Hepatitis C virus-related kidney disease: various histological patterns

BACKGROUND

Although hepatitis C virus (HCV) infection is known to be associated with Type 2 cryoglobulinemic glomerulopathy (CG), only a few reports about other types of nephropathy have been published.

METHODS

68 HCV antibody positive patients in whom renal biopsy had been performed for persistent proteinuria, hematuria, and/or renal dysfunction between 1992 and 2008 at our institute were included. The histological, clinical and laboratory characteristics including the age, gender, hypertension, diabetes mellitus, liver histology (chronic hepatitis or liver cirrhosis), HCV-RNA, HCV genotype, splenomegaly, gastroesophageal varices, serum creatinine, hemoglobin, platelet count, rheumatoid factor, cryoglobulin, IgG, IgA, IgM, CH50, C3, C4, creatinine clearance, 24-h protein excretion, and hematuria, between their nephropathy with and without immune deposition were compared.

RESULTS

Nephropathy was classified into two groups based on the detection of immune deposits by immunofluorescence microscopy: i.e., a positive group (n = 39) and a negative group (n = 29). The former group was further classified into three types of nephropathy: IgG dominant group (n = 10) (including membranous nephropathy (MN)), IgA dominant group (n = 20) (including IgA nephropathy (IgAN)), membranoproliferative glomerulonephritis (MPGN) (IgA type)), and IgM dominant group (n = 9) (MPGN apart from the IgA type). The latter group included diabetic nephropathy (n = 13), focal glomerular sclerosis (n = 4), and benign nephrosclerosis (n = 3), malignant nephrosclerosis (n = 1), tubulointerstitial nephritis (TIN) (n = 2), minimal change nephrotic syndrome (n = 1), cast nephropathy (n = 1), granulomatous TIN (n = 1), and others (n = 3). An increased serum IgM level, hypocomplementemia, splenomegaly, thrombocytopenia, liver cirrhosis, hematuria, and a high HCV RNA level were features of patients with MPGN of IgM dominant group (consistent with "CG").

CONCLUSIONS

Our results showed various histological patterns of HCV-related kidney disease and the specificity of CG, and revealed that a minority of HCV patients (n = 7) presented typical CG, while IgAN, MN, and diabetic nephropathy were more frequent.

Multicentric Castleman disease with secondary AA renal amyloidosis, nephrotic syndrome and chronic renal failure, remission after high-dose melphalan and autologous stem cell transplantation

Multicentric Castleman disease is a systemic lymphoproliferative disease with incomplete understood etiology. The various renal complications of this disease may include minimal change disease, mesangial proliferative glomerulonephritis, membranous glomerulonephritis and nephrotic syndrome, caused by secondary amyloidosis. In several reported cases of localized Castleman disease associated with renal amyloidosis and nephrotic syndrome, resection of organs involved by lymphoid proliferation resulted in complete remission. However, therapy of multicentric Castleman disease with renal amyloidosis is not well-established. We treated a case of a 39-year-old woman with multicentric Castleman disease complicated by nephrotic syndrome caused by secondary AA amyloidosis. The patient underwent autologous peripheral blood stem cell transplantation (auto-PBSCT), achieving complete remission. Autologous stem cell transplantation may be an attractive choice in therapy for refractory multicentric Castleman disease.

A pediatric occurrence of crescentic glomerulonephritis associated with antineutrophil cytoplasmic antibodies and mesangial IgA deposits

Antineutrophil cytoplasmic antibody-(ANCA) associated glomerulonephritis usually shows histopathologic features of pauciimmune crescentic glomerulonephritis and occurs late in life. We report a 14-year-old Japanese girl presenting with proteinuria, hematuria and mildly elevated serum creatinine. A renal biopsy specimen demonstrated crescentic glomerulonephritis, immunofluorescence showed mesangial IgA staining. Electron microscopic examination disclosed paramesangial deposits. Serum ANCA against myeloperoxidase (MPO) were detected at high titers. Myeloperoxidase-ANCA-related nephritis accompanied by IgA nephropathy is considered rare in childhood and teen years. Yet, if ANCA assays and detailed electron microscopic examination of renal specimens were performed routinely in patients with rapidly progressive glomerulonephritis, the diagnosis might be more frequent in young patients.

An intron 4 gene polymorphism in endothelial cell nitric oxide synthase might modulate lipid metabolism in nondiabetic patients on hemodialysis

We investigated the relationship between endothelial constitutive nitric oxide synthase (ecNOS) gene polymorphism and lipid metabolism in patients with nondiabetic chronic renal failure on hemodialysis. Serum from 181 nondiabetic patients on hemodialysis were examined. A genomic DNA fragment was amplified by polymerase chain reaction (PCR) for determining the ecNOS genotype. The PCR products were designated as a and b alleles by electrophoresis. In hemodialysis patients, the frequency of the ecNOS4 for b/b, b/a and a/a genotype was 76.6, 22.8 and 0.6%, respectively. There was not significant difference in the levels of total cholesterol (TC), triglyceride (TG) and calculated low-density lipoprotein cholesterol (LDL-c) in sera between patients (aa and ba) with the a allele and patients (bb) without the a allele. On the other hand, the levels of serum high-density lipoprotein cholesterol (HDL-c) in patients with the a allele (51.9 +/- 3.33 mg/dl) were significantly higher than those in patients without the a allele (43.05 +/- 1.40 mg/dl) (p = 0.005). The frequency of patients with the a allele and low levels of serum HDL-c among patients with a long duration of dialysis (> or =10 years) was significantly lower than that in patients with short duration of dialysis (<10 years) (p = 0.05). It appears that an intron 4 gene polymorphism in ecNOS may modulate lipid metabolism in nondiabetic patients on hemodialysis and the a allele of ecNOS gene polymorphism may affect the prognosis of hemodialysis patients with low levels of serum HDL-c.

A case of mixed connective tissue disease (MCTD) complicated with MPO-ANCA-related necrotizing glomerulonephritis

Renal diseases of mixed connective tissue disease (MCTD) are not unusual. Although most of them are SLE-like renal impairment with immune complex deposits, systemic sclerosis- (SSc) like renal impairments with intimal thickening of interlobular arteries or arterioles are also encountered. Several cases of SSc complicated with MPO-ANCA-related necrotizing glomerulonephritis (nGN) are reported. Here we report a case which developed MPO-ANCA-related nGN 16 years after the diagnosis of MCTD. She exhibited pauci-immune focal nGN and significantly high titer of MPO-ANCA. She was successfully treated with prednisolone and cyclophosphamide. We believe this is the first case in which MPO-ANCA-related nGN was demonstrated in a patient with MCTD.

Splenectomy may improve the glomerulopathy of type II mixed cryoglobulinemia

Many patients with type II mixed cryoglobulinemia have been shown to be infected with hapatitis C virus (HCV). Therefore, interferon-alfa has become the first choice of treatment for patients with HCV-associated cryoglobulinemia. However, the disease often relapses after the discontinuation of interferon therapy. The long-term effect of interferon therapy is controversial. Therefore, a more effective therapy needs to be developed. A 62-year-old Japanese woman was admitted to our hospital for the examination of abnormal liver function tests, severe edema, and purpura in her lower extremities. Glomerulopathy secondary to HCV-related cryoglobulinemia was suspected. Her serum creatinine was increased to 2.1 mg/dL. Interferon therapy was considered initially. However, because of pancytopenia caused by liver cirrhosis and splenomegaly, splenectomy was performed in February 1997, before the start of interferon therapy. Renal biopsy specimen taken at the time of the splenectomy showed typical cryoglobulinemic glomerulonephritis. Gradually, after surgery, the patient's thrombocytopenia and anemia improved, her proteinuria and hematuria were decreased, her cryocrit dropped from 15% to 5%, the Ccr increased from 21.1 mL/min to 48.8 mL/min, and the purpura in her lower extremities disappeared. A repeat renal biopsy performed in May 1998 showed marked histological improvement. Splenectomy is not widely accepted as a treatment for cryoglobulinemia. Our case suggests the possibility that the monoclonal-IgM component of the type II cryoglobulin may be formed in the spleen. In conclusion, splenectomy may be an effective therapy for cryoglobulinemia in patients with HCV-positive liver cirrhosis and pancytopenia secondary to splenomegaly.

Severe ectopic calcification of the intestinal wall in a patient on long-term continuous ambulatory peritoneal dialysis therapy

We report autopsy findings of a 69-year-old man on long-term CAPD therapy for 13 years who showed linear peritoneal calcification. Continuous ambulatory peritoneal dialysis (CAPD) was started in 1982. He has been administered excessive amounts of vitamin D(3) derivatives (VitD) (2.0 to 2.5 microg daily) and calcium carbonate (4 g daily) for secondary hyperparathyroidism since initiation of CAPD. In May 1995, his intact parathyroid hormone (PTH) level increased over 1,000 pg/mL. Immediately after VitD was changed from pill to liquid, the dose was increased to 5 microg daily. Although the serum calcium level remained between 4.5 and 4.9 mEq/L, and serum phosphate level was 5.0 to 7.2 mg/dL, plain abdominal radiography and computed tomography showed continuous calcification along the intestinal wall in October 1995. In spite of the continuation of CAPD therapy, he remained asymptomatic until he died of congestive heart failure in January 1997. He experienced eight episodes of peritonitis during his clinical course. Autopsy showed that numerous calcified plaques were present on the submucosal portion between the thickened serosa and the longitudinal layer of the muscularis externa. The remainder of the subserosa was fibrotic, and the small arteries had markedly thickened intima and severely narrowed lumina.

Transcatheter renal arterial embolization therapy on a patient with polycystic kidney disease on hemodialysis

We report a patient with autosomal dominant polycystic kidney disease (ADPKD) undergoing long-term hemodialysis who underwent transcatheter arterial embolization (TAE) of the renal arteries to shrink enlarged kidneys. In 1983, the patient started hemodialysis because of chronic renal failure secondary to ADPKD. However, renal size continued to increase. In January 1997, he was admitted to our hospital with abdominal distension and anorexia, in addition to progression of anemia. Upper gastroendoscopy showed an esophageal ulcer and severe external compression of the stomach. Renal angiography using the Seldinger technique showed stretched and deformed segmental renal arteries with massive enlargement of the kidneys. TAE with stainless steel coils was performed on both renal arteries. With a rapid and progressive decrease in kidney size, anorexia and anemia were improved, and the gastrointestinal compression was eliminated. In some patients with ADPKD, renal size continues to increase even after the initiation of dialysis. In about 10 years, patients develop gastrointestinal complications, such as dysphagia, ileus, severe constipation, and intestinal perforation. Surgical procedures such as nephrectomy are not satisfactory. This report shows that TAE is a safe and effective therapy for patients with ADPKD with massively enlarged kidneys.

[A case of rheumatoid arthritis with bucillamine-induced myasthenia gravis treated by immunoadsorption therapy]

We report a case of 48-year old female with rheumatoid arthritis (RA) complicated with myasthenia gravis. In 1988, she was diagnosed of having RA, and several therapeutic drugs were administered, but her disease activity was in poor control. In July 1993, bucillamine (BU) was started at a dose of 100 mg/day, and her arthritis subsided. However, in October 1996, she was admitted with a rapidly progressive ptosis and double vision in the left eye, which became prominent in the evening. Because serum concentration of the antibody to acetylcholine receptors (AchR Ab) was elevated at 12.6 nmol/l, and the ptosis was reversed immediately after a tensilon test, ocular type myasthenia gravis (MG) was diagnosed and it was thought to have been induced by BU. Immunoadsorption therapy was started after discontinuation of this drug, and was continued for 6 months, resulting in improvement of neurological symptoms and decrease in AchR Ab level. MG has not recurred since. Although several cases of D-penicillamine (DP) induced MG are reported, only two cases are reported which were induced by BU, sulfhydryl compound which has a structure similar to DP. Since BU has been widely used as one of the disease modifying anti-rheumatic drugs in Japan, MG induced by this drug should be paid attention as one of the adverse effects.

Hypererythropoietinemia and hyperreninemia in a continuous ambulatory peritoneal dialysis patient with chronic severe hypotension

We experienced a patient on continuous ambulatory peritoneal dialysis (CAPD) who showed hypererythropoietinemia (Epo concentration: 86.7 mU/ml, normal range: 8-36 mU/ml), erythrocytosis, high renin concentration (26.5 pg/ml) and chronic hypotension. In this patient the erythrocytosis progressed along with exacerbation of the chronic severe hypotensive state. This patient had systemic circulatory insufficiency as suggested by the fact that he had a fibrous myocardium and an increased anion gap. We hypothesized that circulatory insufficiency due to chronic severe hypotension may lead to the stimulation of the Epo production, due to a decreased oxygen supply to peripheral tissues and/or to the stimulation of the renin angiotensin system even in patients with end-stage renal failure.

LDL adsorption improves the response of focal glomerulosclerosis to corticosteroid therapy

We investigated the therapeutic effect of low density lipoprotein adsorption (LDL-A) in 14 patients who had focal glomerulosclerosis (FGS) with the nephrotic syndrome resistant to steroids. Patients received a total of 6 sessions (2 times a week for 3 weeks). The levels of total cholesterol, triglycerides and low-density lipoprotein were decreased significantly after treatment (by approximately 50%) in all patients (p<0.01). There also seemed to be a possibility that LDL-A improved the response to steroid therapy. The glomerular filtration rate (GFR) increased from 54.4 +/-27.4 ml/min to 70.0+/-30.2 ml/min (p <0.05) and daily urinary protein excretion (Up/day) decreased from 7.24+/-3.58 g/day to 2.56 + 2.00 g/day (p<0.01). Up/day was significantly higher in patients who showed more than 30% improvement of GFR (n = 6) than in patients who showed less than 30% improvement of GFR (n = 7) (9.50+/-3.41 g/day vs 4.59+/-1.17 g/day, p<0.05). The decrease of urinary protein excretion was more marked in younger patients (29.4+/-11.9 vs 49.7+/-14.8, p <0.05). Only electron microscopy was able to detect histological recovery in the patients who showed a decrease of proteinuria after LDL-A therapy and light microscopy was not able to verify or accurately identify the histological response. In conclusion, LDL-A seems to be effective for FGS associated with nephrotic syndrome resistant to steroids, especially in younger patients. Histological assessment of the effect of this treatment requires electron microscopic examination.

Evidence of association of the ecNOS gene polymorphism with plasma NO metabolite levels in humans

Nitric oxide (NO) synthesized by the vascular endothelium regulates mammalian blood vessels and other systems in humans. Recently, an endothelial nitric oxide synthase (ecNOS) gene polymorphism, the 27-bp repeat in intron 4 (ecNOS4), was reported to be related to the pathogenesis of coronary heart disease and terminal renal failure. We analyzed this polymorphism in a group of 413 healthy subjects, and measured their plasma nitrite and nitrate (NOx) levels. The frequency of the b allele was 89.8% , and the frequency of the a allele was 10.2%. The frequency of ecNOS4 b/b, ecNOS4 b/a, and ecNOS4 a/a in the healthy subjects in this study was 0.814 (n=336), 0.169 (n=70) and 0.017 (n=7), respectively. Using this polymorphism as a DNA marker, we found a strong association between the alleles of the ecNOS gene polymorphism and the plasma NOx levels. The basal NO metabolite levels were 28.8 micromol/L in subjects with ecNOS4 a/a, 31.4 micromol/L in those with ecNOS4 b/a, and 35.5 micromol/L in those with ecNOS4 b/b. The mean plasma NOx level of the subjects who were homozygous for the a allele was nearly 20% lower than in the subjects with the b allele. The plasma NOx level of the subjects with the a allele was 31.2+/-2.00 micromol/L, and significantly lower than the 35.5+/-0.93 micromol/L in those without the a allele (P <0.05). The results of this study indicate that the ecNOS4 gene locus may be responsible for variations in the genetic control of plasma NOx and that analysis of ecNOS4 gene polymorphism may be a useful tool for studying the relation between NO and diseases.

Apa I polymorphism in the vitamin D receptor gene may affect the parathyroid response in Japanese with end-stage renal disease

Vitamin D [1,25(OH)2D3] plays a key role in the pathogenesis of secondary hyperparathyroidism. A polymorphism in the vitamin D receptor (VDR) gene is reported to be involved in bone mineral density and the serum level of intact-osteocalcin (i-OC) in patients with osteoporosis. We investigated the relationship between VDR gene polymorphisms and the levels of intact PTH (i-PTH) and i-OC in 129 Japanese patients with end-stage renal disease (ESRD). The VDR gene sequences were PCR-amplified, and the product was cleaved with the restriction enzymes Bsm I and Apa I. Undigested alleles were designated as B and A, and the digested alleles as b and a, respectively. The frequencies for the Bsm I polymorphism were 0.0% BB, 19.4% Bb, and 80.6% bb, while those for Apa I polymorphism were 14.2% AA, 47.2% Aa, and 38.6% aa. The Bsm I polymorphism of VDR was greatly biased in Japanese people. The i-PTH level in the aa group was about twice as high as those in the both AA group and Aa group (P < or = 0.04). The i-OC concentrations in the aa group was also approximately double those in both the AA group and Aa group (P < or = 0.03). In contrast, no significant differences in age, duration of dialysis, male/female ratio, or the incidence of diabetic nephropathy were observed among these three groups. On the other hand, there was no significant differences in i-PTH and i-OC between the Bb and bb groups. These results suggest that VDR gene polymorphisms can affect parathyroid response in ESRD patients, and the Apa I polymorphism is more informative in Japanese patients than the Bsm I polymorphism. The VDR a gene allele may define the pathogenesis of secondary hyperparathyroidism and of high turnover bone disease in patients with ESRD.

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.

Targeting deletion of angiotensin type 1B receptor gene in the mouse

We null mutated the mouse angiotensin type 1B (AT1B) receptor gene (Agtr1b) by gene targeting. To identify the specific cell types carrying high Agtr1b gene transcriptional activities, the AT1B coding exon was replaced with a reporter gene, lacZ. In 6- to 8-wk-old Agtr1b -/- mice, high AT1B transcriptional activity was observed in adrenal zona glomerulosa cells and the testis, including mature and immature spermatic cells, whereas low activity was detected homogeneously in anterior pituitary cells and choroidal plexus vessel walls. A similar pattern was observed in Agtr1b +/- mice with less intensity. Microscopically, the anterior pituitary, heart, adrenal, zona glomerulosa, kidney, and the testis of Agtr1b -/- mice were intact and were indistinguishable from those of Agtr1b +/+ mice. Systemic blood pressure was comparable in Agtr1b -/- and Agtr1b +/+ mice. Moreover, plasma aldosterone level was comparable between the two mouse groups. No compensatory enhancement of AT1A mRNA was found in the kidney and adrenal gland of Agtr1b -/- mice. The observed absence of the abnormal phenotypes in Agtr1b -/- mice, which have been described for homozygous angiotensinogen null mutant mice, indicates that 1) AT1A receptors can take over the role of AT1B receptors in Agtr1b -/- mice or 2) functionally significant non-AT1, non-AT2 receptor(s) may exist for the action of angiotensin.

Desensitization of endothelin-1 binding by vasopressin via a cAMP-mediated pathway in rat CCD

In renal collecting ducts, endothelin-1 (ET-1) inhibits Na+ reabsorption and antagonizes the effects of arginine vasopressin (AVP). Whether AVP may affect ET-1 action in the collecting ducts that mainly express the ETB receptor subtype, however, remains unknown. Since ETB, but not ETA, possesses a consensus amino acid sequence for possible phosphorylation by protein kinase A (PKA), we hypothesized that AVP may influence ET-1 binding to the ETB receptor via PKA. In microdissected rat cortical collecting ducts, the specific ET-1 binding decreased by 35% (15.6 +/- 4.4 vs. 24.0 +/- 3.6 amol/mm in control) following 20-min preincubation with 10(-7) M AVP. This decrease in ET-1 binding was mimicked by 10(-5) M forskolin and by 10(-4) M dibutyryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP), indicating that this heterologous desensitization may be caused by a cAMP-dependent mechanism. Moreover, N-(2([3-(4-bromophenyl)-2-propenyl]-amino]-ethyl)-5- isoquinolinesulfonamide (H-89) and the Rp diastereoisomer of cAMP, Rp-cAMPS, which are both PKA-specific inhibitors, eliminated AVP-induced ETB receptor desensitization. The reduction in ET-1 binding was characterized by a decrease in binding affinity [dissociation constant (Kd) = 4 vs. 2 nM in control] with no change in maximal binding capacity. In contrast, forskolin and DBcAMP had no effect on ET-1 binding in endothelium-denuded aortic strips, which mainly express ETA subtype. These results showed that AVP rapidly downregulates the ETB receptor by reducing Kd through a PKA-dependent pathway. Thus ET-1 and AVP may act in a mutually antagonizing manner in the renal collecting ducts.

Endothelin-1 and endothelin-3 binding to rat nephrons

The existence of endothelin (ET) receptor subtypes has recently been implicated in the different biological effects of ET in various tissues. Indeed, the cDNAs for two types of ET receptors, ETA and ETB, have been cloned. To further gain insights into ET function in the kidney we examined 125I-labeled ET-1 and ET-3 binding to microdissected rat nephron segments. Specific ET-1 binding was highest in the inner medullary collecting duct, whereas the cortical and outer medullary collecting ducts as well as glomeruli showed moderate binding. There was low, although not significant, ET-1 binding to the early portion of the proximal tubule. Other nephron segments displayed little ET-1 binding. The binding profile of ET-3 along the nephron markedly resembled that of ET-1. Scatchard analyses of binding of ET-1 and ET-3 using cortical collecting ducts revealed a single class of receptor for both ET-1 and ET-3; apparent dissociation constants were 2.05 +/- 0.72 and 2.58 +/- 0.32 nM, and maximal binding capacity values were 0.408 +/- 0.058 and 0.511 +/- 0.047 fmol/mm, respectively. Displacement of 125I-ET-1 binding by unlabeled ET-3 was similar to that produced by unlabeled ET-1. Furthermore, a specific ETB agonist, BQ 3020, almost completely inhibited 125I-ET-1 binding in cortical collecting ducts, whereas a specific ETA antagonist, BQ 123, had little effect. These data indicate that cortical collecting ducts express ETB receptors, to which both ET-1 and ET-3 bind equally.

Endothelin-1 and -3 binding to ETB receptors in rat renal tubules

To increase understanding of endothelin (ET) function in the kidney, we investigated binding of the radioligand of endothelin isopeptides to microdissected rat nephron segments. Specific ET-1 binding was highest in the inner medullary collecting duct, whereas the cortical and outer medullary collecting ducts showed moderate binding, as did the glomeruli. There was slight ET-1 binding to the early portion of the proximal tubule. Other nephron segments displayed little ET-1 binding. The binding profile of ET-3 along the nephron markedly resembled that of ET-1. Scatchard analyses of ET-1 and ET-3 binding to cortical collecting ducts revealed a single class of receptor for both ET-1 and ET-3. Displacement of [125I]-ET-1 binding by unlabeled ET-3 was similar to that produced by unlabeled ET-1. Moreover, a specific ETB agonist, BQ-3020, almost completely inhibited [125I]-ET-1 binding in cortical collecting ducts, whereas a specific ETA antagonist, BQ-123, had little effect. These data indicate that cortical collecting ducts express ETB receptors, to which both ET-1 and ET-3 bind equally.

Detection of endothelin-1 mRNA by RT-PCR in isolated rat renal tubules

A combination of reverse transcription and polymerase chain reaction was utilized to detect baseline endothelin-1 (ET-1) mRNA expressed in renal tubules dissected from rats. 5' and 3' primers were constructed according to human ET-1 genomic DNA. Rat ET-1 mRNA was found to be expressed only in cortical through medullary collecting ducts in addition to glomeruli. Sites for tubular synthesis of ET-1 corroborate well with major ET-1 binding sites along the nephron, indicating autocrine/paracrine role of ET-1 in the renal tubules and supporting a prevailing concept on such function of ET-1 in many differing tissues.

Renal adrenergic receptors: localization of [125I]prazosin binding sites along the microdissected rat nephron

Norepinephrine stimulates renal tubular sodium reabsorption, probably through an alpha 1-adrenoceptor-mediated mechanism. Although the distribution of alpha 1-adrenoceptors in the kidney has been studied with autoradiography, the precise location of these receptors in isolated nephron segments is unclear. Using a microassay we determined the specific binding of [125I]iodoarylazidoprazosin ([125I]prazosin), a high specific radioactivity analog of the selective alpha 1-antagonist prazosin, to microdissected glomeruli and tubule segments. Specific binding of [125I]prazosin (3 nM) in the proximal convoluted tubule was time- and concentration-dependent, saturable, and reversible. In this segment the apparent KD by association and dissociation rate constants of [125I]prazosin binding was 0.47 nM, and the maximum receptor density was approximately 0.19 fmol/mm, or 720 fmol/mg protein. Binding specificity was verified in competition studies with excess (3 microM) unlabeled prazosin and probes for alpha 2- (yohimbine), beta- (propranolol), dopamine1- (SCH23390), and dopamine2- (S-sulpiride) receptors. [125I]Prazosin binding was inhibited significantly only by unlabeled prazosin. Mapping of prazosin binding along the nephron revealed that the highest density was in the proximal convoluted tubule, followed by the proximal straight tubule. Lesser binding was found in the thick ascending limb and in the distal convoluted tubule, whereas in the cortical and outer medullary collecting duct and in glomeruli, binding was not significantly different from zero.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine inhibits Na/K-ATPase in single tubules and cultured cells from distal nephron

Dopamine decreases tubular sodium reabsorption, attributed in part to Na/K-ATPase inhibition in the proximal convoluted tubule (PCT). Because the final regulation of sodium excretion occurs in the collecting duct, where we have demonstrated specific dopamine DA1 binding sites, we examined the effects of dopamine, and of DA1 and DA2 receptor agonists on the Na/K pump in the microdissected rat cortical collecting duct (CCD) and in Madin-Darby canine kidney (MDCK) cells, a line derived from the dog distal nephron. Dopamine inhibited pump activity in CCD by approximately 40%-50%, an effect proportionally larger than in the PCT. Unlike in the latter, the effect of dopamine was reproduced by the DA1 agonist fenoldopam, which inhibited the CCD pump in dose-dependent manner (maximum, 10 microM). The DA2 agonist quinpirole was without effect, either alone or in combination with fenoldopam. These actions on Na/K-ATPase paralleled in reciprocal fashion effects on adenylate cyclase: dopamine or fenoldopam, but not quinpirole, produced a significant increase in cAMP content, and the stimulation by dopamine was blocked by SCH 23390. Inhibitors of cAMP phosphodiesterase (3-isobutyl-1-methyl-xanthine and theophylline), as well as forskolin and dibutyryl-cAMP, mimicked the effect of dopamine on the pump, underscoring the role of increased cAMP in this phenomenon. Both dopamine and fenoldopam inhibited Na/K-ATPase activity in MDCK cells. The results indicate that besides the PCT dopamine inhibits Na/K-ATPase activity in cells of the distal nephron, where its effect on the pump appears to be more pronounced and is mediated by activation of the DA1 receptor. The natriuretic effect of dopamine is probably exerted at both proximal and distal nephron sites.

Hormone receptors and sites of action in the kidney

Identification of hormone target sites in the nephron has been achieved in part using autoradiography, and largely with microdissection and microanalysis techniques that permit quantitative measurements of hormone binding or postbinding effects in discrete nephron segments. The nephron target sites of hormones whose intracellular second messenger is known have been located by measuring their stimulatory effect on cyclic AMP or GMP production along the nephron. These hormones include arginine vasopressin, parathyroid hormone, calcitonin, and beta-adrenergic catecholamines. In contrast, the action sites of hormones whose cellular mediators are less well understood have been identified using micro modifications of conventional binding techniques scaled down to the minute (less than or equal to 1 microgram protein) amount of tissue available. In this group are aldosterone, corticosterone, insulin, angiotensin II, alpha-adrenergic catecholamines and dopamine. Atrial natriuretic peptides and glucagon have been studied with both methods. The precise localization of hormone receptors and sites of action in the functionally heterogeneous nephron is critical for understanding the interactions between the kidney and the endocrine system in fluid volume homeostasis, blood pressure control, and in biochemical and metabolic regulation.

Localization of dopamine-1 receptors along the microdissected rat nephron

Dopamine exerts numerous actions on the kidney but the precise location of its receptor subtypes along the nephron is unknown. Using a microassay we determined the specific binding of 125I-Sch 23982, a specific and selective dopamine-1 (DA1) receptor antagonist, to microdissected glomeruli and tubule segments. Binding of 125I-Sch 23982 in the proximal convoluted tubule (PCT) was time- and concentration dependent, saturable and reversible. The linear Scatchard plot of saturation experiments suggested binding to a single site with an apparent Kd of 16.7 nM and Bmax of 0.4 fmol.mm-1 in the PCT, and 6.2 nM and 0.1 fmol.mm-1 in the cortical collecting tubule (CCT). Mapping of DA1 binding sites along the nephron revealed their presence in each of the segments examined, albeit in markedly different concentrations: the highest specific binding was measured in PCT followed by the pars recta. Binding was less in the distal nephron, and least in the medullary and cortical thick ascending limb. Modest binding was also detected in glomeruli. In cortical collecting tubules competition studies with unlabeled dopamine and probes for DA1 (Sch 23390, fenoldopam), DA2 (domperidone, S-sulpiride), serotonergic (serotonin, ketanserin, mianserin), and alpha-(phentolamine) and beta-(propranolol) adrenergic receptors indicated a rank-order potency for displacement of 125I-Sch 23982 binding, consistent with labeling of DA1 receptors. Dopamine inhibited Na/K-ATPase both in PCT and CCT, an effect duplicated in the latter segment by the DA1 agonist fenoldopam, and blocked by the DA1 antagonist Sch23390.(ABSTRACT TRUNCATED AT 250 WORDS)

Early effects of aldosterone on Na-K pump in rat cortical collecting tubules

Sustained exposure to aldosterone (Aldo) increases the abundance and activity of the Na-K pump in cortical collecting tubules (CCT). However, the onset and mechanism of the early interaction of Aldo with the CCT pump, especially in adrenal-intact animals, are unclear. We evaluated the short-term effects of the hormone on Na-K-adenosinetriphosphatase (ATPase) activity and on ouabain-sensitive 86Rb uptake, a measure of the transporting rate of the pump, in microdissected CCT from adrenal-intact rats. Incubation with Aldo (10(-8) M, 2 h) had no effect on Na-K-ATPase activity (Vmax), whereas it produced at least a twofold increase in 86Rb uptake. This effect was generated by physiological concentrations of the hormone (threshold 10(-10) M; apparent K1/2 approximately 10(-9) M), after a short lag of less than or equal to 30 min. Incubation with Aldo in the presence of amiloride or nystatin or in a Na-free medium (choline chloride) did not prevent the enhanced 86Rb uptake seen after Aldo alone; possible interpretations of these observations are discussed. We conclude that Aldo produces a rapid stimulation of pump function in CCT that precedes its induction of new pump synthesis; the physiological significance of this effect is suggested by its occurrence in tubules from adrenal-intact animals within the time frame and concentration range of the hormone's effects on electrolyte transport.

Intranephron PGE2 production in stroke-prone spontaneously hypertensive rats

To investigate whether intranephron prostaglandin E2 (PGE2) production in stroke-prone spontaneously hypertensive rats (SHRSP) differs from that in Wistar-Kyoto rats (WKY), we measured PGE2 accumulation rates in microdissected nephron segments from 4- to 6- and 12- to 14-wk-old male rats by radioimmunoassay. In both young and adult WKY, PGE2 accumulation was highest in the papillary collecting duct (PCD) and outer medullary and cortical collecting tubules, intermediate in the glomerulus (Glm), medullary and cortical thick ascending limbs of Henle's loop, and distal tubule, and negligible in the proximal tubule. PGE2 accumulation in adult WKY was severalfold higher than that in young WKY. PGE2 accumulation in adult and prehypertensive young SHRSP was significantly lower than that of respective WKY in most segments, whereas urinary PGE2 excretion was significantly higher in SHRSP than in age-matched WKY. Plasma arginine vasopressin concentrations in adult SHRSP were significantly higher than in WKY. PGE2 accumulation stimulated by 5 microM arachidonic acid was significantly lower in SHRSP than in WKY in most segments of young rats but was lower only in Glm and PCD of adult rats. PGE2 accumulation stimulated by 2 microM Ca2+ ionophore A23187 was significantly lower in most segments of adult and young SHRSP. These results indicate that a decrease in renal tubular PGE2 productive activities in SHRSP might not be caused by secondary adaptation to hypertension.