The protective role of hawthorn fruit extract against high salt-induced hypertension in Dahl salt-sensitive rats: impact on oxidative stress and metabolic patterns.

In the present study, the renal-protective effect of hawthorn fruit extract (HW) on high-salt hypertension and its effect on metabolic patterns are determined. High salt causes hypertension in Dahl salt sensitive (SS) rats, while HW can effectively attenuate high-salt induced hypertension, and, various antihypertensive ingredients of HW have also been successfully identified using GC/MS. Of note, the biochemical assay indicates that HW significantly increases the concentration of nitric oxide (NO) and decreases the concentration of H2O2 and malonaldehyde. Especially, HW increases the activities of NO synthase and catalase in the renal medulla. Simultaneously, the renal cortex and medulla, harvested from SS rats, are used to perform the metabolomics analysis, and then, 11 and 8 differential metabolites are identified in the renal medulla and cortex with the HW gavage, respectively. All differential metabolites are then used to perform the pathway enrichment analysis. The results show that many metabolic pathways are enriched in both the renal medulla and cortex, especially those in the medulla including 23 enriched pathways. Therefore, it provides evidence that HW confers an antioxidant effect on high-salt induced hypertension and dramatically alters the metabolic patterns of SS rats, and the antihypertensive ingredients of HW also further indicate that it may be used as a nutritional supplemental therapeutic drug to protect against high-salt induced hypertension in the renal medulla.

Reappraisal of Morphologic Differences Between Renal Medullary Carcinoma, Collecting Duct Carcinoma, and Fumarate Hydratase-deficient Renal Cell Carcinoma.

Renal medullary carcinomas (RMCs) and collecting duct carcinomas (CDCs) are rare subsets of lethal high-stage, high-grade distal nephron-related adenocarcinomas with a predilection for the renal medullary region. Recent findings have established an emerging group of fumarate hydratase (FH)-deficient tumors related to hereditary leiomyomatosis and renal cell carcinoma (HLRCC-RCCs) syndrome within this morphologic spectrum. Recently developed, reliable ancillary testing has enabled consistent separation between these tumor types. Here, we present the clinicopathologic features and differences in the morphologic patterns between RMC, CDC, and FH-deficient RCC in consequence of these recent developments. This study included a total of 100 cases classified using contemporary criteria and ancillary tests. Thirty-three RMCs (SMARCB1/INI1-deficient, hemoglobinopathy), 38 CDCs (SMARCB1/INI1-retained), and 29 RCCs defined by the FH-deficient phenotype (FH/2SC or FH/2SC with FH mutation, regardless of HLRCC syndromic stigmata/history) were selected. The spectrum of morphologic patterns was critically evaluated, and the differences between the morphologic patterns present in the 3 groups were analyzed statistically. Twenty-five percent of cases initially diagnosed as CDC were reclassified as FH-deficient RCC on the basis of our contemporary diagnostic approach. Among the different overlapping morphologic patterns, sieve-like/cribriform and reticular/yolk sac tumor-like patterns favored RMCs, whereas intracystic papillary and tubulocystic patterns favored FH-deficient RCC. The tubulopapillary pattern favored both CDCs and FH-deficient RCCs, and the multinodular infiltrating papillary pattern favored CDCs. Infiltrating glandular and solid sheets/cords/nested patterns were not statistically different among the 3 groups. Viral inclusion-like macronucleoli, considered as a hallmark of HLRCC-RCCs, were observed significantly more frequently in FH-deficient RCCs. Despite the overlapping morphology found among these clinically aggressive infiltrating high-grade adenocarcinomas of the kidney, reproducible differences in morphology emerged between these categories after rigorous characterization. Finally, we recommend that definitive diagnosis of CDC should only be made if RMC and FH-deficient RCC are excluded.

Body mass-specific Na+-K+-ATPase activity in the medullary thick ascending limb: implications for species-dependent urine concentrating mechanisms.

In general, the mammalian whole body mass-specific metabolic rate correlates positively with maximal urine concentration (Umax) irrespective of whether or not the species have adapted to arid or mesic habitat. Accordingly, we hypothesized that the thick ascending limb (TAL) of a rodent with markedly higher whole body mass-specific metabolism than rat exhibits a substantially higher TAL metabolic rate as estimated by Na+-K+-ATPase activity and Na+-K+-ATPase α1-gene and protein expression. The kangaroo rat inner stripe of the outer medulla exhibits significantly higher mean Na+-K+-ATPase activity (~70%) compared with two rat strains (Sprague-Dawley and Munich-Wistar), extending prior studies showing rat activity exceeds rabbit. Furthermore, higher expression of Na+-K+-ATPase α1-protein (~4- to 6-fold) and mRNA (~13-fold) and higher TAL mitochondrial volume density (~20%) occur in the kangaroo rat compared with both rat strains. Rat TAL Na+-K+-ATPase α1-protein expression is relatively unaffected by body hydration status or, shown previously, by dietary Na+, arguing against confounding effects from two unavoidably dissimilar diets: grain-based diet without water (kangaroo rat) or grain-based diet with water (rat). We conclude that higher TAL Na+-K+-ATPase activity contributes to relationships between whole body mass-specific metabolic rate and high Umax. More vigorous TAL Na+-K+-ATPase activity in kangaroo rat than rat may contribute to its steeper Na+ and urea axial concentration gradients, adding support to a revised model of the urine concentrating mechanism, which hypothesizes a leading role for vigorous active transport of NaCl, rather than countercurrent multiplication, in generating the outer medullary axial osmotic gradient.

[Increase in the concentration of sEH protein in renal medulla of ISIAH rats with inherited stress-induced arterial hypertension].

The concentration of soluble epoxide hydrolase (sEH) protein was studied in renal medulla of adult rats from hypertensive ISIAH strain and normotensive WAG strain. The sEH is a key enzyme in metabolism of epoxyeicosatrienoic acids capable of activating endothelial NO-synthase and nitrogen oxide formation, and therefore being vasodilators. An increase in the sEH protein concentration (that we found) allows one to assume that the oxidative stress is increased in the renal medulla of hypertensive rats, and the bloodflow is decreased.

Regulation and function of renal medullary cyclooxygenase-2 during high salt loading.

Prostaglandins (PGs) are important autocrine/paracrine regulators that contribute to sodium balance and blood pressure control. Along the nephron, the highest amount of PGE2 is found in the distal nephron, an important site for fine-tuning of urinary sodium and water excretion. Cylooxygenase-2 (COX-2) is abundantly expressed in the renal medulla and its expression along with urinary PGE2 excretion is highly induced by chronic salt loading. Factors involved in high salt-induced COX-2 expression in the renal medulla include the hypertonicity, fluid shear stress (FSS), and hypoxia-inducible factor-1 alpha (HIF-1 alpha). Site-specific inhibition of COX-2 in the renal medulla of Sprague-Dawley rats causes sodium retention and salt-sensitive hypertension. Together, these results support the concept that renal medullary COX-2 functions an important natriuretic mediator that is activated by salt loading and its products promote sodium excretion and contribute to maintenance of sodium balance and blood pressure.

Possible senescence associated change in the predominant a-Na+/K+ ATP-ase isoform in the renal cortex of the rat.

With aging the kidney exhibits progressive deterioration, with a decrease in renal function. Most of the filtered Na+ is actively reabsorbed in the proximal tubules through different transporters located in apical membrane. This process is possible because basolateral Na+/K+-ATP-ase generates electrochemical conditions necessary for energetically favorable Na+ transport. The a-subunit is the catalytic domain of Na+/K+-ATP-ase. There are three isoforms of the a/subunit present in rat kidney. The present study was undertaken to examine the expression pattern of rat a-Na+/K+-ATP-ase during senescence. We tested the impact of aging on mRNA expression of a-Na+/K+-ATP-ase in cortex and medulla of aged Wistar rats. We observed a significant expression decrease in mRNA levels and a possible change of isoform in the cortex of aged animals. These expression changes observed for a subunit could be contributing to affect the renal function in conditions of water and salt stress.

Possible senescence associated change in the predominant &alpha -Na+/K+ ATP-ase isoform in the renal cortex of the rat

With aging the kidney exhibits progressive deterioration, with a decrease in renal function. Most of the filtered Na+ is actively reabsorbed in the proximal tubules through different transporters located in apical membrane. This process is possible because basolateral Na+/K+-ATP-ase generates electrochemical conditions necessary for energetically favorable Na+ transport. The α-subunit is the catalytic domain of Na+/K+-ATP-ase. There are three isoforms of the α/subunit present in rat kidney. The present study was undertaken to examine the expression pattern of rat α-Na+/K+-ATP-ase during senescence. We tested the impact of aging on mRNA expression of α-Na+/K+-ATP-ase in cortex and medulla of aged Wistar rats. We observed a significant expression decrease in mRNA levels and a possible change of isoform in the cortex of aged animals. These expression changes observed for αsubunit could be contributing to affect the renal function in conditions of water and salt stress.

Con el avance de la edad los riñones exhiben un deterioro funcional progresivo con disminución de la función renal. La mayor parte del sodio (Na+) filtrado es reabsorbido activamente en los túbulos proximales a través de diferentes transportadores ubicados en la membrana apical. Este proceso es posible por la existencia de la Na+/K+-ATP-asa basolateral, que genera las condiciones electroquímicas necesarias para que el transporte de Na+ sea energéticamente favorable. La subunidad αde la Na+/K+-ATP-asa es el dominio catalítico de la enzima. Existen tres isoformas de subunidad α, que están presentes en el riñón de la rata. En este trabajo se examinan los patrones de expresión de la α-Na+/K+-ATP-asa durante la senescencia. Se estudió así si el aumento de la edad incidía en la expresión del ARNm de la α-Na+/K+-ATP-asa en corteza y médula renal de ratas Wistar senescentes. Se observó una disminución en la expresión del ARNm de la subunidad αy un posible cambio de isoforma predominante en la corteza de los animales senescentes. Los cambios observados para la expresión de la subunidad αpodrían contribuir a afectar la función renal en condiciones de estrés hídrico y salino.

Renal intramedullary infusion of tempol normalizes the blood pressure response to intrarenal blockade of heme oxygenase-1 in angiotensin II-dependent hypertension.

Previous studies have demonstrated that intramedullary inhibition of heme oxygenase-1 (HO-1) increases the blood pressure and superoxide production response to angiotensin II (Ang II) infusion. The present study was designed to test the hypothesis that increased renal medullary superoxide production contributes to the increase in blood pressure in response to blockade of renal medullary HO-1 in Ang II-induced hypertension. Male C57BL/6J mice (16-24 weeks of age) were implanted with chronic intrarenal medullary interstitial (IRMI) and infused with: saline, tempol (6 mM), the HO-1 inhibitor QC-13 (25 µM), or a combination of tempol + QC-13. Tempol treatment was started 2 days before infusion of QC-13. After 2 days, Ang II was infused subcutaneously at a rate of 1 µg/kg/min for 10 days. Blood pressures on days 7-10 of Ang II infusion alone averaged 150 ± 3 mm Hg in mice receiving IRMI infusion of saline. IRMI infusion of QC-13 increased blood pressure in Ang II-treated mice to 164 ± 2 (P < .05). Renal medullary superoxide production in Ang II-treated mice was significantly increased by infusion of QC-13 alone. Ang II-treated mice receiving IRMI infusion of tempol had a blood pressure of 136 ± 3 mm Hg. Ang II-treated mice receiving IRMI infusion of tempol and QC-13 had a significantly lower blood pressure (142 ± 2 mm Hg, P < .05) than mice receiving QC-13 alone. The increase in renal medullary superoxide production was normalized by infusion of tempol alone or in combination with QC-13. These results demonstrate that renal medullary interstitial blockade of HO-1 exacerbates Ang II-induced hypertension via a mechanism that is dependent on enhanced superoxide generation and highlight the important antioxidant function of HO-1 in the renal medulla.

Activation of protein kinase Cα increases phosphorylation of the UT-A1 urea transporter at serine 494 in the inner medullary collecting duct.

Hypertonicity increases urea transport, as well as the phosphorylation and membrane accumulation of UT-A1, the transporter responsible for urea permeability in the inner medullary collect duct (IMCD). Hypertonicity stimulates urea transport through PKC-mediated phosphorylation. To determine whether PKC phosphorylates UT-A1, eight potential PKC phosphorylation sites were individually replaced with alanine and subsequently transfected into LLC-PK1 cells. Of the single mutants, only ablation of the S494 site dampened induction of total UT-A1 phosphorylation by the PKC activator phorbol dibutyrate (PDBu). This result was confirmed using a newly generated antibody that specifically detected phosphorylation of UT-A1 at S494. Hypertonicity increased UT-A1 phosphorylation at S494. In contrast, activators of cAMP pathways (PKA and Epac) did not increase UT-A1 phosphorylation at S494. Activation of both PKC and PKA pathways increased plasma membrane accumulation of UT-A1, although activation of PKC alone did not do so. However, ablating the PKC site S494 decreased UT-A1 abundance in the plasma membrane. This suggests that the cAMP pathway promotes UT-A1 trafficking to the apical membrane where the PKC pathway can phosphorylate the transporter, resulting in increased UT-A1 retention at the apical membrane. In summary, activation of PKC increases the phosphorylation of UT-A1 at a specific residue, S494. Although there is no cross talk with the cAMP-signaling pathway, phosphorylation of S494 through PKC may enhance vasopressin-stimulated urea permeability by retaining UT-A1 in the plasma membrane.

[The influence of iron ions on ATP-hydrolases activity of cell membranes of rat colon smooth muscle and kidney].

To elucidate the specific features of the ATP-hydrolases structural resistance in the membrane under the action of the prooxidants: Fe2' and hydrogen peroxide, and N-ethylmaleimide (NEM) the colonic smooth muscle (CSM) Na+, K(+)-ATPase activity was compared with activities of the corresponding Mg(2+)-ATP-hydrolase and ATPases from kidney medullar layer of rats. The inhibition study of the CSM Na+, K(+)-ATPase by divalent iron shows the decrease of the activity by 30% at 0.1 µM FeSO4 and in the range of 0.1-10 µM--to 45% of residual activity. When comparing with kidney enzyme (rep- resents exclusively α1-isozyme) the CSM Na+, K(+)-ATPase sensitivity to Fe2+ is reliably higher at its submicromolar concentration. CSM Mg2+-ATPase is much more resistant to iron ions effect, than kidney one. However for two tissues Mg2(+)-ATPase activity is always more resistant as compared with corresponding Na+, K(+)-ATPase activity. Against 1 mM EGTA Na+,K(+)-ATPase and Mg2(+)-ATPase activities of GMOK and kidneys are equally insensitive to effect of hydrogen peroxide in concentration up to 1 mM. But in the presence of 20 µM FeSO4 in the concentration range of 1 nM-1 mM of H2O2 the Na+, K(+)-ATPase is inhibited to greater extent, than Mg2+-ATPase activity. NEM sensitivity of the two ATP-hydrolase systems corresponds to prooxidant sensitivity that indicates the distinct importance of SH-groups for their functioning. It is concluded that Na+, K+-ATPase can serve as a marker of membrane sensitivity to oxidation, Mg(2+)-ATPase is resistant to oxidation and can be considered as criterion of the oxidation resistance when comparing membrane enzyme complexes, es- pecially in GMOK.

Tissue distribution of CysAP activity and its relationship to blood pressure and water balance.

AIMS: To better understand the functional role of soluble (Sol) and membrane-bound (MB) cystinyl-aminopeptidase (CysAP) activities, we studied differentially their organ distribution in adult male Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR)with or without treatment with captopril.We searched for a possible tissue-specific association of CysAP with water balance and blood pressure. MAIN METHODS: We used twenty WKY rats distributed in ten controls and ten captopril-treated, and sixteen SHR divided in eight controls and eight captopril-treated. Captopril (100 mg/kg/day) was administered in drinking water for 4 weeks. Systolic blood pressure, water intake and diuresis were measured individually. CysAP was assayed fluorometrically using L-cystine-di-ß-naphthylamide as substrate. KEY FINDINGS: Sol or MB activities were generally higher in SHR compared to WKY notably in hypothalamus and kidney than in the other tissues. Captopril mainly decreased CysAP in SHR whereas it increased in WKY. The distribution of Sol CysAP was more homogeneous among tissues ofWKY than SHR. In contrast, the distribution of MB CysAP was more heterogeneous than Sol CysAP in both WKY and SHR. This suggests that MB CysAP activity acts in a more tissue-specific manner than Sol CysAP. The majority of the significant correlations between tissue activities and the measured physiological parameters were observed mostly in renal medulla and hypothalamus. SIGNIFICANCE: Sol and MB CysAP activities, acting separately or in concert and mainly in renal medulla, regulate the function of their susceptible endogenous substrates, and may participate meaningfully in the control of blood pressure and fluid balance.

Blood pressure, sex, and female sex hormones influence renal inner medullary nitric oxide synthase activity and expression in spontaneously hypertensive rats.

BACKGROUND: We previously reported that sexually mature female spontaneously hypertensive rats (SHRs) have greater nitric oxide (NO) synthase (NOS) enzymatic activity in the renal inner medulla (IM), compared to age-matched males. However, the mechanisms responsible for this sexual dimorphism are unknown. The current study tested the hypothesis that sex differences in renal IM NOS activity and NOS1 expression in adult SHRs develop with sexual maturation and increases in blood pressure (BP) in a female sex hormone-dependent manner. METHODS AND RESULTS: Renal IM were isolated from sexually immature 5-week-old and sexually mature 13-week-old male and female SHRs. Whereas NOS activity and NOS1 expression were comparable in 5- and 13-week-old male SHRs and 5-week-old female SHRs, 13-week-old females had greater NOS activity and NOS1 expression, compared to 5-week-old female SHRs and age-matched males. NOS3 expression was greater in 5-week-old than 13-week-old SHRs regardless of sex. Treatment with antihypertensive therapy (hydrochlorothiazide and reserpine) from 6 to 12 weeks of age to attenuate age-related increases in BP abolished the sex difference in NOS activity and NOS1 expression between sexually mature SHR males and females. To assess the role of female sex hormones in age-related increases in NOS, additional females were ovariectomized (OVX), and NOS activity was studied 8 weeks post-OVX. OVX decreased NOS activity and NOS1 expression. CONCLUSIONS: The sex difference in renal IM NOS in SHR is mediated by a sex hormone- and BP-dependent increase in NOS1 expression and NOS activity exclusively in females.

Short-term treatment with diminazene aceturate ameliorates the reduction in kidney ACE2 activity in rats with subtotal nephrectomy.

Angiotensin converting enzyme (ACE) 2 is an important modulator of the renin angiotensin system (RAS) through its role to degrade angiotensin (Ang) II. Depletion of kidney ACE2 occurs following kidney injury due to renal mass reduction and may contribute to progressive kidney disease. This study assessed the effect of diminazine aceturate (DIZE), which has been described as an ACE2 activator, on kidney ACE2 mRNA and activity in rats with kidney injury due to subtotal nephrectomy (STNx). Sprague Dawley rats were divided into Control groups or underwent STNx; rats then received vehicle or the DIZE (s.c. 15 mg/kg/day) for 2 weeks. STNx led to hypertension (P<0.01), kidney hypertrophy (P<0.001) and impaired kidney function (P<0.001) compared to Control rats. STNx was associated with increased kidney cortical ACE activity, and reduced ACE2 mRNA in the cortex (P<0.01), with reduced cortical and medullary ACE2 activity (P<0.05), and increased urinary ACE2 excretion (P<0.05) compared to Control rats. Urinary ACE2 activity correlated positively with urinary protein excretion (P<0.001), and negatively with creatinine clearance (P=0.04). In STNx rats, DIZE had no effect on blood pressure or kidney function, but was associated with reduced cortical ACE activity (P<0.01), increased cortical ACE2 mRNA (P<0.05) and increased cortical and medullary ACE2 activity (P<0.05). The precise in vivo mechanism of action of DIZE is not clear, and its effects to increase ACE2 activity may be secondary to an increase in ACE2 mRNA abundance. In ex vivo studies, DIZE did not increase ACE2 activity in either Control or STNx kidney cortical membranes. It is not yet known if chronic administration of DIZE has long-term benefits to slow the progression of kidney disease.

The vertebrate homologue of sulfide-quinone reductase in mammalian mitochondria.

Hydrogen sulfide (H2S) is the first inorganic compound identified as both a substrate for mitochondrial oxidative phosphorylation and a transmitter in mammalian cells. H2S seems to mediate effects that are correlated with those of nitric oxide (NO) by a reciprocal regulation. Moreover, H2S is consumed by mitochondrial oxidation mediated by sulfide-quinone reductase-like protein (SQRDL)-the vertebrate homolog of sulfide-quinone oxidoreductase (SQR). There is evidence that SQR plays an essential role in regulating H2S levels in fission yeast. To start understanding the role of SQRDL in the mammalian metabolism of H2S, we examine rat tissues. Our results show that SQRDL protein is present in all tissues tested, albeit restricted to specific mitochondrial populations at the cellular level. We demonstrate a developmental regulation of Sqrdl transcription in the kidney, where SQRDL protein is detectable in glomerular podocytes and in tubular cells of the renal medulla. We also show that Sqrdl transcription in T cells is responsive to external H2S. Taken together, our results suggest that Sqrdl transcription is adaptively regulated, probably to meet the need of H2S oxidation. Thus far, SQRDL has only been studied in a limited set of tissues. The present report demonstrates the presence and specific localization of SQRDL in various mammalian tissues.

[Activity of antioxidant enzymes of the rat kidneys under mercury dichloride effect].

Salts of heavy metals are excreted by the kidneys and, as pro-oxidants, stimulate the processes of free radical oxidation. Mercury ions are accumulated in the kidneys. So the study of the features of antioxidant enzymes adaptive response of different kidney layers in response to mercury dichloride is important. Catalase and glytathionperoxidase activity within rat kidneys 72 hours after mercury dichloride intoxication in the ratio of 5 ml per 1 kg of the animal weight was studied. It was important to reveal the influence of the mercury salts on rat kidney antioxidative system. Decreasing glytathionperoxidase activity in cortical and cerebral substances and renal papillae were accompanied by increased contents of oxidative modified proteins and lipids and morphological changes in renal tissue under salt and water loading after mercury dichloride poisoning. The results obtained evidence for the inhibition of antioxidative protection of enzymes in rat kidneys under the mercury dichloride effect.

Brain death increases COX-1 and COX-2 expression in the renal medulla in a pig model.

BACKGROUND: Brain death is linked to a systemic inflammatory response that includes prostaglandins and cytokines among its mediators. The levels of cyclooxygenase-1 and cyclooxygenase-2 (COX-1 and COX-2) affect graft survival, but it remains unknown whether these enzymes are modified during brain death. The aims of this study were to investigate the organ expression of COX and to analyse the cytokine response in the plasma, cerebrospinal fluid (CSF), and organs in a porcine model of intracerebral haemorrhage and brain death. METHODS: Twenty pigs were randomly assigned to either a brain death group or a control group. Brain death was induced by an intracerebral injection of blood, and the animals were observed over the next 8 h. Tissue samples were tested for COX-1, COX-2 messenger RNA (mRNA) expression (heart, lung, and kidney), haeme oxygenase-1 (HO-1) (kidney), interleukin-1ß (IL-1ß), IL-6, IL-8, IL-10, and tumour necrosis factor-α. These cytokines were also measured at eight time points in the plasma and CSF. RESULTS: At the organ level, the levels of COX-1 and COX-2 mRNA expression were increased only in the renal medulla (P = 0.03 and P = 0.02, respectively). The cytokine levels in the tissue, plasma, and CSF revealed no differences between the groups. HO-1 expression decreased (P = 0.0088). CONCLUSION: Brain death increases the expression of COX-1 and COX-2 mRNA in the renal medulla. The release of cytokines into the plasma and CSF did not vary between the groups.

Silencing of HIF prolyl-hydroxylase 2 gene in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats.

BACKGROUND: In response to high salt intake, transcription factor hypoxia-inducible factor (HIF) 1α activates many antihypertensive genes, such as heme oxygenase 1 (HO-1) 1 and cyclooxygenase 2 (COX-2) in the renal medulla, which is an important molecular adaptation to promote extra sodium excretion. We recently showed that high salt inhibited the expression of HIF prolyl-hydroxylase 2 (PHD2), an enzyme that promotes the degradation of HIF-1α, thereby upregulating HIF-1α, and that high salt-induced inhibition in PHD2 and subsequent activation of HIF-1α in the renal medulla was blunted in Dahl salt-sensitive hypertensive rats. This study tested the hypothesis that silencing the PHD2 gene to increase HIF-1α levels in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats. METHODS: PHD2 short hairpin RNA (shRNA) plasmids were transfected into the renal medulla in uninephrectomized Dahl S rats. Renal function and blood pressure were then measured. RESULTS: PHD2 shRNA reduced PHD2 levels by >60% and significantly increased HIF-1α protein levels and the expression of HIF-1α target genes HO-1 and COX-2 by >3-fold in the renal medulla. Functionally, pressure natriuresis was remarkably enhanced, urinary sodium excretion was doubled after acute intravenous sodium loading, and chronic high salt-induced sodium retention was remarkably decreased, and as a result, salt-sensitive hypertension was significantly attenuated in PHD2 shRNA rats compared with control rats. CONCLUSIONS: Impaired PHD2 response to high salt intake in the renal medulla may represent a novel mechanism for hypertension in Dahl S rats, and inhibition of PHD2 in the renal medulla could be a therapeutic approach for salt-sensitive hypertension.

Cyclooxygenase-2 mediates induction of the renal stanniocalcin-1 gene by arginine vasopressin.

In rats and mice, the renal stanniocalcin-1 (STC-1) gene is expressed in most nephron segments, but is differentially induced in response to dehydration. In cortical segments STC-1 mRNA levels are upregulated by the hypertonicity of dehydration, while hypovolemia causes gene induction in the inner medulla (papilla). In both cases induction is mediated by arginine vasopressin (AVP) acting via the V2 receptor (V2R). The intent of STC-1 gene upregulation during dehydration has yet to be established. Therefore, to narrow down the range of possible actions, we mapped out the pathway by which V2R occupancy upregulates the gene. V2R occupancy activates two different renal pathways in response to dehydration. The first is antidiuretic in nature and is mediated by direct V2R occupancy. The second pathway is indirect and counter-regulates AVP-mediated antidiuresis. It involves COX-2 (cyclooxygenase-2) and the prostanoids, and is activated by the V2R-mediated rise in medullary interstitial osmolality. The resulting prostanoids counter-regulate AVP-mediated antidiuresis. They also upregulate renal cytoprotective mechanisms. The present studies employed models of COX inhibition and COX gene deletion to address the possible involvement of the COX pathway. The results showed that both general and specific inhibitors of COX-2 blocked STC-1 gene induction in response to dehydration. Gene induction in response to dehydration was also abolished in COX-2 null mice (cortex and papilla), but not in COX-1 null mice. STC-1 gene induction in response to V2R occupancy was also uniquely abolished in COX-2 nulls (both regions). These findings therefore collectively suggest that AVP-mediated elevations in STC-1 gene expression are wholly dependent on functional COX-2 activity. As such, a permissive role for STC-1 in AVP-mediated antidiuresis can be ruled out, and its range of possible actions has been narrowed down to AVP counter-regulation and renal cytoprotection.

Determining the enzymatic activities of iodothyronine 5'-deiodinases in renal medulla and cortex.

INTRODUCTION: Thyroid hormone disorders in patients with chronic kidney disease (CKD) are a result of impaired conversion of T4 to T3. The importance of kidneys in thyroid hormones conversion is not fully understood. The activities of different types of iodothyronine deiodinases in the kidney structures have not been determined yet. The aim of this study was to determine the activity of deiodinase type 1 (D1) and type 2 (D2) in renal cortex and medulla in renal cancer patients. MATERIAL AND METHODS: Samples of renal cortex and medulla (ten patients) or renal cortex alone (13 patients) were taken from kidneys resected because of malignant cancer, from a site opposite to the cancer. Resections were performed in the 23 patients (seven female and 16 male) who were 52-82 years old. The material was stored at -72 oC. RESULTS: Activity of D1 in renal cortex was 3.785 ± 2.041 fmol 125I/mg protein/minute and activity of D2 was 0.236 ± 0.125 fmol 125I/mg protein/minute. There was a strong positive correlation between D1 and D2 activities in renal cortex (r = 0.890, p 〈 0.001). Activity of D1 in renal medulla was 2.157 ± 2.176 fmol 125I/mg protein/minute, and activity of D2 was 0.168 ± 0.095 fmol 125I/mg protein/minute. A positive correlation between D1 and D2 in renal medulla (r = 0.661, p = 0.038) was observed as well. Activities of D1 in cortex and medulla were strongly and positively associated (r = 0.794, p = 0.006), whereas there was no correlation between the activities of D2 in cortex and medulla (r = 0.224, p = 0.553). CONCLUSIONS: Results presented in this study suggest that both cortical and medullary D1 and D2 may be involved in thyroid hormone metabolism. This finding could be of clinical relevance in patients with impaired renal function.

Distinct regulation of inner medullary collecting duct nitric oxide production from mice and rats.

Nitric oxide (NO) and NO synthase 1 (NOS1) maintain sodium and water homeostasis. The NOS1α and NOS1ß splice variants are expressed in the rat inner medulla, but only NOS1ß is expressed in the mouse. Collecting duct NOS1 is necessary for blood pressure control. We hypothesized that NOS1 splice variant expression and NO production in the inner medullary collecting duct (IMCD) are regulated differently in mice and rats by high dietary sodium. Male C57blk/J6 mice and Sprague-Dawley rats were fed a 0.4% (normal salt; NS), or 4% (high salt; HS) NaCl diet for 2 or 7 days. Mean arterial pressure was not altered by HS, whereas urinary sodium excretion in mice and rats was increased significantly. Urinary excretion of nitrate/nitrite (NO(x)) and IMCD nitrite production were significantly greater in mice compared with rats on the HS diet. Western blotting indicated that only NOS1ß and NOS3 were expressed in the mouse IMCD and that expression was unaffected by the HS diet at either time point. In contrast, NOS1α was detected in the IMCD of rats, in addition to NOS1ß and NOS3. Feeding of the HS diet for 2 days increased NOS1α and NOS1ß expression in the rat IMCD and 7 day feeding of the HS diet further increased NOS1ß expression. Expression of NOS3 was unchanged by the HS diet at either time point. In conclusion, IMCD NO production in mice and rats is distinctly regulated under both NS and HS conditions, including expression of NOS1 splice variants.