[Age-related differences in IgA nephropathy].

To clarify age-related differences in the characteristics of IgA nephropathy, we investigated 117 patients of all ages. The number of patients in the second decade of age was larger than that in the other age decades. There was no difference in sex in all age brackets. About one half of the patients under ten years of age presented as acute nephritis, but their prognosis was favorable. Patients over 10 years, most of whom were detected by chance, tended to have a greater degree of proteinuria, a lesser degree of creatinine clearance, a higher frequency of hypertension, and a higher level of serum cholesterol with age. Although the intensity of mesangial cell proliferation was not changed, the grade of glomerulosclerosis, interstitial change, and arteriosclerosis increased and the prognosis became poor as age advanced. Treatment with corticosteroids and antiplatelet agents was less effective in adults, especially in the older age brackets than in children because the frequency of histologically chronic lesions increased. In these cases, lipid-lowering agents and angiotensin-converting enzyme inhibitors may be helpful in preventing the progression.

Murine double nullizygotes of the angiotensin type 1A and 1B receptor genes duplicate severe abnormal phenotypes of angiotensinogen nullizygotes.

Rodents are the unique species carrying duplicated angiotensin (Ang) type 1 (AT1) receptor genes, Agtr1a and Agtr1b. After separately generating Agtr1a and Agtr1b null mutant mice by gene targeting, we produced double mutant mice homozygous for both Agtr1a and Agtr1b null mutation (Agtr1a-/-; Agtr1b-/-) by mating the single gene mutants. Agtr1a-/-, Agtr1b-/- mice are characterized by normal in utero survival but decreased ex utero survival rate. After birth they are characterized by low body weight gain, marked hypotension, and abnormal kidney morphology including delayed maturity in glomerular growth, hypoplastic papilla, and renal arterial hypertrophy. These abnormal phenotypes are quantitatively similar to those found in mutant mice homozygous for the angiotensinogen gene (Agt-/-), indicating that major biological functions of endogenous Ang elucidated by the abnormal phenotypes of Agt-/- are mediated by the AT1 receptors. Infusion of Ang II, AT1 blockers, or an AT2 blocker was without effect on blood pressure in Agtr1a-/-; Agtr1b-/- mice, indicating that AT2 receptor does not exert acute depressor effects in these mice lacking AT1 receptors. Also, unlike Agt-/- mice, some Agtr1a-/-; Agtr1b-/- mice have a large ventricular septum defect, suggesting that another receptor such as AT2 is functionally activated in Agtr1a-/-, Agtr1b-/- mice.

Angiotensinogen gene null-mutant mice lack homeostatic regulation of glomerular filtration and tubular reabsorption.

Chronic volume depletion by dietary salt restriction causes marked decrease in glomerular filtration rate (GFR) with little increase in urine osmolality in angiotensinogen gene null mutant (Agt-/-) mice. Moreover, urine osmolality is insensitive to both water and vasopressin challenge. In contrast, in normal wild-type (Agt+/+) mice, GFR remains remarkably constant and urine osmolality is adjusted promptly. Changes in volume status also cause striking divergence in renal structure between Agt-/- and Agt+/+ mice. Thus, in contrast to the remarkably stable glomerular size of Agt+/+ mice, glomeruli of Agt-/- mice are atrophied during a low salt and hypertrophied during a high salt diet. Moreover, the renal papilla, a structure unique to mammals and essential for urine diluting and concentrating mechanisms, is hypoplastic in Agt-/- mice. Thus, angiotensin is essential for the two fundamental homeostatic functions of the mammalian kidney, namely stable GFR and high urine diluting and concentrating capacity during alteration in extracellular fluid (ECF) volume. This is not only accompanied by angiotensin's tonic effects on renal vasomotor tone and tubule transporters, but also accomplished through its capacity to affect the structure of both the glomerulus and the papilla directly or indirectly.

Long-term effects of immunosuppressants in steroid-dependent nephrotic syndrome.

In order to elucidate long-term effects of immunosuppressants, we studied 60 children with steroid-dependent nephrotic syndrome who were treated with three immunosuppressants: cyclophosphamide (n=34), chlorambucil (n=11), and cyclosporin A (n=15). Each relapse before and after the administration of immunosuppressants was evaluated longitudinally in terms of the relapse-free period and the maintenance dose of prednisolone required. The median follow-up period after immunosuppressants was 5.2 years (range 0.5-20.3 years). The relapse-free period was significantly longer in all groups after the initiation of immunosuppressants. However, the relapse-free period after subsequent relapses as compared with the previous relapse was longer in the cyclophosphamide group, similar in the chlorambucil group, and shorter in the cyclosporin A group. The prednisolone dosage at relapse was reduced in subsequent relapses after cyclophosphamide and chlorambucil treatment, but tended to be higher in later relapses after the initiation of cyclosporin A. These findings suggest that the effects of cyclophosphamide are long lasting, while those of chlorambucil and cyclosporin A are of short duration. Children who relapse after cyclosporin A treatment may experience a worse relapsing course.

Angiotensin-independent mechanism for aldosterone synthesis during chronic extracellular fluid volume depletion.

Wild-type (Agt+/+) and homozygous angiotensinogen deletion mutant (Agt-/-) littermates were placed on normal (NS) or low Na diet (LS) for 2 weeks. Plasma aldosterone levels (P(aldo)) were comparable during NS, and similarly elevated during LS in Agt+/+ and Agt-/-. Moreover, in both, the elevation in P(aldo) was accompanied by marked increase in adrenal zona glomerulosa cells and adrenal P450aldo mRNA. Agt-/- mice were distinguished from Agt+/+ mice by their higher plasma K level, by approximately 1.5 and approximately 3.8 mEq/liter during NS and LS, respectively. Within the Agt-/- group, P(aldo) was directly proportional to plasma K. The importance of K for the hyperaldosteronism during dietary Na restriction was verified by the observation that superimposition of K restriction led to hypotension in Agt+/+ and uniform death in Agt-/- mice along with a reduction in P(aldo) by 75 and 90%, respectively. Thus, suppression of potassium, but not angiotensin, led to a marked attenuation of hyperaldosteronism during dietary Na restriction. Therefore, (a) a powerful angiotensin-independent mechanism exists for the hyperaldosteronism during LS; (b) high K is a central component of this mechanism; (c) contrary to current belief, the tonic effect of high K on aldosterone synthesis and release does not require an intact renin-angiotensin system; and (d) normally, intermediary feedback signals for hyperaldosteronism, i.e., both hypotension and high K, are effectively masked by aldosterone actions.

Temporal and spatial expression pattern of the angiotensinogen gene in mice and rats.

In situ hybridization for mouse angiotensinogen (Ao) mRNA was performed using a Stu I-Pst I 0.43-kb fragment of exon 2 as a template to synthesize RNA probes. The mouse Ao mRNA expression patterns were different from those reported for rats. Ao mRNA was expressed in the fetal liver as early as 12.5 days postcoitus, and the liver remained the predominant organ of its expression in utero. Within the developing kidney, Ao mRNA was demonstrated at 17.5 days postcoitus in the proximal straight tubules undergoing loop formation in the medulla. In the matured mouse kidney, the expression site is within the outer stripe of outer medulla, hence identified as the pars recta, not proximal convoluted tubules. Additional studies revealed that, in rats also, Ao mRNA was localized in the pars recta. This was in contrast to previously published results that showed that Ao mRNA was localized primarily in the proximal convoluted tubules in rats. Thus the pars recta appears to be an important intrarenal source of Ao for both rats and mice throughout pre- and postnatal periods, whereas the liver can be the major extrarenal source in utero in mice, but not in rats.

Risk factors for relapse in childhood nephrotic syndrome.

We investigated the risk factors for relapse in 48 children with steroid-sensitive nephrotic syndrome using univariate and multivariate proportional hazard analysis. All patients were treated with the same corticosteroid regimen. A low serum level of total protein and young age at onset increased the relapse rate. Recurrence risk was not associated with the patient's sex, the percentage body weight gain, blood urea nitrogen level, serum level of creatinine, the hematocrit, or the administration of human albumin. We conclude that young age and a low serum level of total protein at onset were independent risk factors for relapse of childhood nephrotic syndrome.

Chimeric mice carrying 'regional' targeted deletion of the angiotensin type 1A receptor gene. Evidence against the role for local angiotensin in the in vivo feedback regulation of renin synthesis in juxtaglomerular cells.

We have developed chimeric mice carrying 'regional' null mutation of the angiotensin type 1A (AT1A) receptor, the AT1 receptor subtype exclusively present in mouse juxtaglomerular (JG) cells. The chimeric mouse (Agtr1a -/- <--> +/+) is made up of wild-type (Agtr1a +/+) cells or cells homozygous for Agtr1a deletion (Agtr1a -/-). In the latter, the AT1A coding exon was replaced with a reporter gene, lacZ. In Agtr1a -/- <--> +/+ mice, these two clones of cells are found to be clustered and display patchy distributions in the kidney and heart. Tracking of lacZ activities in hetero- (Agtr1a +/-) and homozygous (Agtr1a -/-) deletion mutant offspring from Agtr1a -/- <--> +/+ mice revealed that the promoter activity of Agtr1a is localized in JG cells, afferent arteriolar walls, glomerular mesangial region and endothelial cells, and apical and basolateral proximal tubule membranes. The JG apparatuses of Agtr1a -/- mice are markedly enlarged with intense expression of renin mRNA and protein. In Agtr1a -/- <--> +/+ mice, these changes were proportional to the degree of chimerism. Within a given Agtr1a -/- <--> +/+ mouse, however, the degree of JG hypertrophy/hyperplasia and the expression of renin mRNA and protein were identical between Agtr1a +/+ and Agtr1a -/- cells. Thus, in the in vivo condition tested, the local interaction between angiotensin and the AT1 receptor on the JG cells has little functional contribution to the feedback regulation of JG renin synthesis.

Gene targeting in mice reveals a requirement for angiotensin in the development and maintenance of kidney morphology and growth factor regulation.

Elevated levels of endogenous angiotensin can cause hypertensive nephrosclerosis as a result of the potent vasopressor action of the peptide. We have produced by gene targeting mice homozygous for a null mutation in the angiotensinogen gene (Atg-1-). Postnatally, Atg-1- animals show a modest delay in glomerular maturation. Although Atg-1- animals are hypotensive by 7 wk of age, they develop, by 3 wk of age, pronounced lesions in the renal cortex, similar to those of hypertensive nephrosclerosis. In addition, the papillae of homozygous mutant kidneys are reduced in size. These lesions are accompanied by local up-regulation of PDGF-B and TGF-beta1 mRNA in the cortex and down-regulation of PDGF-A mRNA in the papilla. The study demonstrates an important requirement for angiotensin in achieving and maintaining the normal morphology of the kidney. The mechanism through which angiotensin maintains the volume homeostasis in mammals includes promotion of the maturational growth of the papilla.

Effects on blood pressure and exploratory behaviour of mice lacking angiotensin II type-2 receptor.

There are two major angiotensin II receptor isoforms, AT1 and AT2. AT1 mediates the well-known pressor and mitogenic effects of angiotensin II, but the signalling mechanism and physiological role of AT2 has not been established. Its abundant expression in fetal tissues and certain brain nuclei suggest possible roles in growth, development and neuronal functions. Here we report the unexpected finding that the targeted disruption of the mouse AT2 gene resulted in a significant increase in blood pressure and increased sensitivity to the pressor action of angiotensin II. Thus AT2 mediates a depressor effect and antagonizes the AT1-mediated pressor action of angiotensin II. In addition, disruption of the AT2 gene attenuated exploratory behaviour and lowered body temperature. Our results show that angiotensin II activates AT1 and AT2, which have mutually counteracting haemodynamic effects, and that AT2 regulates central nervous system functions, including behaviour.

Long-term corticosteroid and dipyridamole treatment of membranoproliferative glomerulonephritis type I in children.

Eighteen patients with biopsy-proven membranoproliferative glomerulonephritis (MPGN) type I (16 diffuse, 2 focal) and a minimum of three years of follow-up (median 6.0 years, range 3 to 15.5 years) were treated with corticosteroids combined with dipyridamole. Initial therapy consisted of intravenous methylprednisolone pulses and/or daily oral prednisolone at the dose of 1 mg/kg combined with dipyridamole at the dose of 5 mg/kg, depending on the disease severity. Corticosteroid dosage was then reduced according to clinical improvement. At the start of therapy, 12 patients had microscopic hematuria or mild proteinuria, three patients had heavy proteinuria and three patients had insufficient renal function. At a median of 53 months of treatment, 89% of the children had normal or mildly abnormal urinary findings with normal renal function. Follow-up biopsy revealed improved active glomerular injury in all children. Although one case progressed to end-stage renal failure, the renal survival of our patients was 94% at 4 to 10 years after clinical onset. No patient suffered a relapse during corticosteroid dosage adjustment, nor did any unacceptable complications arise during the regimen. Eleven patients stopped the regimen because their renal function and urinalysis had normalized, and they remained in remission for a median of 32 months. These results suggest that long-term, tapering and limited use of corticosteroids combined with dipyridamole is useful and safe for children with MPGN type I.

[Effect of oral adsorbent AST-120 in rats with chronic renal failure--mechanism of progression of renal failure by dietary protein].

Progression of renal insufficiency was evaluated in partially nephrectomized Sprague-Dawley rats at the age of 10 weeks, fed on the low (6%), usual (20%), and high (36%) protein diet (group 6C, 20C, and 36C). Effects of oral adsorbent AST-120 on these experimental uremic models were also examined (group 6A, 20A, 36A). All the rats underwent paired feeding, and survived during the experimental period of 3 weeks. GFR (inulin clearance) and RPF (para-amino hippurate clearance), as well as Ccr was measured before the sacrifice. Initial serum creatinine and Ccr were 1.7 mg/dl and 0.27 ml/min. The rats of group 36C showed progressive elevation of serum creatinine level and decrease in Ccr. At the end of the study, GFR was significantly lower in group 36C than in group 6C and 20C (0.19, 0.68, 0.87 ml/min respectively). Significant elevation of filtration fraction in group 36C suggested that the decrease in GFR mainly resulted from low RPF. Even in group 36C, no glomerular sclerosis was histologically demonstrated in the remnant kidney, and the mean planar area of the remnant glomeruli was significantly small, which might reflect low RPF. Tubulo-interstitial changes like dilatation of the urinary space and tubular epithelial flattening were prominent in group 36C. Beneficial effect of AST-120 was obvious in high protein diet groups. GFR and RPF were rather well preserved in group 36A (0.36 and 0.78 ml/min) with normal filtration fraction. Tubulo-interstitial damage was evidently mild in group 36A. These data suggested the presence of some humoral factors, which can be adsorbed by AST-120 in gastrointestinal tract, and responsible for the deterioration of renal function and tubulo-interstitial damage induced by high protein diet in the uremic condition. Besides hyperfiltration and glomerular hypertrophy, such humoral factors as suggested in this study may contribute to the progression of chronic renal failure to some extent.

Partial deficiency of cytochrome c oxidase with isolated proximal renal tubular acidosis and hypercalciuria.

We report the case of a 5-year-old boy with mitochondrial cytopathy due to a partial deficiency of cytochrome c oxidase who had isolated proximal renal tubular acidosis and hypercalciuria. The patient developed hypotonia and blepharoptosis and exhibited growth retardation. Biochemical examination of muscle tissue revealed a partial deficiency of cytochrome c oxidase. He was treated with an alkali, hydrochlorothiazide, and indomethacin. After treatment, metabolic acidosis and hypercalciuria improved, and the patient had a catch-up growth phase. This case emphasizes the importance of performing renal tubular functional investigations and treatment in patients with mitochondrial cytopathy, even in the absence of multiple proximal tubular dysfunction.

[Rapid deterioration of renal function in minimal change nephrotic syndrome].

This report concerns two boys with minimal change nephrotic syndrome progressed to renal failure. The first case aged 17 being a steroid sensitive infrequent relapse developed acute renal failure at his third relapse and recovered soon after the treatment with diuretics and corticosteroids. The second case aged 15 being a steroid dependent frequent relapse became steroid resistant at his 11th relapse and progressed to renal failure seven months later. As the causes of renal failure, acute tubular necrosis and tubular obstruction by casts were suspected in the former. Renal vein thrombosis, morphological transition of renal histology, hemodynamic change and change in glomerular permeability might be occurred in the latter. Renal failure is a rare complication of minimal change nephrotic syndrome and the cause is variable. Precise diagnosis and prompt treatment should be needed to improve the prognosis.

Severe glomerulonephritis and tubulo-interstitial nephritis accompanied with urticaria and vasculitis.

We report a 9-year-old girl who developed recurrent urticaria, arthritis and serious renal involvement. She was treated by prednisolone with considerable improvement. Biopsy examinations revealed cutaneous vasculitis and moderate mesangial proliferation with crescents and tubulo-interstitial nephritis on light microscopy. Immunofluorescence study showed IgG, IgM and complement deposits in the mesangium and along the capillary wall. On electron microscopy, electron-dense deposits were identified in the mesangium and paramesangium. Her disease resembled the hypocomplementemic vasculitis syndrome, but her serum complement values were normal throughout the course of the illness. The pathogenesis of her disease is unknown, but it seems to be a sort of systemic immune-complex disease.

Congenital fiber type disproportion myopathy in Lowe syndrome.

Two brothers with the typical clinical features of oculocerebro-renal syndrome of Lowe exhibited delays in developmental milestones, muscular weakness and hypotonia, and high serum creatine kinase activity. The biopsied muscle revealed selective type 1 fiber atrophy and mild type 1 fiber predominance, similar to that observed in congenital fiber type disproportion myopathy. The abnormal fiber type distribution may be responsible for the common finding of muscle hypotonia in this syndrome.