Para-aminohippurate Clearance Research Articles

Effect of dronedarone on renal function in healthy subjects

Background/Aims Creatinine clearance (CL) is used to assess glomerular filtration rate (GFR). During the clinical development of dronedarone, a new antiarrhythmic agent, a 10–15% increase in serum creatinine was noticed, as also shown recently for amiodarone. This study aimed to assess dronedarone effects on renal function and tubular cations handling. Methods 12 healthy males were enrolled in a randomised, cross-over, placebo-controlled, double-blind study. They received 400mg dronedarone or placebo bid for 7 days. Baseline and on-treatment renal function tests were performed under strict standardization of intakes, by assessing creatinine, sinistrin, para-amino-hippurate (PAH) and N-methylnicotinamide (NMN) CLs, and electrolyte excretions. Results Dronedarone did not alter sinistrin CL compared to placebo, but decreased creatinine CL significantly (mean 138 to 119mL/min under dronedarone vs 142 to 149 under placebo; p=0.04) and NMN CL marginally (448 to 368 vs 435 to 431; p=0.06), while PAH CL and other renal parameters remained unaffected. Conclusion Dronedarone compared to placebo reduces renal creatinine and NMN CLs by about 17%, without evidence of a true effect on GFR, renal plasma flow or electrolyte exchanges. This suggests a specific inhibition of tubular organic cation transporters (OCT). A limited increase in serum creatinine is therefore expected under dronedarone treatment, but does not mean a decline in renal function. Clinical Pharmacology & Therapeutics (2005) 77, P10–P10; doi: 10.1016/j.clpt.2004.11.041

Mild hyperhomocysteinemia promotes renal hemodynamic dysfunction without histopathologic changes in adult rats

Hyperhomocysteinemia is able to promote glomerular damage and generate tubulointerstitial lesions. These findings were reported in rats with unilateral nephrectomy or in weanling rats with normal function, two experimental models that are exposed to other concomitant vascular risk factors. The aim of this work is to study whether mild hyperhomocisteinemia per se can induce renal histopathologic changes in adults rats with normal renal function at either 10 or 44 weeks of hyperhomocysteinemia. Two months old male Wistar rats (N= 52) were randomly allocated to either a normal control (N= 26) or hyperhomocysteinemic (N= 26) group. Control and hyperhomocysteinemic groups had free access to either tap water or homocysteine thiolactone 50 mg/kg/day, during 10 or 44 weeks. Plasma homocysteine levels were determined by a high-performance liquid chromatography (HPLC) method. Glomerular filtration rate (GFR) and renal plasma flow (RPF) were calculated from inulin and sodium para-aminohippurate (PAH) clearance determinations. Structural renal changes were investigated in kidneys fixed by perfusion. Histopathologic and morphometric analysis were carried out by standard methods. Plasma total homocysteine levels were 53% (10 weeks) and 56% (44 weeks) higher in hyperhomocysteinemic group compared to the control group. GFR and RPF were significantly lower in hyperhomocysteinemic than in control group. The histopathologic and morphometric studies did not show any differences between the control and hyperhomocysteinemic rats at 10 or 44 weeks. The present results show that mild hyperhomocysteinemia is able to induce renal functional and biochemical alterations in male adult rats that are not associated with renal histopathologic changes.

Inappropriately low angiotensin II generation: a factor determining reduced kidney function and survival in patients with decompensated cirrhosis

Background/ Aims : Angiotensin II contributes to the post-glomerular arteriolar vasoconstriction which maintains the glomerular filtration rate (GFR) in renal hypoperfusion. To explore whether depressed angiotensin II generation, due to reduced angiotensinogen production or low angiotensin-converting enzyme (ACE) levels, could impair kidney function in advanced cirrhosis. Methods : We studied and prospectively followed up 21 diuretic-free ascitic cirrhotic patients, through these determinations: plasma levels of active renin (AR), renin activity (PRA), angiotensin II, ACE and aldosterone; renal clearances of sodium, inulin and para-aminohippurate; antipyrine clearance. Fifteen healthy subjects were also studied. Results : GFR distribution was bimodal, 10 patients had low GFR values (l-GFR group) and 11 had normal-GFR values (n-GFR group) (below and above 105 ml/min per 1.73 m 2 body surface area). Antipyrine clearance and Child-Pugh score did not differ in the two patient groups. l-GFR group had higher AR and PRA values, lower ACE levels and a significantly higher AR/Angiotensin II ratio than n-GFR group (all P<0.01). All 21 patients showed increased values of the AR/PRA ratio, i.e. subnormal angiotensinogen levels ( P<0.03). The 18-month survival rates of l-GFR and n-GFR groups were 20 and 81% ( P<0.02). Conclusions : Low-GFR cirrhotic patients had a worse survival rate associated with more severe contraction of the effective arterial blood volume, higher AR/Angiotensin II ratio and lower ACE levels.

Dietary L-Arginine Supplementation Improves the Glomerular Filtration Rate and Renal Blood Flow After 24 Hours of Unilateral Ureteral Obstruction in Rats

Unilateral ureteral obstruction (UUO) results in a significant change in renal blood flow (RBF) and glomerular filtration rate (GFR) by 24 hours. The intake of L-arginine, a substrate of nitric oxide (NO) synthase (NOS), can augment NO production. NO can maintain renal function through its vasodilatory action. Therefore, we examined the effect of dietary arginine supplementation on renal function in UUO. GFR and RBF were measured by inulin and para-aminohippurate clearance, respectively, in control rats and in rats 24 hours after UUO. Rats were given arginine with or without the concomitant administration of N-nitro-L-arginine methyl ester. Urinary nitrate/nitrite (NO2/NO3) was measured by the Griess reaction and urinary cyclic guanosine monophosphate was determined by enzyme-linked immunosorbent assay. The expression of renal inducible NOS was determined by immunohistochemistry. Urinary NO2/NO3 was significantly increased after 2 weeks of arginine, confirming increased NO production. In control rats GFR and RBF were not significantly different in untreated vs arginine treated groups. In contrast, arginine treatment significantly increased GFR in the obstructed kidney (0.06 +/- 0.01 to 0.14 +/- 0.02 ml per minute per 100 gm) and the contralateral kidney compared with control UUO. RBF was also significantly increased by arginine. The increases in renal function with arginine were blunted by a NOS inhibitor in obstructed and contralateral kidneys. Inducible NOS expression was increased in obstructed and contralateral kidneys. This study demonstrates that L-arginine supplementation can improve renal function in acute UUO. This finding suggests that NO system may be a future site of pharmacological intervention for UUO.

Icatibant has no impact on renal function in healthy subjects

The role of bradykinin (BK) in renal regulations is still controversial. To elucidate whether Icatibant, a potent BK antagonist on B2 receptors, can interfere with renal function under normal conditions, we performed sinistrin and para-aminohippurate (PAH) clearances, plasma levels and excretion rate of electrolytes, albumin, urate, endogenous lithium, as well as plasma renin, aldosterone and endothelin in 14 healthy males under Icatibant infusion. Part I (2 panels of 4 subjects) compared single 4h infusions (0.005 to 0.8 mg/kg) in ascending, double-blind, placebo-controlled design. Part II tested renal function on the 3rd day of a 72h Icatibant or placebo infusion, in a 2-way crossover, double blind design. No changes in glomerular filtration rate (sinistrin), renal blood flow (PAH), or in proximal renal tubular function (lithium and urate clearances) were detected. Sodium, potassium and chloride excretions, micro-albuminuria, urinary volume, and hematocrit remained unchanged. Vital signs (supine and orthostatic blood pressure, heart rate), body weight, and hormone concentrations were also unaltered. The safety and tolerability of Icatibant was excellent. This study had enough power to detect physiologically significant effects but not even trends for changes in renal function could be suspected. In conclusion, these results strongly advocate against a physiological role of BK in the regulation of renal function under normal conditions. Clinical Pharmacology & Therapeutics (2004) 75, P57–P57; doi: 10.1016/j.clpt.2003.11.215

Nondipping and its relation to glomerulopathy and hyperfiltration in adolescents with type 1 diabetes.

To determine whether there is a relation between dipping/nondipping status and end-organ damage (measured as renal glomerulopathy) and long-term renal function in order to predict the development of nephropathy in normoalbuminuric patients with type 1 diabetes. Analysis of renal biopsy and ambulatory blood pressure measurements was done in relation to renal function tests performed during a 10-year period. Forty unselected patients (16 girls), with a mean age of 17.7 years and a mean duration of 10.7 years, were studied. The renal biopsies were examined by electron microscopy. Ambulatory blood pressure was monitored (Space Labs 90 207). Systolic nondippers were defined as a <7%, diastolic nondippers as a <14%, and mean arterial blood pressure (MAP) nondippers as a <12% fall in blood pressure during the night. Renal function was evaluated every other year by clearances of inulin (glomerular filtration rate [GFR]) and para-amino hippurate (effective renal plasma flow [ERPF]), and filtration fraction (GFR/ERPF) was calculated. Overnight urinary albumin excretion rate and long-term mean HbA(1c) were measured. MAP (27% of the patients) and diastolic nondippers (12%) had a significantly thicker basement membrane; larger mesangial matrix volume fraction; and higher long-term GFR, nighttime heart rate, and mean HbA(1c) than dippers. Nondipping status was related to more renal morphological changes and long-term hyperfiltration in normoalbuminuric adolescents and young adults, despite a short duration of type 1 diabetes. Nondipping status may be an early predictor of later nephropathy.

Endothelial-derived vasoactive mediators in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by hypertension and renal vasoconstriction. Mediators of these hemodynamic changes are not well understood, but evidence suggests that endothelial-derived mediators may participate. Baseline measurements of blood pressure, proteinuria, and urinary nitrite/nitrate excretion were performed in control and cystic male Han:SPRD rats (6 weeks of age). They were then treated with the nitric oxide (NO), nitric oxide synthase (NOS) inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), or vehicle, for 6 weeks. After repeat systemic measurements, renal function was determined using inulin and para-aminohippurate (PAH) clearances. Levels of renal endothelin-1 (ET-1) and renal endothelial NOS (eNOS) proteins were determined, and immunohistochemistry localized renal eNOS and neuronal NOS (nNOS). Administration of L-NAME aggravated systemic hypertension and renal vasoconstriction in the cystic rats, but did not affect the progression of proteinuria or cystic expansion. Cystic rats demonstrated marked increases in renal ET-1 and eNOS levels. L-NAME reduced eNOS expression in the membrane compartment, but increased eNOS in the cytosol. Localization studies indicated that renal eNOS was abundant in nonvascular compartments, but not in renal vascular and glomerular structures, whereas renal nNOS was diffusely diminished. These alterations of endothelial-derived mediators (up-regulation of ET-1, and dysfunction of the NO system) contribute to vasoconstriction, and thereby are likely to contribute to the progressive loss of renal function in polycystic kidney disease (PKD).

Interactions between gender and the angiotensin type 1 receptor gene polymorphism

The cardiovascular effects of angiotensin II are mediated by the angiotensin II type 1 receptor (AGT1R); one polymorphism of the AGT1R gene, A1166-->C, has been associated with hypertension. The hemodynamic response to angiotensin II is blunted in women compared to men, but interactions between gender, blood pressure, and AGT1R gene polymorphisms are unclear. A total of 81 young healthy normotensive individuals maintained regulated sodium and protein intake prior to study. They were divided into four groups based on gender and A1166-->C genotype (AA versus AC/CC); serial supine blood pressures were obtained. A subset of 52 individuals received graded infusions of angiotensin II. Inulin and paraaminohippurate clearance techniques were used to measure renal hemodynamic function at baseline and in response to the infusions. Men with the AC/CC genotype exhibited higher blood pressures than men with the AA genotype; however, this relationship was not found among women. Analysis of covariance revealed a significant interaction between gender and AGT1R genotype in the determination of blood pressure. Glomerular filtration rate (GFR) declined variably in the study subjects following infusion of angiotensin II, and a statistical model incorporating gender and genotype best predicted the fall in GFR. There was a trend for females of the AA genotype to have a greater fall in GFR in response to angiotensin II infusion, than any of the other groups. In young healthy subjects, there is an important interaction between gender, the AGT1R A1166-->C gene polymorphism, and blood pressure. In addition, the renal hemodynamic response to angiotensin II infusion is a function of both gender and the AGT1R genotype.

Impaired tubular excretory function as a late renal side effect of chemotherapy in children.

Renal drug excretion is variously influenced by nephrotoxic drugs. This study was designed to evaluate renal function as a late renal side effects in children receiving combination chemotherapy for malignancy. Follow-up studies of 30 newly diagnosed patients were performed a median of 12 months after completion of chemotherapy. The glomerular filtration rate (GFR) was measured using sodium thiosulfate. The following were also assessed: urinary high-molecular-weight fraction (urinary albumin/urinary creatinine ratio); para-aminohippurate (PAH) clearance; urinary low-molecular-weight fraction (urinary beta2-microglobulin/urinary creatinine ratio); and routine serum and urinary parameters. Serum and urinary electrolytes were normal in most patients. GFR was low in four patients (13%). Urinary high-molecular-weight fraction was elevated in two patients. Urinary low-molecular-weight fraction was elevated in one patient. PAH clearance was below the referenced normal value in 73% of the patients. This report demonstrates decreased PAH clearance as a late renal side effect of chemotherapy and suggests disturbed function of the organic anion transport system. The unexpected high serum concentration of drugs excreted through the organic anion transport system may induce severe side effects. Elucidation of the mechanism and clinical relevance of decreased PAH clearance is warranted.

The reduced renal blood flow observed after exposure to shock wave lithotripsy involves intact renal nerves

Treating one kidney with high-energy acoustic shock waves reduces blood flow 65% in that kidney and 33% in the contralateral unshocked kidney. We tested the hypothesis that renal nerves were involved in this response. Six-week old pigs underwent unilateral renal denervation. Nerves along the renal artery of one kidney were cut and the artery was painted with 10% phenol. After 2 weeks, the pigs were anesthetized and bilateral renal function was determined using inulin and PAH (para-aminohippurate) clearance. Glomerular filtration rate (GFR, inulin clearance) and renal blood flow (PAH clearance) were measured both before and after lithotripsy to the lower pole of the innervated kidney (2000 shocks, 24 kV, unmodified Dornier HM-3) or sham lithotripsy. Both kidneys were then removed to measure norepinephrine content in the tissue. Norepinephrine levels were significantly reduced (more than 90%) in denervated kidneys indicating complete denervation. As expected, blood flow and GFR fell (approximately 50%) after lithotripsy in the innervated shocked kidneys, but did not fall significantly in denervated contralateral kidneys or in sham lithotripsy animals. Results suggest that renal nerves mediate the fall in contralateral renal function after lithotripsy. [Work supported by NIH &amp;lt;cn&amp;gt;P01 DK43881.&amp;lt;cnx&amp;gt;]

Increased renal expression of bilirubin glucuronide transporters in a rat model of obstructive jaundice.

Regulation of bilirubin glucuronide transporters during hyperbilirubinemia in hepatic and extrahepatic tissues is not completely clear. In the present study, we evaluated the regulation of the bilirubin glucuronide transporters, multidrug resistance-associated proteins (MRP)2 and 3, in rats with obstructive jaundice. Bile duct ligation (BDL) or sham operation was performed in Wistar rats. Liver and kidneys were removed 1, 3, and 5 days after BDL (n = 4, in each group). Serum and urine were collected to measure bilirubin levels just before animal killing. MRP2 And MRP3 mRNA expressions were determined by real-time RT-PCR. Protein expression of MRP2 and MRP3 was determined by Western blotting. Renal MRP2 function was evaluated by para-aminohippurate (PAH) clearance. The effect of conjugated bilirubin, unconjugated bilirubin, human bile, and sulfate-conjugated bile acid on MRP2 gene expression was also evaluated in renal and hepatocyte cell lines. Serum bilirubin and urinary bilirubin excretion increased significantly after BDL. In the liver, the mRNA expression of MRP2 decreased 59, 86, and 82%, and its protein expression decreased 25, 74, and 93% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. In contrast, the liver expression of MRP3 mRNA increased 138, 2,137, and 3,295%, and its protein expression increased 560, 634, and 612% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. On the other hand, in the kidneys, the mRNA expression of MRP2 increased 162, 73, and 21%, and its protein expression increased 387, 558, and 472% compared with sham-operated animals after 24, 72, and 120 h of BDL, respectively. PAH clearance was significantly increased after BDL. The mRNA expression of MRP2 increased in renal proximal tubular epithelial cells after treatment with conjugated bilirubin, sulfate-conjugated bile acid or human bile. Upregulation of MRP2 in the kidneys and MRP3 in the liver may be a compensatory mechanism to improve bilirubin clearance during obstructive jaundice.

Renal Functional Reserve is Well Maintained in Patients with Advanced Liver Cirrhosis and Ascites

Background: Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) in healthy humans can be induced by amino acid stimulation. The rise in GFR from baseline to maximum is referred to as the renal functional reserve (RFR). Recently, we showed that the RFR is preserved in patients with compensated cirrhosis despite impaired renal function. In the present study, we evaluated RFR in decompensated cirrhotics with ascites. Methods: Steady-state inulin- and para-aminohippurate (PAH) clearances were performed at rest and during amino acid infusion in 22 patients with decompensated liver cirrhosis and ascites. Results: Baseline GFR and ERPF (means +95% confidence intervals) were: GFR 25.2 (21.1-29.2) ml min -1, ERPF 266.6 (229.7-303.5). Amino acid infusion significantly increased GFR by 67% (38.3-95.8) to 34.6 (29.2-40.0) ml min -1 (means + (95% confidence intervals), P < 0.001) and ERPF by 29% (11.9-46.3) to 326.3 (274.1-378.5) ml min -1 ( P = 0.002). Renal vascular resistance dropped by 13.4% (3.3-23.5) from 29.4 (24.8-33.9) mmHg ml -1 min -1 to 26.4 (22.0-30.7) mmHg ml -1 min -1 ( P = 0.036). The improved kidney function was accompanied by a decrease in systemic aldosterone levels ( P < 0.05). Conclusion: In patients with liver cirrhosis and ascites, amino acid infusion improves kidney function. Trials are warranted to test the long-term effects of amino acid infusions in patients with hepatorenal syndrome.

Losartan may modulate erythropoietin production

Erythropoietin (Epo) is distinct amongst haematopoietic hormones, in that it is produced remote from the bone marrow. The tissue oxygen pressure required to trigger the Epo gene under physiological conditions is uniquely sited at a restricted area in the kidney termed the critmeter. Angiotensin II (Ang II) increases sodium reabsorption and hence oxygen consumption at any given bloodflow rate; therefore, it may affect the balance of renal oxygen supply vs. demand and hence Epo production. The purpose of this study was to determine whether Epo production is modulated by the renin-angiotensin system (RAS). Twenty normal subjects on a controlled sodium and protein diet had glomerular filtration rate (GFR) and renal plasma flow (RPF)assessed by standard methods of inulin and para-aminohippurate clearance, respectively, at baseline, hourly after the administration of losartan (25 mg) and after each 30 minute period of the infusion of Ang II at doses of 0.5, 1.5 and 2.5 ng/kg/minute. The baseline GFR was 115+/-4.0 ml/minute/1.73 m2, RPF 650+/-29 ml/minute/1.73 m2 and Epo 12.4+/-0.8 U/L. In spite of a marked increase in filtration fraction (FF) with Ang II, no changes in serum Epo levels were observed at two hours(11.7+/-1.3 U/L, p=n.s. compared with baseline). After the administration of losartan, there was a variable effect on FF, but a strong correlation of the change in serum Epo concentration and the change in FF(r=0.648, p=0.002), suggesting that the RAS may modulate Epo production.

G-protein beta(3) subunit gene (GNB3) 825T allele is associated with enhanced renal perfusion in early hypertension.

The C825T polymorphism of the gene encoding the G-protein beta(3) subunit (GNB3) is associated with increased intracellular signal transduction and arterial hypertension. The aim of the study was to investigate the impact of this polymorphism on early adaptive processes of the left ventricle and renal hemodynamic changes in young normotensive to mildly hypertensive subjects. Ninety-five white male students with normal or mildly elevated blood pressure were genotyped for the GNB3 C825T polymorphism. In each participant, 24-hour ambulatory blood pressure, left ventricular structure and function (2D-guided M-mode echocardiography), renal plasma flow (para-aminohippurate clearance), glomerular filtration rate (inulin clearance), and 24-hour urinary sodium excretion were determined. The GNB3 825T allele was not associated with casual or ambulatory blood pressure, parameters of left ventricular structure or function, glomerular filtration, or 24-hour urinary sodium excretion. However, in T:-allele carriers (CT+TT), renal plasma flow was higher than in CC subjects (CT/TT: 659+/-96 versus CC: 614+/-91 mL/min, P:=0.019). ANOVA disclosed that renal plasma flow was independently influenced by both genotype and blood pressure, with hypertensives having a higher renal plasma flow than normotensive subjects. This was the fact irrespective of the criteria used for the definition of hypertension (World Health Organization or 24-hour ambulatory blood pressure criteria). The GNB3 825T variant is associated with increased renal perfusion in this study. Because early renal hemodynamic changes play a pivotal role in the pathogenesis of essential hypertension, our data suggest a relevance of increased G-protein activation in the pathogenesis of hypertension.

Fading renal hyperfiltration in children following liver transplantation.

In a prospective longitudinal study, we investigated the renal function (RF) of 23 children before and after orthotopic liver transplantation (OLT). The aim was to assess both the outcome of pretransplant hyperfiltration and the clinical nephrotoxic effects of cyclosporin A (CsA); children with decreased RF prior to OLT were therefore excluded. The RF study of the 13 remaining patients included glomerular filtration rate (GFR) and effective renal plasma flow (RPF) measured by inulin (Cin: mL/min/1.73 m2) and para-amino hippurate (Cpah: mL/min/1.73 m2) clearances, respectively. Hyperfiltration prior to OLT was observed in six children, i.e. Cin>170 [range 172-230] and Cpah>800 [808-1,133]. A significant decrease in RF was noted as soon as 6 months after OLT: Cin (mean+/-SD)=107+/-23 vs. 158+/-46 (p<0.003); Cpah=583+/-119 vs. 791+/-243 (p<0.004). This was due to loss of hyperfiltration in the six children, as there was no significant difference in RF before and 6 months after OLT in the other seven children. With a 36-month follow-up, there was no correlation between CsA trough blood level and RF. In conclusion, following OLT, RF underwent early changes owing to loss of prior hyperfiltration in children without impaired RF before OLT. In addition, no evidence of CsA nephrotoxicity was found and RF remained stable during follow-up.

Characterization of tubular functional capacity in humans using para-aminohippurate and famotidine

Renal drug excretion by glomerular filtration and active tubular secretion may be altered by factors such as acute and chronic renal disease, nephrotoxins, and drug interactions. Thus, accurate and reproducible methods for quantitation of glomerular filtration rate (GFR) and tubular functional capacity are critical. We utilized a four-step sequential infusion method to characterize anionic [para-aminohippurate (PAH)] and cationic (famotidine) tubular functional capacity in healthy volunteers. Filtration and secretion rates were quantitated from renal clearance and iothalamate-derived GFR determinations. Concentration-dependent renal clearance of PAH was observed at plasma concentrations> 100 mg/L; renal clearances were 442 +/- 131 (mean +/- SD), 423 +/- 94, 233 +/- 45, and 152 +/- 18 mL/min/1.73 m2 at plasma concentrations of 18 +/- 2, 92 +/- 5, 291 +/- 47 and 789 +/- 28 mg/L, respectively. The apparent affinity (Km) and maximum secretory capacity (TmPAH) were 141 +/- 70 mg/L and 71 +/- 16 mg/min/1.73 m2, respectively. The unbound renal clearance and tubular secretory clearance of famotidine were 384 +/- 70 and 329 +/- 78 mL/min/1.73 m2, respectively, and were not significantly correlated with the unbound plasma concentrations, which ranged from 126 to 2659 ng/mL. The rate of tubular secretion was linear at unbound plasma concentrations up to 2659 ng/mL. These data indicate that a sequential infusion method using PAH may be used to characterize the anionic secretory component of proximal tubular function. The tubular clearance of famotidine may be a suitable index of the cationic secretory capacity of the proximal tubule in humans. Saturation of the cationic secretory pathway was not observed, and further investigation into parallel pathways of cationic secretion, such as p-glycoprotein, may be warranted.

Effect of Antioxidants on Salt-Induced Hypertension and Renal Dysfunction.

43 We have demonstrated that the development of salt-dependent hypertension and renal dysfunction in the Dahl salt-sensitive (DSS) rat is accompanied by the accumulation of reactive oxygen species (ROS). To determine whether oxidative stress contributes to the development of progressive renal dysfunction, we examined the effect of dietary vitamin E, a natural antioxidant, on a model of salt-dependent hypertension. Dahl salt-resistant (DSR) and DSS rats were kept on 8% NaCl (HS) or 8% NaCl + 1000 U./kg chow of vitamin E (HSE) for 2 weeks. During this time blood pressure was monitored using the tail plethismography method. After 14 days on the diets, DSS rats on HS diet were hypertensive, as compared to the DSR rats (171.3 ± 7.4 vs. 138.4 ± 2.4 mmHg; p&lt;0.0001), whereas the animals on the HSE diet remained normotensive (125.1 ± 3.7 vs. 114.0 ± 5.4 mmHg). The animals were then instrumented for the evaluation of renal function, measured as clearance of para-aminohippuric acid (Cl PAH ) and clearance of inulin (Cl In ). As a measure of oxidative stress, kidney and blood samples were harvested for the determination of superoxide production and plasma 8-isoprostanes (8-IP), respectively. Results show that hypertensive DSS rats appear to have lower Cl PAH and Cl In , greater renal superoxide production, and greater plasma 8-IP concentration than the normotensive DSR rats (Cl PAH : 1.93 ± 0.15 vs. 4.11 ± 0.5 ml/min, p&lt;0.005; Cl In : 1.21 ± 0.19 vs. 2.05 ± 0.60 ml/min., p&lt;0.01; O - 2 : 664 ± 33 vs. 374 ± 13 nmol/mg protein/min, p&lt;0.05; and 8-IP: 1494.3 ± 93.4 vs. 386.6 ± 30.0 pM, p&lt;0.001). However, when DSR and DSS rats were kept on the HSE diet, no differences were observed (Cl PAH : 3.31 ± 0.34 vs. 3.29 ± 0.45 ml/min; Cl In : 1.89 ± 0.16 vs. 2.03 ± 0.08 ml/min.; O - 2 : 372 ± 10 vs. 344 ± 23 nmol/mg protein/min; and 8-IP: 276.1 ± 33.2 vs. 278.5 ± 28.3 pM). These results suggest that the incremental production of ROS during salt feeding in DSS rats plays a role in the development of hypertension and renal dysfunction in this model, and that the lipid-soluble antioxidant vitamin E can attenuate the production of ROS and prevent salt-induced hypertension and renal dysfunction.

Angiotensin II type 1 receptor gene polymorphism and the response to hyperglycemia in early type 1 diabetes.

Recent studies suggest that there is an association between the A1166-->C polymorphism of the angiotensin II type 1 receptor (AGT1R), glycemic control, and the risk of diabetic nephropathy in subjects with type 1 diabetes. Because hypertension and renal hemodynamic function are also related to the risk of diabetic nephropathy and because hyperglycemia can activate the renin angiotensin system, we sought to determine if there is an association between the AGT1R polymorphism, baseline renal and peripheral hemodynamic function, and pressor response to high glucose in subjects with early uncomplicated type 1 diabetes. There were 39 diabetic subjects genotyped for the AGT1R polymorphism by polymerase chain reaction and segregated into 2 groups: those with and those without the C1166 allele (AA and AC/CC). The average age was 27 +/- 1 years, and the mean duration of diabetes was 3.5 +/- 0.6 years. HbA(1c) values were <10% in all subjects and were similar in the 2 groups (8.2 +/- 0.3 vs. 9.1 +/- 0.4%). After a 7-day controlled diet (150 mmol sodium, 1.5-2.0 g x kg(-1) x day(-1) protein), renal hemodynamic function was assessed by inulin and para-aminohippurate clearance during clamped euglycemic conditions (4-6 mmol/l). Mean values for glomerular filtration rates did not differ between groups during euglycemia. In contrast, mean values for renal plasma flow and renal blood flow were significantly greater in the AC/CC group compared with the AA group. Values for mean arterial pressure were similar in the 2 groups, whereas renal vascular resistance was significantly reduced in the AC/CC group. In 20 subjects (10 from each genotype subgroup), hemodynamic function was assessed on a second occasion during controlled clamped hyperglycemia (9-11 mmol/l) after a similar preparatory period. In response to high glucose, plasma renin activity increased in both genotype groups to the same extent, but a pressor response was noted only in subjects with the C1166 allele. Mean arterial pressure increased significantly in the AC/CC subgroup and remained unchanged in the AA subgroup. We conclude that there is an association between the AGT1R A1166-->C polymorphism and renal hemodynamic function in early type 1 diabetes. But more importantly, the pressor response to hyperglycemia is augmented in those diabetic patients with the C1166 allele and may represent a factor that predisposes them to renal injury during periods of inadequate glucose control.

Renal substrate metabolism and gluconeogenesis during hypoglycemia in humans.

To examine the potential contribution of precursor substrates to renal gluconeogenesis during hypoglycemia, 14 healthy subjects had arterialized hand vein and renal vein (under fluoroscopy) catheterized after an overnight fast. Net renal balance of lactate, glycerol, alanine, and glutamine was determined simultaneously with systemic and renal glucose kinetics using arteriovenous concentration differences and 6-[2H2]glucose tracer dilution. Renal plasma flow was measured by para-aminohippurate clearance and was converted to blood flow using the mathematical value (1-hematocrit). Arterial and renal vein samples were obtained in the postabsorptive state and during a 180-min hyperinsulinemic period during either euglycemia or hypoglycemia. Insulin increased from 49 +/- 14 to 130 +/- 25 pmol/l (hypoglycemia) and to 102 +/- 10 pmol/l (euglycemia). Arterial blood glucose decreased from 4.5 +/-0.2 to 3.0 +/- 0.1 mmol/l during hypoglycemia but did not change during euglycemia (4.3 +/- 0.2 mmol/l). After 150 min, endogenous glucose production reached a plateau value that was higher during hypoglycemia (10.3 +/0.6 micromol x kg(-1) x min(-1)) than during euglycemia (5.73 +/-0.6 micromol x kg(-1) x min(-1), P < 0.001). Hypoglycemia was associated with a rise in renal glucose production (RGP) from 3.0 +/- 0.7 to 5.4 +/- 0.6 micromol x kg(-1) x min(-1) (P < 0.05), although glucose utilization remained the same (2.0 +/- 0.8 vs. 2.1 +/-0.6 micromol x kg(-1) x min(-1)). As a result, net renal glucose output increased from 1.0 +/- 0.3 to 3.3 +/- 0.40 micromol x kg(-1) x min(-1). Elevations in net renal uptake of lactate (2.4 +/- 0.5 to 3.5 +/- 0.7 vs. 2.8 +/- 0.4 micromol x kg(-1) x min(-1)), glycerol (0.6 +/- 0.3 to 1.3 +/- 0.5 vs. 0.4 +/- 0.2 micromol x kg(-1) x min(-1)), and glutamine (0.7 +/- 0.2 to 1.1 +/- 0.3 vs. 0.1 +/- 0.3 micromol x kg(-1) x min(-1)) during hypoglycemia versus euglycemia (P < 0.05) could account for nearly 60% of all glucose carbons released in the renal vein during hypoglycemia. Our data indicate that extraction of circulating gluconeogenic precursors by the kidney is enhanced and responsible for a substantial fraction of the compensatory rise in RGP during sustained hypoglycemia. Increased renal gluconeogenesis from circulating substrates represents an additional physiological mechanism by which the decrease in blood glucose concentration is attenuated in humans.

Acute cyclosporine A-induced nephrotoxicity: a rabbit model.

Chronic cyclosporine A (CsA) nephrotoxicity has been widely assessed but only few studies have described acute nephrotoxicity. As CsA is now used for short periods, we developed an experimental model of acute CsA-induced nephrotoxicity. Renal clearances of inulin and para-aminohippurate were assessed in 35 New Zealand rabbits. Group 1: control, no treatment; group 2: CsA 25 mg/kg per day in 0.5 ml/kg per day for 5 days; group 3: vehicle Cremophor-EL, 0.5 ml/kg per day for 5 days; group 4: follow-up, the same as group 2, then CsA discontinuation for 31 days. Compared with group 1, CsA significantly decreased glomerular filtration rate (GFR), renal blood flow (RBF), and diuresis, with a significant increase in renal vascular resistance (RVR). The proportional fall in GFR (-32.3%) and RBF (-33.1%) suggests both pre- and postglomerular vasoconstriction. Discontinuation of CsA in group 4 led to normalization of RVR with improvement of other renal function parameters. Compared with group 1, Cremophor-EL induced no significant changes but an increased RBF. Microvacuolization of proximal tubule epithelial cells was the sole histological abnormality observed only in group 2. The overall results suggest that CsA induced a vasomotor acute renal failure which was not due to Cremophor-EL. This effect was partly reversible after discontinuation of treatment.