Sensitization of the Adrenal Cortex to Angiotensin II in Sodium-Deplete Man

Dysregulation of the renin-angiotensin system in septic shock: Mechanistic insights and application of angiotensin II in clinical management

Synergistic physiologic mechanisms involving the renin-angiotensin system (RAS), the sympathetic nervous system, and the arginine-vasopressin system play an integral role in blood pressure homeostasis. A subset of patients with sepsis experience septic shock with attendant circulatory, cellular, and metabolic abnormalities. Septic shock is associated with increased mortality because of an inadequacy to maintain mean arterial blood pressure (MAP) despite volume resuscitation and the use of vasopressors. Vasodilatory shock raises the dose of vasopressors required to maintain a MAP of > 65 mm Hg. The diminished response to endogenous angiotensin II in sepsis-induced vasoplegia may be related to the aberrant RAS activation that stimulates a proinflammatory beneficial antibacterial response, increasing the secretion of proinflammatory cytokines that downregulate AT-1 receptors expression. Moreover, excessive systemic upregulation of nitric oxide synthase, stimulation of prostaglandin synthesis, and activation of ATP-sensitive potassium channels followed by reduced vascular entry of calcium ions are putative mechanisms in the reduced responsiveness to vasopressors. However, intravenous angiotensin II in catecholamine-resistant septic shock patients showed substantial evidence of raising the MAP to target hemodynamic levels, thus allowing time to treat underlying conditions. Nevertheless, evidence of catecholamine-sparing effect by adding angiotensin II, aimed at increasing the therapeutic index of vasopressor therapy, does not show an attenuation of end-organ damage. The use of angiotensin II in septic shock has not been evaluated in patients who are not catecholamine resistant. This, in conjunction with an evolving definition of catecholamine resistance, provides an opportunity for further evaluation of exogenous angiotensin II in septic shock.

Effect of Increased Potassium Intake on Adrenal Cortical and Cardiovascular Responses to Angiotensin II: A Randomized Crossover Study

Background Increased potassium intake lowers blood pressure in patients with hypertension, but increased potassium intake also elevates plasma concentrations of the blood pressure-raising hormone aldosterone. Besides its well-described renal effects, aldosterone is also believed to have vascular effects, acting through mineralocorticoid receptors present in endothelial and vascular smooth muscle cells, although mineralocorticoid receptors-independent actions are also thought to be involved. Methods and Results To gain further insight into the effect of increased potassium intake and potassium-stimulated hyperaldosteronism on the human cardiovascular system, we conducted a randomized placebo-controlled double-blind crossover study in 25 healthy normotensive men, where 4 weeks treatment with a potassium supplement (90 mmol/day) was compared with 4 weeks on placebo. At the end of each treatment period, we measured potassium and aldosterone in plasma and performed an angiotensin II (AngII) infusion experiment, during which we assessed the aldosterone response in plasma. Hemodynamics were also monitored during the AngII infusion using ECG, impedance cardiography, finger plethysmography (blood pressure-monitoring), and Doppler ultrasound. The study showed that higher potassium intake increased plasma potassium (mean±SD, 4.3±0.2 versus 4.0±0.2 mmol/L; P=0.0002) and aldosterone (median [interquartile range], 440 [336-521] versus 237 [173-386] pmol/L; P<0.0001), and based on a linear mixed model for repeated measurements, increased potassium intake potentiated AngII-stimulated aldosterone secretion (P=0.0020). In contrast, the hemodynamic responses (blood pressure, total peripheral resistance, cardiac output, and renal artery blood flow) to AngII were similar after potassium and placebo. Conclusions Increased potassium intake potentiates AngII-stimulated aldosterone secretion without affecting systemic cardiovascular hemodynamics in healthy normotensive men. Registration EudraCT Number: 2013-004460-66; URL: https://www.ClinicalTrials.gov; Unique identifier: NCT02380157.

Roles of angiotensin II as vasopressor in vasodilatory shock

Shock is an acute condition of circulatory failure resulting in life-threatening organ dysfunction, high morbidity and high mortality. Current management includes fluid and catecholamine therapy to maintain adequate mean arterial pressure and organ perfusion. Norepinephrine is recommended as first-line vasopressor, but other agents are available. Angiotensin II is an alternative potent vasoconstrictor without chronotropic or inotropic properties. Several studies, including a large randomized controlled trial have demonstrated its ability to increase blood pressure with catecholamine-sparing effects. Angiotensin II was consequently approved by the US FDA in 2017 and the EU in 2019 as an add-on vasopressor in vasodilatory shock. This review aims to discuss its basic pharmacology, clinical efficacy, safety and future perspectives.

Clinical Experience With IV Angiotensin II Administration: A Systematic Review of Safety

OBJECTIVE

Angiotensin II is an endogenous hormone with vasopressor and endocrine activities. This is a systematic review of the safety of IV angiotensin II.

DATA SOURCES

PubMed, Medline, Scopus, and Cochrane.

STUDY SELECTION

Studies in which human subjects received IV angiotensin II were selected whether or not safety was discussed.

DATA EXTRACTION

In total, 18,468 studies were screened by two reviewers and one arbiter. One thousand one hundred twenty-four studies, in which 31,281 participants received angiotensin II (0.5-3,780 ng/kg/min), were selected. Data recorded included number of subjects, comorbidities, angiotensin II dose and duration, pressor effects, other physiologic and side effects, and adverse events.

DATA SYNTHESIS

The most common nonpressor effects included changes in plasma aldosterone, renal function, cardiac variables, and electrolytes. Adverse events were infrequent and included headache, chest pressure, and orthostatic symptoms. The most serious side effects were exacerbation of left ventricular failure in patients with congestive heart failure and bronchoconstriction. One patient with congestive heart failure died from refractory left ventricular failure. Refractory hypotensive shock was fatal in 55 of 115 patients treated with angiotensin II in case studies, cohort studies, and one placebo-controlled study. One healthy subject died after a pressor dose of angiotensin II was infused continuously for 6 days. No other serious adverse events attributable to angiotensin II were reported. Heterogeneity in study design prevented meta-analysis.

CONCLUSION

Adverse events associated with angiotensin II were infrequent; however, exacerbation of asthma and congestive heart failure and one fatal cerebral hemorrhage were reported. This systematic review supports the notion that angiotensin II has an acceptable safety profile for use in humans.

Adrenomedullin 2 attenuates the pressor but not adrenal responses to angiotensin II in conscious sheep

Biological actions attributed to the adrenomedullin (AM) peptides, AM and AM2, include reduction of arterial pressure and peripheral resistance. While AM has been shown to reduce aldosterone secretion from the adrenal, little information is available regarding possible actions of AM2 on aldosterone. Evidence suggests that AM may act as a functional antagonist to angiotensin II (Ang II) but such a role has not been investigated for AM2. Accordingly, we have examined hemodynamic and adrenal responses to stepped Ang II infusions with or without co-infusions of AM2 (33ng/(kgmin)) in conscious sheep under controlled conditions of a low sodium intake. The dose-dependent pressor response (5-50mmHg) of Ang II was both delayed and attenuated (p<0.001) by AM2 which also stimulated heart rate (p<0.001) and cardiac output (p<0.001). AM2 prevented Ang II-induced increases in peripheral resistance (p<0.001). In contrast, plasma aldosterone responses to Ang II were not significantly altered by concomitant AM2 infusion. In conclusion, low dose infusion of AM2 administered to conscious sheep on a low salt diet clearly antagonized the vasopressor action of administered Ang II while stimulating cardiac output and heart rate. In contrast to AM, AM2 had no restraining influence on the aldosterone response to Ang II. The data suggest a possible role for AM2 in cardiovascular homeostasis in part through antagonism of the vasopressor action of Ang II.

Body fluid volumes and the response of renin and aldosterone to short- and long-term thiazide therapy of essential hypertension

Plasma volume (PV), extracellular fluid volume (ECV) serum electrolytes, renin and aldosterone were measured before and after 1 week and 4 months of hydrochlorothiazide (HCT) treatment, 50 mg twice daily, in nine male patients with uncomplicated essential hypertension. All studies were carried out under strictly standardized conditions in a metabolic ward. After 1 week of HCT treatment, significant reductions were found in PV and ECV, but after 4 months only ECV was significantly reduced. During HCT therapy, renin and aldosterone were permanently elevated whereas serum sodium and potassium were lowered. After 1 week, renin was inversely correlated with PV and ECV and directly correlated with heart rate. After 4 months, renin was inversely correlated with serum sodium. These results indicate a permanent decrease in ECV during long-term HCT therapy. It is further suggested that the mechanisms responsible for the renin response during short- and long-term HCT treatment are different, changes in body fluid volumes and increased neural activity being responsible for the initial rise in renin, and serum sodium being the predominant factor during chronic treatment.

Influence of sodium intake on hydrochlorothiazide-induced changes in blood pressure, serum electrolytes, renin and aldosterone in essential hypertension

To determine the influence of dietary sodium intake on the effects of hydrochlorothiazide (HCT) on blood pressure (BP), serum electrolytes, renin and aldosterone, nine male patients with uncomplicated essential hypertension were studied during the following therapeutic regimes: 1) sodium restriction alone (50 mmol/day), 2) sodium restriction combined with HCT (50 MG TWICE DAILY), 3) HCT alone, and 4) sodium restriction combined with HCT. Low sodium diet alone and HCT alone lowered BP to the same extent. The combination of HCT and sodium restriction had no extra effect on supine BP, but elicited complaints of dizziness and weakness in each patient, and overt orthostatic hypotension in three cases. Sodium restriction during HCT treatment caused hyponatraemia and aggravated hypokalaemia. Hyponatraemia could not be accounted for solely by changes in cumulative sodium balance. Plasma renin concentration rose markedly during the combined treatment. Plasma aldosterone was normal during HCT alone, but elevated when HCT was combined with sodium restriction. These results cast some doubt on the therapeutic value of prescribing a low sodium diet to patients with essential hypertension treated with thiazide diuretics. Overactivity of the renin-angiotensin-aldosterone system during this regime might explain both the lack of a beneficial effect on BP and the adverse influence on serum potassium.

Altered corticosteroid biosynthesis in essential hypertension: A digenic phenomenon

Aldosterone plays an important role in electrolyte and blood pressure homeostasis. Our studies have focused on the role of aldosterone in essential hypertension. We have shown that plasma aldosterone and ARR are heritable characteristics and that aldosterone concentrations in older subjects are inversely correlated with birthweight and positively correlated with blood pressure. Aldosterone levels are also associated with polymorphic variation in the CYP11B2 gene, which encodes aldosterone synthase, the enzyme responsible for aldosterone production. Interestingly, CYP11B2 polymorphisms are also associated with less efficient activity of 11beta-hydroxylase, encoded by the neighbouring, highly homologous CYP11B1 gene. We propose that a digenic effect leads to increased aldosterone production, with inefficient 11beta-hydroxylation causing a long-term increase in ACTH drive to the adrenal gland and enhanced expression of CYP11B2, thereby resulting in chronically raised aldosterone secretion in response to factors such as angiotensin II and potassium. In susceptible subjects this is likely, over many years, to result in hypertension with relative aldosterone excess.

Unilateral renal ischemia causing the hyponatremic hypertensive syndrome in children--more common than we think?

A case report in the journal Pediatric Nephrology describes a 15-month-old girl with the syndrome of hypertension and hyponatremia (HH syndrome) due to underlying unilateral renal artery stenosis. This syndrome is typically associated with hypokalemia and severe volume depletion and sometimes proteinuria, all of which, along with hypertension and hyponatremia, are usually corrected by resolution of the underlying renal ischemia. Gross and probably sudden activation of the renin-angiotensin system in response to renal ischemia is central to the pathophysiology although the cardiac atrial and B-type natriuretic peptides probably contribute also. Initial control of the severe hypertension may, in some cases, require careful volume repletion prior to introduction of blockade of the renin-angiotensin system in order to avoid first-dose hypotension, after which correction of the underlying renal ischemia is required. Whereas the syndrome has rarely been reported in children, it is possible that, as in adults, this reflects its lack of recognition by clinicians. The HH syndrome due to unilateral renal ischemia in children may be much more common than we think.

Adrenomedullin and the renin-angiotensin-aldosterone system

Despite its positive inotropic effects and its propensity to stimulate the renin system, adrenomedullin (AM) is hypotensive as a result of dramatic reductions in peripheral resistance. Furthermore, it does not appear to increase aldosterone secretion in spite of often vigorous activation of circulating renin. Hence, we postulate that AM may act as a functional antagonist to angiotensin II both in the vasculature and the adrenal glomerulosa. In the series of studies performed in sheep and human (normal and circulatory disorders) reviewed here, we report significant hemodynamic and hormonal actions of AM. These actions include consistent reduction of arterial pressure associated with rises in cardiac output and hence a dramatic reduction in calculated total peripheral resistance (CTPR). AM also consistently attenuates the pressor effects of angiotensin II (but not norepinephrine). Furthermore, AM consistently increases plasma renin activity (PRA) and induces either a reduction in plasma aldosterone, dissociation between aldosterone/PRA ratio, or attenuation of angiotensin II-induced aldosterone secretion. Thus, these results clearly point to a role for AM in pressure and volume homeostasis acting, at least in part, by interaction with the renin-angiotensin-aldosterone system (RAAS).

Disorders of mineralocorticoid synthesis

Abnormalities of mineralocorticoid synthesis and/or metabolism profoundly affect the regulation of electrolyte and water balance and of blood pressure. Characteristic changes in extracellular potassium, sodium and hydrogen ion concentrations are usually diagnostic. Serious deficiency may be acquired, for example in Addison's disease, or inherited. In most of the inherited syndromes, the precise molecular changes in specific steroidogenic enzymes have been identified. Mineralocorticoid excess may be caused by aldosterone or 11-deoxycorticosterone by inadequate conversion of cortisol to cortisone by 11beta-hydroxysteroid dehydrogenase type 2 in target tissues (see Chapter 4), by glucocorticoid receptor deficiency or by constitutive activation of renal sodium channels. Changes in electrolyte balance and renin as well as the abnormal pattern of corticosteroid metabolism are usually diagnostic. Where these abnormalities are inherited (e.g. 11beta- or l7alpha-hydroxylase deficiencies, glucocorticoid remediable hyperaldosteronism (GRA), receptor defects, Liddle's syndrome), the molecular basis is again usually known and, in some cases, may provide the simplest diagnostic tests. Primary aldosteronism, although readily identifiable, presents problems of differential diagnosis, important because optimal treatment is different for each variant. Moreover, the mechanisms by which the variants develop are poorly understood. Finally, a significant proportion of patients with essential hypertension show characteristics of mild mineralocorticoid excess, for example low renin levels. Is this relevant to pathophysiology and, if so, is the effect induced via classic mechanisms of action or through newly discovered direct actions on the brain, heart and blood vessels? These questions are the subject of current research.

Adrenomedullin attenuates pressor response to angiotensin II in conscious sheep

Biologic actions attributed to adrenomedullin include reduction of arterial pressure and suppression of aldosterone secretion. To assess possible in vivo antiangiotensin II actions of adrenomedullin, we examined hemodynamic and adrenal responses to stepped angiotensin II infusions with or without co-infusions of adrenomedullin (33 ng/kg/min) in conscious sheep under controlled conditions of a low sodium intake. Plasma adrenomedullin levels rose during peptide infusions (p < 0.001) to plateau at approximately 15-18 pM. The dose-dependent pressor response (15-20 mm Hg) of angiotensin II was both delayed and markedly attenuated (p = 0.017) by adrenomedullin, which also stimulated heart rate (p < 0.001) and cardiac output (p < 0.001). Adrenomedullin prevented the angiotensin II-induced increase in peripheral resistance (p < 0.001). Plasma aldosterone responses to angiotensin II were variable and were not significantly altered by concomitant adrenomedullin infusion. In conclusion, low-dose infusion of adrenomedullin administered to conscious sheep on a low-salt diet clearly antagonized the vasopressor actions of administered angiotensin II while stimulating cardiac output and heart rate. The data suggest a possible role for adrenomedullin in cardiovascular homeostasis in part through antagonism of the vasopressor action of angiotensin II.

Hyponatremic-hypertensive syndrome with renal ischemia: an underrecognized disorder

Renal artery stenosis or occlusion causing the hyponatremic-hypertensive syndrome has been rarely reported. Our impression, however, was that the disorder is not uncommon. Case records from patients in one city (population 350 000) presenting between 1980 and 1997 with hypertension, hyponatremia, and evidence of renal ischemia were scrutinized. Thirty-two patients fulfilling inclusion criteria were identified. Admission supine arterial pressures were high (mean 228/124 mm Hg), but there was a vigorous fall in pressure on standing (26/12.7 mm Hg recorded in 27 patients). Mean plasma concentrations of sodium (129.7 mmol/L) and potassium (2.7 mmol/L) were low, and 24-hour urine protein excretion was elevated in 19 of 26 patients. Twenty-two of the 32 patients were female, the majority were asthenic, and all but 5 were smokers. Symptoms precipitating hospitalization were headache, clouding of consciousness, confusion, weakness, weight loss, thirst, and polyuria. Plasma renin levels, measured in 20 patients, were elevated in most cases and correlated inversely (r=-0.63, P<0.01) with the plasma sodium concentration. The hyponatremic-hypertensive syndrome in patients with renal ischemia is not rare: Rather, it is underreported. It tends to affect elderly asthenic women who smoke heavily. Stimulation of renin release from the ischemic kidney is probably central to the pathophysiology. The syndrome deserves better recognition to ensure appropriate investigations and management.

Aldosterone release during the sleep-wake cycle in humans

The aim of this study was to assess the relative influence on the 24-h aldosterone profile of the adrenocorticotropic system, primarily modulated by a circadian rhythmicity, and the renin-angiotensin system, which is influenced by sleep. Cortisol, plasma renin activity (PRA), and aldosterone were measured for 24 h in healthy subjects under basal conditions, once with nocturnal sleep and once with a night of sleep deprivation followed by 8 h of daytime sleep. The sleep period displayed high mean aldosterone levels, pulse amplitude, and frequency that were reduced during waking periods. During sleep, aldosterone pulses were mainly related to PRA oscillations, whereas they were mainly associated with cortisol pulses during waking periods. Cross-correlation analysis between sleep electroencephalographic activity in the delta band and aldosterone levels yielded significant results, aldosterone following delta waves by approximately 30 min. This study demonstrates that the 24-h aldosterone profile is strongly influenced by sleep processes. A dual influence, by the renin-angiotensin system during sleep and by the adrenocorticotropic system during wakefulness, is exerted on aldosterone pulses throughout the 24-h period.

Hypothesis: aldosterone is synthesized by an alternative pathway during severe sodium depletion. 'A new wine in an old bottle'

1. The last three steps of aldosterone biosynthesis, 11 beta-hydroxylation, 18-hydroxylation and 18-oxidation, have been demonstrated to be catalysed by one enzyme, which is the cytochrome P450(11 beta) (CYP11B) in cow, pig, sheep and bullfrog or cytochrome P450aldo (CYP11B2) in rat, human, mouse and hamster. 2. The related enzyme P450(11 beta) (CYP11B1) from rat, human, mouse and hamster adrenals displays 11 beta-hydroxylation and 18-hydroxylation activities, but not 18-oxidation activity in vitro. No such enzyme has been reported in the cow, pig or sheep to date. 3. Data showing the dissociation of aldosterone secretion from plasma angiotensin II (AngII) levels indicate the presence of other factor(s) that regulate aldosterone biosynthesis in response to changes in body sodium status. Thus, we propose the existence of a 'sodium status factor' that regulates aldosterone biosynthesis in addition to AngII, K+, adrenocorticotropic hormone and atrial natriuretic peptide. 4. We propose that during severe sodium deficiency there is a switch in the aldosterone pathway to a pathway using 18-hydroxy-deoxycorticosterone (18-OH-DOC) rather than corticosterone as an intermediate. This switch may be mediated via the putative 'sodium status factor'. 5. Two models of the hypothesis will be discussed in this paper: (i) a 'one-enzyme' model; and (ii) a 'two-enzyme' model. 6. The one-enzyme model proposes that P450aldo (P450(11 beta) as in the case of the cow, sheep and pig) changes its enzymatic activity during severe sodium deficiency (i.e. switching to the alternative aldosterone biosynthesis pathway). 7. The two-enzyme model proposes that, under normal circumstances, P450aldo synthesizes aldosterone from deoxycorticosterone, while during severe sodium deficiency the P450(11 beta) provides the substrate (i.e. 18-OH-DOC) for the P450aldo.

Losartan blocks aldosterone and renal vascular responses to angiotensin II in humans

In vitro and animal studies have demonstrated that the effect of angiotensin II (Ang II) on aldosterone is mediated through the Ang II type 1 receptor. However, it has been difficult to demonstrate an effect of Ang II type 1 receptor blockade on aldosterone levels in human studies. One possible explanation is that subjects have not been studied under salt-controlled conditions. Therefore, we examined the effects of losartan on the aldosterone and renal plasma flow responses to Ang II infusion in six normotensive subjects under low and high salt conditions. Ang II was infused in graded doses (0.3 to 10 ng/kg per minute) in the presence and absence of losartan (a single 50-mg oral dose). Renal plasma flow was assessed by measurement of para-aminohippurate clearance. Blood pressure, plasma aldosterone levels (low salt conditions only), and para-aminohippurate clearance were measured before and after each Ang II dose. Losartan had no effect on baseline systolic pressure but attenuated the systolic pressure response to exogenous Ang II during both low salt (0.7 +/- 1.9 versus 6.7 +/- 1.4 mm Hg, P = .001) and high salt (2.0 +/- 1.9 versus 12.3 +/- 2.1 mm Hg, P = .006) conditions. Under low salt conditions, losartan reduced the baseline plasma aldosterone level from 1135 +/- 204 to 558 +/- 102 pmol/L (P = .015) and blocked the aldosterone response to Ang II (-49 +/- 110 versus +436 +/- 83 pmol/L, P = .019). During high salt conditions, losartan had no effect on baseline renal plasma flow but attenuated the renal plasma flow response to Ang II (-90.1 +/- 15.1 versus -185.1 +/- 2.6 mL/min per 1.73 m2, P = .013). These data confirm that losartan lowers both basal and exogenous Ang II-stimulated aldosterone levels under low salt conditions. Losartan does not significantly affect baseline renal plasma flow but does attenuate the renal plasma flow response to exogenous Ang II under high salt conditions.

Genetic approaches to understanding the pathophysiology of complex human traits

Genetic approaches to understanding the pathophysiology of complex human traits, for example, hypertension, can complement physiologic analyses and are likely to improve our ability to treat or prevent the disease. A particularly useful approach is to perform linkage analysis with candidate genes using intermediate phenotypes. This has proven successful so far in identifying two genes involved in hypertension. The first was a fusion gene mutation which linked the regulatory region of the 11B-hydroxylase gene to the coding sequence for the protein of aldosterone synthetase. This mutant gene is responsible for the condition glucocorticoid-remediable aldosteronism (GRA). The intermediate phenotype used was increased levels of the adrenal steroids 18-oxo and hydroxycortisol. The gene for GRA was identified using a pedigree approach. It is likely, to identify other genes in hypertension, that the most appropriate population to be affected would be sib pairs, that is, sibling pairs who both have hypertension. In a recent study the angiotensinogen gene also was linked to hypertension in individuals who had severe or early onset hypertension. In addition, a variant of the angiotensinogen gene, substitution of threonine rather than methionine at codon 235, was specifically associated with hypertension. In a separate study, the T235 homozygote of the angiotensinogen gene was associated with the non-modulating intermediate phenotype of essential hypertension. Since converting enzyme inhibitors appear to correct the specific defect underlying the elevated blood pressure in non-modulators, identification of the gene potentially associated with non-modulation raises the strong possibility that genetic screening will allow for more specific therapy.

Role of 21-deoxyaldosterone in human hypertension

21-Deoxyaldosterone has been postulated to be a precursor of aldosterone in an alternative biosynthesis pathway and Kelly's-M1 is considered to be its metabolite. In healthy volunteers, the excretion rate of 21-deoxyaldosterone and of Kelly's-M1 are significantly lower than the aldosterone metabolites, aldosterone-18-glucuronide and tetrahydro-aldosterone and than the aldosterone precursor 18-OH-corticosterone. Essential hypertension patients (with low and normal renin) excrete comparable values of 21-deoxyaldosterone and Kelly's-M1 as normotensives. In 66% of aldosterone-producing adenoma cases (APA) and in 60% of idiopathic hyperaldosteronism (IHA) patients, significantly raised values of 21-deoxyaldosterone and Kelly's-M1 were found. The patients with the high excretion rates of both steroids showed only moderately increased values of the aldosterone metabolites, aldosterone-18-glucuronide and tetrahydro-aldosterone, as well as of the aldosterone precursor 18-OH-corticosterone. In contrast, the latter mentioned steroids were excreted in higher amounts in those patients with normal excretion of 21-deoxyaldosterone and Kelly's-M1. Hence, it is suggested that aldosterone is produced alternatively either via 18-OH-corticosterone alone or additionally via 21-deoxyaldosterone. Furthermore, in three cases of "incidentally" discovered adrenal adenomas, 21-deoxyaldosterone and Kelly's-M1 were the only elevated steroids. After adrenalectomy, excretion of 21-deoxyaldosterone and of Kelly's-M1 and blood pressure returned to normal, which proves that these steroids play a role in blood pressure regulation. In essential hypertension, ACTH infusion induced a significant increase of 21-deoxyaldosterone and Kelly's-M1. However, the increase after angiotensin II was 3- to 6-fold higher than after ACTH. IHA patients proved to be more responsive to angiotensin II; and, in contrast, APA cases proved to be more sensitive to ACTH. The data suggest that beside the main route of aldosterone biosynthesis via 11-deoxycorticosterone, corticosterone and 18-OH-corticosterone an alternative pathway exists via 21-deoxyaldosterone in healthy and in hypertensive patients. There are similarities between the regulation of 21-deoxyaldosterone and the regulation of aldosterone. The determination of 21-deoxyaldosterone and its possible metabolite Kelly's-M1 might be appropriate in the diagnosis of mineralocorticoid-induced forms of hypertension, especially when an adrenal adenoma is discovered.

Chronic inhibition of bradykinin B2-receptors enhances the slow vasopressor response to angiotensin II

The contribution of endogenous kinins in the regulation of blood pressure of angiotensin-treated rats was evaluated using the new bradykinin B2-receptor antagonist Hoe 140 (D-Arg,[Hyp3,Thi5,D-Tic7, Oic8]-bradykinin). Chronic infusion of Hoe 140 at 75 nmol/d (a dose able to inhibit the vasodepressor effect of an intra-aortic bolus injection of 0.85 nmol/kg bradykinin) did not alter systolic blood pressure (tail-cuff plethysmography). Chronic infusion of angiotensin II (Ang II) induced a dose-related increase in systolic blood pressure and plasma Ang II levels. The vasopressor effect of 40 or 100 nmol/d Ang II was enhanced in rats given chronic infusion of Hoe 140 (by 12 and 14 mm Hg, respectively), whereas the increase in plasma Ang II levels remained unaltered. Furthermore, a low nonpressor dose of Ang II (20 nmol/d) was then able to increase blood pressure during chronic blockade of bradykinin receptors by Hoe 140 (from 126 +/- 3 to 137 +/- 3 mm Hg, P < .05). Combined infusion of 20 nmol Ang II and Hoe 140 did not alter the urinary excretion of sodium and water despite the fact that blood pressure was increased. Potentiation of the pressure effect of Ang II by Hoe 140 was confirmed by direct measurement of mean blood pressure (125 +/- 2 versus 108 +/- 2 mm Hg at 20 nmol, 123 +/- 2 versus 110 +/- 2 mm Hg at 40 nmol, and 139 +/- 2 versus 125 +/- 3 mm Hg at 100 nmol Ang II, P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic factor and changes in the aldosterone response to angiotensin II in sodium depleted dogs

The effects of physiological shifts in plasma atrial natriuretic factor (ANF) concentrations on angiotensin II/aldosterone relationships during changes in sodium status were assessed in 6 conscious beagle dogs. Incremental infusions of angiotensin II (3, 9 and 27ng/kg/min) were administered on three occasions. The animals were studied in sodium replete and deplete states and on a third occasion, again while sodium deplete, with a background constant low-dose infusion of ANF (1.5pmol/kg/min) sufficient to enhance the low endogenous plasma ANF values observed in sodium depletion to match those observed in the sodium replete state. Sodium depletion caused a leftward shift and steepened the slope of the relationship between achieved arterial angiotensin II concentrations and the plasma aldosterone response. This effect was significantly attenuated (approximately 50%) by the low dose ANF infusions which tended to flatten the slope of the angiotensin II/aldosterone curve (ns) and shifted it significantly to the right (p < 0.05). These data suggest subtle shifts in endogenous levels of plasma ANF, accompanying changes in sodium status, are a major contributor to the associated alterations in angiotensin II/aldosterone relationships. Low dose ANF also significantly reduced the effect of angiotensin II on arterial pressures but did not alter natriuresis.

Effect of inhibition of endopeptidase 24.11 on responses to angiotensin II in human volunteers

The effects of endopeptidase 24.11 inhibition on angiotensin-induced changes in plasma angiotensin II, aldosterone, and atrial natriuretic factor concentrations and blood pressure were assessed in normal volunteers. Two groups, each consisting of eight normal volunteers, received stepwise infusions of angiotensin II (2, 4, and 8 ng/kg per minute) on day 5 of dose administration with 25 mg every 12 hours (group 1) or 100 mg every 12 hours (group 2) of an oral inhibitor of endopeptidase 24.11 (UK 79300, candoxatril) or placebo in balanced randomized, double-blind, placebo-controlled crossover studies. Both doses of candoxatril significantly enhanced achieved plasma angiotensin II concentrations during infusions (group 1, p < 0.001; group 2, p < 0.01; overall treatment effect for combined data, p < 0.001). This effect was most pronounced at the highest dose of angiotensin II (treatment-time interaction, p < 0.0001 for combined data) and tended to be more marked with the higher dose of candoxatril (treatment-group interaction, p = 0.08). The pressor response to angiotensin II was clearly enhanced by the lower dose of candoxatril; peak systolic and diastolic pressures exceeded placebo values by approximately 10 mm Hg (p < 0.001 and p < 0.05 for systolic and diastolic pressures, respectively). This effect of candoxatril was absent in group 2, which (unlike group 1) had exhibited a modest natriuretic response (sustained cumulative negative sodium balance, -70 +/- 21 mmol; p < 0.01) to the higher dose of inhibitor. Baseline plasma aldosterone concentrations and the incremental aldosterone response to angiotensin II infusions were not significantly altered by low-dose (group 1) candoxatril.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased EGF binding and EGFR mRNA expression in rat aorta with chronic administration of pressor angiotensin II

This study examines the changes in the mRNA expression of epidermal growth factor (EGF), EGF receptor (EGFR), platelet derived growth factor (PDGF-B), and transforming growth factor beta (TGF-beta 1) before and after sustained pressor infusion of angiotensin II (Ang II) for 4 weeks. A threefold increase occurred in the levels of EGFR mRNA (17,240 +/- 827 vs 6403 +/- 1372 units, P less than 0.01) and TGF-beta 1 mRNA (1644 +/- 584 vs 475 +/- 30 units, P less than 0.01) only in the aorta and not in the heart and kidney tissues. This increase in both of the above mRNA transcripts highly correlated (r = 0.96 and 0.92, P less than 0.01) with the elevation of blood pressure. The specific binding of 125I-labeled EGF to aortic membranes also increased (11,429 +/- 728 vs 8630 +/- 420 cpm/mg protein, P less than 0.05) with a parallel increase in the protein tyrosine kinase activity of the membranes indicating that the enhanced EGFR mRNA expression resulted in increased activity of a functional receptor. No significant changes were observed in either EGF mRNA or PDGF-B mRNA levels. These findings suggest that EGFR and TGF-beta 1 participate in the long-term progressive pressor response to Ang II and thus potentially in the progression and the maintenance of chronic hypertension.

Effects of sodium salts on pressor reactivity in salt-sensitive men

Blood pressure in patients with essential hypertension is raised by sodium chloride but not by nonchloride sodium salts. Although a high sodium chloride diet is known to augment the pressor response to norepinephrine and angiotensin II, the effect of nonchloride sodium salts on pressor responsiveness has not been studied so far. To examine whether sodium chloride and nonchloride sodium salts evoke different pressor responses to these agonists, we performed graded norepinephrine and angiotensin II infusions in salt-sensitive (n = 7) and salt-resistant (n = 8) normotensive subjects. The subjects were given a low salt diet (20 mmol/day) for 3 weeks, to which a supplement of 200 mmol sodium per day, provided as either sodium chloride or sodium citrate, or a placebo was added for 1 week each. We found that, although sodium chloride raised mean arterial blood pressure in the salt-sensitive subjects (p less than 0.005), sodium citrate did not. However, under both sodium salts pressor response to norepinephrine and angiotensin II was significantly greater than under placebo (p less than 0.02). Furthermore, with both sodium salts, pressor response in the salt-sensitive subjects was greater than in the salt-resistant subjects (p less than 0.01). This study thus demonstrates that, although blood pressure in salt-sensitive individuals is raised by sodium chloride only, both sodium chloride and sodium citrate evoke similar increases in pressor response to norepinephrine and angiotensin II. Since pressor response increased with both sodium salts but resting blood pressure increased only with sodium chloride, enhanced pressor responsiveness alone cannot account for the sodium chloride-induced rise in resting blood pressure.

Renal and adrenal responsiveness to angiotensin II: influence of beta adrenergic blockade

The increase in aldosterone secretion that occurs in response to Angiotensin II (AII) is enhanced when normal humans are in external balance on a low salt diet. The responsible mechanism has not been identified. Angiotensin converting enzyme inhibition reduces blood levels of AII and aldosterone, but does not decrease PRA or AI and does not modify adrenal responsiveness to AII in the sodium-depleted state. This study was designed to assess the possibility that the enhanced adrenal response reflects plasma renin activity (PRA), plasma AI concentration, or catecholamines acting via a beta adrenergic receptor. Nine healthy males were studied when in balance on a high sodium intake (200 mmol Na/day), a low sodium diet (10 mmol Na) and after 4 days of beta adrenergic blockade with either nadolol or propranolol. The adequacy of beta adrenergic blockade was assessed with a postural stimulus and significant blockade was achieved, somewhat more with nadolol (40 mg/day) than with propranolol (Inderal LA, 80 mg every 12 hrs). Beta blockade enhanced the renal vascular and pressor response to AII but did not modify the adrenal response to posture or to AII. This study confirms the role for AII levels in the modulation of renal vascular and pressor responses to AII and rules out a role for PRA, AI, or catecholamines acting via a beta adrenergic receptor in the modulation of adrenal responsiveness to AII.

The origin and significance of 18-hydroxycortisol: studies in hyperaldosteronism and in bovine adrenocortical cells in vitro

18-Hydroxycortisol has been suggested as a marker compound for a transitional zone between the adrenocortical zonae glomerulosa and fasciculata. The control of secretion of 18-hydroxycortisol has been compared with those of cortisol and aldosterone in normal subjects and patients with primary hyperaldosteronism. Comparisons were also made in isolated bovine zona glomerulosa and zona fasciculata cell preparations. Although there was considerable cross-contamination between fractions, 18-hydroxycortisol secretion occurred with equal facility in both fractions but depended on the availability of cortisol as substrate. Changes in secretion during stimulation following those of cortisol. It is concluded that, in vivo, 18-hydroxycortisol derives mainly from the zona fasciculata. The relevance of these findings to primary hyperaldosteronism and to the nature of the transition is discussed.

Dissociation in plasma renin and adrenal ANG II and aldosterone responses to sodium restriction in rats

In rats, plasma renin activity (PRA) increases sharply, reaching a plateau within hours of sodium restriction. Plasma aldosterone increases gradually, not reaching a plateau for 1-2 days. To determine whether this dissociation is secondary to the time needed to modify adrenal sensitivity to angiotensin II (ANG II) and to assess the role of locally produced ANG II in this process, rats were salt restricted for 0-120 h. Plasma hormone levels were assessed, adrenal ANG II was measured, and basal and ANG II (1 x 10(-8) M)-stimulated steroidogenesis were determined in vitro. Although PRA attained an elevated plateau within 8 h, plasma aldosterone did not peak until after 48 h of sodium depletion. The in vitro aldosterone sensitivity to exogenous ANG II was not apparent until rats had been salt restricted for 16 h. A plateau (4-fold increase above the ANG II response on high salt) was achieved between 24 and 48 h. Adrenal ANG II also exhibited a similar delayed response that correlates significantly with changes in aldosterone biosynthesis and late pathway activity. Thus the dissociation between PRA and plasma aldosterone may be secondary to a lag in the zona glomerulosa's (ZG) steroidogenic response to ANG II as well as a parallel lag in tissue ANG II production, suggesting that changes in tissue ANG II may mediate ZG sensitivity to ANG II during sodium deprivation.

Arteriovenous ratios of angiotensin II during acute infusion experiments: a model-based analysis

The hormone angiotensin II (AII) is a vasoconstrictor known to participate in the natural regulation of blood pressure via the renin-angiotensin system. A third-order model was developed which describes the dynamics of venous and arterial plasma AII concentrations (PAC) and mean arterial blood pressure (BP) during acute constant rate AII infusion experiments. The model is calibrated using approximate blood circulation rates and steady-state PAC and BP data for published experiments in sheep. Analysis of the dynamic model demonstrates that local changes in PAC during the first several minutes of acute infusion are characterized by the comparatively rapid distribution of exogenous AII making its forward passage across the blood circulation, combined with the more gradual elevation of exogenous AII recycled through the circulation. This analysis explains the observed divergence in physiological levels of venous and arterial PAC at steady state in terms of the monotonic net clearance of elevated levels of circulating AII along the circulatory path between the point of infusion and the two sites at which the PAC measurements are taken. The model suggests that the differing arteriovenous AII concentration ratios and differing PAC and BP relationships reported for different dose-response experiments may be explained in part by differences in the specific infusion and measurement sites employed in those experiments.

Sodium-sensitive essential hypertension: emerging insights into an old entity

Essential hypertension has long been assumed to be a multifactorial disease. However, recent evidence suggests that it is a syndrome rather than a disease with a common symptom--an elevated blood pressure. One large segment of the hypertensive population--approximately 60%--has in common an increased blood pressure sensitivity to salt intake. Further analysis of this subgroup suggests that it is also heterogeneous, consisting of at least six major entities: renal parenchymal disease, bilateral renal artery stenosis, primary aldosteronism, acromegaly, low renin essential hypertension, and the most recently described entity--nonmodulating essential hypertension. This subset's name is derived from the fact that sodium intake does not modify (modulate) renovascular and adrenal responses to angiotensin II, as occurs in normotensives and modulating hypertensive patients. The following abnormalities have been reported in these patients: (1) a failure of renal blood flow to increase with salt loading; (2) a reduced ability to excrete a salt load; (3) reduced renin suppression both by salt and angiotensin II; and (4) a hypertensive response to salt load. These patients also have a strong family history for hypertension and an increase in erythrocyte sodium countertransport. With a better understanding of the mechanisms underlying the elevated blood pressure in a specific patient, a more rational approach to therapy is possible. For example, in the salt-sensitive hypertensive patient a diuretic would be the presumed treatment of choice. While this is correct for some salt-sensitive hypertensives, in nonmodulators diuretics may be relative ineffective while converting enzyme inhibitors may be more effective because they specifically correct the underlying pathophysiologic derangement.

Basal and saline-stimulated levels of plasma atrial natriuretic factor in acromegaly

We have studied plasma ANF before and after a 4-h intravenous infusion of normal saline in eight subjects with active acromegaly and in eight age and sex-matched control subjects. Plasma ANF, serum aldosterone and blood pressure were measured basally and after 2 and 4 h and plasma renin activity basally and after 4 h. Basal plasma ANF was similar in each group (4.4 +/- 1.5 pmol/l (mean +/- SEM) in acromegalic subjects and 5.3 +/- 0.7 pmol/l in controls NS). Plasma ANF did not rise significantly after saline in the acromegalic group (2-h value, 5.9 +/- 0.9; 4-h value, 5.1 +/- 0.9 pmol/l) but did rise significantly in the control group (2-h value, 8.9 +/- 1.9; 4-h value 9.5 +/- 1.3 pmol/l, both values P less than 0.05 vs basal level). The 4-h ANF value was significantly higher in the control group than in the acromegalic group (P less than 0.05). Basal and stimulated serum aldosterone values were similar in the two groups. Plasma renin activity suppressed to a lesser extent in the acromegalic group after 4 h. The facts that basal plasma ANF was not raised in acromegalic subjects and did not respond to saline stimulation demonstrate that an abnormality of ANF control may be an important factor in the aetiology of the expanded sodium status of patients with acromegaly and hence may contribute to the hypertension seen in patients with growth hormone excess.

The effect of angiotensin II and noradrenaline alone and in combination on renal sodium excretion in man

1. The renin-angiotensin-aldosterone-system is important for the maintenance of sodium balance in man. Recent animal evidence suggests the angiotensin II can modulate the effect of the renal sympathetic nervous system on renal function. We have investigated the possible interaction of physiological doses of angiotensin II and noradrenaline on sodium excretion in man. 2. Seven normal volunteers were studied on four occasions during maximum water diuresis sustained by oral hydration. Samples were obtained during a baseline and four subsequent 20 min periods (A-E). Placebo or noradrenaline was infused over periods B-E, and angiotensin II infused over period C. 3. There was no change in systemic blood pressure, heart rate or creatinine clearance caused by infusion of either angiotensin II, noradrenaline or both in combination. 4. Noradrenaline alone caused a significant fall in absolute and fractional sodium excretion. Angiotensin II when infused with placebo caused a 37% fall in absolute sodium excretion and a 32% fall when infused with noradrenaline (no significant difference between the 2 days). Similar changes were seen for urinary flow and fractional sodium excretion. 5. We have therefore found no evidence to support a postsynaptic interaction of low doses of angiotensin II and noradrenaline on renal sodium excretion in man.

Prolonged converting enzyme inhibition in non-modulating hypertension

Patients with normal- or high-renin non-modulating essential hypertension fail to shift their adrenal sensitivity on a low sodium diet in response to an infusion of angiotensin II (Ang II). In a prior study, 72 hours of converting enzyme inhibition (CEI) partially corrected this subnormal aldosterone response to Ang II in patients with non-modulating hypertension. Since it was uncertain whether the failure to restore normal adrenal responsiveness reflected a continued abnormality or an insufficient duration of CEI, the present study was performed wherein subjects were studied before CEI and then 72 hours and 6 weeks after CEI. Adrenal and renovascular responses were assessed in 13 subjects with normal- or high-renin hypertension in response to an infusion of Ang II (0.3, 1.0, and 3.0 ng/kg/min) in balance on a 10 meq Na+/100 meq K+ diet. Eight of 13 had a normal plasma aldosterone increment above control levels (greater than or equal to 15 ng/dl) and were classified as modulators; the remaining subjects (five of 13) were classified as non-modulators. Enalapril was then administered for 72 hours and 6 weeks, and the assessment of the Ang II dose-response relations was repeated. In the modulators, there was no change compared with levels before CEI in the aldosterone dose-response curve or threshold sensitivity to infused Ang II at either 3 days or 6 weeks after CEI administration. In the non-modulators, CEI for 72 hours partially restored aldosterone responsiveness, but more prolonged CEI for 6 weeks completely corrected the defect, restoring aldosterone responsiveness on a sodium-restricted diet to that seen in modulators and in normotensive control subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Abnormal regulation of adrenal angiotensin II receptors in spontaneously hypertensive rats

The aldosterone response to angiotensin II is blunted in spontaneously hypertensive rats (SHR). To determine whether this blunting is due to a defect in angiotensin II receptors, we assessed angiotensin II binding to intact adrenal glomerulosa cells in SHR and normotensive Wistar-Kyoto rats (WKY) that had been fed high or low sodium diets before sacrifice. In rats on high salt intake, we observed no difference between the two strains in either receptor affinity (Kd = 1.0-1.2 nM) or binding capacity (36,000-38,000 receptors/cell). When sodium-restricted, WKY increased receptor content more than fourfold to 167,000 sites/cell. SHR increased receptor number to only 103,000 sites/cell, which was significantly (p less than 0.01) less than the WKY increase. The cause of the abnormal receptor regulation remains unclear. Two known receptor regulators, the plasma angiotensin II level and the state of potassium balance, were similar in the two strains. Our results suggest that the blunted aldosterone response to angiotensin previously reported in SHR is due to abnormal angiotensin receptor up-regulation in the adrenal gland in response to sodium restriction.

The effect of angiotensin II on endogenous noradrenaline release in man

1. Considerable data from animal studies suggest that angiotensin II exerts a facilitatory effect on noradrenaline release. We sought evidence for such an effect in man by examining how a subpressor dose of angiotensin II (1.5 ng kg-1 min-1) influences the haemodynamic and plasma noradrenaline responses to physiological stimulation of the sympathetic nervous system. 2. The physiological stimuli investigated were a cold pressor test, the response to standing from lying, bicycle exercise and forearm isometric exercise. 3. The presence of the angiotensin II infusion had no effect on the systolic blood pressure, diastolic blood pressure, heart rate or plasma noradrenaline responses to stimulation of the sympathetic nervous system. 4. We have therefore found no evidence to support the enhancement of noradrenaline release by this low dose of angiotensin II in man.

Cyclosporin A-induced hyperreninemic hypoaldosteronism. A model of adrenal resistance to angiotensin II

We studied the effects of cyclosporin A on the renin-aldosterone axis in Sprague-Dawley rats. Two weeks of intragastric administration of cyclosporin A (5 mg/kg/day or or 20 mg/kg/day) resulted in large increases in plasma renin concentration (23 +/- 5, 70 +/- 12, and 79 +/- 11 ng/ml/hr in control rats and rats receiving 5 mg and 20 mg of cyclosporin A, respectively), with no parallel increments in plasma aldosterone. In vitro angiotensin II (ANG II)-stimulated aldosterone secretion by zona glomerulosa cells obtained from cyclosporin A-treated rats was also reduced (4.8 +/- 0.5, 1.5 +/- 0.2, and 0.2 +/- 0.2 ng/10(5) cells in control rats and rats receiving 5 mg and 20 mg of cyclosporin A, respectively). In contrast, in vitro aldosterone response to graded increments of potassium (3.7-10.7 mmol/L) or adrenocorticotropic hormone (ACTH) (10(-11)-10(-8) M) was preserved in cyclosporin A-treated rats. When added in vitro to zona glomerulosa cells from untreated rats, cyclosporin A also attenuated ANG II-stimulated aldosterone secretion, but did not affect potassium or ACTH-mediated aldosterone production. Thus, cyclosporin A-induced hyperreninemic hypoaldosteronism in the rat depends on opposing renal and adrenal effects, with a direct or feedback stimulation of renin secretion and a specific blockade of ANG II-mediated aldosterone production.

The effects of stress on salt and water balance

The effect of 'stress' on salt and water balance is largely determined by intrinsic renal factors supported by a series of inter-related neuro-humoral mechanisms which serve to enhance salt and water reabsorption and to maintain arterial pressure. As shown by acute hypovolaemic stress, the hormone response is characterized by increased renin-angiotensin production and associated hyperaldosteronism, which is further augmented by states of Na+ depletion. As well as increasing aldosterone secretion, angiotensin II has a direct renal effect to increase Na+ retention, and may stimulate both thirst and arginine vasopressin secretion. Additional support to volume homeostasis is provided by increased secretion of hypothalamic hormones (arginine vasopressin and corticotrophin releasing factor) and activation of the sympathetic nervous system, which further enhances renin secretion. These mechanisms, in restoring extracellular fluid volume and renal perfusion pressure, eventually diminish the stimuli to renin once normovolaemia is achieved. A variety of other acute 'stressors', not associated with major changes in ECF volume or hypotension, also stimulate adrenocortical hormones (cortisol and aldosterone), renin and arginine vasopressin. The biological significance of these changes is uncertain, but their brief duration make it unlikely that the responses contribute significantly to changes in salt or water balance. Atrial peptide hormones could also be important in ECF volume regulation. However, recent studies show little if any change in basal plasma atrial natriuretic peptide levels during acute hypovolaemic stress, whereas severe treadmill exercise (but not surgical stress or acute hypoglycaemia) stimulates venous levels in man. The relevance of these findings to the regulation of salt and water balance during stress clearly requires further study.

Role of angiotensin II in the hormonal, renal, and electrolyte response to sodium restriction

Adrenal responses to angiotensin II (ANG II) are enhanced with restriction of sodium intake. To determine whether increased circulating ANG II levels are responsible for the enhanced responsiveness, the adrenal and blood pressure responses to ANG II in human subjects were assessed four times: in balance on a high and a low salt diet and before and after the administration of a converting enzyme inhibitor (enalapril). Before enalapril administration, sodium restriction significantly increased (p less than 0.02) plasma renin activity, ANG II, and aldosterone levels; the aldosterone response to ANG II was enhanced twofold (p less than 0.01); and the blood pressure response to ANG II infusion was reduced significantly (p less than 0.05). Despite a fixed and low plasma ANG II concentration when enalapril was employed, the adrenal response to ANG II on the low salt diet was enhanced to the same degree as that observed before administration of the converting enzyme inhibitor. Conversely, enalapril substantially altered the blood pressure response to ANG II with sodium restriction, completely preventing the reduction in responsiveness. If the subjects were first given enalapril and then sodium intake was restricted, ANG II levels did not change significantly but renal excretion of both sodium and potassium was substantially modified. The rate at which renal excretion of sodium fell to match intake was retarded strikingly (p less than 0.001); conversely, renal retention of potassium increased significantly (p less than 0.03) as low salt balance was attained. Possibly because of the potassium retention, aldosterone levels rose, but significantly less than when enalapril was absent.

Hypermineralocorticoidism due to adrenal carcinoma: plasma corticosteroids and their response to ACTH and angiotensin II

A 47-year-old female presented with hypertension, hypokalaemia, low plasma renin, high plasma aldosterone and was found to have a left adrenal tumour 4 cm in diameter by computerized tomography. Detailed biochemical studies showed high plasma levels of 11-deoxycorticosterone and corticosterone in addition to aldosterone and 18-hydroxycorticosterone. Basal 11-deoxycorticosterone levels were particularly high. Corticosterone, 18-hydroxycorticosterone and aldosterone concentrations were abnormally sensitive to infusions of ACTH and angiotensin II. Plasma cortisol and assays for sex hormones were normal although there was evidence that cortisol derived from the neoplasm. At operation a well-differentiated adrenocortical carcinoma weighing 50 g (56 X 30 X 36 mm) was removed. There was no evidence of metastases following surgery. Adrenal function returned to normal. Review of the literature suggests that adrenocortical carcinoma should be suspected in patients who otherwise have typical features of Conn's syndrome, but whose tumours are more than 3 cm in diameter. Measurement of steroids such as 11-deoxycorticosterone in addition to aldosterone is recommended since abnormally high values may also help to distinguish between hyperaldosteronism due to adenoma and carcinoma. Previously reported cases of isolated aldosterone production by a carcinoma cannot be substantiated.

Regulation of primate angiotensin II receptors during altered sodium intake

In the rat, angiotensin II receptors of the adrenal glomerulosa and smooth muscle undergo reciprocal regulatory changes that parallel the changes in target cell sensitivity to angiotensin II during altered sodium intake. In primates, the relative importance of angiotensin II receptor regulation during sodium-induced changes in angiotensin II sensitivity is not clear. To evaluate the role of angiotensin II receptor regulation in the primate, we analyzed the changes in angiotensin II receptors of adrenal and bladder membrane-rich particles after 4 to 6 days of high or low sodium intake in the monkey (Macaca fascicularis). Consistent with the decreased pressor response to angiotensin II, smooth muscle angiotensin II receptors were fewer in sodium-restricted monkeys (93 +/- 17 fmol/mg) than in sodium-loaded monkeys (171 +/- 6 fmol/mg). However, in contrast to the rat, changes in zona glomerulosa angiotensin II receptors in monkey adrenal were similar to those in smooth muscle, decreasing with sodium restriction and increasing with sodium loading (344 +/- 64 and 660 +/- 68 fmol/mg, respectively). There was no change in angiotensin II receptor affinity in either smooth muscle or adrenal particles during altered sodium intake. Concomitant with the decrease in adrenal angiotensin II receptors, 18-hydroxylase activity was increased twofold in adrenal mitochondria from sodium-restricted monkeys (74 +/- 8 fmol/mg/min) compared with sodium-loaded animals (28 +/- 11 fmol/mg/min). The increased sensitivity of the primate adrenal to angiotensin II despite a fall in angiotensin II receptors indicates that full activation of steroidogenesis by angiotensin II can be maintained with partial receptor occupancy.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal renal sodium handling in essential hypertension. Relation to failure of renal and adrenal modulation of responses to angiotensin II

This study assessed renal sodium handling in a group of patients with essential hypertension in whom control of the renal blood supply and aldosterone release by angiotensin II is abnormal ("non-modulating") because of recent evidence that these patients have sodium-sensitive hypertension. Sixty-one patients were studied, 25 as balance was achieved with a daily sodium intake of 10 meq and 36 after a shift from a 10 meq to 200 meq sodium intake for five days. Renal and adrenal responsiveness to angiotensin II was assessed by measurement of para-aminohippurate clearance and plasma aldosterone prior to and during the infusion of 3 ng/kg per minute of angiotensin II, to identify the non-modulator group (n = 32). The half-time of the exponential function relating sodium excretion to time during the three to five days when external balance was being achieved with a 10 meq sodium intake was 23.9 +/- 0.3 hours in 60 normal subjects, 24.5 +/- 1.8 hours in the patients with essential hypertension in whom renal responsiveness to angiotensin II was normal, and prolonged (p less than 0.001) to 36.6 +/- 2.1 hours in the non-modulating patients. A prolonged half-time suggests that, with a shift to a high sodium intake, more time will be required to achieve external sodium balance and at the expense of more retained sodium. During the shift from a 10 to 200 meq sodium intake, the non-modulator group showed a delayed rate at which external sodium balance was achieved, greater cumulative positive sodium balance, more weight gain, and a greater frequency of blood pressure rise. The abnormality in the rate at which external sodium balance is achieved in non-modulation results in a difference in total body sodium that varies with sodium intake and that may well contribute to, or cause, sodium-sensitive hypertension.

Chronobiological study of factors affecting plasma aldosterone concentration in cirrhosis

We studied the mechanisms leading to derangement of aldosterone secretion in cirrhosis. The circadian patterns of plasma renin activity (PRA), aldosterone, cortisol, sodium, and potassium were studied in 16 nonazotemic cirrhotics (group 1 without ascites, 7 cases; group 2 with ascites, 9 cases) and 7 healthy controls. Group 1 did not differ from controls in aldosterone, sodium, and potassium mean daily levels (mesors), but had reduced PRA mesor (p less than 0.05). Moreover, minor derangements in circadian patterns of PRA, aldosterone, and potassium were also found. Group 2 not only showed an increased mesor of PRA (p less than 0.05), aldosterone (p less than 0.001), and reduced sodium (p less than 0.005), but also achronia in daily fluctuations of PRA, aldosterone, and potassium. In all groups the mesors of PRA and aldosterone were correlated (r greater than or equal to 0.82; p less than 0.01 or less), but the regression line slopes of patients were steeper than those of controls (group 1, p less than 0.05; group 2, p less than 0.01). Moreover, although in controls and some group 1 patients aldosterone paralleled cortisol rhythmicity, most group 2 patients had aldosterone daily patterns correlated with those of PRA. Finally, no relationships between plasma potassium and aldosterone concentrations were found in patients, whereas they were strictly related in controls. These results suggest that the renin-angiotensin system is the prevalent determinant of aldosterone secretion in cirrhosis.

Endogenous angiotensin-aldosterone-pressure relationships during sodium restriction

The effects of moderate restriction of dietary sodium and potassium supplementation on plasma levels of renin, angiotensin II, aldosterone, and cortisol and on arterial pressure were studied in 12 patients with mild essential hypertension. To define hormone-blood pressure relationships, venous hormone levels were measured hourly and intra-arterial pressure continuously for 24 hours after 4 to 6 weeks of sodium restriction, 4 to 6 weeks of potassium supplementation, and a similar period of control diet. Our results show that compared with the control diet, moderate sodium restriction was associated with increased levels of aldosterone but no overall change in renin, angiotensin II, or cortisol levels. Further, slopes of regression lines relating log renin and log angiotensin II to aldosterone were increased, as were log cortisol/aldosterone regression lines. On the contrary, regression lines of log renin and log angiotensin II versus arterial pressure were unaltered by sodium restriction. Hormone and blood pressure relationships were not changed by the potassium supplemented diet. Although confirmatory data are needed, our findings suggest that moderate sodium restriction enhances aldosterone responsiveness to endogenous angiotensin II and adrenocorticotropic hormone without diminishing the pressor activity of endogenous angiotensin II. These results may explain in part the disappointingly small hypotensive effect of modest sodium restriction in mild essential hypertension.

Reduced responsiveness of glomerulosa cells after prolonged stimulation with angiotensin II

The purpose of this study was to examine whether sustained exposition to angiotensin modifies the responsiveness of adrenal glomerulosa cells when extra-adrenal factors are eliminated. Isolated rat glomerulosa cells were stimulated for 6 h in a superfusion system with angiotensin II or potassium. Their responsiveness to angiotensin II, potassium, and corticotropin (ACTH) was examined before and after the superfusion. Stimulation of the cells during the superfusion with angiotensin II or with potassium reduced their responsiveness to all three stimuli. The steroid synthesis inhibitor aminoglutethimide, applied during the superfusion, overcame the effect of potassium but failed to influence that of angiotensin. This suggests that the reduced responsiveness after stimulation with potassium is related to the increased steroid production whereas the action of angiotensin is independent of that. The results establish the existence of desensitization to angiotensin in the absence of modifying extra-adrenal factors.