Renal Acid Research Articles

A sugar transporter regulates serum urate levels: Implications for prevention and management of hyperuricemia in gout

Introduction: Gout is increasing in prevalence in the United States. More patients with refractory tophaceous disease are being seen, including older patients and those with multiple comorbidities such as diabetes, hypertension, chronic kidney disease, and congestive heart failure. There is also growing but as yet unresolved evidence for the potential of hyperuricemia to directly impact on blood pressure and cardiovascular diseases. New treatments, such as febuxostat and pegloticase, are emerging for refractory hyperuricemia. However, in most gout patients hyperuricemia is caused by long-standing renal underexcretion of uric acid, an abnormality that is often precipitated or exacerbated by diuretic therapy, insulin resistance, hypertension, and development of even moderate degrees of renal insuffi ciency [1]. This scenario points to opportunities to intervene at the level of both prophylaxis and treatment of hyperuricemia by more advanced uricosuric therapies. This will be aided by recent clinical-translational advances in understanding renal uric acid disposition. The primary uricosuric drugs (probenecid, benzbromarone, sulfi npyrazone) and the weaker secondary uricosuric drug (losartan) work in large part by inhibiting the urate anion exchanger URAT1 (SLC22A12) at the apical (brush border) membrane of the renal proximal tubule epithelial cell [2]. Furthermore, several URAT1 single nucleotide polymorphisms (SNPs) were linked with prominent regulatory effects on serum urate and susceptibility to gout in Asian and European cohorts [2]. Although URAT1 appears to be the linchpin for urate reabsorption at the apical surface of the renal proximal tubule epithelial cell, URAT1 knockout mice showed an unexpectedly small loss in renal urate reabsorption [3]. Secondary changes in renal urate secretion were believed to be partly responsible. SLC2A9 (also known as GLUT9, URATv1) promotes transport of hexose sugars and is a potent electrogenic transporter of urate anion [4]. Recently, probenecid and benzbromarone (and also indomethacin) were discovered to inhibit the activity of SLC2A9 at the basolateral membrane of the proximal renal tubule epithelial cell [4], the interface where urate is reabsorbed into the peritubular interstitium and ultimately back into the venous circulation. Not only URAT1, but also SLC2A9 mutations, have now been implicated in the etiology of the uncommon disorder idiopathic renal hypouricemia. Furthermore, SLC2A9 mutations were linked to hyperuricemia and bladder uric acid calculi in dalmatian-breed dogs [5]. This was a stunning observation that indicates how robust the role for SLC2A9 can be in renal urate handling, as dogs, like other lower mammals, are generally protected from hyperuricemia via uricase expression. More recently, several SLC2A9 SNPs have been linked by genome-wide association (GWA) studies with hyperuricemia, altered renal uric handling, and susceptibility to gout [6–9].

腎臓の尿酸トランスポーターを介したアンジオテンシンII受容体拮抗薬による血清尿酸値変動

アンジオテンシンII受容体拮抗薬（ARBs）は血清尿酸値を変動させるが，その影響は誘導体間で異なっている．ARBsによる尿酸値変動機構を解明するため，尿酸排泄及び尿酸生合成に与えるARBsの影響を理解することは重要である． ARBsの中でもロサルタン，プラトサルタンは尿酸再吸収トランスポーターURAT1に対し，阻害及び促進作用を示し，他のARBs（オルメサルタン，カンデサルタン，テルミサルタン，バルサルタン）は阻害あるいは促進作用のいずれか一方を示す．また尿酸分泌トランスポーターOAT3を阻害する可能性も示唆されている．雄性 Sprague-Dawley（SD）ラットの腎皮質より調製した刷子縁膜小胞を用いた検討より，ARBsは近位尿細管細胞の管腔側からの尿酸輸送を変動させることが推察され，雄性SDラットを用いたin vivo試験より，ARBsは尿中尿酸排泄に影響を与え，血清尿酸値を変動させることが示唆されている．またin vitro試験において，キサンチンオキシダーゼによる尿酸生成にARBsは作用しないことより，ABRsは尿酸生合成に影響を与えないと考えられる．これらの結果により，ARBsは腎臓の尿酸排泄を変動させ，血清尿酸値に影響を及ぼすことが推察された．したがって，ARBsが引き起こす腎臓の尿酸トランスポーターの活性変動が，腎臓での尿酸排泄，さらに血清尿酸値に影響を与えていることが考えられ，ARBs誘導体間での尿酸値変動の違いは，腎臓のURAT1， OAT3を中心とした尿酸トランスポーターに対するARBsの作用の違いに起因することが示唆される．

Enhanced insulin sensitivity with loss of collectrin, an important mediator of renal amino acid recovery

The metabolic syndrome is a complex constellation of disorders which places patients at increased risk of diabetes, cardiovascular disease and all‐cause mortality. The objective of this study is to examine the metabolic effect of deletion of collectrin, a novel candidate mediator of the metabolic syndrome. We previously reported that targeted deletion of collectrin in the mouse results in failed recovery of filtered amino acids at the proximal tubule. We now report that collectrin‐deficient (Tmem27−/y) mice develop enhanced insulin sensitivity with age. We observe a statistically significant decrease in blood glucose levels and a delayed hypoglycemic response during insulin tolerance testing (p 0.05). This enhanced insulin sensitivity is associated with a 25% decrease in adiposity by DEXA scanning (p=0.009), despite a 30% increase in food consumption, and persists with high‐fat feeding. Examination of the pancreas reveals no difference in morphometric variables, ‐cell proliferation by in vivo BrdU staining or glucose‐stimulated insulin secretion in isolated islets in Tmem27−/y animals compared to wild‐type. This suggests that the enhanced insulin sensitivity does not arise from a difference in pancreatic physiology. We hypothesize that the increased insulin sensitivity associated with loss of collectrin results from altered amino acid flux in metabolic pathways important in energy homeostasis.

Idiopathic vulvar calcinosis: The counterpart of idiopathic scrotal calcinosis

Calcinosis cutis is characterized by the deposition of hydroxyapatite crystals of calcium phosphate in the skin. It is commonly encountered as a consequence of connective tissue disease or metabolic abnormalities but sometimes could be idiopathic. We report a case of idiopathic calcinosis cutis of the vulva in a healthy woman. A 35-year-old woman presented with multiple asymptomatic yellowish nodules on the external genitalia of one year duration. A few of the nodules broke down spontaneously discharging a chalky white material. She was otherwise healthy and had no systemic complaints. There was neither a history of trauma nor any inflammatory process in the vulvar skin prior to the development of lesions. The hematologic and biochemistry panel such as liver and renal function, serum calcium, phosphorous, electrolytes, uric acid and parathyroid hormone levels were normal. An excision biopsy of the nodule showed features suggestive of calcinosis cutis (Fig. 1). Fig. 1 10× photomicrograph showing the amorphous calcific deposits in the dermis Cutaneous calcification may be divided into four major categories: dystrophic, metastatic, iatrogenic and idiopathic.1 Though dystrophic calcinosis is fairly common, idiopathic calcification is rare, and usually no underlying cutaneous cause can be identified. It commonly presents as painless, firm papules and nodules that appear in childhood and adolescence and gradually increase in number and size. Lesions may be solitary or pedunculated and are initially skin-colored, but as they grow larger they become yellowish and lobulated breaking down spontaneously or when compressed to produce a chalky white material. Microscopic examination typically shows large granular deposits of deeply basophilic material which stains black with Von Kossa stain for calcium.2 The pathogenesis of idiopathic vulvar calcinosis is highly disputed. The principle debate concerning the cause is whether calcium is deposited at the site of inflamed epidermal cysts or whether the calcific nodules are truly idiopathic. Although several authors have suggested that vulvar calcinosis results from dystrophic calcification of the inflammed epidermal cysts, several others have refuted the above facts and found it to be truly idiopathic.3 Idiopathic calcinosis cutis of the vulva is rare with only seven cases reported worldwide. Besides, it has also been reported over the neck after rhytidectomy,4 the sctotal wall5, shaft of the penis6 and the areola of the breast.7 Cornelius et al, have postulated that tiny apatite crystals seen only on electron microscopy in cases of idiopathic calcinosis cutis might act as a source of injury leading to secondary deposition of acid mucopolysaccharides, which become a matrix for crystal formation and calcification. What initiates the deposition of these crystals is not yet known.8 In our case no predisposing cause for calcification could be identified and since the patient was asymptomatic and not keen on surgical removal the lesions were not excised.

Effects of Vanadium(V) and/or Chromium(III) on L-Ascorbic Acid and Glutathione as well as Iron, Zinc, and Copper Levels in Rat Liver and Kidney

This study investigated the selected parameters of the antioxidant system in liver and kidney after in vivo administration of vanadium and/or chromium in rats. Outbred 2-mo-old albino male Wistar rats received drinking water for 12 wk with either sodium metavanadate (SMV; group II); chromium chloride (Cr; group III); or sodium metavanadate and chromium chloride (SMV-Cr; group IV); and group I (control) received deionized water. Chronic treatment with V alone or in combination with Cr produced a significant increase in kidney relative weight. Further, giving rats V alone also led to a significant elevation in liver relative weight. An increase in hepatic Fe concentration and renal Zn content occurred after treatment with V or Cr, respectively. The rats coadministered V and Cr had significantly higher levels of Fe in liver and Zn in kidneys. Simultaneous administration of these two elements resulted in a significant decrease in renal L-ascorbic acid concentration. V given alone significantly decreased GSH content and GSH/GSSG ratio in liver and kidney as well as increased GSSG concentration in liver, whereas Cr alone produced a significant decrease in GSH content in kidney and GSH/GSSG ratio in both organs. In the SMV-Cr-treated group a significant decrease in renal GSH concentration and GSH/GSSG ratio in both organs occurred. A significant increase in liver GSSG content was also found. The observed significant changes in kidney GSH content and in GSH/GSSG ratio in both rat tissues after Cr might result from the pro-oxidant actions of this metal. Thus, oxidative stress, which is a major pathway for V-induced toxicity, might also be associated with Cr(III)-induced adverse effects in rats.

Adaptive response to increased bile acids: induction of MDR1 gene expression and P-glycoprotein activity in renal epithelial cells

Cholestatic liver disease and increased serum bile acid concentrations are known to trigger various adaptive responses including the induction of hepatic, intestinal and renal bile acid transport proteins, but renal P-glycoprotein (Pgp, multidrug resistance protein 1, MDR1) remained uninvestigated in this context. We show that treatment of Madin Darby canine kidney (MDCK) cells with pathophysiologically relevant concentrations of chenodeoxycholic acid (CDCA; 100 microM) for 12 h induces MDR1 transcript levels in vitro more than twofold. CDCA and deoxycholic acid pre-treatment for 24-96 h (100 microM) also increased Pgp activity measured as rhodamine efflux, while cholic acid and taurocholic acid were not effective in concentrations up to 600 microM. CDCA pre-treatment (100 microM, 72 h) also resulted in a doubling of rhodamine123 secretion across an epithelium-like monolayer grown on Transwell filters and decreased the sensitivity towards the kidney toxic drugs cyclosporine A and paclitaxel. These findings predict physiologically as well as pharmacologically relevant consequences of liver disease for Pgp substrate transport and toxicity in the kidneys.

Induction of Renal Cytochrome P450 Arachidonic Acid Epoxygenase Activity by Dietary γ-Linolenic Acid

Dietary gamma-linolenic acid (GLA), a omega-6 polyunsaturated fatty acid found in borage oil (BOR), lowers systolic blood pressure in spontaneously hypertensive rats (SHRs). GLA is converted into arachidonic acid (AA) by elongation and desaturation steps. Epoxyeicosatrienoic acids (EETs) and 20-hydroxyeicosatetraenoic acid (20-HETE) are cytochrome P450 (P450)-derived AA eicosanoids with important roles in regulating blood pressure. This study tested the hypothesis that the blood pressure-lowering effect of a GLA-enriched diet involves alteration of P450-catalyzed AA metabolism. Microsomes and RNA were isolated from the renal cortex of male SHRs fed a basal fat-free diet for 5 weeks to which 11% by weight of sesame oil (SES) or BOR was added. There was a 2.6- to 3.5-fold increase in P450 epoxygenase activity in renal microsomes isolated from the BOR-fed SHRs compared with the SES-fed rats. Epoxygenase activity accounted for 58% of the total AA metabolism in the BOR-treated kidney microsomes compared with 33% in the SES-treated rats. More importantly, renal 14,15- and 8,9-EET levels increased 1.6- to 2.5-fold after dietary BOR treatment. The increase in EET formation is consistent with increases in CYP2C23, CYP2C11, and CYP2J protein levels. There were no differences in the level of renal P450 epoxygenase mRNA between the SES- and BOR-treated rats. Enhanced synthesis of the vasodilatory EETs and decreased formation of the vasoconstrictive 20-HETE suggests that changes in P450-mediated AA metabolism may contribute, at least in part, to the blood pressure-lowering effect of a BOR-enriched diet.

148. The Transgene Cassette Is Not Fully Responsible for Alterations of Renal Cytochrome P450 Expression after Systemic Administration of Recombinant Adenovirus

Gene transfer to the kidney has shown promise in treating severe renal disease and prevention of acute renal graft rejection in several animal models. To date, recombinant adenovirus (Ad) is the most efficient vector for gene delivery to the kidney. Although Ad does not infect the kidney efficiently when administered systemically, transgene products secreted from the liver can reach the kidney at therapeutic levels. We have found that systemic administration of recombinant Ad significantly alters the expression of the cytochrome P450 (CYP) enzymes, largely responsible for the clearance of toxicants and the metabolism of xenobiotics and endogenous compounds, in the kidney. In order to determine if the transgene cassette could be partially responsible for this effect, Sprague-Dawley rats received one of four treatments via a surgically implanted catheter: 0.5 ml of phosphate-buffered saline (control) or 5.7|[times]|1012 viral particles/kg of a first generation Ad expressing either E.coli beta-galactosidase (AdlacZ), murine erythropoietin (Epo) or no transgene (Null). Animals were sacrificed 0.25, 1, 4 and 14 days after injection. Renal CYP protein expression and mRNA levels were analyzed by Western blot and RT-PCR. All treatments significantly induced protein levels of the CYP4A family. Following AdlacZ administration, CYP4A increased by 50%, 32% and 64% above control at 0.25, 1 and 4 days, respectively (p<0.01). The vector expressing Epo raised CYP4A protein levels by 42%, 24% and 64% and the Null vector produced elevations of 74%, 25% and 49% above the control at the same timepoints (p<0.01). CYP4A protein expression recovered by 14 days in each group. RT-PCR revealed that mRNA levels of CYP4A2, the primary CYP4A isoform responsible for renal fatty acid metabolism, increased by 16.8% and 19% above control 24 hours after administration of AdlacZ and Epo, respectively (p<0.01). CYP4F1, an isoform responsible for metabolism of fatty acids, prostaglandins and leukotrienes, was unaffected in all treatment groups. In contrast, renal CYP2E1, which metabolizes small lipophilic compounds and carcinogenic agents, was significantly reduced throughout the study. CYP2E1 mRNA levels in animals treated with AdlacZ were 74%, 78%, 69% and 66% of control at 0.25, 1, 4 and 14 days, respectively (p<0.01). Similar reductions were seen with Epo and Null vectors although levels form animals treated with Epo began to recover by 14 days. Real time quantitative PCR revealed that viral genomes (|[sim]|850/100 ng DNA) were initially present in the kidney and declined throughout the study for all treatments. These results suggest that systemic administration of Ad significantly altered the transcription and translation of several key CYP enzymes in the kidney regardless of the transgene expression cassette. This should be considered for accurate drug monitoring when employing recombinant Ad vectors in the clinic. Additional mechanistic studies assessing the effect of expression of Ad early genes and local and systemic eicosanoid biosynthesis on the expression of renal CYP will allow further explanation of these results.

T06-P-012 Does apolipoprotein E polymorphism affect renal function and serum uric acid levels in healthy subjects?

T06-P-012 Does apolipoprotein E polymorphism affect renal function and serum uric acid levels in healthy subjects?

Renal d-Amino Acid Oxidase Mediates Chiral Inversion ofNG-Nitro-d-arginine

N(G)-nitro-d-arginine (d-NNA), i.v. injected into rats, produced a pressor response, and was presumed to act via chiral inversion into N(G)-nitro-l-arginine (l-NNA), an inhibitor of nitric oxide synthase. We examined the possible role of renal d-amino acid oxidase (DAAO) in the chiral inversion of d-NNA to l-NNA. In pentobarbital-anesthetized rats, l-NNA was detected via capillary electrochromatography in the blood immediately after i.v. injection of d-NNA. The time course of appearance of l-NNA paralleled the increase in blood pressure elicited by d-NNA. Unilateral renal ligation partially, and bilateral ligation completely, blocked the pressor response as well as the conversion of d-NNA to l-NNA. Furthermore, injection into conscious rats of sodium benzoate, a selective DAAO inhibitor, completely blocked the pressor response to naive d-NNA, but not pressor response to d-NNA preincubated with homogenates of the kidney. Homogenates of the kidneys, liver (lesser degree), and brain (much lesser degree) converted d-NNA to l-NNA, and the chiral inversion was blocked by the addition of benzoate. Moreover, d-NNA chiral inversion correlates with the activity of DAAO. Our results reveal a novel pathway of chiral inversion of d-amino acids where the renal DAAO plays an essential role that accounts for the biological activity of d-NNA.

STEPWISE DETERMINATION OF ALUMINUM AND CHROMIUM IN WATER AND BIOMEDICAL SAMPLES BY HPLC-UV, BASED ON THEIR DIFFERENT KINETICS WITH 8-HYDROXYQUINOLINE

ABSTRACT A reversed-phase high performance liquid chromatographic (RP-HPLC) method, with spectrophotometric detection for determination of trace amounts of aluminum (Al) and chromium (Cr) in water and biomedical samples, has been developed using 8-hydroxylquinoline (8-HQ) as a precolumn reagent based on the differential chelation kinetics of these two ions. The analysis is achieved with a Spherisorb ODS 2 column, with an eluent consisting of 4.0 mmol L−1 acetate buffer (pH 6.0) and 3.2 mmol L−1 8-HQ in 57% (v/v) methanol–water, at a flow rate of 1.0 mL min−1. On the basis of the fact that the peaks of Al and Cr chelates appear at the same retention time, the procedure is divided into two stages: 1. (1) determining Al concentration by peak area after precolumn chelation at ambient temperature; 2. (2) measuring total peak area of Al and Cr after reaction at 90°C for 30 min, and the concentration of Cr being determined by the difference between Al peak area and the total area. The response of both Al and Cr is linear from 0.002 to 0.6 µg mL−1 with a detection limit of 0.001 µg mL−1. The analysis is free from interference from common ions except 10-fold excess of cobalt. The values obtained by this method are in good agreement with those of ICP-AES or GF-AAS. The proposed method has been successfully applied to the direct determination of Al and indirect determination of Cr in natural water, serum, synthetic renal dialysate, parenteral solution, and pharmaceutical-grade organic acid with the recoveries of over 90%.

Acute renal damage in infants after first urinary tract infection.

Urinary tract infection (UTI) is one of the most common causes of unexplained fever in neonates. The aim of this study was to determine the incidence of urinary tract anomalies and acute renal damage in neonates who presented with first urinary tract infection in the first 8 weeks of life. We reviewed the records of 95 infants, who were hospitalised with UTI during a 6-year period (1994-1999). Patients with antenatally diagnosed hydronephrosis and incomplete radiological investigations were excluded from the study. Of the remaining 57 patients, 42 were boys and 15 girls. The mean age at diagnosis was 32 days (range 5-60 days). All patients underwent renal ultrasonography (US), voiding cystourethrogram (VCUG) and (99m)Tc-dimercaptosuccinic acid (DMSA) scan. Urinary tract abnormalities were detected in 20 (35%) patients. Vesicoureteral reflux (VUR) was found in 19 (33%) neonates, 7 girls and 12 boys. Acute cortical defects on DMSA scan were present in 19 kidneys of patients with VUR and in 25 of those without reflux. Only one-third of neonates after first symptomatic UTI had VUR. We recommend that US, VCUG, and DMSA scan should be routinely performed after the first UTI in infants younger than 8 weeks.

CAMP-dependent protein kinase inhibits proline transport across the rat renal tubular brush border membrane.

Very little is known about the cellular mechanisms controlling renal tubular amino acid transport. cAMP-dependent protein kinase (cAK) modulates the activity of several ion channels and pumps in biological membranes. The direct influence of cAK on transmembrane amino acid transport has not been investigated. We studied the effect the cAKmediated phosphorylation on Na+ and Cl(-)-linked proline transport across the rat renal brush border membrane (BBM). cAK bioassay and Western hybridization analysis using cAK subunit-specific antibodies demonstrated the presence of the enzyme in the BBM. Brush border membrane vesicles (BBMV) were phosphorylated using the "hyposmotic shock" technique. cAMP, by activating endogenous cAK,and exogenous, highly purified catalytic subunit of cAK inhibited NaCl-dependent proline transport by phosphorylated, lysed/resealed BBMV compared with control vesicles. The cAK-mediated inhibition of proline uptake was completely abolished when phosphorylation at the cytoplasmic (inner side) of the membrane was prevented by isosmotic, rather than hyposmotic, phosphorylation. The cAK-induced inhibition of proline transport was reversed by the specific cAK inhibitor peptide, PK1. These data suggest that cAMP-dependent protein kinase-mediated phosphorylation modulates Na+(-) and Cl(-)-linked proline transport across the tubular luminal membrane.

Epidermal growth factor (EGF) increases the renal amino acid transport capacity in amino acid loaded rats.

In anaesthetized adult female rats, the influence of epidermal growth factor (EGF) on renal amino acid handling was investigated in glutamine, arginine (both 50 mg/100 g b.wt. per hour), or alanine (90 mg/100 g b.wt. per hour) loaded animals. Continuous infusions of the three amino acids were followed by an increase in the fractional excretion (FE) of the administered amino acids as well as of the other endogenous amino acids. Under load conditions (alanine, arginine or glutamine), EGF pretreatment (8 micrograms/100 g b.wt. subcutaneously for 8 days, twice daily 8 a.m. and 4 p.m.) was followed by a stimulation of renal amino acid reabsorption. The increase in the fractional excretion of the administered amino acids was significantly lower than in non-EGF-treated rats. These changes in amino acid transport were connected with a significant reduction of GFR after EGF pretreatment (0.96 +/- 0.10 vs. 0.62 +/- 0.07 ml/min x 100 g b.wt.) and a distinct increase in sodium excretion (2.98 +/- 0.55 vs. 4.97 +/- 0.71 muval/100 g b.wt. x 20 min). After loading with p-aminohippurate (PAH; 200 mg/100 g b.wt.), PAH excretion in EGF rats was increased by about 20%, whereas urinary protein excretion was lower in EGF pretreated rats (control: 0.45 +/- 0.04 vs. EGF: 0.18 +/- 0.03 mg/100 g b.wt. x 20 min). The PAH load reduced amino acid reabsorption as a sign of overloading of renal tubular transport capacity, but in EGF pretreated animals the amino acid excretion was only slightly increased under these conditions. Furthermore, EGF pretreatment depressed normal kidney weight gain significantly (874 +/- 18 vs. 775 +/- 32 mg/100 g b.wt.). EGF can improve the renal tubular transport capacity, but, compared to well-known stimulators of renal transport like dexamethasone or triiodothyronine, its effect is only of a moderate degree.

Influence of an extracellular volume expansion (ECVE) on renal amino acid- and sodium handling in patients with autosomal dominant polycystic kidney disease (ADPKD)

Although ADPKD is one of the first kidney diseases to be understood from the gene to the pathogenesis of clinical abnormalities, there were no data concerning the renal handling of amino acids and possible disorders of amino acid (AA) pattern in these patients. Therefore, in 9 patients suffering from ADPKD and in 8 healthy normal persons (NP) renal amino acid excretion was measured before and after extracellular volume expansion (ECVE) (21 of physiological electrolyte solution). Renal function was stable in both groups (serum creatinine: ADPKD: 85.1 ± 18.4 vs. NP 84.4 ± 13.5 μmol/l; GFR: 93.8 ± 16.4 vs. 104.4 ± 9.4 ml/min/1.73 m2). Mean blood pressure was higher in ADPKD patients than in NP (99.4 ± 2.6 vs. 85.5 ± 2.4 mmHg), but did not change after ECVE. After ECVE in both groups, urine volume increased distinctly, whereas GFR was only slightly enhanced. The plasma concentrations of leucine, glycine, valine, threonine, glutamine, and alanine were significantly higher in controls than in ADPKD patients. The amino acid reabsorption capacity was reduced in ADPKD patients in 12 of 21 amino acids before ECVE. After ECVE, the fractional excretion of amino acids (FEAA) increased only in NP. In parallel with changes in amino acid handling, the FENa (%) after ECVE increased both in ADPKD patients and in NP (before ECVE - ADPKD: 1.22 ± 0.23 vs. NP: 1.53 ± 0.23; after ECVE: 3.17 ± 0.25 (ADPKD) vs. 2.74 ± 0.22/NP; (ADPKD p ≤ 0.01, NP p ≤ 0.02) whereas FELi (%) increased significantly only in ADPKD (p ≤ 0.045) range (before ECVE - ADPKD: 25.8 ± 8.9 vs. NP: 20.5 ± 4.0; after ECVE: 41.4 ±15.4 vs. 25.2 ± 3.9). Furthermore, concentrations of cGMP (pmol/ml) in plasma increased after ECVE (before ECVE - ADPKD: 5.31 ± 0.56 vs. NP: 6.65 ±0.79; after ECVE: 11.31 ± 1.66 vs. 11.30 ± 1.91; p ≤ 0.05). Na+-dependent and, perhaps, NO-mediated processes in the reabsorption of AA in the proximal tubule seem to be different in ADPKD and may be related to different distributions of receptors and ATP-dependent transport systems with pathogenetic impact on abnormal transtubular fluid transport in ADPKD.

Stimulation of renal amino acid reabsorption after treatment with triiodothyronine or dexamethasone in amino acid loaded rats

In adult female anaestetized rats, the influence of triiodothyronine or dexamethasone on renal amino acid handling was investigated in leucine (20mg/100g b.wt.) or glutamine (45mg/100g b.wt.) loaded animals. Bolus injections of both amino acids were followed by temporary increase in fractional excretion of the administered amino acids as well of the endogenous amino acids which were not administered.

Renal oxytocin receptor messenger ribonucleic acid: characterization and regulation during pregnancy and in response to ovarian steroid treatment.

Although the neurohypophyseal hormone oxytocin (OT) is best know for its role in reproduction, OT also stimulates natriuresis at physiological plasma levels. This effect is mediated via specific renal OT receptors (OTRs). In the present study, we have characterized rat renal OTR gene transcripts and assessed their regulation during gestation and in response to gonadal steroid treatment. Using a specific rat OTR probe, two major OTR messenger RNA (mRNA) bands [6.7 and 4.8 kilobases (kb)] were detected in renal extracts, corresponding to two of the three bands present in rat uterus. In contrast to the dramatic rise of OTR mRNA levels at term in the uterus and pituitary, renal OTR mRNA levels underwent a strong more than 3-fold decrease at term. Binding studies using a iodinated specific OT antagonist revealed a concomitant decrease in renal OT-binding sites. On the other hand, estrogen (E2) treatment led to an increase in renal OTR mRNA levels, as is also the case in the uterus and pituitary. However, the predominant E2-induced mRNA species were shorter (3.6 and 3.2 kb) than those present in control rat kidneys (6.7 and 4.8 kb). Analysis by reverse transcriptase-PCR and 5'- and 3'-directed complementary DNA probes indicated that the E2-induced OTR mRNA transcripts possessed the same coding region, but contained a shortened 3'-untranslated region. Binding studies showed that E2 treatment also led to an increase in renal OT-binding sites, suggesting that the shortened OTR transcripts encoded a functional receptor. The present study indicates that the uterine-type OTR gene is expressed in rat kidneys, but that the mechanisms controlling the expression of this gene in the two tissues are markedly different. The differential tissue-specific regulation of OTR gene expression may represent a mechanism by which circulating OT can assume a multifunctional role in both reproduction and sodium homeostasis.

Renal responses to amino acids in the sheep fetus.

Adult animals and humans are known to increase renal blood flow and glomerular filtration rate (GFR) in response to an acute protein load or amino acid infusion; however, the ontogeny of this phenomenon is not known. This study was designed to test the hypothesis that, despite normally high baseline amino acid levels in the fetus, increases in plasma amino acids stimulate increases in GFR before birth. Eight chronically instrumented fetal sheep (126 +/- 1 days gestation) were infused with a mixture of amino acids (0.15 and 0.30 mmol . kg-1 . min-1 i.v.). Plasma alpha-amino nitrogen levels increased significantly from 7.1 +/- 0.3 to 13.0 +/- 0.9 and 25.5 +/- 2.1 mg/dl, respectively, in response to the two doses, and GFR increased significantly from 3.2 +/- 0.4 to 4.0 +/- 0.5 and 4.6 +/- 0.5 ml/min, respectively. Arterial pressure did not change. Renal amino acid reabsorption was significantly increased at all time points during the amino acid infusion, reaching a value nearly five times that of control by the last clearance period. Na+ reabsorption was also increased throughout the infusion. Na+, K+, and Cl- excretions increased significantly only at the very last time point. These data indicate that the mechanism or mechanisms responsible for amino acid-induced hyperfiltration are present and functional even before birth in the sheep. Because maternal eating patterns and protein intake are known to change maternal plasma amino acid levels and amino acids are actively transported across the placenta, our findings suggest that both acute and chronic changes in maternal protein intake may alter fetal renal function.

Influence of triiodothyronine and dexamethasone on renal amino acid handling in rats loaded with various amino acid mixtures

In adult female rats, the influence of dexamethasone or triiodothyronine on renal amino acid handling was investigated in amino acid loaded animals. Amino acids were administered intravenously as two mixtures, each containing four amino acids to overload amino acid reabsorption capacity. Bolus injections of both mixtures were followed by temporary increase in fractional excretion of the administered amino acids as well of the amino acids which were not covered in the mixtures. The administration of the two mixtures was followed by different interactions between various amino acid carriers.After dexamethasone pretreatment (60µg/100g b.wt. for 3 days, once daily) a stimulation of the renal amino acid handling could be shown. Triiodothyronine (20µg/100g b.wt. for 3 days, once daily) did not increase tubular reabsorption capacity for amino acids. It even increased fractional amino acid excretion in amino acid loaded rats as a sign of enhanced amino acid metabolism in the kidney and/or increased amino acid uptake into the tubular cells from the luminal site.

Renal amino acid transport in immature and adult rats during thallium-induced nephrotoxicity

The effect of Tl2SO4 (Tl, 2 mg/100 g b.wt.) on renal amino acid excretion and plasma amino acid composition was investigated in 10- and 55-day-old rats. Tl decreased glomerular filtration rate only in adult rats. On the other hand, the renal fractional excretion (FE) of amino acids was distinctly higher in adult rats as a sign of lower amino acid reabsorption capacity after Tl. In immature animals FE was increased only for a few amino acids. However, in both age groups Tl administration significantly decreased plasma amino acid concentrations, and was more pronounced in immature rats. The investigation of renal amino acid handling (1) confirms that Tl was more nephrotoxic in 55-day-old animals as demonstrated before using other parameters for nephrotoxicity testing and (2) showed that determination of renal amino acid handling is a suitable marker for nephrotoxicity in adult rats.