Renal functional reserve

Cell-free DNA in patients with sepsis: long term trajectory and association with 28-day mortality and sepsis-associated acute kidney injury

Introduction

Outcome-prediction in patients with sepsis is challenging and currently relies on the serial measurement of many parameters. Standard diagnostic tools, such as serum creatinine (SCr), lack sensitivity and specificity for acute kidney injury (AKI). Circulating cell-free DNA (cfDNA), which can be obtained from liquid biopsies, can potentially contribute to the quantification of tissue damage and the prediction of sepsis mortality and sepsis-associated AKI (SA-AKI).

Methods

We investigated the clinical significance of cfDNA levels as a predictor of 28-day mortality, the occurrence of SA-AKI and the initiation of renal replacement therapy (RRT) in patients with sepsis. Furthermore, we investigated the long-term course of cfDNA levels in sepsis survivors at 6 and 12 months after sepsis onset. Specifically, we measured mitochondrial DNA (mitochondrially encoded NADH-ubiquinone oxidoreductase chain 1, mt-ND1, and mitochondrially encoded cytochrome C oxidase subunit III, mt-CO3) and nuclear DNA (nuclear ribosomal protein S18, n-Rps18) in 81 healthy controls and all available samples of 150 intensive care unit patients with sepsis obtained at 3 ± 1 days, 7 ± 1 days, 6 ± 2 months and 12 ± 2 months after sepsis onset.

Results

Our analysis revealed that, at day 3, patients with sepsis had elevated levels of cfDNA (mt-ND1, and n-Rps18, all p<0.001) which decreased after the acute phase of sepsis. 28-day non-survivors of sepsis (16%) had higher levels of cfDNA (all p<0.05) compared with 28-day survivors (84%). Patients with SA-AKI had higher levels of cfDNA compared to patients without AKI (all p<0.05). Cell-free DNA was also significantly increased in patients requiring RRT (all p<0.05). All parameters improved the AUC for SCr in predicting RRT (AUC=0.88) as well as APACHE II in predicting mortality (AUC=0.86).

Conclusion

In summary, cfDNA could potentially improve risk prediction models for mortality, SA-AKI and RRT in patients with sepsis. The predictive value of cfDNA, even with a single measurement at the onset of sepsis, could offer a significant advantage over conventional diagnostic methods that require repeated measurements or a baseline value for risk assessment. Considering that our data show that cfDNA levels decrease after the first insult, future studies could investigate cfDNA as a "memoryless" marker and thus bring further innovation to the complex field of SA-AKI diagnostics.

The Ultrasound Renal Stress Test for the Assessment of Functional Renal Reserve in Kidney Transplantation: A Pilot Study in Living Donors

In the evolving landscape of nephrology and kidney transplants, assessing renal functional reserve (RFR) in living kidney donors is essential for ensuring donor safety and successful transplantation. This study explores the use of the Intra-Parenchymal Renal Resistive Index Variation (IRRIV) test, a novel non-invasive method, to measure RFR in living donors. Our observational study included 11 participants undergoing living kidney donations, evaluated using the IRRIV-based Renal Stress Test (RST) before and 12 months post-nephrectomy. The study demonstrated significant changes in creatinine and eGFR CKD-EPI levels post-donation, with an average creatinine rise from 69 to 97 µmol/L and a reduction in eGFR from 104 to 66 mL/min/1.73 m2. These variations align with the expected halving of nephron mass post-nephrectomy and the consequent recruitment of RFR and hyperfiltration in the remaining nephrons. This pilot study suggests that the IRRIV-based RST is a practical, safe, and reproducible tool, potentially revolutionizing the assessment of RFR in living kidney donors, with implications for broader clinical practice in donor eligibility evaluation, even in borderline renal cases. Furthermore, it confirms the feasibility of RST in living kidney donors and allows us to assess the sample size in 48 donors for a future study.

Renal functional reserve: from physiological phenomenon to clinical biomarker and beyond

Glomerular filtration rate (GFR) is acutely increased following a high-protein meal or systemic infusion of amino acids. The mechanisms underlying this renal functional response remain to be fully elucidated. Nevertheless, they appear to culminate in preglomerular vasodilation. Inhibition of the tubuloglomerular feedback signal appears critical. However, nitric oxide, vasodilator prostaglandins, and glucagon also appear important. The increase in GFR during amino acid infusion reveals a "renal reserve," which can be utilized when the physiological demand for single nephron GFR increases. This has led to the concept that in subclinical renal disease, before basal GFR begins to reduce, renal functional reserve can be recruited in a manner that preserves renal function. The extension of this concept is that once a decline in basal GFR can be detected, renal disease is already well progressed. This concept likely applies both in the contexts of chronic kidney disease and acute kidney injury. Critically, its corollary is that deficits in renal functional reserve have the potential to provide early detection of renal dysfunction before basal GFR is reduced. There is growing evidence that the renal response to infusion of amino acids can be used to identify patients at risk of developing either chronic kidney disease or acute kidney injury and as a treatment target for acute kidney injury. However, large multicenter clinical trials are required to test these propositions. A renewed effort to understand the renal physiology underlying the response to amino acid infusion is also warranted.

Glucagon revisited: Coordinated actions on the liver and kidney

Glucagon secretion is stimulated by a low plasma glucose concentration. By activating glycogenolysis and gluconeogenesis in the liver, glucagon contributes to maintain a normal glycemia. Glucagon secretion is also stimulated by the intake of proteins, and glucagon contributes to amino acid metabolism and nitrogen excretion. Amino acids are used for gluconeogenesis and ureagenesis, two metabolic pathways that are closely associated. Intriguingly, cyclic AMP, the second messenger of glucagon action in the liver, is released into the bloodstream becoming an extracellular messenger. These effects depend not only on glucagon itself but on the actual glucagon/insulin ratio because insulin counteracts glucagon action on the liver. This review revisits the role of glucagon in nitrogen metabolism and in disposal of nitrogen wastes. This role involves coordinated actions of glucagon on the liver and kidney. Glucagon influences the transport of fluid and solutes in the distal tubule and collecting duct, and extracellular cAMP influences proximal tubule reabsorption. These combined effects increase the fractional excretion of urea, sodium, potassium and phosphates. Moreover, the simultaneous actions of glucagon and extracellular cAMP are responsible, at least in part, for the protein-induced rise in glomerular filtration rate that contributes to a more efficient excretion of protein-derived end products.

Haemodynamic or metabolic stimulation tests to reveal the renal functional response: requiem or revival?

Renal stimulation tests document the dynamic response of the glomerular filtration rate (GFR) after a single or a combination of stimuli, such as an intravenous infusion of dopamine or amino acids or an oral protein meal. The increment of the GFR above the unstimulated state has formerly been called the renal functional reserve (RFR). Although the concept of a renal reserve capacity has not withstood scientific scrutiny, the literature documenting renal stimulation merits renewed interest. An absent or a blunted response of the GFR after a stimulus indicates lost or diseased nephrons. This information is valuable in preventing, diagnosing and prognosticating acute kidney injury and pregnancy-related renal events as well as chronic kidney disease. However, before renal function testing is universally practiced, some shortcomings must be addressed. First, a common nomenclature should be decided upon. The expression of RFR should be replaced by renal functional response. Second, a simple protocol must be developed and propagated. Third, we suggest designing prospective studies linking a defective stimulatory response to emergence of renal injury biomarkers, to histological or morphological renal abnormalities and to adverse renal outcomes in different renal syndromes.

Renal Functional Reserve Revisited

Kidney function, like the function of other organs, is dynamic and continuously adjusts to changes in the internal environment to maintain homeostasis. The glomerular filtration rate, which serves as the primary index of kidney function in clinical practice, increases in response to various physiological and pathological stressors including oral protein intake. The difference between the glomerular filtration rate in the resting state and at maximum capacity has been termed renal functional reserve (RFR). RFR could provide additional information on kidney health and renal function prognosis. Despite longstanding interest in RFR as a biomarker in nephrology, its underlying mechanisms remain inadequately understood. Moreover, no consensus has been reached on how it should be quantified. Previous studies on RFR have used various measurement methods and yielded heterogeneous results. A standardized and clinically feasible approach to quantifying RFR would allow for more rigorous appraisal of its value as a biomarker and could pave the way for adoption of "renal stress tests" into clinical practice.

Is renal hyperfiltration protective in chronic kidney disease-stage 1 pregnancies? A step forward unravelling the mystery of the effect of stage 1 chronic kidney disease on pregnancy outcomes

BACKGROUND

The correlation between advanced or proteinuric chronic kidney disease (CKD) and adverse pregnancy outcomes is intuitive, although how early CKD affects pregnancy remains unknown. Glomerular hyperfiltration is a physiological response to pregnancy, correlated with outcomes in hypertension or collagen diseases. The aim of the study was to correlate first trimester hyperfiltration with pregnancy outcomes in stage 1 CKD patients.

METHODS

A historical prospective study was conducted on the database of our Unit, gathering all pregnant CKD patients referred since 1 January 2000. From 383 pregnancies referred in 2000-2013, 75 patients were selected (stage 1 CKD, referred within the 14th gestational week, singleton deliveries, absence of diabetes, hypertension or nephrotic proteinuria at referral, body mass index [BMI] < 30); 267 'low-risk' pregnancies, followed in the same setting, served as controls. Glomerular filtration rate (GFR) was assessed by Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and dichotomized at 120 mL/min. The odds for Caesarean section, prematurity, need for Neonatal Intensive Care Unit (NICU) were assessed by univariate analysis and logistic regression.

RESULTS

Risk for adverse pregnancy outcomes was not affected by hyperfiltration (univariate OR GFR ≥ 120 mL/min: Caesarean section 1.30 (0.46-3.65); preterm delivery: 0.84 (0.25-2.80)). In contrast, even in these cases with normal kidney function, stage 1 CKD was associated with prematurity (17.3% vs 4.9% P = 0.001), lower birth weight (3027 ± 586 versus 3268 ± 500 P < 0.001) need for NICU (12% vs 1.1% P < 0.001). In the multivariate analysis, the risks were significantly increased by proteinuria and maternal age but not by GFR.

CONCLUSIONS

In pregnant Stage 1 CKD patients, hyperfiltration was not associated with maternal-foetal outcomes, thus suggesting a need to focus attention on qualitative factors, eventually enhanced by age, as vascular stiffness, endothelial damage or oxidative stress.

Protein- and diabetes-induced glomerular hyperfiltration: role of glucagon, vasopressin, and urea

A single protein-rich meal (or an infusion of amino acids) is known to increase the glomerular filtration rate (GFR) for a few hours, a phenomenon known as “hyperfiltration.” It is important to understand the factors that initiate this upregulation because it becomes maladaptive in the long term. Several mediators and paracrine factors have been shown to participate in this upregulation, but they are not directly triggered by protein intake. Here, we explain how a rise in glucagon and in vasopressin secretion, directly induced by protein ingestion, might be the initial factors triggering the hepatic and renal events leading to an increase in the GFR. Their effects include metabolic actions in the liver and stimulation of sodium chloride reabsorption in the thick ascending limb. Glucagon is not only a glucoregulatory hormone. It is also important for the excretion of nitrogen end products by stimulating both urea synthesis in the liver (along with gluconeogenesis from amino acids) and urea excretion by the kidney. Vasopressin allows the concentration of nitrogenous end products (urea, ammonia, etc.) and other protein-associated wastes in a hyperosmotic urine, thus allowing a very significant water economy characteristic of all terrestrial mammals. No hyperfiltration occurs in the absence of one or the other hormone. Experimental results suggest that the combined actions of these two hormones, along with the complex intrarenal handling of urea, lead to alter the composition of the tubular fluid at the macula densa and to reduce the intensity of the signal activating the tubuloglomerular feedback control of GFR, thus allowing GFR to raise. Altogether, glucagon, vasopressin, and urea contribute to set up the best compromise between efficient urea excretion and water economy.

Glomerular function reserve and sodium sensitivity

In clinical nephrology, the glomerular filtration rate (GFR) has been recognized as the golden standard to assess renal function. However, a normal GFR does not necessarily mean normal filtration capability of the kidneys, because impaired filtration capability can be compensated for by elevating glomerular hydraulic pressure. Therefore, an early phase of glomerular dysfunction cannot be detected by the baseline GFR alone. On the other hand, glomerular capillary hypertension is widely recognized as one of the strong risk factors for the progression of nephropathies. Now, it is very important to imagine glomerular hemodynamics in each patient with nephropathy for detecting early dysfunction, as well as for evaluating risk factors. Here, I would like to summarize the current status of how an early phase of renal dysfunction can be detected in clinical practice. I truly anticipate that new methods to assess glomerular hemodynamics in humans will be developed in the near future.

Effect of 12-month therapy with omega-3 polyunsaturated acids on glomerular filtration response to dopamine in IgA nephropathy

BACKGROUND

Omega-3 polyunsaturated acids therapy is efficient in primary IgA nephropathy. It is unknown whether doses of omega-3 smaller than those given previously are still effective. The aim of the study was to examine the effect of omega-3 therapy on renal vascular function in relation to proteinuria and urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG).

METHODS

20 IgA patients aged 36.5 +/- 10.77 with creatinine clearance (Cr(cl)) 105.71 +/- 27.3 ml/min and proteinuria 3.31 +/- 2.01 g/24 h were given orally 810 mg EPA and 540 mg DHA daily for 12 months. Before and at the end of the study, 24-hour proteinuria, serum homocysteine, and Cr(cl) were measured. At the same time, renal vascular function was estimated as dopamine-induced glomerular filtration response (DIR). DIR was measured as: two 120-min lasting Cr(cl) (before and during 2 microg/kg b.w./min i.v. dopamine).

RESULTS

The results obtained during follow-up were as follows (baseline vs. after therapy): DIR 14.9 +/- 16.4 vs. 30.3 +/- 14.3% (p < 0.01); urine protein 2.31 +/- 2.01 vs. 1.31 +/- 1.37 g/24 h (p < 0.01); (Cr(cl)) 105.71 +/- 27.3 vs. 103.9 +/- 20.9 ml/min (n.s.); NAG 8.3 +/- 1.8 vs. 6.0 +/- 1.2 U/g(creat) (p < 0.01), and homocysteine 16.2 +/- 3.15 vs. 13.8 +/- 2.6 micromol/l (p < 0.05). The only correlation found was linear correlation between basal DIR and DIR change (r = -0.570; p < 0.010) and basal NAG (r = -0.460; p < 0.50).

CONCLUSIONS

Omega-3 supplementation is associated with the improvement of both renal vascular function and tubule function.

Influence of plasma amino acid level on vasopressin secretion

OBJECTIVES

Vasopressin (VP) is known to be elevated in patients with diabetes mellitus (DM). While the influence of acute hyperglycemia has been ruled out, the mechanism or the osmotically active compound responsible for the increase in VP secretion is still not elucidated. Because the plasma level of several amino acids (AAs) is increased in DM, we evaluated whether AAs could represent an effective osmotic stimulus for VP secretion.

RESEARCH DESIGN AND METHODS

In a cross-over study, eight healthy volunteers randomly received an infusion of isotonic saline (control) or mixed AA solution, i.v., at a low or a high rate (2 or 4.5 mg/min/kg BW, respectively). Plasma VP (P(VP)) was measured for two hours before and three hours during AA or control infusion.

RESULTS

AA infusion induced a dose-dependent elevation in plasma AA concentration but did not alter P(VP). However, effective plasma osmolality (P(osm)) (osmolality minus urea concentration) remained unchanged because a concommittant fall in plasma sodium concentration (P(Na)), likely due to sodium-linked uptake of AA in peripheral cells, compensated for the rise in plasma AA.

CONCLUSION

The stability of effective P(osm) may explain the lack of change observed in P(VP). Because sodium is a very efficient stimulus for VP secretion, it may be assumed that the fall in P(Na) occurring during AA infusion should have reduced VP secretion and thus P(VP). In this setting, the stability of P(VP) suggests that AAs induced an increase in VP secretion which counterbalanced the fall attributable to the decrease in P(Na). In conclusion, in acute experiments, AAs seem to represent an effective stimulus for VP secretion, almost equally potent as sodium. Further studies are needed to evaluate their contribution to the high P(VP) seen in the chronic setting of DM.

Long-term (> or =20 yr) status of 14 cadaveric kidney-transplant recipients

The aim of this study was to analyze the status of patients with a successful long-term (> or =20 yr) kidney graft. Nineteen (8.1%) of the 234 recipients who received a cadaveric kidney transplant between 1968 and 1978 in our center are still alive 21.7+/-1.6 yr (mean+/-standard error of the mean) later with a functioning allograft. Function, including measurement of the renal functional reserve (RFR), histological status, and morbidity were evaluated. Fourteen patients agreed to participate in this study. Their current immunosuppressive regimens combined prednisone (P)+azathioprine (AZA) (n=9), P+AZA+cyclosporine (CsA) (n=3) or P+CsA (n=2). Although they described their quality of life as good, 10 patients had mild hypertension, 5 developed 10 malignancies (9 cutaneous), 5 had replicative hepatitis, 8 had osteopenia, and 6 had cataracts, but none had diabetes mellitus. Proteinuria was detected in 6 patients, but was always less than 1 g/d. Mean serum creatinine was 1.28+/-0.28 mg/dL and glomerular filtration rate was 54.5+/-5.3 mL/min/1.73 m2. RFR was present for 4 patients with a mean value of +14.8+/-1.9 mL/min. Their functional status was not correlated with the histological lesions observed in concomitant transplant biopsies. Kidney grafts are able to function well even more than 20 yr post-transplantation, with some having a RFR whose significance remains unknown. Morbidity is of minor clinical severity, but could be further reduced with optimized management. Moreover, transplantation is much less costly than hemodialysis.

Long-term followup of renal functional reserve capacity after unilateral nephrectomy in childhood

PURPOSE

We establish renal function and renal reserve capacity in the long-term followup of unilateral nephrectomy in childhood.

MATERIALS AND METHODS

We recalled 37 subjects who underwent unilateral nephrectomy during childhood (age less than 16 years) to determine glomerular filtration rate, renal plasma flow and functional renal reserve capacity after oral protein loading. Interval since nephrectomy was 0.5 to 10 years in 10 cases, 11 to 20 in 13 and more than 20 years in 14, during which regular repeated renal function tests were done at our hospital. None of the patients had hypertension or significant proteinuria and all developed normally into adults. A group of 7 healthy normal subjects with 2 kidneys served as controls.

RESULTS

Creatinine clearance increased 34% immediately after surgery from a mean plus or minus standard error value of 78.6 +/- 6 to 105.4 +/- 7.2 ml. per minute per 1.73 m.2, peaked 2 to 6 months postoperatively and then plateaued (approximately 125 ml. per minute per 1.73 m.2). This level of renal function was sustained for more than 20 years. At the present testing glomerular filtration rate and renal plasma flow were not different from those of the controls. Renal reserve capacity was normal (stable) only during the first decade after unilateral nephrectomy (approximately 6% decrease), and it decreased by 50% at 10 to 20 and 66% at 20 to 30 years later.

CONCLUSIONS

This long-term followup study demonstrates that a single remnant human kidney continues to function normally for more than 20 years. The prolonged increased workload does not interfere with normal development and maturation. The renal reserve capacity decreased significantly during the years may, however, indicate a vulnerability of the single kidney and raises the possibility of renal functional impairment with much longer followup.

Long-term followup of renal functional reserve capacity after unilateral nephrectomy in childhood

PURPOSE

We establish renal function and renal reserve capacity in the long-term followup of unilateral nephrectomy in childhood.

MATERIALS AND METHODS

We recalled 37 subjects who underwent unilateral nephrectomy during childhood (age less than 16 years) to determine glomerular filtration rate, renal plasma flow and functional renal reserve capacity after oral protein loading. Interval since nephrectomy was 0.5 to 10 years in 10 cases, 11 to 20 in 13 and more than 20 years in 14, during which regular repeated renal function tests were done at our hospital. None of the patients had hypertension or significant proteinuria and all developed normally into adults. A group of 7 healthy normal subjects with 2 kidneys served as controls.

RESULTS

Creatinine clearance increased 34% immediately after surgery from a mean plus or minus standard error value of 78.6 +/- 6 to 105.4 +/- 7.2 ml. per minute per 1.73 m.2, peaked 2 to 6 months postoperatively and then plateaued (approximately 125 ml. per minute per 1.73 m.2). This level of renal function was sustained for more than 20 years. At the present testing glomerular filtration rate and renal plasma flow were not different from those of the controls. Renal reserve capacity was normal (stable) only during the first decade after unilateral nephrectomy (approximately 6% decrease), and it decreased by 50% at 10 to 20 and 66% at 20 to 30 years later.

CONCLUSIONS

This long-term followup study demonstrates that a single remnant human kidney continues to function normally for more than 20 years. The prolonged increased workload does not interfere with normal development and maturation. The renal reserve capacity decreased significantly during the years may, however, indicate a vulnerability of the single kidney and raises the possibility of renal functional impairment with much longer followup.

Renal functional reserve in patients with severe chronic obstructive pulmonary disease

BACKGROUND

Renal functional reserve is the normal increase in renal blood flow after a protein load, and reduced or absent renal functional reserve is an early index of renal impairment. Renal blood flow is frequently reduced during acute oedematous exacerbations of chronic obstructive pulmonary disease (COPD). It is possible that patients with severe COPD in the stable state may have a reduced or absent renal functional reserve which could be a factor in oedema formation.

METHODS

Sixteen stable patients with severe COPD and five normal controls were studied. The mean (SD) arterial oxygen and carbon dioxide tensions (PaO2, PaCO2) and forced expiratory volume in one second (FEV1) of patients with COPD were 8.1 (1.04) kPa, 6.3 (0.69) kPa, and 0.74 (0.27) 1, respectively. The pulsatility index (PI), an index of renovascular resistance, was measured non-invasively by Doppler ultrasonography at baseline and at intervals after a protein load of 250 g steak.

RESULTS

The PI fell after the protein load in the normal subjects from 1.04 (0.19) to 0.84 (0.17), mean difference 0.20, 95% confidence interval of difference (CI) 0.14 to 0.27, p < 0.001. In the COPD group there was no change; baseline PI = 1.04 (0.16), PI after protein load = 1.08 (0.19), mean difference = -0.04, 95% CI-0.11 to 0.04, p = NS. Six of the patients with COPD were normocapnic and 10 were hypercapnic (PaCO2 > or = 6.0 kPa). The normocapnic patients had no significant change in PI (baseline PI = 1.07 (0.15), PI after protein load = 1.01 (0.16), mean difference = 0.06, 95% CI -0.03 to 0.15) while in the hypercapnic patients the PI tended to rise (baseline PI = 1.03 (0.17), PI after protein load = 1.12 (0.21), mean difference = -0.09, 95% CI 0.18 to 0.007, p = 0.06).

CONCLUSIONS

Renal haemodynamics were unchanged after a protein load in patients with severe COPD, suggesting that they had no renal functional reserve. This may be a factor in the development of oedema frequently seen in patients with severe COPD, particularly in hypercapnic patients.

Combined renal effects of overweight and hypertension

The existence of a direct relationship between body mass and arterial pressure is well recognized; however, the effect of obesity on known target organs of hypertension is not clearly understood. We undertook the present studies to assess the influence of obesity on renal function and urinary albumin excretion in 40 normotensive subjects and 80 nevertreated hypertensive patients matched for age, sex, arterial pressure level, and known duration of hypertension in whom an oral glucose tolerance test was within normal limits. Glomerular filtration rate and effective renal plasma flow (expressed as absolute values or values normalized for height) were increased in overweight compared with lean subjects whether normotensive or hypertensive. Glomerular filtration rate was positively correlated with protein intake (as assessed from urinary excretion of urea) and fasting serum insulin level. Urinary excretion of albumin but not IgG and beta 2 microglobulin was higher in hypertensive patients compared with normotensive subjects. The overweight condition clearly enhanced the influence of arterial pressure on albuminuria; in fact, a steeper regression line between albumin excretion rate and arterial pressure was found in overweight compared with lean subjects. These results indicate that the overweight condition is associated with renal hyperfiltration and hyperperfusion, irrespective of the presence of hypertension, and that obesity magnifies the effect of hypertension on albuminuria, thus raising the possibility of an increased susceptibility of obese hypertensive patients to the development of renal damage.

Albuminuria in normals and essential hypertension

The prevalence and determinants of urinary albumin excretion rate (AER) were assessed in lean and overweight normotensive subjects (NT) and patients with essential hypertension (EH). In NT and EH, the presence of overweight was associated with a significant exacerbation of AER. In the normotensive population, AER was higher in subjects with a positive family history of hypertension. An important role for smoking was observed in the hypertensive population; in fact, the prevalence of microalbuminuria (MA) was almost twofold in lean hypertensive smokers when compared to nonsmokers. Among other determinants of AER, a major influence of systolic arterial pressure, urinary excretion of urea (an estimate of protein intake), and high-density lipoprotein (HDL) cholesterol (inversely correlated with AER) was observed mainly in lean EH patients. The significance of microalbuminuria is unclear. Is it a marker of cardiovascular risk and/or a predictor of the future development of renal disease in EH?

Renal functional reserve in cyclosporin-treated recipients of kidney transplant

The aims of this study were to determine whether renal functional reserve (RFR) is still present in cyclosporin-treated renal transplant recipients, and to examine the relationship between RFR and proximal reabsorption. A serial study was carried out in 12 renal allograft recipients (R) with good renal graft function at 20 +/- 2.5 days (S1) and at 7.6 +/- 0.4 months (S2) post-transplantation, and the results were compared to those in eight subjects who had undergone unine-phrectomy (one-kidney controls: UNx.C) and in 12 healthy volunteers (two-kidney controls: 2K.C). R and C were in similar sodium and protein balance and with similar plasma renin and aldosterone levels. R had normal serum creatinine level on moderate doses of cyclosporin (whole blood cyclosporin concentration: 212 +/- 20 and 125 +/- 20 ng/ml at S1 and S2, respectively). Eight one-hour clearance periods were performed prior to, during and following a three-hour i.v. infusion of a mixture of 20 l-amino acids (Azonutril 25, 4.5 mg amino acids/kg/min). Baseline glomerular filtration rate (GFR) was lower in recipients at S1 and S2 (55 +/- 5 and 54 +/- 4 ml/min/1.73 m2, respectively) than in UNx.C and 2K.C (72 +/- 4 and 113 +/- 4 ml/min/1.73 m2, respectively, P < 0.05 and 0.001). Amino acid infusion elicited significant GFR increases in controls as well as in recipients in spite of higher renal vascular resistances (RVR). The greater measured increase in GFR, which represented RFR, was 18 +/- 3 and 28 +/- 2 ml/min/1.73 m2 in UNx.C and 2K.C, respectively (P < 0.001), and 17 +/- 3 ml/min/1.73 m2 in R at both S1 and S2 (P < 0.001). Contrary to both UNx and 2K controls, the acute hyperfiltration in R at S1 and S2 occurred with a significant increase in effective renal plasma flow, no alteration in filtration fraction and a large decrease (approximately 20 and 17%) in RVR while no correlation could be detected between the RFR and baseline GFR. Baseline lithium clearance, used as a marker of overall proximal fluid delivery (CLi), was significantly lower, whereas baseline fractional excretion of lithium (FELi) was significantly higher in R at S1 and S2 and in UNx.C (41 +/- 4, 40 +/- 3 and 38 +/- 3%, respectively) than in 2K.C (31 +/- 2%, P < 0.05). Consistent and significant increase in CLi, FELi and absolute proximal reabsorption occurred both in R at S1 and S2 and in UNx and 2K controls during elicitation of RFR.(ABSTRACT TRUNCATED AT 400 WORDS)

Sodium-lithium countertransport activity in red blood cells of patients with IgA nephropathy

In this paper we report some results of our studies on patients with immunoglobulin (Ig)A nephropathy regarding (1) the familiar aggregation of erythrocyte sodium-lithium (Na,Li) countertransport; (2) the association of Na,Li countertransport with the presence of arterial hypertension and lipid abnormalities; (3) the correlation between Na,Li countertransport activity and renal functional reserve; and (4) the preliminary results of a longitudinal study. In 13 families of patients with IgA nephropathy, selected because both parents were available, we found a significant correlation between midparent and offspring Na,Li countertransport activity (Spearman's rank correlation = 0.65; P = 0.023), but no husband-wife relationship. In 49 patients, the activity of Na,Li countertransport was significantly higher in erythrocytes from 20 hypertensive patients than from either 29 normotensive patients or from 36 healthy age- and sex-matched normal subjects. Hyperlipidemic patients had an erythrocyte Na,Li countertransport activity significantly higher than normolipidemic patients and controls. In 17 patients a significant inverse correlation was found between the peak variation of creatinine clearance over baseline value after an oral protein load and the erythrocyte Na,Li countertransport activity (Spearman r = 0.54; P = 0.03). In a longitudinal study of 36 patients followed from 12 to 36 months, those showing a progression toward renal failure had an erythrocyte Na,Li countertransport activity higher than median value. The results of our studies show that in patients with IgA nephropathy a high erythrocyte Na,Li countertransport rate, genetically determined, is associated with the presence of arterial hypertension and lipid abnormalities, and perhaps with a less favorable disease outcome.

Renal functional reserve: its significance in normal and salt depletion conditions

The aim of this study was the evaluation, in healthy subjects, of the renal functional reserve (RFR), that is, the GFR increase induced by a combined infusion of amino acids (AA) and dopamine (D), in conditions of extracellular volume depletion caused by diuretic administration. In particular, this study was undertaken: a) to evaluate whether and to which extent, AA + D can reverse the functional GFR impairment induced by salt depletion, without volume restoration; b) to study whether any relationship may be found between the GFR in normal condition (the so-called "resting" GFR), and/or the renal functional reserve and the GFR impairment induced by salt depletion, in order to understand the role of both "resting" GFR and RFR in the degree of renal dysfunction induced by salt depletion. In control conditions the i.v. infusion of AA + D significantly increased RPF (+ 41% vs. baseline period) with a mean absolute increase of 211 ml/min. A similar pattern was observed in GFR behavior (+31.5% with 34 ml/min of mean absolute increase). A significant inverse exponential relationship was observed between GFR before AA + D i.v. infusion ("resting" GFR) and renal functional reserve (P less than 0.05), suggesting that, in normal conditions, these inversely related parameters may widely vary according to the tone of the glomerular arterioles. Following salt depletion, we observed a variable degree of GFR impairment. Both GFR and RPF were significantly decreased (-25.9%, P less than 0.05 and -29%, P less than 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)