iNOS aggravates and cNOS protects against this pulmonary edema.

Renal cortical and medullary blood flow responses to L-NAME and ANG II in wild-type, nNOS null mutant, and eNOS null mutant mice

Experiments in wild-type (WT; C57BL/6J) mice, endothelial nitric oxide synthase null mutant [eNOS(-/-)] mice, and neuronal NOS null mutant [nNOS(-/-)] mice were performed to determine which NOS isoform regulates renal cortical and medullary blood flow under basal conditions and during the infusion of ANG II. Inhibition of NOS with N(omega)-nitro-l-arginine methyl ester (l-NAME; 50 mg/kg iv) in Inactin-anesthetized WT and nNOS(-/-) mice increased arterial blood pressure by 28-31 mmHg and significantly decreased blood flow in the renal cortex (18-24%) and the renal medulla (13-18%). In contrast, blood pressure and renal cortical and medullary blood flow were unaltered after l-NAME administration to eNOS(-/-) mice, indicating that NO derived from eNOS regulates baseline vascular resistance in mice. In subsequent experiments, intravenous ANG II (20 ng x kg(-1) x min(-1)) significantly decreased renal cortical blood flow (by 15-25%) in WT, eNOS(-/-), nNOS(-/-), and WT mice treated with l-NAME. The infusion of ANG II, however, led to a significant increase in medullary blood flow (12-15%) in WT and eNOS(-/-) mice. The increase in medullary blood flow following ANG II infusion was not observed in nNOS(-/-) mice, in WT or eNOS(-/-) mice pretreated with l-NAME, or in WT mice administered the nNOS inhibitor 5-(1-imino-3-butenyl)-l-ornithine (1 mg x kg(-1) x h(-1)). These data demonstrate that NO from eNOS regulates baseline blood flow in the mouse renal cortex and medulla, while NO produced by nNOS mediates an increase in medullary blood flow in response to ANG II.

Selective Sensitization by Nitric Oxide of Sympathetic Baroreflex in Rostral Ventrolateral Medulla of Conscious Rabbits

Nitric oxide (NO) deficiency in the rostral ventrolateral medulla (RVLM) has been implicated in impaired baroreflex control in hypertensive and heart failure animals. However, the role of local NO in normal baroreflex regulation remains unclear. This study aimed to examine the role of NO in tonic and baroreflex control of blood pressure (BP) in the RVLM of conscious rabbits. Microinjections of NO donors, S-nitroso-N-acetylpenicillamine and sodium nitroprusside (5 to 20 nmol), or NO itself (20 to 200 pmol) into the RVLM dose-dependently increased BP. Bilateral microinjections of an NO synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 10 nmol), its inactive enantiomer D-NAME, or soluble guanylate cyclase (sGC) inhibitors, 1-H-[1,2,4]oxadiaolo[4,3-a]quinoxalin-1-one (ODQ, 250 pmol) and methylene blue (10 nmol), into the RVLM did not affect resting BP, heart rate, or renal sympathetic nerve activity (RSNA). However, L-NAME, methylene blue, and ODQ decreased RSNA baroreflex gain by 42% to 55%, whereas D-NAME did not affect this reflex. Co-microinjections of L-NAME and superoxide scavenger tempol (20 nmol) decreased RSNA baroreflex gain by 37+/-8%. Microinjections of a neuronal NOS (nNOS) inhibitor, 7-nitroindazole (500 pmol), into the RVLM decreased RSNA baroreflex gain by 42+/-12%, without altering resting BP, heart rate, or RSNA. Local administration of inducible NOS (iNOS) inhibitors, S-methylisothiourea (0.25 nmol) and aminoguanidine (0.25 and 2.5 nmol), affected neither resting nor baroreflex parameters. These results suggest that nNOS-derived NO facilitates sympathetic baroreflex transmission in the RVLM at least in part via a sGC-dependent, superoxide-independent mechanism. However, local nNOS and iNOS play little role in the tonic support of BP in conscious rabbits.

Nitric Oxide Does Not Cause Extravasation in Endotoxemic Rats

BACKGROUND

Nitric oxide (NO) formed from inducible NO synthase (iNOS) is assumed to promote vascular permeability in sepsis and endotoxemia.

METHODS

Thirty-seven anesthetized rats were examined for the effects of endotoxin. After randomization, 17 animals had lipopolysaccharide (LPS) administered and 20 rats served as controls and were given the corresponding volume of saline. The observation period was 5 hours after administration of endotoxin. Mean arterial blood pressure, heart rate, and hematocrit were recorded in all animals, and transcapillary exchange of albumin, tissue water content, immunohistochemistry for nitric oxide synthase, and blood gases were investigated in subsets of animals.

RESULTS

When anesthetized rats were studied for 5 hours after endotoxin (LPS), the sequestration of albumin decreased in the intestine (double-isotope method) and there was no increased water content (freeze-drying technique) when the elevated tissue plasma volume of the LPS-treated rats was corrected for. Immunohistochemical methods showed a similar distribution and intensity of staining for endothelial NOS and neuronal NOS in LPS and control groups. In the lung of the LPS-treated rats, there was a significantly larger number of infiltrating, inflammatory cells staining for iNOS. There was no iNOS demonstrated in vascular structures or heart.

CONCLUSION

At 5 hours after LPS, there was no increased loss of water or albumin from the circulation. This challenges the notion that NO causes vascular damage in endotoxemia and extravasation as an obligatory sequela to endotoxemia.

Lipopolysaccharide-induced acute renal failure in conscious rats: effects of specific phosphodiesterase type 3 and 4 inhibition

In conscious, chronically instrumented rats we examined 1) renal tubular functional changes involved in lipopolysaccharide (LPS)-induced acute renal failure; 2) the effects of LPS on the expression of selected renal tubular water and sodium transporters; and 3) effects of milrinone, a phosphodiesterase type 3 (PDE3) inhibitor, and Ro-20-1724, a PDE4 inhibitor, on LPS-induced changes in renal function. Intravenous infusion of LPS (4 mg/kg b.wt. over 1 h) caused an immediate decrease in glomerular filtration rate (GFR) and proximal tubular outflow without changes in mean arterial pressure (MAP). LPS-induced fall in GFR and proximal tubular outflow were sustained on day 2. Furthermore, LPS-treated rats showed a marked increase in fractional distal water excretion, despite significantly elevated levels of plasma vasopressin (AVP). Semiquantitative immunoblotting showed that LPS increased the expression of the Na(+),K(+),2Cl(-)-cotransporter (BSC1) in the thick ascending limb, whereas the expression of the AVP-regulated water channel aquaporin-2 in the collecting duct (CD) was unchanged. Pretreatment with milrinone or Ro-20-1724 enhanced LPS-induced increases in plasma tumor necrosis factor-alpha and lactate, inhibited the LPS-induced tachycardia, and exacerbated the acute LPS-induced fall in GFR. Furthermore, Ro-20-1724-treated rats were unable to maintain MAP. We conclude 1) PDE3 or PDE4 inhibition exacerbates LPS-induced renal failure in conscious rats; and 2) LPS treated rats develop an escape from AVP in the CDs, which could be aimed to protect against water intoxication in septic conditions associated with decreased GFR and high levels of AVP.

Glomerular and tubular responses to N(G)-nitro-L-arginine methyl ester are age dependent in conscious lambs

The present experiments were carried out to investigate the role of endogenously produced NO in modulating renal function during postnatal maturation under physiological conditions. In conscious, chronically instrumented lambs aged approximately 1 (n = 8) and approximately 6 wk (n = 8) of postnatal life, various parameters of glomerular and tubular function were measured for 1 h before and 1 h after intravenous injection of 20 mg/kg of N(G)-nitro-L-arginine methyl ester (L-NAME; experiment 1) or its inactive isomer D-NAME (experiment 2). After administration of L-NAME to 1-wk-old lambs, glomerular filtration rate (GFR) and filtration factor (FF) decreased by approximately 50% at 20 min, remaining decreased at 60 min. In 6-wk-old lambs, GFR and FF remained constant after L-NAME. Proximal fractional Na(+) reabsorption decreased after L-NAME administration to lambs aged 6 wk, resulting in a prompt natriuresis; this was sustained for 60 min. There were no effects of L-NAME on proximal fractional Na(+) reabsorption in 1-wk-old lambs. In 6-wk-old lambs, urinary flow rate increased by approximately 500%, free water clearance increased by approximately 50%, and urinary osmolality decreased by approximately 60% after L-NAME administration; no effects on these variables were measured in 1-wk-old lambs. The diuresis after L-NAME administration to 6-wk-old lambs was unaccompanied by any changes in plasma levels of arginine vasopressin. There were no effects of D-NAME on any of the measured variables. We conclude that endogenously produced nitric oxide modulates glomerular and tubular function in an age-dependent manner.

Inhibition of inducible nitric oxide synthase during high dietary salt intake

BACKGROUND

Previous studies indicate that nitric oxide (NO) is involved in the regulation of blood pressure (BP) and natriuresis in response to high sodium intake. We investigated the role of inducible NO synthase (iNOS) in response to an increased salt intake.

METHODS

Conscious, chronically catheterized rats were exposed to a high-salt (6%) diet for 14 days while receiving vehicle or aminoguanidine ([AG]; 250 mg/kg/24 h), which selectively inhibits iNOS. A group of rats on normal salt intake + AG were also studied.

RESULTS

Aminoguanidine had no impact on BP (120 +/- 2 v 116 +/- 1 mm Hg, control v day 14) or 24-h urinary nitrite and nitrate excretion (UNOxV), in rats on normal salt but prevented lipopolysaccharide-induced hypotension. High salt alone had no impact on BP (120 +/- 1 v 121 +/- 1 mm Hg), whereas UNaV (1.3 +/- 0.2 v 3.5 +/- 0.6 microeq/min, P < .001) and UNOxV increased with high salt intake. The natriuretic response persisted (1.5 +/- 0.2 v 4.3 +/- 0.8 microeq/min, P < .005), but the increase in UNOXV was prevented with chronic AG although BP fell slightly (121 +/- 1 v 115 +/- 1 mm Hg, P < .05). There was no change in plasma volume with high salt, and 24-h UNaV increased appropriately in the presence of AG. The in vitro NOS activity was not increased in kidney homogenates by high salt diet, nor was it affected by chronic AG treatment.

CONCLUSION

We conclude that NO from an iNOS source is not essential for the regulation of sodium excretion and BP in the presence of a high-salt diet in a normal rat.

Mechanism underlying diuretic effect of L-NAME at a subpressor dose

The diuretic effects of nitric oxide (NO) synthase inhibitors administered at subpressor dose in rats are controversial, and the tubular segments involved are not known. In the present study, we examined the effect of N(omega)-nitro-L-arginine methyl ester (L-NAME) at a subpressor dose on renal interstitial NO and cGMP activity and on renal tubular segmental reabsorption of fluid in the rat. Intravenous infusion of L-NAME at 1 microg. kg(-1). min(-1) in Sprague-Dawley rats (N = 8), which did not alter mean arterial pressure or glomerular filtration rate, significantly increased urine flow rate (U(v); from 78.2 +/- 12.7 to 117.1 +/- 14.9 microl/min, P < 0.05). Paradoxically, this effect of L-NAME was concomitant with significant increases in nitrite/nitrate (from 10.79 +/- 1.20 to 16.50 +/- 2.60 microM, P < 0.05) and cGMP (from 0.65 +/- 0.09 to 0.98 +/- 0.18 nM, P < 0.05) concentrations in renal cortical microdialysate as well as the nitrite/nitrate concentration in the medullary microdialysate. Micropuncture studies in the superficial nephron revealed that L-NAME significantly increased the flow rate (from 8.3 +/- 0.9 to 12.2 +/- 1.2 nl/min, P < 0.05) and fractional delivery of fluid to the distal tubule, but not those in the late proximal tubule. In conclusion, L-NAME, at the subpressor dose used in this study, increased renal nitrate/nitrite and cGMP and inhibited fluid reabsorption in tubular segments between the late proximal tubule and the distal tubule of superficial nephrons.

Cirrhosis serum induces a nitric oxide-associated vascular hyporeactivity of aortic segments from healthy rats in vitro

OBJECTIVE

Arterial vasodilation with concomitant hyperdynamic circulation are common findings in liver cirrhosis. Nitric oxide acting at a local level has been suggested to be pathophysiologically relevant in this context. Several systemic factors in conjunction with nitric oxide might interfere with the observed phenomena.

DESIGN

The study has been designed to demonstrate the influence of cirrhotic serum on the nitric oxide system and vascular contractility.

METHODS

The contractile response of aortic segments from healthy rats was studied in vitro after incubation with serum of healthy and cirrhosis-induced rats (1 week, 2 weeks, 3 weeks and 4 weeks after bile duct ligation). A cumulative dose response curve to phenylephrine (10--10-4 mol) was established before and after incubation with nitric oxide synthesis blocker N(omega)-nitro-L-arginine, the more selective aminoguanidine (nitric oxide synthase [NOS]-2 inhibitor) and W7 (NOS-3 inhibitor). NOS-2 expression in incubated aortic rings was evaluated by Western blot analysis.

RESULTS

A 4-hour incubation with serum of cirrhosis-induced rats reduced the maximum contractile response to phenylephrine to 66.8 +/- 9.1% after 1 week, 50.4 +/- 7.8% after 2 weeks, 43.2 +/- 2.8% after 3 weeks and 35 +/- 5.2% after 4 weeks of bile duct ligation. This reduction in the contractility response to phenylephrine was completely reversed by blocking nitric oxide synthesis with N(omega)-nitro-L-arginine and aminoguanidine, but not after W7. Incubation with cirrhotic serum induced NOS-2 expression in aortic rings. In Western blot analysis, the most intensive signal for NOS-2 protein was obtained in rings incubated with serum from rats 3 weeks and 4 weeks after induction of cirrhosis.

CONCLUSIONS

Cirrhotic serum decreases the contractile response to phenylephrine even in an early stage of secondary cirrhosis. Reversibility of this effect after nitric oxide synthesis blockade suggests an induction of nitric oxide synthesis by systemic factors as a major point in vascular hyporeactivity to vasoconstrictors in cirrhosis.

The influence of nitric oxide synthase 1 on blood flow and interstitial nitric oxide in the kidney

The role of nitric oxide (NO) produced by NO synthase 1 (NOS1) in the renal vasculature remains undetermined. In the present study, we investigated the influence of systemic inhibition of NOS1 by intravenous administration of N(omega)-propyl-L-arginine (L-NPA; 1 mg. kg(-1). h(-1)) and N(5)-(1-imino-3-butenyl)-L-ornithine (v-NIO; 1 mg. kg(-1). h(-1)), highly selective NOS1 inhibitors, on renal cortical and medullary blood flow and interstitial NO concentration in Sprague-Dawley rats. Arterial blood pressure was significantly decreased by administration of both NOS1-selective inhibitors (-11 +/- 1 mmHg with L-NPA and -7 +/- 1 mmHg with v-NIO; n = 9/group). Laser-Doppler flowmetry experiments demonstrated that blood flow in the renal cortex and medulla was not significantly altered following administration of either NOS1-selective inhibitor. In contrast, the renal interstitial level of NO assessed by an in vivo microdialysis oxyhemoglobin-trapping technique was significantly decreased in both the renal cortex (by 36-42%) and medulla (by 32-40%) following administration of L-NPA (n = 8) or v-NIO (n = 8). Subsequent infusion of the nonspecific NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 50 mg. kg(-1). h(-1)) to rats pretreated with either of the NOS1-selective inhibitors significantly increased mean arterial pressure by 38-45 mmHg and significantly decreased cortical (25-29%) and medullary (37-43%) blood flow. In addition, L-NAME further decreased NO in the renal cortex (73-77%) and medulla (62-71%). To determine if a 40% decrease in NO could alter renal blood flow, a lower dose of L-NAME (5 mg. kg(-1). h(-1); n = 8) was administered to a separate group of rats. The low dose of L-NAME reduced interstitial NO (cortex 39%, medulla 38%) and significantly decreased blood flow (cortex 23-24%, medulla 31-33%). These results suggest that NOS1 does not regulate basal blood flow in the renal cortex or medulla, despite the observation that a considerable portion of NO in the renal interstitial space appears to be produced by NOS1.

Nitric oxide modulates arterial baroreflex control of heart rate in conscious lambs in an age-dependent manner

Experiments were carried out in conscious chronically instrumented lambs aged 1 (n = 6) and 6 wk (n = 5) to evaluate the arterial baroreflex control of heart rate (HR) during postnatal maturation and to investigate any modulatory role of endogenously produced nitric oxide (NO). Before and after intravenous administration of 20 mg/kg of the L-arginine analog N(G)-nitro-L-arginine methyl ester (L-NAME), the arterial baroreflex was assessed by measuring HR responses to increases and decreases in systolic arterial pressure achieved by intravenous administration of phenylephrine and sodium nitroprusside. The HR range over which the baroreflex operates and minimum HR as well as maximum gain were greater at 1 than at 6 wk of age. These age differences were abolished in the presence of L-NAME, which decreased the HR range and gain of the arterial baroreflex control of HR at 1 but not at 6 wk of age. These data provide new information that age-dependent effects of the arterial baroreflex appear to result from effects of endogenously produced NO.

Effect of nitric oxide inhibition on kidney function in experimental renovascular hypertension

We examined the effect of acute systemic blockade of nitric oxide (NO) synthesis on blood pressure and renal function in rats with angiotensin II dependent two-kidney, one-clip Goldblatt hypertension. Hypertensive animals had significantly higher blood pressures, plasma NO metabolite concentrations and urinary NO metabolite excretion rates than control rats. Intravenous administration of N(G)-nitro-L-arginine methylester (L-NAME) (10 mg/kg) increased mean arterial pressure in both hypertensive and control animals with the magnitude of increase being greater in hypertensive than control rats (32 +/- 3 vs. 20 +/- 2 mmHg, p < 0.05). L-NAME did not affect glomerular filtration rates of normal and clipped kidneys but significantly decreased non-clipped kidney glomerular filtration rate (1.1 +/- 0.1 vs. 0.7 +/- 0.1 ml/min per g kidney wt, p < 0.05). Blood flow to normal and non-clipped kidneys fell in response to L-NAME. Percent reduction in renal blood flow produced by L-NAME was significantly greater in non-clipped than normal kidneys (38 +/- 3 vs. 24 +/- 2%, p < 0.05). In contrast, clipped kidney blood flow increased after L-NAME (3.3 +/- 0.2 vs. 4.0 +/- 0.2 ml/min per g kidney wt, p < 0.05). An identical improvement in clipped kidney blood flow occurred when arterial pressure was raised with aortic constriction indicating that the systemic pressor effect of L-NAME was responsible for this finding. These results indicate that NO plays an important role in systemic and non-clipped kidney hemodynamics in renovascular hypertension. Because NO has little influence on stenotic kidney function, the stimulus for increased NO system activity in this disease appears to be vascular shear stress rather than elevated circulating or intrarenal angiotensin II concentrations.

Antineutrophil cytoplasm antibody-induced neutrophil nitric oxide production is nitric oxide synthase independent

BACKGROUND

Antineutrophil cytoplasm antibodies (ANCAs) are implicated in the pathogenesis of systemic vasculitis. We asked whether ANCA could induce nitric oxide (NO) release from human neutrophils and, if so, whether this NO production was dependent on NO synthase (NOS) activity.

METHODS

Neutrophil NO production was measured using a chemiluminescence assay, and NOS activity was determined by the conversion of [(14)C] L-arginine to [(14)C] L-citrulline and NOS mRNA expression by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Human neutrophils isolated from healthy donors were incubated at 37 degrees C with human ANCA, normal human IgG, murine monoclonal myeloperoxidase ANCA, murine proteinase-3 ANCA, or their respective isotypic controls for 6 to 12 hours in RPMI. Both human and monoclonal ANCA led to a dose-dependent increase of NO compared with control IgG. Neutrophils, either freshly isolated or incubated for seven hours with murine monoclonal myeloperoxidase ANCA, proteinase-3 ANCA, or a mixture of interleukin-1 beta, tumor necrosis factor-alpha, interferon-gamma plus lipopolysaccharide showed no NOS activity with low conversion rates of [(14)C] L-arginine to [(14)C] L-citrulline, which could not be inhibited by N(G)-monomethyl-L-arginine (NOS inhibitor). To detect NOS mRNA expression, RT-PCR was performed using oligonucleotide primers derived from mRNA sequences of either human constitutive endothelial NOS (eNOS), constitutive neuroneal NOS (nNOS), or human hepatocyte inducible NOS (iNOS). There was no expression of either eNOS, nNOS, or iNOS in untreated, human and murine monoclonal ANCA-treated, or cytokine-treated neutrophils.

CONCLUSION

These data suggest that human neutrophils produce NO in response to ANCA but in a NOS-independent way. NO can be generated from a nonenzymatic interaction between hydrogen peroxide and arginine. We postulate that this is the predominant pathway of NO synthesis in neutrophils, since ANCAs are capable of inducing reactive oxygen species production from neutrophils.

Male gender predisposes to development of endotoxic shock in the rat

OBJECTIVE

After intravenous (i.v.) injection of lipopolysaccharide (LPS) macrophages release nitric oxide (NO) due to the expression of the inducible NO synthase (iNOS). After LPS NO is abundantly produced also in the cardiovascular system and may contribute to the development of hypotension and shock. Since the immune response, the synthesis of NO and the regulation of blood pressure (BP) differ between males and females, in the present study the effect of LPS on BP, renal function, the plasma and urinary concentration of the metabolites of NO as well as the splenic and aortic expression of the iNOS gene were compared between male and female rats.

METHODS

BP and renal function were measured in anesthetized rats following the i.v. injection of LPS (E. coli, 4 mg/kg). The NO2- and NO3- (metabolites of NO=NOx) concentration was measured by the Griess reaction. The iNOS gene expression was studied by RT-PCR.

RESULTS

Four hours after LPS, BP of males (n=9) was reduced by 63+/-12 mmHg versus 10+/-4 in females (n=7, P<0.005). Aminoguanidine, a selective inhibitor of iNOS, prevented the reduction of BP in males. The plasma concentration of NOx (P(NOx)), microM) was lower in hypotensive males (128+/-20) than in normotensive females (235+/-29, P<0.005). Males also exhibited lower urinary NOx excretion (U(NOx)V) after LPS (P<0.001 vs. females). Prior castration of males provided protection against hypotension (fall of BP: -4+/-4 mmHg, n=6, P<0.02 versus males) and resulted in higher P(NOx) as well as U(NOx)V (both P<0.001 versus males and not different from females). Prior ovariectomy (n=5) had no influence on the hemodynamic and NOx response to LPS. Male rats displayed enhanced aortic iNOS/beta-actin ratio relative to females after LPS (n=3 in each group, P<0.05).

CONCLUSIONS

(1) Male gender may sensitize to LPS-induced shock and (2) sensitivity of males to endotoxin is associated with an attenuated, not exaggerated total rate of NO synthesis.

Nitric oxide synthase activity and isoforms in rat renal vasculature

Experiments were performed to quantify nitric oxide synthase (NOS) activity and identify the NOS isoforms present in the Sprague-Dawley rat renal vasculature. NOS enzymatic activity was measured by adding [(3)H]arginine to microdissected renal blood vessels and quantifying the conversion to [(3)H]citrulline by reverse-phase high-performance liquid chromatography. Total NOS activity was greatest in microdissected vasa recta (123+/-41 pmol. mg(-1). h(-1), n=5) and significantly less in glomeruli (46+/-9 pmol. mg(-1). h(-1), n=6) and afferent arterioles (42+/-10 pmol. mg(-1). h(-1), n=6) and averaged <5 pmol. mg(-1). h(-1) in arcuate (n=8) and interlobular (n=9) arteries. Addition of 1.0 mmol/L EDTA to the reaction decreased NOS activity to <5 pmol. mg(-1). h(-1) in afferent arterioles, glomeruli, and vasa recta (n=5 each), indicating that the NOS enzymatic activity in these segments is primarily a result of constitutive NOS. Both neuronal and endothelial NOS mRNA were identified in each vascular segment by reverse transcription-polymerase chain reaction, but inducible NOS mRNA was detected only in microdissected arcuate arteries. The present experiments indicate that the vasa recta, glomeruli, and afferent arterioles contain large amounts of calcium-dependent NOS enzymatic activity and that neuronal NOS and endothelial NOS mRNA are present in these segments.

Nitric oxide synthase isoforms and glomerular hyperfiltration in early diabetic nephropathy

This study tested the hypothesis that nitric oxide (NO)-mediated renal vasodilation due to the activity of the inducible nitric oxide synthase (iNOS) contributes to glomerular hyperfiltration in diabetic rats. Two weeks after induction of diabetes mellitus by streptozotocin, mean arterial BP (MAP), GFR (inulin clearance), and renal plasma flow (RPF) (para-aminohippurate clearance) were measured in conscious instrumented rats. Diabetic rats had elevated GFR (3129 +/- 309 microl/min versus 2297 +/- 264 microl/min in untreated control rats, P < 0.05) and RPF (10526 +/- 679 microl/min versus 8005 +/- 534 microl/min), which was prevented by chronic insulin treatment. Intravenous administration of 0.1 and 1 mg of L-imino-ethyl-lysine (L-NIL), an inhibitor of iNOS, did not affect MAP, GFR, or RPF, either in diabetic or control rats. A higher L-NIL dose (10 mg) increased MAP and decreased RPF in diabetic rats significantly (n = 6, P < 0.05), but not in controls (n = 6). In addition, 0.1 mg of NG-nitro-L-arginine methyl ester (L-NAME), a nonselective blocker of NOS isoforms, decreased GFR (2389 +/- 478 microl/min) and RPF (7691 +/- 402 microl/min) in diabetic animals to control levels, while renal hemodynamics in normoglycemic rats were not altered. Higher L-NAME doses (1 and 10 mg) reduced GFR and RPF in diabetic and control rats to identical levels. In glomeruli isolated from diabetic and control rats, neither iNOS mRNA nor iNOS protein expression was detected. In contrast, increased protein levels of endothelial constitutive NOS (ecNOS) were found in glomeruli of diabetic rats compared with controls. By immunohistochemistry, ecNOS but not iNOS staining was observed in the endothelium of preglomerular vessels and in diabetic glomeruli. These results support the notion that increased NO availability due to greater abundance of ecNOS contributes to the pathogenesis of glomerular hyperfiltration in early experimental diabetic nephropathy. In contrast, we found no functional or molecular evidence for increased glomerular expression and activity of iNOS in diabetic rats.

Inducible nitric oxide synthase and tumor necrosis factor in animal models of myocardial necrosis induced by coronary artery ligation or isoproterenol injection

BACKGROUND

Increased expression of inducible nitric oxide synthase (iNOS) has been described in humans with cardiomyopathies. Most animal models of ischemia-induced heart failure use the surgical ligation of coronary arteries. However, studies of iNOS expression in these models may be confounded by a robust immune response because of the surgical procedure itself leading to iNOS expression in the heart, as well as in other tissues.

METHODS AND RESULTS

iNOS expression was studied in adult male rats injected subcutaneously with either 250 mg/kg of isoproterenol (ISO) or vehicle on 2 consecutive days. This approach induces diffuse myocardial necrosis and leads to the development of a dilated cardiomyopathy. Hearts from ISO-injected animals harvested at 6 weeks had evidence of apical and subendocardial scarring. These hearts showed a 9.6-fold (left ventricle [LV], P = .004) and an 11.9-fold (right ventricle, P = .002) increase in the expression of tumor necrosis factor (TNF), and a 6.8-fold increase (LV, P = .0183) in iNOS messenger RNA compared with vehicle-injected controls. iNOS protein also was detectable by immmunoprecipitation in left ventricular muscle from ISO-injected animals, as well as by immunohistochemical analysis.

CONCLUSION

Expression of TNF and iNOS in the heart is increased in an experimental model of dilated cardiomyopathy that minimizes the confounding effects of surgery, supporting a role for the activation of innate immunity signaling pathways in the pathogenesis of heart failure.

Role of nitric oxide in the early renal hemodynamic response after unilateral nephrectomy

We evaluated the involvement of nitric oxide (NO) in the early hemodynamic response to uninephrectomy (UNX) in rats. Animals were uninephrectomized, and 48 h after removal of the kidney, the effect of infusing NG-nitro-L-arginine methyl ester (L-NAME) on renal function was studied. Glomeruli were isolated, and glomerular nitrite and cGMP productions were measured. In addition, endothelial constitutive NO synthase (NOS III) and inducible NO synthase (iNOS) were assessed by Western blot and by measuring the conversion of arginine to citrulline. UNX animals showed an increase in renal plasma flow that was inhibited by L-NAME in a higher proportion than in sham-operated (SO) animals. No differences were observed in systemic NO-dependent vascular tone, since mean arterial pressure showed similar increments in SO and UNX rats. Glomeruli from UNX animals showed an increase in glomerular nitrite production that was blunted by L-NAME addition. Also, cGMP levels were increased in glomeruli from UNX animals, and this increase was inhibited by L-NAME. Western blot analysis showed no differences in NOS III but a higher iNOS amount in glomeruli from UNX than in those from SO rats. No significant differences between UNX and SO rats were found in calcium-dependent NOS enzymatic activity in the renal cortex. However, calcium-independent enzymatic activity was markedly higher in the renal cortex of UNX than in those from SO animals. In conclusion, glomeruli from rats 48 h after UNX had a greater production of NO than those from SO animals. This increased glomerular NO production is based on an increase in the iNOS isoform. Increased glomerular NO synthesis seems to play a role in the decreased renal vascular resistance observed after unilateral nephrectomy in rats.

Hemodynamic and renal effects of U-46619, a TXA2/PGH2 analog, in late-pregnant rats

The vasoconstrictor effects of pressor agents are attenuated during pregnancy. Thromboxane A2 (TXA2) is produced in great quantities during hypertension in pregnancy, and therefore it is important to know whether pregnancy modifies the pressor effects of TXA2. The TXA2 analog U-46619 was infused in anesthetized, acutely prepared and conscious, chronically prepared late-pregnant and nonpregnant female rats to examine its systemic hemodynamic and renal effects. Mean arterial pressure (MAP) and total peripheral resistance (TPR) were lower in anesthetized pregnant than nonpregnant rats (P < 0.01). The infusion of U-46619 into the aortic arch resulted in elevation of MAP only in pregnant rats, due to a greater elevation of TPR (60 +/- 17%) compared with nonpregnant rats (36 +/- 6%, P < 0.05). The pressor effect of intravenously infused U-46619 was also enhanced in conscious pregnant versus nonpregnant rats, and the increase in renal vascular resistance was undiminished. U-46619 increased hematocrit and plasma protein concentration more during pregnancy, which suggested greater reduction of plasma volume. The urinary excretion of sodium (-1.49 +/- 0.25 vs. -0.54 +/- 0.24 micromol/min) and water was reduced more in pregnant than nonpregnant rats during U-46619 (P < 0.01). Thus the MAP and renal effects of the TXA2 analog are exaggerated during pregnancy in the rat.