A renin inhibitor from rabbit kidney: conversion of a large inactive renin to a smaller active enzyme

Galectin-7 dysregulates renin-angiotensin-aldosterone and NADPH oxide synthase pathways in preeclampsia

OBJECTIVES

Preeclampsia is a life-threatening disorder of pregnancy unique to humans. Poor placentation in the first trimester of pregnancy is widely accepted to be an underlying cause of preeclampsia. Galectin-7 is abnormally elevated in chorionic villous samples and serum from women that subsequently develop pre-term preeclampsia. Administration of exogenous galectin-7 to pregnant mice causes preeclampsia-like features (hypertension, proteinuria), associated with dysregulation of the renin-angiotensin system (RAS). In this study investigated the mechanism by which galectin-7 induces alterations to tissue RAS homeostasis and ROS production. We hypothesized that galectin-7 induces alterations in the production of either placental RAS or NADPH oxidases (or both) to drive the dysregulated RAS and ROS production seen in preeclampsia.

STUDY DESIGN

Mated female mice (n = 5-6/group) received single (embryonic day [E]12/13) or multiple (E8-12) subcutaneous injections of 400 μg/kg/day galectin-7 or vehicle control and killed on E13 or E18. Human first trimester placental villous and decidual tissue (n = 11) was cultured under 8 % oxygen with 1 µg/mL galectin-7 or vehicle control for 16 h.

RESULTS

Galectin-7 administration to pregnant mice impaired placental labyrinth formation, suppressed circulating aldosterone and altered placental RAS (Agt, Renin) and NADPH oxidase (Cyba, Cybb and Icam1) mRNA expression. In vitro, galectin-7 regulated human placental villous RAS (AGT) and NADPH oxidase (CYBA, ICAM1 and VCAM1) mRNA expression.

CONCLUSIONS

Overall, galectin-7 likely drives hypertension in preeclampsia via its direct regulation of multiple pathways associated with preeclampsia in the placenta. Galectin-7 may therefore be a therapeutic target to improve placental function and prevent preeclampsia.

Crystal structure of N-acyl-D-glucosamine 2-epimerase from porcine kidney at 2.0 A resolution

The X-ray crystallographic structure of N-acyl-d-glucosamine 2-epimerase (AGE) from porcine kidney, which has been identified to be a renin-binding protein (RnBP), was determined by the multiple isomorphous replacement method and refined at 2.0 A resolution with a final R-factor of 16.9 % for 15 to 2.0 A resolution data. The refined structure of AGE comprised 804 amino acid residues (one dimer) and 145 water molecules. The dimer of AGE had an asymmetric unit with approximate dimensions 46 Ax48 Ax96 A. The AGE monomer is composed of an alpha(6)/alpha(6)-barrel, the structure of which is found in glucoamylase and cellulase. One side of the AGE alpha(6)/alpha(6)-barrel structure comprises long loops containing five short beta-sheets, and contributes to the formation of a deep cleft shaped like a funnel. The putative active-site pocket and a possible binding site for the substrate N-acetyl-d-glucosamine (GlcNAc) were found in the cleft. The other side of the alpha(6)/alpha(6)-barrel comprises short loops and contributes to the dimer formation. At the dimer interface, which is composed of the short loops and alpha-helices of the subunits, five strong ion-pair interactions were observed, which play a major role in the dimer assembly. This completely ruled out the previously accepted hypothesis that the formation of the RnBP homodimer and RnBP-renin heterodimer requires the leucine zipper motif present in RnBP.

The expression of renin-binding protein and renin in the kidneys of rats with two-kidney one-clip hypertension

OBJECTIVE

To test the hypothesis that renin-binding protein (RnBP) is involved in modulating the intracellular processing or release of renin, we examined the expression of RnBP in clipped and contralateral kidneys of rats with two-kidney one-clip hypertension, and in left and right kidneys from sham-operated control rats.

DESIGN AND METHODS

Kidneys from rats with two-kidney one-clip hypertension and from control rats were either snap-frozen for extraction of mRNA or fixed for in-situ hybridization and immunochemistry. Reverse-transcription polymerase chain reaction on renal mRNA was performed using primers for renin, RnBP, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and angiotensin-converting enzyme (ACE). In addition, renal total RNA was analysed by Northern blotting for RnBP, GAPDH and angiotensin II type 1A (AT1A) receptor mRNA, and the intensity of the bands was measured by laser densitometry. In situ hybridization for renin mRNA was carried out using digoxygenin-labelled antisense oligonucleotides and for RnBP using labelled antisense oligonucleotides and an antisense riboprobe. Controls included sections treated with RNase and sections stained with sense oligonucleotides.

RESULTS

The level of expression of mRNA for RnBP is similar in clipped and contralateral kidneys of renal hypertensive rats; in contrast, renin mRNA expression is upregulated in the clipped kidney. Renin-binding protein is expressed mainly in renal tubules and collecting ducts unlike renin, which is expressed in the glomerular afferent arteriole. We did not detect lateralization of expression for ACE or the AT1A receptor between clipped and contralateral kidneys.

CONCLUSION

Renin-binding protein expression is unchanged between clipped and contralateral kidneys. Therefore, a physiological stimulus that upregulates renin gene expression in clipped kidneys does not affect RnBP expression. The main sites of RnBP expression are the renal tubules and collecting ducts; in contast renin is expressed at the glomerular pole. The results show that RnBP is not colocalized or coregulated with renin in this model of hypertension.

Molecular cloning and identification of N-acyl-D-glucosamine 2-epimerase from porcine kidney as a renin-binding protein

N-Acetylneuraminic acid (NeuAc) is an important molecule in biological recognition systems. NeuAc is known to be biosynthesized either from UDP-N-acetyl-D-glucosamine by an action of UDP-N-acetyl-D-glucosamine 2-epimerase or from N-acetyl-D-glucosamine by N-acyl-D-glucosamine 2-epimerase (GlcNAc 2-epimerase). However, the physiological function of the GlcNAc 2-epimerase in NeuAc biosynthesis has not been fully evaluated. To clarify the role of GlcNAc 2-epimerase in NeuAc biosynthesis, the enzyme and its gene were isolated from porcine kidney cortex. Escherichia coli cells transformed with the gene expressed the GlcNAc 2-epimerase having the same properties as those of the GlcNAc 2-epimerase from porcine kidney. Sequence analysis indicated that the gene was capable of synthesizing a 46.5-kDa protein (402 amino acids) with a conserved leucine zipper motif. Homology search for the cloned gene revealed that the GlcNAc 2-epimerase was identical with renin-binding protein (RnBP) in porcine kidney (Inoue, H., Fukui, K., Takahashi, S., and Miyake, Y.(1990) J. Biol. Chem. 265, 6556-6561) (identity: 99.6% in nucleotide sequence, 99.0% in amino acid sequence). That GlcNAc 2-epimerase is a RnBP was confirmed by its ability to bind porcine kidney renin and mask its protease activity. These findings provide unequivocal evidence that the enzyme GlcNAc 2-epimerase is a RnBP.

Interaction of acetaldehyde with plasma proteins of the renin-angiotensin system

Chronic alcohol abuse may lead to hypertension by stimulating the activity of the renin angiotensin system (RAS). While there are reports on the alcohol associated increase of angiotensin II in rats and increases of plasma renin activity in rats and human alcoholics, the exact mechanisms of stimulation of the RAS activity is not clear. This study provides evidence for a biochemical interaction of acetaldehyde, the primary oxidative metabolite of ethanol, upon bilaterally nephrectomized (NEPEX) rat plasma that contains significant quantities of angiotensinogen and lacks active renin. Rat plasma served as the source of renin in this study. Preincubation of NEPEX plasma with 0.2 M acetaldehyde at 4 degrees C for 2 h resulted in a 21% increase in the angiotensin I (A I) formation by the rat plasma renin and 27% increase in the A I formation by the trypsinized rat plasma renin. When the rat plasma which contains modest quantities of endogenous angiotensinogen in addition to renin was preincubated with 0.2 M acetaldehyde at 4 degrees C for 2 h, the rate of A I formation was increased by 10%. Equivalent amounts of ethanol did not modify the rate of A I generation when added to NEPEX plasma or rat plasma. These results suggest the possibility of a biochemical interaction of acetaldehyde with the renin substrate which may enhance the activity of the RAS cascade, thereby contributing to hypertension in chronic alcoholics.

Biosynthesis of a renin binding protein

The biosynthesis of a porcine renin binding protein (RnBP), which specifically binds to renin and forms an inactive high molecular weight renin, was investigated. mRNAs from various porcine tissues were used to investigate in vitro protein synthesis. The kidney mRNA directed the synthesis of a high level of RnBP, whereas the liver, adrenal and pituitary gland mRNAs gave as low but significant level of it. The in vitro synthesized RnBP as well as the immunologically detected RnBP synthesized in vivo had the same molecular weight, 42,000, as that of the purified protein. Moreover, both the human and rat kidney mRNAs directed the synthesis of this protein identified with an anti-porcine RnBP antibody. These results strongly indicate that RnBP, present in various mammalian species, is synthesized in renin-producing tissues as the mature size and undergoes binding with renin without proteolytic processing.

Characterization of inactive renin ("prorenin") from renin-secreting tumors of nonrenal origin. Similarity to inactive renin from kidney and normal plasma

Inactive renin comprises well over half the total renin in normal human plasma. There is a direct relationship between active and inactive renin levels in normal and hypertensive populations, but the proportion of inactive renin varies inversely with the active renin level; as much as 98% of plasma renin is inactive in patients with low renin, whereas the proportion is consistently lower (usually 20-60%) in high-renin states. Two hypertensive patients with proven renin-secreting carcinomas of non-renal origin (pancreas and ovary) had high plasma active renin (119 and 138 ng/h per ml) and the highest inactive renin levels we have ever observed (5,200 and 14,300 ng/h per ml; normal range 3-50). The proportion of inactive renin (98-99%) far exceeded that found in other patients with high active renin levels. A third hypertensive patient with a probable renin-secreting ovarian carcinoma exhibited a similar pattern. Inactive renins isolated from plasma and tumors of these patients were biochemically similar to semipurified inactive renins from normal plasma or cadaver kidney. All were bound by Cibacron Blue-agarose, were not retained by pepstatin-Sepharose, and had greater apparent molecular weights (Mr) than the corresponding active forms. Plasma and tumor inactive renins from the three patients were similar in size (Mr 52,000-54,000), whereas normal plasma inactive renin had a slightly larger Mr than that from kidney (56,000 vs. 50,000). Inactive renin from each source was activated irreversibly by trypsin and reversibly by dialysis to pH 3.3 at 4 degrees C; the reversal process followed the kinetics of a first-order reaction in each instance. The trypsin-activated inactive renins were all identical to semipurified active renal renin in terms of pH optimum (pH 5.5-6.0) and kinetics with homologous angiotensinogen (Michaelis constants, 0.8-1.3 microM) and inhibition by pepstatin or by serial dilutions of renin-specific antibody. These results indicate that a markedly elevated plasma inactive renin level distinguishes patients with ectopic renin production from other high-renin hypertensive states. The co-production of inactive and active renin by extrarenal neoplasms provides strong presumptive evidence that inactive renin is a biosynthetic precursor of active renin. The unusually high proportion of inactive renin in plasma and tumor extracts from such patients is consistent with ineffective precursor processing by neoplastic tissue, suggesting that if activation of "prorenin" is involved in the normal regulation of active renin levels it more likely occurs in the tissue of origin (e.g., kidney) than in the circulation.

Synthesis of peptides related to the prosegment of mouse submaxillary gland renin precursor: an approach to renin inhibitors

The complete sequence of the structural gene coding for mouse submaxillary gland renin was recently reported and the amino acid sequence of preprorenin was deduced. This sequence includes a 45-amino acid peptide that corresponds to the prosegment of the renin precursor. To investigate whether peptides related to the renin prosegment are able to inhibit renin activity, we have synthesized four peptides having the following structures: Arg-Ile-Pro-OMe, butyloxycarbonyl(Boc)-Leu-Lys-Lys-Met-Pro-OMe, Boc-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe, and Boc-Glu-Arg-Ile-Pro-Leu-Lys-Lys-Met-Pro-OMe (corresponding to amino acids 12-14, 15-19, 12-19, and 11-19, respectively, of the renin prosegment). All four peptides were found to inhibit the activity of pure mouse submaxillary renin on a porcine synthetic tetra-decapeptide in vitro, and the most potent inhibitors exhibited IC50 values in the micromolar range. Enzymatic kinetic studies carried out using peptide 15-19 showed an uncompetitive or a mixed type of inhibition with a Ki value of 2.3 X 10(-6) M at 37 degrees C in 0.5 M citrate/phosphate buffer (pH 6.0).

Endogenous renin inhibitor in neuroblastoma cells

Cloned neuroblastoma cells (Neuro-2a) in culture were found to contain a renin inhibitory substance. The inhibitor in the extract of cloned neuroblastoma cells was separated from renin activity by anti-renin IgG-Sepharose and selectively concentrated by adsorption to renin-agarose gel. The present study demonstrated the coexistence of renin and its inhibitor in the same cell and suggested a possible regulatory mechanism of intracellular renin activity by an endogenous renin inhibitor in neuronal cells.

Cryoactivation fails to augment plasma renin activity in the cat

1. Active and cryoactivated renin (plasma renin) activity after incubation at -5 degrees C for 4 days, were measured in cat plasma sampled before and during the following procedures: suprarenal aortic stenosis, electrical stimulation of the pons and mild hypotensive haemorrhage. 2. Under all experimental conditions the values of plasma renin activity for both the activated and non-activated samples were similar. 3. The absence of a cryoactivatable aliquot of renin suggests that in cat plasma the inactive form of the enzyme either is actually absent or has a liability to the action of cold different than in other animal species.

Intrarenal localization of renin binding substance in rats

Renin binding substance is a protein that reacts with renin (Mw:40,000) to form a high-molecular-weight renin (Mw:60,000). There is evidence that this substance is present in the renal cortex. However, the exact localization has not been determined. We now report that when glomeruli and tubular segments were isolated from the rat kidney cortex and were frozen and thawed to extract proteins, the high-molecular-weight renin was detected by high performance liquid chromatography, when renin was mixed with an extract of tubular segments, but was not detected with an extract of the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli. Thus, the renin binding substance was demonstrated in the cortical tubular cells but not in the glomeruli, and the renin binding substance probably does not contribute to the process of biosynthesis of renin in juxtaglomerular cells. Rather, this substance may play a role in tubular functions in the kidney.

Apparent molecular size difference between plasma and renal inactive renins

Partially-purified inactive renins from human plasma and kidney seem to be identical in most respects except for apparent molecular size. To evaluate this difference, we determined apparent molecular weights by gel filtration with internal radiolabeled standards, using trypsin activation in the presence of benzamidine and albumin to provide reproducible detection. While there was a suggestion of a shoulder in the 50,000-dalton region of the plasma inactive renin peak, the major form (56,000) was consistently larger than that of renal inactive renin (50,000), confirming our previous observation. Since both renal and plasma inactive renins appear to be glycoproteins, based on their ability to bind to concanavalin A-Sepharose, it is possible that differences in carbohydrate composition might contribute to this discrepancy in gel filtration behavior. The striking similarity of these substances in all other respects, including inhibition of the activated forms by monospecific antirenin antibodies, makes it unlikely that they differ in primary structure.

Biological significance of active and inactive renin in hypertensive patients

The significance of active and inactive renin was investigated by comparison of an in vitro assay of active, total and inactive plasma renin concentration (APRC, TPRC, IPRC) and plasma angiotensin II concentration (PA II) with an in vivo change in mean arterial pressure (MAP) produced by angiotensin antagonism with saralasin and by angiotensin converting enzyme blockade with captopril. A significant relationship between the changes in MAP during saralasin and captopril with the pre-treatment level of APRC, TPRC and PA II were found; while the pre-existing level of inactive renin was not a predictor for the hypotensive effect of saralasin and captopril. During captopril and saralasin significant increases in TPRC and APRC were found and no change in IPRC.

Molecular characterization of inactive renin: complete purification of prorenin in hog kidney and isolation of inactive renin from neuroblastoma cells: evidence for 2 different types of inactive renin

To determine the molecular properties of inactive renin and its relationship to active renin, inactive renin in hog kidney was purified by devising affinity chromatography. Electrophoretically homogeneous inactive renin was prepared by 3 million-fold purification. It consists of a single polypeptide chain and undergoes reduction in molecular weight from 50,000 to 38,000 upon activation by proteases but not by dissociative treatment. This type of inactive renin is considered as a zymogen. However, a stable complex of renin and its inhibitor with a molecular weight of 110,000 was found in cultured neuroblastoma cells indicating the presence of a second type of inactive renin.

Biosynthesis of preprorenin. Studies using whole tissue, a cell-free system, and E. coli containing cDNA inserted at the PstI site of plasmid pBR322

The biosynthesis of renin as a higher molecular weight 'prorenin' was demonstrated by in vitro incorporation of [35S] methionine into nascent polypeptides of submandibular gland tissue from adult male mice. Immunoprecipitation with anti-renin and electrophoresis identified a Mr 44,500, pI 6.4 prorenin which normally represented 5% of renin-immunoreactive protein in tissue extracts and which was rapidly converted during in vitro labeling into a Mr 40,000, pI 6.2 species. The latter was subsequently processed slowly to forms of Mr 35,500, pI 5.6 and Mr 34,000, pI 5.4. The influence of processing enzymes was then eliminated by synthesizing renin in a cell-free translation system containing rabbit reticulocyte lysate and mRNA isolated from submandibular glands. This yielded an even larger species of Mr 46,000 likely to be 'preprorenin'. A clone bank of mouse submandibular gland cDNA was prepared. This consisted of E. coli RRI transformed with plasmid pBR322 in which cDNA had been inserted at the PstI site so that the bacteria could express the encoded polypeptide. Renin-immunoreactive colonies were identified suggesting the expression of renin-like proteins by a prokaryote. The cDNA which was 700-1000 base pairs big was excised for sequencing.

Properties of renin-binding protein

Hog renal renin-binding protein could bind homologous and non-homologous renin but could not bind human renal renin. Renin-binding protein was only detected in the kidney and pituitary in which renin is found in relatively high concentration. The renal binding protein had no interaction with renal acid proteases nor with extrarenal renins obtained from pituitary and submaxillary glands, indicating that the binding is specific for renal renin. Subcellular localization of the binding protein was studied using rat kidney by differential and density gradient centrifugation. Most renin-binding protein was recovered in the cytosol fraction and was not associated with sedimentable subcellular organelles. A renin-secreting tumor (Juxtaglomerular cell tumor) in human kidney produced not only renin but also renin-binding protein in a very large quantity.

Enzyme inhibitors are not helpful in preserving big renin in the rat kidney

The effect of four different homogenization methods, proteolytic enzymes and enzyme inhibitors on rat renal renin was studied. Rat kidney homogenate was treated with trypsin or pepsin. Neither of these enzymes had any effect on the molecular weight pattern. Enzyme inhibitors, 10 mM N-ethylmaleimide, 5.4 mM EDTA, 1.0 mM toluenesulfonyl fluoride, 2.3 mM o-phenanthroline, 2.3 mM p-hydroxymercuribenzoate, which was added to the homogenization medium, all or some of them, as well as 1/20 to the buffer solution used throughout the experiments for dialysis and column chromatography, did not alter the molecular weight pattern. These results suggest that renins, with molecular weights from above 60 000 Dalton to 37 000 Dalton were preformed in the rat kidney and extracted in a native form.

Demonstration of the formation of renin and renin-binding protein complex using high-performance liquid chromatography

A high-performance liquid chromatograph equipped with the newly developed gel, TSK G3000SW, was used to study the interaction between renin and renin-binding protein (RBP). Previously, the interaction could only be demonstrated after overnight gel chromatography in the presence of a non-physiological sulfhydryl reagent. However, this new high-speed gel chromatography provided a clear separation of renin and renin--RBP complex within 40 min. It also demonstrated that the renin--RBP complex was formed at 37 degrees C in the absence of sulfhydryl reagent. Theses results indicate that the binding protein may play an important role in blood pressure regulation.

Active and inactive renin in dog plasma before and after bilateral nephrectomy

No significant amounts of inactive renin could be demonstrated by in vivo treatment (acidification or cryotreatment) of dog plasma obtained before and after bilateral nephrectomy. After bilateral nephrectomy, total and active renin were cleared from the plasma following similar disappearance curves, and dropped to half of their initial value within 30 min.

Biochemical properties of the renin binding substance of rat kidney

Renin extracted from isolated renin granules of the rat is a low molecular weight form (40,000 daltons). The renin binding substance which is capable of binding with the low molecular weight renin to form a high molecular weight renin (60,000 daltons) under sulfhydryl oxidation was found to be contained in the crude extract of rat renal cortex. This substance is presumably a protein with molecular weight of over 47,000 daltons by gel filtration. The most striking event was that rat renin binding substance was bound with dog renin and vice versa.

Reversible activation-inactivation of renin in human plasma

Renin, an aspartate protease, cleaves the alpha-globulin angiotensinogen to produce the decapeptide angiotensin I, which is then converted to the vasoactive hormone angiotensin II by the action of a peptidase 'converting enzyme'. An inactive form of renin sometimes termed prorenin is present in normal human plasma. Its enzymatic activity is increased by exposure to a pH of 3.0 or 3.3 followed by dialysis towards neutral pH. Only a small proportion of the inactive renin is activated during the acid stage of dialysis, most of the activation apparently taking place during the subsequent dialysis to pH 5.7 (ref. 4) or 7.5 (ref. 5). Furthermore, if inhibitors of serine proteases are added to the plasma, the amount of inactive renin activated by this dialysis procedure is reduced. These results suggest that acid-activation is mediated by serine proteases. The role of enzymes such as plasma kallikrein, plasmin and renal kallikrein as physiological activators of inactive renin has recently been discussed. In our study of the activation of plasma inactive renin we have no found that, contrary to previous reports, complete activation of inactive renin takes place during the acid stage of dialysis. This activation can be reversed if plasma is rapidly adjusted to pH 7.4 and warmed. The next step in the acid-activation procedure, that is, dialysis to neutral pH, renders the initial acid-activation irreversible. These results were completely unexpected, and we offer an explanation that reassesses the nature of inactive renin and the activation process.

A qualitative difference in plasma renin activity in Dahl rats susceptible or resistant to salt-induced hypertension

Plasma renin activity (PRA) was studied in the rats bred by Dahl for susceptibility (S-strain) or resistance (R-strain) to salt (NaCl) induced hypertension. The pH curves for PRA had different shapes. The difference in shape of the pH curves was reflected in the ratio of PRA pH 8/PRA pH 6.5. This ratio was shown to be characteristic of the strain and to be independent of changes in absolute PRA level induced by variation in dietary NaCl. The ratio of PRA pH 8/PRA pH 6.5 was also different between strains in weanling as well as adult rats. The underlying cause for the strain difference in the effect of pH on PRA is unknown, but may involve molecular differences between strains in either renin or renin substrate.

Effect of adrenergic agonists on big and small renin

The effect of alpha- and beta-adrenergic agonists on renal and submaxillary renin of different molecular weights was studied using male albino mice as experimental animals. Phenylephrine or isoproterenol was administered intravenously after removal of the submaxillary glands and/or kidneys. Renin was isolated from plasma by column chromatography and then measured by a direct radioimmunoassay. Phenylephrine increased both 68,500-dalton renin (big renin) and 38,000-dalton renin (small renin) in the plasma of nephrectomized mice. Isoproterenol increased big and small renin in the plasma of mice whose submaxillary glands were removed. In both cases, the increase of small renin was significantly greater than that of big renin. The results suggest that the alpha-adrenergic agonist phenylephrine affects the submaxillary gland, leading to the increase of both big and small plasma renin. In contrast, the beta-adrenergic agonist isoproterenol affects the kidney, leading to the increase of both big and small plasma renin.

Sodium balance and renin regulation in rats: role of intrinsic renal mechanisms

Renin secretion was compared in vivo and in vitro among five groups of rats, each group subjected to a different sodium balance for 10 to 14 days. The state of the renin-angiotensin system in vivo was evaluated by measuring the renal renin (RR) and the plasma renin concentration (PRC) in both anesthetized and nonanesthetized animals. The in vitro renin secretion rate (RSR) was determined in isolated perfused kidneys. RR was reduced (-48%) by sodium loading and deoxycorticosterone (DOCA) and increased (+27%) by sodium deprivation and furosemide. Sodium loading and DOCA reduced both the PRC and the RSR to less than 20% of control values. By contrast, sodium deprivation and furosemide induced a more than fourfold rise in the PRC but only a small increase in the RSR (+37%). These results indicate that changes in fractional renin release are induced by sodium balance variation, and these changes are preserved in vitro only in sodium-loaded states. The inability of sodium-deprived kidneys to maintain high renin release in vitro suggests that high plasma renin levels in these rats depend on mechanisms that are not preserved in vitro. There was no evidence supporting the participation of inactive renin secretion in the regulation of fractional renin release under varying sodium balance.

The role of renin in the control of the circulation and in hypertensive disease

Renin is a hormone secreted by the juxtaglomerular cells of the kidney; it interacts with a plasma protein substrate to produce a decapeptide prohormone angiotensin I. Converting hormone located on vascular endothelium converts the decapeptide to an octapeptide, angiotensin II, which effects vasoconstriction, the secretion of aldosterone by the adrenal cortex, and retention of sodium by the kidney. The biosynthesis and control of renin secretion are not well understood, and the question as to whether renin is synthesized and stored in a larger precursor form is as yet unresolved. Whether or not higher molecular weight or inactive forms of renin in plasma have a role in controlling renin activity or whether they simply represent a degradative pathway for renin is as yet uncertain. The availability of several inhibitors of the renin-angiotensin system has served to define the role of renin both in normal cardiovascular homeostasis and in renovascular hypertension. It appears that renin plays an important role in maintaining blood pressure in the salt- or volume-depleted state and that it is responsible for the initial phases of renovascular hypertension in any model of this disease process. Renin's part in chronic renovascular hypertension depends on whether or not sodium is permitted to accumulate. If sodium intake is restricted or if sodium excretion is unimpaired (such as in two-kidney renovascular hypertension models), renin continues to play a significant role during the chronic phase.

Physicochemical properties of non-activated and activated renin from human amniotic fluid

The main physicochemical and enzymic properties of non-activated and activated human amniotic renin (EC 3.4.99.19) were studied in order to clarify the relationships between the two enzymes. Human amniotic renin was activated by dialysis against acidic buffer (pH 3.3), direct acidification or trypsin treatment. All procedures produced similar activation. The physicochemical characteristics of non-activated and activated renin were compared to those of human renal renin. Non-activated renin had a molecular weight of 45,500. A similar molecular weight was obtained by gel eluate activation and by acid treatment of renin prior to gel filtration. Similar isoelectric points were also found for non-activated and activated renin. One major renin peak focused at pH 6.6, whereas no similar renin peak was detected in extracts from normal human kidney. In addition, non-activated and activated renin forms were found to have the same optimal pH, the same Km and the same inhibiting pepstatin concentrations.

Isolation of completely inactive plasma prorenin and its activation by kallikreins. A possible new link between renin and kallikrein

Existing views on prorenin are conflicting and its physiological activation mechanism is not clear. In an attempt to obtain clearcut views on the molecular properties of prorenin in human plasma, the renin zymogen (prorenin) was separated from active renin by two steps of affinity chromatography and it was demonstrated that prorenin is a completely inactivate zymogen contrary to the existing information. Inactive prorenin has an apparent molecular of 56,000 contrary to 46,000-43,000 of partially active prorenin. Isolated and acid-treated human prorenin was shown to be activated by kallikreins from human urine and plasma. This activation was completely blocked by Trasylol. Hog pancreatic kallikrein also activated human prorenin. The kallikrein mediated activation of prorenin indicates the existence of a new link between the vasoconstricting renin-angiotensin system and the vasodilating kallikreinkinin system.

Active and inactive renin in normal human plasma. Comparison between acid activation and cryoactivation

Inactive renin in human plasma is converted to active renin in vitro by acid activation or by cryoactivation. Renin activity was measured at pH 5.5 and renin concentration at pH 7.4. The plasma renin activity before and after cryo-treatment is termed active (APRA) and total (TPRA) plasma renin activity; the plasma renin concentration before and after acid treatment active (APRC) and total (TPRC) plasma renin concentration. In this study we demonstrated that in normal subjects the proportion of active to total renin after cryo-treatment averaged 61%, which was significantly (p less than 0.001) higher than the mean percentage active renin of 34 found with the acid activation procedure. Plasma angiotensin II correlated significantly with APRA, TPRA, TPRC and plasma angiotensin I (PA I), but not with inactive renin, which suggests that inactive renin does not produce angiotensin II in vivo. Cold treatment after acid activation and acid treatment after cryoactivation did not provoke a significant change in the measured renin concentration. Our data support the view that acidification of the plasma activates more than does cryo-treatment, and that inactive renin does not contribute to plasma angiotensin II.

Renin in the mouse submaxillary gland has a molecular weight of 40,000

The availability of pure submaximillary renin, its antibody and pure specific immunoreactive Fab fragments of the antirenin molecule were used in an attempt to detect in which form renin is stored in the submaxillary gland. The proteolytic activity of serine-, metallo- and sulfhydryl enzymes during homogenisation was inhibited, but no inactive or high molecular weight form could be detected enzymatically or antigenically after gelfiltration. Nor were they demonstrable in crossed immuno-electrophoresis by using antibodies elicited against pure renin. Furthermore, pepstatin which additionally inhibits acid proteases, including a possible autoactivation of renin, and renin specific Fab fragments, were added, the latter in order to steric hinder proteolytic attack on a possible renin precursor. The renin-Fab complex was purified by precipitation with anti-Fab antibodies. No high molecular weight renin was demonstrable in SDS polyacrylamide gel electrophoresis. The only form of renin demonstrable in the submaxillary gland of mice was the fully active 40,000 dalton form. Its specific enzymatic activity was identical to that of pure submaxillary renin, being 0.4 . 10(-3) Goldblatt unit . ng-1.

The effects of beta-adrenoceptor blockade on renin, angiotensin, aldosterone and catecholamines at rest and during exercise

1 beta-adrenoceptor blockade with metoprolol provoked, both at rest and during exercise, a decrease of 'active' renin and angiotensin II together with an increase of 'inactive' renin and unchanged 'total' renin. The significant exercise-provoked increases in angiotensin II, plasma renin activity and 'active', 'inactive' and 'total' renin when on placebo, were reduced by metoprolol. 2 No significant change in serum sodium and potassium and in plasma aldosterone was found during beta-adrenoceptor blockade at rest. During exercise plasma aldosterone dropped significantly without any change in serum sodium or potassium. 3 Plasma noradrenaline increased significantly at rest on metoprolol. The increase in plasma noradrenaline and adrenaline during exercise was similar on placebo and on metoprolol.

Conversion between renin and high-molecular-weight renin in the dog

Two forms of renin, one of mol.wt. 43,000 and the other 60,000, were found in the dog kidney. Conversion between the two forms of renin was reversible at neutral pH. Though the molecular weight of renin in kidney-cortex homogenate was 43,000, it was completely converted into high-molecular-weight renin in the presence of substances that react with thiol groups. On the contrary, stored renin in the granules was the form of normal size (mol. wt. 43,000) regardless of the absence or presence of such substances. The present experiments indicated that renin is stored in the granules as the form of normal size and might be converted into high-molecular-weight renin when it is released from the granules and attached to some substance in the soluble fraction of renal-cortical tissue.

Properties of the activation by pepsin of inactive renin in human amniotic fluid

1. The renin present in human amniotic fluid was found to have an apparent Mr of 58 000 by gel filtration and is thus bigger than renin in untreated kidney extracts and plasma (Mr approximately 40 000). 2. Treatment with pepsin (40 microgram/ml pH 4.8, 2 h, 22 degrees C) caused a 6-fold increase in activity of this renin species, although Mr was not very different (57 000). 3. Unlike renal renin, renin in human amniotic fluid was not a glycoprotein and behaved similarly on concanavalin A-Sepharose before and after activation by pepsin. 4. Ion-exchange chromatography demonstrated a small change in the ionization properties of human amniotic fluid renin after activation by pepsin. 5. Pepsin-mediated activation resulted in a five-fold increase in V, but only a small decrease in the Km of renin to 39% of normal, so that the increase in activity observed was not due to an increase in the affinity of the enzyme for its substrate. The kinetic data were consistent with the theory of noncompetitive inhibition. 6. The activation of human amniotic fluid renin by pepsin may be caused by a change in the tertiary structure of the molecule subsequent to a proteolytic action that does not remove detectable polypeptide components.

Big renin in plasma of healthy subjects on high sodium intake

Normal human plasma contains not only active renin but also an inactive form of renin which, after exposure to low pH, can generate angiotensin I from renin substrate. When healthy volunteers were given first a diet containing 400 mmol sodium and then a diet containing 10 mmol sodium for 4 days the changes in salt intake stimulated large changes in active plasma-renin and smaller changes in inactive renin. Inactive renin comprises a larger fraction of total renin in plasma of salt-loaded healthy subjects than salt depleted subjects. When plasma of healthy men on a high-salt diet was applied to a column of 'Sephadex G-100', renin eluted in two peaks, corresponding to big renin (60 000 daltons) and normal renin of lower molecular weight (40 000 daltons). Active and inactive forms of renin were present in both peaks. Plasma from salt depleted healthy subjects showed a large single peak of renin activity with a maximum at 40 000 daltons. These studies demonstrate that both big and small renin can exist as inactive or active enzyme. Big renin, previously found in certain diseases and in pregnancy, is also present in normal human plasma. These observations suggest a possible physiological role for big renin.

In vitro and in vivo inhibition of renin by fatty acids

Circulating neutral lipids inhibit the in vitro renin reaction. To identify the inhibitor(s), free fatty acids were added to human renin and homologous substrate. Capric, lauric, palmitoleic, linoleic, and arachidonic acids each inhibited the rate of angiotensin I production in vitro (P less than 0.01). Inhibition by polysaturated fatty acids (linoleic and arachidonic) was less (P less than 0.01) after catalytic hydrogenation of the double bonds. To evaluate an in vivo effect of renin inhibition intra-arterial blood pressure responses to infusions of renin and angiotensin II (5.0 microgram) were measured in anephric rats (n = 6) before and after infusion of linoleic acid (10 mg iv). Mean increase of blood pressure to angiotensin II before (75 mmHg +/- 9) and after (90 +/- 12) linoleic acid did not differ (P greater than 0.05). However, the pressor response to renin after linoleic acid (18 +/- 3) was less (P less than 0.00)) than that before (102 +/- 13). In summary, several fatty acids inhibit the in vitro renin reaction, and in part inhibition is dependent on unsaturation. Linoleic acid also inhibits the in vivo pressor response to renin. These results suggest that fatty acids may modify the measurement of plasma renin activity and may also affect angiotensin production in vivo.

Adenocarcinoma of the kidney and hypertension: report of 2 cases with special emphasis on renin

Renin studies were done on 2 patients with adenocarcinoma of the kidney and hypertension. In 1 case plasma renin activity was high in the peripheral and renal veins, with a renal vein ratio of 1.7 favoring the side of the tumor. Nephrectomy cured the hypertension and renin values became normal. Tissue renin was elevated in the tumor and surrounding parenchyma. Acidification studies of tissue extracts failed to demonstrate the existence of big renin. In case 2 all renin values were normal and the blood pressure remained elevated after the operation. Although renin-secreting tumors remain an uncommon cause of malignant hypertension the condition should be recognized because it is potentially curable.