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

Elabela Peptide: An Emerging Target in Therapeutics

Elabela, a bioactive micropeptide, is recognized as the second endogenous ligand for the Apelin receptor and is widely distributed in different tissues and organs. Elabela plays an important role in various physiological processes, such as blood pressure control, heart morphogenesis, apoptosis, angiogenesis, cell proliferation, migration, etc. Elabela is also implicated in pathological conditions, like cardiac dysfunctions, heart failure, hypertension, kidney diseases, cancer and CNS disorders. The association of Elabela with these disease conditions makes it a potential target for their therapy. This review summarizes the physiological role of Elabela peptide as well as its implication in various disease conditions.

Inhibition of neprilysin with sacubitril without RAS blockage aggravates renal disease in Dahl SS rats

Salt-sensitive (SS) hypertension is accompanied with severe cardiorenal complications. In this condition, elevated blood pressure (BP) resulting from salt retention is associated with counterintuitively lower levels of atrial natriuretic peptide (ANP). In plasma, ANP is degraded by the neprilysin; therefore, pharmacological inhibition of this metalloprotease (i.e., with sacubitril) can be employed to increase ANP level. We have shown earlier that sacubitril in combination with valsartan (75 μg/day each) had beneficial effects on renal function in Dahl SS rats. The goal of this study was to evaluate the effects of a higher dose of sacubitril on renal damage in this model. To induce hypertension, male Dahl SS rats were fed a 4% NaCl diet (HS) for 21 days, and were administered sacubitril (125 μg/day) or vehicle via s.c. osmotic pumps. At the end of the HS challenge, both groups exhibited similar outcomes for GFR, heart weight, plasma electrolytes, BUN, and creatinine. Sacubitril exacerbated kidney hypertrophy, but did not affect levels of renal fibrosis. We also observed aggravated glomerular lesions and increased formation of protein casts in the sacubitril-treated animals compared to controls. Thus, in Dahl SS rats, administration of sacubitril without renin-angiotensin-system blockage had adverse effects on renal disease progression, particularly in regards to glomerular damage and protein cast formation. We can speculate that while ANP levels are increased because of neprilysin inhibition, there are off-target effects of sacubitril, which are detrimental to renal function in the SS hypertensive state.

Construction of a ceRNA coregulatory network and screening of hub biomarkers for salt-sensitive hypertension

Salt-sensitive hypertension (SSH) is an independent risk factor for cardiovascular disease. The regulation of long non-coding RNAs, mRNAs and competing endogenous RNAs (ceRNAs) in the pathogenesis of SSH is uncertain. An RNA microarray was performed to discover SSH-associated differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs), and 296 DElncRNAs and 44 DEmRNAs were identified, and 247 DElncRNAs and 44 DEmRNAs among these RNAs were included in the coexpression network. The coregulatory network included 23 ceRNA loops, and six hub RNAs (lnc-ILK-8:1, lnc-OTX1-7:1, lnc-RCAN1-6:1, GIMAP8, SUV420H1 and PIGV) were identified for further population validation. The ceRNA correlations among lnc-OTX1-7:1, hsa-miR-361-5p and GIMAP8 were confirmed in SSH and SRH patients. A larger-sample validation confirmed that GIMAP8, SUV420H1 and PIGV were differentially expressed between the SSH and SRH groups. In addition, SUV420H1 was included in the SSH screening model, and the area under the curve of the model was 0.720 (95% CI: 0.624-0.816). Our study explored the transcriptome profiles of SSH and constructed a ceRNA network to help elucidate the mechanism of SSH. In addition, SUV420H1 was identified as a hub element that participates in SSH transcriptional regulation and as a potential biomarker for the early diagnosis of SSH.

ELABELA antagonizes intrarenal renin-angiotensin system to lower blood pressure and protects against renal injury

Emerging evidence has demonstrated that (pro)renin receptor (PRR)-mediated activation of intrarenal renin-angiotensin system (RAS) plays an essential role in renal handling of Na⁺ and water balance and blood pressure. The present study tested the possibility that the intrarenal RAS served as a molecular target for the protective action of ELABELA (ELA), a novel endogenous ligand of apelin receptor, in the distal nephron. By RNAscope and immunofluorescence, mRNA and protein expression of endogenous ELA was consistently localized to the collecting duct (CD). Apelin was also found in the medullary CDs as assessed by immunofluorescence. In cultured CD-derived M1 cells, exogenous ELA induced parallel decreases of full-length PRR (fPRR), soluble PRR (sPRR), and prorenin/renin protein expression as assessed by immunoblotting and medium sPRR and prorenin/renin levels by ELISA, all of which were reversed by 8-bromoadenosine 3',5'-cyclic monophosphate. Conversely, deletion of PRR in the CD or nephron in mice elevated Apela and Apln mRNA levels as well as urinary ELA and apelin excretion, supporting the antagonistic relationship between the two systems. Administration of exogenous ELA-32 infusion (1.5 mg·kg^-1·day^-1, minipump) to high salt (HS)-loaded Dahl salt-sensitive (SS) rats significantly lowered mean arterial pressure, systolic blood pressure, diastolic blood pressure, and albuminuria, accompanied with a reduction of urinary sPRR, angiotensin II, and prorenin/renin excretion. HS upregulated renal medullary protein expression of fPRR, sPRR, prorenin, and renin in Dahl SS rats, all of which were significantly blunted by exogenous ELA-32 infusion. Additionally, HS-induced upregulation of inflammatory cytokines (IL-1β, IL-2, IL-6, IL-17A, IFN-γ, VCAM-1, ICAM-1, and MCP-1), fibrosis markers (TGF-β₁, FN, Col1A1, PAI-1, and TIMP-1), and kidney injury markers (NGAL, Kim-1, albuminuria, and urinary NGAL excretion) were markedly blocked by exogenous ELA infusion. Together, these results support the antagonistic interaction between ELA and intrarenal RAS in the distal nephron that appears to exert a major impact on blood pressure regulation.

Hyperaldosteronism after decreased renal K+ excretion in KCNMB2 knockout mice

The kidney is the primary organ ensuring K(+) homeostasis. K(+) is secreted into the urine in the distal tubule by two mechanisms: by the renal outer medullary K(+) channel (Kir1.1) and by the Ca(2+)-activated K(+) channel (KCa1.1). Here, we report a novel knockout mouse of the β2-subunit of the KCa1.1 channel (KCNMB2), which displays hyperaldosteronism after decreased renal K(+) excretion. KCNMB2(-/-) mice displayed hyperaldosteronism, normal plasma K(+) concentration, and produced dilute urine with decreased K(+) concentration. The normokalemia indicated that hyperaldosteronism did not result from primary aldosteronism. Activation of the renin-angiotensin-aldosterone system was also ruled out as renal renin mRNA expression was reduced in KCNMB2(-/-) mice. Renal K(+) excretion rates were similar in the two genotypes; however, KCNMB2(-/-) mice required elevated plasma aldosterone to achieve K(+) balance. Blockade of the mineralocorticoid receptor with eplerenone triggered mild hyperkalemia and unmasked reduced renal K(+) excretion in KCNMB2(-/-) mice. Knockout mice for the α-subunit of the KCa1.1 channel (KCNMA1(-/-) mice) have hyperaldosteronism, are hypertensive, and lack flow-induced K(+) secretion. KCNMB2(-/-) mice share the phenotypic traits of normokalemia and hyperaldosteronism with KCNMA1(-/-) mice but were normotensive and displayed intact flow-induced K(+) secretion. Despite elevated plasma aldosterone, KNCMB2(-/-) mice did not display salt-sensitive hypertension and were able to decrease plasma aldosterone on a high-Na(+) diet, although plasma aldosterone remained elevated in KCNMB2(-/-) mice. In summary, KCNMB2(-/-) mice have a reduced ability to excrete K(+) into the urine but achieve K(+) balance through an aldosterone-mediated, β2-independent mechanism. The phenotype of KCNMB2 mice was similar but milder than the phenotype of KCNMA1(-/-) mice.

Increased renin excretion is associated with augmented urinary angiotensin II levels in chronic angiotensin II-infused hypertensive rats

Renin expression in principal cells of collecting ducts (CD) is upregulated in angiotensin II (ANG II)-dependent hypertensive rats; however, it remains unclear whether increased CD-derived renin undergoes tubular secretion. Accordingly, urinary levels of renin (uRen), angiotensinogen (uAGT), and ANG II (uANG II) were measured in chronic ANG II-infused Sprague-Dawley rats (80 ng/min for 14 days, n = 10) and sham-operated rats (n = 10). Systolic blood pressure increased in the ANG II rats by day 5 and continued to increase throughout the study (day 13; ANG II: 175 ± 10 vs. sham: 116 ± 2 mmHg; P < 0.05). ANG II infusion increased renal cortical and medullary ANG II levels (cortical ANG II: 606 ± 72 vs. 247 ± 43 fmol/g; P < 0.05; medullary ANG II: 2,066 ± 116 vs. 646 ± 36 fmol/g; P < 0.05). Although plasma renin activity (PRA) was suppressed in the ANG II-infused rats (0.3 ± 0.2 vs. 5.5 ± 1.8 ng ANG I·ml(-1)·h(-1); P < 0.05), renin content in renal medulla was increased (12,605 ± 1,343 vs. 7,956 ± 765 ng ANG I·h(-1)·mg(-1); P < 0.05). Excretion of uAGT and uANG II increased in the ANG II rats [uAGT: 1,107 ± 106 vs. 60 ± 26 ng/day; P < 0.0001; uANG II: 3,813 ± 431 vs. 2,080 ± 361 fmol/day; P < 0.05]. By day 13, despite suppression of PRA, urinary prorenin content increased in ANG II rats [15.7 ± 3 vs. 2.6 ± 1 × 10(-3) enzyme units excreted (EUE)/day, P < 0.01] as was the excretion rate of renin (8.6 ± 2 × 10(-6) EUE/day) compared with sham (2.8 ± 1 × 10(-6) EUE/day; P < 0.05). Urinary renin and prorenin protein levels examined by Western blot were augmented ∼10-fold in the ANG II-infused rats. Concomitant AT(1) receptor blockade with candesartan prevented the increase. Thus, in ANG II-dependent hypertensive rats with marked PRA suppression, increased urinary levels of renin and prorenin reflect their augmented secretion by CD cells into the luminal fluid. The greater availability of renin and AGT in the urine reflects the capability for intratubular ANG II formation which stimulates sodium reabsorption in distal nephron segments.

Relationship between beliefs regarding a low salt diet in chronic renal failure patients on dialysis

OBJECTIVE

The aim of this study was to investigate the relationship between beliefs regarding a low salt diet and the nutritional behavior of sodium consumption as well their relation with sociodemographic and clinical variables among chronic renal failure (CRF) patients on dialysis.

DESIGN AND METHODS

This cross-sectional study enrolled a sample of 117 patients who answered the Brazilian version of the Beliefs about Dietary Compliance Scale (BDCS), the sodium frequency food questionnaire, and the use of discretionary salt/day.

RESULTS

The average of total salt consumption was 10.6 g/day (±6.3) and it was positively correlated with the interdialytic weight gain (r = 0.20 P = .032) and negatively correlated with the education level (r = -0.19 P = .044). The Benefits beliefs were discriminatory of the higher and lower salt consumers, and proportionally related to monthly income (r = 0.22 P = .017). The Barriers beliefs were positively correlated only to time on dialysis (r = 0.25 P = .008). Subjects with lower schooling and those of older age tended to consume more discretionary salt (r = -0.27, P = .005; r = 0.23, P = .016, respectively); however, they reported a lower consumption of foods with high salt content (r = 0.25 P = .006; r = -0.27 P = .004).

CONCLUSIONS

Educational interventions aimed at reducing salt consumption for this group must include interventions targeted at different behaviors related to overall salt consumption, the specificities of age, and level of schooling of the patients.

Mast cell renin and a local renin-angiotensin system in the airway: role in bronchoconstriction

We previously reported that mast cells express renin, the rate-limiting enzyme in the renin-angiotensin cascade. We have now assessed whether mast cell renin release triggers angiotensin formation in the airway. In isolated rat bronchial rings, mast cell degranulation released enzyme with angiotensin I-forming activity blocked by the selective renin inhibitor BILA2157. Local generation of angiotensin (ANG II) from mast cell renin elicited bronchial smooth muscle contraction mediated by ANG II type 1 receptors (AT(1)R). In a guinea pig model of immediate type hypersensitivity, anaphylactic mast cell degranulation in bronchial rings resulted in ANG II-mediated constriction. As in rat bronchial rings, bronchoconstriction (BC) was inhibited by a renin inhibitor, an AT(1)R blocker, and a mast cell stabilizer. Anaphylactic release of renin, histamine, and beta-hexosaminidase from mast cells was confirmed in the effluent from isolated, perfused guinea pig lung. To relate the significance of this finding to humans, mast cells were isolated from macroscopically normal human lung waste tissue specimens. Sequence analysis of human lung mast cell RNA showed 100% homology between human lung mast cell renin and kidney renin between exons 1 and 10. Furthermore, the renin protein expressed in lung mast cells was enzymatically active. Our results demonstrate the existence of an airway renin-angiotensin system triggered by release of mast-cell renin. The data show that locally produced ANG II is a critical factor governing BC, opening the possibility for novel therapeutic targets in the management of airway disease.

Effects of dietary salt on intrarenal angiotensin system, NAD(P)H oxidase, COX-2, MCP-1 and PAI-1 expressions and NF-kappaB activity in salt-sensitive and -resistant rat kidneys

BACKGROUND

Chronic consumption of a high-salt diet causes hypertension (HTN) and renal injury in Dahl salt-sensitive (SSR) but not salt-resistant rats (SRR). These events are, in part, mediated by oxidative stress and inflammation in the kidney and vascular tissues. Activation of the angiotensin II type 1 (AT(1)) receptor plays an important role in the pathogenesis of oxidative stress and inflammation in many hypertensive disorders. However, the systemic renin-angiotensin system (RAS) is typically suppressed in salt-sensitive HTN. This study was designed to test the hypothesis that differential response to a high-salt diet in SSR versus SRR may be related to upregulation of tissue RAS and pathways involved in inflammation and reactive oxygen species (ROS) production.

METHODS AND RESULTS

SSR and SRR were studied 3 weeks after consumption of high- (8%) or low-salt (0.07%) diets. The SSR consuming a low-salt diet exhibited significant increases in AT(1) receptor, cyclooxygenase (COX) 2, plasminogen activator inhibitor (PAI) and phospho-I kappaB in the kidney as compared to those found in SRR. The high-salt diet resulted in severe HTN and proteinuria (in SSR but not SRR) and marked elevations of renal tissue monocyte chemoattractant protein 1, p22(phox), NADPH oxidase subunit 4, angiotensin-II-positive cell count, infiltrating T cells and macrophages and further increases in AT(1) receptor, COX-2, PAI-1 and phospho-I kappaB in the SSR group. The high-salt diet significantly lowered plasma renin activity (PRA) in SRR but not in the SSR. COX-1 abundance was similar on the low-salt diet and rose equally with the high-salt diet in both groups. Among subgroups of animals fed the low-salt diet, kidney glutathione peroxidase (GPX) abundance was significantly lower in the SSR than SRR. The high-salt diet raised GPX and mitochondrial superoxide dismutase (SOD) abundance in the SRR kidneys but failed to do so in SSR. Cu/Zn-SOD abundance was similar in the subgroups of SSR and SRR fed the low-salt diet. The high-salt diet resulted in downregulation of Cu/Zn-SOD in SSR but not SRR.

CONCLUSIONS

Salt sensitivity in the SSR is associated with upregulations of the intrarenal angiotensin system, ROS-generating and proinflammatory/profibrotic proteins and an inability to raise antioxidant enzymes and maximally suppress PRA in response to high salt intake. These events can contribute to renal injury with high salt intake in SSR.

Challenged sodium balance and expression of angiotensin type 1A receptor mRNA in the hypothalamus of Wistar and Dahl rat strains

The present study investigates the influence of a chronic high Na+ diet (8% Na+) on the expression of the angiotensin type 1A (AT1A) receptor gene in the lamina terminalis and paraventricular nucleus of the hypothalamus (PVH) in normotensive Wistar (W) rats, as well as in Dahl salt-resistant (DR) and Dahl salt-sensitive (DS) rats. Three weeks of 8% Na+ diet led to a higher blood pressure in DS rats compared to DR and W rats. Moreover, the high Na+ diet was correlated with a decreased expression of AT1A receptor mRNA in the median preoptic nucleus (MnPO) and in the PVH of DS rats, compared to DR and W rats. Contrastingly, the AT1A receptor mRNA expression was not altered by the high Na+ diet in the forebrain circumventricular organs of all the rat strains. Interestingly, a furosemide-induced Na+ depletion was correlated with an increased expression of AT1A receptor mRNA in the PVH, MnPO and SFO of both the DS and DR rats. It is concluded that chronic high Na+ diet did differently regulate the expression of AT1A receptor mRNA in two hypothalamic integrative centers for hydromineral and cardiovascular balance (the PVH and MnPO) in DS rats, compared to DR and W rats. However, the AT1A receptor mRNA expression was similarly regulated in DS and DR rats in response to an acute Na+ depletion, suggesting a distinct high Na+ -induced regulation of the AT1A receptor gene in the PVH and MnPO of DS rats.

Oxidative stress and nitric oxide deficiency in the kidney: a critical link to hypertension?

There is growing evidence that oxidative stress contributes to hypertension. Oxidative stress can precede the development of hypertension. In almost all models of hypertension, there is oxidative stress that, if corrected, lowers BP, whereas creation of oxidative stress in normal animals can cause hypertension. There is overexpression of the p22(phox) and Nox-1 components of NADPH oxidase and reduced expression of extracellular superoxide dismutase (EC-SOD) in the kidneys of ANG II-infused rodents, whereas there is overexpression of p47(phox) and gp91(phox) and reduced expression of intracellular SOD with salt loading. Several mechanisms have been identified that can make oxidative stress self-sustaining. Reactive oxygen species (ROS) can enhance afferent arteriolar tone and reactivity both indirectly via potentiation of tubuloglomerular feedback and directly by microvascular mechanisms that diminish endothelium-derived relaxation factor/nitric oxide responses, generate a cyclooxygenase-2-dependent endothelial-derived contracting factor that activates thromboxane-prostanoid receptors, and enhance vascular smooth muscle cells reactivity. ROS can diminish the efficiency with which the kidney uses O(2) for Na(+) transport and thereby diminish the P(O(2)) within the kidney cortex. This may place a break on further ROS generation yet could further enhance vasculopathy and hypertension. There is a tight relationship between oxidative stress in the kidney and the development and maintenance of hypertension.

Mast cells: a unique source of renin

In addition to the traditional renin-angiotensin system, a great deal of evidence favors the existence of numerous independent tissue-specific renin-angiotensin systems. We report that mast cells are an additional source of renin and constitute a unique extrarenal renin-angiotensin system. We use renin-specific antibodies to demonstrate that cardiac mast cells contain renin. Extending this observation to the human mast cell line HMC-1, we show that these mast cells also express renin. The HMC-1 renin RT-PCR product is 100% homologous to Homo sapiens renin. HMC-1 cells also contain renin protein, as demonstrated both by immunoblot and immunocytochemical analyses. Renin released from HMC-1 cells is active; furthermore, HMC-1 cells are able to synthesize renin. It is known that, in the heart, mast cells are found in the interstitium in close proximity to nerves and myocytes, which both express angiotensin II receptors. Inasmuch as myocardial interstitium contains angiotensinogen and angiotensin-converting enzyme, and because we were able to detect renin only in mast cells, we postulate that the release of renin from cardiac mast cells is the pivotal event triggering local formation of angiotensin II. Because of the ubiquity of mast cells, our results represent a unique paradigm for understanding local renin-angiotensin systems, not just in the heart, but in all tissues. Our findings provide a rationale for targeting mast cells in conjunction with renin-angiotensin system inhibitors in the management of angiotensin II-related dysfunctions.

Renal and blood pressure phenotype in 18-mo-old bradykinin B2R(-/-)CRD mice

Aberrant gene-environment interactions are implicated in the pathogenesis of congenital renal dysgenesis (CRD), a leading cause of renal failure in infants and children. We have recently developed an animal model of CRD that is caused by gestational salt stress (5% NaCl diet; HS) of bradykinin B2R null mice [B2R(-/-)CRD; El-Dahr SS, Harrison-Bernard LM, Dipp S, Yosipiv IV, and Meleg-Smith S. Physiol Genomics 3: 121-131, 2000.]. Developing B2R(-/-)CRD mice exhibit tubular and glomerular cysts, stromal expansion, and loss of corticomedullary differentiation. In addition, B2R(-/-)CRD mice exhibit transient hypertension from 2 to 4 mo of age. The present study was designed to determine the long-term consequences of CRD on renal morphology and salt sensitivity of blood pressure in B2R(-/-)CRD mice. One-year- and 18-mo-old B2R(-/-)CRD mice exhibited stunted renal growth, glomerular cystic abnormalities, and collecting duct ectasia. Moreover, tumors of mesenchymal cell origin emerged in the dysplastic kidneys of 90% of 1-yr-old and 100% of 18-mo-old B2R(-/-)CRD mice but not in age-matched B2R(-/-) or wild-type mice. When challenged with an HS diet, 18-mo-old B2R(-/-)CRD exhibited a significant rise in systolic and diastolic blood pressures and more pronounced natriuresis and diuresis compared with salt-loaded 18-mo-old wild-type mice. Kidney aquaporin-2 expression was decreased by 50%, whereas renin, ANG type 1 receptor, and Na+-K+-ATPase levels were not different in B2R(-/-)CRD mice compared with controls. In conclusion, this study demonstrates that B2R(-/-)CRD mice exhibit permanent phenotypic and functional abnormalities in renal growth and differentiation. This novel model of human disease links gene-environment interactions with renal development and blood pressure homeostasis.

The Bradykinin B2 receptor is required for full expression of renal COX-2 and renin

Angiotensin converting enzyme (ACE) inhibition leads to increased levels of bradykinin, cyclooxygenase-2 (COX-2), and renin. Since bradykinin stimulates prostaglandin release, renin synthesis may be regulated through a kinin-COX-2 pathway. To test this hypothesis, we examined the impact of bradykinin B2 receptor (B2R) gene disruption in mice on kidney COX-2 and renin gene expression. Kidney COX-2 mRNA and protein levels were significantly lower in B2R-/- mice by 40-50%. On the other hand, renal COX-1 levels were similar in B2R-/- and +/+ mice. Renal renin protein was 61% lower in B2R-/- compared to B2R+/+ mice. This was accompanied by a significant reduction in renin mRNA levels in B2R-/- mice. Likewise, intrarenal angiotensin I levels were significantly lower in B2R-/- mice compared to B2R+/+ mice. In contrast, kidney angiotensin II levels were not different and averaged 261+/-16 and 266+/-15fmol/g in B2R+/+ and B2R-/- mice, respectively. Kidney angiotensinogen, AT1 receptor and ACE activity were not different between B2R+/+ and B2R-/- mice. The results of these studies demonstrate suppression of renal renin synthesis in mice lacking the bradykinin B2R and support the notion that B2R regulation of COX-2 participates in the steady-state control of renin gene expression.

Ischemia promotes renin activation and angiotensin formation in sympathetic nerve terminals isolated from the human heart: contribution to carrier-mediated norepinephrine release

We recently reported that in the ischemic human heart, locally formed angiotensin II activates angiotensin II type 1 (AT(1)) receptors on sympathetic nerve terminals, promoting reversal of the norepinephrine transporter in an outward direction (i.e., carrier-mediated norepinephrine release). The purpose of this study was to assess whether cardiac sympathetic nerve endings contribute to local angiotensin II formation, in addition to being a target of angiotensin II. To this end, we isolated sympathetic nerve endings (cardiac synaptosomes) from surgical specimens of human right atrium and incubated them in ischemic conditions (95% N(2,) sodium dithionite, and no glucose for 70 min). These synaptosomes released large amounts of endogenous norepinephrine via a carrier-mediated mechanism, as evidenced by the inhibitory effect of desipramine on this process. Norepinephrine release was further enhanced by preincubation of synaptosomes with angiotensinogen and was prevented by two renin inhibitors, pepstatin-A and BILA 2157BS, as well as by the angiotensin-converting enzyme inhibitor enalaprilat and the AT(1) receptor antagonist EXP 3174 [2-N-butyl-4-chloro-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl] methyl]imidazole-5-carboxylic acid]. Western blot analysis revealed the presence of renin in cardiac sympathetic nerve terminals; renin abundance increased ~3-fold during ischemia. Thus, renin is rapidly activated during ischemia in cardiac sympathetic nerve terminals, and this process eventually culminates in angiotensin II formation, stimulation of AT(1) receptors, and carrier-mediated norepinephrine release. Our findings uncover a novel autocrine/paracrine mechanism whereby angiotensin II, formed at adrenergic nerve endings in myocardial ischemia, elicits carrier-mediated norepinephrine release by activating adjacent AT(1) receptors.

Secretion of renin-angiotensin system (RAS) components by normal and tumoral lactotropes. A comparative study using reverse hemolytic plaque assay (RHPA) and immunoelectron microscopy

Immunodetection of renin-angiotensin system (RAS) components indicates that there is a local RAS in anterior pituitary cells, particularly in lactotropes. We have attempted to determine if RAS molecules are secreted by lactotropes and the secretory pathways and intracellular sites of maturation. We investigated the secretory activity of individual lactotropes, using the reverse hemolytic plaque assay (RHPA), with GH3B6 tumor cells and normal male rat pituitary cells. We also determined the subcellular distributions of RAS components in these cells. Both tumor and normal cells secreted angiotensinogen, prorenin, renin, angiotensin I, angiotensin-converting enzyme, and angiotensin II, although at different levels. The percentage of secretory cells was generally higher in tumor lactotropes than in normal cells. The subcellular distribution of RAS components obtained by immunoperoxidase was very similar in both cell types, although the intensities of immunoreactivity differed. Cleaved and uncleaved components were found in rough endoplasmic reticulum (RER), Golgi saccules, and secretory granules, all compartments of the secretory pathway. The cleaved components in the RER suggest the existence of early maturation, whereas the presence of uncleaved products in the secretory granules of normal lactotropes might indicate late maturation sites.

Bradykinin B2 null mice are prone to renal dysplasia: gene-environment interactions in kidney development

Congenital abnormalities of the kidney and urinary tract are a common cause of end-stage renal disease in children. Host and environment factors are implicated in the pathogenesis of aberrant renal development. However, direct evidence linking gene-environment interactions with congenital renal disease is lacking. We report an animal model of renal dysgenesis that is dependent on a defined genetic defect and specific embryonic stressor. Specifically, mice that are deficient in the bradykinin type 2 receptor gene (B(2)) and salt loaded during embryogenesis acquire an aberrant kidney phenotype and die shortly after birth. In contrast, B(2) mutant mice maintained on normal sodium intake or salt-loaded wild-type mice do not develop kidney abnormalities. The kidney abnormality is evident histologically on embryonic day 16, shortly after the onset of metanephric B(2) gene expression, and consists of distorted renal architecture, foci of tubular dysgenesis, and cyst formation. The dysplastic tubules are of distal nephron origin [Dolichos biflorus agglutinin (DBA)- and aquaporin-2 (AQP2) positive, and angiotensinogen negative]. Neonatal antihypertensive therapy fails to ameliorate the renal abnormalities, arguing against the possibility that the nephropathy is a consequence of early hypertension. Moreover, the nephropathy is intrinsic to the embryo, because B(2) homozygous offspring from heterozygous parents exhibit the same renal phenotype as offspring from homozygous null parents. Further characterization of the renal phenotype revealed an important genetic background effect since the penetrance of the congenital nephropathy is increased substantially upon backcrossing of 129/BL6 B(2) mutants to a uniform C57BL/6J. We conclude that the type 2 bradykinin receptor is required for the maintenance of metanephric structure and epithelial integrity in the presence of fetal stress. This study provides a "proof-of-principle" that defined gene-environment interactions are a cause of congenital renal disease.

AT(1) receptor regulation in salt-sensitive hypertension

The molecular events governing salt-sensitive hypertension are currently unknown. Because the renin-ANG system plays a central role in blood pressure regulation and electrolyte balance, it may be closely involved in the phenomenon of salt sensitivity. Therefore, we examined the effect of a high-salt diet (8%) and a low-salt diet (0.4%) on ANG II-caused vascular constriction and ANG II type 1 (AT(1)) receptor expression in aorta, brain, and kidney of Dahl S (salt-sensitive) and Dahl R (salt-resistant) rats by means of radioligand binding assays and quantitative PCR. NaCl diet at 8% led to a significant increase of blood pressure in Dahl S but not in Dahl R rats. High-sodium intake caused a profound decrease of ANG II-induced aortic vasoconstriction in both Dahl R and Dahl S rats. The underlying mechanism was a downregulation of aortic AT(1) receptor density and AT(1) receptor mRNA. AT(1) receptor mRNA was downregulated to 57.8% in Dahl R and 59.0% in Dahl S rats by an 8% NaCl diet compared with a 0.4% NaCl diet (P < 0.05). There was a similar decrease in aortic AT(1) receptor density. Additionally, AT(1) receptor mRNA was also downregulated in the kidney but upregulated the brain of Dahl R and S rats on a high-salt diet. Thus high NaCl intake causes organ-specific AT(1) receptor regulation in Dahl R and in Dahl S rats despite the differential blood pressure regulation in these animal models in response to a high-salt diet. These findings suggest that the regulation of vascular AT(1) receptors is influenced by numerous factors such as the renin-ANG system and obviously by various other events that are currently only partly understood.

Delayed recovery of hypertension after single dose losartan in angiotensin II-infused conscious rats

OBJECTIVE

In a conscious unrestrained rat model, it takes approximately 1 week for angiotensin II to increase blood pressure to maximum levels. We investigated the time required for hypertension to fully recover after acute angiotensin II receptor blockade in this angiotensin II dependent hypertensive model.

DESIGN

Conscious unrestrained rats (n = 8) infused with 10 ng/kg per min angiotensin II for 21 days received losartan (10 mg/kg) on day 17 of angiotensin II infusion. Mean arterial pressure (MAP) and heart rate were monitored continuously. The acute pressor response to 50 ng/kg per min angiotensin II was monitored for 2 h on days 15, 17, 18, 19 and 20 of angiotensin II infusion. Plasma renin concentration (PRC) was measured daily.

RESULTS

Angiotensin II increased MAP acutely by 26 +/- 2 mmHg and by a further 23 +/- 4 mmHg between days 4 and 8. Losartan acutely reduced MAP by 75 +/- 2 mmHg; 24 h later MAP had partially recovered but remained suppressed by 47 +/- 3 mmHg. MAP had not fully recovered 4 days later. Some 2 h after losartan, the acute pressor response to angiotensin II had fallen from 24 +/- 2 mmHg to zero. This recovered to 13 +/- 5 and 28 +/- 2 mmHg 24 and 48 h post losartan. After losartan PRC rose from 0.1 +/- 0.05 to above 1 ng/ml per h for less than 24 h.

CONCLUSION

A single dose of losartan reverses both the fast and slow pressor effects of continuous angiotensin II infusions. While losartan is metabolized, the fast vasoconstrictor effect recovers quickly but the slow pressor effect takes almost a week to build up again to maximum levels. Since the slow pressor effect is mediated via the AT1 receptor, any means of blocking the renin-angiotensin system is likely to keep blood pressure below maximum hypertensive levels for several days after the drug has disappeared from the circulation.

Transmural pressure inhibits prorenin processing in juxtaglomerular cell

Pressure control of renin secretion involves a complex integration of shear stress, stretch, and transmural pressure (TP). This study was designed to delineate TP control of renin secretion with minimal influence of shear stress or stretch and to determine its mechanism. Rat juxtaglomerular (JG) cells were applied to a TP-loading apparatus for 12 h. In cells conditioned with atmospheric pressure or atmospheric pressure + 40 mmHg, renin secretion rate (RSR) averaged 29.6 +/- 3.7 and 14.5 +/- 3.3% (P < 0.05, n = 8 cultures), respectively, and active renin content (ARC) averaged 47.3 +/- 4.6 and 38.4 +/- 3.4 ng of ANG I. h(-1). million cells(-1) (P < 0.05, n = 10 cultures), respectively. Total renin content and renin mRNA levels were unaffected by TP. The TP-induced decrease in RSR was prevented by Ca(2+)-free medium and the Ca(2+) channel blocker verapamil and was attenuated by thapsigargin and caffeine, which deplete intracellular Ca(2+) stores. Thapsigargin and caffeine, but not Ca(2+)-free medium or verapamil, prevented TP-induced decreases in ARC. The adenylate cyclase activator forskolin did not modulate TP-induced decreases in RSR or ARC. These findings suggest that TP not only stimulates Ca(2+) influx but also inhibits prorenin processing through an intracellular Ca(2+) store-dependent mechanism and thus inhibits active renin secretion by JG cells.

Renin-angiotensin system and fibronectin gene expression in Dahl Iwai salt-sensitive and salt-resistant rats

OBJECTIVE

The tissue renin-angiotensin system and extracellular matrix are involved in the cardiovascular hypertrophy and remodeling induced by hypertension. In this study, we examined the gene expression of the tissue renin-angiotensin system and fibronectin in inbred Dahl Iwai salt-sensitive and salt-resistant rats.

MATERIALS AND METHODS

Eight pairs of 6-week-old male Dahl Iwai salt-sensitive and salt-resistant rats were fed either a low- or high-salt diet (0.3% or 8% NaCl, respectively) for 4 weeks. Activities of the circulating renin-angiotensin system were measured by radioimmunoassay and the gene expression of tissue angiotensinogen, the angiotensin II type 1 receptor (AT1) and fibronectin were analyzed by Northern blot analysis.

RESULTS

Salt loading significantly increased blood pressure and produced cardiovascular hypertrophy and nephrosclerosis in the salt-sensitive rats. Activities of the circulating renin-angiotensin system were lower in salt-sensitive rats than in salt-resistant rats fed the low-salt diet, and salt loading lowered these activities in salt-resistant rats but not in salt-sensitive rats. In salt-resistant rats, salt loading increased renal, cardiac and aortic angiotensinogen, AT1 and fibronectin messenger (m)RNA expression except for aortic fibronectin mRNA expression. In contrast, in the salt-sensitive rats, salt loading stimulated the expression of cardiac fibronectin and aortic angiotensinogen, AT1 and fibronectin mRNAs. Furthermore, the cardiac and aortic fibronectin mRNA levels in salt-sensitive rats were higher than those in salt-resistant rats when both strains were fed the high-salt diet.

CONCLUSIONS

These results demonstrate that the expression of tissue angiotensinogen, AT1 and fibronectin mRNAs is regulated differently in Dahl Iwai salt-sensitive and salt-resistant rats, and indicate that salt-mediated hypertension activates the cardiac fibronectin gene independently of the tissue renin-angiotensin system and stimulates the aortic fibronectin gene with activation of the tissue renin-angiotensin system.

Abnormal regulation of proximal tubule renin mRNA in the Dahl/Rapp salt-sensitive rat

BACKGROUND

The precise pathogenesis of salt-sensitive hypertension in the Dahl rat is unknown. Abnormalities in renal hemodynamics and NaCl handling have been implicated, and may relate to changes in the activity of the intrarenal renin-angiotensin system.

METHODS

Circulating, juxtaglomerular and intrarenal (glomerular and proximal tubular) renin were studied in Dahl/Rapp salt-sensitive and salt-resistant rats fed with a normal (0.5%) or high (4%) NaCl diet. Circulating and juxtaglomerular renin were assessed by measurement of plasma renin activity and renin secretory rates. Glomerular and proximal tubular renin mRNA were assessed by microdissection and quantitative competitive RT-PCR.

RESULTS

Circulating and juxtaglomerular renin were suppressed by high dietary NaCl in salt-sensitive rats (plasma renin activity, 0.5%, 10.9 +/- 0.7 vs. 4%, 7.9 +/- 0.3 ng/ml/hr, P < 0.05; renin secretory rate, 0.5% 220 +/- 32 vs. 4%, 58 +/- 5 ng/mg/hr, P < 0.05). Glomerular renin mRNA was also suppressed by the higher salt diet in salt-sensitive animals (0.5%, 411 +/- 84 vs. 4%, 67 +/- 22 x 103 copies/glomerulus, P < 0.05). In contrast, proximal tubular renin was not suppressed by a high NaCl diet in salt-sensitive animals (0.5%, 13.9 +/- 2.7 vs. 4%, 12.1 +/- 3.6 x 103 copies/mm tubule, P = NS), but was suppressed in salt-resistant rats (0.5%, 9.5 +/- 2.8 vs. 4%, 3.2 +/- 1.2 x 103 copies/mm, P < 0. 05).

CONCLUSIONS

Failure to suppress proximal tubular renin in response to high dietary NaCl may result in increased local generation of angiotensin II and enhanced proximal tubular NaCl absorption, and thereby contribute to the generation of salt sensitive hypertension.

Identical hemodynamic and hormonal responses to 14-day infusions of renin or angiotensin II in conscious rats

OBJECTIVE

To investigate whether plasma angiotensin II (Ang II) determines the effects of the renin-angiotensin system or whether tissue uptake of renin and localized production of Ang II might account for any cardiovascular, renal, hormonal or drinking effect of circulating renin.

DESIGN

Intravenous infusions of renin (0.6 ng/min; n = 10) and Ang II (3.5 ng/min; n = 10) that produce similar plasma Ang II levels were compared for 2 weeks with vehicle (n = 7) in conscious rats after a 1-week control period. Mean arterial pressure (MAP) and the heart rate were measured continuously. Hormones and renal function were measured twice weekly. Plasma Ang II and recovery data were measured in seven additional rats.

RESULTS

In renin- and Ang II-infused rats, respectively, plasma Ang II increased similarly from 4.5 +/- 0.8 and 4.4 +/- 0.9 to 10.8 +/- 0.7 and 10.6 +/- 0.7 pg/ml and declined similarly in the second week to 7.0 +/- 1.1 and 7.0 +/- 1.5 pg/ml. Plasma renin increased from 4.2 +/- 0.7 to 21.7 +/- 1.3 and fell from 5.9 +/- 0.5 to 0.6 +/- 0.2 ng/ml per h respectively. Plasma prorenin fell similarly (> 70%); angiotensinogen was unchanged. MAP rose initially by 25.6 +/- 1.2 and 23.3 +/- 0.9 mmHg and by an additional 21.1 +/- 2.4 and 27.4 +/- 1.8 mmHg on days 5-8. The heart rate fell gradually but transiently by -11% in both. Although the initial MAP rise was slower in renin-infused rats (P< 0.05) MAP returned to baseline within 2 h after both infusions were stopped. Changes in renal vascular resistance, renal blood flow, glomerular filtration rate, urinary sodium, potassium and water excretion and water intake were not significantly different between renin- and Ang II-infused rats.

CONCLUSIONS

Intravenous infusions of low doses of renin or Ang II into conscious rats increase MAP identically. MAP increases in two phases 5-8 days apart, in coordination with transient falls in the heart rate. Renin- and Ang II-induced chronic hypertension are identically sustained by very small increases in plasma Ang II. Blood pressure increases more slowly with renin infusions, consistent with tissue binding. Notwithstanding, no evidence was obtained for a physiological role of tissue-bound renin in causing the cardiovascular, renal, hormonal and drinking responses measured in this study.

Transgenesis and Gene Targeting in the Mouse

As more effort is made to identify genes responsible for hypertension in human populations and genetically hypertensive animal models, the need for experimental systems in which the functional significance of genes, gene variants, and quantitative trait loci (QTL) can be determined is becoming increasingly important. Over the past five years, transgenic and gene-targeting technology has been utilized to study the cardiovascular effects of over-expression or ablation of genes which have been considered candidates in the genetic basis of hypertension. This review focuses on the most recent major advances in this area, and how this technology aids in our understanding of the molecular mechanisms by which newly discovered genes or gene variants affect blood pressure in the whole organism. We also discuss the potential use of transgenic models in refining the location of a QTL, and discuss some of the limitations and potential pitfalls in the application of these tools to the field of hypertension research. The coupling of genetic manipulations afforded by transgenesis and gene targeting, along with advances in our ability to assess the cardiovascular phenotype in the mouse, provides us with a powerful system for examining the genes responsible for causing essential hypertension.

Hypertension: genes and environment

Hypertension can be classified as either Mendelian hypertension or essential hypertension, on the basis of the mode of inheritance. The Mendelian forms of hypertension develop as a result of a single gene defect, and as such are inherited in a simple Mendelian manner. In contrast, essential hypertension occurs as a consequence of a complex interplay of a number of genetic alterations and environmental factors, and therefore does not follow a clear pattern of inheritance, but exhibits familial aggregation of cases. In this review, we discuss recent advances in understanding the pathogenesis of both types of hypertension. We review the causal gene defects identified in several monogenic forms of hypertension, and we discuss their possible relevance to the development of essential hypertension. We describe the current approaches to identifying the genetic determinants of human essential hypertension and rat genetic models of hypertension, and summarise the results obtained to date using these methods. Finally, we discuss the significance of environmental factors, such as stress and diet, in the pathogenesis of hypertension, and we describe their interactions with specific hypertension susceptibility genes.

Angiotensinogen, prorenin, and renin are Co-localized in the secretory granules of all glandular cells of the rat anterior pituitary: an immunoultrastructural study

In addition to the circulating renin-angiotensin system (RAS), a local system has been postulated in the anterior pituitary because immunodetection of its components in various mammalian species. However, different cell types appear to be involved in different species, and there is no general consensus on the subcellular localization of prorenin, renin and angiotensinogen. In this ultrastructural study, we investigated and quantified the presence of these components using double or triple immunogold labeling methods, in all the immunologically identified glandular cell types of the rat anterior pituitary. In contrast to previous reports, all these components were identified not only in lactotropes and gonadotropes but also in somatotropes, corticotropes, and thyrotropes. The highest levels were detected in lactotropes and gonadotropes, and renin gave the greatest signal. Angiotensinogen, prorenin, and renin were co-localized in the secretory granules of all rat pituitary glandular cell types. The simultaneous detection of the substrate (angiotensinogen) and both its specific cleavage enzyme and its proenzyme within the same granule suggests intragranular processing of this component. Moreover, the localization of these three constituents in the secretory granules also suggests that, in the rat anterior pituitary, they follow the regulated secretory pathway.

Renal growth and development in mice lacking AT1A receptors for angiotensin II

To examine the role of the type 1A (AT1A) angiotensin receptor in renal growth and development, we analyzed F2 progeny from a series of crosses between F1 mice that were heterozygous for a targeted disruption of the AT1A receptor gene [Agtr1A-(+/-)]. Among 21-day-old weanling F2 mice, we found that 194 (32%) were homozygous for the wild-type allele Agtr1A-(+/+), 299 (49%) were Agtr1A-(+/-), and 119 (19%) were Agtr1A-(-/-). This differed significantly from the proportions predicted by Mendelian genetics (P = 0.01), suggesting that the complete absence of AT1A receptors is associated with a mild survival disadvantage. Agtr1A-(-/-) mice grew normally, and we found no significant differences in body weight or heart and kidney weights in Agtr1A-(+/+) and Agtr1A-(-/-) mice examined at 21, 60, and 100 days. Protein and DNA content of kidneys and hearts were also similar in weanling or adult Agtr1A-(+/+) and Agtr1A-(-/-) mice. By light microscopy with immunohistochemistry, kidneys from Agtr1A-(-/-) were essentially normal, with two exceptions: 1) there was marked hypertrophy of the juxtaglomerular apparatus (JGA) and proximal expansion of renin-producing cells along the afferent arterioles, and 2) some glomeruli showed evidence of mesangial expansion. We did not find the severe renal vascular lesions or papillary atrophy that have been observed in angiotensinogen- or angiotensin converting enzyme-deficient animals. We conclude that the AT1A receptor is not essential for the normal organogenesis of the kidney; however, its absence is associated with mild mesangial expansion and JGA hypertrophy.

Complementation of reduced survival, hypotension, and renal abnormalities in angiotensinogen-deficient mice by the human renin and human angiotensinogen genes

The aim of this study was to determine whether elements of the human renin-angiotensin system (RAS) could functionally replace elements of the mouse RAS by complementing the reduced survival and renal abnormalities observed in mice carrying a gene-targeted deletion of the mouse angiotensinogen gene (mAgt). Double transgenic mice containing the human renin (HREN) and human angiotensinogen (HAGT) genes were bred to mice heterozygous for the mAgt deletion and the compound heterozygotes were identified and intercrossed. The resulting progeny (n = 139) were genotyped at each locus and the population was stratified into two groups: the first containing both human transgenes (RA+) and the second containing zero or one, but not both human transgenes (RA-). Despite appropriate Mendelian ratios of RA- mice that were wildtype (+/+), heterozygous (+/-), and homozygous (-/-) for the deletion of mAgt at birth, there was reduced survival of RA- mAgt-/- mice to adulthood (P < 0.001 by chi2). In contrast, we observed appropriate Mendelian ratios of RA+ mAgt+/+, RA+ mAgt+/-, and RA+ mAgt-/- mice at birth and in adults (P > 0.05 by chi2). These results demonstrate that the presence of both human transgenes rescues the postnatal lethality in mAgt-/- mice. The renal histopathology exhibited by RA- mAgt-/- mice, including thickened arterial walls, severe fibrosis, lymphocytic infiltration, and atrophied parenchyma, was also rescued in the RA+ mAgt-/- mice. Direct arterial blood pressure recordings in conscious freely moving mice revealed that BP (in mmHg) varied proportionally to mAgt gene copy number in RA+ mice (approximately 20 mmHg per mAgt gene copy, P < 0.001). BP in RA+ mAgt-/- mice (132+/-3, n = 14) was intermediate between wild-type (RA- mAgt+/+, 105+/-2, n = 9) and RA+ mAgt+/+ (174+/-3, n = 10) mice. These studies establish that the human renin and angiotensinogen genes can functionally replace the mouse angiotensinogen gene, and provides proof in principle that we can examine the regulation of elements of the human RAS and test the significance of human RAS gene variants by a combined transgenic and gene targeting approach.