Sacubitril/valsartan ameliorates renal tubulointerstitial injury through increasing renal plasma flow in a mouse model of type 2 diabetes with aldosterone excess

BACKGROUND

Aldosterone has been assumed to be one of aggravating factors in diabetic kidney disease (DKD). Natriuretic peptides/guanylyl cyclase-A/cGMP signalling has been shown to ameliorate aldosterone-induced renal injury in mice. Sacubitril/valsartan (SAC/VAL) is used clinically for chronic heart failure and hypertension, in part by augmenting natriuretic peptide bioavailability. The effects of SAC/VAL on renal pathophysiology including in DKD, however, have remained unclarified.

METHODS

Eight-week-old male db/db mice fed on a high-salt diet (HSD) were treated with vehicle or aldosterone (0.2 μg/kg/min), and divided into four groups: HSD control, ALDO (aldosterone), ALDO + VAL (valsartan), and ALDO + SAC/VAL group. After 4 weeks, they were analysed for plasma atrial natriuretic peptide (ANP) levels, renal histology, and haemodynamic parameters including glomerular filtration rate (GFR) by FITC-inulin and renal plasma flow (RPF) by para-amino hippuric acid.

RESULTS

The ALDO + SAC/VAL group showed significantly increased plasma ANP concentration and creatinine clearance, and decreased tubulointerstitial fibrosis and neutrophil gelatinase-associated lipocalin expression compared to ALDO and ALDO + VAL groups. SAC/VAL treatment increased GFR and RPF, and suppressed expression of Tgfb1, Il1b, Ccl2, and Lcn2 genes compared to the ALDO group. The percentage of tubulointerstitial fibrotic areas negatively correlated with the RPF and GFR.

CONCLUSION

In a mouse model of type 2 diabetes with aldosterone excess, SAC/VAL increased RPF and GFR, and ameliorated tubulointerstitial fibrosis. Furthermore, RPF negatively correlated well with tubulointerstitial injury, suggesting that the beneficial effects of SAC/VAL could be through increased renal plasma flow with enhanced natriuretic peptide bioavailability.

Whole-body insulin clearance in people with type 2 diabetes and normal kidney function: Relationship with glomerular filtration rate, renal plasma flow, and insulin sensitivity

OBJECTIVE

Kidney insulin clearance, proposed to be the main route of extra-hepatic insulin clearance, occurs in tubular cells following glomerular filtration and peritubular uptake, a process that may be impaired in people with type 2 diabetes (T2D) and/or impaired kidney function. Human studies that investigated kidney insulin clearance are limited by the invasive nature of the measurement. Instead, we evaluated relationships between whole-body insulin clearance, and gold-standard measured kidney function and insulin sensitivity in adults with T2D and normal kidney function.

RESEARCH DESIGN AND METHODS

We determined insulin, inulin/iohexol and para-aminohippuric acid (PAH) clearances during a hyperinsulinemic-euglycemic clamp to measure whole-body insulin clearance and kidney function. Insulin sensitivity was expressed by glucose infusion rate (M value). Associations between whole-body insulin clearance, kidney function and insulin sensitivity were examined using univariable and multivariable linear regressions models.

RESULTS

We investigated 44 predominantly male (77%) T2D adults aged 63 ± 7, with fat mass 34.5 ± 9 kg, lean body mass 63.0 ± 11.8 kg, and HbA1c 7.4 ± 0.6%. Average whole-body insulin clearance was 1188 ± 358 mL/min. Mean GFR was 110 ± 22 mL/min, mean ERPF 565 ± 141 mL/min, and M value averaged 3.9 ± 2.3 mg/min. Whole-body insulin clearance was positively correlated with lean body mass, ERPF and insulin sensitivity, but not with GFR. ERPF explained 6% of the variance when entered in a nested multivariable linear regression model op top of lean body mass (25%) and insulin sensitivity (15%).

CONCLUSIONS

In adults with T2D and normal kidney function, whole-body insulin clearance was predicted best by lean body mass and insulin sensitivity, and to a lesser extent by ERPF. GFR was not associated with whole-body insulin clearance. In contrast to prior understanding, this suggests that in this population kidney insulin clearance may not play such a dominant role in whole-body insulin clearance.

The Role of Thyroid in Renovascular Function: Independent Association of Serum TSH With Renal Plasma Flow

CONTEXT

There are well-established interactions between the thyroid and the kidney. Thyroid hypofunction is associated with reduced renal plasma flow (RPF), and hypothyroidism is highly prevalent in chronic kidney disease; however, less is known about the thyroid-kidney axis in the euthyroid state.

OBJECTIVE

This work aimed to study the association of thyroid function with renovascular parameters in a well-phenotyped cohort of euthyroid normotensive and hypertensive individuals.

METHODS

This cross-sectional, multicenter study of the HyperPATH Consortium took place in 5 US and European academic institutions. A total of 789 individuals, aged 18 to 65 years, with serum thyrotropin (TSH) 0.4 to 5.5 mIU/L, participated; individuals with uncontrolled or secondary hypertension or on medication affecting the hypothalamus-pituitary-thyroid axis were excluded. Hemodynamic parameters including RPF, thyroid function testing, and the Thr92Ala deiodinase 2 (D2) polymorphism were assessed in the setting of a liberal and restricted salt diet. We searched for associations between thyroid function and renovascular parameters and accounted for confounding factors, such as older age, hypertension, and diabetes.

RESULTS

Serum TSH was inversely associated with RPF assessed in the setting both of liberal and restricted salt diets. This association remained significant and independent when accounting for confounding factors, whereas free thyroxine index (fTI) and the Thr92Ala polymorphism, associated with lower D2 catalytic activity and disrupted thyroid hormone tissue availability, were not independently associated with RPF. Serum TSH remained an independent predictor of RPF on a liberal salt diet when the analysis was restricted to healthy young individuals.

CONCLUSION

Serum TSH levels, but not fTI nor the Thr92Ala D2 polymorphism, were independently inversely associated with RPF in individuals of the HyperPATH Consortium. These findings suggest a direct interconnection between TSH and renovascular dynamics even with TSH within reference range, warranting further investigation.

Differential Effects of Levosimendan and Dobutamine on Glomerular Filtration Rate in Patients With Heart Failure and Renal Impairment:A Randomized Double-Blind Controlled Trial

Background The management of the cardiorenal syndrome in advanced heart failure is challenging, and the role of inotropic drugs has not been fully defined. Our aim was to compare the renal effects of levosimendan versus dobutamine in patients with heart failure and renal impairment. Methods and Results In a randomized double-blind study, we assigned patients with chronic heart failure (left ventricular ejection fraction <40%) and impaired renal function (glomerular filtration rate <80 mL/min per 1.73 m2) to receive either levosimendan (loading dose 12 μg/kg+0.1 μg/kg per minute) or dobutamine (7.5  μg/kg per minute) for 75 minutes. A pulmonary artery catheter was used for measurements of systemic hemodynamics, and a renal vein catheter was used to measure renal plasma flow by the infusion clearance technique for PAH (para-aminohippurate) corrected by renal extraction of PAH . Filtration fraction was measured by renal extraction of chromium ethylenediamine tetraacetic acid. A total of 32 patients completed the study. Following treatment, the levosimendan and dobutamine groups displayed similar increases in renal blood flow (22% and 26%, respectively) with no significant differences between groups. Glomerular filtration rate increased by 22% in the levosimendan group but remained unchanged in the dobutamine group ( P=0.012). Filtration fraction was not affected by levosimendan but decreased by 17% with dobutamine ( P=0.045). Conclusions In patients with chronic heart failure and renal impairment, levosimendan increases glomerular filtration rate to a greater extent than dobutamine and thus may be the preferred inotropic agent for treating patients with the cardiorenal syndrome. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT 02133105.

Renin Phenotypes Characterize Vascular Disease, Autonomous Aldosteronism, and Mineralocorticoid Receptor Activity

CONTEXT

Mild cases of autonomous aldosterone secretion may go unrecognized using current diagnostic criteria for primary aldosteronism (PA).

OBJECTIVE

To investigate whether the inability to stimulate renin serves as a biomarker for unrecognized autonomous aldosterone secretion and mineralocorticoid receptor (MR) activation.

PARTICIPANTS

Six hundred sixty-three normotensive and mildly hypertensive participants, who were confirmed to not have PA using current guideline criteria and were on no antihypertensive medications.

DESIGN

Participants had their maximally stimulated plasma renin activity (PRA) measured while standing upright after sodium restriction. Tertiles of maximally stimulated PRA were hypothesized to reflect the degree of MR activation: lowest PRA tertile = "Inappropriate/Excess MR Activity;" middle PRA tertile = "Intermediate MR Activity;"; and highest PRA tertile = "Physiologic MR Activity." All participants underwent detailed biochemical and vascular characterizations under conditions of liberalized sodium intake, and associations with stimulated PRA phenotypes were performed.

RESULTS

Participants with lower stimulated PRA had greater autonomous aldosterone secretion [higher aldosterone-to-renin ratio (P = 0.002), higher urine aldosterone excretion rate (P = 0.003), higher systolic blood pressure (P = 0.004), and lower renal plasma flow (P = 0.04)] and a nonsignificant trend toward lower serum potassium and higher urine potassium excretion, which became significant after stratification by hypertension status.

CONCLUSIONS

In participants without clinical PA, the inability to stimulate renin was associated with greater autonomous aldosterone secretion, impaired vascular function, and suggestive trends in potassium handling that indicate an extensive spectrum of unrecognized MR activation.

Renal plasma flow (RPF) measured with multiple-inversion-time arterial spin labeling (ASL) and tracer kinetic analysis: Validation against a dynamic contrast-enhancement method

PURPOSE

To propose and validate a method for accurately quantifying renal plasma flow (RPF) with arterial spin labeling (ASL).

MATERIALS AND METHODS

The proposed method employs a tracer-kinetic approach and derives perfusion from the slope of the ASL difference signal sampled at multiple inversion-times (TIs). To validate the method's accuracy, we performed a HIPAA-compliant and IRB-approved study with 15 subjects (9 male, 6 female; age range 24-73) to compare RPF estimates obtained from ASL to those from a more established dynamic contrast-enhanced (DCE) MRI method. We also investigated the impact of TI-sampling density on the accuracy of estimated RPF.

RESULTS

Good agreement was found between ASL- and DCE-measured RPF, with a mean difference of 9±30ml/min and a correlation coefficient R=0.92 when ASL signals were acquired at 16 TIs and a mean difference of 9±57ml/min and R=0.81 when ASL signals were acquired at 5 TIs. RPF estimated from ASL signals acquired at only 2 TIs (400 and 1200ms) showed a low correlation with DCE-measured values (R=0.30).

CONCLUSION

The proposed ASL method is capable of measuring RPF with an accuracy that is comparable to DCE MRI. At least 5 TIs are recommended for the ASL acquisition to ensure reliability of RPF measurements.

Relationship between serum TSH levels and intrarenal hemodynamic parameters in euthyroid subjects

OBJECTIVE

Low thyroid function may be associated with a reduced glomerular filtration rate (GFR) calculated on the basis of creatinine metabolism. Thyroid hormone directly affects serum creatinine in muscle and low thyroid function might exert a similar direct effect in the kidney. The goal of the study was to evaluate this possibility by assessment of the inulin-based GFR and to examine the mechanism underlying the reduction of GFR.

PATIENTS AND METHODS

Renal and glomerular hemodynamics were assessed by simultaneous measurements of plasma clearance of para-aminohippurate (CPAH) and inulin (Cin) in 26 patients with serum creatinine <1.00 mg/dl and without thyroid disease. All subjects were normotensive with or without antihypertensive treatment and were kept in a sodium-replete state. Renal and glomerular hemodynamics were calculated using Gomez's formulae.

RESULTS

Serum TSH, including within the normal range (0.69-4.30 μIU/ml), was positively correlated with vascular resistance at the afferent arteriole (Ra) (r=0.609, P=0.0010), but not at the efferent arteriole (Re). Serum TSH was significantly and negatively correlated with renal plasma flow (RPF), renal blood flow (RBF), and GFR (r=-0.456, P=0.0192; r=-0.438, P=0.0252; r=-0.505, P=0.0086 respectively). In multiple regression analysis, serum TSH was significantly positively associated with Ra after adjustment for age and mean blood pressure.

CONCLUSIONS

These findings suggest that low thyroid function, even within the normal range, is associated with reduced RPF, RBF, and GFR, which might be caused by a preferential increase in Ra.

[Methodology for assessment of renal function]

A variety of methods for evaluation of renal function have been discovered, among which glomerular filtration rate (GFR) attracts much attention because of the major determinant of renal function. Recently, novel technique to evaluate glomerular filtration has been developed, including cystatin C, which reflects the changes in GFR at the earlier stage than serum creatinine. Furthermore, a progress has been made in evaluating tubular damage, with the discovery of N-acetyl glucosaminidase and liver-type fatty acid binding protein. More convenient and sensitive methods will be required to assess the changes in renal function in a clinical setting.

Ischemic acute renal failure in the rat: effects of L-arginine and superoxide dismutase on renal function

BACKGROUND

Regulation of renal hemodynamics -- especially intraglomerular hemodynamics -- is closely related to the L-arginine (L-Arg)/nitric oxide (NO) pathway, both under basal conditions and in acute renal failure (ARF). Also, superoxide anions -- which may react with NO -- play a role in ischemic ARF. L-Arg not only has beneficial effects on glomerular filtration rate (GFR) but also reduces O2(-) production and prevents NO synthase isoform I up-regulation. Thus, it is of interest to elucidate whether the potential beneficial effects of L-Arg in reperfusion can be augmented by additional treatment with superoxide dismutase (SOD).

METHODS

ARF was induced by renal artery clamping for 40 minutes. Animals were treated with either L-Arg, SOD, a combination of both, or saline. GFR, renal plasma flow (RPF), filtration fraction (FF) and blood pressure were recorded at baseline, after induction of ARF, during drug infusion and thereafter.

RESULTS

Renal artery clamping induces a severe drop of GFR, RPF and FF, which all are improved by L-Arg and SOD. Increasing GFR is mainly due to better renal perfusion. FF fell after reperfusion and increased with L-Arg and SOD, indicating improvement of disturbed intrarenal hemodynamics. Combined administration of L-Arg and SOD showed similar effects in comparison with each substance alone, but did not induce additional effects on GFR and RPF.

CONCLUSIONS

L-Arg and SOD exert beneficial effects in ischemic ARF. Probably, improvements in reducing NO availability and in enhancing O2(-) formation are both playing a mediating role. The underlying mechanisms regulating the interplay between NO availability and O2(-) formation need to be elucidated in further studies using -- aside from other means -- selective NOS inhibitors, intervention in different experimental phases and treatment for a longer period.

[Preoperative prediction of remnant renal function in nephron-sparing surgery: the usefulness of 99mTc-mercapto-acetyl-triglycine scintigraphy]

A total of 10 patients with the diagnosis of renal cell carcinoma (RCC) underwent nephron-sparing surgery between January 1990 and December 2001. Serial pre- and postoperative 99mTc-mercapto-acetyl-triglycine (MAG3) scans were obtained. To examine preoperative predictability of remnant renal function, values of remnant renal plasma flow (ERPF) predicted prior to surgery were compared with values measured postoperatively. With preoperative MAG3 data, we designed the range of interest (ROI) except for the tumor area and recalculated remnant ERPF values. Remnant ERPF values predicted preoperatively correlated significantly with the postoperatively measured values 99mTc-(196.4 +/- 69.1 ml/min/1.73 vs 171.3 +/- 72.9 ml/min/1.73 [mean +/- SD], p > 0.05, r = 0.806). MAG3 dynamic renoscintigraphy appeared useful for preoperative prediction of remnant renal function after nephron sparing surgery.

Obesity and the kidney: why is the kidney at risk?

Two recent studies may help to account for the increase in risk of renal injury associated with obesity. One study pointed to a role for renin-system activation. In the other study, the pattern of renal hemodynamics was compatible with a renin mechanism.

Predicting blood pressure improvement in hypertensive patients after renal artery stent placement

BACKGROUND

Renal stent placement improves or cures hypertension in only 60-70% of patients with renal artery stenosis (RAS) and uncontrolled hypertension. There is a need to better identify patients who are likely to respond to percutaneous renal revascularization. We investigated whether an abnormal renal fractional flow reserve (FFR) would predict blood pressure improvement in patients undergoing renal artery stent placement.

METHODS

We prospectively enrolled 17 patients with unilateral RAS and medically refractory hypertension (BP > 140/90 mm Hg). Renal FFR was measured at maximal hyperemia induced by papaverine followed by renal stent placement. Blood pressure improvement was defined as a blood pressure of <or=140/90 mm Hg or an absolute decrease in diastolic blood pressure by 15 mm Hg on the same or less number of medications. Patients not meeting the above criteria were nonresponders.

RESULTS

Renal stent placement was successful in all patients. The average follow-up was 10 +/- 2 months. In patients with an abnormal renal FFR (< 0.80) blood pressure improved at 90 days in 86% compared with 30% in the normal renal FFR group (P = 0.04). Translesional pressure gradients (resting, peak, or hyperemic) alone failed to differentiate blood pressure responders from nonresponders.

CONCLUSIONS

Renal FFR is a promising tool to identify patients likely to benefit following renal stent placement. This finding was independent of translesional pressure gradients, which did not predict blood pressure improvement. The ability to segregate patients with RAS and coexisting hypertension from those with renovascular hypertension may help clinicians select patients most likely to benefit from revascularization.

Renal function during normal pregnancy and preeclampsia

Glomerular filtration rate and renal plasma flow increase by 40 to 65 and 50 to 85%, respectively, during normal pregnancy in women. Studies using the gravid rat as a model have greatly enhanced our understanding of mechanisms underlying these remarkable changes in the renal circulation during gestation. Hyperfiltration is largely due to increased renal plasma flow, the latter attributable to profound reductions in both the renal afferent and efferent arteriolar resistances. The ovarian hormone, relaxin, mediates renal vasodilation during pregnancy. Relaxin increases vascular gelatinase activity, thereby converting big ET to ET(1-32), which leads to renal vasodilation, hyperfiltration and reduced myogenic reactivity of small renal arteries via the endothelial ET(B) receptor and nitric oxide. Serum concentration of uric acid falls during normal pregnancy as a consequence of increased GFR and/or reduced proximal tubular reabsorption. The elevated urinary excretion of protein during pregnancy is secondary to increased GFR, reduced proximal tubular reabsorption, and perhaps alteration in the electrostatic charge of the glomerular filter. Whether the tubular secretion of Tamm-Horsfall protein increases during normal pregnancy is uncertain. In most women with preeclampsia, renal plasma flow and glomerular filtration rate are at most only modestly decreased as a consequence of increased afferent arteriolar resistance and/or reduced ultrafiltration coefficient. Serum uric acid concentrations are increased mainly as a consequence of reduced renal clearance. Reduced GFR leads to decreased filtered load of uric acid, and plasma volume contraction contributes to increased proximal tubular reabsorption coupled to sodium. The increase in urinary protein excretion in preeclampsia occurs secondary to alterations in the size and/or charge selectivity of the glomerular filter, possible increases in glomerular capillary pressure, and compromise of proximal tubular reabsorption. The renal histologic lesion characteristic of preeclampsia is termed "glomerular endotheliosis". Recent evidence suggests that anti-angiogenic factors emanating from the placenta in preeclampsia contribute to glomerular endotheliosis, proteinuria, and hypertension during disease.

Impact of pre-dilution and flushing on continuous renal replacement therapy

INTRODUCTION

Infusing the replacement solution before the filter (pre-dilution) and regular flushing have not been accounted for in conventional mathematical equations. Their effects on various continuous renal replacement therapy (CRRT) parameters, such as ultrafiltration fraction and urea clearance, have not been well studied. We incorporated these parameters into mathematical equations to help in understanding and prescribing CRRT.

METHODS

We built a mathematical model to evaluate the plasma flow rate, filter fluid inflow rate with pre- and post-dilution and ultrafiltration rate, plasma clearance of urea, and ultrafiltration fraction.

RESULTS

In pre-dilutional therapy, the volume of replacement needed to be increased in order to achieve the target plasma clearance rate. The extra volume needed increased exponentially with higher target plasma clearance rate. The higher the targeted plasma clearance in relation to blood flow rate (Qb), the greater the increase. Increasing blood flow rate reduced the ultrafiltration fraction for both pre- and post-dilution therapy. It had no effect on plasma clearance with post-dilution therapy but significantly improved the clearance in pre-dilution therapy. Higher haematocrit resulted in higher ultrafiltration fraction in both pre- and post-dilution therapy. Higher haematocrit had no effect on plasma clearance with post-dilution therapy but slightly reduced clearance in pre-dilution therapy. For a given total volume of ultrafiltration, flushing reduced plasma clearance with both pre- and post-dilution therapy. Flushing slightly reduced ultrafiltration fraction of post-dilution therapy but minimally increased the ultrafiltration fraction of pre-dilution therapy. This mathematical model could be utilised in prescribing Qb and replacement rate based on targeted plasma clearance, ultrafiltration fraction, fluid removal rate and haematocrit. There was close approximation of predicted and measured urea plasma clearance.

CONCLUSION

Pre-dilution therapy reduced urea clearance significantly and this needed to be compensated for by increasing the volume of ultrafiltration or Qb. Flushing was of limited benefit and may reduce urea clearance. In prescribing haemofiltration, Qb and replacement rate could be determined with this model.

Insulin clearance in obesity

Insulin uptake and degradation is a complex and not yet completely understood process involving not only insulin sensitive tissues. The most important degradative system is insulin degrading enzyme which is a highly conserved metalloendopeptidase requiring Zn(++) for its proteolytic action, although protein disulfide isomerase and cathepsin D are also involved in insulin metabolism. The liver and the kidney are the principal sites for insulin clearance. In obese subjects with hyperinsulinemia and high levels of free fatty acids, insulin hepatic clearance is impaired, while the glomerular filtration rate, renal plasma flow and albumin excretion are increased, suggesting a state of renal vasodilatation leading to an abnormally transmitted arterial pressure to the glomerular capillaries through a dilated afferent arteriole. Insulin can be cleared also by muscle, adipocytes, gastrointestinal cells, fibroblasts, monocytes and lymphocytes which contain insulin receptors and internalization and regulation mechanism for insulin metabolism.

Prevention of lithotripsy-induced renal injury by pretreating kidneys with low-energy shock waves

Lithotripsy shock waves (SW) to one renal pole damage that pole but protect the opposite pole from the damage inflicted by another, immediate application of SW. This study investigated whether the protection (1) occurs when the first treatment causes no injury, (2) is caused by SW or injury, (3) exhibits a threshold, and (4) occurs when the same pole receives both treatments. Six- to 7-wk-old anesthetized female pigs were studied. The following groups were studied: group 1 (n=4), 2000 SW at 12 kV to one pole and 2000 SW at 24 kV (standard) to the opposite pole; group 2 (n=6), same as group 1 except 500 12-kV SW pretreatment; group 3 (n=8), 500 12-kV, 2000 standard SW, all to the same pole; and group 4 (n=8), same as group 3 except 100 12-kV SW pretreatment. Mean+/-SD lesion size in group 1, first pole treated, was 0.66+/-0.82% of functional renal volume (FRV; P<0.05 versus 5.22+/-3.6% FRV with no pretreatment [NP]; 95% confidence interval [CI] -7.0 to -2.1) and 0.50+/-0.68% FRV in the opposite pole after 2000 standard SW (P<0.05 versus NP; 95% CI -9.4 to -0.08). Mean lesion size (first pole) in group 2 was 0.020+/-0.028% FRV (P<0.01 versus NP; 95% CI -9.2 to -1.2) and 0.43+/-0.54% FRV in the opposite pole after 2000 standard SW (P<0.05 versus NP; 95% CI -8.8 to -0.82). Same-pole SW (groups 3 and 4) also protected. Mean lesion sizes were 0.28+/-0.33% (P<0.01 versus NP; 95% CI -8.0 to -1.9) in group 3 and 0.39+/-0.48% FRV (P<0.01 versus NP; 95% CI -8.2 to -1.7) in group 4. It is concluded that the pretreatment protocol substantially limits the renal injury that normally is caused by SWL and occurs when the pretreatment and standard SW are applied to the same pole. The threshold for the protection may be <100 SW.

Hyperthyroidism and the Kidney

Hyperthyroidism and chronic renal failure (CRF) are both common diseases of older cats. Hyperthyroidism increases GFR by a variety of physiologic effects. Chronic renal failure can suppress total T4 concentrations in cats with concurrent hyperthyroidism, and free T4 is not a useful distinguishing test. Medical therapy (ie, methimazole) is recommended in cats with pre-existing CRF. Overt renal failure occurs in approximately 30% of cats treated for hyperthyroidism. It usually occurs within one month of treatment and tends to remain mild and stable over time. There is no practical way to predict which cats will develop CRF after treatment of hyperthyroidism, although GFR measurement does seem useful.

Long-term effects of maternal diabetes on vascular reactivity and renal function in rat male offspring

Fetal growth impairment can occur in pregnancy complicated by diabetes. Although several studies have focused the effects of nutritional status on intrauterine development, the long-term impact of maternal diabetes on vascular and renal function in the offspring is poorly investigated. In the present study, blood pressure profiles and renal function parameters were investigated in the offspring of diabetic rats (DO). Female rats were made diabetic throughout gestation with a single dose of streptozotocyn (STZ) 10 d before mating. After weaning, the offspring had free access to food and water. Arterial pressure was evaluated every 15 d. Functional and morphometric kidney studies were performed in newborn, 3, 6 and 12-mo-old male rats in DO and in controls, C. Although maternal diabetes did not affect nephron number in the young adult rat, glomerular hypertrophy developed from 3 mo on. Glomerular Filtration Rate and Renal Plasma Flow were observed to be significantly decreased in DO when compared with C, from 3 mo on. In DO, hypertension was observed from 8 wk on and persisted elevated throughout the experimental period (12 mo). Vascular reactivity, evaluated in mesenteric arterial bed showed a decreased endothelium-dependent vasodilatation in 12-mo-old DO animals, while preserved response to sodium nitroprusside was demonstrated. Our data show that exposure to intrauterine diabetes induced by STZ does not affect nephron number in the young offspring but can cause permanent changes in Nitric Oxide (NO)-related vascular response, which, in turn may accelerate the natural age-related nephron loss.

Divergent effects of unilateral and subtotal nephrectomy on insulin sensitivity in rats

OBJECTIVES

Insulin resistance is associated with chronic renal failure, which may amplify its cardiovascular pathologic manifestations. We previously showed the presence of insulin resistance in mild renal insufficiency due to chronic glomerulonephritis. These observations may be explained by a decrease in insulin sensitivity due to renal dysfunction. The aim of the present study was to evaluate the effects of unilateral and subtotal nephrectomy on insulin sensitivity.

METHODS

Unilateral heminephrectomy and five-sixths nephrectomy (5/6Nx) were performed in male Sprague-Dawley rats, measuring steady-state plasma glucose (SSPG) during the insulin suppression test.

RESULTS

The glomerular filtration rate (GFR) decreased significantly from sham-operated rats, to unilateral heminephrectomy group, to 5/6Nx rats. SSPG was unexpectedly lower in the unilateral heminephrectomy group than in controls, suggesting that unilateral heminephrectomy increased the sensitivity to insulin despite a mild decrease in renal function. However, when the analysis was limited to the 5/6Nx group, SSPG was inversely correlated with GFR (r = -0.65, p < 0.05). When renal failure caused by 5/6Nx had reached end stage, the rats became insulin resistant, despite a profound reduction in renal mass.

CONCLUSION

It is suggested that unilateral heminephrectomy reduced GFR and increased the sensitivity to insulin. When rats became uremic, insulin sensitivity decreased, even, in 5/6Nx.

Effect of unilateral nephrectomy on renal function of diabetic rats

Glomerular alterations of experimental diabetes mellitus are observed in animals submitted to a reduction in renal mass, suggesting that some mechanisms responsible for the progression of renal disease are common. The aim of this study was to investigate the effect of nephrectomy on the renal function and morphology of diabetic rats. Male Wistar rats were divided into 4 groups: control (C), n=8; diabetic (DM), n=8; non-diabetic nephrectomized (Nx), n=8; (DMNx), n=9. DM was induced by streptozotocin (65 mg/Kg), and animals were treated with insulin. After 12 weeks, the glomerular filtration rate (GFR), renal plasma flow (RPF) and mean arterial pressure (MAP) were evaluated in unanaesthetized animals. Glomerular volume (GV), glomerular sclerosis index (GSI), mesangial volume density (Vvmes) and glomerular capillary surface density (Svcap) were also evaluated. Results show that kidney weight increased in Nx groups, being higher in DMNx. GFR was higher in Nx groups as was RPF, being higher in DMNx. RVR was lower in Nx groups, especially in DMNx. MAP was not different among the groups. RPF and GFR showed a high correlation for the DMNx group (r=0.95, p=0.02). The DMNx group showed a correlation between RVR and GFR (r=-0.96, p=0.005). The GV increased in Nx groups, and the GSI was higher in DMNx. Vvmes and Svcap increased in DMNx group. In summary, Nx groups developed similar degrees of glomerular hypertrophy, but only DMNx showed an increased value for GSI. The present data suggest that the acceleration of glomerular lesions in DMNx animals was more closely associated to hemodynamic adaptations than to glomerular hypertrophy.

Dietary protein-induced changes in excretory function: a general animal design feature

Mammals are ureotelic and respond to an increased protein intake with an increase in glomerular filtration rate and renal plasma flow. Birds and terrestrial insects are uricotelic and following a high protein intake increase tubular urate secretion by the kidney (birds) or Malpighian tubule (insects). Ureogenic fish given NH(4)Cl increase gill and renal clearance of urea and gill clearance of ammonia. Renal mass increases in mammals, birds and reptiles given a high protein intake. Thus, animals in general respond to an increase in protein intake with a change in excretory function such as to increase the clearance of the major nitrogenous end-products of protein metabolism. The components of this general animal excretory response include; a redistribution of regional perfusion with increased renal and gill blood flow, increased GFR and gill ammonia clearance, increased renal tubular urate clearance, changes in urea transport protein abundance and/or function and renal hypertrophy. Animal groups differ as to which components are accentuated. Amino acid catabolism with generation of ammonia appears to be a necessary prerequisite for this excretory response to occur. A hypothesis is put forward that ammonia itself is a regulatory molecule and an important signal communicating between amino acid catabolism following an increase in protein intake and the sequence of events leading to a change in excretory function.

Acute renal failure after treatment with non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) are known to have adverse effects on kidney function. Situations with a stimulated renin-angiotensin system such as volume depletion or pre-existing chronic renal failure predispose to acute renal failure (ARF) via inhibition of prostaglandin synthesis by NSAIDs. To date, NSAIDs are frequently used as antipyretic drugs even in situations predisposing to ARF. Within 20 months, seven children presenting with diarrhoea and/or vomiting and fever were treated with therapeutic doses (11.5-32 mg/kg per day) of ibuprofen for 1 to 3 days before developing ARF. Maximum plasma creatinine levels were 180-650 micromol/l. One patient required emergency dialysis for hyperkalaemia, uraemia, and hyperphosphataemia. After cessation of NSAID treatment and rehydration, all patients recovered completely with a normalised creatinine level after 3 to 9 days. Once the acute phase is controlled, long-term outcome is excellent. Interstitial nephritis, another possible adverse effect of NSAIDs, might require steroid treatment and is the major differential diagnosis. Only histological examination can confirm the exact pathomechanism of ARF after NSAID exposure. If immunological events are responsible for the ARF, the recovery period is usually longer.

CONCLUSION

non-steroidal anti-inflammatory drugs are potentially dangerous in situations with even moderate volume depletion.

Evaluation of renal graft haemodynamia by 51Cr-EDTA and o-[131I]iodohippurate: its use in the early diagnosis of glomerular hyperfiltration

Chronic rejection is the most important cause of renal graft dysfunction. Non-immunological mechanisms have been suggested as a probable origin of chronic graft rejection, provoking a decrease in renal mass function, followed by glomerular hyperfiltration in the remnant nephrons, which could cause progressive glomerulosclerosis and functional loss. Early, or preclinical, identification of patients with glomerular hyperfiltration, defined as an increase in glomerular filtration fraction (GFF) and in glomerular capillary pressure (GCP), could prolong graft life. The objective of this study was to evaluate, non-invasively, stable renal graft haemodynamia and early glomerular hyperfiltration. We studied 116 renal transplant patients with stable renal function and five healthy living kidney donors with normal renal function. Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were determined using 51Cr-EDTA and o-[131I]iodohippurate, respectively. GFF was obtained from the relation between GFR and ERPF, and GCP from a mathematical model (Hall-Gomez' formula). A simultaneous analysis of renal function was performed. In transplant patients, the GFR and ERPF were significantly lower than in healthy, living, kidney donors (P<0.02). The same trend was observed for GCP (P<0.01), while GFF was not significantly different. Twelve patients (10.3%) had criteria of glomerular hyperfiltration. In patients without criteria of glomerular hyperfiltration, plasma level and clearance of creatinine were 128+/-33 micromol.l-1 and 56+/-15 ml.min-1, respectively; and in those patients with glomerular hyperfiltration criteria were 108+/-18 micromol.l-1 (P=NS) and 83+/-24 ml.min-1 (P=0.002) respectively. It is concluded that determinations of GFR, ERPF, GFF and GCP allow non-invasive evaluation of renal graft haemodynamia and can be useful in the early detection of glomerular hyperfiltration.

Compensation increase in organic anion excretion in rats with acute biliary obstruction: role of the renal organic anion transporter 1

The purpose of the present study was to examine in rats the effects of acute bile duct ligation on the expression of the organic anion transporter 1 in the kidney and the consequences of these effects on the systemic clearance of organic anions, particularly on P-aminohippurate (PAH) clearance, since it has been viewed as the prototypic organic anion. Male Wistar rats underwent bile duct ligation (BDL rats). Pair-fed sham-operated rats served as controls. All studies were carried out 21 h after surgery. Our data revealed that BDL rats had a higher expression of organic transporter 1 protein in kidney cortex homogenates. Accordingly, systemic clearance of PAH and urinary excretion of PAH were both higher in BDL rats. These findings suggest that impairment of the liver function after BDL is followed by a distinct and statistically significant increase in renal excretion of PAH, indicating a possible compensation mechanism.

Liquid chromatography for iothalamate in biological samples

We have previously reported an iothalamate assay for the assessment of the glomerular filtration rate (GFR) that required a long column equilibration time and 22 min run time per sample. We now report a simpler assay that requires a run time of only 5.5 min and is more precise and accurate than the earlier technique. The mobile phase consisted of methanol-acetonitrile-50 mM sodium monobasic phosphate (10:5:85, v/v) at pH 4.4, pumped at a rate of 1.5 ml/min on a C(18) reversed-phase column. Samples of plasma and urine were deproteinized with 1 volume of 4% perchloric acid or 9 volumes of 2% perchloric acid, respectively. No internal standard was used. The diode array detection system collected absorbance at 240 nm and the peak height areas of iothalamate were determined. The iothalamate peak appeared at 3.5 min. Detector response was linear over the range tested (10-2000 microg/ml). Within-run precision was <3% for both plasma and urine and accuracy was 96-102%. Between-day precision for plasma and urine analyses were <7%. The recovery of iothalamate in urine and plasma were 102% and 91%, respectively. There was excellent thermal and pH stability of iothalamate. No interference was found with para-amino hippuric acid (PAH) or N-acetyl PAH, which can be simultaneously assayed, if desired.

Renal Nerves Mediate Changes in Contralateral Renal Blood Flow after Extracorporeal Shockwave Lithotripsy

Renal blood flow falls in both kidneys following delivery of a clinical dose of shockwaves (SW) (2000 SW, 24 kV, Dornier HM3) to only one kidney. The role of renal nerves in this response was examined in a porcine model of renal denervation. Six-week-old pigs underwent unilateral renal denervation. Nerves along the renal artery of one kidney were identified, sectioned and painted with 10% phenol. Two weeks later the pigs were anesthetized and baseline renal function was determined using inulin and PAH clearances. Animals then had either sham-shockwave lithotripsy (SWL) (group 1), SWL to the innervated kidney (group 2) or SWL to the denervated kidney (group 3). Bilateral renal function was again measured 1 and 4 h after SWL. Both kidneys were then removed for analysis of norepinephrine content to validate the denervation. Renal plasma (RPF) flow was significantly reduced in shocked innervated kidneys (group 2) and shocked denervated kidneys (group 3). RPF was not reduced in the unshocked denervated kidneys of group 2. These observations suggest that renal nerves play a pivotal role in modulating the vascular response of the contralateral unshocked kidney to SWL, but only a partial role, if any, in modulating that response in the shocked kidney.

Effects of chronic intake of vegetable protein added to animal or fish protein on renal hemodynamics

BACKGROUND/AIMS

To examine whether chronic intake of vegetable protein added to animal protein diet affects renal hemodynamics or not, we studied effects of three kinds of diets containing various amounts of animal and vegetable protein with 1-week dietary program in each on renal hemodynamics.

METHODS

The crossover design of different amounts of vegetable protein added to the constant amount of animal protein was applied to two groups of 7 healthy individuals after the control dietary program. Renal function and 24 hours' urinary albumin excretion rate (AER) were examined on every 7th day of three consecutive 1-week dietary programs.

RESULTS

Glomerular filtration rate (GFR; sodium thiosulphate clearance) and renal plasma flow (RPF) significantly decreased after decreasing the intake of animal protein by one third with keeping the amount of vegetable protein constant. The results when substituting vegetable protein for some of the animal protein in the diet without changing the total amount of protein were identical. The filtration fraction and AER did not change over the study periods regardless of dietary composition.

CONCLUSION

The lack of an effect a 1-week intake of vegetable protein added to animal protein on GFR and RPF suggests that vegetable protein may be excluded from lists of restriction in low protein diet therapy in patients with renal insufficiency.

Role of neuronal nitric oxide synthase in mediating renal hemodynamic changes during pregnancy

Renal plasma flow (RPF) and glomerular filtration rate (GFR) are markedly increased during pregnancy. We recently reported that the renal hemodynamic changes observed during pregnancy in rats are associated with enhanced renal protein expression of neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine the role of nNOS in mediating renal hemodynamic changes observed during pregnancy. To achieve this goal, we examined the effects of the nNOS inhibitor 7-nitroindazole (7-NI) on kidney function in normal conscious, chronically instrumented virgin (n = 6) and pregnant rats (n = 9) at day 16 of gestation. Infusion of 7-NI had no effect on RPF (4.7 +/- 0.7 vs. 4.8 +/- 0.9 ml/min), GFR (2.2 +/- 0.2 vs. 2.5 +/- 0.4 ml/min), or mean arterial pressure (MAP; 127 +/- 7 vs. 129 +/- 10 mmHg) in virgin rats. In contrast, 7-NI infused into pregnant rats decreased RPF (8.9 +/- 1.6 vs. 6.5 +/- 1.4 ml/min) and GFR (4.4 +/- 0.7 vs. 3.3 +/- 0.7 ml/min) while having no effect on MAP (123 +/- 4 vs. 123 +/- 3 mmHg). In summary, inhibition of nNOS in pregnant rats at midgestation results in significant decreases in RPF and GFR. nNOS inhibition in virgin rats had no effect on renal hemodynamics. These data suggest that nNOS may play a role in mediating the renal hemodynamic changes that occur during pregnancy.

Inducible nitric oxide synthase and glomerular hemodynamics in rats with liver cirrhosis

This study was designed to test the hypothesis that glomerular de novo expression of inducible nitric oxide synthase (iNOS) contributes to renal hemodynamic abnormalities in liver cirrhosis developed 3 wk after common bile duct ligature (CBDL). De novo expression of iNOS mRNA was detected by RT-PCR in RNA extracts from isolated CBDL rat glomeruli whereas no iNOS mRNA was found in control rat glomerular RNA. Immunohistochemical staining for iNOS was negative in control animals whereas, in CBDL rats, positive iNOS staining was detected in an apparently mesangial pattern in all glomeruli. Western blots of protein extracts from isolated glomeruli of CBDL rats, but not control animals, showed a prominent iNOS band of 130 kDa. Mean arterial pressure (MAP), renal plasma flow (RPF; p-aminohippurate clearance), and glomerular filtration rate (GFR; inulin clearance) were unaltered in CBDL rats, but the application of 4 mg/kg L-N(6)-(1-iminoethyl)lysine, a specific inhibitor of iNOS, reduced GFR and RPF significantly in CBDL rats, whereas control animals were not affected. Similar results were obtained with lipopolysaccharide (LPS)-pretreated animals, which were studied as a positive control for iNOS expression and as a model for recent iNOS induction. We conclude that de novo expression of iNOS occurs in glomeruli of rats with liver cirrhosis and that nitric oxide, generated by iNOS, contributes to the maintenance of glomerular filtration in the early state of this disease.

Simultaneous administration of a cocktail of markers to measure renal drug elimination pathways: absence of a pharmacokinetic interaction between fluconazole and sinistrin, p-aminohippuric acid and pindolol

AIMS

Previous studies suggest that estimated creatinine clearance, the conventional measure of renal function, does not adequately reflect changes in renal drug handling in some patients, including the immunosuppressed. The aim of this study was to develop and validate a cocktail of markers, to be given in a single administration, capable of detecting alterations in the renal elimination pathways of glomerular filtration, tubular secretion and tubular reabsorption.

METHODS

Healthy male subjects (n = 12) received intravenously infused 2500 mg sinistrin (glomerular filtration) and 440 mg p-aminohippuric acid (PAH; anion secretion), and orally administered 100 mg fluconazole (reabsorption) and 15 mg rac-pindolol (cation secretion). The potential interaction between these markers was investigated in a pharmacokinetic study where markers (M) or fluconazole (F) were administered alone or together (M + F). Validated analytical methods were used to measure plasma and urine concentrations in order to quantify the renal handling of each marker. Plasma protein binding of fluconazole was measured by ultrafiltration. All subjects had an estimated creatinine clearance within the normal range. The renal clearance of each marker (mean+/- s.d.) was calculated as the ratio of the amount excreted in urine and the area-under-the-concentration-time curve. Statistical comparisons were made using a paired t-test and 95% confidence intervals were reported.

RESULTS

The renal clearances of sinistrin (M: 119 +/- 31 ml min(-1); M + F: 130 +/- 40 ml min(-1); P = 0.32), PAH (M: 469 +/- 145 ml min(-1); M + F: 467 +/- 146 ml min(-1); P = 0.95), R-pindolol (M: 204 +/- 41 ml min(-1); M + F: 190 +/- 41 ml min(-1); P = 0.39; n = 11), S-pindolol (M: 225 +/- 55 ml min(-1); M + F: 209 +/- 60 ml min(-1); P = 0.27; n = 11) and fluconazole (F: 14.9 +/- 3.8 ml min(-1); M + F: 13.6 +/- 3.4 ml min(-1); P = 0.16) were similar when the markers or fluconazole were administered alone (M or F) or as a cocktail (M + F).

CONCLUSIONS

This study found no interaction between markers and fluconazole in healthy male subjects, suggesting that a single administration of this cocktail of markers of different renal processes can be used to simultaneously investigate pathways of renal drug elimination.

The predictive value of 131I-hippurate clearance in the prognosis of acute renal failure

The aim of this investigation was to study the validity of the radionuclide methods in the estimation of kidney function, for prognosis and follow-up of acute renal failure (ARF). In thirty-one ARF patients, the evaluation of glomerular filtration rate (GFR) by 99mTc-DTPA clearance and effective renal plasma flow (ERPF) by 131 I-ortoiodohippurate (131I-OIH) clearance was performed within 7 days and after 6 months from ARF onset. All patients were divided in three groups according to 131I-OIH clearance values obtained within 7 days: group 1, under 150 mL/min; group 2, 150-250 mL/min; and group 3, over 250 mL/min. Seven days clearance values of both radiopharmaceuticals were found to be very low, however, GFR was found more severely impaired than ERPF. Clearance values obtained after 6 months demonstrated no recovery of renal function in the first group, partial recovery in the second and almost complete recovery in the third group. Patients with the lowest 131I-OIH clearance values at the ARF onset had no recovery of renal function, while in the other two groups recovery corresponded to initial 131I-OIH clearance values. In patients with ARF both, 99mTc-DTPA and 131I-OIH clearances were shown suitable for the follow up of renal function, however, only 131I-OIH clearance had a strong predictive prognostic value for renal function recovery in ARF.

Effects of dietary lipids on renal function of aged rats

Normal aging is accompanied by renal functional and morphological deterioration and dietetic manipulation has been used to delay this age-related decline. We examined the effects of chronic administration of diets containing 5% lipid-enriched diet (LD, w/w) on renal function of rats at different ages. Three types of LD were tested: canola oil, fish oil and butter. Mean systemic tail-cuff blood pressure and glycemia remained within the normal range whatever the age and the diet of the animals. Proteinuria began to rise from the 8th month in the groups ingesting LD, while in the control group it increased significantly (above 10 mg/24 h) only after the 10th month. With age, a significant and progressive decline in glomerular filtration rate (GFR) and renal plasma flow was observed in the LD groups but after 6 months of lipid supplementation, the decline in these parameters was more marked in the butter and fish oil groups. By the 18th month, the lowest GFR level was observed in the group ingesting the butter diet (2.93 +/- 0.22 vs 5.01 +/- 0.21 ml min(-1) kg(-1) in control, P<0.05). Net acid excretion, evaluated in 9- and 18-month-old rats, was stimulated in the fish oil group when compared both to control and to the other two LD groups. These results suggest that even low levels of LD in a chronic nutritional regimen can modify the age-related changes in renal function and that the impact of different types of lipid-supplemented diets on renal function depends on the kind of lipid present in the diet.

Analytical validation for a series of marker compounds used to assess renal drug elimination processes

Renal drug elimination is determined by glomerular filtration, tubular secretion, and tubular reabsorption. Changes in the integrity of these processes influence renal drug clearance, and these changes may not be detected by conventional measures of renal function such as creatinine clearance. The aim of the current study was to examine the analytic issues needed to develop a cocktail of marker drugs (fluconazole, rac-pindolol, para-aminohippuric acid, sinistrin) to measure simultaneously the mechanisms contributing to renal clearance. High-performance liquid chromatographic methods of analysis for fluconazole, pindolol, para-aminohippuric acid, and creatinine and an enzymatic assay for sinistrin were developed or modified and then validated to allow determination of each of the compounds in both plasma and urine in the presence of all other marker drugs. A pilot clinical study in one volunteer was conducted to ensure that the assays were suitable for quantitating all the marker drugs to the sensitivity and specificity needed to allow accurate determination of individual renal clearances. The performance of all assays (plasma and urine) complied with published validation criteria. All standard curves displayed linearity over the concentration ranges required, with coefficients of correlation greater than 0.99. The precision of the interday and intraday variabilities of quality controls for each marker in plasma and urine were all less than 11.9% for each marker. Recoveries of markers (and internal standards) in plasma and urine were all at least 90%. All markers investigated were shown to be stable when plasma or urine was frozen and thawed. For all the assays developed, there were no interferences from other markers or endogenous substances. In a pilot clinical study, concentrations of all markers could be accurately and reproducibly determined for a sufficient duration of time after administration to calculate accurate renal clearance for each marker. This article presents details of the analytic techniques developed for measuring concentrations of marker drugs for different renal elimination processes administered as a single dose to define the processes contributing to renal drug elimination.

Mild renal dysfunction is associated with insulin resistance in chronic glomerulonephritis

BACKGROUND

Insulin resistance is associated with advanced and moderate chronic renal failure (CRF). However, insulin resistance in chronic glomerulonephritis (CGN) before onset of frank renal dysfunction is not fully evaluated. We attempted to investigate the association of insulin resistance with mild renal dysfunction and with abnormal calcium homeostasis.

PATIENTS AND METHODS

Eighteen young, lean non-diabetic male patients with biopsy-proven CGN (age 30 +/- 7 years, body mass index 23.0 +/- 2.5 kg/m2) were enrolled. Insulin sensitivity was estimated by the glucose infusion rate (M value) during euglycemic hyperinsulinemic clamping for 60 to 120 min. Calcium-related parameters including intracellular calcium concentrations ([Ca2+]i) in platelets were also measured. Renal function was normal or slightly impaired (serum creatinine, 1.0 +/- 0.2 mg/dl; glomerular filtration rate (GFR), 68 to 131 ml/min/1.48 m2). We divided subjects into an insulin-sensitive (IS) group (M value > 7.3 mg/kg/min, the overall mean) and an insulin-resistant (IR) group (M value < 7.3 mg/kg/min).

RESULTS

During a 75 g oral glucose tolerance test, the plasma glucose concentration at 120 min after glucose loading and the immunoreactive insulin concentration at 60 min were significantly higher in the IR group. GFR was notably lower in the IR group than in the IS group (p = 0.0003), and was significantly correlated with insulin sensitivity (p < 0.02, r = 0.58). The basal [Ca2+]i was significantly higher in the IR than in the IS group (39 +/- 9 vs. 30 +/- 9 nM, p < 0.05).

CONCLUSION

Mild renal dysfunction and elevated basal [Ca2+]i are associated with insulin resistance in CGN.

Renal function in cyanotic congenital heart disease

We performed renal function tests in 18 young patients, 1.8-14.6 years of age, with cyanotic congenital heart disease (CCHD). Glomerular filtration rate was normal (116 +/- 4.5 ml/min/1.73 m2), and renal plasma flow was decreased (410 +/- 25 ml/min/1.73 m2) with a rise in the filtration fraction (29 +/- 1.1%). The suggested pathophysiologic explanation of these findings is that the blood hyperviscosity seen in patients with CCHD causes an overall increase in renal vascular resistance with a rise in intraglomerular blood pressure. Despite a sluggish flow of blood in the glomerular capillary bed, the effective filtration pressure was adjusted to conserve the glomerular filtration rate. In addition to these renal hemodynamic parameters, we also studied renal acidification and tubular sodium and water handling during a forced water diuresis. Our data indicate that children with CCHD have a mild to moderate normal ion gap metabolic acidosis due to a low proximal tubular threshold for bicarbonate. Proximal tubular sodium and water reabsorption under these conditions were somewhat increased, though not significantly, probably due to intrarenal hydrostatic forces, in particular the rise in the oncotic pressure in the postglomerular capillaries in patients with high hematocrit values. The distal tubular functions such as sodium handling and acidification were not affected.

Glomerular hemodynamics in severe obesity

Differential solute clearances were used to characterize glomerular function in 12 nondiabetic subjects with severe obesity (body mass index >38). Nine healthy subjects served as the control group. In the obese group, glomerular filtration rate (GFR) and renal plasma flow (RPF) exceeded the control value by 51 and 31%, respectively. Consequently, filtration fraction increased. The augmented RPF suggested a state of renal vasodilatation involving, mainly or solely, the afferent arteriole. Albumin excretion rate and fractional albumin clearance increased by 89 and 78%, respectively. Oral glucose tolerance tests were suggestive of insulin resistance. Insulin resistance was positively correlated with GFR (r = 0.88, P<0.001) and RPF (r = 0.72, P <0.001). Mean arterial pressure was higher than in the control group. Fractional clearances of dextrans of broad size distribution tended to be lowered. The determinants of the GFR were estimated qualitatively by using a theoretical model of dextran transport through a heteroporous membrane. This analysis suggests that the high GFR in very obese subjects may be the result of an increase in transcapillary hydraulic pressure difference (DeltaP). An abnormal transmission of increased arterial pressure to the glomerular capillaries through a dilated afferent arteriole could account for the augmentation in DeltaP.

Compensatory renal hypertrophy and changes of renal function following nephrectomy

We studied the changes in the serum creatinine level and the volume of the remaining kidney following nephrectomy using contrast-enhanced compounded tomogram (CT) scans. Twenty-five patients undergoing nephrectomy for renal cell carcinoma without obvious disease in the remaining kidney were carefully followed for a period of at least two years at our hospital. Twelve patients received follow-up CT scans each year after nephrectomy. The ellipsoid volume of the kidney was calculated by measuring the 3-dimensional size on CT scans. The mean relative volume (%) of the remaining kidney increased up to year 3 postoperatively, and the final mean relative volume at varying periods from years 2 to 7 was 120%. Kidneys that were smaller prior to nephrectomy showed a tendency to have a larger final relative volume after nephrectomy, although there was no significant correlation between the kidney volume prior to nephrectomy and at final measurement. The mean serum creatinine level was significantly increased at one year after nephrectomy, but it decreased significantly over time. Therefore, both compensatory renal hypertrophy and improved renal function seemed to be established within several years after nephrectomy. However, the improvement of serum creatinine was delayed compared with the increase of kidney volume. That is, renal plasma flow might be increased early by compensatory renal hypertrophy, followed within a few years by an increase in glomerular filtration and a decrease of serum creatinine.

Enhanced tumor necrosis factor in the serum and renal hypoperfusion in nephrosis associated with focal segmental glomerulosclerosis

Enhanced tumor necrosis factor alpha associated with immunocirculatory imbalance expressed as increased ratio between proinflammatory (TNFalpha) and antiinflammatory (IL-10) cytokines was observed in the serum of nephrosis associated with focal segmental glomerulosclerosis. Such altered immunocirculatory balance correlated with the reduction in renal plasma flow determined by the intrarenal hemodynamic study by which it implies that a glomerular endothelial cell injury associated with impaired renal perfusion is likely to be spontaneously induced by enhanced tumor necrosis factor in the presence of inadequate release of antiinflammatory cytokine (IL-10).

Urinary apo(a) excretion is not altered by changes in glomerular filtration rate and renal plasma flow in healthy males

Lipoprotein(a) (Lp(a)) is an independent risk factor for atherosclerotic disease. However, information concerning the site of Lp(a) catabolism and breakdown is scarce. Several studies have shown that, in renal insufficiency, plasma Lp(a) levels are elevated, and that after normalisation of kidney function they return to normal. We have recently shown that fragments of apo(a) are found in the urine of healthy individuals. Despite this evidence that apo (a) is excreted into the urine, the mode of excretion of apo(a) remains unclear. Since it has been reported that intravenous infusion of somatostatin can reduce glomerular filtration rate (GFR) and renal plasma flow (RPF), we analysed urinary apo(a) excretion in ten healthy volunteers receiving somatostatin infusions. The infusion of somatostatin led to reversible changes in GFR and RPF. Apo(a) excretion was constant in all 10 individuals over the entire time course when normalised for creatinine. There was a highly significant correlation between plasma Lp(a) levels and urinary apo(a) values. Changes in renal plasma flow and glomerular filtration rate did not alter urinary apo(a) excretion. We conclude that a constant amount of apo(a) is excreted into urine, depending on plasma Lp(a) levels, and that urinary apo(a) excretion is not altered by changes in GFR and RPF in healthy males.

A definite role for the kallikrein-kinin system in the renal hemodynamic response to an oral protein load during the aging process

The effect of aging on the physiologic responses of renal plasma flow (RPF) and glomerular filtration rate to an acute oral protein load (renal reserve) is a poorly understood process. In this study of 37 healthy human volunteers, distributed among three groups (group 1: n = 13, age range 20-39 years; group 2: n = 13, age range 40-59 years; group 3: n = 11, age range 60-68 years), we evaluated the influence of age on some of the vasoactive systems such as plasma renin activity, urinary kallikrein, plasmatic prokallikrein, plasmatic kallikrein, and plasmatic kininogen on RPF and creatinine clearance (Ccr) in response to an acute oral protein load (1 g/kg body weight). The aging process diminished but did not cease the increments in RPF (group 1: 539.6 vs. 658.9 ml/min/1.73 m(2), p < 0. 001; group 2: 509.0 vs. 570.7 ml/min/ 1.73 m(2), p < 0.001; group 3: 453.9 vs. 506.0 ml/min/ 1.73 m(2), p < 0.001) and Ccr (group 1: 139. 7 vs. 166.5 ml/ min/1.73 m(2), p < 0.001; group 2: 126.6 vs. 142.2 ml/min/1.73 m(2), p < 0.001; group 3: 112.6 vs. 121.4 ml/min/ 1.73 m(2), p < 0.01) after a protein overload. The plasma renin activity did not change after a meat meal. On the other hand, all parameters regarding the kinin system changed significantly in the direction of increased bradykinin formation, despite aging (urinary kallikrein - group 1: 0.25 vs. 0.44 mU/ml, p < 0.005; group 2: 0.25 vs. 0.41 mU/ml, p < 0.005; group 3: 0.33 vs. 0.47 mU/ml, p < 0.005/plasmatic kininogen - group 1: 1.3 vs. 0.9 microg LBK/ml, p < 0.005; group 2: 1.1 vs. 0.7 microg LBK/ml, p < 0.005; group 3: 0.8 vs. 0.7 microg LBK/ml, p < 0.005). These findings indicate that: (1) the aging process narrows but does not cease the increment range in Ccr and RPF after acute oral protein ingestion; (2) increased bradykinin formation plays a definite role in the acute renal vasodilatory response, and (3) contrary to previous clinical studies, our results suggest that the renal reserve is progressively and significantly reduced during the aging process.