The relation of arterial pressure and plasma angiotensin II concentration. A change produced by prolonged infusion of angiotensin II in the conscious dog

Angiotensin II-induced endothelial dysfunction is temporally linked with increases in interleukin-6 and vascular macrophage accumulation

Angiotensin II (Ang II) is associated with vascular hypertrophy, endothelial dysfunction and activation of a number of inflammatory molecules, however the linear events involved in the development of hypertension and endothelial dysfunction produced in response to Ang II are not well defined. The goal of this study was to examine the dose- and temporal-dependent development of endothelial dysfunction in response to Ang II. Blood pressure and responses of carotid arteries were examined in control (C57Bl/6) mice and in mice infused with 50, 100, 200, 400, or 1000 ng/kg/min Ang II for either 14 or 28 Days. Infusion of Ang II was associated with graded and marked increases in systolic blood pressure and plasma Ang II concentrations. While low doses of Ang II (i.e., 50 and 100 ng/kg/min) had little to no effect on blood pressure or endothelial function, high doses of Ang II (e.g., 1000 ng/kg/min) were associated with large increases in arterial pressure and marked impairment of endothelial function. In contrast, intermediate doses of Ang II (200 and 400 ng/kg/min) while initially having no effect on systolic blood pressure were associated with significant increases in pressure over time. Despite increasing blood pressure, 200 ng/kg/min had no effect on endothelial function, whereas 400 ng/kg/min produced modest impairment on Day 14 and marked impairment of endothelial function on Day 28. The degree of endothelial dysfunction produced by 400 and 1000 ng/kg/min Ang II was reflective of parallel increases in plasma IL-6 levels and vascular macrophage content, suggesting that increases in arterial blood pressure precede the development of endothelial dysfunction. These findings are important as they demonstrate that along with increases in arterial pressure that increases in IL-6 and vascular macrophage accumulation correlate with the impairment of endothelial function produced by Ang II.

Investigation of the mechanisms by which chronic infusion of an acutely subpressor dose of angiotensin II induces hypertension

The mechanisms by which chronic infusion of an initially subpressor low dose of angiotensin II (ANG II) causes a progressive and sustained hypertension remain unclear. In conscious sheep ( n = 6), intravenous infusion of ANG II (2 μg/h) gradually increased mean arterial pressure (MAP) from 82 ± 3 to 96 ± 5 mmHg over 7 days ( P < 0.001). This was accompanied by peripheral vasoconstriction; total peripheral conductance decreased from 44.6 ± 6.4 to 38.2 ± 6.7 ml·min−1·mmHg−1 ( P < 0.001). Cardiac output and heart rate were unchanged. In the regional circulation, mesenteric, renal, and iliac conductances decreased but blood flows were unchanged. There was no coronary vasoconstriction, and coronary blood flow increased. Ganglion blockade (125 mg/h hexamethonium for 4 h) reduced MAP by 13 ± 1 mmHg in the control period and by 7 ± 2 mmHg on day 8 of ANG II treatment. Inhibition of central AT1 receptors by intracerebroventricular infusion of losartan (1 mg/h for 3 h) had no effect on MAP in the control period or after 7 days of ANG II infusion. Pressor responsiveness to incremental doses of intravenous ANG II (5, 10, 20 μg/h, each for 15 min) was unchanged after 7 days of ANG II infusion. ANG II caused no sodium or water retention. In summary, hypertension due to infusion of a low dose of ANG II was accompanied by generalized peripheral vasoconstriction. Indirect evidence suggested that the hypertension was not neurogenic, but measurement of sympathetic nerve activity is required to confirm this conclusion. There was no evidence for a role for central angiotensinergic mechanisms, increased pressor responsiveness to ANG II, or sodium and fluid retention.

Historic perspectives and recent advances in major animal models of hypertension

Hypertension and related cardiovascular diseases are the leading causes of death in many countries. The etiology of human essential hypertension is largely unknown. It is highly likely that hypertension is a complex and multifactorial disease resulting from the interaction of multiple genetic and environmental factors. Animal models of hypertension have been proved to be useful to study the pathogenesis of, and to find a new therapy for, hypertension. The aim of this article is to briefly review the most widely used rodent models of experimental hypertension, including history and recent advances. These models are classified as genetically-induced, environmentally-induced, pharmacologically-induced, and renal-induced hypertension according to the way of induction; the typical representatives of each of these major types of experimental hypertension are spontaneous hypertension, cold-induced hypertension, DOCA-salt-induced hypertension, and renal-induced hypertension, respectively. The processes of induction of hypertension, possible pathogenesis, characteristics, advantages, and limitations of these animal models are reviewed. In addition, the clinical implications of the above experimental models of hypertension are addressed.

Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Aldosterone secretion by glomerulosa cells is stimulated by angiotensin II (ANG II), extracellular K(+), corticotrophin, and several paracrine factors. Electrophysiological, fluorimetric, and molecular biological techniques have significantly clarified the molecular action of these stimuli. The steroidogenic effect of corticotrophin is mediated by adenylyl cyclase, whereas potassium activates voltage-operated Ca(2+) channels. ANG II, bound to AT(1) receptors, acts through the inositol 1,4,5-trisphosphate (IP(3))-Ca(2+)/calmodulin system. All three types of IP(3) receptors are coexpressed, rendering a complex control of Ca(2+) release possible. Ca(2+) release is followed by both capacitative and voltage-activated Ca(2+) influx. ANG II inhibits the background K(+) channel TASK and Na(+)-K(+)-ATPase, and the ensuing depolarization activates T-type (Ca(v)3.2) Ca(2+) channels. Activation of protein kinase C by diacylglycerol (DAG) inhibits aldosterone production, whereas the arachidonate released from DAG in ANG II-stimulated cells is converted by lipoxygenase to 12-hydroxyeicosatetraenoic acid, which may also induce Ca(2+) signaling. Feedback effects and cross-talk of signal-transducing pathways sensitize glomerulosa cells to low-intensity stimuli, such as physiological elevations of [K(+)] (< or =1 mM), ANG II, and ACTH. Ca(2+) signaling is also modified by cell swelling, as well as receptor desensitization, resensitization, and downregulation. Long-term regulation of glomerulosa cells involves cell growth and proliferation and induction of steroidogenic enzymes. Ca(2+), receptor, and nonreceptor tyrosine kinases and mitogen-activated kinases participate in these processes. Ca(2+)- and cAMP-dependent phosphorylation induce the transfer of the steroid precursor cholesterol from the cytoplasm to the inner mitochondrial membrane. Ca(2+) signaling, transferred into the mitochondria, stimulates the reduction of pyridine nucleotides.

Effects of different angiotensins during acute, double blockade of the renin system in conscious dogs

Evidence of biological activity of fragments of ANG II is accumulating. Fragments considered being inactive degradation products might mediate actions previously attributed to ANG II. The study aimed to determine whether angiotensin fragments exert biological activity when administered in amounts equimolar to physiological doses of ANG II. Cardiovascular, endocrine, and renal effects of ANG II, ANG III, ANG IV, and ANG-(1-7) (6 pmol.kg-1.min-1) were investigated in conscious dogs during acute inhibition of angiotensin I-converting enzyme (enalaprilate) and aldosterone (canrenoate). Furthermore, ANG III was investigated by step-up infusion (30 and 150 pmol.kg-1.min-1). Arterial plasma concentrations [ANG immunoreactivity (IR)] were determined by an ANG II antibody cross-reacting with ANG III and ANG IV. Metabolic clearance rates were higher for ANG III and ANG IV (391 +/- 19 and 274 +/- 13 ml.kg-1.min-1, respectively) than for ANG II (107 +/- 13 ml.kg-1.min-1). ANG II increased ANG IR by 60 +/- 7 pmol/ml, blood pressure by 30%, increased plasma aldosterone markedly (to 345 +/- 72 pg/ml), and plasma vasopressin transiently, while reducing glomerular filtration rate (40 +/- 2 to 33 +/- 2 ml/min), sodium excretion (50 +/- 7 to 16 +/- 4 micromol/min), and urine flow. Equimolar amounts of ANG III induced similar antinatriuresis (57 +/- 8 to 19 +/- 3 micromol/min) and aldosterone secretion (to 268 +/- 71 pg/ml) at much lower ANG IR increments ( approximately 1/7) without affecting blood pressure, vasopressin, or glomerular filtration rate. The effects of ANG III exhibited complex dose-response relations. ANG IV and ANG-(1-7) were ineffective. It is concluded that 1) plasma clearances of ANG III and ANG IV are higher than those of ANG II; 2) ANG III is more potent than ANG II in eliciting immediate sodium and potassium retention, as well as aldosterone secretion, particularly at low concentrations; and 3) the complexity of the ANG III dose-response relationships provides indirect evidence that several effector mechanisms are involved.

Oxidative stress may explain how hypertension is maintained by normal levels of angiotensin II

It is well known that essential hypertension evolves in most patients with "near normal" levels of plasma renin activity. However, these levels appear to be responsible for the high levels of arterial pressure because they are normalized by the administration of angiotensin II converting inhibitors or angiotensin receptor antagonist. In experimental animals, hypertension can be induced by the continuous intravenous infusion of small doses of angiotensin II that are not sufficient to evoke an immediate pressor response. However, this condition resembles the characteristics of essential hypertension because the high levels of blood pressure exist with normal plasma levels of angiotensin II. It is suggested that small amounts of angiotensin whose plasma levels are inappropriate for the existing size of extracellular volume stimulate oxidative stress which binds nitric oxide forming peroxynitrite. The latter compound oxidizes arachidonic acid producing isoprostaglandin F2alpha (an isoprostane) which is characterized by a strong antinatriuretic vasoconstrictor renal effect. In this chain of reactions the vasoconstrictor effects derived from oxygen quenching of nitric oxide and increased isoprostane synthesis could explain how hypertension is maintained with normal plasma levels of renin.

Aldosterone responses to angiotensin II in anorexia nervosa

Patients with anorexia nervosa (AN) tend to have renin-angiotensin-aldosterone (RAA) abnormalities caused by abnormal behaviors such as strict dieting, fasting, vigorous exercise, self-induced vomiting and abuse of laxatives and/or diuretics. Adrenal responsiveness to angiotensin II (A II) was studied in 13 AN patients before and after therapy and in 6 normal sex- and age-matched controls: adrenal responses to postural change (1 h of walking following 1 h in a supine position) and to exogenous A II injection (A II: 10 ng/kg/min intravenous infusion for 30 min). The 24-h urine sodium concentration was significantly lower in AN patients before therapy than after therapy. Plasma aldosterone secretory response to A II was significantly higher in AN patients before therapy in both postural change and exogenous A II injection tests compared with after therapy response and that of controls. On the other hand, there was no significant difference in adrenal response to postural change or to exogenous A II between AN patients after therapy and controls. In conclusion, increased A II sensitivity caused by chronic sodium deficiency in AN patients normalized over time as the patients recovered.

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

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

Angiotensin receptors in an Australian marsupial, the brushtail possum Trichosurus vulpecula

In this study, the binding properties of angiotensin receptors were examined in the liver, adrenal, brain, and vascular tissue of the brushtail possum, Trichosurus vulpecula. With 125I-Ile5-angiotensin II as the radioligand, the binding affinity (Ka) and receptor number (R0) were estimated for the liver (Ka = 3.60 +/- 0.31 liters/nmol; R0 = 23.8 +/- 1.30 pmol/g tissue; n = 8) and adrenal (Ka = 1.68 +/- 0.29 liters/nmol; R0 = 1.67 +/- 0.23 pmol/g tissue; n = 8). Specific binding was not found in any of seven areas of the possum brain (n = 6), whereas the expected binding was present in similar areas of the rat brain. Using angiotensin III or the antagonist Sar1-Ala8-angiotensin II as radioligands or changing the composition of the incubation buffer did not alter the outcome. Moreover, the intracerebroventricular injection of 1 and 5 nmol of angiotensin II did not elicit an increase in blood pressure which could be attributed to brain angiotensin II (AII) receptors. Ligand affinities of the adrenal and liver receptors were found to be in the following decreasing order: Val5-AII greater than Ile5-AII = Ile5-AIII greater than Sar1-Ala8-AII greater than Sar1-Gly8-AII greater than Sar1-Leu8-AII greater than Ile5-AI greater than hexapeptide greater than Phe3-Tyr8-AII. The cardiovascular AII receptor was investigated by generating dose-response curves of the pressor activity of Ile5-AII and six AII analogs infused intravenously. It was concluded that liver, adrenal, and vascular AII receptors in the marsupial possum have characteristics similar to those in eutherian mammals. However, the failure to find brain AII receptors raises the possibility that those functions mediated by such receptors in the eutherian brain are absent in the possum and perhaps other marsupials.

The change of vascular reactivity to angiotensin II and norepinephrine in the two-kidney, one-clip renovascular hypertensive rabbit

The change of the response to angiotensin II (AII) and norepinephrine (NE) was evaluated in vivo and vitro in the chronic phase of two-kidney, one-clip renovascular hypertensive rabbits. In the constricted group, systemic blood pressure (BP) was significantly higher and plasma renin activity (PRA) was significantly lower than in the control group. Subpressor doses of AII and NE injections in the constricted group produced significant elevations of BP. In the aortic, renal and iliac arterial strips, the reactivity to AII (10(-10) to 10(-8) M) and NE (10(-10) to 10(-7) M) was significantly increased in the constricted group as compared to the control group. In the constricted group, sodium loading produced BP elevation with decreased PRA and shifted the dose-response curves by AII and NE to the left, whereas sodium restriction decreased BP and shifted the curves to the right. In the control group, altered sodium intake did not affect BP but affected only the dose-response curves by AII. These results suggested that in the chronic phase of renovascular hypertensive rabbits, the increased reactivity to AII and NE may contribute to the maintenance of hypertension.

The clinical use of angiotensin converting enzyme inhibitors in hypertension and cardiac failure

The renin-angiotensin system has a range of physiological actions concerned with the control of the circulation. Angiotensin II has both an immediate and a delayed pressor effect, it stimulates the secretion of aldosterone and antidiuretic hormone, promotes thirst, stimulates the sympathetic nervous system at various sites while inhibiting vagal tone, and has a range of direct effects on the kidney. Several aspects of this range of actions can become deranged in a number of forms of hypertension as well as in congestive cardiac failure. Hence much effort has been directed in recent years to the development of agents designed to interfere with the renin-angiotensin system and to apply these clinically in the treatment of hypertension and congestive cardiac failure. Orally active converting enzyme inhibitors are of proven benefit not only in renovascular hypertension, but also, when combined with loop diuretics, in the treatment of intractable hypertension as well as, both alone and in combination with thiazide diuretics, in the treatment of essential hypertension. In congestive cardiac failure controlled trials have shown that converting enzyme inhibitors can improve exercise tolerance while diminishing lassitude, correct potassium deficiency and limit ventricular arrhythmias. Energetic efforts are being made to develop orally active inhibitors of the enzyme renin itself, since these would be more specific in action than the presently available and very successful converting enzyme inhibitors.

Systemic synthesis of prostaglandin I2 following sustained infusion of angiotensin II in conscious dogs

Acute infusion of pharmacological doses of angiotensin II stimulates the release of prostaglandin I2 (PGI2), which may modulate the vasoconstrictor response. It is uncertain whether sustained small increases in the plasma concentration of angiotensin II has the same effect. To investigate this further, low doses of angiotensin II were infused into conscious sodium replete dogs for 3 h. PGI2 synthesis was assessed by measurement of a major metabolite of PGI2, 2,3-dinor-6-keto PGF1 alpha, in urine and plasma, using gas chromatography mass spectrometry. Angiotensin II infusion (15 ng/min per kg body weight) resulted in a 3-fold increase in plasma angiotensin II (50.8 +/- 5.4 to 149 +/- 11.2 pg/ml, P less than 0.01). Mean blood pressure increased (84.8 +/- 4.3 to 108 +/- 4.7 mm Hg, P less than 0.02) and renal blood flow decreased (201 +/- 46 to 127 +/- 13 ml/min, P less than 0.01) throughout the infusion. However there was no change in either the plasma concentration (11.3 +/- 2.5 to 9.1 +/- 1.0 pg/ml) or rate of urinary excretion of dinor-6-keto PGF1 alpha (1.75 +/- 0.28 to 1.85 +/- 0.41 ng/30 min) during the angiotensin II infusion. The results suggest that small sustained elevations of the plasma concentration of angiotensin II such as are likely to occur in conscious animals, do not persistently stimulate release of PGI2 in the systemic circulation.

Pressor sensitivity to angiotensin I and angiotensin II during the development of experimental renal hypertension in the rat

Treatment with the potent angiotensin converting enzyme inhibitor perindopril completely prevented any rise in blood pressure in the 2-kidney, 1-clip (2K1C) model of renal hypertension in rats. Withdrawal of this inhibitor was followed by a slow rise in blood pressure. In 2K1C rats treated with perindopril, pressor responses to angiotensin I fell during the treatment period, but returned to normal after the inhibitor was stopped. Pressor responses to angiotensin II (AII) increased during treatment with perindopril; this was presumably due to increased receptor sensitivity consequent on the falls in endogenous AII levels. Responses to AII fell to control levels after the inhibitor was stopped. It is concluded that an increased pressor sensitivity to AII is not the cause of the slowly developing hypertension in the 2K1C model of hypertension, and that the slow pressor response to AII must be due to other factors.

Norepinephrine-related mechanism in hypertension accompanying renal failure

Various blood pressure (BP)-regulating factors were assessed before and after 4 weeks of selective norepinephrine (NE) inhibition with the sympathetic neurone blocker, debrisoquine, in nine hypertensive, nine normotensive hemodialysis patients (HDP), and 11 normal subjects. On placebo, hypertensive HDP had an increased total blood volume (P less than 0.05) and exchangeable sodium (P less than 0.001), while both HDP groups had increased (P less than 0.05) plasma clearances of NE and angiotensin II (AII), and tended to have higher basal plasma NE, renin, and AII levels, and lower BP responses to NE or AII than normal subjects. Plasma epinephrine and the chronotropic dose of isoproterenol (CDI) did not differ significantly among groups. Debrisoquine lowered supine BP markedly in hypertensive HDP (on average from 181/107 to 148/88 mm Hg) and slightly in normotensive HDP (143/78 to 131/76 mm Hg), but not in normal subjects (116/74 to 120/79 mm Hg). In all groups, plasma NE, CDI, and NE pressor dose were reduced in parallel (by 35 to 75%; P less than 0.05 to less than 0.001), and the relation between stepwise increasing plasma NE and BP changes during NE infusion was commensurably displaced to the left (P less than 0.01). The remaining parameters were not changed consistently.

CONCLUSION

HDP, as normal subjects, respond to decreased sympathetic outflow with increased alpha- and beta-receptor sensitivity. Hypertension in HDP depends strongly on a NE-related mechanism. The latter seems to complement renin-angiotensin, sodium and fluid volume in the pathogenesis of high BP.

Effects of angiotensin and ergonovine on large and small coronary arteries in the intact dog

Angiotensin (ATN) and ergonovine (ERG) are known to cause vasoconstriction of the coronary bed. However, ATN effects have been described mainly on the coronary resistance vessels, while ERG effects have been described on proximal conductance vessels. Recent studies have shown that proximal and distal coronary arteries are regulated independently. To examine both proximal and distal effects of ATN and ERG on the same heart, we studied 7 intact dogs, anesthetized with Innovar (Fentanyl 0.4 mg, Droperidol 20 mg, in 1 ml) and nitrous oxide, which were subjected to direct left anterior (LAD) coronary infusion of angiotensin (0.1, 0.5 and 5 micrograms/min) and ergonovine (0.5, 5, and 25 micrograms/min). Using a quantitative angiographic technique to measure artery dimensions and microspheres to measure flow, ERG infusion showed significant large artery constriction at all doses (maximum: 38.9 +/- 7.8% area reduction), and a significant decrease in LAD coronary artery flow, while endocardial/epicardial flow ratio remained unchanged. ATN produced a biphasic effect on the large coronary arteries. The lowest dose produced constriction (12.3 +/- 3.7% area reduction), which returned toward control value with the 0.5 micrograms/min dose (6.0 +/- 1.0% area reduction), and the 5 micrograms/min dose (1.5 +/- 9.5% area reduction), and no significant changes were observed in LAD flow with ATN infusion. Endocardial/epicardial ratio was unchanged, but aortic pressure was significantly increased during 0.5 and 5 micrograms/min ATN infusion. Coronary resistance (pressure/flow) increased with both ERG and ATN. ERG and ATN produce large and small coronary artery constriction. The coronary response to ERG in dogs is similar to the human coronary response, even though previous data indicated a minimal constrictor response to ERG in canine coronary arteries.

Reduced responsiveness of glomerulosa cells after prolonged stimulation with angiotensin II

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

Effects of nicardipine on aldosterone release and pressor mechanisms

This study evaluated the effects of nicardipine, following intravenous infusion and oral administration, on the pressor and aldosterone responses to infused angiotensin II. Six healthy, normotensive male subjects were studied. Following administration of nicardipine, no significant change in blood pressure was seen. Nicardipine attenuated the pressor response produced by intravenous administration of angiotensin. Nicardipine did not inhibit the aldosterone response to angiotensin.

Enalapril in treatment of hypertension with renal artery stenosis. Changes in blood pressure, renin, angiotensin I and II, renal function, and body composition

The converting enzyme inhibitor enalapril, in single daily doses of 10 to 40 mg, was given to 20 hypertensive patients with renal artery stenosis. The decrease in blood pressure six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II, and to the concurrent decrease in angiotensin II. Blood pressure decreased further with continued treatment; the long-term decrease was not significantly related to pretreatment plasma renin or angiotensin II levels. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low, and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, decreased further. The increase in active renin during long-term treatment was proportionately greater than the increase in angiotensin I; this probably reflects the diminution in renin substrate that occurs with converting enzyme inhibition. Long-term enalapril treatment increased renin secretion by more than 10-fold, and renal venous and peripheral plasma renin concentration by more than 20-fold; however, the mean renal venous renin ratio was not changed. Enalapril caused a reduction in effective renal plasma flow via the affected kidney but a marked and consistent increase on the contralateral side, where renal vascular resistance decreased. The overall increase in effective renal plasma flow was significantly related to the decrease in angiotensin II. Overall glomerular filtration rate was lowered, and serum creatinine and urea increased. Enalapril alone caused a long-term reduction in exchangeable sodium, with slight but distinct increases in serum potassium. In five patients with bilateral renal artery lesions, enalapril given alone for three months did not cause renal function to deteriorate. Enalapril was well tolerated and provided effective long-term control of hypertension; only two of the 20 patients studied required concomitant diuretic treatment.

Enalapril in the treatment of hypertension with renal artery stenosis

The converting enzyme inhibitor enalapril, in single daily doses of 10-40 mg, was given to 20 hypertensive patients with renal artery stenosis. The blood pressure fall six hours after the first dose of enalapril was significantly related to the pretreatment plasma concentrations of active renin and angiotensin II and to the concurrent fall in angiotensin II. Blood pressure fell further with continued treatment; the long term fall was not significantly related to pretreatment plasma renin or angiotensin II concentrations. At three months, 24 hours after the last dose of enalapril, blood pressure, plasma angiotensin II, and converting enzyme activity remained low and active renin and angiotensin I high; six hours after dosing, angiotensin II had, however, fallen further. The rise in active renin during long term treatment was proportionally greater than the rise in angiotensin I; this probably reflects the fall in renin substrate that occurs with converting enzyme inhibition. Enalapril alone caused reduction in exchangeable sodium, with distinct increases in serum potassium, creatinine, and urea. Enalapril was well tolerated and controlled hypertension effectively long term; only two of the 20 patients required concomitant diuretic treatment.

Captopril treatment: inter-dose variations in renin, angiotensins I and II, aldosterone and blood pressure

1 The ability of captopril, 150 mg three times daily by mouth, to effect sustained reduction in plasma angiotensin II, with converse increases in circulating angiotensin I, and in active, inactive and total renin concentrations, has been assessed. 2 During prolonged treatment with captopril alone, and 12 h after the last dose of the drug, plasma angiotensin II remained approximately one-sixth of basal concentrations, while angiotensin I and renin concentrations were proportionately increased. However, further increases in angiotensin I, and in active, inactive and total renin concentrations, were seen 2 and 6 h after the morning dose of 150 mg captopril. 3 Inter-dose variations in plasma aldosterone and blood pressure were not closely related to concurrent variations in the renin-angiotensin system. 4 Arguments are presented for relying on measurements of plasma renin and angiotensin concentrations rather than of renin activity or aldosterone in assessing the effectiveness of converting enzyme inhibition.

Captopril in the long-term treatment of essential hypertension: changes in the renin-angiotensin-aldosterone system

We investigated changes in the renin-angiotensin-aldosterone system in seven patients with essential hypertension during treatment with captopril (SQ 14225) (300 to 450 mg/day) for 12 months. While blood pressure decreased, the plasma-renin concentration increased to 700 percent of the initial value (6.1 +/- 2.5 ng angiotensin l/ml . h) and angiotensin I increased to about 300 percent of the basal value (179 +/- 32 pg/ml). Converting enzyme inhibition resulted in a 30 percent decrease in plasma angiotension II levels from a basal level of 66 +/- 21 pg/ml. Plasma aldosterone decreased 52 percent from 63 +/- 13 pg/ml initially. These changes in hormone levels were maintained throughout the study. There was no significant change in serum sodium and serum potassium concentration.

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.

Captopril in the management of hypertension with renal artery stenosis: its long-term effect as a predictor of surgical outcome

Fifteen patients with hypertension and unilateral renal artery disease were treated with captopril alone; 10 came to operation and were later assessed postoperatively with no drug treatment. Captopril caused both immediate and sustained decreases in plasma angiotensin II and aldosterone, with increases in plasma active renin and blood angiotensin I concentrations. Decrements in systolic and diastolic pressure 2 hours after the first dose of captopril were closely correlated with the initial decreases in plasma angiotensin II. Blood pressure was decreased by long-term captopril therapy irrespective of whether plasma angiotensin II was abnormally high before treatment. The long-term response of both systolic and diastolic pressure correlated well with the response to surgery. By contrast, the blood pressure decrease 2 hours after the initial dose of captopril variously underestimated and overestimated the decrease during prolonged use of the drug and did not relate to surgical outcome. In patients who, before treatment, had secondary aldosteronism, hyponatremia, hypokalemia and sodium and potassium deficiency, captopril corrected these abnormalities. In the remaining patients, long-term captopril therapy did not alter exchangeable sodium, plasma sodium or total body potassium, although plasma potassium levels increased.

Captopril in renovascular hypertension: long-term use in predicting surgical outcome

The angiotensin converting-enzyme inhibitor captopril was used as long-term preoperative treatment in a series of hypertensive patients with unilateral renal arterial disease. There were immediate and sustained falls in plasma angiotensin II and aldosterone concentrations, with converse increases in circulating renin and angiotensin I. In patients with sodium and potassium deficiency and secondary aldosterone excess before treatment captopril corrected the sodium and potassium deficits; in these cases the initial hypotensive response was profound but the later effect was less pronounced. When sodium and potassium state was initially normal it remained unchanged during captopril treatment, while the full hypotensive effect took up to three weeks to be attained. The immediate, but not long-term, falls in arterial pressure with captopril were proportional to the immediate decrements of plasma angiotensin II. Nevertheless, while the immediate blood-pressure reduction with captopril variously overestimated and underestimated the eventual surgical response, the absolute blood-pressure values during long-term captopril related well with those after operation. Pretreatment plasma renin and angiotensin II concentrations, while closely predicting the immediate captopril response, are fallible guides to surgical prognosis. In contrast, long-term treatment with converting-enzyme inhibitors may provide an accurate indication of surgical outcome.

Stimulation of angiotensinogen production: a dose-related effect of angiotensin II in the conscious dog

The hypothesis that angiotensin II (AII) provides a positive feedback stimulus for production of angiotensinogen was examined in conscious dogs. AII was infused intravenously for 24 h at 5, 20, and 50 ng x kg-1 x min-1 and blood pressure, plasma renin activity (PRA), and the concentrations of AII, angiotensinogen, corticosteroids, and total protein in plasma were measured 0, 2, 4, and 24 h after the start of infusion. In addition, the liver content of angiotensinogen and the release of angiotensinogen by liver slices in vitro were measured after the 24-h sampling period. AII infusion increased blood pressure in a dose-related manner. PRA was markedly decreased by all doses of AII. Plasma corticosteroids were increased only at the highest dose of AII and did not bear any relationship to changes in the concentration of angiotensinogen. Plasma protein concentration and hematocrit were unchanged. Plasma angiotensinogen concentration was unchanged at 2 and 4 h but was increased significantly at 24 h by the two highest doses of AII. A linear relationship was found between the dose of AII and plasma angiotensinogen concentration, the liver content of angiotensinogen, and the release from liver slices during a 2-h incubation. These results provide further evidence that AII has a role in angiotensinogen production but suggest that it is of minor importance in physiological conditions.

Angiotensin II and renal hypertension in dog, rat and man: effect of converting enzyme inhibition

The role of the renin-angiotensin system in the pathogenesis of one-clip, two-kidney hypertension has been studied in man, dog and rat. Particular attention has been paid to peripheral plasma concentrations of angiotensin II in different circumstances; angiotensin II infusion has been combined with radioimmunoassay to construct angiotensin II/blood pressure dose-response curves. The effect of converting enzyme inhibitors has been studied, precautions being taken to avoid obtaining falsely high values for plasma angiotensin II because of cross-reaction with angiotensin I in these circumstances. The initial phase of one-clip, two-kidney hypertension is attributable to the direct pressor effect of the immediate rise in plasma angiotensin II. Subsequently, plasma angiotensin II is relatively lower, although blood pressure remains high. This upward resetting of the plasma angiotensin II/blood pressure relationship can be mimicked by infusing angiotensin II chronically at low dose. After reconstruction of a stenosed renal artery, or excision of a post-stenotic kidney, the angiotensin II/blood pressure relationship returns slowly to normal. In this second phase of one-clip, two-kidney hypertension, the long-term administration of saralasin, or of converting enzyme inhibitor, can also return arterial pressure to normal; brief administration of these drugs is less effective or ineffective. The results are compatible with, although they do not conclusively establish, an important slow pressor action of the renin-angiotensin system in the second phase of one-clip, two-kidney hypertension. This provides a rational basis for the use of captopril clinically in this condition.