The distribution of renin in the different segments of the renal arterial tree: immunocytochemical investigation in the mouse kidney

Representation and relative abundance of cell-type selective markers in whole-kidney RNA-Seq data

Bulk-tissue RNA-Seq is increasingly being used in the study of physiological and pathophysiological processes in the kidney; however, the presence of multiple cell types in kidney tissue complicates data interpretation. We addressed the question of which cell types are represented in whole-kidney RNA-Seq data in order to identify circumstances in which bulk-kidney RNA-Seq can be successfully interpreted. We carried out RNA-Seq in mouse whole kidneys and in microdissected renal tubule segments. To aid in the interpretation of the data, we compiled a database of cell-type selective protein markers for 43 cell types believed to be present in kidney tissue. The whole-kidney RNA-Seq analysis identified transcripts corresponding to 17,742 genes, distributed over 5 orders of magnitude of expression level. Markers for all 43 curated cell types were detectable. Analysis of the cellular makeup of mouse and rat kidney, calculated from published literature, suggests that proximal tubule cells account for more than half of the mRNA in a kidney. Comparison of RNA-Seq data from microdissected proximal tubules with data from whole kidney supports this view. RNA-Seq data for cell-type selective markers in bulk-kidney samples provide a valid means to identify changes in minority-cell abundances in kidney tissue. Because proximal tubules make up a substantial fraction of whole-kidney samples, changes in proximal tubule gene expression can be assessed presumptively by bulk-kidney RNA-Seq, although results could potentially be complicated by the presence of mRNA from other cell types.

Intratubular and intracellular renin-angiotensin system in the kidney: a unifying perspective in blood pressure control

The renin-angiotensin system (RAS) is widely recognized as one of the most important vasoactive hormonal systems in the physiological regulation of blood pressure and the development of hypertension. This recognition is derived from, and supported by, extensive molecular, cellular, genetic, and pharmacological studies on the circulating (tissue-to-tissue), paracrine (cell-to-cell), and intracrine (intracellular, mitochondrial, nuclear) RAS during last several decades. Now, it is widely accepted that circulating and local RAS may act independently or interactively, to regulate sympathetic activity, systemic and renal hemodynamics, body salt and fluid balance, and blood pressure homeostasis. However, there remains continuous debate with respect to the specific sources of intratubular and intracellular RAS in the kidney and other tissues, the relative contributions of the circulating RAS to intratubular and intracellular RAS, and the roles of intratubular compared with intracellular RAS to the normal control of blood pressure or the development of angiotensin II (ANG II)-dependent hypertension. Based on a lecture given at the recent XI International Symposium on Vasoactive Peptides held in Horizonte, Brazil, this article reviews recent studies using mouse models with global, kidney- or proximal tubule-specific overexpression (knockin) or deletion (knockout) of components of the RAS or its receptors. Although much knowledge has been gained from cell- and tissue-specific transgenic or knockout models, a unifying and integrative approach is now required to better understand how the circulating and local intratubular/intracellular RAS act independently, or with other vasoactive systems, to regulate blood pressure, cardiovascular and kidney function.

Immunohistochemical localization of renin-containing cells in two elasmobranch species

Renin immunoreactivity was localized at the light and electron microscopic level in two elasmobranch fish species, the Atlantic stingray, Dasyatis sabina, and river ray, Potamotrygon humerosa. At the light microscopic level, the peroxidase-anti-peroxidase method showed a positive immunoreactivity in modified smooth muscle cells in kidney afferent arterioles as well as in arterioles of several organs: rectal gland, inter-renal gland, conus arteriosus, and gill. Electron microscopic renin-positive immunogold localization was confined to the contents of membrane bound granules in the modified smooth muscle cells of these arterioles. The presence of renin-containing granules in the modified smooth muscle, "granular cells," of the renal glomerular afferent arteriole of these two stingray species adds support to earlier studies which showed the structural components of a complete juxtaglomerular apparatus and some of the biochemical and molecular components of a renin-angiotensin system (RAS) as found in teleost fish, reptiles, birds, and mammals. A notable result, however, was the renin-positive immunoreaction in the arteriolar wall of all other organs studied here. The presence of this "diffuse renin system" in the connective tissue of various organs suggests that in these two stingray species in addition to local organ-specific functions, the RAS may act as a systemic mechanism to regulate blood pressure and blood flow in the body.

Deletion of von Hippel-Lindau protein converts renin-producing cells into erythropoietin-producing cells

States of low perfusion pressure of the kidney associate with hyperplasia or expansion of renin-producing cells, but it is unknown whether hypoxia-triggered genes contribute to these changes. Here, we stabilized hypoxia-inducible transcription factors (HIFs) in mice by conditionally deleting their negative regulator, Vhl, using the Cre/loxP system with renin-1d promoter-driven Cre expression. Vhl (−/−(REN)) mice were viable and had normal BP. Deletion of Vhl resulted in constitutive accumulation of HIF-2α in afferent arterioles and glomerular cells and HIF-1α in collecting duct cells of the adult kidney. The preglomerular vascular tree developed normally, but far fewer renin-expressing cells were present, with more than 70% of glomeruli not containing renin cells at the typical juxtaglomerular position. Moreover, these mice had an attenuated expansion of renin-producing cells in response to a low-salt diet combined with an ACE inhibitor. However, renin-producing cells of Vhl (−/−(REN)) mice expressed the erythropoietin gene, and they were markedly polycythemic. Taken together, these results suggest that hypoxia-inducible genes, regulated by VHL, are essential for normal development and physiologic adaptation of renin-producing cells. In addition, deletion of Vhl shifts the phenotype of juxtaglomerular cells from a renin- to erythropoietin-secreting cell type, presumably in response to HIF-2 accumulation.

New insights and perspectives on intrarenal renin-angiotensin system: focus on intracrine/intracellular angiotensin II

Although renin, the rate-limiting enzyme of the renin-angiotensin system (RAS), was first discovered by Robert Tigerstedt and Bergman more than a century ago, the research on the RAS still remains stronger than ever. The RAS, once considered to be an endocrine system, is now widely recognized as dual (circulating and local/tissue) or multiple hormonal systems (endocrine, paracrine and intracrine). In addition to the classical renin/angiotensin I-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II receptor (AT₁/AT₂) axis, the prorenin/(Pro)renin receptor (PRR)/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, and the Ang IV/AT₄/insulin-regulated aminopeptidase (IRAP) axis have recently been discovered. Furthermore, the roles of the evolving RAS have been extended far beyond blood pressure control, aldosterone synthesis, and body fluid and electrolyte homeostasis. Indeed, novel actions and underlying signaling mechanisms for each member of the RAS in physiology and diseases are continuously uncovered. However, many challenges still remain in the RAS research field despite of more than one century's research effort. It is expected that the research on the expanded RAS will continue to play a prominent role in cardiovascular, renal and hypertension research. The purpose of this article is to review the progress recently being made in the RAS research, with special emphasis on the local RAS in the kidney and the newly discovered prorenin/PRR/MAP kinase axis, the ACE2/Ang (1-7)/Mas receptor axis, the Ang IV/AT₄/IRAP axis, and intracrine/intracellular Ang II. The improved knowledge of the expanded RAS will help us better understand how the classical renin/ACE/Ang II/AT₁ receptor axis, extracellular and/or intracellular origin, interacts with other novel RAS axes to regulate blood pressure and cardiovascular and kidney function in both physiological and diseased states.

A computational model of the circulating renin-angiotensin system and blood pressure regulation

The renin-angiotensin system (RAS) is critical in sodium and blood pressure (BP) regulation, and in cardiovascular-renal (CVR) diseases and therapeutics. As a contribution to SAPHIR project, we present a realistic computer model of renin production and circulating RAS, integrated into Guyton's circulatory model (GCM). Juxtaglomerular apparatus, JGA, and Plasma modules were implemented in C ++/M2SL (Multi-formalism Multi-resolution Simulation Library) for fusion with GCM. Matlab optimization toolboxes were used for parameter identification. In JGA, renin production and granular cells recruitment (GCR) are controlled by perfusion pressure (PP), macula densa (MD), angiotensin II (Ang II), and renal sympathetic activity (RSNA). In Plasma, renin and ACE (angiotensin-converting enzyme) activities are integrated to yield Ang I and II. Model vs. data deviation is given as normalized root mean squared error (nRMSE; n points).

IDENTIFICATION

JGA and Plasma parameters were identified against selected experimental data. After fusion with GCM: (1) GCR parameters were identified against Laragh's PRA-natriuresis nomogram; (2) Renin production parameters were identified against two sets of data ([renin] transients vs. ACE or renin inhibition). Finally, GCR parameters were re-identified vs. Laragh's nomogram (nRMSE 8%, n = 9).

VALIDATION

(1) model BP, PRA and [Ang II] are within reported ranges, and respond physiologically to sodium intake; (2) short-term Ang II infusion induces reported rise in BP and PRA. The modeled circulating RAS, in interaction with an integrated CVR, exhibits a realistic response to BP control maneuvers. This construction will allow for modelling hypertensive and CVR patients, including salt-sensitivity, polymorphisms, and pharmacotherapeutics.

Lack of connexin 40 causes displacement of renin-producing cells from afferent arterioles to the extraglomerular mesangium

In the adult kidney, renin-producing cells are typically located in the walls of afferent arterioles at the transition into the glomerular capillary network. The mechanisms that are responsible for restricting renin expression to the juxtaglomerular position are largely unknown. This study showed that in mice that lack connexin 40 (Cx40), the predominant connexin of renin-producing cells, renin-positive cells are absent in the vessel walls and instead are found in cells of the extraglomerular mesangium, glomerular tuft, and periglomerular interstitium. Blocking macula densa transport function by acute administration of loop diuretics strongly enhances renin secretion in vivo and in isolated perfused kidneys of wild-type mice. This effect of loop diuretics is markedly attenuated in vivo and even blunted in vitro in Cx40-deficient mice. Even after prolonged stimulation of renin secretion by severe sodium depletion, renin expression is not seen in juxtaglomerular cells or in cells of more proximal parts of the arterial vessel wall as occurs normally. Instead, renin remains restricted to the extra-/periglomerular interstitium in Cx40-deficient mice. In contrast to the striking displacement of renin-expressing cells in the adult kidney, renin expression in the vessels of the developing kidney was found to be normal. This is the first evidence to indicate that cell-to-cell communication via gap junctions is essential for the correct juxtaglomerular positioning and recruitment of renin-producing cells. Moreover, these findings support the notion that gap junctions are relevant for the macula densa signaling to renin-producing cells.

Reporter gene recombination in juxtaglomerular granular and collecting duct cells by human renin promoter-Cre recombinase transgene

To assess the feasibility of using the renin promoter for expressing Cre recombinase in juxtaglomerular (JG) cells only, we generated five independent transgenic mouse lines (designated hRen-Cre) expressing Cre recombinase under control of a 12.2-kb human renin promoter. In the kidneys of adult mice Cre mRNA (RT-PCR) was found in the renal cortex, with Cre protein (immunohistochemistry) being localized in afferent arterioles and to a lower degree in interlobular arteries. Cre mRNA levels were regulated in a renin-typical fashion by changes in oral salt intake, water restriction, or isoproterenol infusion, indicating the presence of key regulatory elements within 12.2 kb of the 5′-flanking region of the human renin gene. hRen-Cre mice were interbred with both the ROSA26-EGFP and ROSA26-lacZ reporter strains to assess renin promoter activity from Cre-mediated excision of a floxed stop cassette and subsequent enhanced green fluorescent protein (EGFP) and β-galactosidase (β-gal) detection. In adult mice, β-gal staining and EGFP were observed in afferent arterioles and interlobular arteries, overlapping with Cre protein expression. In addition, intense β-gal staining was found in cortical and medullary collecting ducts where Cre expression was minimal. In embryonic kidneys, β-gal staining was detected in the developing collecting duct system beginning at embryonic day 12, showing substantial activity of the human renin promoter in the branching ureteric bud. Our data indicate that besides its well-known activity in JG cells and renal vessels the human renin promoter is transiently active in the collecting duct system during kidney development, complicating the use of this approach for JG cell-specific excision of floxed targets.

Ontogeny of renal renin in congenital hypothyroid rats

In the present study we have found age-related differences between the renal renin activity (RRA) and the immunoreactive renal renin (IRR) profiles during the neonatal development of the rat. RRA was markedly greater in newborn rats than in adult ones, while IRR was low at birth and progressively increased until adulthood. These observations suggest the existence of a control mechanism operating either at the level of the translation of the template or at a post-translational level which varies throughout the development. Since thyroid hormones have been demonstrated to affect several renin-angiotensin components, the neonatal RRA and IRR profiles in congenital hypothyroid rats were evaluated to determine whether renal renin activity or its synthesis could be endogenously regulated by thyroid hormones in the early stages of life. Although significant differences were observed in the RRA profiles of congenital hypothyroid and control rats, no changes were found in the relative amount of immunoreactive protein. These findings indicate that thyroid hormone deficiency does not directly affect renal renin expression during the critical period of the normal morpho-functional development of the newborn.

Plasma and renal prorenin/renin, renin mRNA, and blood pressure in Dahl salt-sensitive and salt-resistant rats

We measured plasma prorenin and renin levels, renal renin mRNA, renal anti-renin and anti-prorenin-prosequence immunoreactivity, and blood pressure in maturing Brookhaven Dahl salt-sensitive (Dahl S) and salt-resistant (Dahl R) rats during 14 days of low (0%), medium (0.4%), or high 4%) NaCl diets. Blood pressure was higher in Dahl S rats and did not increase with high NaCl. Seven-week-old Dahl R rats had twofold and sixfold higher levels of plasma prorenin and renal prosequence immunoreactivity, respectively, which by 9 weeks were the same as in Dahl S rats. The anti-renin antiserum, BR1-5, was found to detect prorenin better than renin; Dahl S rats had suppressed renal anti-renin immunoreactivity relative to Dahl-R rats. Dahl R rats were unresponsive to high NaCl, whereas in Dahl S rats, plasma renin and renal prosequence immunoreactivity fell by 90% (P < .01), renal anti-renin immunoreactivity and renal renin MRNA fell by 35% (P < .05 for both), and plasma prorenin fell by 30% (P = NS). NaCl depletion increased prorenin/renin parameters similarly in both strains. There were direct relationships among all of the prorenin/renin parameters. Between low and high salt diets in Dahl S rats, plasma renin increased 20-fold, plasma total renin (renin plus prorenin) and renal renin mRNA both increased threefold, and plasma prorenin increased twofold. The results indicate that under steady-state conditions, plasma and renal renin/prorenin parameters change concordantly and that plasma total renin (renin plus prorenin) reflects changes in renal renin mRNA. The lower blood pressure of Dahl R rats is associated with later maturation-related declines in plasma and renal prorenin. Suppression of plasma renin may delay the salt-induced blood pressure rise in Dahl S rats. Finally, the renin system and blood pressure of Dahl R rats have remarkable disregard for a high salt diet.

Differential regulation of cytosolic calcium between afferent arteriol ar smooth muscle cells from mouse kidney

Using a combination of whole-cell patch-clamping and calcium microspectrofluorimetry we have examined the calcium regulation and calcium-activated electrical currents in smooth muscle cells along mouse renal afferent arterioles. In cells located at a distance up to 50microm from the glomerular vascular pole, guanosine 5'-[gamma-thio]triphosphate, (GTP[tau -S], 100micromol/l) and angiotensin II (1micromol/l) evoked internal calcium mobilization and oscillations of intracellular calcium concentration. Membrane depolarization up to +30mV did not increase cytosolic free calcium in these cells, which displayed calcium-activated chloride currents. In cells located more distant than 100microm from the glomerular vascular pole, GTP[tau -S] did not increase cytosolic calcium at negative membrane potentials. Depolarization of these cells to 0mV or positive membrane potentials increased intracellular calcium in a dihydropyridine-sensitive manner. These cells responded to angiotensin II with single calcium transients and also displayed calcium-activated chloride currents. These findings suggest that intracellular calcium is differentially regulated between afferent arteriolar smooth muscle cells from mouse kidney: in smooth muscle cells which are distant from the glomerular vascular pole, cytosolic calcium is increased primarily via calcium influx through potential-operated calcium channels, whilst in cells which are close to the vascular pole intracellular calcium is elevated predominantly via mobilization from internal stores. Both cell types are equipped with receptors for angiotensin II and possess calcium-activated chloride channels.

Spectrum of vascular pathology affecting patients with the antiphospholipid syndrome

A thrombotic microangiopathy that is identified in patients with the antiphospholipid syndrome (APS) represents only a part of the vascular pathology that can be associated with antiphospholipid antibodies (aPL). Tissues from two autopsies, four renal biopsies, two skin biopsies, and one amputated leg were obtained from six patients who met criteria for the diagnosis of APS. Three patients had systemic lupus erythematosus (SLE), one had lupus-like disease, and two had a primary APS. Five of the patients were hypertensive. Arteries of three patients disclosed fibrin thrombi along with widespread obstruction by recanalized intimal connective tissue. Small renal, leptomeningeal, and pulmonary arteries showed concentric cellular and fibrous intimal hyperplasia indistinguishable from hypertensive vascular disease. Glomerular capillary and afferent arteriolar thrombi were found in renal biopsies from two SLE patients. One of these SLE patients required a leg amputation in which the popliteal artery demonstrated thrombosis, intimal hyperplasia, and acute inflammation. The findings support clinical and experimental data that indicate aPLs cause thrombosis but suggest diversity in the pathogenetic mechanisms aPLs are capable of promoting. Inflammation seems to be rare and to accompany thrombosis. Intimal hyperplasia is particularly common. Its involvement of renal arteries may contribute to hypertension that develops in some APS patients.

Renin and renin mRNA in proximal tubules of the rat kidney

The present study was undertaken to assess the presence of renin enzymatic activity and renin mRNA in proximal tubules of rat kidneys, and to determine the effect of converting enzyme inhibition (CEI) on proximal tubule renin gene expression. Proximal convoluted tubules (PCT), proximal straight tubules (PST), outer medullary collecting ducts (OMCD), and glomeruli (Gloms) were isolated by microdissection. Renin activity was measured in sonicated segments by radioimmunoassay. Renin mRNA levels were assessed using a quantitative PCR. Renin activity in PCT averaged 51 +/- 15 microGU/mm compared to 405 +/- 120 microGU/glomerulus. No measurable renin activity was found in PST and OMCD. Renin activity in both glomeruli and tubules had the same pH optimum, between 7.0 and 7.5. Renin mRNA was consistently detectable in cDNA prepared from PCT and PST, although its abundance per mm tubule was about 1/500th that found in one glomerulus. Renin mRNA was not detectable in OMCD. Tubular renin PCR product identity was confirmed by restriction digestion. CEI administration increased glomerular renin activity and renin mRNA, but not proximal tubular renin. The absence of a stimulatory effect of CEI on proximal tubule renin gene expression suggests the operation of different intracellular signals in control of renin synthesis in the proximal tubule than in the vascular compartment.

The renin-secreting cell and the glomerular peripolar cell in renal artery stenosis and Addison's disease

The glomerular peripolar cell may be a secretory component of the juxtaglomerular apparatus. To investigate this hypothesis we studied kidneys with the renin-angiotensin system activated by two different stimuli in order to compare the responses of peripolar cells and renin-secreting cells. We examined 10 human kidneys, removed for renal artery stenosis and 11 autopsy cases of Addison's disease with appropriate controls. We counted granulated peripolar cells in serial paraffin-embedded sections and renin-containing cells were quantified using an immunoperoxidase technique with an antiserum to human renin. There was a five-fold increase in the number of renin-containing cells in both renal artery stenosis and in untreated, but not in treated, Addison's disease. Peripolar cells were increased in number in three cases of renal artery stenosis, but were unaltered in both treated and untreated Addison's disease. Therefore, neither a reduction in renal perfusion pressure (renal artery stenosis), nor sodium depletion (Addison's disease) consistently affect peripolar cells in humans. These findings do not support the hypothesis that the peripolar cell is part of the juxtaglomerular apparatus.

Renin distribution in the rabbit renal microvasculature

Immunocytochemical studies have shown that renin, which is normally located in the juxtaglomerular afferent arteriole, may also be found farther upstream toward the interlobular artery during chronic stimulation of the renin-angiotensin system. We assessed the renin distribution along the renal microvasculature using both quantitative analysis and immunocytochemistry in rabbits that received a normal sodium diet (0.48% NaCl), a low sodium diet (0.04% NaCl), or enalapril (1 mg/kg/day) for 4 weeks. From the outer cortex we microdissected 1) the proximal portion of the afferent arteriole (p-AF) extending from the interlobular artery to a point 50 microns from the glomerulus, 2) the distal 50 microns including its intact terminus (d-AF), and 3) the glomerulus without the vascular pole (GL) and measured their renin content. In controls, renin was 0.3 +/- 0.2, 27.0 +/- 5.2, and 2.8 +/- 0.5 ng angiotensin I/hr/arteriole (or GL) in the p-AF, d-AF, and GL, respectively. The low sodium diet and enalapril increased renin in the d-AF (53.1 +/- 6.9 and 68.4 +/- 8.1, respectively) but not in the GL (3.3 +/- 1.0 and 3.6 +/- 0.7). In the p-AF, both caused a small increase (delta = 1.5); however, this increase was minuscule compared with the large increase in the d-AF (delta = 41).(ABSTRACT TRUNCATED AT 250 WORDS)

Renal renin secretion rate and norepinephrine secretion rate in response to centrally administered angiotensin-II: role of the medial basal forebrain

The influence that centrally administered angiotensin-II (ANG-II) and saralasin (SAR) has on renal norepinephrine secretion rate (NESR) and renal renin secretion rate (RSR) were studied. Rats were given thermal lesions of the medial basal forebrain (MBF) or sham surgery. Twenty-four hours later the right kidney was vascularly isolated (but neurally intact) and perfused with an artificial plasma at either a constant pressure (100 mm Hg) or constant flow (600 microliters/min). Renal perfusate was collected before (pre-injection) and at 10 min intervals after central administration of peptides for determination of NESR and RSR. In both perfusion models, intracerebroventricular (ICV) ANG-II increased renal NESR. In MBF lesioned rats pre-injection renal NESR is reduced and the response to ICV ANG-II is blocked. In both perfusion models ICV ANG-II decreases renal RSR. Concomitant administration of SAR blocks the effect of ANG-II on both NESR and RSR. MBF lesioned rats had significantly elevated pre-injection levels of RSR and there is no change in RSR following ICV ANG-II. These experiments indicate that centrally administered ANG-II increases renal NESR concomitant with a decrease in renal RSR and that MBF lesions block those changes.

Three-dimensional reconstruction of human juxtaglomerular apparatus (JGA)

A three-dimensional and morphological study of the human JGA was undertaken to establish a background for understanding the changes in this vital apparatus during various physiological and pathological conditions. Three-dimensional reconstruction was carried out using a computer program "GLOM". Serial sections of normal human kidneys were used after staining with specific human renin antiserum. Three-dimensional reconstruction revealed renin-positive cells in the afferent and efferent arterioles and interlobular arteries away from the JGA area. A close contact was demonstrated between renin-positive cells and the macula densa. The frequency of positively stained JGAs was significantly higher in the superficial glomeruli compared to the deep glomeruli. The high renin content of the superficial glomeruli suggests higher generation of angiotensin, which may contribute to the regulation of the GFR as proposed by other workers. This preliminary study on normal human JGA is to be extended to hypertensive and renal failure patients.

Renovascular effects of neuropeptide-Y in the split hydronephrotic rat kidney: non-uniform pattern of vascular reactivity

1. The renovascular effects of neuropeptide-Y (NPY) were examined in the split hydronephrotic rat kidney. 2. Systemic infusion of low non-pressor doses of NPY (0.2 micrograms kg-1 up to 5.0 micrograms kg-1) produced a non-uniform pattern of vascular reactivity. In general, a significant constriction of the proximal and distal arcuate artery was seen at all doses. No constriction was seen at the interlobular artery or the larger part of the afferent arteriole. These segments initially dilated during the lower dose infusions. The very distal part of the afferent arteriole adjacent to the glomerulus and the proximal efferent arteriole responded in a similar way to the arcuate arteries. 3. NPY, locally applied into the tissue bath at concentrations of 1 nmol l-1 up to 25 nmol l-1, produced non-uniform vascular reactions similar to those of intravenously infused NPY. At the considerably higher local dosage of 1.14 mumol l-1, all vascular segments revealed vasoconstriction. 4. NPY application did not attenuate effects of acetylcholine. This observation suggests that the mechanism of NPY-induced vasoconstriction does not rely upon antagonism of endothelium-derived vasodilatation. 5. The pattern of vascular reactivity to NPY was substantially different from that known for the vasoconstrictors noradrenaline and angiotensin II in our preparation.

Glomerular renin synthesis and storage in the remnant kidney in the rat

The intrarenal renin-angiotensin system can exert local control of the nephron and its circulation. In the subtotally nephrectomized model of chronic renal disease in the rat, angiotensin appears to play a prominent role in glomerular function. Glomeruli in this model demonstrate greater staining for intraglomerular renin by immunofluorescence microscopy than do those in control rats. Glomeruli from remnant nephrons contain increased renin content. Also, glomeruli from remnant nephrons contain an increased proportion of the mRNA for renin. Adriamycin-induced nephrosis did not evoke the same degree of renin staining and did not lead to increased glomerular expression of the renin gene, findings that argue against permselective defects and glomerular trapping as the sole cause of the glomerular renin in the remnant kidney model. Thus, renin synthesis and accumulation occur in the remnant glomerulus and this migration may underlie in part the dependence of glomerular function on the renin-angiotensin system in this model.

Unilateral papillary necrosis complicating renal artery stenosis--evidence of activation of the intrarenal renin-angiotensin system?

We report an association between renal artery stenosis and papillary necrosis. We studied three kidneys with renal artery stenosis, two of which showed ipsilateral acute papillary necrosis. In all three cases there had been a sudden fall in perfusion of the ischaemic kidney. In the case with intact papillae, immunostainable renin was normal in amount and distribution, whereas both kidneys with papillary necrosis showed hyperplasia of renin-containing cells, and these were mainly in the JGAs of the juxtamedullary cortex. Since the contralateral kidneys were spared, we suggest that in an ischaemic kidney with hyperplasia of renin-secreting cells in the deep cortex, local activation of the renin-angiotensin system could cause acute papillary necrosis due to vasoconstriction.

The juxtaglomerular apparatus of the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHR) are used to study the pathogenesis of essential hypertension. This study investigates the role of the renin-angiotensin system (RAS) in the pathogenesis of hypertension in SHRs and the morphometry of the JGA by a three-dimensional computer reconstruction program "GLOM" and electron microscopy. Systolic blood pressure (SBP) (tail cuff method) was higher in SHRs compared to controls (P less than 0.001). Plasma renin concentration (PRC) was lower in SHRs than in controls (P less than 0.001). Reconstruction of the JGA revealed granulated JG cells in the afferent and efferent arterioles and in the vascular tree away from the JGA area. Electron microscopy showed granulated JG cells in the afferent and efferent arterioles. The percentage volume of the granulated JG cells in SHR was significantly higher than in controls (P less than 0.01). A relationship was found between the percentage volume of granulated JG cells and the SBP in SHRs (r = 0.933, P less than 0.05). The wall/lumen perimeter ratio was also significantly higher in the SHRs compared to the controls (P less than 0.05). Low PRC in SHRs has been reported by several workers. The apparent hyperactivity of the JGA may indicate failure of renin release or an abnormal synthesis/secretion rate.

Renin release from microdissected superficial, midcortical, and juxtamedullary afferent arterioles in rabbits

Renal renin content and release decrease from outer to inner cortex; this may be due to a cortical-to-medullary gradient in glomerular density and/or renin content per afferent arteriole. Although low sodium diets have been reported to decrease the tissue renin gradient, little information is available on renin release by different areas of the renal cortex or the effect of a low sodium diet. In the present study, we examined basal- and isoproterenol-stimulated renin release and content in microdissected superficial, midcortical, and juxtamedullary afferent arterioles from rabbits on normal and low sodium diets. Renin content was 25.8 +/- 3.6, 1.4 +/- 0.32, and 0.27 +/- 0.09 ng angiotensin I (Ang I)/hour/arteriole in the superficial, midcortical and juxtamedullary arterioles, respectively. Dietary sodium restriction significantly increased it to 60.1 +/- 7.3, 13.8 +/- 3.1, and 1.48 +/- 0.6, respectively. Renin release was 0.64 +/- 0.13, 0.15 +/- 0.04, and 0.025 +/- 0.013 ng Ang I/hour/arteriole/hour incubation of arteriole in the superficial, midcortical and juxtamedullary arterioles, respectively. With sodium restriction it increased significantly for the superficial, (1.77 +/- 0.27) and midcortical (0.62 +/- 0.11) but not the juxtamedullary arterioles (0.038 +/- 0.02). With either diet, renin release and content among the three types of arterioles were significantly different. Isoproterenol (1.6 x 10(-4) M) significantly stimulated renin release from all three types of arterioles whether rabbits were fed a normal or low sodium diet; however, only in the superficial arterioles was the increase (delta) greater with dietary sodium restriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of macula densa in diuretics-induced renin release

Diuretic therapy may enhance renin release by various mechanisms, principally contraction of extracellular fluid volume and its effects, including a fall in arterial pressure. Awake hydropenic or volume-expanded rats received diuretics (amiloride and hydrochlorothiazide) that are known inhibitors of NaCl transport beyond the macula densa; also the well-known Na(+)-K(+)-2 Cl- transport system inhibitor furosemide was administered. We also evaluated the effect of a dose of ethacrynic acid (a drug that shares the same mechanism of action as furosemide but is not diuretic in the rat). The direct action of the diuretics on renin-producing cells was examined in isolated glomeruli; a rise in renin release was observed with the calmodulin inhibitor trifluoperazine (10(-5) M). Renin release in intact hydropenic rats was not altered by diuretic therapy, but furosemide increased plasma renin activity in hydropenic as well as in volume-expanded rats. This demonstrates the importance of furosemide inhibition of transport in the macula densa for its renin secretory action. None of the diuretics (amiloride, hydrochlorothiazide, ethacrynic acid, or furosemide) elicited changes in renin release from glomeruli (10(-6) to 10(-3) M); amiloride and hydrochlorothiazide (10(-4) to 10(-3) M) did not change renin release from slices, but 10(-3) M ethacrynic acid and furosemide increased renin secretion in this preparation. This suggests that an effect on the macula densa is essential in loop diuretic-mediated renin release.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of renin-containing cells in kidneys with renal artery stenosis--an immunocytochemical study

In 10 kidneys removed for hypertension due to renal artery stenosis, the histological appearances varied from negligible ischaemic damage to end-stage ischaemic atrophy. We stained the renin-containing cells in tissue sections using an antiserum to pure human renin and an immunoperoxidase technique. In all kidneys there was hyperplasia of the renin-containing cells both in juxtaglomerular apparatuses (JGAs) and in arteries outside the JGA, where these cells extended proximally as far as the interlobular arteries. We mapped the distribution of renin-containing cells and found them in all zones of the renal cortex; in three kidneys they were predominantly in the superficial cortex; in four they were distributed more evenly throughout the width of the cortex; but in three kidneys the normal gradient was reversed, with most of the cells being in the juxtamedullary cortex and, in two of the cases, little or no stainable renin in the superficial cortical JGAs. We suggest that these abnormalities in the distribution of renin-containing cells could affect both the pattern of intrarenal blood flow and the site in the kidney at which secreted renin enters the blood.

Visualization of renal autoregulation in the split hydronephrotic kidney of rats

The autoregulatory ability of the renal vascular system in the split hydronephrotic kidney was quantitated with intravital microscopy. The luminal diameters of the arcuate and interlobular arteries as well as the afferent and efferent arterioles were measured. Glomerular blood flow was determined by the dual slit technique. In the first series of experiments, the renal perfusion pressure was reduced by graded clamping of the abdominal aorta. Pressure reduction from 118 mm Hg to 95 mm Hg induced dilation of all preglomerular vessels except for the distal afferent arteriole; there was no change in the efferent arteriole and the blood flow was maintained. Further pressure reductions to 71 and 43 mm Hg caused additional dilations of the preglomerular vessels, a marginal reduction in diameter of proximal efferent arterioles and flow reductions by 15% and 41%, respectively. In the second series, systemic blood pressure was increased by continuous i.v. infusions of norepinephrine (NE). NE constricted pre- and postglomerular vessels except for the distal afferent arteriole; glomerular flow was decreased. Reduction of renal perfusion pressure during NE infusion to the preinfusion value did not diminish glomerular blood flow, but reduced the constrictor response to NE in preglomerular vessels. In a third series of experiments we examined the effect of atrial natriuretic factor (ANF) on renal autoregulation. Addition of ANF (10(-9) to 10(-7) M) to the renal bath induced a dose-dependent dilation of all preglomerular vessels and a constriction of the efferent arteriole. Pressure reduction from 120 to 95 mm Hg resulted in a further preglomerular vasodilation. These experiments demonstrate that autoregulation is mediated primarily by diameter changes in all preglomerular vessels excluding the distal segment of the afferent arteriole. Further, these data suggest that ANF induced dilation of preglomerular vessels does not impair the myogenic response of these vessels.

Immunohistochemical localization of renin in end-stage kidneys

Hypertension in chronic renal failure is usually due to excessive accumulation of salt and water. In some cases, sodium and volume depletion by dialysis fail to reduce the high BP, and plasma renin activity tends to be higher. We performed a semiquantitative analysis of the immunohistochemical distribution of renin in the kidneys of ten patients with end-stage renal disease and hypertension using a specific antihuman renin antibody and a peroxidase-antiperoxidase technique on paraffin sections of nephrectomy and/or autopsy specimens. In five cases with severe, dialysis-resistant hypertension, the degree of immunoreactivity was most striking, exceeding that found in renovascular hypertension and present in arterioles at a distance from the glomeruli. Three cases of advanced diabetic glomerulosclerosis consistently showed minimal immunoreactivity. We conclude that renin often can be detected immunologically in the kidney of patients with chronic renal failure and hypertension, but its pathophysiological role will require further study.

Hypothetical interpretation of the calcium paradox in renin secretion

Most renin-positive cells of the preglomerular arteriole are intermediate in morphological appearence between smooth muscle cells and epithelioid cells. Intermediate cells contain, in addition to secretory granules, contractile proteins arranged as a sublemmal network. The paradoxical (inhibitory) role of calcium in renin secretion is explained, on the basis of these findings, by an increased tone of the sublemmal network; this might impair the preexocytotic access of renin granules to the cell membrane.

The juxtaglomerular apparatus in Bartter's syndrome and related tubulopathies. An immunocytochemical and electron microscopic study

A comparative immunocytochemical and electron microscopic study was performed on renal biopsies from two children with classical Bartter's syndrome (BS) and three children with a recently described variant, the so-called hyperprostaglandin E-syndrome (HES). Compared to age-matched controls, kidney specimens from patients with BS and HES disclosed a marked hypertrophy and hyperplasia of the juxtaglomerular apparatus (JGA). In addition, in HES focal tubular and interstitial calcifications accompanied by interstitial fibrosis and tubular atrophy were noted. On immunocytochemistry, chronic stimulation of the JGA in BS and HES was characterized by an increase in the number of renin-positive cells, particularly in the media of afferent arterioles, but also in efferent arterioles and in the glomerular stalk. The length of the renin-positive portion of the preglomerular arterioles was significantly increased when compared to controls (100 +/- 32 vs. 49 +/- 17 microns; p less than 0.001). In addition, the immunoreactivity of individual renin-positive cells was markedly enhanced. On electron microscopy, "hypertrophy" of the RER and of Golgi complexes with paracrystalline deposits in dilated RER cisterns and protogranules indicated an increased renin synthesis. Renin could be identified in mature secretory granules as well as protogranules by immune electron microscopy. Angiotensinogen was present in hypertrophied epithelial cells of Bowman's capsule. Converting-enzyme reactivity was observed in controls as well as in BS and HES in the brush border of the proximal tubule. In contrast to previous reports, Angiotensin II was completely negative in control as well as in diseased kidneys. We conclude from our results that both BS and HES are characterized by a marked activation of the JGA and severe stimulation of the renin-angiotensin system. Since activation of this system, however, leads--independently of the primary stimulus--to qualitatively very similar morphological reactions, these results do not implicate a common pathogenetic mechanism to both conditions.

Interzonal and intrazonal heterogeneities in the renin status of the preglomerular arterioles in five species

In five species (mouse, rat, rabbit, rhesus monkey and man) the renin status of the preglomerular arterioles was examined using two immunohistochemical methods: the measurement of the renin-positive portion of the vessels, reflecting the respective number of granulated cells, and the semiquantitative assessment of the renin concentration in the juxtaglomerular epithelioid cells with antibody dilution series. The main objective of the study was to compare the interzonal with the intrazonal internephron heterogeneities, i.e. the differences between the average renin status of the preglomerular arterioles in the superficial, intermediate and juxtamedullar cortex with the differences between the renin status of the individual afferent arterioles in one and the same cortex region. In contrast to small interzonal heterogeneities, substantial intrazonal differences in the renin status of the corresponding nephrons were found.

Autoregulation of renal blood flow, glomerular filtration rate and renin release in conscious dogs

The relationship between renal artery pressure (RAP), renal blood flow (RBF), glomerular filtration rate (GFR) and the renal venous-arterial plasma renin activity difference (PRAD) was studied in 22 chronically instrumented, conscious foxhounds with a daily sodium intake of 6.6 mmol/kg. RAP was reduced in steps and maintained constant for 5 min using an inflatable renal artery cuff and a pressure control system. Between 160 and 81 mm Hg we observed a concomitant autoregulation of GFR and RBF with a high precision. The "break off points" for GRF- and RBF-autoregulation were sharp and were significantly different from each other (GFR: 80.5 +/- 3.5 mm Hg; RBF: 65.6 +/- 1.3 mm Hg; P less than 0.01). In the subautoregulatory range GFR and RBF decreased in a linerar fashion and ceased at 40 and 19 mm Hg, respectively. Between 160 mm Hg and 95 mm Hg (threshold pressure for renin release) PRAD remained unchanged; below threshold pressure PRAD increased steeply (average slope: 0.34 ng AI.ml-1.h-1.mm Hg-1) indicating that resting renin release may be doubled by a fall of RAP by only 3 mm Hg. At the "break-off point" of RBF-autoregulation (66 mm Hg) renin release was 10-fold higher than the resting level. It is concluded that under physiological conditions (normal sodium diet) GFR and RBF are perfectly autoregulated over a wide pressure range. Renin release remains suppressed until RAP falls below a well defined threshold pressure slightly below the animal's resting systemic pressure. RBF is maintained at significantly lower pressures than GFR, indicating that autoregulation of RBF also involves postglomerular vessels.(ABSTRACT TRUNCATED AT 250 WORDS)

Myosin content and vasoconstrictive ability of the proximal and distal (renin-positive) segments of the preglomerular arteriole

The PAP-technique and antibodies to myosin were used to demonstrate the prerequisites for vasoconstriction in the juxtaglomerular part of the preglomerular arteriole as compared with its proximal segment in rats and mice. In contrast with the myosin-positive/renin-negative proximal part of the afferent arteriole no myosin-like activity could be demonstrated in its distal, renin-positive part. In accordance, no thick myofilaments were found in fully differentiated juxtaglomerular epithelioid cells replete with mature secretory granules. Stimulation of the renin-angiotensin system was followed by an increase of the renin-positive/myosin-negative portions of the preglomerular arteriole. Marked interspecies and internephron variations in the length of this vessel segment under control and stimulated conditions were observed. The juxtaglomerular part of the preglomerular arteriole close to the macula densa seems therefore to have only limited capabilities for vasoconstriction. This finding may be of importance regarding the tubulo-glomerular feedback, a mechanism allegedly triggered by the so-called 'macula densa-signal'. It is suggested that this non-contractile segment of the afferent arteriole may represent the renal vascular receptor responsible for the increase of renin secretion during pressure reduction. Unlike the afferent arterioles, most of the efferent arterioles showed the highest level of their weak but distinct myosin-like immunoreactivity in the juxtaglomerular region, indicating some efferent juxtaglomerular vasoconstrictive ability.

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.

Anatomy of the renin-angiotensin system in the normal and pathological kidney

In this review we describe the contributions made by immunocytochemistry to our knowledge of the renin-angiotensin system in the normal and the pathological kidney. Most of the renin-secreting cells appear to be on the outer aspect of the vessel wall, supporting the view that renin is secreted mainly into the interstitium of the kidney rather than into the lumen of the vessel. Angiotensin II immunoreactivity is present within renin-secreting cells. The angiotensin II appears to be present in high concentration in the renin storage granules and is therefore presumably secreted from the cell with renin. The pathways by which renin is secreted from the cell have also been clarified. In pathological kidneys, the reactions of renin-secreting cells to variation in functional demand have been confirmed. Renin-containing cells have also been found in most types of renal tumours and occasional cases probably secrete renin or prorenin into the blood. In renal tumours and in the developing kidney (in all species studied) the renin-containing cells are also intimately associated with blood vessels.

Long-term culture of renin containing tissue

Thin cortical tissue explants from kidneys of hydronephrotic mice were excised and incubated in different culture media containing growth and proliferation factors. Over a period of several months the content of renin in the explants and in the culture medium was repeatedly measured, to define the conditions necessary for the maintenance of renin production in a long-term culture. The best results were obtained when culturing the renal tissue in Dulbecco's medium (DMEM) with 10% fetal calf serum, 6 units/100 ml platelet-derived growth factor and 200 ng/ml glycylhistidyllysine. Renin was still present within the cells and in the culture medium after more than six months. Prevention of dedifferentiation, as evidenced in this case by the maintenance of renin production, seemed to be dependent on specific extracellular matrix proteins of renal origin. If the explants were dissociated from their matrix components by collagenase, a gradual loss of renin production was observed within 5 days. Complementation of the collagenase-digested cell suspension with different nonrenal extracellular matrix materials did not afford the stabilizing effect of the original pericellular matrix.

Baroreflex sympathetic activation increases threshold pressure for the pressure-dependent renin release in conscious dogs

Stimulus-response curves relating renal-venous-arterial plasma renin activity difference (P.R.A.-difference) to mean renal artery pressure (R.A.P.) were studied in seven chronically instrumented conscious foxhounds with a daily sodium intake of 6.1 mmol/kg. R.A.P. was reduced in steps and maintained constant for 5 min using an inflatable renal artery cuff and a pressure control system. The stimulus-response curve obtained during control conditions (C) or during common carotid artery occlusion (C.C.O.) could be approximated by two linear sections: a rather flat section or plateau-level of P.R.A.-difference at normal blood pressure or above, and a very steep section between a distinct threshold pressure and 65-70 mm Hg. While the parameters of the curves varied from dog to dog, the curves kept their unique shape in the individual dog for at least 1 week. C.C.O. had no effect on the plateau-level of the P.R.A.-difference (C:0.98 +/- 0.14, C.C.O:0.99 +/- 0.14 ng AI . ml-1 . h-1) and on the slope of the curve below threshold pressure (C:-0.379 +/- 0.041, C.C.O:-0.416 +/- 0.082 ng AI . ml-1 . h-1 . mm Hg-1) but shifted the stimulus-response curve to the right and increased threshold pressure (C:92.7 +/- 2.8, C.C.O:109.7 +/- 4.1 mm Hg; P less than 0.05). Renal blood flow, which was measured simultaneously in three of the dogs, showed good autoregulation down to 70 mm Hg under resting conditions and was not affected by C.C.O. except for a 30% reduction of renal blood flow at the lowest pressure step (70 mm Hg).(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular, plasma membrane aminopeptidase M. Metabolism of vasoactive peptides

Aminopeptidase M (EC 3.4.11.2), an enzyme present on the cell surface of vascular endothelium and/or smooth muscle, rapidly hydrolyzes leucyl- and arginyl-2-naphthylamides and a number of vasoactive peptides at physiologic pH. Utilizing both thin-layer chromatography and high pressure liquid chromatography, it was found that vascular aminopeptidase M converted kallidin to bradykinin and inactivated des(Asp1)angiotensin I, angiotensin III, hepta(5-11)substance P and hexa(6-11)substance P. Aminopeptidase M did not, however, hydrolyze bradykinin, angiotensin I, angiotensin II, saralasin, vasopressin, oxytocin or any form of substance P containing a component of the Arg-Pro-Lys-Pro sequence. Both the naphthylamidase and peptidase activities were inhibited similarly by known amino-peptidase M inhibitors including o-phenanthroline, amastatin, bestatin and puromycin. However, inhibitors of angiotensin I converting enzyme (captopril), carboxypeptidase N (MERGETPA), neutral endopeptidase (phosphoramidon), post proline cleaving enzyme and dipeptidyl(amino)peptidase IV (diisopropylphosphofluoridate, DFP) were without effect. These results demonstrate that vascular, cell surface aminopeptidase M can selectively metabolize vasoactive peptides and may play a role in modulating their levels in the circulation and/or within the vessel wall.

The granular peripolar cell of the human glomerulus: a new component of the juxtaglomerular apparatus?

Using serial sections of resin-embedded tissue we found granular peripolar cells in six human kidneys. They were present in 3% to 28% of the glomeruli. Using an immunoperoxidase staining technique and an antibody to pure human renin we showed that the human peripolar cell contains no immunostainable renin. The number of peripolar cells correlated with the number of juxtaglomerular apparatus (JGAs) with renin-containing cells; their distribution within the renal cortex was similar, both being found predominantly in glomeruli in the superficial cortex. There was a close anatomical relationship between the peripolar cells and the renin containing cells in individual JGAs. These findings suggest the possibility of a functional relationship between the peripolar cell and the other components of the juxtaglomerular apparatus.

Threshold pressure for the pressure-dependent renin release in the autoregulating kidney of conscious dogs

The effect of varying renal artery pressure between 160 and 40 mm Hg on renal blood flow and renin release was studied in seven conscious foxhounds under beta-adrenergic blockade receiving a normal sodium diet (4.1 mmol/kg/day). Pressure was either increased by bilateral common carotid occlusion or reduced in steps and maintained constant by a control-system using an inflatable renal artery cuff. Carotid occlusion itself had no influence on renal blood flow and renin release when renal artery pressure was kept constant and the beta-receptors in the kidney were blocked. Between 160 mm Hg and resting pressure there was no change in renal blood flow; between resting blood pressure and the lower limit of autoregulation (average 63.9 mm Hg) renal blood flow increased slightly (average 7%) indicating a high efficiency of renal blood flow autoregulation. The relationship between renal artery pressure and renin release could be approximated by two linear sections: a low sensitivity to a pressure change (average slope: -0.69 +/- 0.26 ng AI/min/mm Hg) was found above a threshold pressure (average: 89.8 +/- 3.3 mm Hg) and a high sensitivity to a pressure change (average slope: -64.4 +/- 20.8 ng AI/min/mm Hg) was observed between threshold pressure and 60 mm Hg. There was no further increase of renin release between 60 and 40 mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Cellular mechanisms of renin release

In the isolated perfused rat kidney renin release is increased by physiological agents which stimulate adenylate cyclase activity, such as beta-adrenoceptor agonists, prostaglandins, histamine (histamine H2-receptor mediated) and adenosine (adenosine RA-receptor mediated). The role of adenylate cyclase and cAMP in the stimulatory pathway for renin release was confirmed by the effect of forskolin, a receptor-independent stimulator of adenylate cyclase, which also stimulated renin release. The intracellular calmodulin-calcium complex was identified as part of an opposing inhibitory pathway. This conclusion is based on the observation that various inhibitors of calmodulin stimulated renin release and that the calcium-dependent inhibition of renin release by angiotensin II was abolished in the presence of these inhibitors. The intracellular control mechanisms for renin release are discussed with respect to the vascular smooth muscle origin of renin-producing cells.

Immunohistochemistry of the renin-angiotensin-system in the kidney

Changes of the intrarenal localization and concentration of renin in comparison to those of angiotensin II (ANG II) are shown under various conditions of stimulation and inhibition of the renin-angiotensin-system. Evidence is presented that ANG II which is detectable by immunocytochemical methods in epitheloid cells is formed locally within the kidney either intra- or extracellularly. ANG II-like activity was found not only in the epitheloid cells of the JGA, but also further upstream in non specialized, "plain" smooth muscle cells of the renal arterial tree and in the medial muscle cells of resistance vessels in other organs and tissues. This ANG II-like activity of resistance vessels is increased in spontaneously hypertensive rats suggesting a possible role in the long-term regulation of blood pressure.

The intrarenal renin-angiotensin-system. An immunocytochemical study on the localization of renin, angiotensinogen, converting enzyme and the angiotensins in the kidney of mouse and rat

The localization of renin, converting enzyme (CE) and angiotensin II (ANG II) in the kidneys of rats and mice was investigated with immunocytochemical methods. According to the presence and specific intrarenal localization of these components of the renin-angiotensin-system (RAS) our results suggest that in addition to the well known systemic effects of the RAS, there are interactions of its components inside the kidney. These interactions may lead to the generation of an extra portion of ANG II in the renal blood stream with its target cells determined by the localization of CE at the luminal side of well defined endothelial areas. These intrarenal-intravasal reactions may or may not reinforce the action of "systemic" ANG II, generated prerenally. In addition, the existence of true intrarenal-interstitial interactions, with the different components and actions of this intrarenal RAS restricted entirely to the kidney is suggested by our results, particularly the demonstration of ANG II within epitheloid cells and the dissociation of systemic renin and ANG II from their local concentrations in renal hypertensive rats.

The localization of converting enzyme in kidney vessels of the rat

An antibody against pure rabbit lung converting enzyme (CE) showing cross-reaction with CE from other species was used for immunocytochemical studies in the kidney of rats. Using the indirect labelling PAP-technique, specific immunostaining was found in the endothelial layer of all arteries and arterioles of kidney cortex and in some descending vasa recta. CE-positive reactions were also seen in most glomeruli, the reaction product being confined to only a few capillary loops in connection with the glomerular stalk. A few immunostained capillaries in the cortical labyrinth were suspected to belong to the first ramifications of the efferent arteriole. The bulk of all other of the glomerular and peritubula capillaries as well as all veins of the kidney showed no obvious immunostaining. The functional significance of this specific localization pattern of CE in the endothelium of kidney vessels is discussed with respect to the actions of the systemic and the local, intrarenal renin-angiotensin-system on kidney functions.

Immunoreactive renin and angiotensin II in the afferent glomerular arterioles of rats with hypertension due to unilateral renal artery constriction

The immunoreactivity for renin and angiotensin II (ANG II) in the ischaemic and non-ischaemic kidney of rats with renovascular hypertension was compared with that of the kidneys of sham operated controls. In addition, the renin concentration of these kidneys and the plasma level of ANG II were determined in hypertensive and control animals. In parallel with the renin concentration of kidney cortex, the immunoreactivity, i.e. the JG-index for renin of the afferent arterioles from the ischaemic kidney was slightly increased, that from the non-ischaemic kidney drastically decreased as compared to control kidneys. Similarly, the JG-index for ANG II was increased in the ischaemic and decreased in the non-ischaemic kidney although the plasma level of ANG II was elevated in the animals with renovascular hypertension. This difference in the immunocytochemically detectable ANG II and especially the decrease of ANG II in the non-ischaemic kidney in spite of elevated plasma ANG II levels is interpreted to result from similar differences in the local (extravascular) formation of ANG II by the intrarenal renin-angiotensin system.