Effects of dietary salt intake on plasma arginine

NRF2 prevents hypertension, increased ADMA, microvascular oxidative stress, and dysfunction in mice with two weeks of ANG II infusion

Nuclear factor erythyroid factor 2 (Nrf2) transcribes genes in cultured endothelial cells that reduce reactive oxygen species (ROS) and generate nitric oxide (NO) or metabolize asymmetric dimethylarginine (ADMA), which inhibits NO synthase (NOS). Therefore, we undertook a functional study to test the hypothesis that activation of Nrf2 by tert-butylhydroquinone (tBHQ) preserves microvascular endothelial function during oxidative stress. Wild-type CB57BL/6 (wt), Nrf2 wt (+/+), or knockout (-/-) mice received vehicle (Veh) or tBHQ (0.1%; activator of Nrf2) during 14-day infusions of ANG II (to induce oxidative stress) or sham. MAP was recorded by telemetry. Mesenteric resistance arterioles were studied on isometric myographs and vascular NO and ROS by fluorescence microscopy. ANG II increased the mean arterial pressure (112 ± 5 vs. 145 ± 5 mmHg; P < 0.01) and excretion of 8-isoprostane F_2α (2.8 ± 0.3 vs. 3.8 ± 0.3 ng/mg creatinine; P < 0.05) at 12-14 days. However, 12 days of ANG II reduced endothelium-derived relaxation (27 ± 5 vs. 17 ± 3%; P < 0.01) and NO (0.38 ± 0.07 vs. 0.18 ± 0.03 units; P < 0.01) but increased microvascular remodeling, endothelium-derived contractions (7.5 ± 0.5 vs. 13.0 ± 1.7%; P < 0.01), superoxide (0.09 ± 0.03 vs. 0.29 ± 0.08 units; P < 0.05), and contractions to U-46,619 (87 ± 6 vs. 118 ± 3%; P < 0.05), and endothelin-1(89 ± 4 vs. 123 ± 12%; P < 0.05). tBHQ prevented all of these effects of ANG II at 12-14 days in Nrf2^+/+ mice but not in Nrf2^-/- mice. In conclusion, tBHQ activates Nrf2 to prevent microvascular endothelial dysfunction, remodeling, and contractility, and moderate ADMA and hypertension at 12-14 days of ANG II infusion, thereby preserving endothelial function and preventing hypertension.

Transport of asymmetric dimethylarginine (ADMA) by cationic amino acid transporter 2 (CAT2), organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1)

Asymmetric dimethylarginine (ADMA), inhibiting the nitric oxide (NO) synthesis from L-arginine, is a known cardiovascular risk factor. Our aim was to investigate if ADMA and/or L-arginine are substrates of the human cationic amino acid transporters 2A (CAT2A, SLC7A2A) and 2B (CAT2B, SLC7A2B), the organic cation transporter 2 (OCT2, SLC22A2), and the multidrug and toxin extrusion protein 1 (MATE1, SLC47A1). We systematically investigated the kinetics of ADMA and L-arginine transport in human embryonic kidney (HEK293) cells stably overexpressing CAT2A, CAT2B, OCT2, or MATE1. Vector-only transfected HEK293 cells served as controls. Compared to vector control cells, uptake of ADMA and L-arginine was significantly higher (p < 0.05) in cells expressing CAT2B and OCT2 at almost all investigated concentrations, while cells expressing CAT2A only showed a significant uptake at concentrations above 300 μM. Uptake of MATE1 overexpressing cells was significantly (p < 0.05) higher at pH 7.8 and 8.2 than controls. Apparent V max values (nmol mg protein(-1) min(-1)) for cellular uptake of ADMA and L-arginine were ≈11.8 ± 1.2 and 19.5 ± 0.7 for CAT2A, ≈14.3 ± 1.0 and 15.3 ± 0.4 for CAT2B, and 6.3 ± 0.3 and >50 for OCT2, respectively. Apparent K m values (μmol/l) for cellular uptake of ADMA and L-arginine were ≈3,033 ± 675 and 3,510 ± 419 for CAT2A, ≈4,021 ± 532 and 952 ± 92 for CAT2B, and 967 ± 143 and >10,000 for OCT2, respectively. ADMA and L-arginine are substrates of human CAT2A, CAT2B, OCT2 and MATE1. Transport kinetics of CAT2A, CAT2B, and OCT2 indicate a low affinity, high capacity transport, which may be relevant for renal and hepatic elimination of ADMA or L-arginine.

Changes in the arginine methylation of organ proteins during the development of diabetes mellitus

AIM

In this study, we examined changes in asymmetric dimethylarginine (ADMA), dimethylarginine dimethylaminohydrolase (DDAH), nitric oxide synthesis (NOS), and the arginine methylation of organ proteins during the development of diabetes in mice.

METHODS

Db/db mice developed significant obesity and fasting hyperglycemia during diabetogenesis. During diabetogenesis, the expression of ADMA and nNOS was increased, while that of DDAH1 and protein-arginine methyltransferase 1 (PRMT1) was decreased. Additionally, arginine methylation in the liver and adipose tissue was altered during diabetogenesis.

RESULTS

Changes were evident at 75, 60, and 52 kDa in liver tissue and at 38 and 25 kDa in adipose tissue. Collectively, DDAH and ADMA are closely associated with the development of obesity and diabetes, and the arginine methylation levels of certain proteins were changed during diabetes development.

CONCLUSION

Protein arginine methylation plays a role in the pathogenesis of diabetes.

Decreased arteriolar tetrahydrobiopterin is linked to superoxide generation from nitric oxide synthase in mice fed high salt

OBJECTIVE

Impaired endothelium-dependent arteriolar dilation in mice fed high salt (HS) is due to local oxidation of nitric oxide (NO) by superoxide anion (O(2) (-)). We explored the possibility that "uncoupled" endothelial nitric oxide synthase (eNOS) is the source of this O(2) (-).

METHODS

Levels of L-arginine (L-Arg), tetrahydrobiopterin (BH(4)), and O(2) (-) (hydroethidine oxidation) were measured in spinotrapezius muscle arterioles of mice fed normal salt (0.45%, NS) or (4%, HS) diets for 4 weeks, with or without dietary L-Arg supplementation. The contribution of NO to endothelium-dependent dilation was determined from the effect of N(omega)-nitro-L-arginine methyl ester (L-NAME) on responses to acetylcholine (ACh).

RESULTS

Arterioles in HS mice had lower [BH(4)] and higher O(2) (-) levels than those in NS mice. ACh further increased arteriolar O(2) (-) in HS mice only. L-Arg supplementation prevented the reduction in [BH(4)] in arterioles of HS mice, and O(2) (-) was not elevated in these vessels. Compared to NS mice, arteriolar ACh responses were diminished and insensitive to L-NAME in HS mice, but not in HS mice supplemented with L-Arg.

CONCLUSIONS

These findings suggest that eNOS uncoupling due to low [BH(4)] is responsible for O(2) (-) generation and reduced NO-dependent dilation in arterioles of mice fed a HS diet.

Cellular ADMA: regulation and action

Asymmetric (N(G),N(G)) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitric oxide synthase (NOS) that generates nitric oxide (NO) and cationic amino acid transporters (CATs) that supply intracellular NOS with its substrate, l-arginine, from the plasma. Therefore, ADMA and its transport mechanisms are strategically placed to regulate endothelial function. This could have considerable clinical impact since endothelial dysfunction has been detected at the origin of hypertension and chronic kidney disease (CKD) in human subjects and may be a harbinger of large vessel disease and cardiovascular disease (CVD). Indeed, plasma levels of ADMA are increased in many studies of patients at risk for, or with overt CKD or CVD. However, the levels of ADMA measured in plasma of about 0.5micromol.l(-1) may be below those required to inhibit NOS whose substrate, l-arginine, is present in concentrations many fold above the Km for NOS. However, NOS activity may be partially inhibited by cellular ADMA. Therefore, the cellular production of ADMA by protein arginine methyltransferase (PRMT) and protein hydrolysis, its degradation by N(G),N(G)-dimethylarginine dimethylaminohydrolase (DDAH) and its transmembrane transport by CAT that determines intracellular levels of ADMA may also determine the state of activation of NOS. This is the focus of the review. It is concluded that cellular levels of ADMA can be 5- to 20-fold above those in plasma and in a range that could tonically inhibit NOS. The relative importance of PRMT, DDAH and CAT for determining the intracellular NOS substrate:inhibitor ratio (l-arginine:ADMA) may vary according to the pathophysiologic circumstance. An understanding of this important balance requires knowledge of these three processes that regulate the intracellular levels of ADMA and arginine.

A rational design approach for amino acid supplementation in hepatocyte culture

Improvement of culture media for mammalian cells is conducted via empirical adjustments, sometimes aided by statistical design methodologies. Here, we demonstrate a proof of principle for the use of constraints-based modeling to achieve enhanced performance of liver-specific functions of cultured hepatocytes during plasma exposure by adjusting amino acid supplementation and hormone levels in the medium. Flux balance analysis (FBA) is used to determine an amino acid flux profile consistent with a desired output; this is used to design an amino acid supplementation. Under conditions of no supplementation, empirical supplementation, and designed supplementation, hepatocytes were exposed to plasma and their morphology, specific cell functions (urea, albumin production) and lipid metabolism were measured. Urea production under the designed amino acid supplementation was found to be increased compared with previously reported (empirical) amino acid supplementation. Not surprisingly, the urea production attained was less than the theoretical value, indicating the existence of pathways or constraints not present in the current model. Although not an explicit design objective, albumin production was also increased by designed amino acid supplementation, suggesting a functional linkage between these outputs. In conjunction with traditional approaches to improving culture conditions, the rational design approach described herein provides a novel means to tune the metabolic outputs of cultured hepatocytes.

Reduced nitric oxide in diabetic kidneys due to increased hepatic arginine metabolism: implications for renomedullary oxygen availability

Nitric oxide (NO) is a potent regulator of both vascular tone and oxygen utilization. Diabetes is commonly associated with both NO deficiency and reduced renomedullary oxygen availability. Arginine availability as regulator of NO production has gained growing interest. We hypothesized that arginine limitation causes diabetes-induced renomedullary NO deficiency, which directly influences renomedullary oxygen tension (Po2). Medullary NO, Po2, and blood flow were measured in control and streptozotocin-induced diabetic rats, which were treated or not treated with α-tocopherol, and administered l-arginine followed by Nω-nitro-l-arginine methyl ester. Major components of arginine metabolism were also investigated. Diabetic rats had reduced renomedullary NO levels compared with controls. Arginine selectively increased NO levels in diabetic rats and totally restored NO levels in α-tocopherol-treated animals. Tocopherol prevented the reduction in medullary Po2 in the diabetic animals. Although blood flow increased equally in all groups, arginine increased Po2 exclusively in the diabetic groups. Diabetes decreased plasma arginine and asymmetric dimethylarginine concentrations, but increased hepatic CAT-2A and plasma ornithine independently of α-tocopherol treatment. In conclusion, diabetic rats had reduced renomedullary NO due to decreased plasma arginine following increased hepatic arginine uptake and degradation. This was unrelated to oxidative stress. The diabetes-induced reduction in renomedullary Po2 was restored by either acute arginine administration, which also restored NO levels, or long-term antioxidant treatment. Arginine increased medullary NO and Po2 independently of altered hemodynamics in the diabetic groups. This reveals a direct regulatory function of NO for renomedullary Po2 especially during situations of elevated oxidative stress.

Salt-sensitive blood pressure in mice with increased expression of aldosterone synthase

To study the effects of modestly increased expression of aldosterone synthase (AS), we generated mice (AS(hi/hi)) by replacing the 3' untranslated region of AS mRNA with that from a stable mRNA. AS(hi/hi) mice on a normal-salt diet had 1.5 times the wild-type AS mRNA in adrenals, although their blood pressure and plasma aldosterone did not differ from wild-type mice. Changes in dietary salt did not affect the blood pressure of wild-type mice, but AS(hi/hi) mice had approximately 10-mm Hg higher blood pressure on a high-salt diet than on a low-salt diet and than wild-type mice on either diet. The AS(hi/hi) mice on a high-salt diet also had higher plasma aldosterone, lower plasma potassium, and greater renal expression of the alpha subunit of epithelial sodium channel compared with wild-type mice. The AS(hi/hi) mice on a high-salt diet also had more water intake and urine volume and less urine osmolality than wild-type mice. On a low-salt diet, AS(hi/hi) mice maintained normal blood pressure with less activation of the renin-angiotensin-aldosterone system than wild-type mice. The AS(hi/hi) mice also had less water intake and urine volume and higher urine osmolality than wild-type mice. On a medium high-salt diet, AS(hi/hi) mice were more susceptible than wild-type mice to infusion of angiotensin II, having a higher blood pressure, greater cardiac hypertrophy, and increased oxidative stress. Thus, a modest increase in AS expression makes blood pressure more sensitive to salt, suggesting that genetically increased AS expression in humans may contribute to hypertension and cardiovascular complications in societies with high-salt diets.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.

High salt intake reduces endothelium-dependent dilation of mouse arterioles via superoxide anion generated from nitric oxide synthase

In skeletal muscle arterioles of normotensive rats fed a high salt diet, the bioavailability of endothelium-derived nitric oxide (NO) is reduced by superoxide anion. Because the impact of dietary salt on resistance vessels in other species is largely unknown, we investigated endothelium-dependent dilation and oxidant activity in spinotrapezius muscle arterioles of C57BL/6J mice fed normal (0.45%, NS) or high salt (7%, HS) diets for 4 wk. Mean arterial pressure in HS mice was not different from that in NS mice, but the magnitude of arteriolar dilation in response to different levels of ACh was 42–57% smaller in HS mice than in NS mice. Inhibition of nitric oxide synthase (NOS) with NG monomethyl l-arginine (l-NMMA) significantly reduced resting diameters and reduced responses to ACh (by 45–63%) in NS mice but not in HS mice. Arteriolar wall oxidant activity, as assessed by tetranitroblue tetrazolium reduction or hydroethidine oxidation, was greater in HS mice than in NS mice. Exposure to the superoxide scavenger 2,2,6,6-tetramethylpiperidine- N-oxyl (TEMPO) + catalase reduced this oxidant activity to normal and restored normal arteriolar responsiveness to ACh in HS mice but had no effect in NS mice. l-NMMA also restored arteriolar oxidant activity to normal in HS mice. ACh further increased arteriolar oxidant activity in HS mice but not in NS mice, and this effect was prevented with l-NMMA. These data suggest that a high salt diet promotes increased generation of superoxide anion from NOS in the murine skeletal muscle microcirculation, thus impairing endothelium-dependent dilation through reduced NO bioavailability.

Reduced nitric oxide concentration in the renal cortex of streptozotocin-induced diabetic rats: effects on renal oxygenation and microcirculation

Nitric oxide (NO) regulates vascular tone and mitochondrial respiration. We investigated the hypothesis that there is reduced NO concentration in the renal cortex of diabetic rats that mediates reduced renal cortical blood perfusion and oxygen tension (P O2). Streptozotocin-induced diabetic and control rats were injected with l-arginine followed by Nomega-nitro-L-arginine-metyl-ester (L-NAME). NO and P O2 were measured using microsensors, and local blood flow was recorded by laser-Doppler flowmetry. Plasma arginine and asymmetric dimethylarginine (ADMA) were analyzed by high-performance liquid chromatography. L-Arginine increased cortical NO concentrations more in diabetic animals, whereas changes in blood flow were similar. Cortical P O2 was unaffected by L-arginine in both groups. L-NAME decreased NO in control animals by 87 +/- 15 nmol/l compared with 45 +/- 7 nmol/l in diabetic animals. L-NAME decreased blood perfusion more in diabetic animals, but it only affected P O2 in control animals. Plasma arginine was significantly lower in diabetic animals (79.7 +/- 6.7 vs. 127.9 +/- 3.9 mmol/l), whereas ADMA was unchanged. A larger increase in renal cortical NO concentration after l-arginine injection, a smaller decrease in NO after L-NAME, and reduced plasma arginine suggest substrate limitation for NO formation in the renal cortex of diabetic animals. This demonstrates a new mechanism for diabetes-induced alteration in renal oxygen metabolism and local blood flow regulation.

L-arginine reverses p47phox and gp91phox expression induced by high salt in Dahl rats

Derangements in the production and degradation of reactive oxygen species (ROS) as well as nitric oxide (NO) have been implicated in cardiovascular diseases. We explored how supplementation with l-arginine, an NO synthase substrate, restores such derangements of ROS/NO systems in Dahl salt-sensitive, hypertensive (DS) rats. We detected an increase of NADPH oxidase activity, a key enzyme that produces superoxide, in the membrane fraction of the renal cortex derived from DS rats loaded with high salt for 4 weeks; high salt loading also remarkably increased urinary H2O2, 8-isoprostane, and thromboxane B2 excretion and decreased plasma NO end products. These changes from high salt loading were counteracted by oral l-arginine supplementation. We further examined expression patterns of NADPH oxidase subunits in renal cortex derived from these animals. High salt loading increased gp91phox and p47phox but not p22phox or Rac1 or mRNA abundance, which were counteracted with L-arginine supplementation. Western blot analyses after subcellular fractionation revealed that l-arginine supplementation distinctly decreases membrane localization of p47phox protein, as it decreases total expression of Rac1 protein in DS rats with high salt loading. These results disclose that high salt loading causes a deficiency in available L-arginine amounts for NO synthases and induces NADPH oxidase activation in the renal cortex of DS rats, which l-arginine supplementation markedly restores. Since superoxide rapidly eliminates NO, which inhibits sodium reabsorption in the cortical collecting duct, superoxide production caused by upregulated NADPH oxidase activity in the renal cortex of high salt-loaded DS rats may accelerate sodium reabsorption and hypertension.

Effects of L-arginine on spontaneous contraction of the rat portal vein

The effects of L-arginine on spontaneous contraction of endothelium-denuded longitudinal preparations of the rat portal vein were studied. L-arginine increased the frequency of spontaneous contraction concentration-dependently between 10 microM and 1 mM. Changes in contraction amplitude and duration were not remarkable. D-arginine had a negligible effect on spontaneous contraction. N(omega)-nitro-L-arginine (1 mM) did not affect spontaneous contraction or the response to L-arginine. Addition of N(G)-monomethyl-L-arginine (1 mM), l-lysine (1 mM) or N-ethymaleimide (0.1 mM) increased the frequency of spontaneous contractions and inhibited the effect of L-arginine. Glibenclamide (10 microM) did not affect spontaneous contraction or the response to L-arginine. Spontaneous increase in concentration of intracellular Ca2+, estimated as the ratio of Fura-PE3 fluorescence occurred synchronously with spontaneous contraction. Spontaneous increase in concentration of intracellular Ca2+ occurred more frequently in the presence of L-arginine (1 mM). L-arginine (1 mM) also increased the number of action potential bursts/min in the longitudinal smooth muscle layer. L-arginine (1 mM) also depolarized cell membranes. This study indicates that L-arginine increases the frequency of spontaneous contraction of longitudinal muscle in the rat portal vein by membrane depolarization through mechanisms that do not involve nitric oxide or the inhibition of ATP-sensitive K+ channels.

High-salt diet increases sensitivity to NO and eNOS expression but not NO production in THALs

L-Arginine inhibits thick ascending limb (THAL) NaCl absorption by activating endothelial NO synthase (eNOS) and increasing NO production. Inhibition of renal NO production combined with a high-salt diet produces hypertension, and the THAL has been implicated in salt-sensitive hypertension. We hypothesized that a high-salt diet enhances the inhibitory action of L-arginine on NaCl absorption by THALs because of increased eNOS expression and NO production. To test this, we used isolated THALs from rats on a normal-salt (NS) or high-salt diet (HS) for 7 to 10 days. L-Arginine (1 mmol/L) decreased chloride absorption by 56+/-10% in THALs from rats on a HS diet, but only 29+/-3% in THALs from rats on a NS diet. eNOS expression in isolated THALs from rats on a HS diet was increased by 3.9-fold compared with NS (P<0.03). However, L-arginine increased NO levels to the same extent in THALs from both groups, as measured with DAF-2 DA or a NO-sensitive electrode. To determine whether a HS diet increases the sensitivity of the THAL to NO, we tested the effects of the NO donor spermine NONOate on chloride absorption. In THALs from rats on a HS diet, 1 and 5 micromol/L spermine NONOate reduced chloride absorption by 35+/-5% and 58+/-6%, respectively. In contrast, these same concentrations of spermine NONOate reduced chloride absorption by 4+/-4% (P<0.03 versus HS diet) and 43+/-9% in THALs from rats on a NS diet. We conclude that a HS diet enhances the effect of NO in the THAL. L-Arginine-stimulated NO production was not enhanced by a HS diet, despite increased eNOS protein.

Oral arginine reduces systemic blood pressure in type 2 diabetes: its potential role in nitric oxide generation

OBJECTIVES

Arginine is converted in the endothelial cells to nitric oxide (NO) and citrulline. NO is a potent vasodilator in humans, but diabetics may have a reduced generation of NO which results in endothelial dysfunction. The aim of this study was to evaluate the effects of oral arginine on nitric oxide production, counter-regulatory hormones and blood pressure in mildly hypertensive type 2 diabetic patients.

METHODS

A prospective, crossover clinical trial was performed over a three-day stay in the General Clinical Research Center. Six patients with type 2 diabetes mellitus and mild hypertension consented and were given orally three grams of arginine per hour for 10 hours on either day 2 or day 3. On both days 2 and 3, blood pressure was monitored between 5 AM and 4 PM and mean pressure determined.

RESULTS

Oral arginine increased plasma citrulline from 31.3 +/- 6.0 to 41.5 +/- 6.0 micro mol/L (mean +/- SEM; p < 0.05) which may reflect an increased conversion of arginine into NO and citrulline. Arginine reduced systolic BP from 135 +/- 7 to 123 +/- 8 mmHg; p < 0.05. Diastolic BP fell from 86.9 +/- 1.7 to 80.7 +/- 2.4 mmHg; p < 0.05). The reduction in BP was noted to occur two hours after starting oral arginine, and BP returned to normal within one hour of stopping the arginine. The oral arginine had no effect on C-peptide, insulin or other hormone concentrations.

CONCLUSIONS

These data suggest that oral arginine may increase endothelial nitric oxide synthase (NOS) to increase vascular NO and temporally reduce blood pressure in mildly hypertensive type 2 diabetic patients.

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.

Expression and cellular localization of classic NADPH oxidase subunits in the spontaneously hypertensive rat kidney

Phagocytes generate superoxide anion (O(2)(-)) by a classic, 5-component NADPH oxidase. O(2)(-) contributes to hypertension in spontaneously hypertensive rats (SHR). Therefore, we tested the hypothesis that NADPH oxidase expression is enhanced in the SHR kidney. We also analyzed the localization of NADPH oxidase components in SHR kidney. Renal NADPH oxidase was quantified by reverse transcription-polymerase chain reaction and Western blotting and was localized in SHR and Wistar Kyoto rat (WKY) kidney by immunohistochemistry. The mRNA for 5 subunits of phagocyte NADPH oxidase, and also for MOX1 and RENOX (NOX4), was detected in adult rat kidney. Kidneys of adult (10 weeks old) SHR had a significantly (P<0.01) greater mRNA for p47phox (SHR 0.81 +/- 0.05 versus WKY 0.37 +/- 0.01, arbitrary unit), which was confirmed by Western blotting (SHR 0.58 +/- 0.04 versus WKY 0.42 +/- 0.04, arbitrary unit; P<0.05) and by immunohistochemistry. This higher p47phox protein expression was also detected in young prehypertensive SHR (SHR 0.61 +/- 0.05 versus WKY 0.39 +/- 0.04, arbitrary unit; P<0.01). The 10-week-old SHR contained more modest but significantly (P<0.05) greater protein for p67phox (SHR 0.54 +/- 0.02 versus WKY 0.46 +/- 0.02). Immunostaining localized p47phox, p67phox, and p22phox in vasculature, macula densa, distal convoluted tubule, cortical collecting duct, and outer and inner medullary collecting ducts. The kidney of SHR expresses genes for all the main components of phagocyte NADPH oxidase, RENOX, and MOX1. There is a prominent increase in the SHR kidney of the mRNA, and protein expression of p47phox in the vasculature, macula densa, and distal nephron, which precedes development of hypertension.

Expression, regulation and function of carrier proteins for cationic amino acids

Different carrier proteins exhibiting distinct transport properties participate in cationic amino acid transport. There are sodium-independent systems, such as b+, y+, y+L and b0,+, and a sodium-dependent system B0,+, most of which have now been identified at the molecular level. In most non-epithelial cells, members of the cationic amino acid transporter (CAT) family mediating system y+ activity seem to be the major entry pathway for cationic amino acids. CAT proteins underlie complex regulation at the transcriptional, post-transcriptional and activity levels. Recent evidence indicates that individual CAT isoforms are necessary for providing the substrate for nitric oxide synthesis, for example CAT-1 for Ca2+-independent nitric oxide production in endothelial cells and CAT-2B for sustained nitric oxide production in macrophages.