Low molecular weight proteins in children with renal disease

Low molecular weight proteins are of interest in children because their increased urinary excretion is a sign of renal tubular disease and their increased plasma concentration is inversely related to glomerular filtration rate. These proteins include ₂-microglobulin (B2M), retinolbinding protein (RBP), ₁-microgloulin (A1M) and lysozyme. B2M is unstable in acid urine, in contrast to RBP and A1M which are more stable. Any increase in the urinary excretion of B2M or RBP is highly specific for tubular disease, whereas increased excretion of A1M may be seen with glomerular proteinuria. Areas of clinical application include tubular and glomerular diseases, detection of drug toxicity, reflux nephropathy, birth asphyxia and insulin-dependent diabetes mellitus. Methods of sample collection and analysis of these proteins are discussed.     

Serum α1-microglobulin and β2-microglobulin for the estimation of fetal glomerular renal function

As proteins cannot cross the placenta levels of the microproteins ₁-microglobulin (₁MG) and ₂-microglobulin (₂MG) can be used to assess fetal glomerular renal function. ₁MG, ₂MG and creatinine were routinely determined in cord and maternal blood of 133 newborns [gestational age (GA) 25–42 weeks]. Twenty-nine patients with suspected impaired maternal or fetal renal function were studied separately and two fetuses were studied in utero. The mean fetal ₂MG concentration fell from 3.87±0.56 mg/l in the 25–31 weeks GA group to 2.60±0.50 mg/l in the mature newborn group. ₁MG concentration fell from 3.10±0.51 to 2.25±0.49 mg/dl. In contrast, the mean maternal ₁MG concentration rose from 1.73±0.69 mg/l in the 25–31 weeks GA group to a mean of 1.83±0.48 mg/l in the mature newborn group; ₁MG rose from 3.96±0.58 to 4.33±1.6 mg/dl. Maternal and fetal creatinine levels were identical. Fetal microprotein levels fall during intra-uterine development as glomerular filtration rate (GFR) rises. There is no correlation between cord blood and maternal ₁MG or ₂MG concentrations. In 13 children with urological anomalies only 1 had elevated microprotein levels and he later developed renal insufficiency. Determination of microprotein levels in fetal serum can be used to detect severe renal function disturbances and to estimate GFR independently of maternal renal function.     

Bone-resorbing activities of 24-epi-1α-hydroxyvitamin D2 and 24-epi-1α,25-dihydroxyvitamin D2

Bone-resorbing activities of 24-epi-1-hydroxyvitamin D₂ [24-epi-1(OH)D₂], 24-epi-1,25-dihydroxyvitamin D₂ [24-epi-1,25(OH)₂D₂], and 1,24S,25-trihydroxyvitamin D₂ [1,24S,25(OH)₃D₂], which might be a metabolite of 24-epi-1,25(OH)₂D₂, were investigated. In an in vitro bone resorption test, the activity of 24-epi-1(OH)D₂ was similar to that of 1-hydroxyvitamin D₃ [1(OH)D₃] at 10^-9 M-10^-6 M. The activity of 24-epi-1,25(OH)₂D₂ was weaker than that of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] at 10^-11 M-10^-8 M. On the other hand, the activity of 1,24S,25(OH)₃D₂ was similar to that of 24-epi-1,25(OH)₂D₂ at 10^-11 M-10^-9 M. In the formation assay of osteoclast-like cells, the activity of 24-epi-1(OH)D₂ was weaker than that of 1(OH)D₃ at 10^-7 M. The activity of 24-epi-1,25(OH)₂D₂ was almost similar to that of 1,25(OH)₂D₃ at 10^-11 M-10^-7 M. The activity of 1,24S,25(OH)₃D₂ was significantly weaker than that of 24-epi-1,25(OH)₂D₂ at 10^-11 M-10^-9 M. In the two experiments, the potencies of 24-epi-1,25(OH)₂D₂ were about 100 times higher than those of 24-epi-1(OH)D₂. In an in vivo/in vitro bone resorption test, the activity of 24-epi-1(OH)D₂ was almost similar to those of 1(OH)D₃ and 1,25(OH)₂D₃ and higher than those of 24-epi-1,25(OH)₂D₂ and 1,24S,25(OH)₃D₂. 24-epi-1-(OH)D₂ and 1(OH)D₃ were longer lasting than 24-epi-1,25(OH)₂D₂ and 1,25(OH)₂D₃ in this experiment. These results suggested that 24-epi-1(OH)D₂ as well as 1(OH)D₃ was converted into dihydroxy form in vivo.     

Receptor function studies in specimens from the proximal human urethra obtained by transurethral resection

Summary During transurethral resection (TUR) for prostatic hyperplasia, specimens were taken from the proximal urethra. Muscle strips thus obtained were mounted in an organ bath and muscle contraction was induced by adding increasing concentrations of noradrenaline (NA), methoxamine (₁-agonist) and clonidine (₂-agonist). NA and methoxamine induced a dose-dependent muscle contraction, but clonidine had no effect. The influence of prazosin (₁-antagonist) and yohimbine (₂-antagonist) on the NA-induced muscle contraction was also evaluated. Both antagonists had an inhibitory effect,which was much more potent with prazosin. The specimens taken during TUR were found to be suitable for in vitro receptor function studies. The -adrenergic receptor function in the proximal human urethra was found to be mainly of the -type.     

Urinaryα 1 as an index of proximal tubular function in early infancy

Urinary ₁-microglobulin (U-A₁M) was measured in healthy term infants on days 1, 4, 7, 14, 28, 90 and 180 of life. U-A₁M was high until day 14 and declined thereafter. It was significantly correlated with urinary ₂-microglobulin (U-B₂M) throughout the study, but not with serum A₁M on days 1 or 7. Similar to U-B₂M, U-A₁M in the clinically stable term infants with intrauterine growth retardation (n=4–7) was not elevated on days 1–7. In the sick infants who needed immediate resuscitatio at birth (n=4–8), U-A₁M as well as U-B₂M was high on days 1–7 and then decreased to normal levels, suggesting that U-A₁M can be used as a sensitive marker of acute proximal tubular damage and its recovery. These observations indicate that U-A₁M is a useful index of proximal tubular function in early infancy.     

A case of renal sarcoidosis: a special reference to calcium metabolism as a diagnostic and the therapeutic implications

Sarcoidosis is a systemic granulomatous disease of unknown etiology and is associated with a wide variety of renal disorders including nephrolithiasis, hypercalciuria, hypercalcemia, nephrocalcinosis, tubular defect, glomerulonephritis, and granulomatous interstitial nephritis. We report a case of renal sarcoidosis in which we could not detect any evidence of extrarenal involvements that was diagnosed by renal biopsy and abnormal calcium metabolism incompatible with chronic renal insufficiency. On laboratory findings, decreased creatinine clearance, proteinuria, hypercalcemia, hypercalciuria, and mildly elevated serum angiotensin-converting enzyme (ACE) were seen. Serum intact parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,-25 vit D) were lower and higher than normal range, respectively, whereas the patient was already in chronic renal insufficiency. He was treated with oral corticosteroid. Serum ACE tended to fall, and 1,-25 vit D level decreased with substantial fall of serum calcium and daily calcium excretion. In contrast, intact PTH increased slowly in accordance with a fall of serum calcium compatible with the level of renal impairment. Creatinine clearance and daily excretion of protein improved. The case reported here may propose that serial measurement of serum level of 1,-25 vit D, calcium level, and magnitude of daily calcium excretion into urine is a simple and meaningful tool to detect the therapeutic response in sarcoidosis with abnormal calcium metabolism.This case was reported at the 38th Kanagawa nephritis research meeting in 2002 and the 32nd eastern regional meeting, Japanese Society of Nephrology, in 2002.     

Effects of 1α-hydroxyvitamin D3 on lumbar bone mineral density and vertebral fractures in patients with postmenopausal osteoporosis

The effects of 1-hydroxyvitamin D₃ [1(OH)D₃] on bone mineral density, fracture incidence, and bone metabolism were evaluated by a double-blind, placebo-controlled study. Eighty postmenopausal osteoporotic Japanese women (71.9±7.3 years, mean±SD) were randomly assigned to 1 g of 1(OH)D₃ daily or inactive placebo for 1 year. All patients were given supplemental calcium (300 mg of elemental calcium daily). Lumbar (L2–L4) bone mineral density (BMD) determined by dual energy X-ray absorptiometry increased 0.65% with 1(OH)D₃ treatment and decreased 1.14% with placebo (P=0.037). BMD in both the femoral neck and Ward's triangle did not yield any significant differences between the two groups, whereas trochanter BMD in the 1(OH)D₃-treated group increased 4.20% and decreased 2.37% with placebo (P=0.055). X-ray analysis demonstrated that new vertebral fractures occurred in two patients with 1(OH)D₃ and in seven patients with placebo. The vertebral fracture rate in the treated group was significantly less (75/1000 patient years) than in the control group (277/1000 patient years; P=0.029). Hypercalcemia (12.1 mg/100 ml) occurred in one patient receiving 1(OH)D₃; however, the serum calcium level in this patient promptly decreased to the reference range after cessation of the treatment. There were no significant changes in serum creatinine level in either group. A significant increase in urinary excretion of calcium was found but there was no significant change in urinary excretion of hydroxyproline in the treated group. The serum level of bone-derived alkaline phosphatase activity significantly decreased by–26±26 (mU/ml) after the treatment (P=0.003). These results indicate that 1(OH)D₃ treatment is effective for maintaining trabecular bone mass and prevents further vertebral fractures without any serious adverse effects in postmenopausal osteoporosis.     

Identification of α1-adrenoceptor subtypes in the dog prostate

Summary The ₁-adrenoceptor subtypes of dog prostate were characterized in binding and functional experiments. In saturation experiments, [³H]prazosin bound to ₁-adrenoceptors with high affinity. In the displacement experiments, unlabelled prazosin and WB4101 biphasically inhibited the binding of 400 pM [³H]prazosin, suggesting the presence of at least two distinct affinity sites for prazosin or WB4101. The proportion of high-affinity sites was approximately 10%. HV723 also recognized two distinct affinity sites but the proportion of high-affinity sites was approximately 20%. From these results the presence of three distinct ₁-adrenoceptor subtypes was suggested: presumably subtypes _1A (high affinity for prazosin and WB4101), _1N (high affinity for only HV723) and _1L (low affinity for the three antagonists) according to the recently proposed ₁-adrenoceptor subclassification. The density of subtype _1L was much higher than that of subtypes _1A and _1N subtypes. In the functional experiments, prazosin, WB4101 and HV723 competitively antagonized the contractile response to noradrenaline with low affinities close to those estimated for the _1L subtypes. These results suggest that the contractile response to noradrenaline in the dog prostate is mediated predominantly through _1L subtype -adrenoceptors.     

A boy with mitochondrial disease: asymptomatic proteinuria without neuromyopathy

Mitochondrial disorder is a relatively rare disease during childhood. Previous studies concluded that renal complications in this disease most often occur in patients with mitochondrial encephalomyopathies. We describe a boy with mitochondrial disease who presented with proteinuria while lacking neuromyopathy. Proteinuria was detected at the age of 6 years, including large amounts of low-molecular-weight proteins such as ₂- and 1-microglobulin. Renal functions were normal. Proximal tubular dysfunction and other renal manifestations were absent. Episodic neurologic problems such as migraine and nervous system diseases including epilepsy, depression, schizophrenia and amytrophic lateral sclerosis (ALS) were found in the boys family members. Renal tubular basement membrane atrophy and interstitial fibrosis with mononuclear cell infiltration were observed. Ultrastructural examination showed mitochondria, mainly in the proximal tubules, which varied in size and had disoriented cristae. Mutation analysis using mitochondrial DNA (mtDNA) extracted from renal tissues demonstrated a AG point mutation at nucleotide position 3243 in the tRNA^Leu(UUR) gene, while there was no mutation found in mtDNA extracted from peripheral leukocytes. Awareness among pediatricians of mitochondrial disorders, detection of low-molecular-weight proteinuria, renal ultrastructural examination and mutation analysis of mtDNA obtained from renal tissues could be important for early diagnosis of this disease.     

Renal α-adrenergic receptors and genetic hypertension

The hypothesis has been proposed that an increase in the number of renal -adrenergic receptors may contribute to the pathogenesis of genetic hypertension. Herein we review recent findings regarding expression of renal ₁ (_{1 a},_{1 b})- and ₂ (_{2 a},_{2 b})-adregenergic subtypes and we provide an updated revision of the above-stated hypothesis. Enhancement in receptor number or in post-receptor components responsible for ₁- and ₂-adregenergic mediated sodium reabsorption in proximal tubule may contribute to sodium retention and an elevation in blood pressure. Perhaps such changes contribute to the increase in blood pressure in genetically determined hypertension in humans, although direct tests of this notion have not yet been performed.     

Comparison of adrenoceptor subtype expression in porcine and human bladder and prostate

We have quantified and characterized ₁-, ₂-and -adrenoceptor subtypes in porcine bladder detrusor and bladder neck, human bladder detrusor, and porcine and human prostate. ₁-, ₂- and -adrenoceptor were identified in radioligand binding studies using [³H]prazosin, [³H]RX 821002 and [¹²⁵I]iodocyanopindolol, respectively, as the radioligands. In porcine male and female detrusor and bladder neck and male prostate, adrenoceptors were detected in the order of abundance > _{2 1} (not detectable), with no major differences between the sexes or between detrusor and bladder neck. In human detrusor and prostate the order of abundance was > _{2 1} (not detectable) and ₁ > ₂. respectively. The ₂-adrenoceptors in all tissues were homogeneously of the _2A-subtype as evidenced by competition binding studies with yohimbine, prazosin, ARC 239 and oxymetazoline. The -adrenoceptors represented a mixed population with a dominance of the ₂-subtype in all tissues as demonstrated by competition binding with ICI 118,551 and CGP 20,712A. We conclude that pigs may be a suitable model for studies of detrusor function with respect to adrenoceptor expression. They may be less suitable for studies of bladder neck or prostate function.     

Changes in the productivity of cytokines and active-oxygen in peripheral blood cells following surgery

An investigation was carried out on the productivity of cytokines and active-oxygen by peripheral blood cells during the pre- and post-operative periods. While the preoperative production of tumor necrosis factor (TNF) and interleukin-l (IL-1) was elevated, that of lymphotoxin (LT) and interferon- (IFN-) were slightly suppressed. In the postoperative period the peak TNF and IL-1 and active-oxygen productivity was elevated, while LT and IFN- productivity was suppressed in patients with an intraoperative bleeding volume of more than 1,000 ml compared to those with that of less than 1,000 ml. Thus, stress stimulates the TNF and IL-1 and active-oxygen producing system, that is, the macrophage-neutrophil system, and suppresses the LT and IFN- system, being, the inflammatory helper T cell system, in the early postoperative period.     

Calcium regulating activity of 26,27-dialkyl analogs of 1α,25-dihydroxyvitamin D3

Summary A series of analogs of 1,25-dihydroxyvitamin D₃[1,25(OH)₂D₃] with alkyl substitutions in 26- and 27-positions were tested for calcium (Ca) regulating activity. The potencies of dialkyl analogs in stimulating bone resorption in neonatal mouse calvaria cultures were the highest in 1,25-dihydroxy-26,27-dimethylvitamin D₃[1,25(OH)₂-(Me)₂D₃], followed by 1,25(OH)₂D₃, 1,25-dihydroxy-26,27-diethylvitamin D₃[1,25(OH)₂(Et)₂D₃], and 1,25-dihydroxy-26,27-dipropylvitamin D₃[1,25(OH)₂(Pr)₂D₃] in that order. A similar order of potential regarding formation of osteoclast-like cells in mouse bone marrow cell cultures and on bone Ca mobilization with long-term vitamin D-deficient rats was observed in the same series. The relative potencies of 1,25(OH)₂D₃, 1,25(OH)₂(Me)₂D₃, 1,25(OH)₂(Et)₂D₃, and 1,25(OH)₂(Pr)₂D₃ in competing with 1,25(OH)₂D₃ for binding to chick intestinal cytosol receptors were 1:1:0.16:0.036. A similar order of potential in case of intestinal Ca transport in situ was observed in the same series. The potencies of dialkyl analogs in competing with 25-hydroxy-vitamin D₃ for binding to rat serum vitamin D binding protein were much lower than that of 1,25(OH)₂D₃. Effect of 1,25(OH)₂(Me)₂D₃ on osteopenia in rats induced by ovariectomy and right sciatic neurotomy was higher than that of 1,25(OH)₂D₃. From these results, the lengthening by one carbon at 26- and 27-positions was shown to maintain the Ca regulatory activity of 1,25(OH)₂D₃.     

Urinary prostaglandins in hyperglycaemic ketoacidosis of type I diabetes mellitus

Urinary excretion of various renal prostaglandins was measured by radioimmunoassay and gas chromatography-mass spectrometry in children who had different degrees of metabolic control. Excretion in PGE₂ in diabetic children was twice control values irrespective of the presence or absence of diabetic ketoacidosis (DKA). The urinary excretion of PGF₂ was significantly increased in diabetic children with ketoacidosis, but not when diabetes was well controlled. The excretion of 13, 14 dihydro-15-keto PGE₂, the major metabolite of circulating PGE₂, was increased in all diabetic children, and was most elevated in ketoacidosis when it averaged 10 times basal excretion. Urinary excretion of PGI₂ and of 6-keto-PGF₁, the metabolite of PGI₂, was approximately doubled in DKA compared with values from healthy subjects. Excretion of PGE₂ was twice control values in children with stable diatetes, whereas the equivalent value for TXB₂, the metabolite of the active vasoconstrictor TXA₂, was reduced by approximately 50%. We suggest that the increased excretion of prostacyclin metabolite may result from a protective biological action on the kidney opposing other vasoconstrictor hormone activity. PGE₂ appears not to be involved in this process. The highly elevated excretion of PGE₂ metabolite may represent an activation of systemic PGE metabolism during DKA.     

Urinary excretion of adenosine deaminase binding protein in neonates treated with tobramycin

The potential tubulotoxicity of tobramycin and cefotaxim were assessed in neonates by measuring the urinary level of adenosine deaminase binding protein (ABP) and urinary ₁-microglobulin and ₂-microglobulin. In a prospective study, 33 neonates who received tobramycin and cefotaxim for suspected neonatal sepsis were compared with 48 untreated newborns during the first 10 days of life. The urinary concentrations of ABP and its excretion rates, corrected for body weight and body surface area, were significantly increased from the 1st day of treatment. Urinary ₁-microglobulin and ₂-microglobulin were not elevated under tobramycin and cefotaxim during the first 2 days of treatment. We conclude that ABP may be a sensitive marker for the detection of proximal renal tubular injury during tobramycin and cefotaxim treatments of neonates. The increase in urinary ABP which occurs before an elevation of urinary ₁-microglobulin and ₂-microglobulin may reflect earlier structural than functional alterations. However, since none of the treated infants had signs of electrolyte disorders or glomerular dysfunction, the clinical relevance of ABP measurement should be reevaluated.     

Natural human IgG inhibits the production of tumor necrosis factor-α and interleukin-1α through the Fc portion

The overproduction of cytokines such as the tumor necrosis factor- (TNF-) and interleukin-1 (IL-1) may cause further deterioration in the already critical condition of patients with shock, sepsis, and acute inflammation. The effectiveness of infusion therapy of natural human IgG to such patients is suggested to depend partly upon the inhibition of the productivity of these cytokines. In this study, we investigated the modulation effects of IgG and its fragments on the production of TNF- and IL-1, on human peripheral blood mononuclear cells (PBMC). The production of TNF- and IL-1 was found to be dose-dependently inhibited by IgG when stimulated by lipopolysaccharide (LPS), phytohemagglutinin (PHA), concanavalin A (Con A), and interleukin-2 (IL-2). However, no inhibition was seen when stimulated by phorbormyristate acetate (PMA). The F(ab)₂ fragment showed enhancing effects on cytokine production by LPS, while the Fc fragment showed not as much inhibitory effect as whole intact IgG. IgG showed no direct cytotoxic effect on PBMC. These data suggest that natural human IgG inhibits TNF- and IL-1 production by PBMC through the Fc portion. The results of this study led us to conclude that whole intact IgG may be the best form of therapeutic delivery.     

A Prostacyclin Analogue,OP-41483α-CD,Restores the Ability of a β<Subscript>2</Subscript>-Adrenergic Agonist to Stimulate Alveolar Fluid Clearance in Rats

Purpose. It is not yet known whether a prostacyclin analogue can affect alveolar fluid clearance. According to recent studies, high-dose (10^–3M) terbutaline, a ₂-adrenergic agonist, failed to increase alveolar fluid clearance. Therefore, we examined the effects of OP-41483-CD, a prostacyclin analogue, on alveolar fluid clearance in the presence of high-dose terbutaline in rats.Methods. Albumin solution containing Evans blue dye and various drugs was instilled into the alveolar airspaces of isolated rat lungs, which were then inflated with 100% oxygen at an airway pressure of 8cmH₂O. Alveolar fluid clearance was measured by the progressive increase in dye concentrations over 1h.Results. Although 10^–5 and 10^–4M terbutaline increased alveolar fluid clearance, 10^–3M terbutaline did not. OP-41483-CD restored the ability of 10^–3M terbutaline to stimulate alveolar fluid clearance. The effect of OP-41483-CD was consistent with the effect of atenolol, a ₁-adrenergic antagonist. The effect of OP-41483-CD on alveolar fluid clearance was unchanged in lungs inflated with nitrogen. Prostaglandin E (PGE)₁ and PGE₂ analogues had similar effects to OP-41483-CD on alveolar fluid clearance.Conclusion. These results indicate that a prostacyclin analogue restores the ability of high-dose terbutaline to stimulate alveolar fluid clearance.     

G-Proteins in alpha1-adrenoceptor mediated prostatic smooth muscle contraction

The role of signal transducing guanine-nucleotide binding proteins (G-proteins) in ₁-receptor mediated smooth muscle contractions was investigated in human hyperplastic prostatic tissue. The selective ₁-receptor agonist phenylephrine (PE) evoked dose dependent contractions antagonized by the ₁-receptor blockers prazosin (EC₅₀ 10 nM) and YM 617 (EC₅₀ 3 nM). Application of nifedipine (1–10,000 nM), a blocker of voltage-dependentl-type Ca^2--channels (VDCC), inhibited the PE evoked contraction up to 65.4%. Pretreating the tissue strips with pertussis toxin (PTX, exotoxin from Bordetella pertussis; 5–25 g/ml), inactivating a subpopulation of G-proteins, inhibited the PE induced contractions up to 73.9%. PTX pretreatment had no effect on contractions elicited by 125 mMK^-. Application of nifedipine to PTX pretreated tissue led to an additional inhibition of 13.7%. Our findings demonstrate the involvement of PTX-sensitive G-proteins in the signal transduction pathway of ₁-receptor induced contractions of prostatic smooth muscle. The remaining contractility of PTX pretreated tissue suggests additional participation of PTX insensitive mechanisms in ₁-receptor mediated prostatic smooth muscle contractions.     

Role of intracellular Ca2+ stores in smooth muscle contractions of the guinea pig vas deferens

Summary Guinea pig vas deferens was used as an animal model for alpha-1 adrenoceptor (₁-receptor) mediated contractions in human hyperplastic prostatic tissue. The selective ₁-receptor agonist, phenylephrine (PE), induced fully reversible, dose-dependent contractions antagonized by increasing concentrations of the ₁-receptor blockers prazosin (1–100 nM) and YM 617 (0.1–10 nM). Removal of extracellular Ca²⁺ reduced PE-evoked contractions in a time-dependent manner. Nifedipine (1–1000 nM), a blocker of voltage-dependent L-type Ca²⁺ channels (VDCC), inhibited the PE-induced response by up to 65%. Removal of extracellular Ca²⁺ abolished the ₁-agonist reactivity in a time-dependent fashion. To elucidate the participation of intracellular Ca²⁺ stores in ₁-receptor contractions, the tissue was pretreated with ryanodine (10 M) or thapsigargin (0.1 M), established inhibitors of Ca²⁺ release from intracellular pools. Both substances reduced the PE contractions by up to 80%. Nifedipine suppressed the remaining contractions completely. This provides evidence that Ca²⁺ influx through VDCC and Ca²⁺ release from intracellular stores contribute to ₁-receptor contractions in the guinea pig vas deferens and may be important in obstructive benign prostatic hyperplasia.     

Microheterogeneity of urinary albumin and tubular proteinuria in juvenile diabetes mellitus

We studied differential urinary albumin excretion by a double one-dimensional gel electrophoresis with decyl sodium sulphate-polyacrylamide gel electrophoresis in the first, and isoelectric focusing in the second dimension in 37 diabetic children and 20 healthy subjects. In addition, total proteins, albumin, ₂-microglobulin and molecular size distribution of urinary proteins were measured. the latter using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Whilst albuminuria was not significantly different from controls we found an increased microheterogeneity of urinary albumin in 38% of patients. In addition, low molecular weight protein (P<0.05) and ₂-microglobulin excretion (P<0.01) were elevated. It is suggested that the appearance of highly heterogenous albumin in the pI range of 5.3–5.9 is the result of a decreased tubular reabsorption.