Levels of angiotensin peptides in healthy and cardiovascular/renal-diseased paediatric population-an investigative review

The renin-angiotensin-aldosterone system (RAAS) plays a major role in the regulation of blood pressure and homeostasis. Therefore, it is a commonly used target for pharmacotherapy of cardiovascular diseases in adults. However, the efficacy of this pharmacotherapy can only be limitedly derived into children. Comprehensive knowledge of the humoral parameters acting in the paediatric RAAS (e.g. angiotensin I, angiotensin II, angiotensin 1-7, angiotensin III, and angiotensin IV) might facilitate a more effective and rational pharmacotherapy in children. Therefore, this review aims to provide an overview of the maturing RAAS. Out of 925 identified records, 35 publications were classified as relevant. Physiological and pathophysiological concentrations of angiotensin peptides were compiled and categorised according to European Medicines Agency age groups. Age has a major impact on circulating angiotensin I, angiotensin II, and angiotensin 1-7, which is reflected in an age-dependent decrease during childhood. In contrast to data obtained in adults, no gender-related differences in angiotensin levels were identified. The observed increase in peptide concentrations regarding cardiac- and renal-diseased children is influenced by surgical repair, while evidence for a pharmacological impact is conflicting. A comprehensive set of angiotensin I, angiotensin II, and angiotensin 1-7 values from neonates up to adolescents was compiled. Indicating age as a strong effector. However, evidence about potential promising targets of the RAAS like angiotensin III and angiotensin IV is still lacking in children.

Systemic effects of angiotensin III in conscious dogs during acute double blockade of the renin-angiotensin-aldosterone-system

AIMS

The study was designed to determine (i) whether the effects of angiotensin III (AngIII) are similar to those of angiotensin II (AngII) at identical plasma concentrations and (ii) whether AngIII operates solely through AT1- receptors.

METHODS

Angiotensin II (3 pmol kg(-1) min(-1)-3.1 ng kg(-1) min(-1)) or AngIII (15 pmol kg(-1) min(-1)-14 ng kg(-1) min(-1)) was infused i.v. during acute inhibition of angiotensin converting enzyme (enalaprilate; 2 mg kg(-1)) and of aldosterone (canrenoate; 6 mg kg(-1) plus 1 mg kg(-1) h(-1)). Arterial plasma concentrations of angiotensins were determined by radioimmunoassay using a cross-reacting antibody to AngII. During ongoing peptide infusion, candesartan (2 mg kg(-1)) was administered to block the AT1-receptors.

RESULTS

Angiotensin immunoactivity in plasma increased to 60 +/- 10 pg mL(-1) during infusion of AngII or infusion of AngIII. AngII significantly increased mean arterial blood pressure (+14 +/- 4 mmHg) and plasma aldosterone by 79% (+149 +/- 17 pg mL(-1)) and reduced plasma renin activity and sodium excretion (-41 +/- 16 mIU L(-1) and -46 +/- 6 micromol min(-1) respectively). AngIII mimicked these effects and the magnitude of AngIII responses was statistically indistinguishable from those of AngII. All measured effects of both peptides were blocked by candesartan.

CONCLUSION

At the present arterial plasma concentrations, AngIII is equipotent to AngII with regard to effects on blood pressure, aldosterone secretion and renal functions, and these AngIII effects are mediated through AT1- receptors. The metabolic clearance rate of AngIII is five times that of AngII.

Antianginal efficacy of omapatrilat in patients with chronic angina pectoris

Angiotensin-converting enzyme inhibition is not an effective antianginal therapy. Experimental data suggest that broader vasopeptidase inhibition may decrease the magnitude of demand-induced myocardial ischemia. A randomized, double-blind, placebo controlled parallel study evaluated omapatrilat, an inhibitor of angiotensin-converting enzyme and neutral endopeptidase. The primary objective was to compare maximum duration of exercise at peak plasma concentrations. Exercise treadmill studies were performed in 348 patients who had chronic angina at baseline and after 4 weeks of therapy with 80 mg/day omapatrilat or placebo. Safety data were collected and reported for all patients. Treadmill exercise duration at peak was significantly prolonged in the omapatrilat group compared with the placebo group (76.6 +/- 84.2 vs 28.7 +/- 82.2 seconds difference from baseline, p <0.001). Similar statistically significant increases were seen in time to onset of level III/IV angina and time to onset of >/=0.1-mV ST-segment depression (p <0.001). The significant improvements in exercise duration and measurements of myocardial ischemia were not sustained 20 to 28 hours after dosing. Omapatrilat was generally well tolerated in this predominantly normotensive population. The incidence of serious adverse events was 5.2% in the 2 groups. Thus, omapatrilat, an investigational vasopeptidase inhibitor, is effective in prolonging exercise duration and parameters of demand-induced myocardial ischemia in patients who have chronic angina at peak concentrations. The data confirm the proof of principle that broader vasopeptidase inhibition beyond angiotensin-converting enzyme inhibition is required to alleviate symptoms of chronic angina.

Integrated protein microchip assay with dual fluorescent- and MALDI read-out

A pore chip protein array (PCPA) concept based on a dual readout configuration, fluorescence imaging, and MALDI-TOF MS has been developed. Highly packed, (>4000 spots/cm2), antibody arrays were dispensed on the porous chip by using a piezo-electric microdispenser. Sandwich assay was made after blocking by addition of a secondary antibody either IgG-FITC-labeled or anti-Ang II. The antigen in the first system was a large protein (IgG), and in the other system, a FITC marked peptide Angiotensin II (Ang II) was used. Ang II antibodies showed specificity for Ang II, while the Ang I antibodies showed binding properties for Ang I, II, and Renin. Fluorescence and MALDI TOF MS read-out was made for IgG and Ang II. A major advantage of the dual read-out PCPA approach is that both affinity binding and mass identity are derived. Detection limits for Ang II on the chip is as low as 500 zmol (Ang II).

Hypercholesterolemia stimulates angiotensin peptide synthesis and contributes to atherosclerosis through the AT1A receptor

BACKGROUND

Hypercholesterolemia-induced atherosclerosis is attenuated by either pharmacological antagonism of AT1 receptors or AT1A receptor deficiency. However, the mechanism underlying the pronounced responses to angiotensin II (Ang II) antagonism has not been determined. We hypothesized that hypercholesterolemia stimulates the production of angiotensin peptides to provide a rationale for the profound effect of AT1A receptor deficiency on atherogenesis.

METHODS AND RESULTS

Atherosclerotic lesions were analyzed in LDL receptor-deficient mice. Immunocytochemical analysis demonstrated that atherosclerotic lesions contained all the components of the conventional pathway for Ang II synthesis. AT1A receptor deficiency caused a marked decrease in atherosclerotic lesion size in both the aortic root and arch of male and female mice, without a discernible effect on composition. AT1A receptor deficiency-induced reductions in atherosclerosis were independent of systolic blood pressure and measurements of oxidation and chemoattractants. Aortic AT2 receptor mRNA expression was not altered in AT1A receptor-deficient mice, and AT2 receptor deficiency had no effect on lesion area or cellular composition. Hypercholesterolemia greatly augmented the systemic renin-angiotensin system, as demonstrated by large increases in plasma concentrations of angiotensinogen and angiotensin peptides (Ang II, III, IV, and 4-8). These increases were ablated in hypercholesterolemic AT1A receptor-deficient mice.

CONCLUSIONS

AT1A receptor deficiency had a striking effect in reducing hypercholesterolemia-induced atherosclerosis in LDL receptor-negative mice. Hypercholesterolemia was associated with increased systemic angiotensinogen and angiotensin peptides, which were reduced in AT1A receptor-deficient mice. These results demonstrate that hypercholesterolemia-induced stimulation of angiotensin peptide production provides a basis for the marked effect of AT1A receptor deficiency in reducing atherosclerosis.

Effects of truncated angiotensins in humans after double blockade of the renin system

Angiotensins different from ANG II exhibit biological activities, possibly mediated via receptors other than ANG II receptors. We studied the effects of 3-h infusions of ANG III, ANG-(1-7), and ANG IV in doses equimolar to physiological amounts of ANG II (3 pmol. kg-1. min-1), in six men on low-sodium diet (30 mmol/day). The subjects were acutely pretreated with canrenoate and captopril to inhibit aldosterone actions and ANG II synthesis, respectively. ANG II infusion increased plasma angiotensin immunoreactivity to 53 +/- 6 pg/ml (+490%), plasma aldosterone to 342 +/- 38 pg/ml (+109%), and blood pressure by 27%. Glomerular filtration rate decreased by 16%. Concomitantly, clearance of endogenous lithium fell by 66%, and fractional proximal reabsorption of sodium increased from 77 to 92%; absolute proximal reabsorption rate of sodium remained constant. ANG II decreased sodium excretion by 70%, potassium excretion by 50%, and urine flow by 80%, whereas urine osmolality increased. ANG III also increased plasma aldosterone markedly (+45%), however, without measurable changes in angiotensin immunoreactivity, glomerular filtration rate, or renal excretion rates. During vehicle infusion, plasma renin activity decreased markedly ( approximately 700 to approximately 200 mIU/l); only ANG II enhanced this decrease. ANG-(1-7) and ANG IV did not change any of the measured variables persistently. It is concluded that 1) ANG III and ANG IV are cleared much faster from plasma than ANG II, 2) ANG II causes hypofiltration, urinary concentration, and sodium and potassium retention at constant plasma concentrations of vasopressin and atrial natriuretic peptide, and 3) a very small increase in the concentration of ANG III, undetectable by usual techniques, may increase aldosterone secretion substantially.

Determination of endogenous peptides with in vitro ACE inhibitory activity in normotensive human plasma by the fluorometric HPLC method

An in vitro degradation test of angiotensin (ANG) II or III in normotensive supine human plasma from 9 healthy male subjects confirmed the production of smaller ANG metabolites with angiotensin I-converting enzyme inhibitory activity. These metabolites were identified as ANG (3-8), ANG (5-8), and ANG (3-4), whose respective peptide concentrations were determined by our proposed naphthalene-2,3-dialdehyde (NDA)-HPLC method to be 64 +/- 9, 39 +/- 5, 176 +/- 22, and 197 +/- 35 fmol/ml of plasma.

Plasma angiotensin in binephrectomised mice

Plasma renin-angiotensin parameters were measured before and 24h after binephrectomy (BNx) in male Swiss (Ren-1, Ren-2) and BALB/c (Ren-1) female mice (representing the extremes of differences in tissue renin expression), together with in vivo inhibition of residual renin. Plasma Ang II increased from 18.9 +/- 7.3 to 48.1 +/- 16.9 pg/ml after BNx in conscious Swiss mice (+/- sd, p < 0.001, n = 11&12), renin activity (PRA) increased 2.76 times, angiotensinogen (aogen) increased 4.57 times and renin concentration (PRC) fell by 65%. In BALB/c, Ang II+Ang III decreased slightly (56.6 +/- 11 to 37.7 +/- 14.7, p < 0.05, n = 5&6), PRA was unchanged, aogen increased 12 times and PRC fell by 93%. Plasma ACE decreased by 26% and 28% respectively. Aogen did not increase further when post BNx plasma renin was inhibited with antirenin in vivo during 20h. Thus plasma angiotensin is maintained or considerably increased following BNx in mice and the change is consistent with first-order kinetics with respect to renin and aogen in the circulation. Whether the strain carries one or two renin genes, high renal and extrarenal renin production combined with a low plasma aogen phenotype yields resting angiotensin levels similar to other mammals. A kinetic regulation of aogen levels is proposed in mice wherein Ang II production is limited by low substrate concentration thereby ensuring normotension in the face of abundant extrarenal renin secretion.

Thrombus formation and platelet-vessel wall interaction in the nephrotic syndrome under flow conditions

Increased in vitro platelet aggregability and hypercoagulability are generally held to be main determinants in the prethrombotic state in nephrosis. In vivo, however, thrombotic events depend on the dynamic interaction of flowing blood with the vessel wall. The present study confirms that aggregability of platelets of nephrotic patients is significantly increased by mere stirring or by exogenous stimuli as adenosine diphosphate and arachidonic acid. Moreover, the nephrotic patients have high von Willebrand factor and decreased red blood cell deformability, which normally increase platelet-vessel wall interaction. However, perfusion studies under well-defined flow conditions, in which anticoagulated nephrotic blood was exposed to deendothelialized human umbilical artery segments and sprayed collagen, showed normal platelet adhesion and only a modest increase in the deposition of platelet aggregates. This suggests that some factor counteracts platelet-vessel wall interaction under flow conditions in the nephrotic syndrome. When tissue factor associated with endothelial extracellular matrix (ECM) was allowed to generate thrombin, perfusions with nephrotic blood over this ECM resulted in a strong increase in fibrin generation. The capacity of patient blood to form increased amounts of fibrin appeared strongly correlated with the level of hyperfibrinogenemia. Platelet adhesion as well as aggregation in these experiments was even decreased below control values. This suggests that fibrin coverage may block the direct contact between blood platelets and matrix. We therefore also studied the isolated effect of high fibrinogen on platelet-vessel wall interaction by increasing fibrinogen concentrations in normal blood. Modulation of fibrinogen concentrations in normal blood could mimic all the observations in nephrotic blood: platelet aggregation in suspension increased with increasing concentrations of fibrinogen, while platelet adhesion and aggregate formation under flow conditions decreased. In perfusions over tissue factor-rich matrix, fibrin deposition increased. Therefore, our observations indicate that nephrotic hyperaggregability in suspension is not associated with increased platelet vessel wall-interaction under flow conditions. The latter is probably counteracted by high levels of fibrinogen. Our observations further suggest that hyperfibrinogenemia may be a major thrombotic risk factor in nephrosis by inducing more fibrin depositions.

The renin angiotensin system and hymenoptera venom anaphylaxis

Components of the renin angiotensin system, namely renin, angiotensinogen, angiotensin I and II and aldosterone were measured in plasma of patients with hymenoptera venom anaphylaxis (n = 50) and healthy non-allergic controls (n = 25). Patients with a history of anaphylactic reactions to hymenoptera venom who did not undergo immunotherapy showed significantly reduced renin, angiotensinogen, angiotensin I and angiotensin II in plasma as compared with controls (P < 0.05). There was no difference in the aldosterone concentration between patients and controls. Angiotensin I, angiotensin II, renin and angiotensinogen levels were the same in male and female patients. There was also no difference in the angiotensin I, II, renin or angiotensinogen levels between young and older patients. A significant inverse correlation between the severity of clinical symptoms and the plasma levels of renin (r = -0.382, P < 0.001), angiotensinogen (r = -0.567, P < 0.0001), angiotensin I (r = -0.656, P < 0.0001) and angiotensin II (r = 0.0762, P < 0.0001) was found: the lower the levels the more severe the clinical symptoms. No correlation was found for aldosterone. Hymenoptera venom allergic patients with repeated anaphylactic reactions during hyposensitization did not tolerate the sting of a living insect (n = 6). In these patients, renin, angiotensinogen, angiotensin I and II remained significantly lower than in healthy non-allergic controls. Patients with successful immunotherapy (n = 27) who tolerated the sting of a living insect had renin, angiotensin I and II significantly higher than patients without immunotherapy. These findings suggest a possible role of the renin angiotensin system in hymenoptera venom anaphylaxis.

Response of plasma renin-angiotensin system to a single captopril administration in patients receiving long-term treatment with captopril

1. The responses of angiotensin II (AII), AIII, aldosterone and plasma renin activity (PRA) to a single dose of captopril were investigated in hypertensive patients receiving long-term (more than 1 year) captopril therapy (CT patients) and compared with those of non-treated hypertensive patients (NT patients). 2. Baseline levels of AII and aldosterone were significantly lower in CT patients than in NT patients. AIII tended to be lower and PRA was slightly higher in CT than in NT patients, but these differences were not significant. 3. A single administration of captopril (50 mg orally) significantly decreased plasma levels of AII, AIII and aldosterone as well as blood pressure in both CT and NT patients. 4. These results demonstrate that chronically repeated administration of captopril to hypertensive patients effectively reduces the daily blood pressure and concomitantly the plasma AII level to acceptable levels in patients with no experience of ACE inhibition.

Effects of angiotensin II, ACTH, and KCl on the adrenal renin-angiotensin system in the rat

Angiotensin II, ACTH and potassium chloride were administered to rats for 6 days and the effects on adrenal renin-like activity and adrenal angiotensin II/III immunoreactivity were investigated. Rats infused with angiotensin II (140 pmol/min) either ip or sc showed increases in adrenal angiotensin II/III immunoreactivity (p less than 0.05) and plasma aldosterone concentration (p less than 0.05), but no change in adrenal renin-like activity. Captopril treatment of angiotensin II-infused rats caused a slight decrease in angiotensin II/III immunoreactivity which did not reach statistical significance. In contrast, rats treated with ACTH (Cortrosyn-Z, 3 IU/day, sc) showed an increase in adrenal renin-like activity (p less than 0.01), but no significant change in adrenal angiotensin II/III immunoreactivity. Rats treated with KCl in drinking water showed increases (p less than 0.05) in adrenal renin-like activity, adrenal angiotensin II/III immunoreactivity, and plasma aldosterone. These results suggest that angiotensin II, ACTH and potassium, three major regulators of aldosterone secretion by the adrenal gland, have different effects on the adrenal renin-angiotensin system when administered in vivo.

Re-evaluation of the plasma renin-angiotensin system in anephric patients

In view of recent observations that a number of extrarenal tissues have the potential to produce angiotensin II and release it in a regulated fashion, we made measurements of immunoreactive angiotensin I (irAng I) and angiotensin II (irAng II), along with active and inactive renin, and angiotensinogen in plasma of seven anephric patients and of 16 normal healthy volunteers to gain insight into possible sources of plasma Ang II. High performance liquid chromatography clearly demonstrated that the predominant component of irAng II in anephric plasma is the biologically active octapeptide Ang II. Plasma renin activity (PRA), and active and inactive renin all were detected in all of the anephrics but their levels were decreased to 33% for PRA, 12% for active renin, and 18% for inactive renin when compared with those in healthy subjects. While plasma angiotensinogen was significantly but only slightly increased in anephric patients (+28% over the mean value for normal subjects), irAng I and irAng II both were present in quantities almost comparable with those in normals. These results suggest that local angiotensin production contributes, in part at least, to the circulating plasma Ang II. Vascular tissue seems to be the best candidate responsible for such a mechanism, on the basis of recent demonstrations of unequivocal, regulated release of Ang II from diverse vascular beds.

Measurement of angiotensin II concentration in rat plasma: pathophysiological applications

A very reliable isocratic reverse phase high performance liquid chromatography (HPLC) system has been developed to separate angiotensins, which combined with a very sensitive radioimmunoassay, provided precise measurements of the endogenous angiotensin II (AII) concentration in the rat plasma in different experimental circumstances. The overall recoveries of AII were 95.2 +/- 15.8% (means +/- SD) when 10 pg of this peptide was added to 1 ml of human plasma. The coefficient of variation for within-assay precision was 10% (n = 6). The plasma AII, measured by this method, of normal male pentobarbital-anesthetized rats was 53.0-141.6 pg/ml (mean: 103.9 +/- 29.7 pg/ml). The plasma AII of rats fed a sodium deficient diet was 300.0 +/- 100.6 pg/ml, while that of rats given oral Enalapril, an angiotensin converting enzyme (ACE) inhibitor, for 1 week was 35.7 +/- 28.0 pg/ml. The plasma AII of bilaterally nephrectomized rats was 2.7 +/- 2.9 pg/ml 24 hours after nephrectomy and below the detection limit 48 hr after nephrectomy. This method, therefore, can be used to study AII in different pathophysiological states or after treatment with renin-angiotensin system inhibitors.

Enzymatic formation of angiotensins II and III in the hindlimb circulation of dogs

Experiments were performed in 14 anesthetized dogs to (1) to determine if the reductions in hindlimb blood flow produced by [des-Asp1] angiotensin I were due to its local enzymatic (kininase II) conversion to angiotensin III and (2) to quantitate the extent of conversion of angiotensin I to angiotensin II and of [des-Asp1] angiotensin I to angiotensin III in the hindlimb circulation. Graded doses of these peptides were administered as bolus injections directly into the left external iliac artery while measuring flow in this artery electromagnetically. Dose-response relationships were determined before and during the inhibition of kininase II activity with captopril or antagonism of angiotensin receptor sites with [Ile7] angiotensin III. Captopril inhibited the vasoconstrictor responses to angiotensin I and [des-Asp1] angiotensin I, but did not affect the responses to angiotensins II or III, or norepinephrine. [Ile7] angiotensin III inhibited the vasoconstrictor responses to all four angiotensin peptides but did not alter the responses to norepinephrine. These findings indicate that the hindlimb vasoconstrictor responses to [des-Asp1] angiotensin I were due to the local formation of angiotensin III. The extent of conversion of [des-Asp1] angiotensin I to angiotensin III that occurred in one transit through the hindlimb arterial circulation was estimated to be 36.7%, which was not different from the estimated 36.4% conversion of angiotensin I to angiotensin II. We conclude that angiotensin I and [des-Asp1] angiotensin I are converted to their respective vasoactive forms (angiotensins II and III) to a similar extent in the hindlimb circulation via the action of kininase II.

A sensitive method for precise measurement of endogenous angiotensins I, II&III in human plasma

We measured endogenous angiotensins (ANGs) I, II&III using a system of extraction by Sep-Pak column followed by high performance liquid chromatography (HPLC) combined with radioimmunoassay (RIA). An excellent separation of ANGs was obtained by HPLC. The recovery of ANGs I, II&III was 80-84%, when these authentic peptides were added to 6 ml of plasma. The coefficient of variation of the ANGs was 0.04-0.09 for intra-assay and 0.08-0.13 for inter-assay, thereby indicating a good reproducibility. Plasma ANGs I, II&III measured by this method in 5 normal volunteers were 51,4.5 and 1.2 pg/ml. In the presence of captopril, ANGs II&III decreased by 84% and 77%, respectively, while ANG I increased 5.1 times. This method is therefore useful to assess the precise levels of plasma ANGs.

Specific measurement of angiotensin metabolites and in vitro generated angiotensin II in plasma

Combining high-performance liquid chromatography with radioimmunoassay enabled the precise measurement of different angiotensins and their metabolites in plasma. Peptides were extracted from 2 ml of plasma by reversible adsorption to phenylsilyl-silica, separated by isocratic high-performance liquid chromatography, and quantitated by radioimmunoassay using a sensitive but suitably cross-reacting angiotensin II antiserum. For the C-terminal angiotensin II metabolites (2-8)heptapeptide, (3-8)hexapeptide, and (4-8)pentapeptide, overall recoveries of 10 fmol peptide added to 1 ml of plasma were (mean +/- SD), 74 +/- 6, 68 +/- 8, and 67 +/- 11%, respectively. The detection limit for these peptides in plasma was 0.2 fmol/ml. Blanks were below the detection limits. In eight seated normal subjects treated for 4 days with enalapril, 20 mg p.o., q.d., angiotensin II metabolites tended to decrease during the 4 postdrug hours. However, their cumulated concentration in relation to octapeptide increased from 54 to 163% on Day 1 and from 62 to 103% on Day 4. After 4 hours of converting enzyme inhibition with enalapril there was still a close correlation between plasma renin activity and angiotensin-(1-8)octapeptide level (r = 0.83, p less than 0.05) and between blood angiotensin I and angiotensin-(1-8)octapeptide levels (r = 0.86, p less than 0.01). Adding angiotensin I in vitro raised the angiotensin-(1-8)octapeptide levels after incubation at 4 degrees C for 4 hours. Thus, immunoreactive "angiotensin II" does not disappear after converting enzyme inhibition largely because of the cumulated contribution of cross-reacting metabolites and partly because of in vitro generation of true angiotensin II.

Cerebroventricular and intravascular metabolism of [125I]angiotensins in rat

This study compared the metabolism of [125I]angiotensin II (AII), [125I]angiotensin III (AIII), and [125I]Sar1,Ile8-AII (SI-AII) in the vascular and cerebroventricular compartments. Using HPLC methods to monitor degradation the following t1/2 values were established in the vascular compartment: AII, 12.7 +/- 1.4 s; AIII, 16.3 +/- 0.7 s; and SI-AII, 100.7 +/- 7.3 s. HPLC analysis also revealed that [125I]AII is converted in an obligatory manner to [125I]AIII during its degradation sequence. Cerebrospinal fluid contained no degradative capacity for [125I]AII but exhibited a significant capacity to degrade [125I]AIII. A technique that combined the intra-cerebroventricular injection of [125I]angiotensins followed by focused microwave fixation to stop all peptidase activity was used to determine the half-life of [125I]angiotensins in the ventricular space. Results indicated very rapid metabolism of angiotensins with the following t1/2 values: AII, 23.0 s; and AIII, 7.7 s. This extremely rapid, differential, and sequential metabolism of AII and AIII in two relevant body fluid compartments underscores the need for caution when interpreting data derived from intravascular and intracerebroventricular application of angiotensins. In addition the faster metabolism of AIII than AII in the ventricular space indicates that the actual potency of AIII at central angiotensin receptors is being underestimated.

Evidence for the existence of des-Asp1-angiotensin II in human uterine and adrenal tissues

Renin is present in various tissues outside the kidney. In contrast, the levels of angiotensins (ANG), the active products of the renin-angiotensin system, have not been thoroughly evaluated in tissues. In this study, we demonstrated the presence of immunoreactive (ir) ANG I and ANG II in various human tissues by RIA. Of the tissues examined, uterine tissue contained the most ir-ANG II. Since the anti-ANG II antibody used had significant cross-reactivity with ANG III, high performance liquid chromatography was performed to separate ANG II from ANG III. The major portion of the ir-ANG II in the plasma was ANG II. In contrast, the major portion of the ir-ANG II in uterine tissue was determined to be ANG III, a known biologically active peptide. The adrenal gland and testis also contained ANG III. From these results, it can be postulated that ANG III may contribute to the biological activity of ANG in some tissues.

Activation and inhibition of Hageman factor-dependent pathways and the complement system in uncomplicated bacteremia or bacterial shock

Levels of components of the contact activation, coagulation, and complement systems and their main inhibitors were measured in 45 critically ill patients during 61 episodes of uncomplicated bacteremia or bacterial shock. Levels of Hageman factor (factor XII), prekallikrein, high-molecular-weight kininogen, factor XI, factor VII, total hemolytic complement, alternative pathway activity, and C3 were within the normal range during uncomplicated bacteremia (n = 29), but during fatal bacterial shock (n = 13) a significant decrease by 40%-50% was observed in all measurements. During nonfatal bacterial shock (n = 19) a moderate decrease was observed in most of these measurements. The capacity of plasma to inactivate kallikrein was significantly higher during bacteremia than during bacterial shock because of a significant increase in the level of C1 esterase inhibitor. Levels of antithrombin III and alpha 2-macroglobulin were below normal in all groups. Thus increased inhibition of the contact activation and complement systems is beneficial during bacteremia.

The enzymatic renin reaction in vivo is inhibited in mice during inter-male aggressiveness

In aggressive male mice with very high plasma renin concentrations the plasma angiotensin II (ANG II) and III (ANG III) concentrations were measured in single mice in order to study whether this renin was active in vivo. The angiotensins were purified and identified by ion-exchange chromatography and High Pressure Liquid Chromatography (HPLC) and quantitated by a specific and sensitive radioimmunoassay. Plasma ANG II and ANG III values were not elevated in aggressive mice compared to normals, in spite of the fact that the plasma renin concentration was increased up to 100 fold and almost equal to the plasma renin-substrate concentration. This indicates an inhibition of the enzymatic renin reaction in vivo during aggression, which is in accordance with the lack of blood pressure increase, and an unchanged pressure sensitivity to ANG II.

Kinase II-dependent formation of angiotensins II and III in the hepatic circulation

Experiments were performed in 14 pentobarbital-anesthetized dogs to 1) determine if the hepatic arterial vasoconstrictor effects of [des-Asp1]angiotensin I [( des-Asp1]ANG I) were due to its local conversion to angiotensin III (ANG III) and 2) to evaluate the magnitude of conversion of ANG I to angiotensin II (ANG II) and of [des-Asp1]ANG I to ANG III in the hepatic arterial vascular bed. Graded doses of these peptide agonists were administered as bolus injections directly into the hepatic artery; hepatic arterial blood flow was measured with an electromagnetic flow probe. Dose-response relationships were determined before and during the inhibition of kinase II activity with captopril (2-D-methyl-3-mercaptopropanoyl-L-proline) and antagonism of angiotensin receptor sites with [Ile7]angiotensin III [( Ile7]ANG III). ANG I and [des-Asp1]ANG I were equipotent at all doses tested, as were ANG II and III. At all doses tested, ANG II and III were approximately three times more potent than ANG I and [des-Asp1]-ANG I. Captopril attenuated the vasoconstrictor responses to ANG I and [des-Asp1]ANG I only, whereas [Ile7]ANG III inhibited the responses to all four angiotensin peptides. These data indicate that the hepatic arterial vasoconstrictor responses to [des-Asp1]ANG I were due to the intrahepatic formation of ANG III. The extent of intrahepatic conversion of [des-Asp1]-ANG I to ANG III that occurred in one transit through the hepatic arterial vascular bed was estimated to be 33%, which was similar to the estimated 38% conversion of ANG I to ANG II.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of infused captopril on blood pressure and the renin-angiotensin-aldosterone system in normal dogs subjected to varying sodium balance

Infusion of captopril at 20, 200, 2,000 and 6,000 micrograms/kg/hour into sodium-depleted conscious dogs produced a rapid, dose-dependent decrease in blood pressure and plasma angiotensin II and III, maximal suppression being achieved at 200 micrograms/kg/hour (97 +/- 14 to 65 +/- 8 [standard deviation] mm Hg, 38 +/- 10.6 to 3.2 +/- 1.5 pmol/liter and 7.0 +/- 4.8 to 1 +/- 0.5 pmol/liter, respectively). Angiotensin I concentration increased with each infusion rate to a maximal 16-fold increase at 6,000 micrograms/kg/hour (26 to 416 pmol/liter). For all infusion rates the percentage decrease in blood pressure correlated with the percentage decrease in plasma angiotensin II (r = 0.65, p less than 0.001). Infusion of captopril at 6,000 micrograms/kg/hour into sodium-loaded dogs also produced a decrease in both blood pressure (117 +/- 9 to 96.6 +/- 11 mm Hg) and plasma angiotension II (11.0 +/- 3 to 1.6 +/- 1.3 pmol/liter). Plasma aldosterone concentrations decreased whereas both blood angiotensin I and renin concentration increased. In another experiment angiotensin II was infused at 2, 6, 18 and 54 ng/kg/min into sodium-depleted dogs firstly without modification and secondly combined with captopril (6,000 micrograms/kg/hour) given for 1 hour before the angiotensin dose-response study and continued throughout. Angiotensin II infusion raised mean arterial pressure and plasma angiotensin II in each animal. However, the angiotensin II blood pressure dose-response curve was shifted downwards and to the right in the captopril-treated animals. These results suggest that arterial pressure and aldosterone secretion in normal dogs are partly dependent on the renin-angiotensin system but that not all of the acute decrease in blood pressure produced by captopril can be explained by the suppression of the acute vasoconstrictor effect of circulating angiotensin II.

Effects of angiotensin III and ACTH on aldosterone secretion

ACTH and des-Asp1-angiotensin II (AIII) can raise plasma aldosterone. To assess the threshold for ACTH and AIII stimulated adrenal steroidogenesis we infused ACTH (from 0.03 to 10 ng ACTH/min) and AIII (from 0.1 to 20 ng/kg/min) to dexamethasone pretreated sodium deplete normal subjects and patients with primary aldosteronism, chronic renal failure, and end stage renal disease maintained with continuous ambulatory peritoneal dialysis. Plasma aldosterone in the primary aldosteronism group increased significantly at 0.3 ng ACTH/min compared with 1 to 3 ng ACTH/min in all other groups. The threshold dose for an ACTH stimulated rise in plasma aldosterone was as at least as low as the dose necessary to raise cortisol in all groups. The threshold dose for an AIII stimulated rise in plasma aldosterone was 4 ng/kg/min in normals and between 1 and 3 ng/kg/min in primary aldosteronism. The metabolic clearance rate (MCR) of aldosterone was determined by constant infusion of [3H]-aldosterone. The decline in MCR during AIII infusion contributed less than 15% to the rise in plasma aldosterone in normals and patients with primary aldosteronism.

The effect of captopril on renin, angiotensin II, cortisol and aldosterone during ACTH-infusion in man

Prolonged low-dose ACTH infusion (5 or 10 iU/24h) leads to a transient increase in plasma renin activity and angiotensin II concentration in normal man. In order to find out whether the increase in angiotensin II stimulates aldosterone secretion, 12 normal men received ACTH (10 IU/24h) for 34 hours altogether, 6 with and 6 without simultaneous administration of captopril, 50 mg every 6 hours. Captopril prevented the increase in plasma angiotensin II during ACTH infusion and lowered its levels below those on the control day two hours after a new dose of the converting enzyme inhibitor was given. The increase in plasma cortisol was similar in both groups. The increase in plasma aldosterone was significantly blunted by captopril. The early blood pressure rise and the kaliuresis during ACTH infusion were also significantly decreased in the captopril group. These results suggest that angiotensin II mediates in part the effect of ACTH on aldosterone and blood pressure during the first 2 days of infusion. Since captopril reduced plasma angiotensin II for some time below normal, it is alternatively possible that ACTH requires normal plasma angiotensin II levels for a full effect on aldosterone secretion.

Angiotensin I, II, and III in sheep. A model of angiotensin production and metabolism

The arterial and central venous concentrations of angiotensin I (AI), Val5-angiotensin II ([Val5]AII), and Val5-angiotensin III ([Val5]AIII(2-8)) were quantitatively determined in conscious sheep before and after sodium depletion. All three angiotensins were elevated in blood with progressive sodium loss. During sodium deficiency the arteriovenous concentration ratios (A:V) of AI, [Val5]AII, and [Val5]AIII(2-8) were found to be 0.48 +/- 0.03 (n = 9), 1.30 +/- 0.05 (n = 16), and 1.52 +/- 0.05 (n = 11) respectively. Intravenous infusion of [Val5]AII or [Val5]AIII(2-8) significantly elevated the A:V of respective angiotensins, being 2.09 +/- 0.28 (n = 5) for [Val5]AII and 2.2 +/- 0.37 (n = 6) for [Val5]AIII(2-8). The blood clearance rates of exogenous [Val5]AII and [Val5]AIII(2-8) in sodium-depleted sheep were calculated to be 135 +/- 15 liter/hr (n = 10) and 140 +/- 13 liter/hr (n = 10) respectively. Based on these experimental data, a steady-state model of angiotensin metabolism was constructed. If it is assumed that endogenous arterial blood [Val5]AII and [Val5]AIII(2-8) cleared metabolically at a similar rate as exogenous arterial blood angiotensins, it can be calculated that at steady-state 55% of the arterial [Val5]AII concentration was derived from the peripheral vascular bed. For [Val5]AIII(2-8), 63% of the arterial concentration was derived from the pulmonary circulation. The concentration of [Val5]AIII(2-8) in arterial blood was 42% of [Val5]AII.

Effect of converting enzyme inhibition with captopril on in vitro angiotensin production in sheep

1. The effect of captopril on in vitro production of angiotensin I (ANG I), [Val5]-angiotensin II ([Val5]-ANG II) and [Val4]-angiotensin III ([Val5]-ANG-(2-8)) in central venous blood taken from sodium-deficient sheep was studied. 2. Captopril enhances in vitro production of ANG I but blocks the in vitro production of [Val5]-ANG II and [Val5]-ANG-(2-8). 3. The production of ANG I in blood is faster than that of [Val5]-ANG II and [Val5]-ANG-(2-8). 4. The half-life of [Val5]-ANG II and [Val5]-ANG-(2-8) in vitro in blood in the presence of captopril was 10 and 14 min, respectively. 5. This in vitro study suggests that the production of [Val5]-ANG II and [Val5]-ANG-(2-8) in blood forms a small part of the total body production of each peptide.

des-Asp-angiotensin I: its identification in rat blood and confirmation as a substrate for converting enzyme

The observation that angiotensin III is present in the circulation of the rat in amounts similar to those of angiotensin II has led to the notion that it may, in part, be formed by the action of converting enzyme on des-Asp-angiotensin I without the prior formation of angiotensin II. This possibility was studied in conscious rats using a combination of RIA and chromatographic techniques which allowed the separate measurement of angiotensin I, des-Asp-angiotensin I, angiotensin II, and angiotensin III in rat blood. Infusion of des-Asp1-[Ile5]angiotensin I at 50, 150, and 450 ng/kg . min resulted in a progressive increase in the plasma concentration of angiotensin III up to 279 +/- 50 (SD) pg/ml compared to 9 +/- 9 (SD) pg/ml after dextrose infusion. Regardless of the infusion of des Asp-[Ile5]angiotensin I, plasma angiotensin III made up a constant 46 +/- 8% (+/- SD) of the total immunoactive material, the remainder being composed of smaller metabolic fragments, indicating a rapid rate of clearance of angiotensin III. Captopril completely inhibited the rise in angiotensin III after des-Asp1-[Ile5]angiotensin I infusion. A substance which chromatographed as des-Asp-[Ile5]angiotensin I was detected in rat blood and made up 19% of the angiotensin I immunoactive material, while angiotensin III made up 44% of the angiotensin II immunoactive material. These results confirm that des-Asp1-[Ile5]angiotensin I is a substrate for converting enzyme in the rat, and the presence of a chromatographically similar substance in the circulation suggests that at least part of the angiotensin III in rat blood may be formed by the action of converting enzyme on endogenous des-Asp-angiotensin I. (Endocrinology 108: 406, 1981)

The effects of hemorrhage and sodium depletion on plasma concentrations of angiotensin II and [des-Asp1]angiotensin II in the rat

Plasma concentrations of angiotensin II (PAII) and [des-Asp1]angiotensin II (Pdes-Asp1-AII) were measured before and after hemorrhage and acute and chronic depletion of sodium. Graded hemorrhage increased PAII from 30 +/- 5 to 220 +/- 41 and 989 (526-1290) pmol/liter and Pdes-Asp1-AII from 47 +/- 11 to 216 +/- 72 and 532 +/- 178 pmol/liter. Furosemide increased PAII from 26 +/- 4 to 178 +/- 37 but did not change Pdes-Asp1-AII (31 +/- 3 to 31 +/- 4 pmol/liter). Deprivatin of dietary sodium increased PAII from 25+/- 6 to 136+/- 22 pmol/liter and Pdes-Asp1-AII from 41 +/- 4 to 71 +/- 15 pmol/liter. The ratio of PAII to Pdes-Asp1-AII was increased by all three stimuli (P < 0.05 to P < 0.001). Pdes-Asp1-AII II is unlikely to mediate the effects of hemorrhage and changes in sodium balance on aldosterone secretion in the rat.

Peripheral production of angiotensin II and III in sheep

The present experiments have allowed the calculation of concentrations of angiotensin I, II, and III in arterial and central venous blood. Assuming that endogenous arterial angiotensin II and III are handled as reflected by exogenous infusion, it can be calculated that 55% of the steady state arterial concentration of angiotensin II has arisen in passage across the peripheral vascular bed, that 40% of angiotensin III is also produced there, and that the arterial concentration of angiotensin III is 42% of the arterial concentration of angiotensin II.

The effect of captopril on blood pressure and angiotensins I, II and III in sodium-depleted dogs: problems associated with the measurement of angiotensin II after inhibition of converting enzyme

1. Changes in arterial blood pressure, blood angiotensin I, plasma angiotensin II and plasma angiotensin III were measured in conscious sodium-depleted dogs after infusion of captopril, an orally active inhibitor of converting enzyme. 2. Angiotensins II and III were measured after chromatography to remove angiotensin I, which increased in concentration after inhibition of converting enzyme and which interfered in the direct assay for angiotensin II. 3. Infusion of captopril at 20, 200, 2000 and 6000 microgram h-1 kg-1, each for 3 h, produced a rapid fall in blood pressure and in concentration of angiotensin II. Angiotensin II was undetectable at 6000 microgram h-1 kg-1 (mean pre-infusion value for all samples was 39 +/- SD 15 pmol/1, n = 14). 4. The percentage fall in blood pressure correlated with the percentage fall in plasma angiotensin II (r = 0.65, P < 0.001). 5. These results suggest that the initial fall in blood pressure may be mediated in part by the suppression of angiotensin II. 6. Blood angiotensin I concentration rose with each rate of infusion of drug to a maximum 16-fold increase at 6000 microgram h-1 kg-1 (26-416 pmol/l). The rise in angiotensin I was inversely related to the fall in angiotensin II (r = 0.68, P < 0.001).

Effect of isoprenaline on the plasma concentrations of angiotensin III in rats

1. A new column-chromatographic method is described for the simple and reproducible determination of the concentration of [des-Asp1]angiotensin II (angiotensin III) in rat plasma. 2. The method uses the different abilities of the ion-exchange resins Dowex 1 (X8) and Bio Rex 70 to bind angiotensin II and angiotensin III. Under the conditions used, Bio Rex 70 binds only angiotensin III. Angiotensin II and its hexapeptide metabolite [des-Asp1,des-Arg2]angiotensin II pass the resin with the effluent. Dowex 1 (X8) binds angiotensin II and the hexapeptide metabolite, whereas it does not extract angiotensin III. It does not separate angiotensin II from the hexapeptide. Therefore the sum of both peptides is expressed as angiotensin II-like activity. The ratio of the concentrations, angiotensin II/hexapeptide, was 5:1. 3. In normal rats the plasma concentration of angiotensin III was 20 fmol/ml (SD 15; n = 8), and angiotensin II-like activity was 60 fmol/ml (SD 35; n = 8). 4. The beta-sympathomimetic amine isoprenaline caused a time- and dose-dependent increase in plasma angiotensin III and angiotensin II-like activities. 5. Under the conditions studied angiotensin III contributed approximately 25% to the total amount of angiotensins in plasma.

Effect of adrenal arterial infusion of P-113 on aldosterone secretion in Na-deficient sheep

To examine the role of the renin-angiotensin system in aldosterone regulation, P-113 ([Sar1,Ala8]angiotensin II) was infused into the arterial blood supply of the transplanted adrenal gland in conscious sheep. Effects on the aldosterone response to infused angiotensin II and III in sodium-replete sheep were compared with effects of P-113 on aldosterone secretion in sodium deficiency. P-113 infusion up to 1,000 microgram/h for 1-2 h did not consistently alter aldosterone secretion in sodium-deficient sheep. However, in sodium-replete sheep P-113 infusion for 20 min at 10 microgram/h or more abolished aldosterone responses to high blood levels of angiotensin II and III produced by systemic intravenous or adrenal intra-arterial infusion. P-113 infusions alone had minor agonist activity on aldosterone secretion in sodium-replete sheep. These results indicate that the increased secretion of aldosterone in Na-depleted sheep is not simply and commensurately determined by increase of angiotensin II and III concentration in the arterial blood perfusing the adrenal gland.

Inhibitors of the renin-angiotensin system in experimental hypertension, with a note on the measurement of angiotensin I, II and III during infusion of converting-enzyme inhibitor

1 Prolonged infusion (11 h) of both saralasin and angiotensin-converting enzyme inhibitor (SQ20881) gradually lowered BP in two-kidney hypertensive rats to levels similar to that in normotensive rats infused with dextrose. 2 Saralasin did not lower BP in DOCA-salt hypertensive rats. 3 These observations support the notion that in chronic renal hypertension, angiotensin II may maintain hypertension by a slowly developing action. 4 Plasma angiotensin II in rats infused with SQ20881 was suppressed relative to renin, but was not eliminated. 5 Chromatography of angiotensin II extracts from dogs infused with converting enzyme inhibitor (SQ14,225) showed that the very high levels of angiotensin I achieved after treatment with SQ14,225 can lead to falsely high estimated angiotensin II levels as a result of angiotensin I cross-reacting with the angiotensin II assay.

[des-Asp1]angiotensin II in the dog: blood levels and effect on aldosterone

Circulating levels of [des-Asp1]angiotensin II ([des-Asp1]-AII), angiotensin II (AII), and aldosterone were measured in five conscious beagle dogs before and during iv infusion of [des-Asp1]AII at rates of 3, 6, 12, and 24 ng/kg/min. The animals were studied after 4 days on a normal sodium and potassium diet and again after a period of sodium depletion accomplished by iv furosemide (2-5 mg/kg) and 4 days of low sodium diet (2-5 mmol/day). Compared to the normal sodium diet, sodium depletion resulted in increases in the plasma levels of aldosterone from 10 +/- 2 (SE) to 66 (16-116) ng/100 ml of AII from 16 +/- 4 to 52 +/- 13 pmol/liter and of [des-Asp1]AII from 2 +/- 0.7 to 12 +/- 4 nmol/liter. Incremental infusions of [des-Asp1]AII in the sodium replete state resulted in progressive increases in the plasma levels of aldosterone in all dogs. In comparison with a previous study in which dogs were infused with AII, it was apparent that [des-Asp1]AII was equally or slightly more potent in stimulating aldosterone and had a higher metabolic clearance rate than AII. [des-Asp1]AII stimulated aldosterone in four of the five sodium-depleted dogs but no steepening of the [des-Asp1]AII/aldosterone dose-response curves was apparent. These results do not support the hypothesis that circulating [des-Asp1]AII mediates the effect of AII on aldosterone in the dog.

The half-lives of angiotensin II, angiotensin II-amide, angiotensin III, Sar1-Ala8-angiotensin II and renin in the circulatory system of the rat

1. Methods are described for estimating the half-life of angiotensin analogues and renin in the rat, from the time course of the blood pressure changes they evoke. 2. The following half-life values were measured: angiotensin II, 16 +/- 1 sec; angiotensin III, 14 +/- 1 sec; angiotensin II-amide, 15 +/- 1 sec; Sar1-Ala8-angiotensin II, 6.4 +/- 0.6 min; renin, 3.0 +/- 0.4 min. The distribution volume of angiotensin was found to be 18 ml./kg body wt. 3. It is inferred that the Asp1 residue does not reduce the rate of angiotensin II catabolism, but that substitution of this residue by sarcosine may inhibit catabolism while substitution by asparagine has no effect. 4. Five experimental criteria were identified which indicate that these methods give reliable estimates of the half-life. It is suggested that these results are more accurate than most previous half-life estimates. 5 When tachyphylaxis to angiotensin II-amide occurs, the pressor activity of the plasma is not reduced.