Extrarenal Renin Research Articles

Resemblance in Physiological Systems during Phylogeny and Ontogeny

Although it is not certain whether some characteristics of the mammalian fetus/embryo may repeat the adult stage of ancestral vertebrates, comparison of these two time‐dependent processes should provide new insight into the molecular and functional evolution and its significance. Here we discuss two important biological models: 1) Renin‐angiotensin system (RAS) and 2) Urine concentration mechanism.Renin is a hormone and substrate‐dependent enzyme secreted mostly by the juxtaglomerular (JG) cells of the afferent arteriole located at the vascular pole of the glomerulus. Renin acts on renin substrates and forms angiotensin (Ang) I which is subsequently converted to Ang II by Ang converting enzyme (ACE). Renin containing cells evolved early both in phylogeny and ontogeny, whereas, the macula densa (tubule component), and extracellular mesangium appeared at later stages.Renin containing cells are distributed more widely intrarenally and/or extrarenally in early stages during phylogeny and ontogeny. Granulated cells and renin expression become progressively restricted to JG areas with phylogenic and ontogenic advancement. Kidney renin activities tend to be higher in primitive fishes than in more advanced, while the relative level of extrarenal renin expression to that of the kidney is higher in embryos than in more mature chicken and mice. Extra renal renin is noted in primitive vertebrates. Also, in both the mammalian fetus and nonmammalian vertebrates, the vasopressor and vascular action of Ang II evolved early. A single application of ACE inhibitors decreases the basal level of blood pressure and increase plasma renin activity in conscious adult teleost fish. Ang II stimulates, whereas ACE inhibitors inhibit, arteriolar branching in zebrafish. Likewise, the RAS is important during early ontogeny of mammals in vascular growth and development.Distal tubules of freshwater trout show secondary active NaCl cotransport mechanism without accompaniment of water and act as the so‐called “diluting segment.” Teleost fish cannot concentrate urine because they lack structural and functional countercurrent mechanisms. Only birds and mammals can form urine clearly hyperosmotic to plasma and conserve body water. The structure and function of adult quail kidneys have similarities to those of developing rodents. Both have a loop of Henle, consisting of descending limb and thick ascending limb, but they lack the thin ascending limb. Countercurrent urine concentration of adult quail and developing rodents heavily depends on NaCl recycling without participation of urea transport. Moreover, in both adult quail and developing rodent kidneys, aquaporin 2 gene expression and protein are present in the apical membrane of the collecting tubules, but the water conservation effect of neurohypophysial hormones is smaller than that of adult rodent kidneys. Hence, comparing these two time‐dependent processes may provide new insights into the interpretation of existing findings and provide perspective for future investigations.

Leukemia development initiated by deletion of RBP-J: mouse strain, deletion efficiency and cell of origin.

ABSTRACTConditional deletion of RBP-J, the major transcriptional effector of Notch signaling, specifically within renin-expressing cells leads to the development of B-cell leukemia. However, the influence of contributing factors such as mouse strain, cell of origin and Cre recombinase copy number are unknown. In this study, we compared RBP-J deletion efficiency using one versus two copies of Cre recombinase. Further, we compared the incidence and timing of leukemia development in two unique strains of mice, C57BL/6 and 129/SV, as well as at different B-cell developmental stages. We found that animals expressing two copies of Cre recombinase developed B-cell leukemia at an earlier age and with more fulminant disease, compared with control animals and animals expressing one copy of Cre recombinase. In addition, we found a difference in leukemia incidence between C57BL/6 and 129/SV mouse strains. Whereas deletion of RBP-J in renin-expressing cells of C57BL/6 mice leads to the development of B-cell leukemia, 129/SV mice develop dermatitis with a reactive, myeloproliferative phenotype. The difference in phenotypes is explained, in part, by the differential expression of extra-renal renin; C57BL/6 mice have more renin-expressing cells within hematopoietic tissues. Finally, we found that deletion of RBP-J in Mb1- or CD19-expressing B lymphocytes does not result in leukemia development. Together, these studies establish that renin progenitors are vulnerable cells for neoplastic transformation and emphasize the importance of genetic background on the development of inflammatory and malignant conditions.This article has an associated First Person interview with the first author of the paper.

FITC localization of renin in rat mesometrial tissue

Renin, a hormone produced primarily by the kidneys in response to low blood pressure, is an immediate downstream gene product of Class I HOX gene regulation in the embryo. Examination of transgenic mice in which renin was linked to gfp reveals renin in renal, adrenal, and gonadal arteries in the embryo, giant trophoblast cells of the placenta, kidney and submandibular gland in both male and female, and uterine artery. In rat, giant trophoblast cells, other cells in fetal and maternal regions of the placenta, and cells of the tunica adventita of uterine artery as well as in the wall of the afferent arteriole of the kidney were labeled with antibody stain. This project examines pregnant and nonpregnant rat mesometrial tissues to identify cells that localize FITC labeled sheep anti‐rat renin antibody. Fluorescent granules were seen in cells resembling fibroblasts throughout the mesometrium and along the walls of small vessels within the mesometrium. Afferent arterioles were labeled and control tissues were not. These results demonstrate that the mesometrium is another site within rat female reproductive tissues in which renin is located, adding support to the hypothesis that extrarenal renin production may play a role in preecclampsia. Work is supported by NSF grant #0132823 and 0726185, and D’Youville College faculty council research funding.

Delineating the contributions of AT1a and AT1b receptor-mediated uptake of ANG II in kidneys and adrenals

inappropriately elevated angiotensin ii (ANG II) levels induced by infusion of ANG II or overexpression of the renin-angiotensin system (RAS) commonly result in increased intrarenal and intra-adrenal ANG II content ([8][1]). Derangement of renal function due to inappropriate activation of intrarenal

Sandford Lloyd Skinner (1933–2005)

Sandford Lloyd (“Sandy”) Skinner, one of the pillars of the renin-angiotensin system, died on May 29, 2005, after a long illness. Sandy was a gentleman, scientist, teacher, and family man who touched the lives of the many who were fortunate to know him.⇓ Sandy was born in Clare, South Australia, on August 6, 1933. He graduated MBBS from The University of Adelaide in 1957. Following his medical studies, he researched the effects of vasoactive substances on the circulation and respiration of humans in the Department of Physiology, The University of Adelaide, for which he was awarded an MD degree in 1962. He also reported the artifactual elevation of plasma potassium levels during venepuncture.1 His first postdoctoral position during 1962–1963 was at the Cleveland Clinic working with Irvine Page and James McCubbin. This was the start of his life-long passion for the renin-angiotensin system. At the Cleveland Clinic he performed seminal studies demonstrating the role of the baroreceptor mechanism of control of renin release.2 Importantly, his studies demonstrated that renin release could be stimulated by reduction in renal perfusion pressure within the physiological range without significant change in renal blood flow, thus demonstrating that renin release was caused by a baroreceptor mechanism and not renal ischemia. He also showed that renal compression could stimulate renin release. These studies were important in showing that variation in renin release may have …

Lectin chromatography of extrarenal renin protein in human plasma and tissues: Potential endocrine function via the renin receptor

Secretion of prorenin from extrarenal tissues comprises approximately half of the renin protein in plasma; its origin is unknown. The discovery of a prorenin/renin receptor that activates vascular tissue kinases raises interest in this otherwise inactive component. We have studied its glycosylation as this may distinguish it from renal renin. The binding of renin protein (active and prorenin) in human plasma and tissues to concanavalin (Con A) and wheat germ lectins was deployed. Immunoradiometric and enzyme kinetic assays were applied to column fractions. Mannosylated renin protein binds to Con A and has been shown to be taken up by human vascular and hepatic cells on mannose-6-phosphate receptors, possibly as a clearance mechanism. But the other binding sites of prorenin/renin that elicit a cellular phosphorylation response are apparently independent of glycosylation. The tissues examined (kidney, adrenal, ovary) each contain high proportions of Con A binding renin, but the plasma of normal resting males and females contain mainly non-binding renin, the proportion increasing as renal renin secretion decreases. The extreme of this relationship is seen in anephric patients and in some normal women on oral contraceptives with suppressed renal renin, in whom plasma renin is entirely non-binding to Con A. Conversely, when renal renin secretion was stimulated, the increased plasma active renin bound to Con A. However, extrarenal tissues containing exclusively Con A non-binding renin protein, and hence potential sources of anephric plasma renin protein, were not identified, but are unlikely to include adrenal or female reproductive tract. The findings are consistent with the view that normal human plasma contains a considerable amount of amannosylated prorenin of extrarenal origin that escapes hepatic clearance and has a longer half-life than renal renin. This plasma renin form would be expected to be activated in association with the recently described renin/prorenin aspartyl protease receptor and to participate in local pathophysiological processes.

Potassium control of extrarenal renin secretion in transgenic (mRen-2)27 and normal rats.

Plasma active renin and prorenin were followed for 12 h after bilateral, unilateral, and sham nephrectomy (BNx, UNx, and SNx) in anesthetized transgenic (mRen-2)27 rats to compare them with Sprague-Dawley and spontaneously hypertensive rats (SDR and SHR). In Ren-2 rats, active renin and prorenin increased with plasma potassium post-BNx and were augmented by potassium infusion. The increase in prorenin but not active renin was abolished by bilateral adrenalectomy (BADRx). However, this did not reduce prorenin below normal, indicating that the high plasma prorenin Ren-2 phenotype is not only of adrenal origin. SNx and UNx also raised plasma active renin and prorenin in Ren-2 rats, with positive correlations to plasma potassium. In SDR and SHR, active renin fell below prorenin post-BNx, and adrenal ablation and potassium loading (in SDR) modified the decreasing active renin profile consistent with low levels of regulated extrarenal secretion. In Ren-2 rats, adrenal but not extra-adrenal prorenin secretion is potassium sensitive and stress related. The unidentified source of active renin in BNx+BADRx Ren-2 rats is also potassium and stress related.

Renin-angiotensin system in the adrenal.

Extrarenal renin has been found in a number of tissues. All the components of the renin-angiotensin system have been identified in the adrenal cortex. Adrenal renin has been found in many animal species, including the human, but most of the studies have been carried out in the rat. Renin is present and synthesized mainly in the zona glomerulosa cells. Renin production is under physiological control and can be influenced by ACTH, changes in electrolyte balance and the genetic background of the rat. The evidence suggests that adrenal renin plays a role as a local hormone in regulating aldosterone production by the zona glomerulosa cells.

Analysis of phenotypic consequences of renin gene polymorphism in Lyon rats.

To investigate phenotypic consequences of renin gene polymorphism between Lyon hypertensive (LH) and normotensive (LN) rats because previously we demonstrated cosegregation of the LH allele with increased blood pressure in a cross of LH with LN rats. Two studies were conducted. Study 1 used a cohort of male F2 rats from a LH x LN cross. Eighty-two rats homozygous for the hypertensive (HH) renin gene allele were compared with 82 rats homozygous for the normotensive (NN) allele. Urinary steroid excretion was measured in 24 h urine samples collected from rats aged 6 weeks. The direct aortic blood pressure was recorded in 30-week-old rats and, after they had been killed, their kidney renin concentration (KRC) was measured. In study 2, renin, angiotensinogen and angiotensin converting enzyme plasma concentrations and renin messenger RNA (mRNA) levels were measured in renal and extra-renal tissues from 6- and 25-week-old LH and LN parental and HH and NN F2 male rats. Urinary steroids and plasma components of the renin-angiotensin system (RAS) were measured using specific radioimmunoassays. mRNA levels were quantified by northern blotting. In study 1, HH F2 rats had a higher blood pressure (151.5 +/- 8.2 versus 146.0 +/- 7.4 mmHg, P < 0.001) and a lower KRC (514 +/- 203 versus 666 +/- 304 micrograms A1/h per g cortex, P < 0.01) than did NN rats aged 30 weeks. In covariate analysis the decrease in KRC in HH rats was attributable to their increased blood pressure rather than to the renin genotype. The renin genotype of rats aged 6 weeks was not associated with a change in the urinary excretion of aldosterone, desoxycorticosterone, corticosterone or 18-hydroxy desoxycorticosterone. In study 2, we found no difference either in plasma levels of RAS components or in renal or extrarenal renin mRNA levels either between parental LH and LN rats or between HH and NN F2 rats apart from a higher plasma renin concentration in LH rats aged 6 weeks. Renal, but not extra-renal, renin mRNA levels declined with age. We found no evidence of a renin genotype-dependent phenotypic difference in the RAS that could account for the effect of the renin locus on blood pressure in Lyon rats. Our findings suggest that the effect of the locus on blood pressure might be due to an as yet unidentified gene linked to renin.

Plasma angiotensin in binephrectomised mice.

Plasma renin-angiotensin parameters were measured before and 24h after binephrectomy (BNx) in male Swiss (Ren-1, Ren-2) and BALB/c (Ren-1) female mice (representing the extremes of differences in tissue renin expression), together with in vivo inhibition of residual renin. Plasma Ang II increased from 18.9 +/- 7.3 to 48.1 +/- 16.9 pg/ml after BNx in conscious Swiss mice (+/- sd, p < 0.001, n = 11&12), renin activity (PRA) increased 2.76 times, angiotensinogen (aogen) increased 4.57 times and renin concentration (PRC) fell by 65%. In BALB/c, Ang II+Ang III decreased slightly (56.6 +/- 11 to 37.7 +/- 14.7, p < 0.05, n = 5&6), PRA was unchanged, aogen increased 12 times and PRC fell by 93%. Plasma ACE decreased by 26% and 28% respectively. Aogen did not increase further when post BNx plasma renin was inhibited with antirenin in vivo during 20h. Thus plasma angiotensin is maintained or considerably increased following BNx in mice and the change is consistent with first-order kinetics with respect to renin and aogen in the circulation. Whether the strain carries one or two renin genes, high renal and extrarenal renin production combined with a low plasma aogen phenotype yields resting angiotensin levels similar to other mammals. A kinetic regulation of aogen levels is proposed in mice wherein Ang II production is limited by low substrate concentration thereby ensuring normotension in the face of abundant extrarenal renin secretion.

Ontogenetic regulation of mouse Ren-2d renin gene in transgenic hypertensive rats, TGR(mREN2)27

TGR(mREN2)27 is a new monogenetic rat model with fulminant hypertension, low kidney renin, and high extrarenal renin gene expression. This study characterizes and compares expression of the Ren-2 gene in TGR(mREN2)27 with that in DBA/2 mice and with renin gene expression in rats. Except in the submandibular gland, the tissue-specific expression of Ren-2 is similar in TGR(mREN2)27 and DBA/2. This demonstrates maintenance of tissue specificity. Organs that are involved in cardiovascular regulation, such as the adrenal gland, kidney, and brain, express the Ren-2 gene before hypertension has developed, consistent with the possibility of a causal relationship between transgene expression in these tissues and hypertension. Because these tissues express the renin gene in nontransgenic rats as well, we suggest that this model can be used to study the regulation of renin gene expression and its role in hypertension at these sites. In addition, as an indication that interactions may exist between blood pressure and renin gene expression, we describe reciprocal changes in blood pressure and Ren-2 mRNA levels in the kidney and brain.

Physiological concentrations of ANP exert a dual regulatory influence on renin release in conscious dogs.

The influence of physiological increments in circulating atrial natriuretic peptide (ANP) on renin release was determined in conscious dogs. Renin stimulus-response curves (RSRCs) were obtained by controlled reductions of renal perfusion pressure (RPP) under control conditions and during intrarenal or intravenous ANP infusions. Under all experimental conditions, the RSRCs were characterized by a plateau, a threshold pressure (Pth), and a steep slope below Pth. Intrarenal ANP infusion (0.9 ng.kg-1.min-1), which induced a calculated threefold elevation of renal arterial ANP concentration (but did not change systemic arterial ANP levels), increased the slope of the RSRC by 81% (P less than 0.05) with no effect on Pth. A quantitatively similar effect on the slope of the RSRC (+90%; P less than 0.05) was observed when systemic ANP levels were raised (from 37 +/- 2 to 71 +/- 9 pg/ml; P less than 0.05) by intravenous infusions (3.6 ng.kg-1.min-1). In addition, however, intravenously infused ANP reduced Pth from 91 to 85 mmHg (P less than 0.05), which caused a complete suppression of the renin response to a reduction of RPP down to 85 mmHg. These findings indicate that ANP can inhibit renin release at physiological plasma concentrations by shifting the RSRC to a lower pressure level; this shift is mediated by a modulation of extrarenal renin control mechanisms. The direct effect of ANP on renin release is one of stimulation.

Extrarenal Renin and Blood Pressure Regulation

Extrarenal Renin and Blood Pressure Regulation

6 The effects of ACE inhibition on extrarenal renin mRNA levels

6 The effects of ACE inhibition on extrarenal renin mRNA levels

The Role of Extrarenal Renin in Goldblatt Hypertension

Renin-like activity can be demonstrated in arterial extracts from normal rats and from rats with Goldblatt hypertension. We have found no evidence, however, for elevated arterial renin levels in relation to plasma renin activity. Studies of the reversal of renovascular hypertension indicate that the fall in blood pressure produced by renal artery deconstriction is not renin-dependent. However, molecular biological techniques indicate that extrarenal renin gene expression is altered in some tissues, such as the adrenal gland in Goldblatt hypertension, and it is possible therefore that extrarenal renin synthesis is important in blood pressure control. This has to be distinguished from renin derived from plasma uptake.

Quantitative measurement of extra-renal renin mRNA by polymerase chain reaction

We established a simplified method of the quantitative measurement of extra-renal renin messenger RNA using polymerase chain reaction system. We could detect the renin messenger RNA in the kidney, heart, aorta and adrenal gland from a single RNA sample obtained from a Wistar-Kyoto rat. In the kidney, heart, aorta and adrenal gland, the contents of renin messenger RNA were found to be 55.8 ± 17.8, 0.15 ± 0.05, 0.11 ± 0.03 and 0.16 ± 0.07 pgμg of total RNA (n=5, mean ± s.d.), respectively. The present method is very useful to study the extra-renal renin-angiotensin system.

Renal and extra-renal levels of renin mRNA in experimental hypertension

1. Using a ribonuclease-protection assay, renin mRNA levels were compared in the kidneys, livers, brains, hearts and adrenal glands of two-kidney, one-clip Goldblatt hypertensive rats with those of age-matched control rats at 4 weeks ('early') and 20 weeks ('chronic') after clipping, and in the kidneys and adrenal glands of rats treated for 3 weeks with deoxycorticosterone and salt (deoxycorticosterone-salt hypertension) with those of control rats. 2. While marked changes were observed in kidney renin mRNA levels in all three experimental groups compared with their respective controls, in most of the extra-renal tissue studied minimal, if any, difference was seen in renin mRNA levels between the hypertensive and control rats. 3. The findings suggest that in these extra-renal tissues renin gene expression is differently regulated from that in the kidney, and particularly that it is not profoundly affected by changes in the level of circulating angiotensin II. 4. An increase in renin mRNA was observed in the adrenal glands of the 'chronic' Goldblatt rats, which may be of relevance to the maintenance of hypertension in this model.

Production of Renin, Angiotensin II, and Aldosterone by Adrenal Explant Cultures: Response to Potassium and Converting Enzyme Inhibition*

The existence of renin in a number of extrarenal tissues has been well documented, but the physiological role of extrarenal renin remains unknown. To study the physiological role of adrenal renin, we developed a serum-free culture system for adrenal capsular/zona glomrulosa explants. Explants showed good viability in culture (greater than 80%), and demonstrated net production of aldosterone, angiotensin II, and prorenin. Aldosterone production was consistently stimulated by an increase in potassium (6 mM) in the culture medium. Both aldosterone and angiotensin II production could be attenuated by adding the angiotensin converting enzyme inhibitor lisinopril to the culture medium (0.1 mM). These data suggest that rat adrenal explants are capable of producing all of the components of a functional renin-angiotensin-aldosterone system and that these components can interact in response to physiological stimuli. These findings support the hypothesis that a local adrenal renin system may play a physiological role in the control of adrenal aldosterone production.

Prorenin and renin as separate mediators of tissue and circulating systems.

The renin gene is expressed in extrarenal tissues. High concentrations of renin occur in female reproductive organs: the adrenals of rats and mice have intermediate levels. The testis also synthesizes renin, as does the anterior pituitary. In contrast, very low levels of renin (ie, below plasma levels) are found in the heart and extrarenal vascular tissues. The predominant form of renin in the human ovary, placenta, and uterus is prorenin and the human ovary, testis, and adrenals have been shown to secrete prorenin into the circulation. The kidney is the only organ that secretes active renin and it is also the major source of plasma prorenin. We have used the ovary as a model to study extrarenal renin. Ovarian prorenin secretion changes dynamically during the menstrual cycle and during gestation. Secretion occurs during the LH surge and when hCG is present in the blood during pregnancy. Plasma active renin does not change concurrently and only low levels of active renin are found in association with very high concentrations of prorenin in ovarian follicular fluid after gonadotropin stimulation. To explain the preponderance of prorenin, and the virtual absence of renin in the ovary we hypothesize that prorenin need not be converted to active renin to have effect. In vitro, when prorenin is acidified to pH 3.3 or cooled to 0 degrees C, it develops intrinsic catalytic activity without cleavage of the prosegment.(ABSTRACT TRUNCATED AT 250 WORDS)

Extrarenal renin and blood pressure regulation. An alternative viewpoint.

There is increasing evidence that a major site of production of angiotensin I and II is peripheral tissue. Both angiotensin I and II are present in venous blood in amounts far too high to be explained by their generation in blood alone, given the extensive conversion of angiotensin I to angiotensin II and clearance of both peptides across peripheral tissues. Much indirect evidence supports this argument for angiotensin production in tissues, and indicates that tissue production of angiotensin plays an important role in regulation of blood pressure. Tissue renin may represent uptake from plasma and/or local synthesis, but despite the ease with which renin-like activity can be measured in tissues, its interpretation is problematic because of interference by nonrenin enzymes and inadvertent activation of inactive renin. Moreover, given that enzymes other than renin are able to liberate angiotensin I and angiotensin II from angiotensinogen, there is no obligatory role for renin in angiotensin production in tissues. Inasmuch as tissue production is the major source of plasma angiotensin, the fall in plasma angiotensin levels after bilateral nephrectomy indicates that kidney-derived renin is the major contributor to tissue angiotensin production. This argument is supported by evidence that vascular renin-like activity is kidney-derived, and plays a dominant role in angiotensin-dependent pressor mechanisms. Near-normal levels of inactive renin in plasma of anephric subjects indicates extrarenal synthesis of inactive renin, and renin mRNA has been identified in various nonrenal tissues. Whether these tissues are also able to process inactive renin to active renin, and its role in local angiotensin production and blood pressure regulation, are currently being investigated.