The influence of work intensity on postexercise proteinuria

Rehabilitation of a Patient With Minimal Change Nephrotic Syndrome and Acute Kidney Injury: A Case Report

Patients with minimal change nephrotic syndrome (MCNS) are prone to loss of motor skills due to urinary protein leakage, steroid myopathy, and other factors. Acute kidney injury (AKI) is a common complication that contributes to the loss of physical function. Rehabilitation is crucial, but its efficacy and safety are unknown. Here we present a case of a patient with MCNS complicated by AKI, who commenced rehabilitation after dialysis was discontinued and experienced improved mobility. The patient, a woman in her 70s, was admitted to our hospital with bilateral lower limb edema and decreased urine output for approximately 5 days. Treatment with prednisolone and furosemide was initiated, but then dialysis was initiated due to AKI. Rehabilitation was started after dialysis was discontinued. The patient's muscle strength and physical activity improved, and her exercise capacity and exercise tolerance improved without adverse effects. Rehabilitation may contribute to the improvement of exercise capacity without worsening renal function and urinary protein in patients with MCNS complicated by AKI.

Post-exercise urinary alpha-1 acid glycoprotein is not dependent on hypoxia

Proteinuria is a transient physiological phenomenon that occurs with a range of physical activities and during ascent to altitude. Exercise intensity appears to dictate the magnitude of postexercise proteinuria; however, evidence also indicates the possible contributions from exercise-induced hypoxemia or reoxygenation. Using an environmental hypoxic chamber, this crossover-designed study aimed to evaluate urinary alpha-1 acid glycoprotein (α1-AGP) excretion pre/postexercise performed in hypoxia (HYP) and normoxia (NOR). Sixteen individuals underwent experimental sessions in normoxia (NOR, 20.9% O₂) and hypoxia (HYP, 12.0% O₂). Sessions began with a 2-h priming period before completing a graded maximal exercise test (GXT) on a cycle ergometer, which was followed by continuation of exposure for an additional 2 h. Physiological responses (i.e., blood pressure, heart rate, and peripheral oxygenation), Lake Louise Scores (LLSs), and urine specimens (analyzed for albumin and α1-AGP) were collected pre- and postexercise (after 30, 60, and 120 min). Peak power output was significantly reduced in HYP (193 ± 45 W) compared with NOR (249 ± 59 W, P < 0.01). Postexercise urinary α1-AGP was greater in NOR (20.04 ± 14.84 µg·min⁻¹) than in HYP (15.08 ± 13.46 µg·min⁻¹), albeit the difference was not significant (P > 0.05). Changes in urinary α1-AGP from pre- to post-30 min were not related to physiological responses or performance outcomes observed during GXT in NOR or HYP. Despite profound systemic hypoxemia with maximal exercise in hypoxia, postexercise α1-AGP excretion was not elevated above the levels observed following normoxic exercise.

NEW & NOTEWORTHY By superimposing hypoxic exposure and maximal exercise, we were able to investigate the impact of hypoxia on postexercise proteinuria. Urinalysis for α1-AGP (via particle-enhanced immunoturbidimetry) in specimens collected pre-/postexercise enabled the sensitive detection of altered glomerular permeability. Data indicated that exercise intensity, rather than the degree of exercise-induced hypoxemia, determines postexercise proteinuria.

Physical activity and renal function in the Italian kidney transplant population

Background

The well-documented benefits of physical activity (PA) are still poorly characterized in long-term kidney transplant outcome. This study analyzed the impact over a 10-year follow-up of PA on graft function in Italian kidney transplant recipients (KTRs).

Methods

Since 2002, the Italian Transplant-Information-System collected donor and recipient baseline and transplant-related parameters in KTRs. In 2015, ‘penchant for PA’ (PA ≥ 30-min, 5 times/week) was added. Stable patients aged ≥18 years at the time of first-transplantation were eligible. KTRs with at least 10-year follow-up were also analyzed. Mixed-effect regression models were used to compare eGFR changes over time in active versus non-active patients.

Results

PA information was available for 6,055 KTRs (active 51.6%, non-active 48.4%). Lower penchant for PA was found in overweight and obese patients (OR = 0.84; OR = 0.48, respectively), in those with longer dialysis vintage (OR = 0.98 every year of dialysis), and older age at transplant. Male subjects showed greater penchant for PA (OR = 1.25). A slower decline of eGFR over time was observed in active KTRs compared to non-active, and this finding was confirmed in the subgroup with at least 10-year follow-up (n = 2,060). After applying the propensity score matching to reduce confounding factors, mixed-effect regression models corroborated such better long-term trend of graft function preservation in active KTRs.

Conclusions

Penchant for PA is more frequent among male and younger KTRs. Moreover, in our group of Italian KTRs, active patients revealed higher eGFR values and preserved kidney function over time, up to 10-years of follow-up.

Kidney physiology and pathophysiology during heat stress and the modification by exercise, dehydration, heat acclimation and aging

The kidneys' integrative responses to heat stress aid thermoregulation, cardiovascular control, and water and electrolyte regulation. Recent evidence suggests the kidneys are at increased risk of pathological events during heat stress, namely acute kidney injury (AKI), and that this risk is compounded by dehydration and exercise. This heat stress related AKI is believed to contribute to the epidemic of chronic kidney disease (CKD) occurring in occupational settings. It is estimated that AKI and CKD affect upwards of 45 million individuals in the global workforce. Water and electrolyte disturbances and AKI, both of which are representative of kidney-related pathology, are the two leading causes of hospitalizations during heat waves in older adults. Structural and physiological alterations in aging kidneys likely contribute to this increased risk. With this background, this comprehensive narrative review will provide the first aggregation of research into the integrative physiological response of the kidneys to heat stress. While the focus of this review is on the human kidneys, we will utilize both human and animal data to describe these responses to passive and exercise heat stress, and how they are altered with heat acclimation. Additionally, we will discuss recent studies that indicate an increased risk of AKI due to exercise in the heat. Lastly, we will introduce the emerging public health crisis of older adults during extreme heat events and how the aging kidneys may be more susceptible to injury during heat stress.

Urinary Biomarkers: Diagnostic Tools for Monitoring Athletes' Health Status

Acute or intense exercise is sometimes related to infections of the urinary tract. It can also lead to incorrect hydration as well as incorrect glomerular filtration due to the presence of high-molecular-weight proteins that cause damage to the kidneys. In this context, our study lays the foundations for the use of a urine test in a team of twelve male basketball players as a means of monitoring numerous biochemical parameters, including pH, specific weight, color, appearance, presence of bacterial cells, presence of squamous cells, leukocytes, erythrocytes, proteins, glucose, ketones, bilirubin, hemoglobin, nitrite, and leukocyte esterase, to prevent and/or treat the onset of pathologies, prescribe personalized treatments for each athlete, and monitor the athletes’ health status.

Hypoxia is not the primary mechanism contributing to exercise-induced proteinuria

Introduction

Proteinuria increases at altitude and with exercise, potentially as a result of hypoxia. Using urinary alpha-1 acid glycoprotein (α1-AGP) levels as a sensitive marker of proteinuria, we examined the impact of relative hypoxia due to high altitude and blood pressure-lowering medication on post-exercise proteinuria.

Methods

Twenty individuals were pair-matched for sex, age and ACE genotype. They completed maximal exercise tests once at sea level and twice at altitude (5035 m). Losartan (100 mg/day; angiotensin-receptor blocker) and placebo were randomly assigned within each pair 21 days before ascent. The first altitude exercise test was completed within 24–48 hours of arrival (each pair within ~1 hour). Acetazolamide (125 mg two times per day) was administrated immediately after this test for 48 hours until the second altitude exercise test.

Results

With placebo, post-exercise α1-AGP levels were similar at sea level and altitude. Odds ratio (OR) for increased resting α1-AGP at altitude versus sea level was greater without losartan (2.16 times greater). At altitude, OR for reduced post-exercise α1-AGP (58% lower) was higher with losartan than placebo (2.25 times greater, p=0.059) despite similar pulse oximetry (SpO₂) (p=0.95) between groups. Acetazolamide reduced post-exercise proteinuria by approximately threefold (9.3±9.7 vs 3.6±6.0 μg/min; p=0.025) although changes were not correlated (r=−0.10) with significant improvements in SpO₂ (69.1%±4.5% vs 75.8%±3.8%; p=0.001).

Discussion

Profound systemic hypoxia imposed by altitude does not result in greater post-exercise proteinuria than sea level. Losartan and acetazolamide may attenuate post-exercise proteinuria, however further research is warranted.

Both hyperthermia and dehydration during physical work in the heat contribute to the risk of acute kidney injury

Occupational heat stress increases the risk of acute kidney injury (AKI) and kidney disease. This study tested the hypothesis that attenuating the magnitude of hyperthermia (i.e., increase in core temperature) and/or dehydration during prolonged physical work in the heat attenuates increases in AKI biomarkers. Thirteen healthy adults (3 women, 23 ± 2 yr) exercised for 2 h in a 39.7 ± 0.6°C, 32 ± 3% relative-humidity environmental chamber. In four trials, subjects received water to remain euhydrated (Water), continuous upper-body cooling (Cooling), a combination of both (Water + Cooling), or no intervention (Control). The magnitude of hyperthermia (increased core temperature of 1.9 ± 0.3°C; P < 0.01) and dehydration (percent loss of body mass of -2.4 ± 0.5%; P < 0.01) were greatest in the Control group. There were greater increases in the urinary biomarkers of AKI in the Control trial: albumin (increase of 13 ± 11 μg/mL; P ≤ 0.05 compared with other trials), neutrophil gelatinase-associated lipocalin (NGAL) (increase of 16 ± 14 ng/dL, P ≤ 0.05 compared with Cooling and Water + Cooling groups), and insulin-like growth factor-binding protein 7 (IGFBP7) (increase of 227 ± 190 ng/mL; P ≤ 0.05 compared with other trials). Increases in IGFBP7 in the Control trial persisted after correcting for urine production/concentration. There were no differences in the AKI biomarker tissue inhibitor of metalloproteinase 2 (TIMP-2) between trials (P ≥ 0.11). Our findings indicate that the risk of AKI is highest with greater magnitudes of hyperthermia and dehydration during physical work in the heat. Additionally, the differential findings between IGFBP7 (preferentially secreted in proximal tubules) and TIMP-2 (distal tubules) suggest the proximal tubules as the location of potential renal injury.NEW & NOTEWORTHY We demonstrate that the risk for acute kidney injury (AKI) is higher in humans with greater magnitudes of hyperthermia and dehydration during physical work in the heat and that alleviating the hyperthermia and/or limiting dehydration equally reduce the risk of AKI. The biomarker panel employed in this study suggests the proximal tubules as the location of potential renal injury.

The Influence of a Health-Related Fitness Training Program on Motor Performance as Well as Hematological and Biochemical Parameters

The study was aimed at designing a health exercise program appealing to inactive young men, and then testing the men's metabolic responses to the program using common diagnostic markers of general health. Six men, aged 22-29 years, took a part in training program to increase their motor performance and improve general health conditions. Body composition parameters, clinical chemistry variables (metabolites, albumin, total protein, ferritin, C reactive protein, lipid profile, ions, and selected enzymes activities) and blood morphology parameters were determined. Motor performance measured before and after a 4-month-long macrocycle indicated an increase in endurance, pace, and agility of the participants. Significant differences were found in analyzed enzymes activities. There was a significant increase in C-reactive protein levels from pre- to post-training. Additionally, changes in hematological biomarkers were seen that suggest erythropoiesis might significantly increase, specifically during the last 2-month-long mesocycles. The proposed training program induced small improvements in endurance, pace, and agility. It was also confirmed that changes in aspartate (AST) and alanine (ALT) activities emerge before any increase in creatine kinase (CK) activity that is important in monitoring of the training loads. Observed changes in red blood cell-related parameters suggest increase in erythropoiesis in the second half of the training cycle.

Factors influencing post-exercise proteinuria after marathon and ultramarathon races

Post-exercise proteinuria is one of the most common findings observed after short and intensive physical activity, but is observed also after long runs with low intensity. The aim of this study was to analyze factors influencing proteinuria after marathon runs. Two groups of male amateur runners were studied. The results of 20 marathon finishers (42.195 m), with a mean age of 49.3 ± 6.85 years; and 17 finishers of a 100-km ultramarathon with a mean age of 40.18±4.57 years were studied. Urine albumin to creatinine ratio (ACR) was calculated before and after both races. The relationship between ACR and run pace, metabolites (lactate, beta hydroxybutyrate), markers of inflammation (CRP, IL-6) and insulin was studied. The significant increase in ACR was observed after both marathon races. ACR increased from 6.41 to 21.96 mg/g after the marathon and from 5.37 to 49.64 mg/g after the ultramarathon (p<0.05). The increase in ACR was higher after the ultramarathon that after the marathon. There was no correlation between run pace and proteinuria. There was no correlation between ACR and glucose, free fatty acids, lactate, beta-hydroxybutyrate and insulin levels. There was significant negative correlation between ACR and interleukin 6 (IL-6) (r =-0.59, p< 0.05) after ultramarathon. Proteinuria is a common finding after physical exercise. After very long exercises it is related to duration but not to intensity. There is no association between metabolic and hormonal changes and ACR after marathon runs. The role on inflammatory cytokines in albuminuria is unclear.

The Renin-Angiotensin System, Not the Kinin-Kallikrein System, Affects Post-Exercise Proteinuria

BACKGROUND/AIMS

Temporary proteinuria post-exercise is common and is caused predominantly by renal haemodynamic alterations. One reason is up-regulation of angiotensin II (Ang II) due to the reducing effect of angiotensin-converting enzyme (ACE) inhibitors. However, another, ignored, reason could be the kininase effect of ACE inhibition. This study investigated how ACE inhibition reduces post-exercise proteinuria: by either Ang II up-regulation inhibition or bradykinin elevation due to kininase activity inhibition.

METHODS

Our study included 10 volunteers, who completed 3 high-intensity exercise protocols involving cycling at 1-week intervals. The first protocol was a control arm, the second evaluated the effect of ACE inhibition and the third examined the effect of angiotensin type 1 receptor blockade. Upon application, both agents reduced systolic and diastolic blood pressure; however, there were no statistically significant -differences. In addition, total protein, microalbumin and -β2-microglobulin excretion levels in urine specimens were analysed before, 30 min after and 120 min after the exercise protocols.

RESULTS

Total protein levels in urine samples were elevated in all 3 protocols after 30 min of high-intensity exercise, compared to baseline levels. However, both ACE inhibition and angiotensin type 1 receptor blockade suppressed total protein in the 30th min. In each protocol, total protein levels returned to the baseline after 120 min. Urinary microalbumin and β2-microglobulin levels during the control protocol were significantly higher 30 min post-exercise; however, only angiotensin type 1 receptor blockade suppressed microalbumin levels.

CONCLUSION

The results indicated Ang II up-regulation, not bradykinin elevation, plays a role in post-exercise proteinuria.

Assessment of urinary protein composition in response to consecutive days of wildland firefighting

The purpose of this study was to examine the pattern of urinary protein excretion induced by 3 consecutive days of wildland firefighting. Eighteen male active-duty military personnel served as the participants. All testing on the 3 consecutive days was conducted at a Northwestern USA fire camp. All participants consumed military-based foods containing 2620-2864 kcal/day. The work activity was evaluated with an accelerometer in association with body weight and hydration markers over the experimental period. Urinary samples were collected pre and post workshift on days 1 and 3 to assess glomerular and tubular protein excretion (total protein, albumin, β₂-microglobulin, N-acetyl-β-d-glucosaminidase and creatinine). The urinary levels of glomerular and tubular protein were not significantly different. The main findings of the present study indicate that similar alterations of urinary protein composition can be observed over consecutive days of wildland firefighting, which appears to be dependent on intensity rather than total work output.

Acute exercise does not impair renal function in nondialysis chronic kidney disease patients regardless of disease stage

Exercise has been overlooked as a potential therapy in chronic kidney disease (CKD), mainly because of a lack of understanding on its safety aspects. Notably, there are no data on renal function after exercise in CKD considering its stages. We investigated the acute effects of a 30-min moderate-intensity aerobic exercise bout on glomerular filtration rate (GFR) and albuminuria in 22 nondialysis CKD patients divided into: CKD stages 1 and 2 (CKD_1-2) and CKD stages 3 and 4 (CKD_3-4). Eleven body mass index-, age-, and sex-matched healthy individuals served as control (CON). Blood and urine samples were collected before, immediately after, and up to 90 min postexercise for creatinine and albumin assessments. GFR was determined by creatinine clearance (GFR_Cr-Cl). All CKD patients had significantly lower peak oxygen uptake than CON. CKD_1-2 and CKD_3-4 had increasingly higher serum creatinine than CON (9.6 ± 2.6, 25.6 ± 1.01, and 7.5 ± 1.4 mg/l, respectively); however, no within-group changes in serum or urinary creatinine were observed across time. GFR_Cr-Cl was decreased in CKD_1-2 and CKD_3-4 compared with CON (91 ± 17 ml·min^-1·1.73 m^-2; 34 ± 15 ml·min^-1·1.73 m^-2; 122 ± 20 ml·min^-1·1.73 m^-2, respectively). Most importantly, exercise did not affect GFR_Cr-Cl in none of the groups across time. Albuminuria was significantly higher in CKD_3-4 (297 ± 284 µg/min) than in CON (5.4 ± 1.4 µg/min), but no within-group changes were observed after exercise. In conclusion, a single 30-min moderate-intensity aerobic exercise bout does not impair renal function in nondialysis CKD patients, regardless of disease stage, supporting the notion that exercise training can be safe in this disease.

Effects of exercise on the urinary proteome

Exercise-induced proteinuria has been observed and studied for more than a century. It was found that different sport disciplines alter the urinary proteome in different ways. Moderate-intensity exercise results in increased glomerular filtration, meaning that medium-sized proteins are excreted in higher amounts, while high-intensity exercise of short duration also increases the excretion of low molecular weight proteins as a result of tubular dysfunction. Exhaustive exercise may lead to the excretion of hemoglobin or myoglobin, which changes the urinary proteome considerably. Studies comparing protein maps of different sport types compared to a control group showed that quality and quantity of urinary proteins are interindividually different. In addition, urine samples collected before and after exercise exhibit substantially different protein patterns even from the same person. Therefore, further studies investigating the urinary proteome are desirable. As the variation of protein content and composition in urine are generally much higher than in other matrices, respective studies need to be well controlled and homogenous groups of volunteers should be chosen. In addition to the sport-related physiological and biochemical interest, exercise-induced protein changes also need to be considered for biomarker measurements from urine samples for kidney or other diseases.

Post-effort chances in C-reactive protein level among soccer players at the end of the training season

Numerous literature data point out the differences in immunological parameters as a result of physical effort and the relation of those changes to the subject's fitness level. This study was aimed at the assessment of soccer players' condition and adaptation to physical effort based on the changes in C-reactive protein (CRP) blood level. C-reactive protein, total protein, and albumin plasma levels before and after 60-minute-long outdoor running were determined among 16 (8 men and 8 women) soccer players. Statistically significant increase in total blood protein level was observed in both studied groups. However, there were no statistically significant changes in albumin level in soccer players' blood. Determination of CRP showed that the exercise test caused changes in its level among both women and men; yet, statistically significant increase in CRP level was found only in women's blood. The different influence of effort on CRP plasma level may be explained by the involvement of various mechanisms in regulation of acute-phase responses in different conditions. It was found in our study that CRP level could be a valuable tool to assess the metabolic response to aerobic exercise.

Moderate-intensity single exercise session does not induce renal damage

BACKGROUND

The aim of this study was to determine whether a single moderate-intensity exercise session induces renal injury based on various parameters that reflect kidney dysfunction, including urinary L-type fatty acid-binding protein (L-FABP).

METHODS

Adult outpatients (n = 31) with chronic kidney disease (CKD) not receiving renal replacement therapy participated in this study. Urine was collected before and after a single 20-min moderate-intensity exercise session. Urinary levels of L-FABP, albumin, N-acetyl-β-d-glucosaminidase (NAG), and α1-microglobrin (α1MG) were measured. In addition, 12 patients with estimated glomerular filtration fraction less than 30 ml/min/1.73 ml(2) were selected from all patients and evaluated using the same analysis.

RESULTS

Urinary values of L-FABP, albumin, NAG, and α1MG did not increase significantly after exercise compared with before exercise (urinary L-FABP, from 8.3 to 9.4 μg/g of creatinine; urinary albumin, from 293.1 to 333.7 mg/g of creatinine; urinary NAG, from 9.2 to 8.2 U/g of creatinine; urinary α1MG, from 11.4 to 9.8 mg/g of creatinine, not significant). Similar findings were seen in all patients, regardless of degree of renal dysfunction.

CONCLUSIONS

A single session of moderate-intensity exercise was not associated with an increase in renal parameters used to assess renal damage.

Effect of exercise intensity on albuminuria in adolescents with Type 1 diabetes mellitus

AIMS

Exercise may be useful to detect patients with diabetes prone to develop persistent microalbuminuria. We studied the relationship between exercise intensity, measured as maximal oxygen consumption (VO(2)max), and microalbuminuria in patients with Type 1 diabetes mellitus patients.

METHODS

We studied 10 patients, age range 10-18 years, with Type 1 diabetes who were normotensive and normoalbuminuric, with less than 10 years since diagnosis. Patients had normal renal function, without infections or clinical evidence of complications. Metabolic control was intensively adjusted in all patients. They underwent three consecutive physical exercise tests, reaching 100, 80 and 60% of the maximal cardiac frequency response.

RESULTS

Eight patients had adequate to regular metabolic control. All patients had lower than predicted VO(2)max values. At 60%, only three patients showed microalbuminuria in excess of 20 μg/min, two of them had inadequate metabolic control. Post-exercise microalbuminuria exceeded normal values in nine, seven and three patients when submitted to 100, 80 and 60% of exercise intensity, respectively.

CONCLUSIONS

Microalbuminuria increased with exercise intensity. Sex, body composition and VO(2)max were the main factors associated with microalbuminuria. The prognostic significance of albuminuria induced by intense exercise in these subjects with Type 1 diabetes is not yet known.

Exercise-induced changes in renal URAT1 activity and expression in rats

During exercise, the plasma urate levels and urinary excretion increase due to the enhanced purine degradation in skeletal muscle. Although urate transporter-1 (URAT1) is the main transporter responsible for the reabsorption of filtered urate, potential changes in its activity and expression during exercise have not been studied yet. Therefore, the effect of heavy muscle activity on renal URAT1 activity and expression was investigated in this study. Wistar rats were used in the study and the experimental design consisted of three groups: a control group, an exercise group where animals were exhausted once a day for 5 days, and a hyperuricemia group, which was induced by an uricase inhibitor, oxonic acid. URAT1 activity measurements were performed in isolated proximal tubule segments and expression of URAT1 mRNA and protein levels were determined by the reverse transcription polymerase chain reaction and western blot analyses, respectively. Increased citrate synthase activity in soleus muscle of exercised animals proved the efficiency of our exercise protocol. Proteinuria, glucosuria, and hypoglycemia were observed only in exercised animals; however, plasma and urinary urate levels were found to be elevated in both exercising and hyperuricemia groups. Moreover, in both of the groups URAT1 transporter activity was found to be increased despite the significant decrease in URAT1 protein levels. Considering the similar changes of urate metabolism observed in both exercising and hyperuricemic rats, our results suggest that exercise-induced changes in URAT1 expression and activity depend on the increased urate concentration in plasma.

The effect of heavy muscle activity on renal cytoresistance in rats

Cytoresistance is the term used to describe the response of the proximal tubule cells to various stress inducers via cholesterol accumulation. However, the role of extensive exercise as a renal insult has not been examined. In this study, the effect of heavy muscle activity on proximal tubule cytoresistance was investigated. Results obtained from rats subjected to running a treadmill for five days were compared to those of controls. Extensive muscle activity-induced soleus citrate synthase and blood lactate elevation were associated with normal MAP, RBF, and GFR. Blood electrolytes and cholesterol levels remained unchanged, whereas the total and free cholesterol accumulations in the proximal tubule cells of the exercised group were higher than controls. Cholesterol-loaded tubules were more resistant (as proved by LDH release) to an ATP-depleted/calcium overloaded second stress. These data clearly demonstrate that heavy muscle activity induces cholesterol accumulation in the proximal tubules of kidney, without influencing ATP generation.

Effects of exercise on the isoelectric patterns of erythropoietin

OBJECTIVES

Recombinant erythropoietin has a strong impact on aerobic power and is therefore one of the most potent doping agents in endurance sports. The anti-doping control of this synthetic hormone relies on the detection, in the urine, of its isoelectric pattern, which differs from that of the corresponding natural hormone, the latter being typically more acidic than the former. However, a small number of natural urinary patterns, referred to as "atypical patterns," are less acidic than the dominant form. Based on anecdotal evidence, the occurrence of such patterns seems to be related to particular strenuous exercises. This study aimed to demonstrate this relation using a strenuous exercise protocol.

DESIGN

Seven athletes took part in a training protocol including a series of supramaximal short-duration exercises. Urine and blood samples were collected throughout the protocols.

SETTINGS

World Cycling Center, Aigle, Switzerland, and research laboratories.

PARTICIPANTS

Seven top-level athletes (cyclists) were involved in this study.

MAIN OUTCOME MEASURES

Erythropoietin (EPO) isoelectric patterns were obtained by submitting blood and urine samples to isoelectric focusing. Additional protein dosages were performed.

RESULTS

Supramaximal short-duration exercises induced the transformation of typical urinary natural EPO patterns into atypical ones. None of the obtained atypical patterns fulfilled the 3 criteria mandatory for reporting an adverse analytical finding. Serum EPO patterns were not affected by the exercises that caused the transformation of urinary patterns.

CONCLUSION

An exercise-induced transient renal dysfunction is proposed as a hypothetic explanation for these observations that rely on parallel investigations of proteinuria in the same samples.

Renal alterations during exercise

Proteinuria and hematuria are common during exercise. Proteinuria is usually due to glomerular or tubular changes or to an excessive production of protein as in myeloma. Certain clinical conditions can, however, result in a functional or temporary proteinuria, especially during pregnancy, fever, orthostasis, or following physical activity. Sport-related proteinuria following marching, exercise, and stress, was first observed in soldiers after long marching. Prevalence of proteinuria during exercise ranges from 18% up to 100% depending on type of exercise and its intensity. A higher incidence of proteinuria has been observed in some sports requiring great exercise intensity and it is certainly related to muscular work intensity and would decrease after prolonged training. Indeed, exercise-induced proteinuria is strictly related to exercise intensity rather than to exercise duration. Exercise aggravates the proteinuria of various nephropathies and that of renal transplant recipients. The prevalence of hematuria is higher in the athletic than the general population and the main difference is that sport-related hematuria resolves spontaneously after physical exercise while hematuria found in nonathletic population can be chronic. Sport-induced hematuria is influenced by exercise duration and intensity. Among the mechanisms underlying the exercise induced hematuria are increased body temperature, hemolysis, increased production of free radicals, and excessive release of catecholamines. Lactic acidosis, generated during anaerobic conditions, causes the passage of erythrocytes into the urine, through increased glomerular permeability.

Glomerular Filtration Rate and Albumin Excretion After Maximal Exercise in Aging Sedentary and Active Men

BACKGROUND

From 30 years onwards there is a linear reduction of renal function of about 0.41% per year. Aging induces progressive impairment of glomeruli leading to an increase in protein excretion. The purpose of the present study was to investigate the effect of maximal exercise on glomerular filtration rate (GFR) and albumin excretion in an aging population.

METHODS

This is a cross-sectional study from 213 healthy men, sedentary or endurance-trained, aged 20-30 and 50-80 years submitted to maximal exercise on a cycle ergometer. Blood and urine samples were obtained at rest and after the strenuous exercise. We evaluated the GFR by measuring creatinine clearance and the urine albumin excretion rate.

RESULTS

After exercise, the older adults had a lesser reduction in GFR (mean 12%) than the young participants (mean 28%). As compared to those at rest, the increase of postexercise albumin excretion rates was lower in older participants (mean 7-fold) versus the young population (mean 20-fold). It appears that the exercise impact on some renal functions is related to the absolute load imposed on the individuals (r2 = 0.693).

CONCLUSION

As far as GFR and urine albumin excretion are concerned, regular endurance training does not induce any signs of potential incipient nephropathy in a healthy aging population.

Continuous versus intermittent exercise effects on urinary excretion of albumin and total protein

Several studies have reported post-exercise increases of urinary concentrations of plasma proteins. However, under normal conditions, through mechanisms of size and electrical charge selection, the kidney restricts the clearance of molecules as large as albumin. Post-exercise increases in albuminuria occur following the physiological stress of intense exercise, most likely as a result of the exercise induced blood acidity changes which lead to a change in the arrangement of the albumin molecule, and subsequently the filtration characteristics of the glomerular capillary wall. The purpose of the present study was therefore to determine the extent to which different types of exercise could induce a transient condition of post-exercise increases in the urinary output of total protein and albumin. All 14 males, who agreed to participate in the study, performed a continuous and an intermittent cycling protocol on a stationary bicycle ergometer. The results showed that: a) intermittent exercise had a greater influence than continuous exercise on the total output of urine albumin, and of urine total protein; b) concentrations of blood pH and blood lactate, were associated with changes in the clearance of urine albumin and urine total protein. Post-exercise proteinuria response seems to be transient and therefore renal trauma is not suspected at the early stages of observation. Furthermore, these results indicate that the kidney undergoes distinct physiological adjustments during exercise, and that these adjustments are relative to the intensity of the exercise stress.

Influence of running different distances on renal glomerular and tubular impairment in humans

Strenuous exercise has been claimed to modify renal glomerular and tubular function, the relative involvement of the two sites being unknown. These changes may be assessed by the determination of plasma high and low molecular mass proteins. A group of 13 man performed five runs (100, 400, 800, 1,500, 3,000 m) at maximal speed. The excretion rates and renal clearances of creatinine, albumin (Alb), beta 2-microglobulin (beta 2-m) and retinol-binding protein (RBP) were determined before and after each run. The glomerular filtration rate remained stable during the shorter runs and declined by about 40% during the longer runs. The excretion rate for Alb rose from 10-fold above the basal value (6 micrograms.min-1) for the 100 m to 49-fold for the 800 m and then declined for distances up to 3,000 m. The beta 2-m and RBP had a lesser initial increase, 3.5-(rest 55 ng.min-1) and 7.6-(rest 116 ng.min-1) fold, respectively, for the 100 m run and thereafter showed a higher excretion rate than Alb for the 400 m and 800 m runs. The renal clearances of these high (Alb) and low molecular mass (beta 2-m and RBP) proteins followed the changes observed for excretion rates. There was a linear relationship (r2 = 0.996) between plasma lactate concentration and total protein excretion in the postexercise period when taking all five runs into consideration. Glomerular permeability was primarily affected by the 100-m run while the longer runs modified both the glomerular and the tubular sites. To conclude, the present study demonstrated a differential response of the kidney to strenuous exercise with respect to the intensity and duration of the events.

Decreased glomerular basement membrane heparan sulfate proteoglycan in essential hypertension

Heparan sulfate proteoglycans are major components of the glomerular basement membrane and play a key role in the molecular organization and function of the basement membrane. Moreover, their presence is essential for maintenance of the selective permeability of the glomerular basement membrane. Recently, we isolated and characterized a novel small basement membrane-associated heparan sulfate proteoglycan from human aorta and kidney. Partial amino acid sequence data clearly show that this heparan sulfate proteoglycan is distinct from the large basement membrane-associated heparan sulfate proteoglycan (perlecan). Using specific monoclonal antibodies, we have shown that the novel heparan sulfate proteoglycan is located predominantly in the glomerular basement membrane and, to a lesser extent, in the basement membrane of tubuli. Turnover or, in the course of kidney diseases, degradation of heparan sulfate proteoglycan from glomerular basement membranes may lead to urinary excretion of heparan sulfate proteoglycan, which can be measured by a sensitive enzyme immunoassay. The aim of the present study was to analyze whether changes in the structure and function of glomerular basement membranes can be directly detected by measurement of the excretion of a component of this basement membrane, eg, heparan sulfate proteoglycan into urine. The excretion of this small heparan sulfate proteoglycan was compared after physical exercise in normotensive and hypertensive subjects. Normotensive subjects and treated, essential hypertensive patients underwent a standardized workload on a bicycle ergometer. Biochemical characterization of the urinary proteins and heparan sulfate proteoglycan was performed before and 15 and 45 minutes after exercises.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline phosphatase isozymes of serum and urine and urinary protein in young men before and after running 3 km

Urine samples were collected from seven healthy male students 1 h before (control fraction) and 5-15 min (5-15 min fraction), 1 h (1-h fraction) and 3 h (3-h fraction) after running 3 km at a perceived exertion equal to approximately 15-17 Borg's scale. Venous blood was also collected from the subjects 1 h before and 1 h after the run. Urine was studied by measuring protein excretion, patterns of sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of proteins, total alkaline phosphatase (ALP) excretion, intestinal alkaline phosphatase (IAP) excretion and ALP isozyme analysis by PAGE. Serum ALP was studied by measuring the total ALP activity and isozyme analysis by PAGE. The following results were observed: firstly, an increase was seen in the excretion of total protein, total ALP and IAP after the exercise. Statistical significance was seen in the first two of these parameters; secondly, albumin was the only detectable protein band in the control, 5-15 min and 3-h fraction by SDS-PAGE; thirdly, no significant changes were seen in total ALP activity and ALP isozymes in the serum; and fourthly, three to five ALP bands (bands 1, 2, 3, 4 and 5, from the cathodal side) were detected in the zymograms of urinary ALP. Bands 1-3 were high molecular mass ALP. Bands 4 and 5 were intestine-like and liver-like ALP, respectively. An increase of ALP activity of high molecular mass ALP and/or decrease of that of band 5 or appearance of band 4 were seen in the 1-h fraction, in comparison to the control fraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobic threshold can provoke microalbuminuria in non-insulin-dependent diabetics

We examined two groups of non-insulin-dependent diabetic men (group A, 13 patients without microalbuminuria; group B, 9 patients with intermittent microalbuminuria) to ascertain whether the anaerobic threshold (AT) can provoke microalbuminuria, comparing them with 12 healthy subjects matched for age and sex (group C). All subjects exercised on a bicycle ergometer until the AT was reached. In intermittent microalbuminuria, the albumin:creatinine ratio (ACR) was over 0.25 mg/mmol.Cr 1-3-fold in 5 measurements. The ACR after exercise was increased to over 0.25 mg/mmol.Cr in 4/9 cases in group B (P < 0.05), in 2/13 cases in group A, but not at all in group C. We also studied the mechanism of exercise-induced microalbuminuria. In group B, ACR before exercise correlated positively with the baseline plasma glucose. Furthermore, positive correlation was found between ACR after exercise and HbA1c in group B. The AT did not affect the urinary beta 2-microglobulin in any groups. The plasma atrial natriuretic factor (ANF) after exercise was elevated most prominently in group B (P < 0.05). Positive correlation was found between increments of ACR and increments of plasma ANF after exercise in group B. We conclude that the AT can provoke microalbuminuria in some non-insulin-dependent diabetics. The plasma ANF and metabolic control may play an important role in the pathophysiology of exercise-induced microalbuminuria.

Involvement of the renin angiotensin system in the pathogenesis of postexercise proteinuria

Proteinuria after strenuous exercise is common in healthy subjects. The pathophysiologic mechanism of postexercise proteinuria (PEP) is not clear, although the phenomenon has long been known and many explanatory theories have been proposed. It is widely recognized that angiotensin II may increase filtration of protein through the glomerular membrane, and that its concentration in plasma increases during exercise. The aim of this study was to evaluate possible involvement of angiotensin II in the pathogenesis of PEP. Of 25 young volunteers who performed maximal aerobic exercise, eight showed PEP. The exercise was repeated after an interval of at least one week, now 90 minutes after administration of captopril (25 mg). Captopril did not affect the achieved work load of the maximal blood pressure and heart rate during the exercise, but PEP was not found. As it was possible to prevent PEP by administering an angiotensin-converting enzyme inhibitor, the study supports the theory that the renin angiotensin system is involved in the pathogenesis of PEP.

Intensity-related exercise albuminuria in insulin dependent diabetic patients

Normoalbuminuric insulin-dependent diabetic (IDDM) patients may present higher rates of urinary albumin excretion after submaximal exercise at a standard intensity. To evaluate whether the urinary albumin excretion of IDDM patients is increased after maximal and submaximal exercise when exercise intensities are adjusted according to individual lactate thresholds, 16 normoalbuminuric IDDM patients (mean time from diagnosis 8 years) and 13 normal controls exercised for 20 min at intensities corresponding to 90% of the first and second lactate thresholds and to maximal tolerance on different days. Urinary albumin excretion, blood lactate concentration, heart rate and blood pressure were measured. Metabolic and cardiovascular responses to submaximal and maximal exercise were similar for patients and controls. After exercise at 90% of the first lactate threshold neither patients or controls demonstrated significant changes in urinary albumin excretion. After exercise at 90% of the second lactate threshold both patients and controls demonstrated a similar increase in urinary albumin excretion. After maximal exercise both patients and controls demonstrated marked and similar elevation in the urinary albumin excretion. There was a significant correlation (r = 0.74, P < 0.001) between blood lactate levels at the end of exercise and the decimal logarithm of post-exercise urinary albumin excretion of the diabetic patients. Thus, when exercise intensities are adjusted for lactate thresholds, normoalbuminuric IDDM patients present normal intensity-related urinary albumin excretion during exercise. These data suggest that previously observed differences in exercise induced albuminuria in IDDM patients might be related to inappropriate standardization of submaximal exercise intensities.

Protein excretion after prolonged exercise

Random urine samples were obtained from 16 healthy subjects (nine men and seven women) before and after a 100 Km hill walk for the estimation of total protein, albumin, N-acetyl-beta-glucosaminidase (NAG), retinol binding protein (RBP) and creatinine. The excretion of total protein, albumin and NAG (expressed in relation to creatinine excretion) increased significantly after the walk. The relative clearance of protein and albumin also increased. In four subjects serial measurements were made for 4 days and the excretion of albumin and NAG on the fourth day were similar to the pre-walk values. We conclude that proteinuria of prolonged exercise is at least partly due to reduced tubular reabsorption.

Urine screening in outdoor volunteers: day versus night versus 24 hour collection

Urine constituents were measured in 12 healthy outdoor volunteers on four occasions within a month. Day, night, and 24 hour collection periods were compared. Measurements made on the four occasions did not differ. The amount of water, creatinine, electrolytes, proteins, and enzymes were higher during the day (up to three fold, p always less than 0.05), while equal amounts of amino acids were excreted in the day and the night period. A comparison of all values from all individuals for all four sampling occasions showed that the variation was lowest in the 24 hour samples. Relating the values to creatinine did not consistently reduce the variation. Twenty-four hour samples correlated better with the day than with the night samples. Day and night samples did not correlate. Twenty-four hour collection is superior to day or night collection in healthy outdoor volunteers. Based on the normal variation of values found in the present study, criteria for suspected kidney damage and therefore for the withdrawal of drugs in pharmacological studies can be defined for each collection period.

Renal protein excretion after exercise in man

Thirteen men were submitted to graded exhaustive cycle exercise to determine the kinetics of proteinuria in the recovery period. Venous blood samples were analysed for haematocrit, lactate, creatinine, total protein and albumin for 1 h following exercise. Urine samples were collected during a 3-h recovery period. Total protein, albumin, and creatinine levels were determined for these samples. Total protein and albumin urinary excretion increased to 581 and 315 micrograms min-1, respectively, at the end of the 1st h of recovery as compared to 42 and 15 micrograms.min-1 for resting values. Plasma volume returned to pre-exercise levels between 30 and 60 min after cessation of exercise, while urinary total protein and albumin content still remained above the resting values for the following 2 h. Both post-exercise urinary total protein and albumin excretion followed a logarithmic decline with the same half-life of 54 min, thus requiring about 4 h to regain resting values. The reduction of plasma volume and the degree of dehydration do not seem to be involved in the process. The present study indicates the delayed recovery of protein handling by the kidney, as compared with other biochemical parameters, and provides accurate information on the kinetics of post-exercise proteinuria.