The glomerulo-tubular junction: a target in renal diseases.

Both global and segmental glomerulopathies may damage specific areas of the renal glomerulus. Diseases associated with glomerular hyperperfusion cause lesions at the vascular pole, while diseases associated with proteinuria often damage the tubular pole. Atubular glomeruli are now known to be plentiful in a variety of common renal diseases. These glomeruli are disconnected from their tubule at the tubular pole and therefore cannot participate in the production of urine. It is widely believed that the disconnection is a result of external compression by periglomerular fibrosis. However, the variable anatomy and cell populations within both the glomerulus and the beginning of the proximal tubule at the glomerulo-tubular junction may also have important roles to play in the response to damage at this sensitive site of the nephron.

Renin gene expression in fetal kidneys of pregnancies complicated by twin-twin transfusion syndrome.

Twin-twin transfusion syndrome (TTTS) complicates one in five monochorionic pregnancies and is generally associated with high mortality and morbidity. One twin (the recipient) grows appropriately and has polyhydramnios while the other (the donor) may have a reduced growth velocity and severe oligohydramnios. The disparities in amniotic fluid volumes represent differences in fetal urine output. These differences occur secondary to hemodynamic changes, in which the vascular arrangement of placental anastomoses in TTTS leads to unidirectional flow from the donor to the recipient twin. A better understanding of the pathophysiology may contribute to improved management of this morbid condition. We studied three consecutive prospectively diagnosed stillborn twin pairs affected by early-onset TTTS. Renin gene expression was studied in sections of fetal kidneys with immunocytochemistry using a renin antiserum and with in situ hybridization using riboprobes complementary to renin mRNA, and renin-secreting cells (RCC) were counted. The overall maturation of the renal cortex was assessed by the percentage of immature glomeruli. The donor twin kidneys were smaller than those of the recipients, but the maturation of the renal cortex was not significantly different (28.2% immature glomeruli in the donor and 24.4% in the recipient kidney). The donor kidney showed increased renin gene expression with hyperplastic juxtaglomerular apparatuses (JGAs) that contained excess RCCs (median 20.02 [25th-75th centiles, 5.4, 25.1 RCCs per 100 glomeruli]). In contrast, the recipient kidney was virtually devoid of these cells (0.04 [0, 0.36] RCCs per 100 glomeruli; P < 0.05). In the donor kidney, increased renin release may, by a local action, contribute to renal vasoconstriction and oliguria. Increased renin and/or angiotensin II in the blood passing through the placental anastomoses may, by an endocrine action, suppress renin synthesis in the recipient kidney, thereby increasing renal blood flow and causing polyuria and polyhydramnios. These changes in the renal RAS could thus contribute to the pathogenesis of TTTS. The renal renin changes noted here may represent a contributory or compensating mechanism, the success of which may dictate the overall survival of the twin pregnancy and allow better understanding of the pathophysiology and perhaps therapy that may be employed in this condition.

Effects of angiotensin II on remodelling of the airway and the vasculature in the rat.

Airway remodelling occurs in chronic asthma. Angiotensin II promotes growth in cardiovascular remodelling. Since the renin-angiotensin system is activated in acute severe asthma, we hypothesized that angiotensin II has a role in airway remodelling. A total of 14 young male Wistar rats were randomly divided into two groups. All received 2-week infusions of bromodeoxyuridine, and the experimental group also received angiotensin II. Blood pressure rose in the angiotensin II-infused group [mean levels: pre-infusion, 134.9 (S.D. 14.7) mmHg; post-infusion, 197.1 (22.5) mmHg], and expression of renin mRNA in the renal juxtaglomerular cells was suppressed in these animals. The proportion of bromodeoxyuridine-positive cell nuclei was no different in the airways of control and angiotensin II-infused animals for smooth muscle [mean bromodeoxyuridine index: control, 8. 6% (S.E.M. 1.1%); angiotensin II, 9.3% (1.1%)], epithelium [control, 16.7% (2.3%); angiotensin II, 16.0% (2.2%)] and adventitia [control, 26.4% (2.2%); angiotensin II, 26.6% (2.4%)]. In the arteries, bromodeoxyuridine indices were higher in the angiotensin II-infused rats [18.4% (2.3%)] than in the control animals [9.4% (2.8%)], but no difference was found in the veins [12% (2.9%) and 11.4% (2.6%) respectively]. Morphometry of the airway wall and mesenteric vasculature was no different in the two groups. Therefore a 2-week infusion of angiotensin II increases blood pressure and DNA synthesis in the mesenteric arteries, but does not cause airway remodelling, in the rat.

Intrauterine growth restriction is associated with persistent juxtamedullary expression of renin in the fetal kidney.

BACKGROUND: Intrauterine growth restriction (IUGR) has been linked to impaired renal function and hypertension, suggesting that an adverse prenatal environment could alter kidney development and renin production. METHODS: Immunohistochemistry and in situ hybridization were employed to localize renin-containing cells (RCCs) in the deep, middle, and superficial zones of autopsy kidney sections, in parallel with histologic maturation, from unexplained stillborn fetuses of normal weight (N = 26) and stillborn fetuses with IUGR (N = 17). RESULTS: In the control group, the number of RCC per 100 glomeruli in the deep zone decreased with advancing gestation from 40 at 20 weeks gestation to five at term (P < 0.001), whereas the opposite change was found in the superficial zone (increase from 5 per 100 to 55 per 100; P < 0.001). In the IUGR group, the density of RCCs in both the superficial and deep zones was similar to the control group at 20 weeks, and no shift in renin gene expression was observed as gestation advanced. Histologic maturation was unaltered. CONCLUSIONS: Renin gene expression persists and predominates in the deep renal cortex of the stillborn IUGR fetus, and could contribute to the pathogenesis of neonatal oliguria and/or hypertension during postnatal life.

Tuft-to-capsule adhesions and their precursors: differences between the vascular and tubular poles of the human glomerulus.

Human glomerular capillary tufts were removed by microdissection and scanning electron microscopy was used to examine the surface of the capillary tuft and the interior of its Bowman's capsule in order to identify connections between the tuft and capsule. Glomeruli were examined in histologically normal renal cortex from 12 kidneys removed for tumour and 12 renal allografts removed for end-stage rejection. In normal kidney, the glomerular tuft was connected to Bowman's capsule by single podocytes and their processes. At the vascular pole, these were predominantly associated with parietal podocytes which lined Bowman's capsule. At the tubular pole, occasional podocytic processes derived from the capillary tuft bridged Bowman's space and connected to Bowman's capsule where there were no parietal podocytes. These podocytic connections were also found in all rejected transplants, but in addition adhesions were identified which consisted of thicker connections between the tuft and capsule. At the vascular pole, tuft-to-capsule adhesions were found in all 12 kidneys; these were always associated with parietal podocytes. Tubular pole adhesions were identified in ten of the 12 transplants. They were associated with abnormal squamous cells, but not with parietal podocytes. When the capillary tuft herniated into the proximal tubule, the tuft sometimes formed an adhesion with the origin of the proximal tubule. These observations suggest that podocyte connections between the glomerular tuft and Bowman's capsule may be precursors of glomerular adhesions at the vascular pole. Since tuft-to-capsule adhesions at the vascular pole differ morphologically from those at the tubular pole, this may reflect different pathogenetic mechanisms at the opposite poles of the glomerulus.

A renin secreting ovarian steroid cell tumour associated with secondary polycythaemia.

A 67-year-old woman presented with dry skin, facial hair, hoarse voice, and weight gain. She was hypertensive (168/ 96 mm Hg), her haemoglobin concentration was 19 g/l, and haematocrit was 55.7%. The diagnosis of probable secondary polycythaemia was made. Blood testosterone concentration was 44 nmol/l (normal < 5) and was not suppressed by dexamethasone, suggesting a neoplastic source rather than a pituitary abnormality. Transvaginal ultrasound revealed a hypoechoic solid mass in the left ovary suggestive of a solid ovarian tumour. Hysterectomy and bilateral salpingo-oophorectomy were performed following which testosterone concentration returned to normal. Immunocytochemistry provided evidence of renin synthesis. This is a case of an unusual steroid cell tumour that caused virilisation accompanied by symptoms of secondary polycythaemia presumably as a result of erythropoietin production. This is the second case of a steroid cell tumour with an erythropoietic effect and the first that shows evidence of renin synthesis.

Nonsteroidal anti-inflammatory drug associated diaphragm disease.

We present a case of anaemia and intestinal obstruction in a 78-year-old woman taking nonsteroidal anti-inflammatory drugs who was found to have diaphragm disease at laparotomy.

Vascular remodelling in intramyocardial resistance vessels in hypertensive human cardiac transplant recipients.

OBJECTIVE: Cardiac transplant recipients often develop hypertension as a side effect of immunosuppressive treatment. The aim of this study was to use the serial endomyocardial biopsies taken to monitor rejection to study the early and sequential arterial changes in human myocardial resistance arteries as hypertension develops. METHODS: At least 14 biopsies were studied from each of 23 patients, divided into a normotensive group (12 patients with a diastolic pressure never greater than 90 mm Hg) and a hypertensive group (11 patients with more than 10% of diastolic pressure measurements above 100 mm Hg). Morphometric analysis of between 30 and 50 arteries and arterioles in two widely separated histological levels from each biopsy was undertaken using an Optomax image analyser. RESULTS: There was a correlation between blood pressure, particularly diastolic pressure, and rate of medial thickening of intramyocardial coronary resistance arteries and arterioles (P = 0.0025). There was also a correlation between serum cyclosporin A concentrations and mean artery wall thickness (P = 0.003). CONCLUSIONS: Hypertension and cyclosporin A treatment are associated with significant wall thickening of intramyocardial resistance vessels in cardiac allograft recipients. These changes may be functionally and clinically important.

An assessment of the distortion of arteries due to sectioning in endomyocardial biopsies.

Arteries are usually studied morphometrically after pressurized fixation and resin embedding. These procedures are impracticable when dealing with diagnostic biopsies. The accuracy of arterial morphometry is determined partly by the degree of tissue distortion during section preparation. The axial ratios of 7340 arteries were measured in 353 endomyocardial biopsies from 23 patients and then compared with those expected from mathematical modelling. An excess of elliptical arteries was found. The distribution of orientation of the long axes of these best fitted a simulated 10 per cent linear distortion in the direction of microtomy. In conclusion, these results suggest that although there is some tissue distortion during sectioning, useful data may be obtained from morphometry of arteries in routinely processed endomyocardial biopsies.

Three-dimensional reconstruction of abnormal intramural coronary arteries in human cardiac allograft biopsies.

A novel abnormality of intramural coronary arteries has been recently described in allograft cardiac biopsies. Three-dimensional (3-D) models of these abnormal arteries have now been constructed from serial histological sections of diagnostic post-transplant endomyocardial biopsies. These revealed that there was an interlacing meshwork of longitudinal smooth muscle bundles in abnormal arteries. In addition, the lumen and external surface of these arteries were irregular. This contrasted with reconstructions of normal control arteries in the same sections, which were smooth and straight. This elucidation of an unusual abnormality suggests that 3-D reconstruction of arteries in forceps biopsies may be a useful technique.

Demonstration of renin gene expression in nephroblastoma by in situ hybridization.

Most patients with nephroblastoma have high levels of plasma renin and some are hypertensive. Blood pressure falls after removal of the affected kidney, suggesting that nephroblastoma is associated with renin production either by the tumour or by the kidney. In this study, direct evidence was sought of renin gene expression in nephroblastoma using in situ hybridization. Digoxigenin-labelled riboprobes and an immunoperoxidase technique were used to detect cells containing renin mRNA: this showed renin gene expression in 9 out of 12 cases. There were positive cells within metanephric blastema and in occasional neoplastic glomeruloid structures, confirming that in seven cases nephroblastoma tumour cells expressed the renin gene. However, renin gene expression was also demonstrated in perivascular cells of uncertain lineage in seven cases; in five cases there was evidence of renin gene expression in both tumour cells and perivascular cells. The latter finding raises the possibility that some of the cells expressing the renin gene could be stromal cells. It is concluded that nephroblastomas contain cells that express the renin gene and that some are tumour cells, while other perivascular cells may be stromal cells.

Atubular glomeruli and glomerular cysts--a possible pathway for nephron loss in the human kidney?

Glomerular tufts were removed and scanning electron microscopy was used to study the interior of Bowman's capsule, in order to identify atubular glomeruli. Normal renal cortex was studied from six kidneys removed for tumour and six renal transplants removed for end-stage rejection. Atubular glomeruli occurred in normal renal cortex in less than 1 percent of glomeruli, but were more common in transplant nephropathy, representing up to 61 percent of glomeruli. Glomerular cysts were identified which also lacked a tubular connection. Both atubular glomeruli and glomerular cysts contained a contracted glomerular capillary tuft and in both, Bowman's capsule was lined mostly by parietal podocytes. It is suggested that atubular glomeruli may be precursors of the glomerular cysts. The glomerular tuft may produce filtrate which exits the glomerulus via the parietal podocytes on Bowman's capsule. In normal human kidney, the formation of atubular glomeruli by disconnection from the tubule may represent an alternative pathway for the gradual nephron loss that is associated with ageing. This process may be amplified in disease: disconnection from the tubule may be an important part of irreversible nephron damage in chronic allograft nephropathy.

Control of cell proliferation in the rat adrenal gland in vivo by the renin-angiotensin system.

Adrenal cytogenesis was investigated in response to 1) subcutaneous infusions of angiotensin (ANG) II (200 ng.kg-1.min-1); 2) high and low sodium intake; and 3) captopril treatment (10 mg.kg-1.day-1). Cell proliferation was assessed as uptake of 5-bromo-2'-deoxyuridine (BrdUrd) into nuclei. BrdUrd, infused continuously throughout 2 wk of treatment, was detected immunocytochemically. ANG II and sodium restriction caused hypertrophy of the zona glomerulosa with two- to threefold increases in BrdUrd indexes. After captopril, the glomerulosa appeared atrophied with pyknotic nuclei, but the BrdUrd index was unchanged. Zonae intermedia and fasciculata were unaffected by any treatment. Zona reticularis epithelial cells proliferated in response to ANG II and sodium restriction but were unaffected by captopril. In the medulla, captopril increased BrdUrd uptake, whereas ANG II, but not low sodium, caused a decrease. In conclusion, 1) proliferation of the glomerulosa and reticularis cells is specifically controlled by ANG II, 2) captopril may cause glomerulosa cells to die, and 3) blood pressure may control proliferation of the medulla.

Arterial lesions associated with medial disorganization and fibrosis in endomyocardial biopsies from human cardiac allografts.

We describe distinctive arterial lesions in endomyocardial biopsies from patients with human cardiac allografts. The lesions affected principally the media of small arteries and consisted of misorientation of smooth muscle cells and fibrosis. This remodelling was most prevalent in the subadventitial zone, but sometimes extended to involve the full thickness of the media. In the most extreme cases medial smooth muscle cells ran parallel to the long axis of the vessel and were segregated into small bundles and single cells separated by collagen which merged with the adventitial fibrosis. The intima was always normal. Abnormal arteries were present in 16% of 603 consecutive biopsies from 44 patients, and 39% of lesions occurred in 16% of patients. No lesions were found in endomyocardial biopsies from 25 non-transplanted patients, nor in mucosal biopsies from both transplanted and non-transplanted patients, confirming that the appearances were not due to biopsy artefact. There was early arterial remodelling in biopsies within two weeks of transplantation and none of the stages resembled vascular rejection. Fifty per cent of biopsies from some patients contained arterial lesions, suggesting that in susceptible patients they are common.

Development and progression of atherosclerosis in aorta from heterozygous and homozygous WHHL rabbits. Effects of simvastatin treatment.

This study was conducted to define progression of atherosclerosis in both homozygous and heterozygous Watanabe heritable hyperlipidemic (WHHL) rabbits and to investigate the ability of the HMG CoA reductase inhibitor simvastatin to attenuate progression of the disease. We examined contractile responses to phenylephrine and endothelium-dependent relaxation in response to carbachol in thoracic aorta at 3, 6, 9, and 12 months in control New Zealand White (NZW) rabbits, homozygous WHHL rabbits, and heterozygous WHHL rabbits. Homozygous and heterozygous rabbits were treated with simvastatin (10 mg/kg per day) from 3 to 6 months and from 9 to 12 months of age. Simvastatin significantly reduced serum cholesterol levels in young heterozygotes, with a nonsignificant trend toward a reduction in older heterozygotes. In homozygotes, no significant fall was observed. Contractile function declined progressively with age in all groups--most in homozygotes and least in NZW rabbits. Relaxation was unaffected by age in NZW rabbits; relaxation declined in the heterozygotes and declined to a greater extent in homozygotes. Simvastatin retarded the loss of function in the young heterozygotes. Similar trends were observed in young homozygotes and older heterozygotes, with no effect in older homozygotes. Histological studies revealed the progressive development of early atherosclerosis in heterozygotes, and more advanced atherosclerosis was observed in homozygotes. Simvastatin did not inhibit development of atheroma. A correlation was observed between vascular function and structure. However, functional changes preceded the development of atheroma. In addition, we have demonstrated that simvastatin can help to reduce the loss of vascular function associated with the progression of atherosclerosis in the heterozygous WHHL rabbit.

Vascular structure, smooth muscle cell phenotype and growth in hypertension.

The media of most blood vessels is occupied by vascular smooth muscle cells. In areas they may be replaced by glomus cells, pericytes or renin-secreting myoepithelioid cells. These cells may be regarded as phenotypic variants of vascular smooth muscle cells. In disease, ordinary vascular smooth muscle cells may also assume a spectrum of phenotypes ranging from contractile to largely secretory types. Therefore, the phenotype of smooth muscle cells that is involved in a disease process such as hypertension or one of its complications is likely to affect the structural outcome in blood vessels.

In vivo studies of the control of DNA synthesis in the rat adrenal cortex and medulla.

The control of zonation in the adrenal cortex has been studied by measuring DNA synthesis using an analogue of thymidine, bromodeoxyuridine (BrDUrd). Groups of rats were infused with BrDUrd for 10-14 days whilst being treated with: high or low sodium diets; captopril; angiotensin II; dexamethasone; an inhibitor of nitric oxide synthesis, L-NAME. DNA synthesis in the zona glomerulosa was increased by low sodium food and angiotensin and was decreased by dexamethasone, captopril L-NAME and a high sodium diet. Dexamethasone, not manipulations of the renin-angiotensin system, affected DNA synthesis in the outer zona fasciculata. The BrDUrd index in the zona intermedia was unaffected by any of the treatments and was generally lower than in adjacent zona fasciculata and zona glomerulosa cells. Cells of the zona reticularis appeared to be regulated independent of the zona fasciculata. BrDUrd uptake in nuclei of the adrenal medulla was inversely related to blood pressure. We conclude that DNA synthesis in each adrenocortical zone is independently controlled. Migration of cells within zones after proliferation is likely.

A comparative study of the glomerular peripolar cell and the renin-secreting cell in twelve mammalian species.

The peripolar cell is a glomerular epithelial cell situated within Bowman's capsule at its vascular pole. It is believed to be a secretory cell which forms part of the juxtaglomerular apparatus. Scanning electron microscopy was used to perform a comparative study of the morphology and number of peripolar cells in twelve mammalian species. The number of renin-secreting cells in kidney sections stained by renin antibodies and immunocytochemistry was counted. There was a marked inter-species variation in the number, size and appearance of peripolar cells. They were largest and most abundant in sheep and goat and fewest in dog, cow and human. There was no correlation between the numbers of peripolar cells and renin-secreting cells. This does not support the view that the peripolar cell is part of the juxtaglomerular apparatus.