Evidence for the presence of an unusual nitric oxide- and citrulline-producing enzyme in rat kidney

Hypoxic-ischemic brain injury exacerbates neuronal apoptosis and precipitates spontaneous seizures in glucose transporter isoform 3 heterozygous null mice

We examined the effects of 45-min hypoxia (FiO(2) 0.08; Hx) vs. normoxia (FiO(2) 0.21; Nx) on the ipsilateral (Ipsi) and contralateral (Ctrl) sides of the brain in neuronal glucose transporter isoform 3 (Glut3) heterozygous null mice (glut3(+/-)) and their wild-type littermates (WT), undergoing unilateral carotid artery ligation. Glut3(+/-) mice, under Nx, demonstrated a compensatory increase in blood-brain barrier/glial Glut1 protein concentration and a concomitant increase in neuronal nitric oxide synthase (nNOS) enzyme activity and Bax protein, with a decrease in procaspase 3 protein (P < 0.05 each). After Hx, reoxygenation in FiO(2) of 0.21 led to no comparable adaptive up-regulation of the ipsilateral brain Glut3 or Glut1 protein at 4 hr and Glut1 at 24 hr in glut3(+/-) vs. WT. These brain Glut changes in glut3(+/-) but not WT mice were associated with an increase in proapoptotic Bax protein and caspase-3 enzyme activity (P < 0.01 each) and a decline in the antiapoptotic Bcl-2 and procaspase-3 proteins (P < 0.05 each). Glut3(+/-) mice after Hx demonstrated TUNEL-positive neurons with nuclear pyknosis in most ipsilateral (hypoxic-ischemia) brain regions. A subset (∼55%) of glut3(+/-) mice developed spontaneous seizures after hypoxic-ischemia, confirmed by electroencephalography, but the WT mice remained seizure-free. Pentylenetetrazole testing demonstrated an increased occurrence of longer lasting clinical seizures at a lower threshold in glut3(+/-) vs. WT mice, with no detectable differences in monamine neurotransmitters. We conclude that hypoxic-ischemic brain injury in glut3(+/-) mice exacerbates cellular apoptosis and necrosis and precipitates spontaneous seizures.

Renal nitric oxide production in rat pregnancy: role of constitutive nitric oxide synthases

Functional studies show that increased renal nitric oxide (NO) mediates the renal vasodilation and increased glomerular filtration rate that occur during normal pregnancy. We investigated whether changes in the constitutive NO synthases (NOS), endothelial (eNOS) and neuronal (nNOS), were associated with the increased renal NO production in normal midterm pregnancy in the rat. In kidneys from midterm pregnant (MP: 11-13 days gestation), late-term pregnant (LP: 18-20 days gestation), and similarly aged virgin (V) rats, transcript and protein abundance for eNOS and the nNOSα and nNOSβ splice variants, as well as the rate of L-arginine-to-L-citrulline conversion, were determined as a measure of NOS activity. At MP, renal cortical abundance of the total eNOS protein and phosphorylated (Ser(1177)) eNOS was reduced, and L-arginine-to-L-citrulline conversion in the cortical membrane fraction was decreased; these declines were also seen in LP. There were no changes in the eNOS transcript. In contrast, L-arginine-to-L-citrulline conversion in the soluble fraction of renal cortex increased at MP and then declined at LP. This MP increase was ablated by S-methylthiocitrulline, a nNOS inhibitor. Using Western blotting, we did not detect a change in the protein abundance or transcript of the 160-kDa nNOSα, but protein abundance and transcript of the nNOSβ were increased at MP in cortex. Collectively, these studies suggest that the soluble nNOSβ is responsible for the increased renal cortical NO production during pregnancy.

Inhibition of cystathionine-beta-synthase activity during renal ischemia-reperfusion: role of pH and nitric oxide

Our recent study (Prathapasinghe GA, Siow YL, O K. Am J Physiol Renal Physiol 292: F1354-F1363, 2007) indicates that homocysteine (Hcy) plays a detrimental role in ischemia-reperfusion-induced renal injury. Elevation of renal Hcy concentration during ischemia-reperfusion is attributed to reduced activity of cystathionine-beta-synthase (CBS) that catalyzes the rate-limiting step in the transsulfuration pathway for the metabolism of the majority of Hcy in the kidney. However, the mechanisms of impaired CBS activity in the kidney are unknown. The aim of this study was to investigate the effects of pH and nitric oxide (NO) on the CBS activity in the kidney during ischemia-reperfusion. The left kidney of a Sprague-Dawley rat was subjected to ischemia-reperfusion. The CBS activity was significantly reduced in kidneys subjected to ischemia alone (15-60 min) or subjected to ischemia followed by reperfusion for 1-24 h. The pH was markedly reduced in kidneys upon ischemia. Injection of alkaline solution into the kidney partially restored the CBS activity during ischemia. Further analysis revealed that reduction of CBS activity during reperfusion was accompanied by an elevation of NO metabolites (nitrate and nitrite) in the kidney tissue. Injection of a NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), restored the CBS activity in the kidneys subjected to ischemia-reperfusion. Treatment with PTIO could abolish ischemia-reperfusion-induced lipid peroxidation and prevent cell death in the kidney. These results suggested that metabolic acidosis during ischemia and accumulation of NO metabolites during reperfusion contributed, in part, to reduced CBS activity leading to an elevation of renal Hcy levels, which in turn, played a detrimental role in the kidney.

Postanoxic functional recovery of the developing heart is slightly altered by endogenous or exogenous nitric oxide

Nitric oxide synthase (NOS) is strongly and transiently expressed in the developing heart but its function is not well documented. This work examined the role, either protective or detrimental, that endogenous and exogenous NO could play in the functioning of the embryonic heart submitted to hypoxia and reoxygenation. Spontaneously beating hearts isolated from 4-day-old chick embryos were either homogenized to determine basal inducible NOS (iNOS) expression and activity or submitted to 30 min anoxia followed by 100 min reoxygenation. The chrono-, dromo- and inotropic responses to anoxia/reoxygenation were determined in the presence of NOS substrate (L-arginine 10 mM), NOS inhibitor L-NIO (1-5 mM), or NO donor (DETA NONOate 10-100 microM). Myocardial iNOS was detectable by immunoblotting and its activity was specifically decreased by 53% in the presence of 5 mM L-NIO. L-Arginine, L-NIO and DETA NONOate at 10 microM had no significant effect on the investigated functional parameters during anoxia/reoxygenation. However, irrespective of anoxia/reoxygenation, DETA NONOate at 100 microM decreased ventricular shortening velocity by about 70%, and reduced atrio-ventricular propagation by 23%. None of the used drugs affected atrial activity and hearts of all experimental groups fully recovered at the end of reoxygenation. These findings indicate that (1) by contrast with adult heart, endogenously released NO plays a minor role in the early response of the embryonic heart to reoxygenation, (2) exogenous NO has to be provided at high concentration to delay postanoxic functional recovery, and (3) sinoatrial pacemaker cells are the less responsive to NO.

Nitric Oxide Production Within Rat Urothelial Cells

PURPOSE

Recent studies have suggested that nitric oxide (NO) synthase (NOS) may be localized in the urothelium of the proximal part of the mammalian ureter. We investigated endogenous NO production in the proximal half of the rat ureter, localized its cellular source, characterized the NOS isoforms involved and assessed the impact of NO on ureteral motility.

MATERIALS AND METHODS

Direct detection of NO production was performed on primary cultures of living rat ureteral cells with the fluorescent indicator diaminofluorescein. Cultures were incubated with the NO precursor L-arginine or the NOS inhibitors L-NAME (N-nitro-L-arginine-methyl ester) and 1400W. NOS expression was determined by immunofluorescence and Western blot analysis. The functional effects of NO donors were assessed on isolated ureters.

RESULTS

Significant basal NO production was demonstrated by the high fluorescence level detected in diaminofluorescein treated cell cultures. NO production was strictly limited to urothelial cells since no fluorescence was seen in smooth muscle cells. Pretreatment with L-NAME or 1400W resulted in a significant decrease in fluorescence. Constitutive and inducible NOS isoforms were detected in urothelial cultured cells and in lysates of the urothelial layer. NO donors inhibited in a concentration dependent manner the agonist induced contractile activity of isolated ureters.

CONCLUSIONS

These results suggest that NO production stems from the urothelium and the NO pathway inhibits contractile activity in the proximal half of the rat ureter. Hence, the nitrergic pathway may be an important target for drugs producing relaxation of the mammalian ureter.

Expression of NOS1 and soluble guanylyl cyclase by human kidney epithelial cells: morphological evidence for an autocrine/paracrine action of nitric oxide

BACKGROUND

Nitric oxide plays an important role in the kidney through effects on both renal hemodynamics and tubular functions. Tubular epithelial cells are thus a target for nitric oxide. However, as to whether tubular epithelial cells endogeneously produce nitric oxide under physiologic conditions in human kidney is currently unknown. The aim of the present study was to characterize and localize in situ the nitric oxide synthase (NOS) isoforms (NOS1, NOS2, and NOS3) expressed in human normal kidney, and soluble guanylyl cyclase, the well-known target for nitric oxide.

METHODS

Five complementary experimental approaches were used: (1) detection of NOS reductase activity by nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry, (2) immunolocalization of the NOS isoforms (NOS1, NOS2, NOS3), (3) immunoblot analysis, (4) quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis of NOS mRNA, and (5) measurement of NOS activity as the conversion rate of l-[14C]-arginine to l-[14C]-citrulline. In addition, in situ detection of soluble guanylyl cyclase was assessed by immunohistochemistry.

RESULTS

All these techniques led to consistent results showing that epithelial cells of most tubules along the human nephron exhibit functional NOS1, with a corticomedullary gradient observed both at the protein and mRNA levels. Moreover, epithelial cells expressing NOS1 also express soluble guanylyl cyclase, indicating that these cells possess the machinery for autocrine/paracrine effect of nitric oxide.

CONCLUSION

The present study demonstrates that NOS1 is strongly expressed in most tubules of the human nephron and therefore invites to consider epithelial cells as one of the major source of nitric oxide in the human kidney under physiologic conditions.

Impact of pregnancy on underlying renal disease

Normal pregnancy involves marked renal vasodilation and large increases in glomerular filtration rate (GFR). Studies in rats reveal that the gestational renal vasodilation is achieved by parallel reductions in tone in afferent and efferent arterioles so GFR rises without a change in glomerular blood pressure. There is some evidence from animal studies that increased renal generation of nitric oxide (NO) may be involved. Although chronic renal vasodilation has been implicated in causing progression of renal disease in nonpregnant states by glomerular hypertension, there are no long-term deleterious effects of pregnancies on the kidney when maternal renal function is normal because glomerular blood pressure remains normal. When maternal renal function is compromised before conception, there are no long-term adverse effects on renal function in most types of renal disease, providing that the GFR is well maintained before conception. When serum creatinine exceeds approximately 1.4 mg/dL, pregnancy may accelerate the renal disease increases and when serum creatinine >2 mg/dL, the chances are greater than 1 in 3 that pregnancy will hasten the progression of the renal disease. The available animal studies suggest that glomerular hypertension does not occur despite diverse injuries. Thus, the mechanisms of the adverse interaction between pregnancy and underlying renal disease remain unknown.

TNF-alpha enhances contraction and inhibits endothelial NO-cGMP relaxation in systemic vessels of pregnant rats

Tumor necrosis factor-alpha (TNF-alpha) is elevated in the plasma of preeclamptic women and may have a role in pregnancy-induced hypertension. However, whether the hemodynamic effects of TNF-alpha reflect the direct effects on vascular reactivity is unclear. We tested the hypothesis that TNF-alpha impairs endothelium-dependent relaxation and enhances vascular contraction in systemic vessels of pregnant rats. We measured isometric contraction in aortic strips isolated from virgin and pregnant Sprague-Dawley rats (nontreated vs. treated for 2 h with 10-1,000 pg/ml TNF-alpha). In endothelium-intact vascular strips, TNF-alpha caused greater enhancement of phenylephrine (Phe) contraction in pregnant than virgin rats. TNF-alpha caused significant inhibition of ACh- and bradykinin-induced vascular relaxation and nitrite/nitrate production that were more prominent in pregnant than virgin rats. N(G)-nitro-L-arginine methyl ester [L-NAME, 100 microM, an inhibitor of nitric oxide (NO) synthase] or 1H-[1,2,4]oxadiazolo[4,3]-quinoxalin-1-one (ODQ, 1 microM, an inhibitor of cGMP production in smooth muscle) inhibited ACh relaxation and enhanced Phe contraction in nontreated but to a lesser extent in TNF-alpha-treated vessels, particularly those of pregnant rats. Endothelium removal enhanced Phe contraction in nontreated but not TNF-alpha-treated vessels, especially those of pregnant rats. Relaxation of Phe contraction with the NO donor sodium nitroprusside was not different between nontreated and TNF-alpha-treated vessels. Thus TNF-alpha enhances vascular contraction and inhibits endothelium-dependent NO-cGMP-mediated vascular relaxation in systemic vessels, particularly those of pregnant rats. The results support a direct role for TNF-alpha as a possible mediator of increased vascular resistance associated with pregnancy-induced hypertension.

Intrarenal detection of nitric oxide using electron spin resonance spectroscopy in hypertensive lipopolysaccharide-treated rats

The inhibition of nitric oxide (NO) synthesis by chronic administration of NG-nitro-l-arginine methyl ester (l-NAME) in rats is responsible for systemic hypertension. However, the mechanisms involved in this hypertension remain unclear. The effects of chronic l-NAME on kidney and blood NO production were studied in rats in a state of endotoxic shock due to lipopolysaccharide (LPS). A nitric oxide spin trapping technique using electron spin resonance (ESR) spectroscopy has been used to identify and measure the production of NO in the kidney. This method is based on the trapping of nitric oxide by a metal-chelator complex consisting of N-methyl-d-glucamine dithiocarbamate (MGD) and reduced iron (Fe2+) forming a water-soluble NO-FeMGD complex detected by ESR. After LPS injection (14 mg/kg, IV, 6 h before the sacrifice) to rats pretreated with l-NAME (10 mg/kg/d over 14 days), the NO-FeMGD complex was evaluated in the kidney (arbitrary units [AU]/g of kidney) and the density of polynuclear neutrophils was counted by light microscopy. Chronic inhibition of NO synthase by l-NAME, a nonspecific inhibitor, was responsible for a decrease of the NO-FeMGD complex levels in the kidney (24.9 +/- 1.6 AU versus 13.8 +/- 1.3 AU). LPS administration was responsible for a large increase in both NO-FeMGD complex and neutrophil levels in the kidney of normotensive rats (332.6 +/- 12.8 AU versus 24.9 +/- 1.6 AU for NO-FeMGD complex and 1.36 +/- 0.41 versus 0.11 +/- 0.03 for neutrophils). Conversely, LPS administration in hypertensive, l-NAME-pretreated rats was linked to a smaller increase in the NO-FeMGD complex (85.1 +/- 7.9 AU versus 332.6 +/- 12.8 AU) and a larger increase in glomerular neutrophils (2.48 +/- 0.36 versus 1.36 +/- 0.41) compared with normotensive rats. These results are in agreement with a direct implication of NO during LPS-and l-NAME-induced kidney injuries.

Inducible nitric oxide synthase in renal transplantation

The importance of the endothelial isoform of nitric oxide synthase (eNOS) has been well established. Endothelium-derived nitric oxide has been shown to be essential for vascular homeostasis and modulation of eNOS has thus become a target in prevention of cardiovascular disease. The role of the inducible form of nitric oxide synthase (iNOS) in vascular biology, however, is less clear. Classically, iNOS has been regarded as an enzyme that produces nmolar amounts of the nitric oxide radical, thereby leading to cellular damage. More recent data, however, have shown that the iNOS can be a superoxide, peroxynitrite as well as a nitric oxide-producing enzyme, while the biological effects of iNOS probably depend upon the sort of radical species released by the enzyme as well as the anti-oxidant capacity of the cellular microenvironment of the enzyme. This brief review discusses these aspects in relation to renal transplantation.

Reduced endothelial NO-cGMP vascular relaxation pathway during TNF-alpha-induced hypertension in pregnant rats

Placental ischemia during pregnancy is thought to release cytokines such as tumor necrosis factor-alpha (TNF-alpha), which may contribute to the increased vascular resistance associated with pregnancy-induced hypertension. We have reported that a chronic twofold elevation in plasma TNF-alpha increases blood pressure in pregnant but not in virgin rats; however, the vascular mechanisms are unclear. We tested the hypothesis that increasing plasma TNF-alpha during pregnancy impairs endothelium-dependent vascular relaxation and enhances vascular reactivity. Active stress was measured in aortic strips of virgin and late-pregnant Sprague-Dawley rats untreated or infused with TNF-alpha (200 ng x kg(-1) x day(-1) for 5 days) to increase plasma level twofold. Phenylephrine (Phe) increased active stress to a maximum of 4.2 +/- 0.4 x 10(3) and 9.9 +/- 0.7 x 10(3) N/m2 in control pregnant and TNF-alpha-infused pregnant rats, respectively. Removal of the endothelium enhanced Phe-induced stress in control but not in TNF-alpha-infused pregnant rats. In endothelium-intact strips, ACh caused greater relaxation of Phe contraction in control than in TNF-alpha-infused pregnant rats. Basal and ACh-induced nitrite/nitrate production was less in TNF-alpha-infused than in control pregnant rats. Pretreatment of vascular strips with 100 microM N(G)-nitro-L-arginine methyl ester, to inhibit nitric oxide (NO) synthase, or 1 microM 1H-[1,2,4]oxadiazolo[4,3-]quinoxalin-1-one, to inhibit cGMP production in smooth muscle, inhibited ACh-induced relaxation and enhanced Phe-induced stress in control but not in TNF-alpha-infused pregnant rats. Phe contraction and ACh relaxation were not significantly different between control and TNF-alpha-infused virgin rats. Thus an endothelium-dependent NO-cGMP-mediated vascular relaxation pathway is inhibited in late-pregnant rats infused with TNF-alpha. The results support a role for TNF-alpha as one possible mediator of the increased vascular resistance associated with pregnancy-induced hypertension.

Citrulline is not the major product using the standard "NOS activity" assay on renal cortical homogenates

A standard approach to assessing nitric oxide synthase (NOS) activity in tissue homogenates is 1) removal of small-molecular-weight substances by size-exclusion chromatography, 2) adding back of substrates/cofactors in precise concentrations with a radioactive isotope of arginine (Arg), and 3) quantification of labeled citrulline (Cit) after separation of Arg and Cit by cation-exchange column chromatography. Using this approach and L-[2,3-3H]Arg, we found that the major product(s) was not Cit in cortical homogenates prepared from rat, mouse, and human kidneys. The product(s) mimicked Cit, insofar as it passed freely through cation-exchange columns and comigrated with Cit on both one-dimensional and two-dimensional straight-phase thin-layer chromatography systems. However, it was clearly resolved from Cit by precolumn derivatization and reverse-phase HPLC. The maximum velocity and Michaelis-Menten constant were approximately 100 pmol x mg protein(-1) x min(-1) and 100 microM, respectively, in renal cortical homogenates from rats. The enzyme activity was the same in the presence or absence of cofactors including Ca2+, calmodulin, tetrahydrobiopterin, and NADPH. It was only modestly inhibited by L-Arg analogs and was mainly in the supernatant after a 100,000 g centrifugation. These enzyme characteristics contrasted markedly with those simultaneously obtained for NOS activity in placental homogenates. Thus results from the conventional NOS activity assay should be viewed cautiously.

Real-time profiling of kidney tubular fluid nitric oxide concentrations in vivo

To directly determine intratubular nitric oxide concentrations ([NO]) in vivo, we modified amperometric integrated electrodes (WPI P/N ISO-NOP007), which are highly sensitive to NO and not affected by ascorbic acid, nitrite, L-arginine, or dopamine. Although reactive lengths were as short as 5 microm long, the electrode still responded rapidly. With the use of kidney surface fluid as the "zero point," the electrode tip was inserted into tubular segments along the track of a perforation made by a beveled glass pipette. The surface fluid zero point was usually stable as distal, late proximal, and early proximal tubule [NO] levels were measured sequentially in the same nephron. In eight normal rats, distal, late proximal, and early proximal [NO] concentrations were each approximately 110 nM. In contrast, in nine 5/6 nephrectomized rats 2 wk postsurgery, although [NO] also did not differ among distal, late proximal, and early proximal segments, levels were approximately fourfold higher than those in normal rats and were significantly reduced after N(G)-monomethyl-L-arginine administration. These are the first quantitative in vivo tubular fluid [NO] measurements and show a significant increase in tubular fluid [NO] after renal ablation.

[Ca(2+)](i) signaling in renal arterial smooth muscle cells of pregnant rat is enhanced during inhibition of NOS

Vascular resistance and arterial pressure are reduced during normal pregnancy, but dangerously elevated during pregnancy-induced hypertension (PIH), and changes in nitric oxide (NO) synthesis have been hypothesized as one potential cause. In support of this hypothesis, chronic inhibition of NO synthesis in pregnant rats has been shown to cause significant increases in renal vascular resistance and hypertension; however, the cellular mechanisms involved are unclear. We tested the hypothesis that the pregnancy-associated changes in renal vascular resistance reflect changes in contractility and intracellular Ca(2+) concentration ([Ca(2+)](i)) of renal arterial smooth muscle. Smooth muscle cells were isolated from renal interlobular arteries of virgin and pregnant Sprague-Dawley rats untreated or treated with the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME; 4 mg. kg(-1). day(-1) for 5 days), then loaded with fura 2. In cells of virgin rats incubated in Hanks' solution (1 mM Ca(2+)), the basal [Ca(2+)](i) was 86 +/- 6 nM. Phenylephrine (Phe, 10(-5) M) caused a transient increase in [Ca(2+)](i) to 417 +/- 11 nM and maintained an increase to 183 +/- 8 nM and 32 +/- 3% cell contraction. Membrane depolarization by 51 mM KCl, which stimulates Ca(2+) entry from the extracellular space, caused maintained increase in [Ca(2+)](i) to 292 +/- 12 nM and 31 +/- 2% contraction. The maintained Phe- and KCl-induced [Ca(2+)](i) and contractions were reduced in pregnant rats but significantly enhanced in pregnant rats treated with L-NAME. Phe- and KCl-induced contraction and [Ca(2+)](i) were not significantly different between untreated and L-NAME-treated virgin rats or between untreated and L-NAME + L-arginine treated pregnant rats. In Ca(2+)-free Hanks', application of Phe or caffeine (10 mM), to stimulate Ca(2+) release from the intracellular stores, caused a transient increase in [Ca(2+)](i) and a small cell contraction that were not significantly different among the different groups. Thus renal interlobular smooth muscle of normal pregnant rats exhibits reduction in [Ca(2+)](i) signaling that involves Ca(2+) entry from the extracellular space but not Ca(2+) release from the intracellular stores. The reduced renal smooth muscle cell contraction and [Ca(2+)](i) in pregnant rats may explain the decreased renal vascular resistance associated with normal pregnancy, whereas the enhanced cell contraction and [Ca(2+)](i) during inhibition of NO synthesis in pregnant rats may, in part, explain the increased renal vascular resistance associated with PIH.

Gastrointestinal motility during pregnancy: role of nitrergic component of NANC nerves

This study evaluated whether increased release of nitric oxide (NO) from the nitrergic component of the nonadrenergic, noncholinergic (NANC) nerves may be partly responsible for the decrease in gastrointestinal motility observed during pregnancy. Segments of fundal strip, ileum, and colon were obtained from nonpregnant rats, rats in midpregnancy (days 9-11), and rats in late pregnancy (days 18-20). NANC activity was studied by assessing changes in tone after application of electric field stimulation (EFS). The role of NO was determined by observing the effects of EFS in the presence and absence of the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) and the reversibility of the effects of L-NAME by L-arginine. The magnitude of change in cGMP levels in the tissues after application of EFS was also assessed. Our studies indicate that there was increased magnitude of relaxation of isolated strips of rat gastric fundus and rat colon, after application of EFS to tissues obtained only from animals in late pregnancy. These results paralleled the changes in cGMP levels in tissues. NOS activity in the gastric fundus was significantly increased in animals in late pregnancy compared with nonpregnant controls. Our studies suggest that the delay in gastric emptying and increase in colonic transit time observed in rats during pregnancy may be caused in part by increased activity of the nitrergic component of the NANC nerves innervating these organs.

Gender-dependent effect of L-NAME on polycystic kidney disease in Han:SPRD rats

To determine whether the renal nitric oxide (NO) system has a role in the pathogenesis of polycystic kidney disease (PKD) in Han:Sprague-Dawley (SPRD) rats, the NO synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), 70 mg/L, or L-arginine, 0.5 g/L, was administered to heterozygous diseased (cy/+) and homozygous normal animals. Urine nitrate and nitrite excretion was reduced by L-NAME treatment and, in the male cy/+ rats, increased by L-arginine administration. The administration of L-NAME significantly increased blood pressure in all groups, whereas L-arginine had no effect. L-NAME and L-arginine had a modest but significant overall effect on the severity of cystic disease in male rats, reflected by relative kidney weights and cyst volume densities. This effect was gender dependent because it was not observed in female animals. The administration of L-NAME resulted in a significant increase in plasma creatinine concentration of the cy/+ rats, which was more marked in male than female animals. These observations support the recently reported gender differences in the renal NO system and a small role for NO synthesis that can be inhibited by L-NAME in the pathogenesis of PKD in Han:SPRD rats. These observations do not exclude a more important role for the endogenous renal NO production in the pathogenesis of PKD in view of a recent report of a major NOS resistant to conventional inhibitors in the rat kidney.

Castration increases and androgens decrease nitric oxide synthase activity in the brain: physiologic implications

Sex differences in nitric oxide synthase (NOS) activity in different regions of the rat brain and effects of testosterone and dihydrotestosterone (DHT) treatment in orchidectomized animals were investigated. Regional but no sex differences in NOS activity were detected in gonadectomized animals. Orchidectomy significantly increased NOS activity in the hypothalamus, "amygdala," and cerebellum but not in the cortex. In the hypothalamus, the increase in NOS activity after castration and its reversal by androgen treatment was mimicked by changes in neuronal NOS mRNA level. In contrast, androgen receptor (AR) mRNA level in the hypothalamus was slightly reduced by castration and increased by treatment with DHT. Again in the hypothalamus, the increase in NOS activity in castrated rats was accompanied by an increase in the number of neuronal NOS+ cells determined immunohistochemically, whereas androgen treatment prevented this increase. The changes in NOS+ neurons correlated with the changes in the number of AR+ cells to a degree. Overlap of AR in NOS+ cells was not present in the regions of the hypothalamus analyzed. These results indicate that testosterone or, most likely, its metabolite DHT down-regulates NOS activity, mRNA expression or stabilization, and the number of neuronal NOS+ neurons.

Castration increases and androgens decrease nitric oxide synthase activity in the brain: Physiologic implications

Sex differences in nitric oxide synthase (NOS) activity in different regions of the rat brain and effects of testosterone and dihydrotestosterone (DHT) treatment in orchidectomized animals were investigated. Regional but no sex differences in NOS activity were detected in gonadectomized animals. Orchidectomy significantly increased NOS activity in the hypothalamus, "amygdala," and cerebellum but not in the cortex. In the hypothalamus, the increase in NOS activity after castration and its reversal by androgen treatment was mimicked by changes in neuronal NOS mRNA level. In contrast, androgen receptor (AR) mRNA level in the hypothalamus was slightly reduced by castration and increased by treatment with DHT. Again in the hypothalamus, the increase in NOS activity in castrated rats was accompanied by an increase in the number of neuronal NOS+ cells determined immunohistochemically, whereas androgen treatment prevented this increase. The changes in NOS+ neurons correlated with the changes in the number of AR+ cells to a degree. Overlap of AR in NOS+ cells was not present in the regions of the hypothalamus analyzed. These results indicate that testosterone or, most likely, its metabolite DHT down-regulates NOS activity, mRNA expression or stabilization, and the number of neuronal NOS+ neurons.

1,25-Dihydroxyvitamin D3 induces nitric oxide synthase and suppresses growth of Mycobacterium tuberculosis in a human macrophage-like cell line

Inducible synthesis of nitric oxide (NO) by macrophages is an important mechanism of the host defense against intracellular infection in mice, but the evidence for significant levels of inducible NO production by human macrophages is controversial. Here we report that the human promyelocytic cell line HL-60, when differentiated to a macrophage-like phenotype, acquires the ability to produce substantial amounts of NO on stimulation with LPS or 1, 25-dihydroxyvitamin D3 (1,25-D3) in the absence of activating factors such as gamma interferon. Expression of the inducible nitric oxide synthase (NOS2) was confirmed by sequencing of the reverse transcription-PCR product from stimulated HL-60 cells. Kinetic studies after lipopolysaccharide stimulation show that NOS2 mRNA levels rise within 3 to 6 h, that conversion of [14C]arginine to [14C]citrulline is maximal at 5 to 6 days, and that levels of reactive nitrogen intermediates stabilize at around 20 microM at 7 to 8 days. We find that 1,25-D3 acts to suppress the growth of Mycobacterium tuberculosis in these cells and that this effect is inhibited by NG-monomethyl-L-arginine, suggesting that vitamin D-induced NO production may play a role in the host defense against human tuberculosis.

NADPH-diaphorase-stained neurons after experimental epilepsy in rats

The aim of this study was to determine the neuronal participation of nitric oxide (NO) in experimental epilepsy. To reach this objective, we established the amount of cells presenting nitric oxide synthase (NOS) and the amygdaline concentrations in the L-arginine-nitric oxide synthesis pathway. A group of fully epileptic rats, induced by the kindling procedure and that had reached at least 10 generalized seizures, was studied. We evaluated behavioral stages, electroencephalographic activities, and histochemical NOS-positive cells and carried out high-pressure liquid chromatography (HPLC) determinations of arginine, citrulline, and glutamic acid. Our results showed that behavioral and electrographic frequency, and duration of epileptic activities, were increased during the kindling process. Image processing system of NOS cells showed two types of intensities in cell stains in hippocampus, caudate-putamen, and amygdala. When we independently counted the two types of NOS stain cells, a selective increase in the number and density of weak-stained cells was observed, while dark-stained cells did not change in the studied structures. Additionally, arginine, citrulline, and glutamic acid concentrations in amygdala increased in kindled animals. The differential and specific increase in the stained cells expressing the nitric oxide synthase, as well as the increase in concentrations of the L-arginine-nitric oxide pathway in amygdala, suggested a relationship with the progressive augmentation in the electrophysiological hyperactivity characteristic of generalized epilepsy.

17 beta-estradiol regulation of human endothelial cell basal nitric oxide release, independent of cytosolic Ca2+ mobilization

Estradiol retards the development of atherosclerosis. Animal models have suggested that NO may be a critical effector molecule in this cardiovascular protection. In this study, female human umbilical vein endothelial cells (HUVECs) were propagated in phenol red-free gonadal hormone-free medium and pretreated with 17 beta-estradiol (E2). Reduced NO2- and NO3- (NOx) concentration, determined by chemiluminescence, demonstrated a rapid increase in basal HUVEC NO release in response to physiological concentrations of E2. The estrogen receptor (ER) antagonist ICI 164,384 inhibited the augmented NO release, demonstrating an ER-mediated component of this response. Because endothelial NO synthase (eNOS) activity is largely regulated by cytosolic Ca2+, relative [Ca2+]i in response to E2 was determined in a fluorometric assay. E2 did not promote HUVEC Ca2+ fluxes. Furthermore, eNOS activity in E2-pretreated endothelial whole-cell lysates was not dependent on additional Ca2+. Despite involving the ER, this is a nongenomic effect E2, as demonstrated by maintained responses in transcriptionally inhibited cells and by the rapidly (10 minutes) of cGMP formation in an NO bioassay. We demonstrate, for the first time, that independent of cytosolic Ca2+ mobilization, there is augmentation of eNOS activity with a resultant increase in HUVEC basal NO release in response to short-term estradiol exposure. Implications for the cardiovascular protective role of estrogen are discussed.

Superoxide generation by renal proximal tubule nitric oxide synthase

Lipid A, the biologically active component of lipopolysaccharide, initiates a specific cytotoxic signaling cascade in the renal proximal tubule that involves a rapid release of intracellular calcium, the activation of nitric oxide synthase (NOS) and NO production. Superoxide (O2-) generation is also a component of this cascade and both NO and O2- are required for the development of oxidant stress and cytotoxicity. Here we examined whether NOS activity was responsible for O2- generation. In renal proximal tubules isolated from the rat, the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) but not D-NMMA blocked lipid A (50 microg/ml)-stimulated O2- generation as measured by the reduction of cytochrome c during a 30-min incubation period. When L-arginine (2 mM) was added to the tubule suspensions, O2- generation was significantly inhibited, while NO2- (a marker of NO generation) was significantly increased. The addition of L-arginine also reduced lipid A-stimulated malondialdehyde formation at 30 min (a marker of lipid peroxidation) and lactate dehydrogenase release at 90 min (a marker of cell death). Thus, lipid A-stimulated the generation of both NO and O2- via NOS activation. Furthermore, increasing L-arginine availability shifted NOS activity toward NO generation and reduced oxidant injury. These results offer an explanation of why scavengers of NO or oxygen radicals ameliorate endotoxin-induced acute renal failure in vivo.