Renin Enzymatic Activity Research Articles

Estimation of Renin enzyme activity and some biochemical parameters among chronic renal failure patients in Tikrit city.

Chronic renal failure is a deficiency and failure in the excretory function of the kidneys, which causes a general imbalance in the body by retaining and accumulating nitrogenous waste and harmful substances as a result of metabolic reactions. Other functions of the kidneys, such as the regulation of fluids and electrolytes, may also be affected. This study's primary purpose is to estimate some parameters in the serum of chronic renal failure patients. Data and blood samples were obtained from 90 patients with chronic renal failure and 50 healthy volunteers for this cross-sectional study, conducted between 11 April and 26 July 2022. The results of this study show a considerable rise in the level of renin enzyme in patients (4.824±0.045) compared to the control (2.86±0.39), a high level of ALT in patients (19.56±8.13) compared to the control (11.24±0.98), high level of ALP in patients (95.34±67.71) compared to the control (38.81±5.14), high level of AST in patients (25.33±8.63) compared to the control (11.58±0.94), low level of albumin in patients with chronic renal failure (3.12±0.44) compared to the control (3.90±0.49), high level of globulin in patients with chronic renal failure (8.34±0.68) compared to the control (3.01±0.41), low level of calcium in patients with chronic renal failure (1.731±0.053) compared to the control (2.510±0.063), high level of potassium in the serum of patients with chronic renal failure (6.256±0.068) compared to the control (4.513±0.22), low level of sodium in patients with chronic renal failure (119.82±2.15) compared to the control group (143.76±2.11). According to this study, all physiological systems are significantly impacted by chronic renal failure. According to the results, chronic renal failure affects several electrolytes and liver function tests and causes a considerable increase in renin levels.

Activation of the Human Angiotensin-(1-12)-Chymase Pathway in Rats With Human Angiotensinogen Gene Transcripts.

Angiotensin-(1-12) [Ang-(1-12)], an alternate substrate for tissue angiotensin II (Ang II) formation, underscores the importance of alternative renin-independent pathway(s) for the generation of angiotensins. Since renin enzymatic activity is species-specific, a transgenic model of hypertension due to insertion of the human angiotensinogen (AGT) gene in Sprague Dawley rats allowed for characterizing the contribution of a non-renin dependent mechanism for Ang II actions in their blood and heart tissue. With this in mind, we investigated whether TGR(hAGT)L1623 transgenic rats express the human sequence of Ang-(1-12) before and following a 2-week oral therapy with the type I Ang II receptor (AT1-R) antagonist valsartan. Plasma and cardiac expression of angiotensins, plasma renin activity, cardiac angiotensinogen, and chymase protein and the enzymatic activities of chymase, angiotensin converting enzyme (ACE) and ACE2 were determined in TGR(hAGT)L1623 rats given vehicle or valsartan. The antihypertensive effect of valsartan after 14-day treatment was associated with reduced left ventricular wall thickness and augmented plasma concentrations of angiotensin I (Ang I) and Ang II; rat and human concentrations of angiotensinogen or Ang-(1-12) did not change. On the other hand, AT1-R blockade produced a 55% rise in left ventricular content of human Ang-(1-12) concentration and no changes in rat cardiac Ang-(1-12) levels. Mass-Spectroscopy analysis of left ventricular Ang II content confirmed a >4-fold increase in cardiac Ang II content in transgenic rats given vehicle; a tendency for decreased cardiac Ang II content following valsartan treatment did not achieve statistical significance. Cardiac chymase and ACE2 activities, significantly higher than ACE activity in TGR(hAGT)L1623 rats, were not altered by blockade of AT1-R. We conclude that this humanized model of angiotensinogen-dependent hypertension expresses the human sequence of Ang-(1-12) in plasma and cardiac tissue and responds to blockade of AT1-R with further increases in the human form of cardiac Ang-(1-12). Since rat renin has no hydrolytic activity on human angiotensinogen, the study confirms and expands knowledge of the importance of renin-independent mechanisms as a source for Ang II pathological actions.

Improving Health-Promoting Effects of Food-Derived Bioactive Peptides through Rational Design and Oral Delivery Strategies.

Over the last few decades, scientific interest in food-derived bioactive peptides has grown as an alternative to pharmacological treatments in the control of lifestyle-associated diseases, which represent a serious health problem worldwide. Interest has been directed towards the control of hypertension, the management of type 2 diabetes and oxidative stress. Many food-derived antihypertensive peptides act primarily by inhibiting angiotensin I-converting enzyme (ACE), and to a lesser extent, renin enzyme activities. Antidiabetic peptides mainly inhibit dipeptidyl peptidase-IV (DPP-IV) activity, whereas antioxidant peptides act through inactivation of reactive oxygen species, free radicals scavenging, chelation of pro-oxidative transition metals and promoting the activities of intracellular antioxidant enzymes. However, food-derived bioactive peptides have intrinsic weaknesses, including poor chemical and physical stability and a short circulating plasma half-life that must be addressed for their application as nutraceuticals or in functional foods. This review summarizes the application of common pharmaceutical approaches such as rational design and oral delivery strategies to improve the health-promoting effects of food-derived bioactive peptides. We review the structural requirements of antihypertensive, antidiabetic and antioxidant peptides established by integrated computational methods and provide relevant examples of effective oral delivery systems to enhance solubility, stability and permeability of bioactive peptides.

(Pro)renin receptor: Involvement in diabetic retinopathy and development of molecular targeted therapy.

The renin–angiotensin system (RAS), a crucial regulator of systemic blood pressure (circulatory RAS), plays distinct roles in pathological angiogenesis and inflammation in various organs (tissue RAS), such as diabetic microvascular complications. Using ocular clinical samples and animal disease models, we elucidated molecular mechanisms in which tissue RAS excites the expression of vascular endothelial growth factor (VEGF)‐A responsible for retinal inflammation and angiogenesis, the two major pathological events in diabetic retinopathy (DR). Furthermore, we showed the involvement of (pro)renin receptor [(P)RR] in retinal RAS activation and its concurrent intracellular signal transduction (e.g., extracellular signal‐regulated kinase); namely, the (P)RR‐induced dual pathogenic bioactivity referred to as the receptor‐associated prorenin system. Indeed, neovascular endothelial cells in the fibrovascular tissue collected from eyes with proliferative DR were immunoreactive for the receptor‐associated prorenin system components including prorenin, (P)RR, phosphorylated extracellular signal‐regulated kinase and VEGF‐A. Protein levels of soluble (P)RR increased with its positive correlations with prorenin, renin enzymatic activity and VEGF in the vitreous of proliferative DR eyes, suggesting a close link between (P)RR and VEGF‐A‐driven angiogenic activity. Furthermore, we revealed an unsuspected, PAPS‐independent role of (P)RR in glucose‐induced oxidative stress. Recently, we developed an innovative single‐strand ribonucleic acid interference molecule selectively targeting human and mouse (P)RR, and confirmed its efficacy in suppressing diabetes‐induced retinal inflammation in mice. Our data using clinical samples and animal models suggested the significant implication of (P)RR in the pathogenesis of DR, and the potential usefulness of the ribonucleic acid interference molecule as a therapeutic agent to attenuate ocular inflammation and angiogenesis.

Abstract TP214: Serum Activity of Angiotensin Converting Enzyme 2 is Decreased During Ischemic Stroke in Humans

Introduction: Abundant preclinical studies show efficacy for therapies targeted to the protective axis of the renin-angiotensin system in stroke. The expression and activity of angiotensin converting enzyme 2 (ACE2), a cardio and neuro-protective carboxypeptidase in this axis, have recently been shown to be dynamically altered during stroke in animal models. Hypothesis: The aim of this study was to characterize the previously unexplored changes in activity of ACE2, and other RAS enzymes, in the serum of patients experiencing acute ischemic stroke. Methods: Blood samples were obtained from patients with acute ischemic stroke (n=20) at presentation and again at three days post-stroke and enzyme activity levels in isolated serum were analyzed by fluorometric assay. These were compared to enzyme activity levels in samples obtained from a cohort of patients presenting with transient ischemic attack or other clinical presentations mimicking stroke and from healthy control participants (n=20). Results: Ischemic stroke resulted in significantly lower levels of serum ACE2 activity at an average of 3.5 hours after stroke as compared to both transient ischemic attack/stroke mimic and healthy control participant levels, followed three days later by an increase back to control levels. ACE activity was also significantly decreased following stroke, but without increases at three days. Renin enzyme activity during stroke did not significantly differ from controls at either time point. Serum ACE2 activity was negatively correlated with systolic blood pressure at presentation among stroke patients, while activity levels from a separate cohort of healthy young adults were positively correlated. Multiple regression analyses indicated that ACE2 activity levels were significantly correlated with a diagnosis of ischemic stroke, with those in the lowest tertile of all participants were at 7.7 times increased odds of having had a stroke. Conclusions: The characterization of the dynamic and novel changes in serum ACE2 activity in human stroke, which concur with preclinical studies, along with the demonstration of correlations with systolic blood pressure, provides new insight for the development of therapies that target this protective system in ischemic stroke.

The Dissociation of the Soluble Prorenin Receptor in Plasma and Urine of Diabetic Patients

Diabetic patients display low‐to‐normal plasma levels of renin but increased prorenin levels. In contrast, their urine contains high levels of “active” renin but low prorenin. Our hypothesis is that the soluble form of the prorenin receptor (sPRR) contributes to the enhancement renin activity in the urine of diabetic patients. We measured plasma and urinary sPRR levels by enzyme‐linked immunosorbent assays (ELISA; IBL, Japan) in 60 patients, including: Controls (CT; n=20), Diabetics (DM; n=20) and Diabetics with hypertension (DM+HTN; n=20). Plasma sPRR levels were augmented in DM compared to CT and DM+HTN (DM: 9849±828 vs. CT: 7310±715 and DM+HTN: 7121±373 pg/mL; p<0.05). In contrast, in the urine of DM and DM+HTN patients, sPRR levels were decreased (DM: 576.5±130.9 and DM+HTN: 486.1±81.64 vs. CT: 1248.0±345.6 pg/mg; p<0.05) but urinary renin content was increased (DM: 130±14; DM+HTN: 162±31 vs. CT: 10±1.3 ng AngI/mL/hr; p<0.0001). uCre levels were similar among groups. The dissociation between plasma and urine levels of sPRR suggests that lower pH in the urine of diabetic patients may increase the capability of sPRR to enhance renin enzymatic activity. Further studies will be performed to verify it the sPRR is bound or unbound to renin/prorenin in the urine of these patients.

The (pro)renin receptor ((P)RR) can act as a repressor of Wnt signalling

The (pro)renin receptor ((P)RR) and Wnt signalling are both involved in different diseases ranging from cardiac and renal end-organ damage to cancer. (P)RR function involves signalling via the transcription factor promyelocytic leukemia zinc finger protein (PLZF) as well as the furin-mediated generation of vacuolar proton-translocating ATPase (V-ATPase)-associated and soluble (P)RR isoforms. Recently, the (P)RR was described as adaptor protein of Wnt (co)receptors. The aim of this study was to analyse the contribution of these distinct (P)RR functions to Wnt signalling.Using Tcf/Lef reporter gene systems in HEK293T and HepG2 cells and quantification of endogenous axin2 mRNA and protein levels in HEK293T cells we were able to demonstrate that full-length (P)RR acts as a repressor of Wnt signalling in a system preactivated either by Wnt3a stimulation or by constitutively active β-catenin. These repressive effects are mediated by Dvl but are independent of the mutation status of β-catenin. Furthermore, the V-ATPase complex, but not PLZF translocation or renin enzymatic activity, is necessary for the induction of Tcf/Lef-responsive genes by Wnt3a.Our data indicate interference of (P)RR and Wnt cascades, a fact that has to be considered concerning pathophysiology of cardio-renal and oncological entities as well as in drug development programs targeting (P)RR or Wnt pathways.

Inhibition of renin activity by aliskiren ameliorates diabetic nephropathy in type 1 diabetes mouse model

Renin is the rate-limiting enzyme of the reninangiotensin system (RAS). In addition to its enzymatic activity to generate angiotensin I, renin also signals through the (pro)renin receptor to exert angiotensin II-independent effects. In this study we examined the effect of renin inhibition on the development of diabetic nephropathy. Male DBA/2J mice were induced to diabetes with streptozotocin, and the diabetic mice were treated for 16 weeks with saline or aliskiren, a renin enzymatic inhibitor. Aliskiren treatment had little effects on blood glucose and blood pressure in diabetic mice. Saline-treated mice developed progressive albuminuria and glome-rulosclerosis, and aliskiren treatment effectively alleviated albumiuria and glomerulosclerosis. Morphologically aliskiren treatment prevented the thickening of the glomerular basement membrane and reduced podocyte loss. At the molecular levels, aliskiren prevented the decline of slit diaphragm proteins and blocked the synthesis of extracellular matrix and pro-fibrotic factors in the diabetic kidney. Aliskiren treatment results in compensatory renin increase in the glomeruli due to blockade of the negative feedback loop, and also partially suppressed the intracellular signaling mediated by the (pro)renin receptor activated in hyperglycemia. These observations suggest that the therapeutic activity of aliskiren to prevent diabetic renal injury is contributed by inhibition of both the angiotensin II-dependent and -independent pathways. Taken together, it is concluded that inhibition of renin enzymatic activity ameliorates diabetic renal injury in type 1 diabetes, and support the use of aliskiren in diabetes kidney disease.

Direct Renin Inhibition

Nowadays, social and economic burden related to cardiovascular and renal diseases still remains extremely high, although there has been a dramatic improvement of diagnostic options and therapeutic strategies reported in the last 30 years. The progressively higher attention towards integrated pharmacological strategies, which are able to interfere with different pathophysiological mechanisms, has certainly led to better control of cardiovascular and renal diseases. In view of the large involvement of the renin-angiotensin system (RAS) in the vast majority of pathophysiological mechanisms leading to the development and progression of cardiovascular and renal diseases, it can be easily understood why it has been long viewed as the 'ideal' target for the pharmacological treatment of several clinical conditions. Recently, besides the well known therapeutic approaches for RAS blockade, based on the use of ACE inhibitors, angiotensin II type 1 receptor antagonists (angiotensin receptor blockers [ARBs]) and aldosterone antagonists, both the scientific and medical community have focused their attention on a novel therapeutic option. In 2007, aliskiren, the first compound of a new drug class, the direct renin inhibitors (DRIs), has become available for clinical use, being a novel and innovative therapeutic option. Aliskiren is able to interfere with the enzymatic activity of renin by blocking the catalytic site of the molecule and inducing an 'upstream' RAS blockade. This leads to a modulation of the biological properties of renin, thus resulting in the missed cleavage of angiotensinogen to angiotensin I. Aliskiren has demonstrated antihypertensive efficacy comparable or even superior to that of other classes of antihypertensive drugs, both in monotherapy and in combination therapies. Its safety and tolerability are comparable with those of other antihypertensive drug classes and almost similar to placebo. In addition, it has been demonstrated to reduce progression of cardiac and renal organ damage in addition to ACE inhibitors or ARBs. An ambitious and large clinical trial programme specifically designed for this innovative antihypertensive drug will evaluate the efficacy of aliskiren in terms of reduced incidence of major cardiovascular and renal outcomes in patients with hypertension and cardiovascular disease, besides the use of optimal (standard) therapeutic strategies, including ACE inhibitors and ARBs.

Aliskiren: clinical experience and future perspectives of renin inhibition

Background: Aliskiren, the first renin inhibitor with sufficient bioavailability for oral use, is now available to clinicians treating hypertension. Objective: The novel mechanism by which aliskiren works was used to provide understanding of its therapeutic and adverse effects. Methods: After reviewing physiology and preclinical studies, human studies of aliskiren in hypertension were reviewed. Effects of aliskiren on serum levels and enzymatic activity of renin were explored. Results/conclusions: Aliskiren has antihypertensive efficacy similar to existing medications such as thiazide diuretics, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, and can be used in drug combinations. Preclinical studies indicate possible cardioprotective and renoprotective effects, similar to other inhibitors of the renin–angiotensin cascade, but future studies are needed in humans.

The (pro)renin receptors

Two (pro)renin receptors have been characterized so far, the mannose-6-phosphate receptor (M6P-R) and a specific receptor called (P)RR for (pro)renin receptor. Each receptor controls a different aspect of renin and prorenin metabolism. The M6P-R is a clearance receptor, whereas (P)RR mediates their cellular effects by activating intracellular signaling and up-regulating gene expression. Moreover, binding to (P)RR increases renin enzymatic activity and fully activates prorenin, the inactive proenzyme form of renin. Experimental models suggest that increased (P)RR synthesis and/or activation may be relevant to diseases, especially to high blood pressure, to cardiac fibrosis associated with hypertension, and to diabetic nephropathy.

Renin Enhancer Is Crucial for Full Response in Renin Expression to an In Vivo Stimulus

We showed recently that deletion of a strong enhancer located 2.7 kb upstream of the renin gene in mice produces a strain with mild hypotension and salt-sensitivity. Here we set out to compare responses in renin expression in kidney and extrarenal tissues in these "REKO" mice. REKO and wild-type mice were placed on a low NaCl/enalapril regimen for 1 week, and then Ren-1(c) mRNA and renin enzyme activities were measured in tissues and plasma. In untreated REKO mice, renin and Ren-1(c) mRNA were reduced significantly in kidney, submandibular gland, adrenal, heart, and brain. In situ hybridization indicated a marked reduction in Ren-1(c) mRNA in juxtaglomerular cells and granular ducts of submandibular gland. After the chronic stimulus response in renal Ren-1(c) mRNA in REKO mice was blunted by 54% compared with wild-type mice, and was accompanied by almost complete exhaustion of renin stores. Response in plasma renin was blunted by 47%, this being mirrored in heart (54% decline), in which renin is derived mostly from the bloodstream. In adrenal a 55% reduction was seen. These data are consistent with inability of REKO mice to adequately replenish renal renin stores during chronic stimulation of renin secretion. In conclusion, the renin enhancer is critical for replenishment of renin stores and response in renin to a chronic in vivo stimulus.

Benzyl Ether Structure—‐Activity Relationships in a Series of Ketopiperazine‐Based Renin Inhibitors.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Renin, Prorenin and the Putative (Pro)renin Receptor

Renin is an aspartic protease that consists of 2 homologous lobes. The cleft in between contains the active site with 2 catalytic aspartic residues.1 Unlike other aspartic proteases such as pepsin or cathepsin D, renin is monospecific and only cleaves angiotensinogen, to generate angiotensin (Ang) I. Ang I is the precursor of the active end-product of the renin-angiotensin system (RAS), Ang II. Renin has also been called active renin to underline that an enzymatically inactive form of renin exists. In 1971, Lumbers found that amniotic fluid, left at low pH in the cold, acquired renin activity.2 Later, Skinner described a similar phenomenon in plasma.3 Acidification was not strictly necessary for this increase in Ang I-generating activity, because incubation at low temperature also increased renin activity, albeit to only 15% of activity after acidification. Soon it was postulated that this inactive, but activatable “big” renin (its molecular weight was 5 kDa higher than that of renin) was the biosynthetic precursor of renin. Hence, it was named prorenin. Only with the cloning of the renin gene in 1984 was prorenin definitively proved to be the precursor of renin.4 For reasons that are unknown, prorenin circulates in human plasma in excess to renin, sometimes at concentrations that are 100-times higher.5 Prorenin has also been demonstrated in plasma of cat, dog, cattle, pig, horse, sheep, rabbit, rat, and mouse. A 43-amino acid N-terminal propeptide explains the absence of enzymatic activity of prorenin. This propeptide covers the enzymatic cleft and obstructs access of angiotensinogen to the active site of renin. (Pro)renin is synthesized as a preprohormone. It contains a signal peptide that directs the protein to the endoplasmic reticulum and ultimately to the exterior of the cell. Both renin and prorenin can be fractionated into multiple species by isoelectric focusing. …

Benzyl ether structure–activity relationships in a series of ketopiperazine-based renin inhibitors

Inhibition of renin enzymatic activity by a series of ketopiperazine-based compounds containing a C6 benzyloxymethyl substituent correlated with a +( π + σ) effect. A 3-pyridinyloxymethyl substituent was also found to be equipotent as higher molecular weight analogs, and exhibited decreased CYP3A4 inhibition levels and improved pharmacokinetic properties.

Myocardial enzymatic activity of renin and cathepsin D before and after bilateral nephrectomy.

A local renin-angiotensin system is present within the myocardium and can play a role in the initiation and maintenance of cardiac hypertrophy. The source of myocardial renin maybe direct cardiac renin gene expression, or plasma renin of renal origin. A primary indication that myocardial renin is derived from plasma renin of renal origin was from work showing that cardiac renin activity was no longer detected 30 hours after bilateral nephrectomy (BNX). However, more recent studies have been able to detect myocardial renin after BNX. We measured normal rat cardiac renin before and after 48-hour BNX using a myocardial renin assay with improved sensitivity. The myocardial renin assay was also used to assess normal rat cardiac myocyte renin levels. Since cardiac tissue contains cathepsin D, a lysosomal enzyme capable of renin-like activity, a rat cathepsin D assay was also developed to assess cathepsin D contribution to renin-like activity. Several artifacts were shown to contribute to myocardial renin-like enzymatic activity levels after BNX, including initial plasma renin stimulation during BNX surgery, assay pH, and cardiac cathepsin D activity. Myocardial renin concentration after 48-BNX was found to be only approximately 1% of normal control levels, and renin concentration in normal cardiac myocytes was only 2-fold greater than assay blanks. Both results were probably overestimated due to cathepsin D contamination. In conclusion, no evidence was found for myocardial renin synthesis in the normal adult rat heart, and myocardial renin decays to near zero levels after 48-hour BNX.

Renin expression in COX-2-knockout mice on normal or low-salt diets.

Experiments were performed in mice to investigate whether cyclooxygenase-2 (COX-2) in epithelial cells near the tubulovascular contact point (macula densa and TAL cells) may regulate renin gene expression in juxtaglomerular granular cells. Renin activity, afferent arteriolar granularity, and renin mRNA were determined in wild-type mice and in COX-2-knockout mice on control and low-NaCl diets. Renin activity in microdissected glomeruli assessed as angiotensin I formation in the presence of excess substrate and afferent arteriolar granularity determined by direct visualization and immunostaining were significantly reduced in COX-2 -/- compared with wild-type animals. Similarly, renal cortical mRNA levels were lower in COX-2 -/- than in wild-type mice. Maintaining mice on a low-salt diet for 14 days induced an increase in renin mRNA, afferent arteriolar granularity, and renin activity in wild-type mice. In contrast, renin mRNA and renin granularity did not significantly increase in low-salt-treated COX-2 -/- mice, whereas the increase in juxtaglomerular renin enzyme activity was markedly attenuated, but not fully blocked. In additional experiments we found that COX-2 mRNA was increased in angiotensin type 1A receptor-knockout mice compared with wild-type mice. We conclude that COX-2 in the tubulovascular contact region is a critical determinant of renin synthesis in granular cells under resting conditions and that it participates in the stimulation of renin expression caused by a low-NaCl intake.

Stored Renin Isoforms in the Developing Rat Kidney

Fetal rat kidney contains renin in renal microvasculature, whereas adult rat kidney contains renin predominantly in juxtaglomerular cells. It is hypothesized that renin isoforms stored within these renal tissues may differ chemically and functionally. To test this hypothesis, stored renin isoforms in fetal and adult rat kidney were compared by isolating renin from adult and fetal kidney homogenate with pepstatin agarose. Pepstatin-eluted renin isoforms were separated by relative molecular size using one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE), or by isoelectric point (pI) and size using two-dimensional (2D) gel electrophoresis. Isoforms were identified either by silver staining or immunoblotting. One-dimensional polyacrylamide gel electrophoresis of pepstatin-treated kidney homogenates showed a silver-stained band in the range of ∼45 kDa, which corresponded to a silver-stained spot consistently seen on 2D gels. In fetal kidney homogenate, the ∼45 kDa band had a pI of 5.3 ± 0.1, whereas the corresponding band in adult samples had a basic pI of 6.0 ± 0.05. Angiotensin I generation was measured to assess renin enzymatic activity. There was significantly more inactive renin in fetal kidney homogenate than in adult kidney homogenate (60.2 ± 22.4 v 9.6 ± 4.0 ng AI/mg protein/h, P < .05). There was significantly less active renin in fetal kidney homogenate than in adult kidney homogenate (5.4 ± 0.4 v 36.5 ± 14.2 ng AI/mg protein/h, P < .05). The average total renin activity in fetal kidney homogenate was significantly higher than in adult kidney homogenate (65.6 ± 22.3 v 46.0 ± 15.2, P < .05). These results demonstrate major differences in the physical and enzymatic forms of stored renin found in fetal and adult kidney. It is speculated that these variations in stored renin isoforms play a role in the developmental differential regulation of the intrarenal renin angiotensin system.

Plasma Renin Activity: Temperature Optimum at ∼45 °C

Renin (EC 3.4.23.15) catalyzes the proteolytic degradation of angiotensinogen to angiotensin-I. Plasma renin activity can be assessed by detection of the amount of angiotensin-I produced under well-defined incubation conditions. Despite numerous studies of incubation conditions (1)(2)(3)(4)(5)(6)(7)(8), the temperature optimum of the renin enzyme activity and the effect of the assay temperature on the reproducibility of renin activity measurement have not been reported. Here we draw attention to the temperature effect on the human plasma renin activity over the range between 30 and 50 °C. Blood samples from two men, coded A and B, ages 34 and 40 years, were collected in 10-mL EDTA-containing evacuated polyester tubes (Venoject II, type VP-100DK; Omnilabo Nederland, Breda, The Netherlands) and mixed for 1 min. Within 10 min of collection, each sample was centrifuged at ambient temperature for 15 min at 1300 g . The plasma obtained was separated from the blood cells within 10 min thereafter and, with the use of polyethylene pipettes, was transferred into polystyrene tubes in small aliquots. Also used were an EDTA-anticoagulated plasma selected without conscious bias from leftover laboratory (“waste”) samples (coded C) and a RIANEN Renin …

Characterization of the Effects of Low Salt (LS) Diet and Cyclosporin-A (CsA) on Rat Kidney Renin Enzymatic Activity. † 1678

It has been shown that chronic CsA treatment is associated with increased expression of an acidic renin isoform and the development of arteriolopathy in rat kidney. Since dietary sodium restriction enhances these effects, it is hypothesized that renal renin enzymatic activity also will be changed by these conditions. Male Sprague Dawley rats received a LS diet for 3 (n=4) or 5 (n=4) weeks. In addition, an equal number of rats in each group received CsA 25 mg/kg/d orally, a dose known to cause renal toxicity. Kidneys were removed and homogenized. Renin enzymatic activity was measured for 1 hr at 37°C in rat kidney homogenate at pH 6.2, the optimum pH, and pH 5.2. Angiotensin I assayed by RIA indicated renin enzymatic activity in the samples. Data are expressed as ng AI/ mg protein/hr. Table