Severe West Nile virus meningoencephalitis in a pediatric renal transplant recipient: successful recovery and long-term neuropsychological outcome

West Nile Virus is an arbovirus that has rapidly spread throughout the United States since the first case was described in Queens, New York in 1999. There has been increasing reports of both community-acquired and organ-derived infections in renal transplant recipients. In immunocompromised individuals, WNV infection is a life-threatening disease with significant neurological morbidity. We report the only pediatric case of community-acquired WNV disease in a renal transplant recipient to undergo detailed long-term neuropsychological assessment. Increased surveillance and prompt treatment of WNV meningoencephalitis is critical, and our report highlights the effectiveness of immunosuppression reduction without compromising allograft outcomes.

Hodgkin lymphoma in a renal transplant recipient associated with low peripheral blood Epstein-Barr virus genome copies

Posttransplant lymphoproliferative disorders are often accompanied by >500 Epstein-Barr virus (EBV) genome copies/10(5) lymphocytes, and they occur shortly after transplantation. Hodgkin lymphoma occurs rarely after transplantation, appearing a mean of 4.2 years posttransplant, and although Hodgkin lymphoma has strong associations with EBV, no quantitative analysis of peripheral blood EBV genome copies has been reported. A mixed cellularity Hodgkin lymphoma developed in a 17-year-old boy 4 years after a renal transplant. Serial EBV genome copy numbers from blood by competitive polymerase chain reaction had been obtained to assess for lymphoproliferative disease. Epstein-Barr virus genome copy numbers peaked at 500 copies/10(5) lymphocytes 8 months prior to Hodgkin lymphoma diagnosis but fell to 8 copies/10(5) lymphocytes at diagnosis. Reliance on EBV levels greater than 500 copies may result in delay of biopsy and diagnosis of Hodgkin disease in the posttransplant setting.

Low birth weight-associated adult hypertension in the rat

Epidemiological surveys have suggested that intrauterine growth retardation is a risk factor for the development of hypertension in later life. A rat model of intrauterine growth retardation, induced by maternal low-protein diet during the second half of pregnancy, was used to study the relationship between birth weight and adult hypertension. The offspring were born at term and were allowed to nurse normally until weaned to standard chow at 4 weeks of age. They had 15% lower birth weights than control offspring, with complete catch-up growth by age 4 weeks. Both females and males developed progressively worsening hypertension beginning at 8 weeks. The 11-month survival rate was 69% versus 100% in control animals. During the early stages of the hypertension, plasma creatinine was normal, plasma sodium concentration was slightly higher than that of control animals, plasma renin activity was suppressed, and the males had mild proteinuria. Renal function remained normal throughout the 11-month observation period, but plasma renin activity gradually rose above control values. Angiotensin-converting enzyme inhibition by enalapril, begun at 8 weeks of age, was effective in completely normalizing the blood pressure, but did not totally prevent the extra mortality. Sprague-Dawley and Wistar rat strains developed equally severe hypertension after maternal protein deprivation, despite their different susceptibilities to nephrosclerosis with aging. In conclusion, maternal low-protein diet resulted in low birth weight and adult hypertension in the rat. Primary sodium retention and expanded extracellular volume may be critical factors during the development of the hypertension.

Prenatal programming of adult hypertension in the rat

BACKGROUND

Epidemiological studies have suggested that low birthweight is a risk factor for the development of essential hypertension in adulthood, but the mechanism is unknown.

METHODS

A rat model of intrauterine growth retardation was employed. Pregnant Sprague-Dawley rats were kept on 6% protein or on control isocaloric 20% protein diet from gestational day 12 until term. Systolic blood pressures of the offspring were monitored by the tail cuff method. Apoptosis was determined by the TUNEL method, cell proliferation by anti-Ki67 antibody, and the total number of glomeruli by the maceration method. Results are mean +/- SD.

RESULTS

The kidney and body sizes of the offspring from the low-protein pregnancies (LP) were proportionately decreased at birth. Full catch-up growth occurred during the first two weeks of life. The kidneys were normal by standard histology but exhibited increased apoptosis without increased cell proliferation at eight weeks of age. The total number of glomeruli per kidney was decreased by 28% in males (P < 0.001) and by 29% in females (P < 0.01). By eight weeks of age, both male and female LP had systolic blood pressures that were 20 to 25 mm Hg higher than those of control animals (P < 0.001), and their 18-month survival was significantly decreased (44 vs. 93%, P < 0.01). During the prehypertensive stage, at four weeks of age, PRA in LP was low (1.7 +/- 1.4 vs. 19.7 +/- 5.5 ng/mL/hour in males, P < 0.0001; 4.9 +/- 2.2 vs. 14.9 +/- 7.2 ng/mL/hour in females, P < 0.0005), and aldosterone was high (93 +/- 15 vs. 54 +/- 27 pg/mL in males, P < 0. 005; 93 +/- 20 vs. 48 +/- 20 pg/mL in females, P < 0.0001). Smaller but significant differences persisted at eight weeks of age.

CONCLUSIONS

Adult blood pressure profile is susceptible to prenatal programming by maternal low-protein diet in the rat. The mechanism may involve an altered renin-aldosterone axis and a deficit in total nephron number.

Aggressive treatment of severe idiopathic focal segmental glomerulosclerosis

When focal segmental glomerulosclerosis (FSGS) has reached the stage of chronic renal insufficiency, further progression is usually considered inevitable. African-American patients are believed to exhibit a particularly aggressive form of FSGS. We have treated five African-American patients, aged 11-18 years, with FSGS and reduced renal function using intensive intravenous methylprednisolone protocol, combined with chlorambucil in three cases. All patients had a pretreatment creatinine clearance of less than 50 ml/min per 1.73 m2. Three patients responded with normalization of creatinine clearance and serum albumin levels and had no or only minimal proteinuria at latest follow-up. One patient showed no improvement and one patient progressed to end-stage renal disease. These findings indicate, for the first time, that even severe FSGS may respond to aggressive methylprednisolone with or without alkylating agent treatment, and that African-American race does not preclude a favorable response.

Treatment practices of FSGS among North American pediatric nephrologists

A survey of North American pediatric nephrologists was conducted to assess the variability in the treatment of primary steroid-resistant focal segmental glomerulosclerosis (FSGS) of native kidneys. The most widely used immunosuppressive drug was cyclosporin A, with 73.9% using it often or sometimes. Only 44.3% used intravenous methylprednisolone combined with an alkylating agent at least sometimes; the use of methylprednisolone without cytotoxic drugs was slightly more common. Prolonged oral steroid therapy (>3 months) was used often or sometimes by 50.3%. The use of angiotensin converting enzyme inhibitors was very common, while lipid-lowering agents were rarely used. The variability in the treatment of FSGS most likely results from lack of evidence-based information and underscores the need for controlled pediatric multicenter treatment trials.

Water transport in the immature rabbit collecting duct

Immature animals have limited ability to concentrate the urine. This is in part the result of end-organ resistance to arginine vasopressin (AVP). To characterize this response, we measured water absorption in microperfused cortical collecting ducts (iCCD) and outer medullary CD (iOMCD) derived from 2- to 12-day-old rabbits. The roles of adenosine 3',5'-cyclic monophosphate (cAMP) and prostaglandins were investigated. Baseline osmotic water permeability (L(p), 10(-7) cm/atm per s) in the iCCD (20.3+/-2.4) and iOMCD (19.7+/-5.6) was not different from mature CCD (mCCD) (14.6+/-3.1). After AVP, L(p) in the iCCD (46.7+/-10.0) was significantly lower than in the mCCD (114.3+/-21.8). Neither stimulation with cAMP (85.6+/-51.3) nor inhibition of endogenous prostaglandin production with indomethacin (57.6+/-29.8) abolished the blunted response to AVP in the iCCD. We conclude that AVP-stimulated water transport in the iCCD is impaired. The disruption in AVP response is, at least in part, localized distal to cAMP, and is not mediated by prostaglandins.

Developmental regulation of ENaC subunit mRNA levels in rat kidney

To assess the role of distal nephron apical Na channel (ENaC) gene expression in Na wasting by the immature kidney, ENaC alpha-, beta-, and gamma-subunit mRNA levels were examined in the rat by RT-PCR. In microdissected nephron segments, all three ENaC subunit mRNAs were detected in the distal convoluted tubule, connecting tubule, cortical collecting duct, and outer medullary collecting duct. The inner medullary collecting duct and all other nephron segments were consistently negative. The mRNA levels were quantified in kidneys at different developmental stages by multiplex RT-PCR with "primer dropping," with endoplasmic reticulum-specific cyclophilin mRNA as an internal standard. All three ENaC mRNA levels were low or undetectable on gestational day 16 and only slightly higher 3 days before birth. A sharp rise was observed between 3 days before and 1-3 days after birth; the levels at postnatal days 1-3 were already similar to those of adult kidneys. The results suggest that ENaC subunit gene expression is not a limiting factor in the full-term newborn rat kidney, but low levels of expression may limit distal Na absorption in more immature kidneys, such as those of very premature human infants.

Distribution and regulation of guanylyl cyclase type B in the rat nephron

C-type natriuretic peptide (CNP) has been localized to the proximal and distal nephron. In this study, we examined the distribution and regulation of the CNP receptor, guanylyl cyclase type B (GC-B), in the rat kidney. GC-B mRNA was detected most frequently in microdissected glomeruli, thin and thick limbs of the loop of Henle, and outer and inner medullary collecting ducts by reverse transcription-polymerase chain reaction (RT-PCR). This pattern of expression is supported by immunofluorescent staining, using anti-GC-B-specific antiserum. Nearly equivalent levels of GC-B and guanylyl cyclase type A (GC-A) mRNAs were found by quantitative RT-PCR (5,662 +/- 1,622 and 5,187 +/- 1,204 molecules of cDNA/microgram total RNA, respectively; means +/- SE, n = 6). Renal inner medulla GC-B mRNA levels, but not renal CNP mRNA levels, were 3.2-fold greater in hypervolemic and 2.3-fold less in hypovolemic rats compared with euvolemic controls. Immunohistochemical staining also supports a greater GC-B expression with increased volume status. These data link hydration status and GC-B expression and suggest an additional and novel mechanism for regulating intravascular volume.

Ontogeny of cortical collecting duct sodium transport

The postnatal maturation of Na transport in the rabbit cortical collecting duct (CCD) was investigated. CCD segments from rabbits of three different age groups (3-9 days, 10-15 days, and 22-27 days) were perfused in vitro. Lumen-to-bath 22Na fluxes were 38.5 +/- 4.7, 17.0 +/- 2.9, and 30.2 +/- 4.0 pmol.mm-1.min-1 in the three groups, respectively. The high flux in the youngest group was explained by a high passive flux (28.3 +/- 4.2 pmol.mm-1.min-1) determined in the presence of ouabain; the passive 22Na flux in the two other groups (7.1 +/- 2.6 and 3.1 +/- 2.4 pmol.mm-1.min-1) was not significantly different from previously reported adult values. Ouabain-sensitive 22Na flux, reflecting active transport, was low in the two younger groups (10.3 +/- 2.5 and 9.9 +/- 1.9 pmol.mm-1.min-1), but exhibited a rapid increase to 27.1 +/- 2.6 pmol.mm-1.min-1 by 22-27 days of age. In vivo glucocorticoid pretreatment did not affect the Na transport in any age group. Mineralocorticoid pretreatment for 2 days had no effect in the two younger groups, but increased lumen-to-bath 22Na flux from 30.2 +/- 4.0 to 51.1 +/- 4.3 pmol.mm-1.min-1 in the 22- to 27-day-old group. The findings demonstrate that the maturation of rabbit CCD Na transport occurs in two stages, with the first consisting of a decrease in passive permeability during the first 2 wk of life, followed by an increase in active transport and simultaneous development of mineralocorticoid responsiveness.

Renal acidification in children with idiopathic hypercalciuria

Distal renal tubular acidosis is frequently associated with hypercalciuria. To further investigate the cause-and-effect relationships between the two conditions, we examined 20 children (5 to 18 years of age) with idiopathic hypercalciuria for evidence of renal tubular acidosis. Serum electrolytes and urine citrate levels were normal in all subjects. After a single dose of furosemide, 1 of the 20 subjects did not show a decrease in urine pH < 5.5, which suggests an acidification defect in the cortical collecting duct. Three other patients failed to show an increase in urine-minus-blood partial pressure of carbon dioxide > 20 mmHg after urine alkalinization with orally administered acetazolamide, a finding compatible with a rate-dependent distal renal tubular acidosis. These four subjects underwent acute acid loading with arginine hydrochloride. In all four subjects urine pH decreased < 5.5 but urinary ammonium excretion failed to increase normally; this supports the diagnosis of a defect in distal acidification. Four of six patients with nephrolithiasis had evidence of distal renal tubular acidosis, in contrast to none of the 14 patients without stones (p = 0.003). We conclude that distal acidification abilities seem to be intact in children with hypercalciuria in the absence of nephrolithiasis. We speculate that calcium precipitation may lead to tubular damage, including distal renal tubular acidosis.

Synthesis and localization of C-type natriuretic peptide in mammalian kidney

We have previously demonstrated the synthesis of atrial natriuretic factor (ANF) in the distal cortical nephron of the rat kidney. We now report the synthesis of C-type natriuretic peptide (CNP) in the rat, mouse, and human nephron. CNP mRNA was initially detected in the rat and mouse kidney, as well as in three transformed cell lines isolated from the proximal and distal nephron, using reverse transcription-polymerase chain reaction (RT-PCR). Confirmation of the kidney PCR product was performed by nucleotide sequence analysis and Southern hybridization. Northern hybridization of rat brain CNP cDNA to human kidney polyadenylated RNA detected a 1.4-kb gene transcript. Rat nephron segments were microdissected and subjected to RT-PCR to localize CNP mRNA. CNP mRNA was detected in the proximal convoluted tubule, cortical collecting duct, medullary thick limbs, and inner medullary collecting ducts. CNP, as detected by immunohistochemistry, was found to colocalize with CNP mRNA.

Response of cortical collecting ducts from remnant kidneys to arginine vasopressin

Chronic renal failure is associated with impaired urine concentration. Previous studies have demonstrated that cortical collecting ducts (CCD) from uremic rabbits (with remnant kidneys) have an impaired response to arginine vasopressin (AVP). To determine whether this defect is an early, integral component of compensatory renal growth by the remnant kidney, we studied the response of CCD derived from rabbits one week after 75% nephrectomy. At one week, hypertrophy and adaptation in sodium transport are fully developed, but azotemia and interstitial fibrosis are absent. The animals with remnant kidneys failed to respond normally to water deprivation and dDAVP (maximum urine osmolality 738 +/- 29.1 mOsm/kg compared to 1378 +/- 207 in sham operated). However, in isolated, perfused CCD from remnant kidneys, AVP stimulated hydraulic water permeability to the same extent as in normal CCD or CCD from sham operated animals. AVP-induced cAMP generation per mm tubule length was significantly higher in the CCD from remnant kidneys (137.4 +/- 14.5 fmol/mm) than in the control group (82.4 +/- 11.9 fmol/mm), but not different when expressed per micrograms protein. These studies demonstrate that one week after reduction in renal mass there is no defect in the response of CCD to AVP, suggesting that the mechanisms responsible for the hyposthenuria after loss of renal mass are not related to any intrinsic cellular changes that occur in CCD early during compensatory renal growth.

Mechanism of sodium transport inhibition by epidermal growth factor in cortical collecting ducts

Epidermal growth factor (EGF) inhibits Na transport in the cortical collecting ducts (CCD). To gain insight into the signal transduction of this effect, several potential mechanisms were examined in rabbit CCD perfused in vitro. Pretreatment with pertussis toxin, indomethacin, or the protein kinase C inhibitor H7 did not prevent the acute 34-50% decrease in lumen-to-bath 22Na flux (JNa) on exposure to peritubular EGF, indicating that the inhibition is not mediated by a Gi protein, prostaglandin E2 (PGE2), or protein kinase C. Inhibition of the basolateral Na-H exchanger was also without an effect. Lowering the bath Ca concentration from 1.2 to 0.11 mM did not prevent the inhibition of JNa by EGF (JNa decreased significantly by 38.7 +/- 6.9% and 29.1 +/- 5.3%, respectively); in contrast, reduction of the bath free Ca to 0.005 mM totally abolished the effect of EGF. The response to EGF was also assessed in the setting of chronic stimulation of Na transport; inhibition of JNa by EGF was still observed in CCD from remnant kidneys and in CCD from mineralocorticoid-treated rabbits. The results demonstrate that the inhibition of CCD Na transport by EGF is dependent on peritubular Ca. This suggests that the signal transduction involves Ca influx across the basolateral membrane and that increased cytosolic free Ca may be a common pathway for the counterregulatory control of Na reabsorption by several agonists.

Role of mineralocorticoids in adaptation of rabbit cortical collecting duct after loss of renal mass

The mechanism of compensatory adaptation and hypertrophy of the cortical collecting duct (CCD) was studied by in vitro microperfusion technique after surgical loss of functioning nephrons in the rabbit. Sodium transport was increased at 1 wk (lumen-to-bath sodium transport of 127 +2- 9 vs. 61 +/- 11 pmol.mm-1.min-1 in sham-operated animals, P less than 0.01) and 3 wk (111 +/- 19 vs. 54 +/- 7 pmol.mm-1.min-1, P less than 0.05) but not 16 h (81 +/- 13 vs. 78 +/- 8 pmol.mm-1.min-1) after loss of renal mass. The functional adaptation was accompanied by an increase in the size of the CCD. A rise in plasma aldosterone levels preceded and accompanied the increased sodium transport rate. Adrenalectomy at the time of reduction of renal mass totally prevented the development of both hypertrophy and sodium transport adaptation (sodium transport 15 +/- 8 pmol.mm-1.min-1). When adrenalectomy was combined with clamping the plasma aldosterone level in the nonstressed physiological range, compensatory hypertrophy and adaptation also failed to develop (sodium transport, 66 +/- 10 pmol.mm-1.min-1), but with high-dose aldosterone replacement both the hypertrophy and adaptation of sodium transport (130 +/- 23 pmol.mm-1.min-1) were restored. The results document the importance of increased mineralocorticoid activity in the development of compensatory hypertrophy and adaptation of sodium transport in rabbit CCD after loss of renal mass.

Compensatory hypertrophy and adaptation in the cortical collecting duct

The cortical collecting duct (CCD) undergoes hypertrophy and functional adaptation following reduction of renal mass. The nature and mechanisms of these changes have been investigated using microperfusion of isolated CCD from rabbit remnant kidneys. By 1 week after reduction of renal mass, tubule hypertrophy and increased sodium transport are fully developed. The transport adaptations are specific or selective, since bicarbonate transport in these CCD is unchanged. Mineralocorticoids may play an important role in the hypertrophy and increased sodium transport, since plasma aldosterone increases early after reduction of renal mass. Also, adrenalectomy abolishes the changes in size and sodium transport, even with supplementation of aldosterone to unstressed physiologic levels. Epidermal growth factor also has immediate effects on CCD sodium transport; however, the direction of the effect is opposite--an inhibition of transport.

Increased sodium transport by cortical collecting tubules from remnant kidneys

To determine whether intrinsic changes in cortical collecting tubule (CCT) transport contribute to the maintenance of sodium and acid-base balance after loss of renal mass, we studied transport functions in isolated perfused CCT from rabbit remnant kidneys. The rabbits were sacrificed three weeks after surgical reduction of renal mass (by 3/4 to 7/8) at which time they were mildly azotemic but had no systemic electrolyte or acid-base disturbances. When perfused by standard methods in vitro, CCT from remnant kidneys exhibited sodium transport rates (lumen-to-bath 22Na-flux) approximately twice as high as those in CCT from control animals (111 +/- 19 vs. 54 +/- 7 pmol/min mm, P less than 0.02). A similar difference was present in the ouabain-sensitive sodium fluxes (81 +/- 16 vs. 39 +/- 8 pmol/min mm, P less than 0.05). In contrast, there were no significant differences in net bicarbonate transport. Significant hypertrophy of the remnant kidney CCT was reflected by 30 to 45% increases in tubule diameters. To examine the possible role of differences in food intake, we studied a separate group of weight-matched, pair-fed sham-operated and remnant kidney rabbits. Similar differences in total and ouabain-sensitive 22Na-flux, and in tubule size persisted in the pair-fed animals. A dissociation between active sodium transport and tubule hypertrophy was documented in the outer medullary collecting tubule: despite the lack of active sodium transport, hypertrophy was present. Our studies show that loss of renal mass results in a selective augmentation of certain transport processes in the CCT, implying selective or specific signals and mechanisms.

Effect of epidermal growth factor on sodium transport in the cortical collecting tubule

Receptors for epidermal growth factor (EGF) have been demonstrated in the distal tubule. To determine whether there are acute functional correlates, we studied the effect of EGF on cortical collecting tubule (CCT) transepithelial voltage and transport of sodium and bicarbonate. Rabbit CCT were perfused in vitro and EGF was added to either the bathing medium or the luminal perfusate after base-line measurements of transport. Peritubular EGF in concentrations of 0.1 to 100 ng/ml (1.7 X 10(-11) to 1.7 X 10(-8) M) decreased sodium reabsorption, measured as 22Na absorption from the lumen, by 44-59%. There was a corresponding fall in the lumen-negative transepithelial voltage. Lower doses of EGF were without effect on transepithelial voltage or sodium transport. Pretreatment of the tubules with ouabain eliminated the effect of EGF on sodium transport. In contrast to peritubular EGF, luminal EGF (100 ng/ml) did not affect sodium transport. Peritubular EGF had no effect on either bicarbonate secretion or net bicarbonate transport in the CCT and no effect on net bicarbonate reabsorption in the medullary collecting tubule. Using the pH sensitive, fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, no change in principal cell intracellular pH was found after peritubular EGF. Two other growth factors, insulin and insulin-like growth factor I were without effect on sodium transport. We conclude that EGF inhibits active sodium absorption in CCT via receptors located at the basolateral membrane.

Control of bicarbonate transport in collecting tubules from normal and remnant kidneys

Bicarbonate transport in the rabbit cortical collecting tubule (CCT) and outer medullary collecting tubule (MCT) in vitro was studied under two types of conditions that were anticipated to alter distal tubule bicarbonate transport: 1) reduction of renal mass, and 2) acid and base loading in vivo. Bicarbonate secretion (both total and acetazolamide sensitive) and bicarbonate reabsorption (studied separately) in CCT and bicarbonate reabsorption in the MCT were not different between tubules from normal and remnant kidneys. The control or conditioning of the separate processes of bicarbonate secretion and bicarbonate reabsorption was also studied in CCT from normal and remnant kidneys. Bicarbonate secretion was not increased by base-loading animals with either normal or remnant kidneys. In contrast, bicarbonate secretion was consistently decreased by acid loading (studied in CCT from remnant kidneys). Bicarbonate reabsorption in the CCT was not altered by acid or base loads given to animals with normal kidneys. And bicarbonate reabsorption in MCT was not increased by acid loading of animals with remnant kidneys. These studies demonstrate that bicarbonate transport (and its conditioning by acid or base loads in vivo) in both CCT and MCT in vitro is not altered by reduction of renal mass in rabbits. The predominant conditioning effect of acid or base loads in vivo is for acid loads to inhibit CCT bicarbonate secretion.

The effects of polycations on vascular permeability in the rat. A proposed role for charge sites

This study investigated whether charge sites in the walls of the microvasculature may play a role in maintaining the impermeability of the nonrenal capillaries to albumin. All experiments were performed in nephrectomized rats, studied in the awake state. The intravenous injection of protamine sulfate (4 mg/100 g body wt dissolved in 0.9% saline) was followed by a mean increase of 29.1% in hematocrit and a decrease of 28.4% in plasma albumin concentration over a 10-min period, indicating a significant 50-60% loss of albumin from the vascular space; a finding confirmed by studies using exogenous 125I-labeled albumin. Changes persisted for the remaining 80 min of observation, and could be reproduced by the injection of two other polycations, hexadimethrine and poly-l-lysine. These effects were not prevented by the antihistamine diphenhydramine hydrochloride. In contrast to 125I-labeled albumin, 14C-labeled neutral dextran of comparable size was not confined to the vascular space; its apparent volume of distribution progressively increased during the 90 min of observation. Intravenous injection of protamine sulfate was followed by a significantly smaller loss of 14C-dextran (36.5%) than albumin (59.1%) from the vascular space (P less than 0.01). Protamine sulfate could not be demonstrated to result in any changes in the physicochemical characteristics of albumin. These observations suggest that the negative charge sites present in nonglomerular capillary walls have functions similar to equivalent sites present in the glomerular capillaries. Thus, charge sites could contribute to the low permeability of the microvasculature to negatively charged macromolecules such as albumin. This may be an important mechanism for retaining albumin in the vascular space and preventing edema formation in health.

Isolated proteinuria: analysis of a school-age population

Proteinuria was found in at least one of four specimens in 10.7% and in at least two of four specimens in 2.5% of 8,594 schoolchildren, ages 8 to 15 years. To determine the risk of renal disease in isolated proteinuria, the screening program was followed by a systematic clinical evaluation of the proteinuric children. After those with both proteinuria and hematuria were excluded, none of the remaining children was found to have an overt renal disease. Despite urinary protein concentrations in excess of 1,000 mg/dl and protein excretion rates of up to 1 gm in 24 hours, proteinuria proved to be transient or intermittent in every child when a large enough number of urine samples was tested. Children with the highest protein excretion rates (more than 6 mg/hour/m2 at night or more than 20 mg/hour/m2 during the day) and those with the most persistent patterns of proteinuria underwent renal function studies, intravenous pyelography, and renal biopsy. No significant abnormalities was found. Mild nonspecific changes were seen in 12 of 28 biopsies, with mesangial deposits in four. The results show that if hematuria and other signs have been excluded, a benign renal morphologic picture is almost invariably to be expected in intermittent proteinuria; renal biopsy, therefore, is not indicated.

Glomerular charge and urinary protein excretion: effects of systemic and intrarenal polycation infusion in the rat

To study the role of the fixed anionic sites of the glomerular capillary wall in protein filtration, the negative charges were neutralized in vivo. With systemic infusion of the polycation protamine sulfate, glomerular staining for polyanion was reduced and protein excretion increased by 154%. To avoid systemic side effects in subsequent studies, small doses of a polycation were infused directly into one renal artery. The contralateral kidney was infused with the vehicle solution. Albumin excretion from the experimental kidneys in the first 1-hr collection after infusing 0.5 mg protamine sulfate was 24.3 +/- 6.3 micrograms/min/kidney (N = 13; P less than 0.01). Albuminuria declined during the subsequent 3 hr with a second infusion inducing a second proteinuric response. The degree and longevity of the albuminuric response was correlated directly to the dose of protamine sulfate. The polycations hexadimethrine and poly-l-lysine also induced proteinuria. The increased protein excretion consisted of albumin; the excretion of nonalbumin protein was identical in the experimental and control kidneys. Hemodynamic factors did not explain the increase in proteinuria. Morphologically, the polycation-treated kidneys showed scanty foot process fusion and a decrease in free negative sites in the lamina rarae of the glomerular basement membrane. The results strongly support an important role for glomerular charge in preventing filtration of circulating plasma albumin.

Microscopic hematuria in school children: epidemiology and clinicopathologic evaluation

An unselected population of 8,954 children, age 8 to 15 years, was screened for hematuria. Four urine specimens from each were examined; microscopic hematuria was found in one or more specimens in 4.1%, and in two or more specimens in 1.1% of the children. The prevalence was not age or sex dependent. Those with two or more positive samples were re-examined twice during a half-year period: 33 had hematuria of 6 or more RBC/0.9 mm3, or more than 100,000 RBC/hour, on both occasions; renal biopsy performed on 28 of them revealed two cases of IgA-IgG nephropathy, one of focal segmental sclerosis, one of extracapillary glomerulonephritis, and one of possible hereditary nephritis. In 12 patients the biopsy was entirely normal; the rest showed equivocal changes. Co-existing proteinuria and the degree of hematuria correlated well with the severity of the morphologic alterations. Pathologic findings in microscopic hematuria seem to be less frequent than in hematuria in general; in most such patients, renal biopsy is probably not indicated. In some children the low-grade hematuria may merely represent the upper end of physiologic variation.