THE EFFECT OF ANGIOTENSIN II ON THE BLOOD PRESSURE IN HUMANS WITH HYPERTENSIVE DISEASE

Tolerance to Sodium in Patients With CKD-Induced Metabolic Acidosis: Does the Accompanying Anion Matter?

Patients with chronic kidney disease (CKD) continue to produce endogenous acids but have a reduction in net acid excretion, resulting in a primary decrease in serum bicarbonate concentration, which is termed chronic metabolic acidosis. Recent prospective studies, along with retrospective cohort analyses, demonstrate a higher risk for CKD progression with untreated metabolic acidosis. To normalize serum bicarbonate levels, acidemic patients are often treated with sodium bicarbonate (NaHCO₃) or sodium citrate, which have been shown to slow the progression of CKD. However, studies using this approach have routinely excluded patients with common sodium-sensitive comorbid conditions, such as poorly controlled hypertension, congestive heart failure, volume overload, or edema. This article examines the effect of the anion that accompanies sodium delivered with these therapies. Do the negative effects on blood pressure (BP) and sodium retention, as measured by an increase in edema, weight gain, and congestive heart failure, observed with oral administration of sodium chloride (NaCl) differ when a similar amount of sodium is given with bicarbonate or citrate in this patient population? A review of the literature suggests that NaHCO₃ does not increase BP or sodium retention when administered to patients with CKD during a concurrent severe NaCl dietary restriction (∼10 mEq/d). However, this degree of NaCl restriction is feasible only under strict control in clinical research environments. In contrast, when NaHCO₃ is given to patients without severe dietary NaCl restriction, there is an increase in BP and sodium retention. Thus, unless patients with CKD can tolerate a diet virtually devoid of NaCl, additional sodium, regardless of the accompanying anion, appears to increase BP and sodium retention.

Arterioventricular interaction after coarctation repair

BACKGROUND

Hypertension is common in patients with coarctation of the aorta (CoA), even after successful repair. Increased aortic stiffness has been implicated in the pathology of CoA-associated hypertension. This study aimed to investigate aortic vascular function and its relationship with hypertension in well-repaired CoA-patients at long-term follow-up. Furthermore, we assessed the additive effect of hypertension to adverse arterioventricular coupling associated with increased aortic stiffness.

METHODS

Twenty-two CoA-patients (age 30 ± 10.6 years) with successful surgical repair (n = 12) or balloon angioplasty (BA) (n = 10) between 3 months and 16 years of age with a follow-up of >10 years and 22 healthy controls underwent cardiac magnetic resonance imaging (CMR), at mean follow-up of 29.3 years, to study aortic pulse wave velocity (PWV), aortic distensibility, global left ventricular (LV) function, LV dimensions, and LV myocardial deformation.

RESULTS

CoA-patients had significantly increased aortic arch PWV (5.6 ± 1.9 m/s vs. 4.5 ± 1.0 m/s, P = .02) and decreased distensibility (4.5 ± 1.8 × 10-3 mmHg^-1 vs. 5.8 ± 1.8 × 10-3 mmHg^-1, P = .04) compared to controls. Significant differences in aortic arch PWV were found between hypertensive patients, normotensive patients and controls (6.1 ± 1.8 m/s vs. 4.9 ± 1.9 m/s and 4.5 ± 1.0 m/s, respectively, P = .03). Aortic arch PWV and distensibility were correlated with systolic blood pressure (R = 0.37 and R = -0.37, respectively, P = .03 for both). Global LV function, LV mass, LV dimensions and myocardial deformation were similar in CoA-patients when compared to controls.

CONCLUSIONS

Central aortic stiffness is significantly increased in well-repaired CoA-patients long-term after repair, and is associated with hypertension. Global LV function, myocardial deformation indices and LV dimensions are however preserved.

Preserved Myocardial Deformation after Successful Coarctation Repair: A CMR Feature-Tracking Study

Arterial vasculopathy and residual aortic obstruction can lead to left ventricular (LV) dysfunction in patients with coarctation of the aorta (CoA) related to adverse ventriculo-arterial coupling. This study aimed to investigate potential differences in LV myocardial deformation indices between repaired CoA patients and healthy controls. Twenty-two CoA patients (age 30 ± 10.6 years) after surgical repair (n = 12) or balloon angioplasty (BA) (n = 10) without residual stenosis, between 3 months and 16 years of age with > 10 years follow-up were compared to 22 healthy age- and gender-matched controls (age 30 ± 3.8 years). Cardiac magnetic resonance feature tracking (CMR-FT) was used for LV longitudinal-, circumferential-, and rotational deformation indices. Global systolic LV function was preserved in CoA patients (LV ejection fraction 58 ± 4.8 vs. 60 ± 6.8%, p = 0.56) when compared to controls, with normal LV dimensions and mass (p > 0.05). Twelve CoA patients (55%) were hypertensive, of whom 4 were on anti-hypertensive medication. LV global longitudinal strain was preserved in the four-chamber (- 18 ± 4.4 vs. - 16 ± 4.7%, p = 0.06) and two-chamber (- 22 ± 5.1 vs. - 20 ± 6.0%, p = 0.22) orientations in CoA patients. Global circumferential strain was preserved at basal (- 29 ± 4.1 vs. - 28 ± 4.8%, p = 0.43), mid-ventricular (- 27 ± 4.2 vs. - 25 ± 3.0%, p = 0.09), and apical levels (- 35 ± 7.8 vs. - 32 ± 34.9%, p = 0.32). No differences were found in global torsion (2.4 ± 1.3° vs. 2.0 ± 1.4°/cm, p = 0.28), twist (14 ± 5.8° vs. 12 ± 6.3°, p = 0.34), and recoil rate (- 17 ± 9.7° vs. - 17 ± 7.1°/cm s, p = 0.97). Analysis of intra-observer variability demonstrated good reproducibility for all CMR deformation indices. Global and rotational myocardial deformation indices are preserved in CoA patients long-term after repair without residual stenosis, despite a high incidence of hypertension.

Exercise intensity modulates capillary perfusion in correspondence with ACE I/D modulated serum angiotensin II levels

During exercise the renin-angiotensin system is stimulated. We hypothesized that the increase in serum angiotensin II (AngII) levels after exercise is dependent on exercise intensity and duration and secondly that people with the ACE-II genotype will show a higher increase in AngII serum levels. We also assumed that perfusion of upper limbs is transiently reduced with maximal cycling exercise and that subjects with the ACE-II compared to the ACE-ID/DD genotype will have a higher capillary perfusion due to lower AngII levels. Ten healthy subjects completed a maximal exercise test, a 12-min exercise test at ventilatory threshold and a 3-min test at the respiratory compensation point. AngII serum levels and capillary recruitment of the skin in the third finger were measured before and after exercise and breath-by-breath gas exchange during exercise was assessed. Baseline levels of AngII levels were lower prior to the 3-min test which took place on average 5 days after the last exercise. A two-fold increase compared to baseline levels was found for AngII only immediately after the 3-min test and not after the maximal exercise test and 12-min of exercise. Subjects without the I allele showed a decrease in AngII values after the maximal test in contrast to subjects with the ACE-II/ID genotype. Subjects with the ACE-II genotype had a 1.8 times significant higher capillary perfusion in the finger after exercise. A trend was observed for a 34.3% decreased capillary recruitment in the ACE-ID/DD genotype after exercise. We conclude that the rise in AngII after exercise is intensity dependent and that variability in serum AngII and capillary perfusion is related to the ACE I/D polymorphism.

Altered systemic hemodynamic and baroreflex response to angiotensin II in postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) is characterized by excessive orthostatic tachycardia and significant functional disability. We have previously found that patients with POTS have increases in plasma angiotensin II (Ang II) that are twice as high as healthy subjects despite normal blood pressures (BPs). In this study, we assess systemic and renal hemodynamic and functional responses to Ang II infusion in patients with POTS compared with healthy controls.

METHODS AND RESULTS

Following a 3-day sodium-controlled diet, we infused Ang II (3 ng/kg per minute) for 1 hour in patients with POTS (n=15) and healthy controls (n=13) in the supine position. All study subjects were women with normal BP. Ages were similar for patients with POTS and controls (mean±SEM, 30±2 versus 26±1 years; P=0.11). We measured the changes from baseline mean arterial pressure, renal plasma flow, plasma renin activity, aldosterone, urine sodium, and baroreflex sensitivity in both groups. In response to Ang II infusion, patients with POTS had a blunted increase compared with controls in mean arterial pressure (10±1 versus 14±1 mm Hg, P=0.01) and diastolic BP (9±1 versus 13±1 mm Hg, P=0.01) but not systolic BP (13±2 versus 15±2 mm Hg, P=0.40). Renal plasma flow decreased similarly with Ang II infusion in patients with POTS versus controls (-166±20 versus -181±17 mL/min per 1.73 kg/m(2), P=0.58). Postinfusion, the decrease in plasma renin activity (-0.9±0.2 versus -0.6±0.2 ng/mL per hour, P=0.43) and the increase in aldosterone (17±1 versus 15±2 pg/mL, P=0.34) were similar in both groups. The decrease in urine sodium excretion was similar in patients with POTS and controls (-49±12 versus -60±16 mEq/g creatinine, P=0.55). The spontaneous baroreflex sensitivity at baseline was significantly lower in patients with POTS compared with controls (10.1±1.2 versus 16.8±1.5 ms/mm Hg, P=0.003), and it was further reduced with Ang II infusion.

CONCLUSIONS

Patients with POTS have blunted vasopressor response to Ang II and impaired baroreflex function. This impaired vasoconstrictive response might be exaggerated with upright posture and may contribute to the subsequent orthostatic tachycardia that is the hallmark of this disorder. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00962949.

Failure of Verapamil and Diltiazem to Attenuate the Pressor Response to Hypothalamic Stimulation: A Possible Mechanism

The effects of verapamil or diltiazem on pressor responses to posterior hypothalamic stimulation, injected noradrenaline or tyramine were studied in urethane-anaesthetized normotensive, deoxycorticosterone acetate (DOCA), renal and spontaneously hypertensive rats at the early and established phases of hypertension. Pressor responses to the pressor stimuli were significantly enhanced in the early and established phases of hypertension when compared with the normotensives. While the magnitude of pressor responses in the established phase of renal or spontaneously hypertensive rats was significantly higher (P < 0·05) than the corresponding value in the early phase, in contrast, the pressor response in the early phase of DOCA hypertension was significantly higher than that of the established phase. Verapamil or diltiazem significantly (P < 0·005) inhibited pressor responses to injected noradrenaline or tyramine in all groups of rats but not that to hypothalamic stimulation, irrespective of the stage of hypertension. When the probable mechanism of the hypothalamic pressor response's resistance to the calcium antagonists was studied in-vitro, ATP significantly (P < 0·005) inhibited the relaxant effect of the calcium antagonists in the rat aortic strips. Our data indicate that verapamil or diltiazem is ineffective in inhibiting the pressor response to posterior hypothalamic stimulation. The probable mechanism of the resistance and the clinical implication of the findings are discussed.

Abnormalities of angiotensin regulation in postural tachycardia syndrome

BACKGROUND

Postural tachycardia syndrome (POTS) is a disorder characterized by excessive orthostatic tachycardia and significant functional disability. We previously reported that POTS patients have low blood volume and inappropriately low plasma renin activity (PRA) and aldosterone. In this study, we sought to more fully characterize the renin-angiotensin-aldosterone system (RAAS) to gain a better understanding of the pathophysiology of POTS.

OBJECTIVE

The purpose of this study was to prospectively assess the plasma levels of angiotensin (Ang) peptides and their relationship to other RAAS components in patients with POTS compared with healthy controls.

METHODS

Heart rate, PRA, Ang I, Ang II, Ang (1-7), and aldosterone were measured in POTS patients (n = 38) and healthy controls (n = 13) while they were consuming a sodium-controlled diet.

RESULTS

POTS patients had larger orthostatic increases in heart rate than did controls (52 ± 3 [mean ± SEM] bpm vs 27 ± 6 bpm, P = .001). Plasma Ang II was significantly higher in POTS patients (43 ± 3 pg/mL vs 28 ± 3 pg/mL, P = .006), whereas plasma Ang I and angiotensin 1-7 [Ang-(1-7)] were similar between groups. Despite the twofold increase of Ang II, POTS patients trended to lower PRA levels than did controls (0.9 ± 0.1 ng/mL/h vs 1.6 ± 0.5 ng/mL/h, P = .268) and lower aldosterone levels (4.6 ± 0.8 pg/mL vs 10.0 ± 3.0 pg/mL, P = .111). Estimated angiotensin-converting enzyme-2 (ACE2) activity was significantly lower in POTS patients than in controls (0.25 ± 0.02 vs 0.33 ± 0.03, P = .038).

CONCLUSION

Some patients with POTS have inappropriately high plasma Ang II levels, with low estimated ACE2 activity. We propose that these abnormalities in Ang regulation may play a key role in the pathophysiology of POTS in some patients.

The Effects of Angiotensin II on Renal Water and Electrolyte Excretion in Normal and Caval Dogs

The effects of intravenous administration of angiotensin II on renal water and electrolyte excretion were examined during hydropenia, water diuresis, and hypotonic saline diuresis in anesthetized normal dogs and dogs with thoracic inferior vena cava constriction and ascites (caval dogs). The effects of unilateral renal artery infusion of a subpressor dose were also examined.During hydropenia angiotensin produced a decrease in tubular sodium reabsorption, with a considerably greater natriuresis in caval dogs, and associated with a decrease in free water reabsorption (T(c) (H(2)O)). Water and hypotonic saline diuresis resulted in an augmented angiotensin natriuresis, with a greater effect still observed in caval dogs. In these experiments free water excretion (C(H(2)O)) was limited to 8-10% of the glomerular filtration rate (GFR), although distal sodium load increased in every instance. In the renal artery infusion experiments a significant ipsilateral decrease in tubular sodium reabsorption was induced, particularly in caval dogs.These findings indicate that angiotensin has a direct effect on renal sodium reabsorption unrelated to a systemic circulatory alteration. The attenuation or prevention of the falls in GFR and effective renal plasma flow (ERPF) usually induced by angiotensin may partially account for the greater natriuretic response in caval dogs and the augmentation during water or hypotonic saline diuresis. However, a correlation between renal hemodynamics and the degree of natriuresis induced was not always present and, furthermore, GFR and ERPF decreased significantly during the intrarenal artery infusion experiments. Therefore, the present experiments indicate that another mechanism is operative in the control of the angiotensin natriuresis and suggest that alterations in intrarenal hemodynamics may play a role.The decrease in T(c) (H(2)O) and the apparent limitation of C(H(2)O) associated with an increase in distal sodium load localize the site of action of angiotensin to the ascending limb of Henle's loop and the proximal tubule.

Bartter's syndrome without hyperplasia of the juxtaglomerular apparatus, treated with indomethacin

The present report describes a case of potassium-wasting nephropathy with the physiological and endocrinological findings that are typical for Bartter's syndrome (BS). However, the renal juxtaglomerular apparatus showed no hyperplasia at two renal biopsies two years apart. The short-term (9 days) effect of indomethacin in combination with spironolactone was a suppression of hyperreninemia and hyperaldosteronism and an increase in vascular sensitivity to angiotensin II associated with potassium and sodium retention. Subsequently, on indomethacin alone, potassium balance was obtained on a lower level with persistent hypokalemia and persistent renal potassium leakage. Hypokalemia persisted during long-term (9 months) treatment with indomethacin despite normalization of the activity of the renin-aldosterone system. The results indicate that indomethacin as long-term treatment may be ineffective in maintaining a normal potassium balance in BS.

The adrenocortical response to angiotensin II infusion in anephric and non-nephrectomized patients on regular hemodialysis

In the present study 8 anephric and 4 non-nephrectomized patients were stimulated with angiotensin II (A-II). In 5 of the anephric patients, an increased plasma aldosterone concentration (PAC) in response to ACTH stimulation had previously been demonstrated. After A-II stimulation, all 8 anephric patients responded with a significant rise in PAC although the increase was less pronounced than in 4 non-nephrectomized patients. In both groups of patients the increase in PAC was correlated to the increase in diastolic and systolic BP and to the A-II dose. Furthermore, in the non-nephrectomized patients, the plasma renin activity showed a significant decline, which was inversely correlated to the increase in PAC. When all 12 patients, regardless of the difference in remaining renin-angiotensin system, were considered as one population, the variable basal levels of PAC correlated significantly to the increase in PAC during A-II and ACTH stimulation. It is concluded that the adrenals of anephric man respond to A-II with an increase in PAC and that the reason for a lower response appears to be the lack of the renin-angiotensin system.

The renin-angiotensin system in conscious newborn sheep: metabolic clearance rate and activity

The role of the renin-angiotensin system (RAS) in regulating newborn mean arterial blood pressure (MAP) and tissue blood flow remains unclear. Although postnatal MAP increases, vascular responsiveness to infused angiotensin II (ANG II) is unchanged, possibly reflecting increased metabolic clearance rate of ANG II (MCR(ANG II)). To address this, we examined MAP, heart rate, plasma ANG II and renin activity (PRA), and MCR(ANG II) in conscious postnatal sheep (n = 9, 5-35 d old) before and during continuous systemic ANG II infusions to measure MCR (ANG II). Postnatal MAP increased (p < 0.02), whereas plasma ANG II decreased from 942 +/- 230 (SEM) to 471 +/- 152 and 240 +/- 70 pg/mL at <10 d, 10-20 d, and 21-35 d postnatally (p = 0.05), respectively. Despite high plasma ANG II, PRA remained elevated, averaging 6.70 +/- 1.1 ng/mL.h throughout the postnatal period, but decreased 35% (p = 0.01) during ANG II infusions. MCR(ANG II) decreased approximately sixfold after birth and averaged 115 mL/min.kg during the first month. Circulating ANG II is markedly increased after birth, reflecting placental removal, high fetal MCR(ANG II), and enhanced RAS activity. Although circulating ANG II decreases as MAP increases, MCR(ANG II) is unchanged, suggesting decreased ANG II production. Persistent vascular smooth muscle (VSM) AT2 receptor subtype (AT2R) expression after birth may modify the hypertensive effects of ANG II postnatally.

Effects of chronic portal hypertension on agonist-induced actin polymerization in small mesenteric arteries

The ability of arterial smooth muscle to respond to vasoconstrictor stimuli is reduced in chronic portal hypertension (PHT). Additional evidence supports the existence of a postreceptor defect in vascular smooth muscle excitation contraction coupling. However, the nature of this defect is unclear. Recent studies have shown that vasoconstrictor stimuli induce actin polymerization in smooth muscle and that the associated increase in F-actin is necessary for force development. In the present study we have tested the hypothesis that impaired actin polymerization contributes to reduced vasoconstrictor function in small mesenteric arteries derived from rats with chronic prehepatic PHT. In vitro studies were conducted on small mesenteric artery vessel rings isolated from normal and PHT rats. Isometric tension responses to incremental concentrations of phenylephrine were significantly reduced in PHT arteries. The ability to polymerize actin in portal hypertensive mesenteric arteries stimulated by phenylephrine was attenuated compared with control. Inhibition of cAMP-dependent protein kinase (PKA) restored agonist-induced actin polymerization of arteries from PHT rats to normal levels. Depolymerization of actin in arteries from normal rats reduced maximal contractile force but not myosin phosphorylation, suggesting a key role for the dynamic regulation of actin polymerization in the maintenance of vascular smooth muscle contraction. We conclude that reductions in agonist-induced maximal force development of PHT vascular smooth muscle is due, in part, to impaired actin polymerization, and prolonged PKA activation may underlie these changes.

The hyperdynamic circulation in cirrhosis: an overview

The hyperdynamic circulation begins in the portal venous bed as a consequence of portal hypertension due to the increased resistance to flow from altered hepatic vascular morphology of chronic liver disease. Dilatation of the portal vein is associated with increased blood flow, as well as the opening up or formation of veno-venous shunts and splenomegaly. At the same time, portal hypertension leads to subclinical sodium retention resulting in expansion of all body fluid compartments, including the systemic and central blood volumes. This blood volume expansion is associated with vasorelaxation, as manifested by suppression of the renin--angiotensin--aldosterone system, initially only when the patient is in the supine position. Acute volume depletion in such patients results in normalisation of the hyperdynamic circulation, whilst acute volume expansion results in exaggerated natriuresis. As liver disease progresses and liver function deteriorates, the systemic hyperdynamic circulation becomes more manifest with activation of the renin--angiotensin--aldosterone system. The presence of vasodilatation in the presence of highly elevated levels of circulating vasoconstrictors may be explained by vascular hyporesponsiveness due to increased levels of vasodilators such as nitric oxide, as well as the development of an autonomic neuropathy. However, vasodilatation is not generalised, but confined to certain vascular beds, such as the splanchnic and pulmonary beds. Even here, the status may change with the natural history of the disease, since even portal blood flow may decrease and become reversed with advanced disease. The failure of these changes to reverse following liver transplantation may be due to remodelling and angiogenesis.

Altered adrenal sensitivity to angiotensin II in low-renin essential hypertension

Low-renin essential hypertension (LREH) describes a widely recognized classification validated by clinical features, including salt-sensitive blood pressure and diuretic responsiveness. Classic physiological teaching has cited normal plasma aldosterone concentration despite suppressed renin as evidence for adrenal supersensitivity to angiotensin II (Ang II). We studied 94 patients with LREH, 242 normal-renin hypertensives, and 135 normal subjects as controls. Low-renin hypertensives did not differ significantly from the other groups in either basal or Ang II-stimulated aldosterone concentrations on a high-sodium diet. Stimulated with a low-sodium diet, LREH patients demonstrated the smallest rise in basal aldosterone secretion. Ang II responsiveness was also subnormal: the rise in aldosterone after Ang II infusion in LREH (613+/-39 pmol/L), although greater than in nonmodulators (180+/-17 pmol/L; P=0.001), was less than either the patients with intact modulation (940+/-53 pmol/L; P=0.001) or normotensives (804+/-50 pmol/L; P<0.05). Blacks with LREH demonstrated an even lower response than low-renin whites ((388+/-50 versus 610+/-47 pmol/L; P=0.0001). In contrast, the rise in systolic blood pressure with Ang II infusion on a low-salt diet was greatest among LREH patients (P=0. 001). Patients with LREH and nonmodulators were equally salt-sensitive. These results indicate that the adrenal response in LREH is normal on a high-salt diet but becomes progressively more abnormal as sodium control mechanisms are stressed. The factors that mediate enhanced adrenal response to Ang II with sodium restriction may be defective, suggesting the existence of alternative physiological mechanisms for sodium homeostasis in the low-renin state.

Hyper-responsiveness to angiotensin II is related to cardiac structural adaptation in hypertensive subjects

BACKGROUND

Angiotensin II has been found to be a growth stimulating factor for myocardial cells. In humans, angiotensin II infusion causes vasoconstriction in systemic and renal vasculature and leads to aldosterone secretion. Our hypothesis was that hyper-responsiveness to angiotensin II is related to left ventricular mass in human essential hypertension.

METHODS AND RESULTS

In 30 normotensive individuals and 30 subjects with mild essential hypertension (white men, mean age 26+/-3 years), the responsiveness to angiotensin II was assessed by measuring changes in mean arterial pressure, renal blood flow, glomerular filtration rate and aldosterone secretion in response to i.v. angiotensin II infusion (0.5 and 3.0 ng/kg per min). The provoked changes to angiotensin II infusion were similar in the normotensive and hypertensive group with the exception of an exaggerated increase in mean arterial pressure in hypertensives (14+/-5 versus 10+/-5 mm Hg, P<0.001 at 3.0 ng/kg per min angiotensin II). The increase in mean arterial pressure was correlated with left ventricular mass in hypertensive subjects (angiotensin II 0.5 ng/kg per min: r = 0.49, P<0.005; angiotensin II 3.0 ng/kg per min: r = 0.35, P<0.05); no such correlation was found in the normotensive group. After taking into account baseline mean arterial pressure and body mass index, the increase in mean arterial pressure to angiotensin II 0.5 ng/kg per min was still correlated with left ventricular mass (partial r = 0.50, P<0.01). Similarly, the change of glomerular filtration rate but not of renal blood flow in response to angiotensin II 0.5 ng/kg per min was correlated with left ventricular mass, (r = 0.42, P<0.02) in the hypertensive group but not in the normotensive one. This relationship remained significant even after taking baseline glomerular filtration rate, mean arterial pressure and body mass index into account (partial r = 0.43, P<0.05).

CONCLUSION

Hyper-responsiveness to angiotensin II is related to an increased left ventricular mass in hypertensive subjects independent of blood pressure.

Circulating plasma prekallikrein and tissue kallikrein in normotensive and hypertensive humans: effects of angiotensin II infusion

Kinins lower blood pressure but the stimuli leading to kinin generation and their origin are less well known. We administered angiotensin II in graded infusion doses to patients with primary hypertension and normotensive controls to study the effects of on circulating kallikreins. Angiotensin II infusion did not significantly alter plasma prekallikrein or tissue kallikrein levels and the plasma levels and their changes did not correlate with blood pressure levels or changes. In the normotensive group prekallikrein levels and renin activity correlated negatively with urinary sodium and chloride excretion during basal conditions and partially during the infusion. U-tissue kallikrein concentration increased in the normotensive group. Thus, acute elevation of blood pressure induced by angiotensin II does not activate the circulating kallikrein-kinin systems. Data rather indicate that the circulating kallikrein-kinin systems may be related to alterations in volume and sodium balance and that these mechanisms may be altered in primary hypertension.

Orthostatic hypertension due to vascular adrenergic hypersensitivity

Autoregulatory mechanisms ensure relatively small fluctuations of blood pressure with postural changes in healthy people. Although orthostatic hypotension is well recognized and commonly encountered, there are only a few reports of orthostatic hypertension. Most of the reported cases of orthostatic hypertension were related to excessive venous pooling, with an initial drop in cardiac output followed by overcompensation with an excessive release of catecholamines, or to nephroptosis with orthostatic activation of the renin-angiotensin system. We describe a 44-year-old woman with normal supine blood pressure and severe orthostatic hypertension who did not demonstrate an initial decrease in cardiac output and had normal plasma and urinary catecholamines and renin release. Pharmacological tests of autonomic nervous system function showed an increased pressor sensitivity to norepinephrine (11 to 14 times normal), normal sensitivity to isoproterenol, diminished baroreceptor reflex sensitivity, and exquisite sensitivity to alpha-adrenergic blockers. This unusual case of orthostatic hypertension appears to be secondary to vascular adrenergic hypersensitivity.

Diurnal variation in angiotensin sensitivity in pregnancy

OBJECTIVE

Our purpose was to study the diurnal variation in angiotensin II sensitivity.

STUDY DESIGN

Angiotensin sensitivity tests were performed at 9 AM and at 2 PM in 12 normotensive pregnant women, with each woman serving as her own control.

RESULTS

In all patients the effective pressor dose was higher in the afternoon.

CONCLUSION

We suggest the greater sensitivity to angiotensin in the morning is related to an intrinsic circadian variation in vascular reactivity. When the result of an angiotensin sensitivity test is interpreted, the time of day it is performed should be taken into account.

Angiotensin converting enzyme inhibition does not affect the response to exogenous angiotensin II in the human forearm

Suppression of endogenous levels of angiotensin II by angiotensin converting enzyme inhibition, may result in up-regulation of vascular AT1 receptors. We have evaluated the effects of orally administered enalapril on angiotensin II induced vasoconstriction in the human forearm. Subjects received in random order, enalapril (20 mg) or matched placebo daily for 2 weeks. Forearm blood flow response to increasing doses of angiotensin II was measured using venous occlusion plethysmography at the beginning of the study and at the end of each 2 week treatment period. Treatment with enalapril significantly reduced plasma angiotensin II levels and supine blood pressure compared with placebo. The percentage reductions in forearm blood flow in the infused arm, in response to the maximum dose of angiotensin II (50,000 fmol min-1) were 48.1 +/- 3.6% at baseline, 57.5 +/- 3.6% on placebo and 54.5 +/- 4.2% on enalapril. The differences were not significantly different. This demonstrates that suppression of plasma angiotensin II for a 14 day period does not enhance the response to exogenous intra-arterial angiotensin II in the human forearm of healthy salt replete subjects.

Angiotensin converting enzyme inhibition does not affect response to exogenous angiotensin II in the forearm of mild-moderate hypertensive patients

It has been proposed that the suppression of endogenous levels of angiotensin II by angiotensin converting enzyme inhibition, may result in up-regulation of vascular AT1 receptors. This study evaluated the effects of orally administered enalapril on angiotensin II induced vasoconstriction in the human forearm of patients with mild-moderate hypertension. Patients received in random order, enalapril (20 mg) or matched placebo daily for 2 weeks. Forearm blood flow response to increasing doses of angiotensin II was measured using venous occlusion plethysmography at the beginning of the study and at the end of each 2 week treatment period. Treatment with enalapril significantly reduced plasma angiotensin II levels and supine blood pressure compared to placebo. The percentage reductions in forearm blood flow in the infused arm, in response to the maximum dose of angiotensin II (50 pmol.min-1) were 53.2% at baseline, 51.4% on placebo and 59.5% on enalapril. The differences were not significantly different. This study demonstrates that suppression of plasma angiotensin II does not enhance the response to exogenous intra-arterial angiotensin II in the human forearm of mild-moderately hypertensive patients.

Primary hyperparathyroidism and hypertension: persistently abnormal pressor sensitivity in normotensive patients after surgical cure

To examine the effects of primary hyperparathyroidism separately from those of hypertension per se on blood pressure regulation in patients with primary hyperparathyroidism, we studied the pressor response to infused angiotensin II (AII) and to norepinephrine (NE) in 7 normotensive patients with primary hyperparathyroidism before and after surgical cure, and compared it to that observed in 10 subjects with idiopathic hypertension and 10 normal controls. While the subjects were on an ad libitum diet, we measured urinary and plasma electrolytes, creatinine, and plasma renin activity. Except for calcium, these values were not significantly different among the three groups. The blood pressure was measured basally and in response to graded doses of AII or of NE until a 20-mmHg increase in the diastolic blood pressure was reached ("pressor dose"). The pressor doses of AII and of NE were lower in the normotensive patients with primary hyperparathyroidism than in normal controls [4.6 +/- 2.0 vs. 7.3 +/- 3.5 ng/kg/min (p < 0.05) and 164 +/- 114 vs. 302 +/- 176 ng/kg/min (p < 0.05) respectively] and not significantly different from those found in idiopathic hypertension (3.1 +/- 1.2 and 137 +/- 95 ng/kg/min). When the patients with primary hyperparathyroidism were studied again between 2-6 months after surgical cure, their pressor doses of AII and of NE remained unchanged from their preoperative values (5.4 +/- 2.9 and 137 +/- 80 mg/kg/min). We conclude that the hyperparathyroid condition can disrupt the normal responsiveness to pressor agents even if the blood pressure remains within normal limits, and that this abnormality may persist after surgical cure.

Vascular responses to angiotensin II in anorexia nervosa

Anorexia nervosa (AN) patients have a tendency to develop renin-angiotensin-aldosterone (RAA) abnormalities caused by abnormal behaviors expressed over long periods of time. Short-term dietary sodium intake is a known modulator of blood pressure response to infused angiotensin II (A II) in normal subjects. Therefore AN patients and normal gender-matched and age-matched controls were studied for vascular responses to exogenous A II. Untreated AN patients needed significantly greater quantities of exogenous A II to raise diastolic blood pressure (DBP) to over 20 mmHg for 30 min compared with controls (12.1 +/- 0.47 versus 7.6 +/- 0.69 ng/kg/min, p < 0.01). The amount of A II required to raise DBP to over 20 mmHg in AN patients in tests before and after completion of treatment (4.2 +/- 0.33 months later) was significantly different (12.1 +/- 0.47 versus 8.1 +/- 0.25 ng/kg/min, p < 0.01). There was no significant difference between AN patients following treatment and controls. Our results indicate that it requires long time before decreased A II responsiveness caused by chronic sodium depletion normalizes in AN patients.

Effect of omega-3 fatty acids on the vascular response to angiotensin in normotensive men

There is a widespread interest in fish oil as a dietary supplement and possible nonpharmacologic adjunct in the treatment of hypertension. The effect of dietary fish oil on blood pressure is controversial and the effect on systemic hemodynamics and regional vascular reactivity in humans is unknown. To address these questions, a double-blind, placebo-controlled, crossover study on the effect of dietary fish oil substitution was performed during a carefully controlled diet in 8 normotensive men. Systemic hemodynamics and the forearm vascular response to intrabrachial artery infusions of norepinephrine, phentolamine and angiotensin II were obtained. Compared with a safflower oil placebo, dietary fish oil had no effect on cardiac output (6.42 +/- 0.38 vs 6.87 +/- 0.28 liters/min, p = not significant) or 24-hour blood pressure (122/68 +/- 3/3 vs 122/68 +/- 3/2 mm Hg, p = not significant). The vascular response to norepinephrine and phentolamine was unchanged. Fish oil, however, significantly (p < 0.05) reduced forearm vascular resistance responses to angiotensin II. These changes were associated with a reduction in plasma triglycerides (64 +/- 9 vs 39 +/- 4 mg/dl, p = 0.02) and an increase in plasma eicosapentaenoic acid levels (0.51 +/- 0.25 vs 1.72 +/- 0.35 microM, p < 0.05). Substitution of a moderate dose of fish oil for fat in a "Western diet" selectively attenuates the vascular response to angiotensin independently of changes in alpha-adrenergic vasoconstriction or systemic hemodynamics.

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.

Prostaglandins and systolic blood pressure, but not angiotensin II, independently affect atrial natriuretic peptide levels in man

1. Two hours after a single dose of indomethacin (INDO), plasma renin activity (PRA) and atrial natriuretic peptide (ANP) levels decreased, which is consistent with an effect of lowering prostaglandins (PG). 2. After 48 h of INDO, PRA remained low but ANP had increased, which is consistent with the known effect of prostaglandin inhibitors to cause sodium retention, with a resulting volume expansion. 3. Infusions of angiotension II (AII), which raises diastolic blood pressure (BP) 20 mmHg or more, consistently raised ANP levels. The ANP response to AII infusion was reduced 48 h after INDO, which is consistent with an important role for PG in AII-stimulated ANP release. 4. After PG were blocked with INDO, the stimulating effect of AII on ANP at doses that increased diastolic BP less than 20 mmHg was insignificant, whereas before INDO it was significant. 5. In dose-response studies, INDO increased the systolic BP response but decreased the ANP response to AII, which is consistent with a direct effect of PG on ANP that is independent of systolic BP. 6. Prostaglandins and BP are important in the ANP response to AII infusion in normal subjects, but AII itself appears to have little direct effect on ANP.

Large-volume paracentesis and intravenous saline: effects on the renin-angiotensin system

Fourteen cirrhotic patients with tense ascites were treated with total paracentesis and intravenous isotonic saline infusion. Standard liver and kidney function tests, plasma renin activity and aldosterone concentration were measured before, at 48 hrs and at 7 days after total paracentesis. The volume of ascites removed was 7.7 +/- 5.6 l (mean +/- S.E.M.). None of the treated patients had clinical complications or significant alterations in liver or kidney function test results. Paracentesis and intravenous isotonic saline infusion were not associated with significant changes in mean plasma renin activity or plasma aldosterone concentration. These results suggest that this therapeutic procedure could be a safe and cost-effective alternative treatment of tense ascites in patients with cirrhosis.

Exogenous insulin augments in healthy volunteers the cardiovascular reactivity to noradrenaline but not to angiotensin II

Hyperinsulinemia has been implicated in the pathogenesis of the blood pressure elevation in patients with noninsulin-dependent diabetes mellitus, obesity, but also essential hypertension. In these conditions an increased cardiovascular reactivity to noradrenaline (NA) and angiotensin II (AII) can be observed. Using the euglycemic clamp technique, we determined the cardiovascular reactivity to graded infusions of NA and AII in nine healthy males before (Bas), and 1 and 6 h after infusion of insulin (50 mU/kg per h) was started. On separate days control experiments were carried out to control for any circadian variation. Insulin led to a decrease of the amount of circulating NA necessary to increase the diastolic blood pressure (DBP) 20 mmHg (actual experiment [mean +/- SEM]: Bas, 23.1 +/- 5.0; 1 h, 14.8 +/- 3.0; and 6 h, 12.3 +/- 3.1; and control experiment: Bas, 20.7 +/- 5.0; 1 h, 18.6 +/- 3.5; and 6 h, 17.3 +/- 3.3 nmol/liter; Bas vs. 1 and 6 h: P less than 0.05). Although the amount of NA infused to raise DBP 20 mmHg showed a similar decline after 1 h of insulin infusion, no such change from baseline could be observed at 6 h. This appeared to be due to an increase in NA clearance with more prolonged insulin infusion. Insulin exerted no effect on the amount of AII infused to increase DBP 20 mmHg (actual experiment: Bas, 27.6 +/- 6.4; 1 h, 28.8 +/- 10.0; and 6 h, 21.2 +/- 5.3; and control experiment: Bas, 33.6 +/- 5.7; 1 h, 34.2 +/- 6.1; and 6 h, 23.4 +/- 4.7 ng/kg/min; NS). We did observe a circadian variation in AII reactivity. Whether the increase in cardiovascular responsiveness to NA after administration of insulin contributes to the elevation in blood pressure frequently observed in patients with insulin resistance remains to be proven.

A comparison of the haemodynamic and hormonal effects of low and conventional dose cyclopenthiazide in normal volunteers

In this study we compared low (125 micrograms) and conventional (500 micrograms) doses of cyclopenthiazide on the renin angiotensin system, plasma and extracellular fluid volumes and the pressor responsiveness to angiotensin II since we have previously shown that the two doses have the same antihypertensive effect but different effects on plasma renin activity. Following a two week placebo run-in period, 8 healthy male volunteers received 125 micrograms or 500 micrograms of cyclopenthiazide for 2 treatment periods of 4 weeks as part of a double blind, 2-part crossover study with treatment periods separated by a 4-week placebo washout phase. Measurements were made on two study days at the beginning and end of the active treatment periods. On the first day serum potassium, plasma renin activity and plasma angiotensin II levels were measured after a 1 h period of supine rest. Plasma and extracellular fluid volumes were also measured after appropriate equilibration times. The blood pressure responses to angiotensin II were assessed on day 2. The 500 micrograms dose of cyclopenthiazide had a greater effect than the 125 micrograms dose on plasma renin activity, serum potassium, angiotensin II levels and extracellular fluid volumes. Neither drug had any effect on plasma volume or the responsiveness to infused angiotensin II. Low dose cyclopenthiazide failed to increase angiotensin II levels, contract body fluid volumes or attenuate vascular reactivity in normotensive volunteers.

The diuretic and natriuretic action of human atrial natriuretic peptide in humans: lack of effect of exogenous insulin

The interaction of exogenous, synthetic human atrial natriuretic peptide [(hANP) (ANF 99-126)] and of exogenous insulin was investigated in six healthy men and in seven type I diabetic patients using the euglycemic clamp technique. A primed-continuous (1.0 mU/kg x min) infusion of biosynthetic human insulin was administered to acutely raise and maintain plasma insulin concentrations at approximately 75 to 100 microU/mL during four hours while plasma glucose concentrations were maintained constant at the fasting level by a variable infusion of glucose. In healthy men a decrease in natriuresis (P less than .01) was seen during a euglycemic clamp study without exogenous hANP. No changes in diuresis and natriuresis were seen during a control experiment without exogenous insulin and glucose. Both in healthy men and in the type I diabetics sequential IV bolus doses of hANP of 100, 200, and 400 micrograms induced an increase in urine flow (P less than .01) and in natriuresis (P less than .01). In healthy men these effects were comparable to those achieved by hANP in the absence of induced hyperinsulinemia. It is concluded that the antinatriuretic action of insulin is of no major relevance in counteracting the pharmacologic action of hANP in healthy men. The effects of pharmacologic doses of hANP on diuresis and natriuresis in patients with type I diabetes mellitus is comparable to that in healthy men.

Yohimbine and aldosterone responsiveness to angiotensin II or corticotrophin in normal subjects

In normal man the sympathetic nervous system exerts an inhibitory influence on aldosterone responsiveness to angiotensin II. The possible role of alpha-2 adrenoceptors was assessed by studying the changes of plasma aldosterone during an angiotensin II infusion at the dose of 1, 2, 5 and 10 ng/kg. min or after corticotrophin infusion, 0.25 mg, in 8 normal subjects before and after treatment with the selective alpha-2 adrenoceptor antagonist, yohimbine, at a maximal dosage of 60 mg daily. Yohimbine did not modify blood pressure, body weight, the supine levels of angiotensin II, renin and aldosterone, the pressor response to angiotensin II and the correlation relating plasma aldosterone to plasma angiotensin II obtained during infusion studies. These findings suggest that the inhibitory influence of the sympathetic nervous system on aldosterone responsiveness to angiotensin II.

Vasoconstriction and hypersensitivity to vasoactive substances after acute volume expansion in dogs

In a search for factors contributing to the sustained blood pressure (BP) elevation in acutely volume-loaded animals, dextran dissolved in lactated Ringer's solution (20 ml/kg) was infused into 34 mongrel dogs over a period of 1 hour under pentobarbital anesthesia and changes in hemodynamic and humoral variables were monitored during its infusion and for 3 hours after its infusion. BP elevation during volume loading (from 114 +/- 3 to 128 +/- 3 [SEM] mm Hg) was attributed to an increase in cardiac output. After volume loading, some dogs maintained BP elevation whereas others did not. The former group showed an increase in total peripheral resistance, demonstrating a transformation of cardiac output to total peripheral resistance as a responsible factor in maintenance of the elevated BP. The plasma levels of norepinephrine, vasopressin, and plasma renin activity were not elevated, indicating that these vasoactive factors were not responsible for elevation of the BP or total peripheral resistance. The changes in the hematocrit, atrial natriuretic factor, urine volume, and urinary sodium excretion were identical in the two groups, and natriuresis was not prominent when total peripheral resistance was high. Pressor responses to norepinephrine and angiotensin II were potentiated 3 hours after stopping infusion in both groups, but this potentiation was not correlated with the increase in total peripheral resistance or mean BP. Thus, acute volume expansion produced resistance-dependent hypertension following the initial volume-dependent hypertension. It is unlikely that a vascular sensitizing natriuretic factor plays a role in the resistance-dependent BP elevation. The mechanism and physiological importance of hypersensitivity to vasoactive substances remain to be elucidated.

Pregnancy induced hypertension: will treatment with dietary eicosapentaenoic acid be effective?

The current understanding of endothelial membrane prostaglandin metabolism is presented together with an explanation of how this may be altered in pregnancy induced hypertension (PIH). A hypothesis is proposed to explain why dietary supplementation with eicosapentaenoic acid (EPA) may reverse abnormal prostaglandin metabolism, increase membrane fluidity and lower blood pressure in PIH.

Effect of sodium balance and calcium channel blocking drugs on blood pressure responses

To study the role of calcium movements in mediating the effects of sodium chloride on the response of blood pressure to angiotensin II (ANG II), we infused ANG II before and after giving calcium channel blocking drugs (nifedipine and diltiazem) and calcium infusions to normal subjects during high and low sodium intakes. ANG II was also in nine patients with essential hypertension eating a low sodium diet. In preliminary studies, the effects of nifedipine, 20 mg p.o., on blood pressure and plasma renin activity were determined. Sensitivity to infused ANG II was calculated as the slope of the linear regression of the increase in diastolic blood pressure (DBP) expressed as a function of the ANG II infusion rate (mm Hg/ng ANG II/kg/min). During intake of a high sodium diet (Na, 200 mEq/day) both drugs significantly (p less than 0.05) reduced ANG II sensitivity, while on a low sodium diet (10 mEq Na), neither drug reduced ANG II sensitivity. There was a significant (p less than 0.001) inverse correlation between the initial ANG II-DBP sensitivity and the change in sensitivity induced by the calcium channel blocking drugs in normal subjects (r = -0.78) and in hypertensive patients (r = -0.70). Five hypertensive patients had greater than normal ANG II-DBP sensitivity that was significantly (p less than 0.05) reduced by nifedipine. Calcium infusion did not affect the ANG II-DBP sensitivity on either diet. The results suggest that in normal subjects increased DBP responses to ANG II, induced by an increase in sodium intake, are partially mediated by increased extracellular to intracellular calcium movements, since they are blocked by the structurally different calcium channel blocking drugs nifedipine and diltiazem. In hypertensive patients on a low sodium diet, increased DBP responses to ANG II infusion were blocked by nifedipine, indicating they are at least partly mediated by increased extracellular to intracellular calcium flux.

Potassium and norepinephrine- or angiotensin-mediated pressor control in pre-hypertension

Blood pressure (BP), plasma electrolytes, renin, aldosterone, angiotensin II (AII) or catecholamines, the chronotropic effects of intravenous isoproterenol, norepinephrine (NE) or AII, the pressor responses to NE or AII, and the relationship between plasma AII and aldosterone concentrations were studied before and after 10 days of dietary supplementation with potassium 100 mmol/day, in normotensive members of normotensive (N = 12) or hypertensive (N = 12) families, and 11 patients with borderline essential hypertension. Under control conditions, the pressor responsiveness to NE was significantly enhanced in normotensive with positive family history for hypertension and hypertensive subjects; the other variables were comparable in the groups. After potassium supplementation, plasma potassium, renin, aldosterone or AII, and the relationship between AII and aldosterone levels increased significantly, while body weight, plasma catecholamines, the chronotropic effects of isoproterenol, AII or NE, the pressor effects of AII and plasma clearance of AII or NE were unchanged in all groups. In normotensive members of hypertensive families and patients with hypertension, BP was decreased and the exaggerated pressor responsiveness to NE was normalized; these variables were not modified in normotensive members of normotensive families. These observations are consistent with a potassium-remediable disturbance in NE- but not AII-dependent regulation of BP in the pathogenesis of essential hypertension.

Correction of hypokalemia in Bartter's syndrome by enalapril

Seven patients with Bartter's syndrome were investigated before and after 3 months' treatment by enalapril. Serum potassium rose from 2.4 +/- 0.5 to 3.9 +/- 0.6 mmol/L. In all patients, serum magnesium rose and bicarbonate fell. Hormonal changes were as suspected: a further stimulation of renin and a decline in aldosterone. The BP sensitivity to angiotensin II normalized in the five patients in whom the test was performed. Clearance studies during maximal water diuresis, performed in four patients, were compatible with a high proximal fractional tubular sodium reabsorption and a relatively low distal fractional sodium reabsorption. Fractional free water excretion after furosemide was also low, confirming the concept of a primary sodium reabsorption defect in the furosemide-insensitive part of the nephron in Bartter's syndrome. The only consistent change after enalapril was a further decline in distal fractional sodium reabsorption. Initiation of therapy produced a BP fall in each subject. Clinical important hypotension associated with oliguria was seen twice, but these reactions were short-lasting. The BP rose to pretreatment values within 72 hours, despite continuation of converting-enzyme inhibition. Renal function recovered, though a moderate fall in function persisted. No other side effects were noticed. We conclude that converting-enzyme inhibition improves the potassium metabolism of patients with Bartter's syndrome, without ameliorating the abnormal renal sodium handling.

Adrenergic activity and aldosterone regulation: no evidence for an alpha-1 adrenoceptor-mediated influence in normal subjects

In normal man the sympathetic nervous system could exert an inhibitory influence on aldosterone responsiveness to angiotensin II. The possible role of alpha-1 adrenoceptors in the modulation of aldosterone response was assessed by studying the changes of plasma aldosterone during infusion of angiotensin II at the doses of 1, 2, 5 and 10 ng/kg.min or after corticotrophin injection, 0.25 mg, in 9 normal subjects before and after treatment with the selective alpha-1 adrenoceptor antagonist, prazosin. Prazosin, given during 3 weeks, did not modify supine arterial pressure, heart rate and the plasma levels of angiotensin II, renin, aldosterone or adrenaline but caused a significant (P less than 0.05) increase of plasma noradrenaline. The correlation relating plasma aldosterone to plasma angiotensin II levels before and during angiotensin II infusion and the response of plasma aldosterone to corticotrophin was not modified by prazosin. These findings suggest that in normal man there is no inhibitory influence of the noradrenergic system on aldosterone responsiveness to angiotensin II mediated by an alpha-1 dependent mechanism.

Blood pressure control in normotensive members of hypertensive families

The cardiovascular pressor responses to a stepwise increase in plasma norepinephrine or angiotensin II concentrations, induced by infusions, were studied in 23 normotensive subjects with a negative and 25 with a positive family history of essential hypertension. The two study groups had a similar mean age (24 +/- 2 (SD) yr), body weight, blood pressure (112/64 +/- 10/7 mmHg), heart rate, plasma and urinary sodium and potassium, and plasma norepinephrine, epinephrine, angiotensin II, renin and aldosterone levels. However, subjects with positive history differed from those with negative history of hypertension by a decreased pressor dose of infused norepinephrine (89 +/- 29 vs. 135 +/- 66 ng/kg/min; P less than 0.005), and a significant (P less than 0.01) shift to the left of the relationship between norepinephrine-induced changes in mean arterial pressure and concomitant changes in plasma norepinephrine. In contrast, the relation between stepwise increasing plasma angiotensin II levels and induced changes in diastolic blood pressure or plasma aldosterone did not differ significantly between the two study groups. These findings delineate a distinct abnormality which may often occur in normotensive offspring of hypertensive families. It is characterized by a selectively disturbed noradrenergic blood pressure control in the presence of a normal angiotensin-mediated blood pressure and aldosterone regulation.

Effect of pregnancy in the rabbit on the pressor response to angiotensin and noradrenaline

The pressor responses to angiotensin II injections of 29, 117 and 468 pmol/kg and infusion at 54 pmol/kg per min were compared in near-term pregnant and matched non-pregnant rabbits. The responses to noradrenaline injections of 652, 2608 and 10 432 pmol/kg and infusion at 1185 pmol/kg per min were similarly compared. At all doses of angiotensin and noradrenaline, whether by injection or infusion, the response of the pregnant animals was significantly greater. However the control arterial pressures of the pregnant rabbits were lower and fell in a range where the baroreceptor reflex might be less effective. Thus less efficient buffering could contribute to the greater response to the vasoconstrictor agents. To test the effect of pregnancy on the vascular response to angiotensin and noradrenaline when reflex and central effects were excluded, hexamethonium was used to produce autonomic ganglion blockade. The response to both vasoconstrictors was now less in the pregnant rabbits than in the non-pregnant. Thus in assessing the effects of pregnancy on the responses of the rabbit to angiotensin and noradrenaline the effect of pregnancy on mean blood pressure must be taken into account, since this can influence the extent to which the arterial baroreceptors may modulate the response.

Pressor factors and responsiveness in hypertension accompanying diabetes mellitus

Hypertension accompanying diabetes mellitus may involve abnormalities in at least two major blood pressure-regulating systems: the body sodium-fluid volume state and cardiovascular reactivity. In metabolically stable nonazotemic diabetes, exchangeable sodium is increased by 10% on average, regardless of age, insulin dependence or nondependence, or the presence or absence of diabetic retinopathy or clinical nephropathy (proteinuria greater than or equal to 0.3 g/24 hr). Possible contributing mechanisms include renal sodium retention and an extravascular shift of fluid and sodium; intracellular accumulation is not excluded. Circulatory volume is normal or low and the total exchangeable sodium/blood volume ratio increased. In hypertensive diabetes, the latter abnormality is particularly pronounced; systolic pressure tended to correlate with exchangeable sodium (r = 0.47, p less than 0.001) and diastolic pressure with the plasma sodium/potassium ratio (r = 0.25, p less than 0.05). Plasma aldosterone, renin, epinephrine, and norepinephrine levels are generally normal or sometimes low in metabolically stable nonazotemic diabetic patients with normal or high blood pressure; the plasma clearance of norepinephrine also appears to be unaltered. The cardiovascular pressor responsiveness to norepinephrine is often exaggerated relative to concomitant plasma concentrations, regardless of age, type of antidiabetic treatment, or presence or absence of diabetic retinopathy, peripheral neuropathy, or high blood pressure. Pressor responsiveness to angiotensin II also may sometimes be increased relative to plasma renin levels. Sodium retention and diabetic vasculopathy of resistance vessels could be important complementary mechanisms of hyperreactivity. In diabetes with mild hypertension, diuretic treatment restored exchangeable sodium, norepinephrine pressor responsiveness, and blood pressure toward normal. Thus sodium retention and cardiovascular hyperreactivity tend to occur even at the normotensive, nonazotemic stage of diabetes and may concomitantly predispose for the frequent development of hypertension in the diabetic population.

Diminished pressor response to exogenous norepinephrine and angiotensin II in septic, unanesthetized rats: evidence for a prostaglandin-mediated effect

Despite elevated plasma concentrations of norepinephrine (NE), septic patients generally have normal or low mean arterial pressure (MAP) and systemic vascular resistance. We tested the hypothesis that sustained sepsis in rats results in relative hyporesponsiveness to the pressor actions of NE and angiotensin II (AII). Sprague-Dawley rats were studied 48 hr after sepsis was induced by cecal ligation. Sham-operated rats served as controls. Carotid artery and jugular venous catheters were placed under halothane anesthesia and the rats were allowed to waken fully in restraining cages. Peak increments in MAP were measured after bolus iv doses of NE (0.125-8.0 micrograms/kg) or AII (0.0125-0.5 microgram/kg). Some rats were pretreated with indomethacin (5 mg/kg, iv) 30 min prior to the dose-response study. Data were fitted to a two-parameter hyperbolic function and the resulting curves were compared by analysis of variance. Compared with controls, sepsis decreased the pressor response to both NE (P less than 0.0001) and AII (P less than 0.0001). Indomethacin restored responsiveness toward normal for both pressor agents (P less than 0.0001). It is concluded that sepsis is associated with hyporesponsiveness to two chemically dissimilar vasopressors and that this phenomenon may be mediated by prostaglandins.

Isolated perfused mesenteric arteries of hypertensive and normotensive rats; response to norepinephrine, lysine vasopressin and angiotensin II

The aim of this study was to assess the pressure response of mesenteric arteries isolated from various hypertensive rat models to the 3 pressor agonists norepinephrine, lysinevasopressin and angiotensin II. The isolated mesenteric arterial beds were perfused with a Krebs-solution and then exposed to increasing doses of the 3 different pressor agents. Compared to Wistar Kyoto controls, spontaneously hypertensive rats exhibited a clearly enhanced vascular response to norepinephrine and lysine vasopressin but not to angiotensin II. In animals with hypertension produced by angiotensin II continuously released by an osmotic micropump, the vascular response to lysine vasopressin and angiotensin II was increased while that to norepinephrine was unchanged. Rats rendered hypertensive by the administration of deoxycorticosterone and salt exhibited an increased vascular response exclusively to angiotensin II. In all models taken together, the magnitude of the vascular response to norepinephrine and lysine vasopressin was related to the blood pressure of the intact animal but this was not the case for angiotensin II. These observations are not incompatible with the concept that changes in the vascular response are predominantly due to structural changes of the vascular wall. However, they suggest that more specific alterations of responsiveness of the vascular smooth muscle must also take place.

Urinary prostaglandins in Bartter's and pseudo-Bartter's syndrome

Renal secretion of prostaglandins (PG) in Bartter's syndrome and in different forms of hypokalemic normotensive syndromes (pseudo-Bartter's syndrome) was measured to determine if it is possible to use the measurement of urinary prostaglandins for the discrimination of different etiologies. Prostaglandins E2, F2 alpha, 6-keto-PGF1 alpha and thromboxane B2 (TxB2) were measured after extraction and chromatography by radioimmunoassay in 19 patients and in 26 control healthy subjects. Bartter's syndrome may be characterized as primary renal hyperprostaglandinism with high urinary PGE2 excretion. It can be dissociated from pseudo-Bartter's syndrome because the urinary PGE2 excretion is always in the normal range in the pseudosyndrome. Abuse of loop diuretics may have effects that mimic Bartter's syndrome since these diuretics stimulate urinary prostaglandin excretion. Therefore, loop diuretics should always be excluded prior to the diagnosis of Bartter's syndrome.

In vitro autoradiographic localization of [125I]-angiotensin II binding sites in the rat and dog kidney

Light microscopic autoradiographic techniques have been utilized to demonstrate specific regions of the rat and dog kidney where angiotensin II receptors exist. Slide mounted tissue sections were labeled with [125I]-angiotensin II using conditions which provided for highly specific binding. These angiotensin II binding sites were localized to several distinct renal structures. In the renal cortex, angiotensin II binding sites were found concentrated in all parts of the glomeruli including the vascular components, the macula densa and the juxtaglomerular apparatus. Angiotensin II binding in the medulla was more diffusely associated with the vasa recta, and to a lesser extent, the thick ascending segment of the loop of Henle. Binding sites specific for angiotensin II were also found in the smooth muscle laminae of the ureter. Scatchard analysis of the binding kinetics allowed the demonstration of two subpopulations of binding sites which differ slightly in their affinities for [125I]-angiotensin II. These subpopulations appear to be associated with distinct components of the renal structure.

Identification of the angiotensin II receptor in rat mesenteric artery

Specific binding sites of high affinity and low capacity for 125I-angiotensin II have been identified in a membrane fraction derived from arterial arcades of the rat mesentery. Heterogeneity of binding sites and extensive tracer degradation necessitated the use of nonlinear regression methods for the analysis of radioligand binding data. Forward and reverse rate constants for the high affinity sites obtained by three experimental approaches were in good agreement and gave a dissociation equilibrium constant (Kd) of 19-74 pM (95% confidence interval). Affinities for a number of angiotensin-related peptides calculated from competitive binding curves were in the order 125I-angiotensin II = angiotensin II greater than angiotensin III greater than [Sar1,Ile8]angiotensin II greater than [Sar1,Gly8]angiotensin II. Angiotensin I and biochemically unrelated peptides had virtually no effect on binding of tracer angiotensin II. The divalent cations Mn2+, Mg2+ and Ca2+ stimulated 125I-angiotensin II binding at concentrations of 2-10 mM, as did Na+ at 50-100 mM. In the presence of Na+ or Li+, K+ had a biphasic effect. The chelating agents EDTA and EGTA were inhibitory, as were the thiol reagents dithiothreitol and cysteine. This study defined angiotensin II binding sites in a vascular target tissue of sufficiently high affinity to interact rapidly with plasma angiotensin II at physiological concentrations.