Sensing and response generation in the renin–angiotensin system and the actions of angiotensins. A: Mechanisms mediating renin release and formation of angiotensin I and angiotensin II. Signals are received and integrated by the kidney to cause the release of renin in response to the coordinated messenger regulation and integration by calcium and cAMP. Inside the juxtaglomerular cells, prorenin is processed to renin, most probably by an aspartic protease. Renin and prorenin are trafficked through the cell to the outside. Renin subsequently processes angiotensinogen to angiotensin I, whereas angiotensin‐converting enzyme processes angiotensin I to generate angiotensin II. Angiotensin II achieves its physiological responses by signaling through various subtypes of its receptor. B: Multiplicity of systemic actions of angiotensin II and some metabolites. ECF, extracellular fluid; AT₁, AT₂, angiotensin II receptor subtypes 1, 2; RBF, renal blood flow; CNS, central nervous system; ADH, antidiuretic hormone. [From Navar et al. 179 with permission.]

Renin gene organization, activation, and suppression. A: Physiologically relevant functional elements associated with human and mouse renin genes. These include a far upstream enhancer that, together with a Pit‐1‐like sequence in proximal promoter DNA, is required to achieve normal activity of the renin promoter. A classical silencer element also exists in intron 1. Regulatable expression is mediated via an action of cAMP‐response element (CRE)–binding (CREB) protein on the CRE. Part of the cAMP response also involves the Pit‐1‐like site via a CREB protein‐independent mechanism. B: Hypothesis for mechanism by which cAMP and Ca²⁺ mediate physiological control of the human renin gene. In renin‐synthesizing cells, an increase in cAMP activates protein kinase A (PKA), which in turn phosphorylates CREB protein, causing it to bind to the CRE. This appears to involve a CREB protein/activating transcription factor (ATF)‐1 heterodimer or a CREB protein homodimer. In unstimulated cells, ATF‐1 is phosphorylated and, by binding to the CRE, may suppress the promoter. The fact that the CRE has low binding affinity coupled with the low phosphorylation of CREB protein and its ability to undergo rapid dephosphorylation as well as the capacity for greatly enhanced responsiveness of the promoter under conditions that cause CREB‐1 phosphorylation provides a mechanism for establishing a considerable regulatable response range for transcription of the renin gene under various physiological conditions. Since PKA and Ca²⁺‐calmodulin (CaM)‐dependent protein kinase can phosphorylate CREB protein and ATF‐1 selectively, the present view includes a possible mechanism for the convergence and integration of multiple extracellular signals that stimulate (via cAMP) or inhibit (via Ca²⁺–(calmodulin) renin gene expression in renin‐expressing cells in vivo. [From Morris 169 with permission.]

Processing and granular activity of renin and prorenin. A: Precursor and processing sites in mouse, rat, and human renin. Initial hydrolysis of the N‐terminal signal (pre) peptide occurs prior to completion of synthesis of the nascent protein (site indicated by small arrow nearer left end of polypep tide chain in each case). The question mark at the rat signal peptide cleavage site and the range of values for amino acids in rat pre and pro fragments refer to the uncertainty as to the actual site of hydrolysis. After synthesis of precursor (prorenin), activation in vivo is achieved by hydrolysis at the site indicated by the large vertical arrow. (This differs for rats because rat prorenin has a lysine instead of the arginine at the activation site that is used in the other species). At least a portion of the active renin is later cleaved at the site shown by the small arrow toward the right side of the polypeptide chain, to give twochain renin. The position of this cleavage differs for humans, where the two chains are not held together by disulfide bridges (‐S‐S‐), as is the case for mice and rats. Numbers preceded by + indicate amino acid number with respect to the first amino acid of the mature protein, designated +1. Numbers followed by aa indicate number of amino acids in each polypeptide segment. [From Morris 169 with permission.] B: Chemiosmotic process for renin release from isolated renin‐containing granules. Possible mechanisms of action for some of the drugs used to study renin release from granules. The chemiosmotic process is driven by two major components: the first (component a) is a proton ATPase in the granular membrane which is sensitive to oligomycin and N, N′‐dicyclohexylcarbodiimide (DCCD); the second (component b) is an antiport–symport exchanger which is insensitive to oligomycin and DCCD. Component b exchanges the outflow of proton for the influx of K⁺ and CI⁻. [From Sigmon and Fray 225 with permission.] C: Effects of changing Ca and K on renin and prorenin secretion. a: Effect of Ca²⁺ concentration on release of active and inactive (prorenin) renin by rabbit kidney cortex slices. b: Effect of changing K⁺ concentration in the presence of 2.3 mM Ca²⁺ (control) and in Ca²⁺‐depleted media (O Ca²⁺ + 5 mM EGTA) on release of active and inactive (prorenin) renin by rabbit kidney cortex slices. (pro)Renin, renin plus prorenin. [From King and Fray 132 with permission.]

Distribution and trafficking pathways and relative values for renin in human plasma. A: Subcellular particulate renin distribution in endoplasmic reticulum (ER) and Golgi transport vesicles a, mature secretory granules (b), and plasma membrane vesicles and light microsomes (c) in three rodent models of low‐renin syndrome. All low‐renin kidneys were removed from rats with low plasma renin activity and renin secretory hyporesponsiveness to acute stimulation. All values are means ± SEM of renin‐specific activities after subfractionation (^*P < 0.05; ^**P < 0.01). [From Fray 79 with permission.] B: Renin content from partially purified subfractions of juxtaglomerular cells from three rodent models of low‐renin syndrome. All low‐renin kidneys were removed from rats with low plasma renin activity and renin secretory hyporesponsiveness to acute stimulation. All values are means ± SEM of renin‐specific activities after subfractionation (^*P < 0.05; ^*P < 0.01). [From Fray 79 with permission.] C: At least three pathways have been identified for renin and prorenin secretion. Pathway 1, conventional regulative degranulation pathway whereby preprocessed and stored renin are liberated from mature secretory granules on demand. Pathway 2, constitutive vesiculation route emanating from post‐Golgi immature vesicles. Pathway 3 begins as pre‐Golgi vesicles bypass Golgi transport to export their contents at the plasma membrane. [From Morris 167 and King and Fray 132 with permission.] D: Relative plasma renin levels in normal subjects under different conditions and impaired patients under pathological conditions. [From Laragh and Sealey 140 with permission.]

Generation and metabolism of angiotensin peptides and differences in angiotensinogen (renin substrate) concentration and angiotensin I generation. A: Generation and metabolism of angiotensin peptides from the precursor, angiotensinogen. From the generation of angiotensin I by renin processing there are at least five processing enzymes responsible for metabolizing angiotensinogen to “inactive” fragments. [From Ballermann and Onuigbo 9 with permission.] B: Effect of differences in angiotensinogen (renin substrate) concentration on rate of generation of angiotensin. There was no difference in rate when undiluted plasma samples exhibiting various angiotensinogen concentrations were compared with various dilutions of plasma that had endogenously high renin substrate. These samples were obtained at various times during oral contraceptive administration. Normal substrate concentration is ∼1800 ng/ml. Data suggest that concentration of angiotensinogen in human plasma is normally rate‐limiting and that observed differences in rate of angiotensin generation are related to differences in renin substrate concentration and not to variations in concentration of renin activator or inhibitor. [From Newton et al. 181 with permission.]

Genetic and evolutionary comparisons of elements of angiotensin I–converting enzyme (ACE) from testis and endothelium. A: Relationship between testis ACE and endothelial ACE cDNAs. Open bars, regions of identity; cross‐hatched bar, homologous region; solid and stippled bars, absence of homology. [From Ehlers et al. 67 with permission.] B: Cysteine positions, potential asparagine‐linked glycosylation sites, and positions of putative residues of the active site (one‐letter code). [From Soubrier et al. 235 with permission.] C: Dendrogram showing relationships between core sequences of mammalian N and C domains and Drosophila melanogaster ACE (AnCE). The line below gives estimated time points for the original divergence (450 million years before present), the duplication event (270 million years before present), and the radiation of mammals (50 million years before present) as calculated by the KITSCH algorithm based on these sequences. The table at right summarizes the average relative percent similarities within and between domains and between the N and C domains of the mammalian enzyme and ACE, as calculated using the GCG Distances program. [From Cornell et al. 47 with permission.]

Summary of kinetic and inhibition constants of angiotensin I–converting enzyme (ACE). A: Kinetic constants for hydrolysis of Hip‐His‐Leu, angiotensin I, and AcSDKP, a specific substrate for the domain active site. B: Inhibition constants using specific ACE inhibitors. C: Structures of specific ACE inhibitors. Enalaprilat, Lisinopril, and trandolaprilat coordinate the active‐site zinc ion of ACE via their carboxyl groups, whereas captopril and fosinoprilat coordinate the active‐site zinc via their sulfydryl and phosphoryl groups, respectively. Captopril does not interact with the theoretical S₁ subsite of ACE. [From Williams et al. 272 with permission.]

Generation and metabolism of angiotensin peptides. A: Classic pathway of angiotensin generation and subsequent cleavage steps. B: Generation of angiotensin III bypassing angiotensin II. C: Generation of angiotensin (1–7) from angiotensin I and subsequent cleavage steps. D: Generation of angiotensin (1–7) from angiotensin II. [From Ballermann and Onuigbo 9 with permission.]

Biosynthesis and effect of aldosterone on sodium excretion. A: Biosynthetic pathways from cholesterol to mineralocorticoids (aldosterone), glucocorticoids (cortisol), and androgens (androstenedione) and structures of cholesterol, aldosterone, Cortisol, and androstenedione (small amounts of tetosterone and estrogen are also synthesized in adrenal gland). Positions 3, 11, 17, 18, and 21 are marked on the diagram of a steroid molecule (bottom right). Arrows indicate individual biosynthetic conversions. The enzyme specifically mediating each step is indicated at top or left with enzymatic activity in parentheses; note that one protein can mediate more than one step. OH hydroxyl; CMO, corticosterone methyl oxidase. [From White et al. 269 with permission.] B: Relation of renin activity in plasma samples obtained at noon and of corresponding 24 h urinary excretion of aldosterone to concurrent daily rate of sodium excretion. For normal subjects, data describe dynamic hyperbolic relationship between each hormone and sodium excretion. Dynamic fluctuations in renin in response to changes in sodium intake help to maintain blood pressure constant during wide changes in sodium balance. Renin and aldosterone responses work together in kidney to conserve or eliminate sodium in response to changes in dietary sodium intake. Subjects studied on random diets outside the hospital or while on carefully controlled diets in the hospital exhibited similar relationships, validating use of this nomogram in studying outpatients or subjects not receiving constant diets. [From Laragh and Sealey 140 with permission.]

Structures of steroid hormone receptor superfamily and transcriptional regulation by mineralocorticoid and glucocorticoid receptors. A: Receptors of steroid and other members of the superfamily along with mineralocorticoid receptor (MR) structure scheme. Solid black area represents DNA‐binding domain and hatched area, ligand‐binding region. [From Funder 89 with permission.] B: Transcriptional regulation by mineralocorticoid and glucocorticiod receptors (GR). Glucocorticoid hormones, such as Cortisol and corticosterone (Cort), and mineralocorticoids, such as aldosterone (Aldo), enter the cell and bind to mineralocorticoid‐glucocorticoid receptors; Cort activates both types of receptor, whereas at physiological concentrations Aldo activates only mineralocorticoid receptors. In cells expressing 11β‐hydroxysteroid dehydrogenase (11‐HSD) Cort is selectively metabolized and inactivated. Activated receptors enter the nucleus and bind to DNA sequences termed glucocorticoid‐response elements (GREs) (the mineralocorticoid receptor is shown here with Aldo bound; Cort is equally effective). Mineralocortoid and glucocorticoid receptors can each bind to simple and composite GREs, and both receptors enhance transcription from simple GREs. In contrast, glucocorticoid, but not mineralocorticoid, receptors alter transcription from the composite GRE; the direction of glucocorticoid receptor regulation depends on the subunit composition of the transcription factor activator protein‐1 (AP‐1), which also binds to the composite element. Hence, response elements are either promiscuous or selective in mediating the activities of different bound receptors. In addition, the pattern of regulation by a given response element is shaped by ligand availability, by 11‐HSD expression, and by the functional composition of nonreceptor factors (such as activator protein‐1) that interact with the receptor. PR, progesterone receptor; AR, androgen receptor; ER, estrogen receptor, T₃R, triiodothyronine receptor, RAR, retinoic acid receptor; VDR, vitamin D receptor. [From Funder 88 with permission.]

Urinary sodium excretion is displayed against plasma renin activity and urinary aldosterone. Data from Figure 9 replotted to illustrated mean urinary sodium excretion for given ranges of plasma renin activity and urinary aldosterone excretion. Differences in sodium excretion are significant at all higher rates, suggesting that angiotensin and aldosterone continue to exert regulatory effects on urinary sodium excretion even when circulating concentrations are low. [From Laragh and Sealey 140 with permission.]

Periodic fluctuations in urine sodium excretion, sodium balance, plasma renin activity, and urine aldosterone excretion after initiation of high‐sodium diet (270 mEq), preceded by 11 days of sodium deprivation (10 mEq/day). Mean values ± SD from three normal subjects. Each subject exhibited similar periodic fluctuations in urine sodium, renin, and aldosterone. After 4 days of diet, natriuresis occurred for 3 days, and these high levels of sodium excretion were associated with the lowest levels of plasma renin activity and aldosterone excretion. [From Sealey et al. 217 with permission.]

Angiotensin II infusion as a function of salt intake and angiotensin‐converting enzyme inhibition. A: Prolonged continuous angiotensin infusion in normal subject for 11 days. Dose of angiotensin adjusted to maintain mildly pressor response. Angiotensin II induced a marked and selective increase in adrenal cortical aldosterone secretion. Together with a direct effector of angiotensin II on proximal tubule sodium reabsorption, the rise in aldosterone caused sodium retention. As sodium was retained, angiotensin became more pressor. Because of this increasing pressor sensitivity to angiotensin, the dose of angiotensin II had to be serially reduced to maintain the same level of blood pressure. Consequently, aldosterone secretion fell to near control levels. Thus, pressor sensitivity to angiotensin increases as sodium retention produces and then sustains hypertension in progressively smaller amounts and sodium volume gain turns off the need for angiotensin. [From Laragh and Sealey 140 with permission.] B: When angiotensin II is fixed during changes in sodium intake, blood pressure increases with sodium loading and is at its lowest level with sodium depletion. Changes in mean arterial pressure during chronic changes in sodium intake in control dogs and in dogs during angiotensin II blockade with the converting enzyme inhibitor SQ 14,225 or during angiotensin II infusion (5 mg · kg⁻¹ · min⁻¹) also shown. Values are means ± SE. [From Hall et al. 101 with permission.]

Integrative aspects of the hormonal double‐cyclic feedback and renal synchronization. A: Interrelationship of the renin–aldosterone hormonal system with changes in sodium and potassium balance in the hormonal double‐cycle feedback loop. B: Coordination of intrarenal physical factors with hormonal factors for sodium and potassium homeostasis to highlight the significance of renal synchronization and the role of distal tubular supply. Rate of excretion of each cation is determined by interaction of aldosterone with distal tubular sodium supply. [From Laragh and Sealey 140 with permission.] C: Effect of sodium depletion on urine aldosterone excretion and potassium balance, combined results from five normal subjects. Despite hyperaldosteronism induced by sodium depletion, potassium, balance became progressively positive. Therefore, other factors counterbalance the kaliuretic action of aldosterone. An increase in the aldosterone: renin ratio most likely reflects a gradual increase in potassium balance; this change was accompanied by only modest increases in plasma potassium. [From Laragh and Sealey 140 with permission.]

Metabolism balance study of patient with pseudoprimary aldosteronism. Dotted lines indicate intake of potassium and sodium. Normal ranges for aldosterone secretion and for midday serum renin in ambient subjects of each dietary sodium intake are indicated by range bars. Aldosterone secretion was always markedly elevated, and serum renin levels were abnormally low. Responses of aldosterone and renin to manipulations in sodium intake were blunted. Potassium repletion was more easily accomplished when dietary sodium was reduced. [From Laragh and Sealey 140 with permission.]

Biphasic plasma renin activity levels in three animal models of progressive low‐renin syndrome. A: Sequential changes in systemic (aortic) and renal arterial pressure and plasma renin activity (PRA) in experimental benign hypertension. B: Responses in the conscious dog to thoracic inferior vena caval constriction and development of moderate congestive heart failure. MAP, mean arterial pressure. C: Plasma levels of glucose and renin activity in streptozotocin‐diabetic rats as a function of duration. [From Lush et al. 152 with permission.]

Biphasic plasma renin time line in generalized pathogenesis of renin‐related clinical disorders. The initial phase of pathogenesis is consistent with the definition of high‐renin state (HRS) because renin secretory expression is elevated at baseline and exaggerated when challenged. The later phase has been termed low‐renin syndrome (LRS) because an identical challenge results in impaired secretory expression. Although renovascular hypertension, congestive heart disease, diabetes mellitus, and essential hypertension have demonstrated the biphasic plasma renin profile, polycystic kidney disease, nephrotic syndrome, and chronic stress remain undetermined. [From King and Fray 132 with permission.]

Classification of post translational processing systems of regulatory peptides into three classes (A, B, C) and diagrammatic representation of three basic designs for processing of precursors to bioactive peptides. A: Some peptides (For example, renin, neurotensin) appear to be fully processed before secretion. B: Other peptides (for example, angiotensin, bradykinin) are formed primarily via extracellular cleavage of secreted precursors. C: Although speculative at this point, a third possibility involves processing after endocytosis by target or other cells (for example, mineralocorticoid receptors). E, enzyme; S, substrate; P, product; N, nucleus; ANP, atrial natriuretic peptide; ET‐1, endothelin‐I; LTC₄, leukotriene C₄; EGF, epidermal growth factor; TGFα, transforming growth factor‐α. [From Carraway and Loh 31 with permission.]