A microassay for active and total renin concentration in human plasma based on antibody trapping

Renal Haemodynamics are not Related to Genotypes in Offspring of Parents with Essential Hypertension

Introduction. The pathogenesis of essential hypertension (EH) has a major genetic component and is associated with renal abnormalities. Normotensive offspring of hypertensive parents are likely to develop EH and are a suitable population for identifying possible relations between genetic and renal abnormalities.

Methods. We investigated if renin-angiotensin-aldosterone system associated genotypes (angiotensinogen [M235T] and ACE [I/D]) are related to blood pressure (BP), renal haemodynamics and sodium excretion in sex and age-matched (18—35 years) healthy Caucasian offspring of either two parents with EH (n=101, EH-offspring) or two normotensive parents (n=50, controls). The alpha-adducin polymorphism (G460W) was also investigated.

Results. Compared to controls, BP, heart rate, renal vascular resistance (RVR) and urinary sodium excretion were, respectively, 5%, 7%, 15% and 20% higher in EH-offspring. In controls, the TT-genotype of the M235T angiotensinogen polymorphism was associated with higher BP and higher plasma angiotensinogen. By contrast, in EHoffspring the TT-genotype was associated with lower BP and unchanged plasma angiotensinogen. Plasma angiotensinogen correlated positively with BP in EH-offspring, with a similar tendency (p=0.08) in controls. The distributions of the three candidate polymorphisms were similar in EH-offspring and controls. There were no associations between any of the polymorphisms and any of the renal parameters measured.

Conclusion. The markedly greater RVR, proportionally larger than the greater BP, supports a role for RVR in the pathogenesis of EH. The lack of association between the candidate polymorphisms and the investigated parameters, even in this homogenous and for hypertension strongly predisposed group, suggests that the polymorphisms investigated do not play important roles in the pathogenesis of hypertension.

Long-term L-Triiodothyronine (T3) treatment in stable systolic heart failure patients: a randomised, double-blind, cross-over, placebo-controlled intervention study

BACKGROUND

Chronic heart failure (HF) is characterized by reduced serum T3 levels and increased activity of the T3 degrading enzyme deiodinase D3. This may result in an intracellular composition of the cardiomyocyte mimicking that of hypothyroidism. Short-term T3-administration to systolic HF patients might be beneficial.

QUESTION

Does long-term treatment with T3 have a beneficial effect on cardiac function and neurohormonal activation in chronic systolic HF patients with serum T3 levels below 1·6 nmol/l?

DESIGN

A randomized, double-blind, cross-over, placebo-controlled intervention study with oral T3 treatment twice daily for 3 months. The T3 dose was uptitrated to a final dose avoiding reduced TSH levels.

PRIMARY END-POINT

Left-ventricular ejection fraction (LVEF).

METHODS

Cardiac imaging was performed using multiple gated tomographic radionuclide ventriculography (MUGA-SPECT). Neurohormonal stimulation was evaluated by plasma measurements of natriuretic peptides, aldosterone, renin, noradrenalin and copeptin levels. The patients were monitored for potential cardiac arrhythmias at the start of each treatment period.

RESULTS

Thirteen patients completed the protocol. Mean LVEF was 43%, range: 37-52 and serum T3 levels 1·4 nmol/l (0·9-1·6). The T3 dose was 20 μg per day (10-40). TSH levels did not change between groups, whereas serum T3 levels increased in the active arm. Cardiac function as measured by LVEF, end-diastolic and end-systolic volumes and cardiac output did not change during T3-treatment and neither did the neurohormonal profile. There were no side-effects in terms of cardiac arrhythmias and no change in resting heart rate.

CONCLUSIONS

This study does not support the hypothesis that oral T3 treatment might be beneficial to patients with chronic, stable systolic HF with a modest degree of reduced LVEF and low-normal serum T3 concentrations. The study included both functional studies of heart contractility as well as measures of the neurohormonal activation.

Development and validation of an ultra-sensitive method for the measurement of plasma renin activity in human plasma via LC–MS/MS

Background: Renin catalyzes the conversion of angiotensinogen to angiotensin I (Ang I), the first and rate-limiting step in the renin–angiotensin–aldosterone system. Plasma renin activity (PRA) is an important target engagement biomarker in the clinical development of renin inhibitors. We have developed and validated an improved PRA assay that incorporates an Ang I trapping antibody followed by extraction and quantification of Ang I using a highly sensitive and specific LC–MS/MS method. Results: The following assay performance characteristics were assessed as part of analytical validation: precision, LOQ, spike recovery, dilution linearity, stability, absolute recovery and biological variability. The assay demonstrated excellent performance characteristics. Notably, the sensitivity of the assay was increased 140-fold when compared with a previous enzyme immunoassay-based assay. Conclusion: The improved sensitivity allowed the measurement of >95% PRA inhibition from baseline levels. In addition, we compared the LC–MS/MS-based assay to an enzyme immunoassay-based assay.

The effect of spironolactone upon corticosteroid hormone metabolism in patients with early stage chronic kidney disease

CONTEXT

Aldosterone has emerged as an important mediator of disease progression and mortality in patients with chronic heart and kidney disease (CKD). Despite the increasing use of mineralocorticoid receptor antagonists in these patients, little is known about the effects on corticosteroid hormone secretion and metabolism.

OBJECTIVE

To assess corticosteroid hormone secretion and metabolism in patients with early stage CKD before and after spironolactone (Spiro).

DESIGN

Randomized, double-blind, placebo-controlled interventional study.

SETTING

Single tertiary referral centre.

PATIENTS

A total of 112 patients with stable stage 2/3 CKD.

INTERVENTIONS

Patients were randomized to receive either Spiro 25 mg once daily or placebo for 36 weeks.

MAIN OUTCOME MEASURES

Plasma renin activity (PRA), angiotensin II (AngII) and steroid hormones were analysed by standard assays; urinary corticosteroid hormone metabolites (5α+5β-tetrahydro-cortisol (5α+5β-THF), TH-cortisone (THE), 3α5β-TH-aldosterone (TH-Aldo), 5α+5β-TH-deoxycorticosterone (5α+5β-TH-DOC), TH-11-desoxycortisol (THS)) were analysed by gas chromatography/mass spectrometry.

RESULTS

Plasma aldosterone concentration (PAC) was inversely correlated with eGFR (r = -0·331, P < 0·001). Urinary 24-h excretion of TH-Aldo was correlated with PAC (r = 0·214, P < 0·05) and diastolic blood pressure (BP) (r = 0·212, P = <0·05), whereas total 24-h urinary cortisol metabolite excretion was correlated with systolic BP (r = 0·316, P < 0·01). In addition, 11β-hydroxysteroid dehydrogenase (11β-HSD) type 1 activity (urinary 5α+5β-THF)/THE) ratio) was correlated with PRA (r = 0·277, P < 0·01). Spiro treatment significantly reduced BP (123 ± 11/76 ± 7 vs 119 ± 11/73 ± 8 mmHg, P < 0·01) despite renin-angiotensin-aldosterone system induction, reflected by increased urinary 24-h TH-Aldo excretion (17·6 (12, 86) vs 26 (18, 80) μg/24 h, P < 0·05). By contrast, Spiro had no effect on total urinary cortisol metabolite excretion, 11β-hydroxylase, 11β-HSD type 1 and 2 activity.

CONCLUSIONS

Aldo and cortisol are positively associated with BP suggesting that adrenal hyperactivity may in part explain the increased cardiovascular risk in patients with early end-stage CKD. Addition of Spiro had no effect on glucocorticoid metabolism or total 24-h corticosteroid production.

Activity Assays and Immunoassays for Plasma Renin and Prorenin: Information Provided and Precautions Necessary for Accurate Measurement

Background: Measurement of plasma renin is important for the clinical assessment of hypertensive patients. The most common methods for measuring plasma renin are the plasma renin activity (PRA) assay and the renin immunoassay. The clinical application of renin inhibitor therapy has thrown into focus the differences in information provided by activity assays and immunoassays for renin and prorenin measurement and has drawn attention to the need for precautions to ensure their accurate measurement.

Content: Renin activity assays and immunoassays provide related but different information. Whereas activity assays measure only active renin, immunoassays measure both active and inhibited renin. Particular care must be taken in the collection and processing of blood samples and in the performance of these assays to avoid errors in renin measurement. Both activity assays and immunoassays are susceptible to renin overestimation due to prorenin activation. In addition, activity assays performed with peptidase inhibitors may overestimate the degree of inhibition of PRA by renin inhibitor therapy. Moreover, immunoassays may overestimate the reactive increase in plasma renin concentration in response to renin inhibitor therapy, owing to the inhibitor promoting conversion of prorenin to an open conformation that is recognized by renin immunoassays.

Conclusions: The successful application of renin assays to patient care requires that the clinician and the clinical chemist understand the information provided by these assays and of the precautions necessary to ensure their accuracy.

Hemostatic factors and renin in Greenland Eskimos on a high eicosapentaenoic acid intake. Results of the Fifth UmanaK Expedition

The Fifth UmanaK expedition compared the fatty acid composition of platelets, bleeding times before and after ingestion of acetylsalicylic acid, 24-hour urinary tetranorprostanedioate, creatinine and Na output, as well as plasma renin, serum electrolytes and antithrombin III in 20 Greenland Eskimos and 20 Danes. The results indicate that the prostaglandin production was not inhibited in the Eskimos, and that the antiaggregatory prostanoids predominate in Eskimos compared to Danes. Although blood pressure and 24-hour urinary Na output were similar, the plasma renin level was significantly higher in the Eskimos on a high eicosapentaenoic acid intake.

Clinical Use of Laboratory Tests for the Identification of Secondary Forms of Arterial Hypertension

The prevalence of secondary hypertension can be underestimated if appropriate tests are not performed. The importance of selecting patients with a high pre-test probability of secondary forms of hypertension is first discussed. The laboratory tests currently used for seeking a cause of hypertension are critically reviewed, with emphasis on their operative features and limitations. Strategies to identify primary aldosteronism, the most frequent form of secondary hypertension, and to determine its unilateral or bilateral causes are described. Treatment entails adrenalectomy in unilateral forms, and mineralocorticoid receptor blockade in bilateral forms. Renovascular hypertension is also a common, curable form of hypertension, that should be identified as early as possible to avoid the onset of cardiovascular target organ damage. The tests for its confirmation or exclusion are discussed. The various tests available for the diagnosis of pheochromocytoma, which is much rarer than the above but extremely important to identify, are also described, with emphasis on recent developments in genetic testing. Finally, the tests for diagnosing some rarer monogenic forms and other renal and endocrine causes of arterial hypertension are explored.

Effect of variation in CYP11B1 and CYP11B2 on corticosteroid phenotype and hypothalamic-pituitary-adrenal axis activity in hypertensive and normotensive subjects

BACKGROUND

Aldosterone is important in the development of hypertension. We have shown that a single nucleotide polymorphism (SNP) (-344T) in the 5' regulatory region (UTR) of the gene encoding aldosterone synthase (CYP11B2) associates with aldosterone excess and hypertension as well as altered adrenal 11-hydroxylation efficiency (deoxycortisol to cortisol). This conversion is carried out by the enzyme 11beta-hydroxylase, encoded by the adjacent gene, CYP11B1. We proposed that the effects of CYP11B2 are explained by linkage disequilibrium (LD) across the CYP11B locus. We have demonstrated high LD across this locus and identified two SNPs in the 5' UTR of CYP11B1 (-1859 G/T, -1889 A/G) that associate with reduced transcription in vitro and altered 11-hydroxylation efficiency in vivo. Accordingly, we hypothesized that the reduced adrenal 11-hydroxylation may lead to chronic resetting of the pituitary-adrenal axis, with chronically increased ACTH drive resulting in aldosterone excess.

METHODS

To test this, we examined hypothalamic-pituitary-adrenal (HPA) axis activity in hypertensive and normotensive individuals stratified according to genotype at CYP11B2 (-344T/C) and CYP11B1 (-1859 G/T, -1889 A/G). Fifty-six subjects homozygous for CYP11B2 SNP (27 TT, 12 CC), and 38 homozygous for CYP11B1 SNPs (18 TTGG, 20 GGAA) were recruited. Diurnal variation and the effects of dexamethasone suppression and ACTH stimulation on plasma aldosterone, cortisol and ACTH under controlled conditions were studied.

RESULTS

Subjects with SNPs associated with reduced 11-hydroxylation efficiency (-344T CYP11B2; TTGG CYP11B1) showed reduced inhibition of ACTH after dexamethasone (P = 0.05) and an altered cortisol-ACTH relationship (decreased cortisol-ACTH ratio, P < 0.02). The same individuals also demonstrated close correlations between plasma cortisol and aldosterone (-344T CYP11B2 r = 0.508, P < 0.004; TTGG CYP11B1 r = 0.563, P < 0.003) suggesting that there was common regulation (possibly ACTH) of these hormones in genetically susceptible subjects.

CONCLUSIONS

Variation in CYP11B2 and CYP11B1 associates with chronic up-regulation of the HPA axis. These novel data support the suggestion that chronic aldosterone excess, in genetically susceptible individuals, may be a consequence of increased ACTH drive to the adrenal and identify novel molecular mechanisms that may lead to the development of hypertension within the general population.

Time course of the antiproteinuric and antihypertensive effects of direct renin inhibition in type 2 diabetes

Inhibition of renin with an active site inhibitor, aliskiren, lowers blood pressure (BP) in diabetic patients. Here, we studied the time course of the antihypertensive and antiproteinuric effect of renin inhibition in 15 patients with type 2 diabetes and elevated urinary albumin/creatinine ratios (UACRs) to check whether aliskiren can decrease proteinuria. After a 4-week washout of previous medications, patients received aliskiren and furosemide daily for 28 days followed by a 4-week withdrawal period. Twenty-four-hour BPs were measured at baseline throughout treatment and withdrawal periods. The UACR was significantly reduced after 2-4 days of treatment with another significant reduction after 28 days. Systolic blood pressure (SBP) was significantly lower after 7 days with no further reduction after 28 days. The BP returned toward baseline 3 days after withdrawal, whereas the UACR was still significantly reduced compared with baseline 12 days after withdrawal. Our study shows that aliskiren reduced 24 h SBP, and this was associated with a reduction in albuminuria in type 2 diabetic patients.

Angiotensin-converting enzyme activity and cognitive impairment during hypoglycaemia in healthy humans

Introduction: In type 1 diabetes increased risk of severe hypoglycaemia is associated with high angiotensin-converting enzyme (ACE) activity. We tested in healthy humans the hypothesis that this association is explained by the reduced ability of subjects with high ACE activity to maintain normal cognitive function during hypoglycaemia.

Methods: Sixteen healthy volunteers selected by either particularly high or low serum ACE activity were subjected to hypoglycaemia (plasma glucose 2.7 mmol/L). Cognitive function was assessed by choice reaction tests.

Results: Despite a similar hypoglycaemic stimulus in the two groups, only the group with high ACE activity showed significant deterioration in cognitive performance during hypoglycaemia. In the high ACE group mean reaction time (MRT) in the most complex choice reaction task was prolonged and error rate (ER) was increased in contrast to the low ACE group. The total hypoglycaemic symptom response was greater in the high ACE group than in the low ACE group (p=0.031).There were no differences in responses of counterregulatory hormones or in concentrations of substrates between the groups.

Conclusion: Healthy humans with high ACE activity are more susceptible to cognitive dysfunction and report higher symptom scores during mild hypoglycaemia than subjects with low ACE activity.

Dietary electrolyte-driven responses in the renal WNK kinase pathway in vivo

WNK1 and WNK4 are unusual serine/threonine kinases with atypical positioning of the catalytic active-site lysine (WNK: With-No-K[lysine]). Mutations in these WNK kinase genes can cause familial hyperkalemic hypertension (FHHt), an autosomal dominant, hypertensive, hyperkalemic disorder, implicating this novel WNK pathway in normal regulation of BP and electrolyte balance. Full-length (WNK1-L) and short (WNK1-S) kinase-deficient WNK1 isoforms previously have been identified. Importantly, WNK1-S is overwhelmingly predominant in kidney. Recent Xenopus oocyte studies implicate WNK4 in inhibition of both thiazide-sensitive co-transporter-mediated Na+ reabsorption and K+ secretion via renal outer medullary K+ channel and now suggest that WNK4 is inhibited by WNK1-L, itself inhibited by WNK1-S. This study examined WNK pathway gene expression in mouse kidney and its regulation in vivo. Expression of WNK1-S and WNK4 is strongest in distal tubule, dropping sharply in collecting duct and with WNK4 also expressed in thick ascending limb and the macula densa. These nephron segments that express WNK1-S and WNK4 mRNA have major influence on long-term NaCl reabsorption, BP, K+, and acid-base balance, processes that all are disrupted in FHHt. In vivo, this novel WNK pathway responds with significant upregulation of WNK1-S and WNK4 with high K+ intake and reduction in WNK1-S on chronic lowering of K+ or Na+ intake. A two-compartment distal nephron model explains these in vivo findings and the pathophysiology of FHHt well, with WNK and classic aldosterone pathways responding to drivers from K+ balance, extracellular volume, and aldosterone and cross-talk through distal Na+ delivery regulating electrolyte balance and BP.

Inhibition of aldosterone biosynthesis by staurosporine

Staurosporine (STS) is a very potent broad-range kinase inhibitor, and its antiproliferative properties made it a lead compound for protein kinase C (PKC) inhibitors with therapeutic potential. Because STS also causes hypotension, we investigated in this study whether it directly interferes with the terminal steps of aldosterone biosynthesis; these are catalysed by a mitochondrial steroid hydroxylase system consisting of adrenodoxin reductase, adrenodoxin, and the cytochrome P450 enzyme hCYP11B2 (aldosterone synthase). Here we demonstrate that nanomolar concentrations of STS significantly reduced aldosterone synthase activity in transiently transfected COS-1 cells and in stably transfected V79MZh11B2 cells (IC50=11 nM). However, STS did not inhibit bovine aldosterone synthase in a reconstituted steroid hydroxylation assay. In transiently transfected COS-1 cells, the protein level of adrenodoxin (but not that of adrenodoxin reductase or of hCYP11B2) was significantly reduced after treatment with 2 nM STS. Finally, we show that STS treatment (1 μg/day) of mice reduced their aldosterone/renin ratio by almost 50% (p=0.015). To the best of our knowledge, this is the first report of a directin vivoeffect of STS on the renin-angiotensin-aldosterone system. We conclude (i) that the hypotensive effect of staurosporine is at least partly due to inhibition of aldosterone biosynthesis via adrenodoxin depletion, and (ii) that aldosterone biosynthesis can be regulatedin vivoat the level of adrenodoxin availability.

Elevated blood pressure linked to primary hyperaldosteronism and impaired vasodilation in BK channel-deficient mice

BACKGROUND

Abnormally elevated blood pressure is the most prevalent risk factor for cardiovascular disease. The large-conductance, voltage- and Ca2+-dependent K+ (BK) channel has been proposed as an important effector in the control of vascular tone by linking membrane depolarization and local increases in cytosolic Ca2+ to hyperpolarizing K+ outward currents. However, the BK channel may also affect blood pressure by regulating salt and fluid homeostasis, particularly by adjusting the renin-angiotensin-aldosterone system.

METHODS AND RESULTS

Here we report that deletion of the pore-forming BK channel alpha subunit leads to a significant blood pressure elevation resulting from hyperaldosteronism accompanied by decreased serum K+ levels as well as increased vascular tone in small arteries. In smooth muscle from small arteries, deletion of the BK channel leads to a depolarized membrane potential, a complete lack of membrane hyperpolarizing spontaneous K+ outward currents, and an attenuated cGMP vasorelaxation associated with a reduced suppression of Ca2+ transients by cGMP. The high level of BK channel expression observed in wild-type adrenal glomerulosa cells, together with unaltered serum renin activities and corticotropin levels in mutant mice, suggests that the hyperaldosteronism results from abnormal adrenal cortical function in BK(-/-) mice.

CONCLUSIONS

These results identify previously unknown roles of BK channels in blood pressure regulation and raise the possibility that BK channel dysfunction may underlie specific forms of hyperaldosteronism.

Delayed diagnosis of congenital adrenal hyperplasia with salt wasting due to type II 3beta-hydroxysteroid dehydrogenase deficiency

Classical 3beta-hydroxysteroid dehydrogenase (3beta-HSD) deficiency is a rare cause of congenital adrenal hyperplasia. We report two sisters presenting with delayed diagnoses of classical 3beta-HSD, despite salt wasting (SW) episodes in infancy. Sibling 1 was referred for premature pubarche, slight growth acceleration, and advanced bone age, whereas sibling 2 had no signs of virilization. At referral, increased 17alpha-hydroxyprogesterone associated with premature pubarche at first suggested a nonclassical 21-hydroxylase deficiency. Sequencing of the CYP21 gene showed both girls only heterozygotes (V281L mutation). This result, combined with SW in infancy, suggested a 3beta-HSD deficiency because of increased dehydroepiandrosterone sulfate levels. Further hormonal studies showed markedly elevated Delta5-steroids, in particular 17alpha-hydroxypregnenolone greater than 100 nmol/liter (the clue to the diagnosis) and elevated Delta5-/Delta4-steroid ratios. Sequencing of the type II 3beta-HSD gene documented that both girls were compound heterozygotes for T181I and 1105delA mutations. Retrospectively, elevated levels of 17alpha-hydroxyprogesterone were found on blood spots from Guthrie's test. There is no previous report of the combination of SW and premature pubarche due to mutations in the type II 3beta-HSD gene. Because neonatal diagnosis could have prevented life-threatening crises in these girls, this report further supports the benefits for neonatal screening for congenital adrenal hyperplasia whatever the etiology.

Effect of eprosartan on catecholamines and peripheral haemodynamics in subjects with insulin-induced hypoglycaemia

ANG II (angiotensin II) facilitates catecholamine release from the adrenal medulla and neuronal NE (noradrenaline) release. Since animal experiments point to specific sympatho-inhibitory properties of the AT1 (ANG II type 1)-receptor blocker EPRO (eprosartan), the primary aim of this study was to clarify if EPRO inhibits sympathetic reactivity in humans as determined by the effect of EPRO on insulin-induced catecholamine release. Sixteen healthy male volunteers were randomized in a double-blind cross-over study to receive a single dose of EPRO (600 mg) compared with placebo, followed by insulin-induced hypoglycaemia [0.15 IU (international unit)/kg of body weight; intravenous bolus] on two study days 1 week apart. From baseline to the end of hypoglycaemia (170 min), the sympatho-adrenal reactivity was mapped by invasive continuous blood pressure monitoring and repeated measurements of FBF (forearm blood flow), arterial and venous concentrations of glucose, catecholamines [EPI (adrenaline) and NE (noradrenaline)], renin, ANG II and aldosterone. EPRO induced an 8–10-fold increase in plasma renin and ANG II concentrations compared with placebo. Plasma glucose decreased equally during placebo and EPRO from baseline 5.9 mmol/l to 1.9 mmol/l and 2.1 mmol/l respectively, inducing a 17-fold increase in arterial EPI concentration at peak. The AUC (area under the curve) during hypoglycaemia for arterial EPI concentrations was 314±48 nmol·min·l−1 in placebo compared with 254±26 nmol·min·l−1 following EPRO treatment (P=0.14). EPRO attenuated the corresponding AUC for the EPI-induced pulse pressure response (4670±219 mmHg·min in EPRO compared with 5004±266 mmHg·min in placebo; P=0.02). Moreover, EPRO caused a less pronounced increase in FBF compared with placebo (402±30 compared with 479±46 ml·100 g−1 of body weight; P=0.04). Musculocutaneous NE release was not affected by EPRO and the AUC for NE release was 51.69±15.5 pmol·min−1·100 g−1 of body weight in placebo compared with 39.35±18.2 pmol·min−1·100 g−1 of body weight after EPRO treatment (P=0.57). In conclusion, EPRO did not significantly inhibit sympathetic reactivity compared with placebo; however, it blunted the haemodynamic responses elicited by the sympatho-adrenal stimulation which only tended to be attenuated by this drug.

Glucocorticoid exposure in late gestation in the rat permanently programs gender-specific differences in adult cardiovascular and metabolic physiology

Glucocorticoid overexposure in utero may underlie the association between low birth weight and subsequent development of common cardiovascular and metabolic pathologies. Previously, we have shown that prenatal dexamethasone (DEX) exposure in rat reduces birth weight and programs the hypothalamic-pituitary axis and fasting and postprandial hyperglycemia in adult males and hypertension in adult males and females. This study aimed to determine 1) whether there were gender differences in prenatal DEX-programmed offspring, and 2) whether the renin-angiotensin system (RAS) plays a role in the programming of hypertension. Rats exposed to DEX in utero (100 microg.kg(-1).day(-1) from embryonic days 14-21) were of lower birth weight (by 12%, P < 0.01) and displayed full catch-up growth within the first month of postnatal life. DEX-treated male offspring in adulthood selectively displayed elevated plasma adrenocorticotropic hormone (by 221%) and corticosterone (by 188%, P < 0.05), postprandial insulin-glucose ratios (by 100%, P < 0.05), and hepatic expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (by 38%, P < 0.05). Conversely, DEX-programmed females were hypertensive (by 11%, P < 0.05), with elevated hepatic angiotensinogen mRNA expression (by 9%, P < 0.05), plasma angiotensinogen (by 61%, P < 0.05), and renin activity (by 88%, P < 0.05). These findings demonstrate that prenatal glucocorticoids program adulthood cardiovascular and metabolic physiology in a gender-specific pattern, and that an activated RAS may in part underlie the hypertension associated with prenatal DEX programming.

Is inappropriate left ventricular mass related to neurohormonal factors and/or arterial changes in hypertension? a LIFE substudy

We investigated whether inappropriately high left ventricular (LV) mass, defined as observed LV mass exceeding the level of individual LV mass predicted from gender, height, and stroke work, may be associated with an imbalance between growth-promoting and growth-inhibitory factors and/or structural vascular changes. In 53 patients with hypertension and electrocardiographic LV hypertrophy, 24-h ambulatory blood pressure (BP); echocardiographic LV mass, stroke volume and stroke work; minimal forearm vascular resistance (MFVR); and intima-media cross-sectional area in common carotid arteries (IMA) were evaluated after 2 weeks of placebo treatment. Serum insulin, plasma epinephrine, norepinephrine, endothelin, angiotensin II, aldosterone, and brain natriuretic peptide (BNP) were also measured. High observed LV mass was related to high IMA (r=0.46, P<0.001), MFVR (in men: r=0.36, P<0.05), 24-h ambulatory systolic BP (r=0.30, P=0.06), and lower plasma angiotensin II (r=-0.33, P<0.05), but not to other circulating growth factors. Stroke work was similarly related to IMA (r=0.42, P<0.01), MFVR (in men: r=0.41, P<0.05), and plasma angiotensin II (r=-0.32, P<0.05). Inappropriate LV mass, identified by the ratio between observed LV mass and the value predicted for gender, height, and stroke work, was not significantly related to any of the arterial or neurohormonal variables. In this small series of older hypertensive patients, inappropriate LV mass was not significantly related to arterial changes or to measured circulating growth factors, although weak relations cannot be excluded. Alternatively, inappropriately high LV mass might be related to unmeasured factors such as local myocardial alterations in growth factors and/or genetic predisposition to develop excessive LV hypertrophy.

Renoprotective effects of adding angiotensin II receptor blocker to maximal recommended doses of ACE inhibitor in diabetic nephropathy: a randomized double-blind crossover trial

OBJECTIVE

We evaluated the renoprotective effects as reflected by short-term changes in albuminuria of dual blockade of the renin-angiotensin system (RAS) by adding an angiotensin II receptor blocker (ARB) to treatment with maximal recommended doses of an ACE inhibitor (ACEI) in patients with type 2 diabetes and nephropathy.

RESEARCH DESIGN AND METHODS

A total of 20 patients (17 men and 3 women) with type 2 diabetes along with hypertension and nephropathy were enrolled in this double-blind, randomized, two-period, crossover trial of 8 weeks of treatment with the ARB candesartan 16 mg daily and placebo added in random order to existing treatment with lisinopril/enalapril 40 mg daily or captopril 150 mg daily. At the end of each treatment period, we evaluated albuminuria in three 24-h urinary collections by turbidimetry, 24-h ambulatory blood pressure (ABP) using the Takeda-TM2420, and glomerular filtration rate (GFR) by the (51)Cr-EDTA plasma-clearance technique.

RESULTS

During monoblockade of the RAS by ACEI treatment, albuminuria was 706 (349-1,219) mg/24 h [geometric mean (IQR)]; 24-h ABP was 138 +/- 3/72 +/- 2 mmHg (mean +/- SE); and GFR was 77 +/- 6 ml x min(-1) x 1.73 m(-2) (mean +/- SE). During dual blockade of the RAS by addition of candesartan 16 mg daily, there was a mean (95% CI) reduction in albuminuria of 28 (17-38) compared with ACEI alone (P < 0.001). There was a modest reduction in systolic/diastolic 24-h ABP of 3/2 mmHg (-2 to 8 systolic, -2 to 5 diastolic; NS). Changes in albuminuria did not correlate to changes in ABP. Addition of candesartan 16 mg daily induced a small, insignificant decrease in GFR of 4 (-1 to 9) ml x min(-1) x 1.73 m(-2).

CONCLUSIONS

Dual blockade of the RAS provides superior short-term renoprotection independent of systemic blood pressure changes in comparison with maximally recommended doses of ACEI in patients with type 2 diabetes as well as nephropathy.

Dual blockade of the renin-angiotensin system versus maximal recommended dose of ACE inhibition in diabetic nephropathy

BACKGROUND

Albuminuria and hypertension are predictors of poor renal and cardiovascular outcome in diabetic patients. We tested whether dual blockade of the renin-angiotensin system (RAS) with both an angiotensin-converting enzyme (ACE) inhibitor and an angiotensin II receptor blocker (ARB) is superior to maximal recommended dose of ACE inhibitor in type 1 diabetic patients with diabetic nephropathy (DN).

METHODS

We performed a randomized, double-blind, crossover trial with 8 weeks treatment with placebo and irbesartan 300 mg (once daily), added on top of enalapril 40 mg (once daily). We included 24 type 1 patients with DN. At the end of each treatment period, albuminuria, 24-hour blood pressure, and glomerular filtration rate (GFR) were measured.

RESULTS

Values on ACE inhibitors + placebo were: albuminuria [mean (95% CI)], 519 (342 to 789) mg/24 hours; blood pressure [mean (SEM)], 131 (3)/74 (1) mm Hg, and GFR [mean (SEM)], 65 (5) mL/min/1.73 m2. Dual blockade of the RAS induced a reduction in albuminuria [mean (95% CI)] of 25% (15, 34) (P < 0.001), a reduction in systolic blood pressure of 8 mm Hg (4, 12) (P = 0.002), and a reduction of 4 mm Hg (2, 7) (P = 0.003) in diastolic blood pressure. GFR and plasma potassium remained unchanged during both treatment regimes. Dual blockade was safe and well tolerated.

CONCLUSION

Dual blockade of the RAS is superior to maximal recommended dose of ACE inhibitors with regard to lowering of albuminuria and blood pressure in type 1 patients with DN. Long-term trials are needed to further establish the role of dual blockade of the RAS in renal and cardiovascular protection.

Optimal dose of candesartan for renoprotection in type 2 diabetic patients with nephropathy: a double-blind randomized cross-over study

OBJECTIVE

We evaluated the optimal dose of the angiotensin II receptor antagonist candesartan cilexetil for renoprotection as reflected by short-term changes in albuminuria in hypertensive type 2 diabetic patients with nephropathy.

RESEARCH DESIGN AND METHODS

A total of 23 hypertensive patients with type 2 diabetes and nephropathy were enrolled in this double-blind randomized cross-over trial with four treatment periods, each lasting 2 months. Each patient received placebo and candesartan: 8, 16, and 32 mg daily in random order. Antihypertensive medication was discontinued before enrollment, except for long-acting furosemide, which all patients received throughout the study in median (range) doses of 40 (30-160) mg daily. End points were albuminuria (turbidimetry), 24-h blood pressure (BP) (Takeda-TM2420), and glomerular filtration rate (GFR) (51Cr-labeled EDTA plasma clearance technique).

RESULTS

Values obtained during placebo treatment: albuminuria [geometric mean (95% CI)] 700 (486-1,007) mg/24-h, 24-h BP (mean +/- SE) 147 +/- 4/78 +/- 2 mmHg, and GFR 84 +/- 6 ml/min/1.73 m2. All three doses of candesartan significantly reduced albuminuria and 24-h BP compared with placebo. Mean (95% CI) reductions in albuminuria were 33% (21-43), 59% (52-65), and 52% (44-59) with increasing doses of candesartan. Albuminuria was reduced significantly more by the two highest doses than by the lowest dose (P < 0.01); 24-h systolic BP was reduced by 9 (2-16), 9 (2-16), and 13 (6-20) mmHg and 24-h diastolic BP was reduced by 5 (2-8), 4 (1-7), and 6 (3-9) mmHg with increasing doses of candesartan. There were no significant differences in the reductions in BP between the three doses. GFR was decreased by approximately 6 ml/min/1.73 m2 by all three doses of candesartan (P < 0.05 versus placebo).

CONCLUSIONS

The optimal dose of candesartan is 16 mg daily for renoprotection, as reflected by short-term reduction in albuminuria, in hypertensive type 2 diabetic patients with nephropathy.

Is cardiovascular remodeling in patients with essential hypertension related to more than high blood pressure? A LIFE substudy. Losartan Intervention For Endpoint-Reduction in Hypertension

BACKGROUND

Blocking the renin-aldosterone-angiotensin II system has been hypothesized to induce blood pressure-dependent as well as blood pressure-independent regression of cardiovascular hypertrophy. However, the relative influence of elevated blood pressure (BP) and various neurohormonal factors on cardiovascular remodeling in hypertension is unclear.

METHODS

In 43 untreated patients with hypertension with electrocardiographic left ventricular hypertrophy, we measured relative wall thickness and left ventricular mass index by echocardiography and by magnetic resonance imaging (n = 32), intima-media cross-sectional area, and distensibility of the common carotid arteries by ultrasound, media/lumen ratio of isolated subcutaneous resistance arteries by myography, and median 24-hour systolic BP (n = 40), serum insulin, and plasma levels of epinephrine, norepinephrine, renin, angiotensin II, aldosterone, and endothelin.

RESULTS

In multiple regression analyses, left ventricular mass index by echocardiography (R2 = 0.14, P <.05) and by magnetic resonance imaging (R2 = 0.32, P =.001) were associated with 24-hour systolic BP, whereas relative wall thickness was associated with plasma epinephrine (R2 = 0.12, P <.05) and aldosterone (R2 = 0.10, P <.05). Intima-media cross-sectional area/height was associated with 24-hour systolic BP (beta = 0.40) and plasma epinephrine (beta = 0.43) (adjusted R2 = 0.32, P <.001), whereas carotid distensibility was associated with 24-hour systolic BP (beta = 0.40) and plasma angiotensin II (beta = -0.41) (adjusted R2 = 0.30, P <.001). Media/lumen ratio in subcutaneous resistance arteries was associated with plasma epinephrine (R2 = 0.22, P <.01).

CONCLUSION

Apart from being associated with a high BP burden, cardiovascular remodeling was associated with high levels of circulating epinephrine, aldosterone, as well as angiotensin II, suggesting a beneficial effect above and beyond the effect of BP reduction when using antihypertensive agents blocking the receptors of these neurohormonal factors.

Vasoactive modulators during and after craniotomy: relation to postoperative hypertension

Hypertension after craniotomy is frequent. To establish an association between vasoactive modulators and postoperative hypertension, we followed the arterial blood pressure and plasma concentrations of selected substances in patients undergoing craniotomy. Twelve consecutive patients scheduled for operation of a supratentorial brain tumor were anesthetized with thiopental, fentanyl, isoflurane, and pancuronium. None of the patients had a history of arterial hypertension or were hypertensive before the operation. Arterial blood pressure and heart rate measurements were obtained preoperatively, after incision, during closure, and four times in the 50-minute interval after stopping isoflurane. At the same time, plasma concentrations of norepinephrine, epinephrine, renin, aldosterone, atrial natriuretic peptide, endothelin, and cortisol were measured. Data are given as mean +/- SD (range). The postoperative concentrations of these substances were significantly higher than the baseline concentrations measured preoperatively. Six of the patients developed postoperative hypertension defined as a mean arterial pressure (MAP) > 20% more than the baseline MAP (group H), and six had normal blood pressure postoperatively (group N). The mean value of the maximal postoperative MAPs measured in groups H and N, respectively, was 118 +/- 16 mm Hg (range: 96-132) and 103 +/- 9 mm Hg (range: 92-115) (P =.01). Only renin levels were higher intraoperatively in group H when compared to group N. However, postoperative levels of catecholamines, aldosterone, renin, and endothelin levels were higher in group H patients. The results suggest that in addition to an increased discharge of the sympathetic system, activation of the renin-angiotensin aldosterone system may also play an important role in the development of postoperative hypertension after craniotomy.

Hypertension and renovascular disease: follow-up on 100 renal vein renin samplings

The clinical value of renal vein renin sampling (RVRS) as a prognostic tool in the treatment of renovascular hypertension was evaluated. One hundred consecutive patients were included over a 4-year period of time. About half of the patients (49%) were treated interventionally by PTRA (21%), nephrectomy (20%), or vascular surgery (8%). Seven patients (15%) were cured and 15 (32%) had improved (reduction in antihypertensive medicine) after 6 months follow-up, whereas three patients (6%) were cured and 12 (26%) improved after 3-4 years follow-up. Thus, the number of patients cured or improved is comparable with the results from our department reported 20 years ago. However, in the present report, more than twice as many patients were enrolled, leading to double costs. Different indices of lateralisation of the renin generation were calculated for the use in cases of a shrunken kidney (functional share < or =15%). None of the indices clearly discriminated between the patients who did benefit from intervention, and those who did not. The only positive finding was that a peripheral renin concentration lower than 8 mlU/l predicted no effect of intervention, which might lead to the exclusion of 11% of the patients before entering the diagnostic programme. We conclude that the RVRS demands a very restrictive referral pattern if it should be of prognostic value for the blood pressure outcome after intervention. No indices of lateralised renin concentrations proved high predictive value. However, a peripheral renin concentration low in the normal range seems useful as an indicator of no benefit from intervention.

Mutations in aldosterone synthase gene of Milan hypertensive rats: phenotypic consequences

Using in vitro and in vivo methods, we have demonstrated increased sensitivity of adrenocortical steroidogenesis to ACTH in Milan hypertensive (MHS) compared with normotensive (MNS) rats and have investigated whether this is caused by mutations of steroidogenic enzymes. Genes encoding aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) in MHS and MNS have been cloned and sequenced. Nucleotide 752 (G) in exon 4 of MHS CYP11B2 differs from that of MNS (A); CYP11B1 sequences were identical. The nucleotide 752 mutation caused a Q251R substitution in the amino acid sequence of MHS CYP11B2. The phenotype of MHS CYP11B2 alleles, when expressed in COS-1 cells, differed from that of MNS alleles. The relative activities of the three reactions catalyzed by CYP11B2 (11beta-hydroxylation of deoxycorticosterone, 18-hydroxylation of corticosterone, and dehydrogenation of 18-hydroxycorticosterone) were estimated after incubation of transfected cells with [(14)C]deoxycorticosterone and analysis of radioactivity associated with deoxycorticosterone, corticosterone, 18 hydroxycorticosterone, and aldosterone. Both 11- and 18-hydroxylase activities were lower (19 and 12%, respectively; P < 0.01 and P < 0.05) in cells transfected with MHS compared with MNS alleles, whereas 18-oxidase activity was 42% higher (P < 0.01). To assess the significance of the CYP11B2 mutation in vivo, DNA from F2 hybrid MHS x MNS rats was genotyped. MHS alleles were associated with lower urine volumes in both sexes, lower ventricle weights in male rats, but no difference in systolic or diastolic blood pressures between the sexes. We conclude that a mutation in CYP11B2 may affect aldosterone secretion in MHS; however, under normal environmental circumstances, we were unable to demonstrate any influence of this mutation on blood pressure.

ADEPT: Addition of the AT1 receptor antagonist eprosartan to ACE inhibitor therapy in chronic heart failure trial: hemodynamic and neurohormonal effects

BACKGROUND

Persistent activation of the renin-angiotensin-aldosterone-system (RAAS) is known to occur in patients with chronic heart failure (CHF) despite treatment with angiotensin-converting enzyme inhibitor (ACE) therapy. When added to ACE inhibitors, angiotensin II type 1 (AT1) antagonists may allow more complete blockade of the RAAS and preserve the beneficial effects of bradykinin accumulation not seen with AT1 receptor blockade alone.

METHODS

Thirty-six patients with stable New York Heart Association class II-IV CHF receiving ACE inhibitor therapy were randomly assigned in a double-blind manner to receive either eprosartan, a specific competitive AT1 receptor antagonist (400 to 800 mg daily, n = 18) or placebo (n = 18) for 8 weeks. The primary outcome measure was left ventricular ejection fraction (LVEF) as measured by radionuclide ventriculography, and secondary measures were central hemodynamics assessed by Swan-Ganz catheterization and neurohormonal effects.

RESULTS

There was no change in LVEF with eprosartan therapy (mean relative LVEF percentage change [SEM] +10.5% [9.3] vs +10.1% [5.0], respectively; difference, 0.4; 95% confidence interval [CI], -20.8 to 21.7; P =.97). Eprosartan was associated with a significant reduction in diastolic blood pressure and a trend toward a reduction in systolic blood pressure compared with placebo (-7.3 mm Hg [95% CI, -14.2 to -0.4] diastolic; -8.9 mm Hg [95% CI, -18.6 to 0.8] systolic). No significant change in heart rate or central hemodynamics occurred during treatment with eprosartan compared with placebo. A trend toward an increase in plasma renin activity was noted with eprosartan therapy. Eprosartan was well tolerated, with an adverse event profile similar to placebo, whereas kidney function remained unchanged.

CONCLUSIONS

When added to an ACE inhibitor, eprosartan reduced arterial pressure without increasing heart rate. There was no change in LVEF after 2 months of therapy with eprosartan.

Glomerular permselectivity in early stages of overt diabetic nephropathy

BACKGROUND

Impairment of glomerular size selectivity has been demonstrated by the dextran-sieving technique in nephropathic diabetics with heavy, but not mild proteinuria. The purpose of the present study was to determine whether such a barrier defect could be demonstrated with mild proteinuria by substituting Ficoll 70, a polysucrose, for dextran as a probe of the filtration barrier.

METHODS

Differential solute clearances were performed in 12 individuals with early diabetic nephropathy on two occasions: after 60 days of treatment with losartan 50 mg daily or a placebo. An uncharged preparation of nonreabsorbable Ficoll 70 was infused along with inulin. Fractional clearance (theta) of Ficoll of discrete size was determined after separating molecules in urine and plasma in narrow 2 A fractions over a 20 to 60 A radius interval by size exclusion high-performance liquid chromatography (HPLC). A hydrodynamic theory of hindered ficoll transport through water-filled pores was used to characterize the pore size distribution of the glomerular barrier.

RESULTS

The theta for Ficoll molecules with radii> 50 A was selectively enhanced in placebo-treated diabetic nephropathy versus corresponding theta in healthy control subjects (N = 12). Computations revealed a lower distribution of glomerular pores that was unaltered in nephropathic diabetics. However, an upper distribution of large, shunt-like pores was more prominent, exceeding healthy controls by one order of magnitude in diabetic nephropathy (P = 0.01). A trend to lower theta for Ficoll in the 56 to 60 A radius range during losartan therapy is computed to have lowered the fraction of shunted filtrate by 26 to 44%, depending on whether glomerular pressure declined. The corresponding reduction in theta for endogenous albumin, IgG, and IgG4 was by 19 to 23% (P < 0.05).

CONCLUSION

Our findings suggest that shunt-like defects, partially reversible by angiotensin II blockade, are present early in the course of diabetic nephropathy. We estimate that such defects can account for immunoglobulinuria in this disorder. Additional impairment of either charge- or shape-selectivity must be invoked to explain the observed level of albuminuria, however.

Bradykinin B(2) receptor antagonism attenuates blood pressure response to acute angiotensin-converting enzyme inhibition in normal men

The physiological effects of angiotensin-converting enzyme (ACE) inhibition may be in part mediated by bradykinin. We investigated the effect of coadministration of the specific bradykinin B(2) receptor antagonist icatibant on hemodynamic and neurohormonal responses to acute intravenous ACE inhibition in normal men on a normal sodium diet. We performed a 4-phase, double-blind, double-dummy, placebo-controlled study in 12 male volunteers. The bradykinin antagonist icatibant (10 mg IV) was coadministered over the first 15 minutes of a 2-hour infusion of the ACE inhibitor perindoprilat (1.5 mg IV). Perindoprilat inhibited ACE activity and elicited the expected changes in active renin concentration and angiotensin peptides. Over the 3 hours after the start of drug infusion, perindoprilat lowered and icatibant increased mean arterial blood pressure (each P<0.0005 versus placebo). Coadministration of icatibant attenuated the mean arterial blood pressure response to perindoprilat (P<0.0005) but had no effect on neurohormonal responses to perindoprilat. Our study indicates that the bradykinin B(2) receptor antagonist icatibant attenuates the short-term blood pressure-lowering effect of acute ACE inhibition in normal men on a normal sodium diet. Bradykinin B(2) receptor antagonism alone increases resting blood pressure. Bradykinin may be involved in the control of blood pressure in the resting state in humans.

Endothelial dysfunction in renal transplant recipients maintained on cyclosporine

BACKGROUND

Hypertension is almost universal following renal transplantation and may contribute to the already poor cardiovascular prognosis of this group. Cyclosporine-induced hypertension is a particular problem and has variously been attributed to increased sympathetic nerve activity, salt and water retention, and increased circulating endothelin levels. However, the effects of cyclosporine on the L-arginine/nitric oxide (NO) system in vivo in humans are unknown. In this present study, we examined basal and stimulated NO production from the vascular endothelium in cyclosporine-treated renal transplant recipients using the technique of forearm venous plethysmography.

METHODS

In study 1, stimulated NO production was assessed in 9 cyclosporine-treated renal transplant recipients (CsA), 7 azathioprine-treated renal transplant recipients (AZA), and 12 controls, using carbachol (an endothelium-dependent vasodilator) and sodium nitroprusside (an endothelium-independent vasodilator). In study 2, basal NO production was assessed in 9 cyclosporine-treated patients and 11 controls using L-NMMA (inhibits NO synthase), with norepinephrine as a control vasoconstrictor. Drugs were infused into the nondominant forearm through a sterile 27-gauge needle, and changes in forearm blood flow (FBF) were measured using venous occlusion plethysmography.

RESULTS

In study 1, sodium nitroprusside caused a similar dose-dependent increase in FBF in all groups. However, the median (range) percentage increase FBF to carbachol (3 micrograms/min) was markedly reduced in the CsA patients (188.8; 72.5 to 385.1) compared with AZA patients (378.1; 124.0 to 548.9; P = 0.042) and to controls (303.8; 124.8 to 813.3; P = 0.028). In study 2, the maximum percentage reduction in FBF to L-NMMA (4 mumol/min) was less pronounced in CsA patients (-19.5; -4.7 to -63.1) compared with controls (-39.5; -15.7 to -52.8; P = 0.056), and while controls vasoconstricted to the maximum dose of norepinephrine (240 pmol/min) as expected (-26.9; -1.4 to -38.6), CsA patients as a group tended to vasodilate (7.9; -36.8 to 92.6; P = 0.02).

CONCLUSION

These data demonstrate impaired stimulated and basal NO production in CsA patients, indicating endothelial dysfunction. This may predispose patients to atherosclerosis and may be involved in the etiology of post-transplant hypertension.

Titration of vasodilator therapy in chronic heart failure according to plasma brain natriuretic peptide concentration: randomized comparison of the hemodynamic and neuroendocrine effects of tailored versus empirical therapy

BACKGROUND

Most patients with chronic heart failure (CHF) receive the same dose of angiotensin-converting enzyme (ACE) inhibitors because there is currently no measure of treatment efficacy. We sought to determine whether titration of vasodilator therapy according to plasma brain natriuretic peptide (BNP) concentration may be of value in the individual optimization of vasodilator therapy in CHF.

METHODS AND RESULTS

Twenty patients with mild to moderate CHF receiving stable conventional therapy including an ACE inhibitor were randomly assigned to titration of ACE inhibitor dosage according to serial measurement of plasma BNP concentration (BNP group) or optimal empirical ACE inhibitor therapy (clinical group) for 8 weeks. Only the BNP-driven approach was associated with significant reductions in plasma BNP concentration throughout the duration of the study and a significantly greater suppression when compared with empiric therapy after 4 weeks [-42.1% (-58.2, -19.7) vs -12.0% (-31.8, 13.8), P =.03]. Both treatment strategies were well tolerated and associated with favorable neurohormonal and hemodynamic effects; however, in comparison between groups, mean heart rate fell (P =.02) and plasma renin activity rose (P =.03) in the BNP group when compared with the clinical group.

CONCLUSIONS

Plasma BNP concentration may be chronically reduced by tailored vasodilator therapy in CHF. Furthermore, titration of vasodilator therapy according to plasma BNP was associated with more profound inhibition of the renin-angiotensin-aldosterone system and significant fall in heart rate when compared with empiric therapy.

Comparison of the short-term effects of candoxatril, an orally active neutral endopeptidase inhibitor, and frusemide in the treatment of patients with chronic heart failure

BACKGROUND

Candoxatril is a novel neutral endopeptidase inhibitor that increases plasma concentrations of atrial natriuretic factor and thereby produces natriuresis, diuresis, and vasorelaxation. This profile of action offers theoretical advantages over standard diuretic therapy in the treatment of patients with heart failure. The aims of the study were to compare the effects of candoxatril with those of frusemide in the treatment of patients with mild heart failure.

METHODS

Male patients with mild heart failure were randomly assigned to 9 days of therapy with 20 mg frusemide twice a day, 200 mg candoxatril twice a day, or 400 mg candoxatril twice a day (n = 10 per group) after a 14-day placebo washout phase. Systemic hemodynamic measurements, exercise tolerance, and urinary and plasma hormone concentrations were assessed during the placebo run-in and at the beginning and end of the double-blind therapy.

RESULTS

Frusemide and candoxatril caused similar diuresis and natriuresis. Candoxatril caused a slight decrease in systolic blood pressure and a dose-dependent increase in plasma and urinary concentrations of atrial natriuretic factor without elevating plasma renin activity. Frusemide reduced plasma concentrations of atrial natriuretic factor and increased plasma renin activity. Treadmill exercise capacity decreased 30 +/- 26 seconds after use of frusemide, compared with increases of 12 +/- 35 seconds after use of 200 mg candoxatril twice a day and 35 +/- 31 seconds after use of 400 mg candoxatril twice a day (P =.13; frusemide versus 400 mg candoxatril twice a day).

CONCLUSIONS

In the treatment of patients with mild heart failure, candoxatril has diuretic effects equivalent to those of 20 mg frusemide twice a day without the associated and potentially detrimental activation of the renin-angiotensin-aldosterone system. The trend for improved exercise capacity with candoxatril warrants further investigation.

Hypertension in mice lacking 11beta-hydroxysteroid dehydrogenase type 2

Deficiency of 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) in humans leads to the syndrome of apparent mineralocorticoid excess (SAME), in which cortisol illicitly occupies mineralocorticoid receptors, causing sodium retention, hypokalemia, and hypertension. However, the disorder is usually incompletely corrected by suppression of cortisol, suggesting additional and irreversible changes, perhaps in the kidney. To examine this further, we produced mice with targeted disruption of the 11beta-HSD2 gene. Homozygous mutant mice (11beta-HSD2(-/-)) appear normal at birth, but approximately 50% show motor weakness and die within 48 hours. Both male and female survivors are fertile but exhibit hypokalemia, hypotonic polyuria, and apparent mineralocorticoid activity of corticosterone. Young adult 11beta-HSD2(-/-) mice are markedly hypertensive, with a mean arterial blood pressure of 146 +/- 2 mmHg, compared with 121 +/- 2 mmHg in wild-type controls and 114 +/- 4 mmHg in heterozygotes. The epithelium of the distal tubule of the nephron shows striking hypertrophy and hyperplasia. These histological changes do not readily reverse with mineralocorticoid receptor antagonism in adulthood. Thus, 11beta-HSD2(-/-) mice demonstrate the major features of SAME, providing a unique rodent model to study the molecular mechanisms of kidney resetting leading to hypertension.

Control of adrenal cell proliferation by AT1 receptors in response to angiotensin II and low-sodium diet

The effects of angiotensin II (ANG II), the angiotensin type 1 (AT1) receptor antagonist losartan, and low-sodium diet on rat adrenal cell proliferation were studied in vivo with immunocytochemistry. Both ANG II and low-sodium diet increased proliferation of endothelial cells of the zona glomerulosa. Losartan prevented ANG II-induced hyperplasia of glomerulosa cells but not the effects of a low-sodium diet. Glomerulosa cells after ANG II + losartan treatment appeared hypertrophied compared with those of controls. Proliferative effects of ANG II and low-sodium diet in the reticularis were blocked by losartan. No changes were seen in the fasciculata. Proliferation in the medulla was increased with losartan, was decreased by ANG II, but was unaffected by low-sodium diet. In conclusion, 1) cell hypertrophy and proliferation of glomerulosa cells are mediated by AT1 receptor-dependent and -independent processes, 2) proliferation of reticularis cells is controlled by AT1 receptors, and 3) reciprocal control of chromaffin cell proliferation by ANG II may involve indirect AT1-dependent processes.

Differential effects of angiotensin II on cardiac cell proliferation and intramyocardial perivascular fibrosis in vivo

BACKGROUND

Growth effects of angiotensin II (Ang II) contribute to cardiac remodeling. Remodeling, in turn, may be influenced by proliferation of nonmyocytes. The aims of this study were to determine in vivo which cardiac cell types proliferate in response to Ang II, to evaluate whether proliferation is mediated by the Ang II AT1 receptor, and to establish whether blood pressure affects cell proliferation by comparing proliferation in the normotensive right atrium and ventricle and pressure-overloaded left ventricle.

METHODS AND RESULTS

Groups of 8 Wistar rats were implanted with miniosmotic pumps releasing 5-bromo-2'-deoxyuridine (BrdU) as a cell proliferation marker for 2 weeks. Two groups received Ang II infusions via a second minipump and drinking water+/-losartan. Two groups received vehicle+/-losartan. Cell proliferation was assessed as the percentage of nuclei that incorporated BrdU. Ang II increased proliferation within medial vascular smooth muscle cells (VSMCs) and in associated adventitial/interstitial fibroblasts of intramyocardial coronary arterioles but decreased proliferation of myoendothelial cells. Despite increased blood pressure, proliferation in atria and ventricles was similar. Aldosterone levels were not significantly elevated, suggesting direct proliferative effects of Ang II. Losartan reduced Ang II-induced VSMC and adventitial fibroblast proliferation but had no effect on myoendothelial cell proliferation.

CONCLUSIONS

These results indicate direct, differential effects of Ang II on proliferation of atrial and ventricular nonmyocytes. VSMC and fibroblast proliferation is AT1 receptor-dependent, whereas myoendothelial cells are controlled by an AT1-independent mechanism. The effects are independent of aldosterone and blood pressure and have important implications in renin-dependent hypertension and chronic cardiac failure when circulating Ang II is elevated.

ACE (I/D) genotype as a predictor of the magnitude and duration of the response to an ACE inhibitor drug (enalaprilat) in humans

BACKGROUND

We have investigated the possible effects of contrasting ACE (I/D) genotypes on the responses to the ACE inhibitor enalaprilat in normotensive men.

METHODS AND RESULTS

Subjects with DD (n=12) and II (n=11) ACE genotypes received an intravenous infusion of enalaprilat or placebo. Pressor responses to stepwise, incremental doses of angiotensin I were measured at 1 and 10 hours after dosing. The dose required to raise mean blood pressure by 20 mm Hg (PD20) was calculated individually, and the ratio of PD20 during enalaprilat to that during placebo (dose ratio, DR) was used for assessment of the extent of ACE inhibition. The pressor response was significantly attenuated at 1 hour after enalaprilat in both groups, but significant attenuation was evident at 10 hours after dose only in the II subjects. The DRs at both 1 hour (median, 5.43 versus 2.82, P=0.0035) and 10 hours (2.06 versus 0.84, P=0.0008) after enalaprilat were significantly higher in II subjects than in DD subjects.

CONCLUSIONS

The effect of enalaprilat was significantly greater and lasted longer in normotensive men homozygous for the II ACE genotype. By multivariate analysis, ACE (I/D) genotype and plasma angiotensin II levels were predictive of >50% of the variation in response to ACE inhibition.

Human alpha-adducin gene, blood pressure, and sodium metabolism

The adducin genes contribute significantly to population variation in rat blood pressure and cell membrane sodium transport. The 460Trp mutation of the human alpha-adducin gene has been associated with hypertension, in particular hypertension sensitive to sodium restriction. We studied the relationship between the 460Trp mutation and population variation in blood pressure and sodium metabolism. From 603 Scottish families, we selected 151 offspring and 224 parents with blood pressures in either the upper (high) or bottom (low) 30% of the population distribution and measured the 460Trp mutation using allele-specific hybridization. In offspring, we also measured exchangeable sodium, plasma volume, and total body water. Plasma levels of components of the renin-angiotensin system, atrial natriuretic peptide, and cellular sodium and transmembrane sodium efflux were also estimated. The overall frequency of the 460Trp mutation was 27.1%. In offspring and parent groups, we found no difference in the genotype or allele frequencies of the 460Trp mutation between subjects with high or low blood pressure. There was no overall association between the alpha-adducin genotypes and blood pressure variation. In offspring, the 460Trp mutation was not associated with any significant differences in body fluid volumes or exchangeable sodium; levels of plasma renin, angiotensin II, aldosterone, or atrial natriuretic peptide; intracellular sodium; or ouabain-sensitive transmembrane sodium efflux. These findings suggest that in our Scottish population, the alpha-adducin 460Trp polymorphism is not related to blood pressure and does not affect whole body or cellular sodium metabolism.

Inhibition of neutral endopeptidase causes vasoconstriction of human resistance vessels in vivo

BACKGROUND

Neutral endopeptidase (NEP) degrades vasoactive peptides, including the natriuretic peptides, angiotensin II, and endothelin-1. Systemic inhibition of NEP does not consistently lower blood pressure, even though it increases natriuretic peptide concentrations and causes natriuresis and diuresis. We therefore investigated the direct effects of local inhibition of NEP on forearm resistance vessel tone.

METHODS AND RESULTS

Four separate studies were performed, each with 90-minute drug infusions. In the first study, 10 healthy subjects received a brachial artery infusion of the NEP inhibitor candoxatrilat (125 nmol/min), which caused a slowly progressive forearm vasoconstriction (12+/-2%; P=0.001). In a second two-phase study, 6 healthy subjects received, 4 hours after enalapril (20 mg) or placebo, an intra-arterial infusion of the NEP inhibitor thiorphan (30 nmol/min). Thiorphan caused similar degrees of local forearm vasoconstriction (P=0.6) after pretreatment with both placebo (13+/-1%, P=0.006) and enalapril (17+/-6%, P=0.05). In a third three-phase study, 8 healthy subjects received intra-arterial thiorphan (30 nmol/min), the endothelin ETA antagonist BQ-123 (100 nmol/min), and both combined. Thiorphan caused local forearm vasoconstriction (13+/-1%, P=0.0001); BQ-123 caused local vasodilatation (33+/-3%, P=0.0001). Combined thiorphan and BQ-123 caused vasodilatation (32+/-1%, P=0.0001) similar to BQ-123 alone (P=0.98). In a fourth study, 6 hypertensive patients (blood pressure >160/100 mm Hg) received intra-arterial thiorphan (30 nmol/min). Thiorphan caused a slowly progressive forearm vasoconstriction (10+/-2%, P=0.0001).

CONCLUSIONS

Inhibition of local NEP causes vasoconstriction in forearm resistance vessels of both healthy volunteers and patients with hypertension. The lack of effect of ACE inhibition on the vasoconstriction produced by thiorphan and its absence during concomitant ETA receptor blockade suggest that it is mediated by endothelin-1 and not angiotensin II. These findings may help to explain the failure of systemic NEP inhibition to lower blood pressure.

Effect of angiotensin II on histamine-induced bronchoconstriction in the human airway both in vitro and in vivo

The renin-angiotensin system is activated in acute severe asthma. Angiotensin II causes bronchoconstriction in mild asthmatics and potentiates methacholine-evoked bronchoconstriction both in vitro and in vivo. To evaluate the effect of angiotensin II on histamine-induced bronchoconstriction, human bronchial rings (n = 6) were obtained from lung tissue at thoracotomy and were prepared in organ baths. Contractions were measured isometrically and cumulative concentration-response curves obtained to angiotensin II alone and to histamine in the presence and absence of threshold concentrations of angiotensin II. Eight asthmatic patients with bronchial hyper-reactivity to histamine were challenged with histamine during intravenous infusion of placebo, angiotensin II 1 ng kg-1 min-1 and angiotensin 2 ng kg-1 min-1 administered in a randomized, double-blind fashion, FEV1 was measured prior to, during the infusion and during the histamine challenge. Angiotensin II (3 x 10(-7)M and 10(-6)M) alone evoked small contractions (< 0.25 g) of human bronchi in vitro, but pre-incubation with threshold concentrations of angiotensin II (10(-7)M, 3 x 10(-7)M and 10(-6)M) had no effect on histamine-evoked contractions. In asthmatic patients, angiotensin II alone had no effect on baseline FEV1 at the low levels infused and did not affect the response to nebulized histamine as measured by the PC20 histamine: Geometric mean (range) PC20 histamine (mg ml-1) screening day 3.58 (1.26-7.75), placebo infusion 2.67 (0.89-9.57), angiotensin II 1 ng kg-1 min-1 2.45 (0.42-6.97) and angiotensin II 2 ng kg-1 3.09 (0.8-10.78). It is concluded that, in contrast to its potentiating effect on methacholine-induced bronchoconstriction, angiotensin II has no effect on histamine-evoked bronchoconstriction in human bronchi in vitro or in vivo.

Potent in vivo inhibitors of rat renin: analogues of human and rat angiotensinogen sequences containing different classes of pseudodipeptides at the scissile site

Using solid-phase methodology we have synthesised peptides based on the 8-14 or 6-14 human and rat angiotensinogen sequences, containing the following different isosteric units at the P1-P1' cleavage site: Leu-psi[CH2NH]Leu; Leu-psi[CH(OH)CH2]Val; Leu-psi[CH(OH)CH2]Leu and Leu-psi[CH(NH2)CH2]Val. In vitro, peptide Piv-His-Pro-Phe-His-Leu-psi[CH(OH)CH2]Leu-Tyr-Tyr-Ser-NH2(XXI) is the most potent inhibitor of rat plasma renin reported having an IC50 of 0.21 nM; it is a much weaker inhibitor of human renin (IC50 45 nM). Peptide Boc-His-Pro-Phe-His-Leu-psi[CH(OH)CH2] Leu-Val-Ile-His-NH2 (XX) was a highly effective inhibitor of rat renin in vivo. When infused (1 mg/kg/h) into two-kidney, one-clip chronic renal hypertensive rats, it lowered blood pressure and suppressed both plasma renin and angiotensin II. When given as a bolus (1 mg/kg) there was a divergence between the rapid rebound of renin levels and blood pressure, which remained suppressed. These results indicate that potent in vivo inhibitors of rat renin could be useful not only in examining the role of circulating renin but also in elucidating the equally important involvement of extracirculatory renin pools.

Enhanced natriuretic response to neutral endopeptidase inhibition in patients with moderate chronic renal failure

Atrial natriuretic factor (ANF) has natriuretic, renin-suppressing and chronic hypotensive actions that may be utilized by inhibition of ANF degradation by neutral endopeptidase, E.C.24.11 (NEP). Three groups of 8 male patients [GFR 103 +/- 8 (Normal), 64 +/- 6 (Moderate CRF), and 16 +/- 2 ml/min (Severe CRF)] received 100 mg i.v. bolus of the NEP inhibitor candoxatrilat or placebo in random order in a double-blind crossover study. GFR (51CR-EDTA), ERPF (125I-hippuran). ANF (IRMA), urinary cGMP (RIA) and albumin (RIA) and sodium excretion and flow rate were measured hourly for two hours before and for seven hours after candoxatrilat administration. After candoxatrilat plasma ANF rose two- to threefold from baseline, and remained elevated for 5(N) and 7(M,S) hours (P < 0.01(N,S), P < 0.03(M)) associated with an immediate rise in urine cGMP excretion from 23.5(N), 25.4(M) and 10.4(S) nmol/hr (base) to 51.7(N), 73.8(M) and 27.5(S)(peak) lasting 7(N,M,S) hours (P < 0.01(N,M,S)). There was a marked natriuresis in all three groups, the cumulative sodium excretion at seven hours post-candoxatrilat being 104(N), 140(M), 102(S) mmol (P < 0.05(N,M,S)). This was greatest in those with moderate CRF (moderate CRF vs. normal, P = 0.036, moderate vs. severe CRF, P = 0.01, normal vs. severe CRF, P = 0.74). Following candoxatrilat there was a near doubling of the urine flow rate (P < 0.01(N,S), P < 0.02(M)). Urine albumin excretion increased in patients with renal failure (P < 0.01), but there was no change in GFR, ERPF or systemic blood pressure. We conclude that the marked natriuretic effects of acute NEP inhibition seen in normal subjects are enhanced in the presence of moderate CRF and sustained even in severe renal impairment.

New renin inhibitors containing novel analogues of statine

Solid-phase methodology has been used to synthesize a series of peptides based on the N-terminal sequence of human angiotensinogen in which statine (Sta) or the novel analogues (3S,4S)-3,4-diamino- or (3R,4S)-3,4-diamino-6-methylheptanoic acid (Ads or R-Ads) and (3S,4S)-4-amino-3-aminomethyl- or (3R,4S)-4-amino-3-aminomethyl-6-methylheptanoic acid (Amd or R-Amd) replace either residue 10 or both residues 10-11 at the P1-P1' cleavage site. The synthesis of these novel analogues of statine together with biological results on the inhibition of human and rat renin by peptides derived from them is reported. The absolute stereochemistry of the (3S,4S) Ads was determined by an X-ray crystallographic analysis of its N gamma-Boc, B beta-Z, R(+)-1-methyl benzamide derivative. Peptide Boc-His-Pro-Phe-His-Sta-Val-Ile-His-NH2 (VI) is the best inhibitor of human renin containing Sta at position 10. However, peptides containing Ads and Amd gave better rat renin inhibitors than the corresponding Sta-containing peptides. Peptides Boc-His-Pro-Phe-His-Ads-Val-Ile-His-NH2 (VII) having Ads at position 10 had an IC50 of 12 nM against rat renin. Although Sta has come to be accepted as an isosteric replacement for a dipeptide unit rather than for a single amino acid residue, in our series of inhibitors Sta is more effective when replacing only the amino acid at position 10 in the natural angiotensinogen sequence. None of the peptides gave any effect in vivo in a hypertensive rat model.

Pressor and hormonal responses to angiotensin I infusion in healthy subjects of different angiotensin-converting enzyme genotypes

The effects of incremental infusion of angiotensin I on pressor and hormonal responses in relation to the angiotensin-converting enzyme (ACE) genotype were compared in healthy men of genotype DD (n = 8) and II (n = 8). The R(d)25 was the rate of angiotensin I infusion required to achieve a 25-mm Hg increase in diastolic pressure, and the R(s)25, that which caused a 25-mm Hg increase in systolic pressure. Changes in heart rate (HR25) were analysed at the time the R(d)25 was achieved. Serum ACE activity and plasma renin, angiotensin II, and aldosterone concentrations were measured at the start and end of the angiotensin I infusion. Serum ACE activity differed significantly between the genotypes with significantly higher mean values in DD subjects (46.3 +/- SEM 5.2 U/L) than II subjects (12.3 +/- 1.4 U/L; p < 0.001). Age, weight, and baseline blood pressure, heart rate, urinary sodium excretion, plasma renin, angiotensin II, and aldosterone concentrations did not differ between genotypes. The geometric mean infusion rates of angiotensin I required to achieve R(d)25 were 2.53 micrograms/min in II subjects and 2.67 micrograms/min in DD subjects (ratio of infusion rates, 0.95; 95% CI, 0.44-2.02; p > 0.05). The corresponding infusion rates for systolic blood pressure (R(s)25) were 4.47 micrograms/min in II subjects and 3.39 micrograms/min in DD subjects (ratio, 1.32; 95% CI, 0.49-3.55; p > 0.05). At the time of R(d)25, changes in heart rate from baseline were +1.2 beats/min for DD subjects and -9.5 beats/min for II subjects (diff II-DD = 10.7 beats/min; 95% CI, 6.7-14.8; p = 0.01). There were no differences in plasma renin, angiotensin, and aldosterone responses to angiotensin I infusion between the DD and II genotypes. We showed no difference in blood pressure or renin-angiotensin-aldosterone system responses to infusion of angiotensin I related to the deletion or insertion allele of the ACE gene polymorphism, but the study has insufficient power to exclude with certainty such differences. There was a significant difference between II and DD subjects in the chronotropic response to angiotensin I infusion.

AT1 receptor blockade and the sympathoadrenal response to insulin-induced hypoglycemia in humans

An important facilitating effect of angiotensin II on adrenal catecholamine release has been demonstrated in several species. To determine whether specific AT1 receptor blockade affects medullary epinephrine secretion and musculocutaneous norepinephrine release during insulin-induced hypoglycemia, 16 healthy volunteers received losartan vs. placebo followed by an intravenous insulin bolus and measurement of effect variables at short intervals for 150 min. AT1 receptor blockade was effective, as evidenced by substantially increased circulating renin and angiotensin II levels, a 60% inhibition of circulating aldosterone, and an 8.5% decrease of mean arterial pressure over time compared with placebo. Arterial glucose concentration fell to a nadir of 1.9 mM, arterial epinephrine concentration increased 23-fold, forearm musculocutaneous norepinephrine release increased 4-fold, heart rate increased 40%, and forearm blood flow increased 3-fold. All absolute values and the time course of these changes were independent of AT1 receptor blockade. It is concluded that a putative interaction between angiotensin II and the sympathoadrenal axis may not be mediated by AT1 receptors in humans.

The effect of nebulized albuterol on the activity of the renin-angiotensin system in asthma

STUDY OBJECTIVE

We have previously described activation of the renin-angiotensin system (RAS) in acute severe asthma and have also reported activation of the RAS in normal subjects by single doses of nebulized beta 2-agonists. In the present study, we have examined the effect of single and multiple doses of nebulized albuterol on the activity of the RAS in mild asthma.

DESIGN

Eight patients with mild asthma were studied. The effect of single and multiple doses of nebulized albuterol (5 mg) on the activity of the RAS was compared with that of placebo using a randomized, double-blind crossover study design. Nebulized drugs were administered at time 0 and 30 min.

MEASUREMENTS

Plasma renin, angiotensin II (Ang II), and serum potassium levels were measured at baseline following a short rest, and thereafter at intervals up to 150 min.

RESULTS

Renin levels increased after both the single (S) and double (D) nebulized doses of albuterol and were significantly greater than placebo at 30 min after S, and at 45 and 120 min after D. Plasma Ang II level also increased after S and D and was significantly greater than placebo at 30 and 45 min after S, and at 30 min and all timepoints thereafter following D. In addition, the effect of D was significantly greater than S at 45 min.

CONCLUSIONS

These results confirm that there is activation of the RAS in asthmatic subjects by single doses of nebulized beta 2-agonists and that repeated dosing with nebulized albuterol has further, additive effects on plasma Ang II levels. It therefore seems likely that these agents are contributing to activation of the RAS in acute asthma, although the exact clinical significance of these transient changes in plasma Ang II levels in asthma is at present unclear.

Reduced plasma aldosterone concentrations in randomly selected patients with insulin-dependent diabetes mellitus

Abnormalities of the renin-angiotensin system have been reported in patients with diabetes mellitus and with diabetic complications. In this study, plasma concentrations of prorenin, renin, and aldosterone were measured in a stratified random sample of 110 insulin-dependent (Type 1) diabetic patients attending our outpatient clinic. Fifty-four age- and sex-matched control subjects were also examined. Plasma prorenin concentration was higher in patients without complications than in control subjects when upright (geometric mean (95% confidence intervals (CI): 75.9 (55.0-105.6) vs 45.1 (31.6-64.3) mU I-1, p < 0.05). There was no difference in plasma prorenin concentration between patients without and with microalbuminuria and between patients without and with background retinopathy. Plasma renin concentration, both when supine and upright, was similar in control subjects, in patients without complications, and in patients with varying degrees of diabetic microangiopathy. Plasma aldosterone was suppressed in patients without complications in comparison to control subjects (74 (58-95) vs 167 (140-199) ng I-1, p < 0.001) and was also suppressed in patients with microvascular disease. Plasma potassium was significantly higher in patients than in control subjects (mean +/- standard deviation: 4.10 +/- 0.36 vs 3.89 +/- 0.26 mmol I-1; p < 0.001) and plasma sodium was significantly lower (138 +/- 4 vs 140 +/- 2 mmol I-1; p < 0.001). We conclude that plasma prorenin is not a useful early marker for diabetic microvascular disease. Despite apparently normal plasma renin concentrations, plasma aldosterone is suppressed in insulin-dependent diabetic patients.

Enhanced pressor response to angiotensin I in normotensive men with the deletion genotype (DD) for angiotensin-converting enzyme

The insertion (I)/deletion (D) polymorphism of the human angiotensin-converting enzyme gene has emerged as a genetic risk factor for ischemic heart disease. However, the functional consequences of this polymorphism in humans are not known. Ten normotensive men with the DD genotype and 10 with the II genotype participated in a study in which pressor responses to stepwise infusions of incremental doses of angiotensin I (Ang I) and Ang II and Ang II production during Ang I infusion were measured. Pressor responses were expressed as PD20, which reflects the angiotensin dose required to raise mean blood pressure by 20 mm Hg. The PD20 for Ang I in subjects with the DD genotype was significantly lower than that in II genotype subjects (8.8 versus 14.8 ng/kg per minute, P = .0091), whereas the PD20 for Ang II between the two groups did not differ significantly. The ratio of PD20 for Ang I and Ang II in DD subjects was significantly lower than that in II subjects (0.85 versus 0.96, P = .0452), and the venous levels of Ang II during Ang I infusion in DD subjects were significantly higher than those in II subjects (P < .01). Our study has shown increased pressor responsiveness to Ang I, probably as a consequence of the generation of increased Ang II levels, in subjects homozygous for the DD allele of the angiotensin-converting enzyme gene. This result may be relevant to the reported adverse cardiovascular risk conferred by the D allele, as it provides a mechanistic rationale for the association between this polymorphism and cardiovascular disease.