Effect of apelin on glomerular hemodynamic function in the rat kidney

Apelin is a vasoactive peptide identified as the endogenous ligand of an orphan G protein-coupled receptor called APJ. Apelin and its receptor have been found in the brain and the cardiovascular system. Here we show that the apelin receptor mRNA is highly expressed in the glomeruli while its level of expression is lower in all nephron segments including collecting ducts that express vasopressin V2 receptors. Intravenous injection of apelin 17 into lactating rats induced a significant diuresis. Apelin receptor mRNA was also found in endothelial and vascular smooth muscle cells of glomerular arterioles. Apelin administration caused vasorelaxation of angiotensin II-preconstricted efferent and afferent arterioles as shown by an increase in their diameter. Activation of endothelial apelin receptors caused release of nitric oxide which inhibited angiotensin II-induced rise in intracellular calcium. In addition, it appears that apelin had a direct receptor-mediated vasoconstrictive effect on vascular smooth muscle. These results show that apelin has complex effects on the pre- and post glomerular microvasculature regulating renal hemodynamics. Its role on tubular function (if any) remains to be determined.     

Vascular endothelial growth factor (VEGF121) protects rats from renal infarction in thrombotic microangiopathy

BACKGROUND: Renal thrombotic microangiopathy, typified by the hemolytic uremic syndrome, is associated with endothelial cell injury in which the presence of cortical necrosis, extensive glomerular involvement, and arterial occlusive lesions correlates with a poor clinical outcome. We hypothesized that the endothelial survival factor vascular endothelial growth factor (VEGF) may provide protection. METHOD: Severe, necrotizing, thrombotic microangiopathy was induced in rats by the renal artery perfusion of antiglomerular endothelial antibody, followed by the administration of VEGF or vehicle, and renal injury was evaluated. RESULTS: Control rats developed severe glomerular and tubulointerstitial injury with extensive renal necrosis. The administration of VEGF significantly reduced the necrosis, preserved the glomerular endothelium and arterioles, and reduced the number of apoptotic cells in glomeruli (at 4 hours) and in the tubulointerstitium (at 4 days). The prosurvival effect of VEGF for endothelium may relate in part to the ability of VEGF to protect endothelial cells from factor-induced apoptosis, as demonstrated for tumor necrosis factor-alpha (TNF-alpha), which was shown to be up-regulated through the course of this model of renal microangiopathy. Endothelial nitric oxide synthase expression was preserved in VEGF-treated rats compared with its marked decrease in the surviving glomeruli and interstitium of the antibody-treated rats that did not receive VEGF. CONCLUSIONS: VEGF protects against renal necrosis in this model of thrombotic microangiopathy. This protection may be mediated by maintaining endothelial nitric oxide production and/or preventing endothelial cell death.     

Interaction between adrenomedullin and angiotensin II in DNA synthesis and extracellular matrix accumulation in cultured rat kidney interstitial cells

Background. To investigate the role of adrenomedullin (AM) in the regulation of renal fibrosis, we assessed the effects of AM on angiotensin II (AT II)-induced cell proliferation and extracellular matrix (ECM) accumulation in cultured NRK 49F cells, a cell line derived from normal rat kidney fibroblasts. Methods. Northern blot analysis was performed, using cDNA probes against rat AM, human calcitonin-receptor-like receptor (CRLR), human receptor-activity-modifying protein 2 (RAMP 2), human collagen α-1 (I) (Col-I), human fibronectin (FN), and rat transforming growth factor (TGF)-β1. Polymerase chain reaction (PCR) analysis for CRLR was amplified for 35 cycles. Cell proliferation was determined by the measurement of [³H]thymidine incorporation. Results. We have shown that NRK 49F cells express AM and its receptor, which consists of a CRLR and RAMP 2. Rat AM significantly inhibited cell proliferation and mRNA expression of ECM in the absence and presence of AT II through an AM receptor, because calcitonin gene-related peptide (8-37) [CGRP (8-37)], an antagonist to AM receptor, completely reversed these inhibitory actions. The inhibitory effects appeared to be mediated by a marked increase in intracellular cAMP. While AT II enhanced ECM accumulation by a process depending upon autocrine TGF-β1 secretion in NRK 49F cells, AM suppressed the induction of TGF-β1. Conclusions. The inhibitory action of AM on ECM accumulation may be caused by the suppression of TGF-β1. AM may play an important role in the inhibition of renal interstitial fibrosis under pathological conditions, through acting in an autocrine and/or paracrine fashion. Received: May 2, 2001 / Accepted: November 27, 2001     

The effect of elastase on aminonucleoside nephrosis--on renal vascular system]

This study was performed to investigated the relationship between cross sectional areas of glomerular arterioles and glomerular volume in rats with puromycin aminonucleoside (PAN)-induced nephrosis, which is an experimental model of glomerular sclerosis. We also evaluated the effect of an anti-arteriosclerotic agent, elastase on these parameters. Six-week-old male Sprague-Dawley rats were divided into 3 groups; control, PAN-treated (70 mg/kg i.p.), or PAN+elastase-treated (5 mg/kg/day i. m.) group. After 12 weeks of experimental period, microvascular cast of the kidney was prepared, and the cross sectional areas of afferent and efferent arterioles as well as glomerular volume were measured using scanning electron microscopy. In the juxtamedullary glomeruli with minor abnormalities, the efferent arteriole was narrower in PAN-treated rats than in the control rats and the elastase-treatment partially corrected it (control 55.7, PAN 35.9, PAN+elastase 43.7 x 10 microns 2). On the other hand, the cross sectional area of afferent arteriole was not different among the 3 groups. In glomeruli showing sclerosis, the cross sectional area of efferent arteriole correlated positively with the glomerular volume. There results suggest that constriction of the efferent arterioles contributes to the development of glomerular sclerosis in PAN-induced nephrosis. In addition, elastase possibly inhibits this process and thereby protect glomeruli from sclerosis.     

Real-time observation of glomerular hemodynamic changes in diabetic rats: effects of insulin and ARB

BACKGROUND: The progression of diabetic nephropathy is closely related to disturbances in glomerular hemodynamics, such as glomerular hypertension and/or hyperperfusion. The aim of this study was to observe and to analyze glomerular hemodynamics in rats with diabetes mellitus (DM) in vivo using confocal laser scan microscopy (CLSM). We also examined the effects of candesartan cilexetil (TCV-116), a selective angiotensin II type 1 receptor blocker (ARB), on glomerular hemodynamics in DM. METHODS: Munich-Wistar rats were divided into six groups: (1) four-day control; (2) four-day DM; (3) 28-day control; (4) 28-day DM; (5) DM treated with insulin; (6) DM treated with TCV-116. The kidney-to-body weight ratio, glomerular volume, and proteinuria were estimated. Glomerular hemodynamic changes were observed using CLSM and renal expression of endothelial nitric oxide synthase (eNOS), and neuronal nitric oxide synthase (nNOS) was evaluated by immunofluorescence. RESULTS: The kidney-to-body weight ratio, glomerular volume, the diameters of afferent arterioles (AA) and efferent arterioles (EA), erythrocyte velocities within glomeruli, and volume flow in glomerular capillary loops in four-day DM were significantly higher than in control rats, and increases were even more pronounced in the 28-day DM. TCV-116 treatment ameliorated all these findings and significantly decreased proteinuria, but there was no effect on the blood glucose level. On the other hand, insulin treatment was followed by normalization of all these changes induced in DM. Enhanced renal expression of eNOS in DM was suppressed when treated with either TCV-116 or insulin, while expression of nNOS was unaltered among the four groups. CONCLUSION: This imaging procedure allowed us to evaluate glomerular microcirculation in vivo, including the diameters of AA and EA, erythrocyte velocity, and volume flow. DM significantly induced glomerular hemodynamic alteration and renal hypertrophy. DM treated with either insulin or ARB ameliorated these changes. This study shows that progress in imaging technology promises to make major contributions to revealing the involvement of hemodynamic changes in glomerular diseases, aiding prognosis and the monitoring of therapeutic effects, as well.     

Tubular and glomerular L-arginine transport (uptake and transporters) and the nitric oxide synthases in ischemic acute renal failure (iARF) in streptozotocin-induced diabetic rats (STZ-DM)

BACKGROUND: L-arginine or its metabolites may be important pathogenetic factors in ischemic acute renal failure (iARF) in rats. It was found that the L-arginine-nitric oxide synthase-nitric oxide system plays an important role in the renal hemodynamic alterations in the early stages of diabetes. The iARF in diabetic rats is much more severe than the normal rats exposed to a same ischemia time. The purpose of the present study was to evaluated L-arginine uptake and its transporters and nitric oxide synthase isoform expression in tubuli and glomeruli of STZ-induced diabetic rats with iARF. METHODS: iARF was induced by right nephrectomy and left renal artery clamping for 60 min followed by a 60 min reflow period. iARF was induced in STZ diabetes rats two weeks after intraperitoneal streptozotocin (60 mg/kg body weight) and in normal control rats. L-arginine uptake, L-arginine transporters (CAT1 and CAT2) and nitric oxide synthases (iNOS, eNOS, and bNOS) were determined by RT-PCR) in both glomeruli and tubuli preparations. RESULTS: The STZ diabetic rats compared with the non diabetic normal rats have a higher glomerular L-arginine uptake, higher iNOS mRNA, lower eNOS mRNA, and lower tubular CAT1 mRNA, eNOS mRNA, and bNOS mRNA. The diabetic iARF after one hour of reperfusion had lower glomerular L-arginine uptake, lower CAT1 mRNA, lower eNOS mRNA, lower bNOS, and higher tubular iNOS mRNA compared with iARF in normal rats. CONCLUSIONS: Our findings suggest a prolonged and more severe post-glomerular vasoconstriction very early after the reflow in the iARF of STZ diabetic rats compared with the iARF in the normal control rats. That may be a plausible explanation to the very significant decline in GFR and tubular necrosis that characterize the iARF in diabetic rats.     

Blockade of serotonin 2A receptor improves glomerular endothelial function in rats with streptozotocin-induced diabetic nephropathy

Background Serotonin (5-HT) is involved in vascular inflammation and atherosclerogenesis. Serum 5-HT concentrations are elevated in diabetes, and 5-HT is involved in diabetic vasculopathies. Sarpogrelate hydrochloride, a 5-HT2A receptor antagonist, has renoprotective effects, but its effect in diabetic nephropathy is not elucidated. The aim of this study was to examine the effects of sarpogrelate on endothelial dysfunction in rats with streptozotocin (STZ)-induced diabetes. Methods Rats with STZ-induced diabetes were either untreated or treated with sarpogrelate (30 mg/kg P.O.) for 8 weeks. At the end of the experiment, we measured urinary albumin excretion, serum adiponectin concentration and platelet-derived microparticles. Intraglomerular coagulation was detected by immunostaining for platelets. Production of renal reactive oxygen species (ROS) and nitric oxide (NO) was investigated by confocal laser microscopy and used as an index of glomerular endothelial dysfunction. Results Diabetic nephropathy was associated with enhanced production of ROS and diminished bioavailable NO in the glomeruli. Treatment with sarpogrelate improved ROS/NO imbalance in glomeruli, suppressed platelet aggregation in glomeruli, reduced platelet-derived microparticles, increased serum adiponectin level and reduced the level of albuminuria, compared with non-treated diabetic rats. Conclusions Our results indicate that sarpogrelate improves endothelial function in rats with STZ-induced diabetes through a reduction of glomerular platelet activation and an increase in serum adiponectin concentrations and suggest that sarpogrelate is potentially useful for the treatment of diabetic nephropathy.     

Pathomorphological studies on arterial cushion. 2. Aminonucleoside nephrotic rat

The present study is an attempt to solve the problem of pathogenesis of focal glomerular sclerosis (FGS), especially in juxtamedullary cortex, we were investigated by measurement of luminal diameters of afferent arterioles (Aff), efferent arterioles (Eff) of numerous glomeruli, arterial cushion (AC), afferent arterioles (AC-aff) at a region of branching arteries from the interlobular arteries, using scanning electron micrographs of methyl methacrylate casts of intrarenal arteries of aminonucleoside nephrotic rats. As regards luminal diameters, Eff were nearly equal Aff in minor glomerular abnormalities (Minor). Nevertheless Eff of glomeruli with segmental sclerosis (FSHS) were smaller than Aff (t-test). AC with FSHS were smaller than ones of Minor, statistically (t-test). The results of these examination, the cushion may be important factor for the regulation of blood flow in sclerotic glomeruli.     

Tubular and Glomerular L-Arginine Transport (Uptake and Transporters) and the Nitric Oxide Synthases in Ischemic Acute Renal Failure (iARF) in Streptozotocin-Induced Diabetic Rats (STZ-DM)

Background. L-arginine or its metabolites may be important pathogenetic factors in ischemic acute renal failure (iARF) in rats. It was found that the L-arginine-nitric oxide synthase-nitric oxide system plays an important role in the renal hemodynamic alterations in the early stages of diabetes. The iARF in diabetic rats is much more severe than the normal rats exposed to a same ischemia time. The purpose of the present study was to evaluated L-arginine uptake and its transporters and nitric oxide synthase isoform expression in tubuli and glomeruli of STZ-induced diabetic rats with iARF. Methods. iARF was induced by right nephrectomy and left renal artery clamping for 60 min followed by a 60 min reflow period. iARF was induced in STZ diabetes rats two weeks after intraperitoneal streptozotocin (60 mg/kg body weight) and in normal control rats. L-arginine uptake, L-arginine transporters (CAT1 and CAT2) and nitric oxide synthases (iNOS, eNOS, and bNOS) were determined by RT-PCR) in both glomeruli and tubuli preparations. Results. The STZ diabetic rats compared with the non diabetic normal rats have a higher glomerular L-arginine uptake, higher iNOS mRNA, lower eNOS mRNA, and lower tubular CAT1 mRNA, eNOS mRNA, and bNOS mRNA. The diabetic iARF after one hour of reperfusion had lower glomerular L-arginine uptake, lower CAT1 mRNA, lower eNOS mRNA, lower bNOS, and higher tubular iNOS mRNA compared with iARF in normal rats.

Conclusions. Our findings suggest a prolonged and more severe post-glomerular vasoconstriction very early after the reflow in the iARF of STZ diabetic rats compared with the iARF in the normal control rats. That may be a plausible explanation to the very significant decline in GFR and tubular necrosis that characterize the iARF in diabetic rats.     

一氧化氮在糖尿病肾病中的作用

目的探讨糖尿病（ＤＭ）和高血压大鼠肾脏一氧化氮（ＮＯ）途径与ＤＭ肾病的关系。方法将自发性高血压大鼠（ＳＨＲ）制成链脲佐菌素（ＳＴＺ）ＤＭ模型。设ＷＫＹ、ＳＨＲ和ＳＨＲＤＭ三组。除形态学观察外,还测定各组大鼠肌酐清除率（Ｃｃｒ）、２４小时尿蛋白、血及肾组织ＮＯ含量、肾脏ＮＯ合成酶（ＮＯＳ）活性和ＮＯＳｍＲＮＡ表达水平。结果ＳＨＲＤＭ组大鼠２４小时尿蛋白定量２０周时明显高于其余两组,Ｃｃｒ无明显改变。血ＮＯ水平升高,肾ＮＯ含量降低。肾脏结构型ＮＯＳ（ｃＮＯＳ）活性下降,诱导型ＮＯＳ（ｉＮＯＳ）活性或ｉＮＯＳ／ｃＮＯＳ（ｉ／ｃ）比值增加。肾小球ＮＯＳｍＲＮＡ表达面积扩大,入球动脉及小叶间动脉ＮＯＳ基因表达明显下降。肾小球系膜增生,有形成ＫＷ结节或纤维蛋白帽的趋势,系膜区基质增多,基底膜增厚,肾小动脉壁厚腔窄。结论（１）ＳＴＺＳＨＲＤＭ模型出现的２４小时尿蛋白增加、肾小球系膜及肾小血管病变提示ＤＭ肾病的产生;（２）肾脏ＮＯ系统异常与ＤＭ肾病有关。     

Glomerular-specific protein kinase C-β-induced insulin receptor substrate-1 dysfunction and insulin resistance in rat models of diabetes and obesity

Insulin resistance has been associated with the progression of chronic kidney disease in both diabetes and obesity. In order to determine the cellular mechanisms contributing to this, we characterized insulin signaling in renal tubules and glomeruli during diabetic and insulin-resistant states using streptozotocin-diabetic and Zucker fatty-insulin-resistant rats. Compared with nondiabetic and Zucker lean rats, the insulin-induced phosphorylation of insulin receptor substrate-1 (IRS1), Akt, endothelial nitric oxide synthase, and glycogen synthase kinase 3α were selectively inhibited in the glomeruli but not in the renal tubules of both respective models. Protein, but not mRNA levels of IRS1, was decreased only in the glomeruli of streptozotocin-diabetic rats likely due to increased ubiquitination. Treatment with the protein kinase C-β inhibitor, ruboxistaurin, enhanced insulin actions and elevated IRS1 expression. In glomerular endothelial cells, high glucose inhibited the phosphorylation of Akt, endothelial nitric oxide synthase, and glycogen synthase kinase 3α; decreased IRS1 protein expression and increased its association with ubiquitin. Overexpression of IRS1 or the addition of ruboxistaurin reversed the inhibitory effects of high glucose. Thus, loss of insulin's effect on endothelial nitric oxide synthase and glycogen synthase kinase 3α activation may contribute to the glomerulopathy observed in diabetes and obesity.     

Oxidant stress is increased within the glomerulus in experimental diabetic nephropathy

SUMMARY: The mechanisms by which the metabolic consequences of hyperglycaemia induce diabetic renal injury remain ill-defined. We hypothesized that oxidant stress, a consequence of hyperglycaemia, is increased in glomeruli from Lewis rats with streptozotocin (STZ)-induced diabetes prior to major structural and functional glomerular damage. After 12 weeks of diabetes, Lewis rats had not developed proteinuria and their glomeruli appeared normal by light microscopy. However, kidneys of diabetic animals had higher levels of lipid peroxides and malondialdehyde (MDA) than control rats. Immunohistochemistry demonstrated MDA–lysine adducts in glomeruli of diabetic rats, and that lipid peroxides and MDA were increased in glomerular lysates of diabetic rats. A possible mechanism for this finding was suggested by the observation that freshly isolated whole glomeruli from STZ rats showed a greater capacity than glomeruli from control rats to produce H₂O₂. Activity of the inducible form of superoxide dismutase (SOD) Mn-SOD was increased in glomerular lysates from STZ rats, consistent with its induction by oxidant stress. Immunostaining for Cu,Zn SOD showed increased protein in glomeruli, although compared with the increase in Mn-SOD activity, Cu,Zn-SOD activity was not substantially increased, potentially as a result of partial inactivation of this enzyme by glycation. The increased oxidant stress in untreated diabetic rats was a consequence of hyperglycaemia and not due to a direct nephrotoxic effect of STZ, as at least some of these changes were attenuated by insulin treatment of diabetic animals. Collectively, these results demonstrate that experimental diabetes mellitus is accompanied by increased oxidant stress within glomeruli.     

Increased shear stress-released NO and decreased endothelial calcium in rat isolated perfused juxtamedullary nephrons

BACKGROUND: Nitric oxide is an important vasodilator released from endothelial cells by the calcium-dependent endothelial nitric oxide synthase (NOS). We considered it important to investigate how shear stress/perfusion pressure influenced endothelial cell calcium concentration, nitric oxide release, and autoregulation of the afferent arteriole, since this arteriole controls glomerular filtration rate (GFR) and renin release. METHODS: We used an isolated perfused juxtamedullary nephron preparation and measured calcium with Fura 2, nitric oxide with 4-amino-5 methylamino-2', 7'-difluorescein (DAF-FM) and diameter with an imaging system. A mathematical model was applied to calculate changes in nitric oxide concentration and shear stress/wall tension during perfusion with and without erythrocytes at perfusion pressures varying from 50 to 150 mm Hg. RESULT: Cell-free perfusion increased nitric oxide concentration and abolished autoregulation; addition of erythrocytes or l-arginine analog N-nitro-l-arginine methyl ester (L-NAME) decreased nitric oxide concentration and reinstated autoregulation. Elevated perfusion pressure/elevated shear stress increased nitric oxide release and surprisingly decreased the endothelial cell calcium concentration, with perfusion pressure increase from 50 to 150 mm Hg, using blood perfusion endothelial calcium concentration decreased from 186 +/- 39 to 76 +/- 25 nmol/L and with cell-free perfusion from 116 +/- 33 to 56 +/- 21 nmol/L. CONCLUSION: Nitric oxide scavenging by erythrocytes has a high impact on arteriolar nitric oxide concentration and autoregulatory response. Nitric oxide measurements in endothelial cells of the afferent arteriole showed that increased perfusion pressure/shear stress increased nitric oxide release, while simultaneously endothelial cell calcium concentration decreased, possibly indicating a feedback control of this calcium by nitric oxide release.     

Microvascular protection induced by late preconditioning was abolished in STZ-induced acute diabetic rats

The authors attempted to determine whether ischemic preconditioning (IPC) can provide microvascular protection in skeletal muscle of diabetic rats against injury from a subsequent (24 hr later) prolonged period of ischemia and reperfusion. Male Sprague Dawley rats weighting 80 to 100 g were injected intraperitoneally with either streptozotocin (STZ, 65 mg/kg) or vehicle (sodium citrate, pH 4.5). Rats with a fasting blood glucose level over 300 mg/dl 1 week after injection of STZ were considered acute diabetic. The cremaster muscle of the rats underwent 45 min of IPC and 24 hr later, 4 hr of warm ischemia followed by reperfusion (I/R). Four groups were compared: IPC in normal rats (n=8); sham IPC in normal rats (n=8); IPC in diabetic rats (n=6); and sham IPC in diabetic rats (n=4). Microvascular responses in the cremaster muscle to IPC were determined by measuring the diameter of feeding, terminal arterioles and capillary perfusion using intravital microscopy, and by the evaluation of the endothelium-dependent nitric oxide system in the terminal arterioles. The average diameter of the feeding and terminal arterioles, as well as capillary perfusion, were significantly decreased in diabetic animals, compared to normal animals. There was a significant endothelial dysfunction detected in the terminal arterioles of diabetic rats. Ischemic preconditioning provided significant microvascular protection against prolonged ischemia/reperfusion in normal rats, but not in diabetic rats. IPC-induced microvascular protection in the normal skeletal muscle was abolished in STZ-induced acute diabetic rats.     

Immunocytochemical localization of renin and kallikrein in the rat renal cortex

Immunocytochemical studies in the past, using alternate serial sections to localize individual antigens, concluded that there was no close relationship between renin- and kallikrein-containing structures in the rat kidney. We have investigated this relationship by simultaneously localizing renin and kallikrein in the same section using immunoperoxidase with two different chromogens. Analysis of serial kidney sections from three rats indicated that kallikrein-containing late distal tubular cells corresponded in their distribution to connecting tubule cells. They were observed in the proximity (less than 3 micrograms) of renin-containing JG cells in 66.6% of the superficial (N = 30), 46.6% of the midcortical (N = 15) and 26.7% of the juxtamedullary (N = 15) afferent arterioles surveyed. When traced through serial sections, 90% of the afferent arterioles from superficial glomeruli (N = 30), 86.7% of the afferent arterioles from midcortical glomeruli (N = 15) and 73.3% of those from juxtamedullary glomeruli (N = 15) came within 3 micrograms of a late distal tubule showing some kallikrein-positive cells. These cells were adjacent to the afferent arteriole in 67 to 80% of the arterioles surveyed. This spatial relationship suggests an anatomical basis for a possible interaction between the afferent arteriole, containing renin-positive JG cells, and kallikrein-positive late distal tubular cells.     

Vascular architecture modifications in the steroid-induced polycystic kidney

This paper presents a study of the renal vascular architecture in polycystic kidneys induced in newborn rabbits by a single injection of methylprednisolone acetate. Ink perfusion and polyester resin corrosion casts were utilized, and the vasculature was studied by light and scanning electron microscopy. Vascular alterations were observed in the two main evolutive stages of the renal polycystosis: the stage of tubular cysts and the stage of glomerular cysts. These alterations were compared with the normal vascular pattern of control kidneys. At the tubular cyst stage the sinusoidal vascular cortical plexus persisted for a long period of time and the superficial cortical glomerular tufts were poorly developed. At the glomerular cyst stage, the vascular architecture of the superficial cortex showed numerous alterations. The glomerular tufts were small and their structural pattern was affected. Frequently the hilum was very wide and the afferent and efferent arterioles were on opposite sides of the glomerular tufts. The afferent arterioles were variable in size and length. Sometimes the glomeruli showed several afferent arterioles. There were numerous cases of double efferent arterioles in the superficial glomeruli of the polycystic kidneys. Various types of aglomerular shunts were observed regardless of the cystic stage or age. These data indicate that, in addition to the cysts, the corticoid-induced polycystic kidneys showed alterations of the renal vascular architecture which are interpreted as a malformation. We suggest, on the basis of these morphologic observations, that the pathogenesis of the polycystic kidneys is not related to the vascular alterations.     

Hypertensive renal damage: Modulation expression of smooth muscle myosin heavy chain isoforms

Summary: The aim of this study was to determine the phenotypic modulation in preglomerular vascular smooth muscles and glomerular cells in hypertension. Eight-week-old stroke-prone spontaneously hypertensive rats (SHRSP) fed high sodium pellets (3%) were untreated or treated with a calcium antagonist, manidipine HCI (2 mg/kg per day), for 8 weeks. the expression of myosin heavy chain isoforms (MHC), SM2 (muscletype) and SMemb (non-muscle-type) or α-actin was examined by the immunohistochemical technique. In normotensive Wistar-Kyoto rats, both SM2 and α-actin were expressed equally in the smooth muscles of preglomerular vessels, and SMemb was expressed slightly in the glomerular epithelial cells. In the SHRSP, however, the expression of SM2 and α-actin was significantly decreased or disappeared in the afferent arterioles, depending on the degree of vascular damage. In damaged glomeruli, SMemb and α-actin were newly expressed in mesangial cells. Manidipine HCI attenuated the renal damage and restored the expression of α-actin in the afferent arterioles. There was a significant correlation between the glomerular damage and the attenuation of SM2 expression (r=0.87). In conclusion, phenotypic modulation of vascular smooth muscles occurred in hypertensive renal damage and was correlated with the glomerular damage, where the phenotypic modulation also took place in the mesangial cells. These results indicate that the phenotypic modulations revealed by the expression of myosin isoforms might play an important role in the development of hypertensive renal damage.     

Differential distribution of insulin-like growth factor-1 and insulin-like growth factor binding proteins in experimental diabetic rat kidney

Insulin-like growth factor-1 (IGF-1) is a peptide growth factor, and its activity is modulated by interaction with the family of IGF binding proteins (IGFBP-1 to 6). IGF-1 is detected in rat kidney and has metabolic and growth effects. To explore the possible involvement of IGFBPs in glomerular hypertrophy in streptozotocin (STZ)-induced diabetic rat, the immunolocalization of IGF-1 and IGFBPs were investigated. IGF-1 was gradually increased in the glomeruli of diabetic rats and correlated with glomerular hypertrophy. IGFBP-1 was transiently increased at 1 week after the STZ injection and declined to control level during the following period. In contrast, IGFBP-4 was increased in the diabetic glomeruli throughout the observation period. With insulin treatment, the levels of IGF-1, IGFBP-1 and 4 were normalized and glomerular hypertrophy was prevented. Initial glomerular hypertrophy of diabetic nephropathy is a related IGF-1 action, which may be modulated by IGFBP-1 and 4.     

T-type voltage-gated calcium channels regulate the tone of mouse efferent arterioles

Voltage-gated calcium channels are important for the regulation of renal blood flow and the glomerular filtration rate. Excitation-contraction coupling in afferent arterioles is known to require activation of these channels and we studied their role in the regulation of cortical efferent arteriolar tone. We used microdissected perfused mouse efferent arterioles and found a transient vasoconstriction in response to depolarization with potassium; an effect abolished by removal of extracellular calcium. The T-type voltage-gated calcium channel antagonists mibefradil and nickel blocked this potassium-induced constriction. Further, constriction by the thromboxane analogue U46619 was significantly inhibited by mibefradil at a concentration specific for T-type channels. Using PCR, we found that two channel subtypes, Ca(v)3.1 and Ca(v)3.2, were expressed in microdissected efferent arterioles. Ca(v)3.1 was found by immunocytochemistry to be located in mouse efferent arterioles, human pre- and postglomerular vasculature, and Ca(v)3.2 in rat glomerular arterioles. Inhibition of endothelial nitric oxide synthase by L-NAME or its deletion by gene knockout changed the potassium-elicited transient constriction to a sustained response. Low concentrations of nickel, an agent that blocks Ca(v)3.2, had a similar effect. Thus, T-type voltage-gated calcium channels are functionally important for depolarization-induced vasoconstriction and subsequent dilatation in mouse cortical efferent arterioles.