Interrelationships between angiotensin, norepinephrine, epinephrine, aldosterone secretion, and electrolyte metabolism in man

Comparison of Intravenous Dexmedetomidine versus Esmolol for Attenuation of Hemodynamic Response to Tracheal Intubation after Rapid Sequence Induction: A Systematic Review and Meta-Analysis

The present study aims to investigate whether intravenous dexmedetomidine shows superiority to esmolol for hemodynamic response to tracheal intubation after rapid sequence induction. In the present meta-analysis, PubMed, EMBASE, and the Cochrane Library were searched for trials comparing dexmedetomidine with esmolol for the attenuation of the hemodynamic response to intubation. Ten trials were selected in the present meta-analysis. Compared to esmolol, the use of dexmedetomidine maintains stable heart rates (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean arterial pressure (MAP) at 1 min, 3 min, and 5 min after tracheal intubation. Dexmedetomidine causes less hemodynamic response to tracheal intubation after rapid sequence induction compared with esmolol.

Hormones and the pathogenesis of congestive heart failure: vasopressin, aldosterone, and angiotensin II. Further evidence for renal-adrenal interaction from studies in hypertension and in cirrhosis

The role of hormones that can influence renal tubular reabsorption of salt and water in congestive heart failure and other states of abnormal fluid retention has been discussed.

Available evidence indicates that the antidiuretic hormone of the neurohypophysis plays a nonessential role in the pathogenesis of edema.

Oversecretion of aldosterone can be an important, or even an essential, mechanism in the pathogenesis of certain states of edema, such as those of nephrosis and cirrhosis. Advanced congestive heart failure, however, can occur with a normal or only a moderately elevated rate of aldosterone secretion. The observations perhaps suggest that more immediate hemodynamic consequences of heart failure, such as a reduced glomerular filtration rate, also play an important role in causing renal retention of sodium. Increased aldosterone secretion is provoked by an unidentified hemodynamic consequence of cardiac decompensation. When oversecretion occurs, it undoubtedly adds to circulatory embarrassment by promoting more sodium retention.

An understanding of the exact role of aldosterone in heart failure awaits clarification of the fundamental problem of the mechanisms involved in the normal control of the secretion of the hormone. Studies of other diseases have yielded helpful clues in this latter regard. The finding of oversecretion of aldosterone in malignant nephrosclerosis led to the demonstration that angiotensin is a potent stimulus to aldosterone secretion and to the suggestion that sodium balance may be regulated by a renal-adrenal (angiotensin-aldosterone) mechanism, which is deranged in malignant hypertension.

Recent studies in our laboratory have been designed to determine whether increased amounts of circulating angiotensin could be responsible for the oversecretion of aldosterone of typical secondary aldosteronism. In a model state of secondary aldosteronism (cirrhosis with ascites), it has been found that the pressor responsiveness to infused angiotensin is reduced, a finding that could explain the absence of manifest arterial hypertension even if angiotensin were present in increased amounts in secondary aldosteronism. Angiotensin also failed to increase the rate of aldosterone secretion in cirrhosis with ascites. This might mean that the adrenal cortex is maximally engaged by increased amounts of endogenous trophic hormone (? angiotensin). In further contrast to its effects in normal subjects, in cirrhosis with ascites angiotensin caused a marked natriuresis by modifying the renal tubular reabsorption of sodium. The very potent effects of angiotensin on sodium transport also raised the possibility that an intrarenal action for this substance may be physiologically more important than its effect on aldosterone release.

Thus far, crucial experiments are lacking, and other interpretations are possible. It remains to be shown that increased amounts of renin or of angiotensin appear in the circulation of either sodium-depleted normal subjects or patients forming edema. The observations to date suggest, however, that a renal humoral factor (? angiotensin) may be involved in the normal regulation of sodium balance and in the pathogenesis of various states of fluid retention. Furthermore, this renal factor may mediate various stimuli that are known to increase aldosterone secretion to the adrenal cortex. Some critical change in the renal circulation may determine the release of this factor.

PLASMA VASOCONSTRICTOR ACTIVITY IN PATIENTS WITH RENAL, MALIGNANT, AND PRIMARY HYPERTENSION

Polypeptide vasoconstrictor activity was assayed in the peripheral venous blood of 45 hypertensive patients and 20 normal subjects. The average activity was significantly increased in all hypertensive groups, and activity tended to be much higher in patients with renovascular and malignant hypertension than in primary hypertension.

In confirmation of previously reported results by Helmer and Judson, there was no correlation between vasoconstrictor activity and renal excretory function. The plasma level of vasoconstrictor activity did not correlate with mean arterial pressure except when malignant or renovascular hypertension was present.

A significant inverse relationship was found between the serum potassium concentration and vasoconstrictor activity: as activity levels increased, the potassium fell. The data suggest that a renin-like substance may be present in various hypertensive states in amounts sufficient to depress serum potassium, presumably by activation of the renin-angiotensin-aldosterone mechanism.

RENAL EFFECTS OF ANGIOTENSIN II INFUSIONS IN NORMOTENSIVE PREGNANT AND NONPREGNANT WOMEN

Normotensive pregnant women are relatively resistant to angiotensin II in that they give smaller pressor responses and show smaller reductions in urine flow and sodium and chloride excretions than do normotensive nonpregnant women.

Women early in the third trimester of pregnancy are more resistant to angiotensin II than are women at term, with respect to the effect upon sodium and chloride excretions.

The less pronounced renal effects of angiotensin II in pregnant women cannot be attributed merely to error caused by increase in the dead space of the urinary tract.

Angiotensin II and catecholamines interaction in short-term low protein feeding

Renal and systemic hemodynamic responses to an alpha-adrenergic agonist (norepinephrine, NE) and an alpha-adrenergic antagonist (phentolamine, PHEN) were studied in weanling rats pair-fed isocaloric diets containing either normal (NP, 23%) or low (LP, 6%) protein. Mean arterial pressure (MAP) rose less with NE and fell more with PHEN in LP than in NP. Plasma NE and epinephrine (E; 46 +/- 5 and 51 +/- 4 ng/ml) were higher in LP than in NP (26 +/- 3 and 39 +/- 3 ng/ml). These could not be attributed to changes in red cell mass nor the volumes of plasma, extracellular, or interstitial fluid in LP versus NP. Plasma angiotensin II (Ang II), renin (PRA), and aldosterone (PA) were lower in LP than in NP. An increased number without changes in affinity of glomerular Ang II receptors was found in LP compared to NP, while alpha 1- and alpha 2-adrenergic receptors were down-regulated in LP as compared to NP without changes in affinity for the alpha 1 receptor but with an increase in renal alpha 2 receptor affinity. LP (vs. NP) decreased GFR and RPF, and increased renal vascular resistance (RVR). NE decreased RPF equally in NP versus LP but raised RVR approximately twofold in NP versus LP. PHEN decreased RPF and increased RVR less in LP than in NP. Moreover, PHEN increased renal renin content approximately seven-fold over the basal NP values. Exogenous Ang II increased RVR and lowered RPF more in LP than in NP. Enalapril abolished all the hemodynamic changes of LP and restored the systemic response to NE.(ABSTRACT TRUNCATED AT 250 WORDS)

Renin-angiotensin system in dogs following chronic bile-duct ligation. Relation to vascular reactivity

The pressor response to angiotensin II, blood volume, angiotensin II in arterial blood, renin substrate, renin concentration, renin activity and aldosterone in venous blood, liver function tests, kidney function tests, glucose, sodium, potassium, plasma osmolality and complete blood count were examined before and 1, 2, 3 and 5 weeks after ligation of bile ducts in nine conscious trained dogs. The pressor response to angiotensin II was markedly suppressed after bile-duct ligation, especially at 1-3 weeks postoperation. A maximal decrease in plasma renin substrate, and maximal increases in plasma renin concentration, plasma renin activity and aldosterone were noted at 1 week postoperatively. Plasma angiotensin II levels were elevated at 1 and 5 weeks postoperatively but were near normal 2 weeks postoperatively despite suppression of the angiotensin II pressor response. Endogenous levels did not correlate with suppression of the pressor response to exogenous angiotensin II.

Renin, calcium metabolism and the pathophysiologic basis of antihypertensive therapy

The renin-angiotensin-aldosterone system regulates blood pressure and volume homeostasis in addition to sodium and potassium metabolism, and may be linked to divalent cation metabolism as well as hypertensive disease. In essential hypertension, circulating serum magnesium and Ca++, and the calcium regulating hormones, parathyroid hormone, calcitonin and 1,25 dihydroxyvitamin (1,25D) are different in the various renin subgroups. Elevated blood pressure induced by such maneuvers as dietary salt loading is associated with exacerbations of these calcium metabolic deviations, and appears related to salt-induced changes in serum Ca++ or 1,25D levels. Short- or longer-term lowering of blood pressure with the calcium-channel blocker, nifedipine, or with calcium or magnesium supplementation is associated with a shift of renin system activity and calcium metabolic indexes back to average normotensive values in those subjects most susceptible to these hypotensive agents. These observations suggest that deviations in calcium metabolism in essential hypertension may be related to the pathophysiology of the hypertensive process. Further, renin system activity and calcium metabolic indexes such as serum Ca++ levels may help target specific subgroups of hypertensive populations most susceptible to various dietary or drug maneuvers, and thus may provide a basis to better understand and treat clinical hypertension.

The Influence of Sodium Intake on Physiological Responses to Angiotensin II in Conscious Dogs

The renin-angiotensin system (RAS) is suppressed either by high sodium intake or by high levels of angiotensin II (A II). Therefore in prior studies it has been difficult to sort out the influence on the cardiovascular homeostases of different levels of A II and different levels of sodium in the diet respectively. The present study examines the quantitative effects of A II on mean arterial blood pressure (MABP), electrolyte excretion and hormone secretion in conscious dogs on low, normal and high sodium intake with the endogenous RAS blocked with continous intravenous infusion of enalapril (MK-421). Fourteen dogs on three different Na diets, low, normal and high (5, 30 and 250 mmol/day), were infused continously with enalapril, 4 mg/kg/day and studied with superinfused A II at rates of 0, 1, 3, 6 and 12 ng/kg/min., each period lasting one week. Convening enzyme inhibitor (CEI) decreased MABP equally in dogs on low and normal sodium intake to about 80% of control, but did not have a significant effect in dogs on high sodium intake. The initial infusion of angiotensin II at the lowest rate had a pronounced effect on MABP in the normal and high sodium states, but had no effect on MABP in the sodium depleted dogs. However, at the higher rates of infusion, the angiotensin II increased the pressure to a similar degree at all levels of sodium intake. All four dogs in the high sodium group developed circulatory difficulties at the 6 or 12 ng level of A II infusion: One hemorrhaged in the feces, one developed congestive failure, and in the other two the arterial pressure remained elevated an average of 23 mm Hg after removal of all drugs. Plasma renin activity increased in all groups after CEI; however, renin secretion was suppressed by much smaller rates of angiotensin II infusion in the normal and sodium loaded dogs than in the sodium depleted dogs. CEI suppressed plasma aldosterone 30% in the low sodium dogs but by a lesser percentage in the normal sodium dogs; plasma aldosterone increased in all groups after A II. The present study indicates that when the endogenous RAS is blocked with CEI, small increments in angiotensin II infusion rate can cause almost linear increments in the chronic level of mean arterial pressure at varying levels of sodium intake. Also A II infusion and high dietary sodium can have independent effects on both plasma renin activity and plasma aldosterone concentration.

Effect of oral glucose loading on plasma insulin, potassium, renin and aldosterone in normal subjects and patients with primary hyperaldosteronism

The effects of standard oral glucose loading (100 g) on plasma aldosterone and some regulatory factors were assessed in patients with primary hyperaldosteronism and normal subjects. Following overnight fast, mean plasma glucose was identical (10 patients and normal subjects approximately matched per age and sex); plasma insulin, potassium and renin levels were lower and plasma aldosterone higher in the patients. Glucose loading significantly increased plasma glucose and insulin concentrations and decreased plasma potassium and aldosterone levels in both groups; plasma renin activity was significantly increased only in normal subjects. The increases in plasma insulin and the decreases in plasma potassium or aldosterone tended to be blunted in primary hyperaldosteronism. Relationships among glucose-induced changes in plasma aldosterone and other factors were assessed by multiple regression analysis in these patients and normal subjects as well as an additional group of 21 normal subjects; in the latter, plasma cortisol was also measured and found to decrease significantly after glucose loading. Changes in plasma aldosterone correlated (P less than 0.025) more closely with those in plasma potassium in the patients and with variations in plasma renin activity in the normal subjects. These findings suggest that complex metabolic changes occur following glucose ingestion which are capable of modifying aldosterone secretion in normal subjects and primary hyperaldosteronism. The aldosterone-inhibitory effect of glucose tends to be blunted in the latter disorder. This could be related at least in part to an impaired insulin response in primary hyperaldosteronism.

Control of vascular responsiveness during human pregnancy

Normal human pregnancy is characterized by vascular refractoriness to AII. This pregnancy-induced vascular refractoriness appears to be mediated principally by decreased vascular smooth muscle responsiveness to AII rather than by alterations in blood volume or plasma concentrations of renin or AII. The mechanism that controls vascular refractoriness during normal pregnancy likely involves a localized prostaglandin or prostaglandin-like action mediated through cyclic nucleotides. The action of progesterone or one of its metabolites appears to mediate the synthesis or the catabolism of locally produced prostaglandins or prostaglandin-like agents.

Renal responses to angiotensin II and 1-sar-8-ala-aII in sodium replete and deplete dogs

In order to elucidate the effects of angiotensin II on renal function, angiotensin II (AII; 1 ng/kg per min) and the AII antagonist 1-sar-8-ala-angiotensin II (AIIA; 200 ng/kg per min) were infused into the renal artery of anesthetized dogs (pentobarbital), on either a high (8 mmol/kg per day for seven days) or a low sodium intake (0.5 mmol/kg). In sodium replete dogs AII produced renal vasoconstriction with decreased RBF (-28%; P less than 0.001), but with less decrease of GFR (-14%; P less than 0.001), leading to an increase of FF (+19%, P less than 0.001), andantidiuresis (-39%, P less than 0.001); the antinatriuresis (-58%; P less than 0.001) exceeded the antidiuresis (P less than 0.001). delatRBF (-10%; P less than 0.001) was less pronounced (P less than 0.001) during AII in sodium deplete dogs, GFR remained unchanged, but FF increased to the same extent (+16%; P less than 0.05); diuresis and urinary electrolyte excretion were however not affected. AIIA did not affect RBF, GFR, FF, nor diuresis in sodium replete dogs suggesting that endogenous AII has no tonic influence on renal function in these conditions. In sodium deplete animals AIIA produced an 11% (P less than 0.001) increase of RBF, without changes of GFR; FF decreased by 12% (P less than 0.01), but diuresis, natriuresis and kaliuresis were not affected.

Acute effects of acetylsalicylic acid on renal function in normal man

The acute effects of therapeutic doses of acetylsalicylic acid (ASA) on renal water and solute output, and the possible interaction of ASA with the diuretic effects of furosemide, have been studied in a double blind double cross over study in healthy human subjects. There was a significant decrease in 24 h sodium excretion and Na/K ratio in urine in the ASA-treated subjects. The effect of ASA on urinary sodium excretion was most prominent during day time (8 a.m.-10 p.m.) and on days with low sodium intake, as confirmed by control sodium excretion and plasma renin activity. A decrease in urine volume and an increase in tubular reabsorption of free water were caused by ASA, the antidiuretic effect being most marked at night (10 p.m.-8 a.m.). No action of ASA on the effect of furosemide on urinary sodium excretion was found. Creatinine clearance remained unaltered by ASA treatment, and ASA did not interfere with the increase in urinary creatinine excretion after furosemide treatment.

Vascular angiotensin receptors and their role in blood pressure control

The renin angiotensin system has an important role in regulating arterial blood pressure in homeostasis and disease. A reciprocal relationship exists between sodium balance and the circulating levels of renin and angiotensin II. The vascular responsiveness to angiotensin II, the major vasconstrictor component of the renal pressor system, can be impaired by numerous factors including sodium depletion or a reduction in effective plasma volume. In situations in which the renin-angiotensin system is activated, a negative relationship between the angiotensin II pressor response and the circulating angiotensin II level is observed. This effect seems to involve a change of the angiotensin II receptor interaction in the vascular smooth muscle. The prevention of angiotensin II generation by the inhibition of converting enzyme causes an immediate increase in the pressor response to angiotensin; after bilateral nephrectomy, it takes much longer to develop. In addition, the depressor response to angiotensin antagnoists and converting enzyme inhibitor is preserved after bilateral nephrectomy for much longer periods than can be accounted for by the disappearance of circulating renin. These observations support the view that the decrease in vascular response to angiotensin II during sodium deprivation or when body fluid volumes are reduced is the result of prior occupancy of the receptor sites by endogenous hormone generated both in the plasma and locally within blood vessel walls. Therefore, a change in the number or affinity of receptors consequent to a change in sodium balance or as a modulating function of the renin-angiotensin system need not be postulated to explain changes in angiotensin vascular responsiveness.

Angiotensin. II. Important role in the maintenance of arterial blood pressure

An angiotensin II antagonist, [1-sarcosine, 8-alanine]-angiotensin II, was given intravenously to anesthetized dogs with thoracic caval constriction and ascites to investigate the role of angiotensin II in the control of arterial pressure. The antagonist produced a striking fall in arterial pressure and in aldosterone secretion and an accompanying increase in plasma renin activity. In a control experiment, normal anesthetized dogs were given the angiotensin analog, but it failed to reduce arterial pressure or to influence plasma renin activity. In conscious dogs with caval constriction, the antagonist produced essentially the same drop in arterial pressure as observed in anesthetized animals. These results suggest an important role for angiotensin II in the maintenance of arterial pressure by its action on specific receptor sites in arteriolar smooth muscle and in the adrenal cortex.

O comportam en to da pressão arterial na esquistossomose hepática e outras hepatopatias

O estudo de 911 pacientes hospitalizados para tratamento de variados casos de patologia interna mostrou 26,8% de hipertensos e 34,7% de doentes com alteração hepática, 17,7% dêstes apresentando hepatopatia esquistossomótica. A análise das observações resultem, na seleção de seis casos em que havia a coexistência de hipertensão e hepatopatia e que são estudados em separado. Outros seis casos foram encontrados em que a necrópsia revelou alteração hepática e o "rim da hipertensão essencial", mas em cujas observações clinioas não constava qualquer evidência de doença hipertensiva. A comparação da média das pressões arteriais mostrou diferença estatisticamente significante para as pressões sistólicas e diastólicas, sendo mais altas entre os pacientes não hepatopatas. Fêz-se, também, minuciosa revisão da literatura.

Toxemia of pregnancy in sheep: a clinical, physiological, and pathological study

Toxemia was induced in 13 of 20 pregnant ewes by the stress of a change in environment and food deprivation late in pregnancy. Of the toxemic ewes, eight developed prominent neurological findings with convulsions, motor weakness, and blindness, whereas five ewes developed azotemia without neurological signs. Proteinuria and azotemia occurred in all but one of the toxemic animals. Seven animals did not develop clinical or laboratory evidence of toxemia. Hypertension did not occur with the onset of toxemia but all toxemic animals showed glomerular changes by light and electron microscopy. These abnormalities, which were similar to those seen in human preeclampsia, included endothelial cell swelling, focal reduplication of the basement membrane, and fusion of the epithelial cell foot processes. The toxemia could not be attributed to changes in hematocrit, plasma glucose, Na, Cl, CO(2), K, Ca, fibrinogen, arterial pH, lactate, or pyruvate concentrations. Cardiac output fell only in ewes with prominent neurological signs. Plasma renin rose strikingly in animals developing toxemia, without change in substrate concentration. In contrast to human and other species, sheep uterus and amniotic fluid contained no detectable quantities of renin. Thus in response to stress the pregnant ewe develops a toxemia which in the absence of hypertension has clinical and pathological similarities to human preeclampsia.

Inhibition of the effects of angiotensin II on adrenal steroid production by dietary sodium

The pressor octapeptide, angiotensin II, can stimulate the production of aldosterone by the adrenal cortex. The present results show that in the dog a high-sodium diet can eliminate the steroidogenic action of angiotensin II, which is thus dissociated from the pressor action which remains. Angiotensin II was infused intravenously for 48 hours into conscious, undisturbed hypophysectomized dogs that were receiving each day either 60 or 200 mEq of dietary sodium. Blood pressure and secretion of aldosterone, corticosterone, and cortisol were measured (1) throughout the infusion in some dogs, and (2) at the end of the infusion in all dogs. In those dogs receiving 60 mEq of sodium, angiotensin II elevated the blood pressure and produced sustained increases of secretion of aldosterone, corticosterone, and cortisol. In those dogs receiving 200 mEq of sodium, angiotensin II, while retaining its pressor activity, had no effect on the production of aldosterone, corticosterone, or cortisol after 24 hours. Thus, if angiotensin II can produce hypertension clinically, there need not be secondary aldosteronism as well.

Activation of aldosterone secretion in primary aldosteronism

Angiotensin infusion evokes marked increases in aldosterone secretion in primary aldosteronism and little change in secondary aldosteronism. The low plasma renin activity of primary aldosteronism and the elevated plasma renin activity of secondary aldosteronism are thought to account for this differential response. The effect of angiotensin on aldosterone and 18-hydroxycorticosterone secretion was studied during adrenal vein catheterization in seven patients with primary aldosteronism (whose plasma renin activity had been elevated following spironolactone therapy), one hypertensive patient with normal plasma renin activity and normal aldosterone secretion, two patients with secondary aldosteronism who had elevated plasma renin activity, and one anephric patient whose plasma renin activity was 0. Adrenal venous aldosterone and 18-hydroxycorticosterone were measured before and after a ten min sub-pressor angiotensin infusion. The cells of the aldosterone-producing adenoma (APA) respond to small increases in plasma angiotensin with large increases in secretion of aldosterone and 18-hydroxycorticosterone. The dose of angiotensin capable of evoking this response from the aldosterone-producing adenoma produces little or no change in the secretion of the steroids from nontumorous glands. The augmentation of aldosterone secretion, induced by angiotensin, in primary aldosteronism is due solely to increased secretion by the adenoma and not by the contralateral zona glomerulosa. The increased sensitivity of the aldosterone-producing adenoma is characteristic of the tumor. This response is independent of fluctuations in endogenous plasma renin activity. This sensitivity is not blunted by high plasma renin activity, nor is it a function of tumor mass for the effect is observed in aldosterone-producing adenomas regardless of size. ACTH injection after angiotensin infusion resulted in a marked increase in aldosterone concentration in the effluent from the nontumorous adrenal, but was not capable of producing further increases in aldosterone concentration in the effluent from the APA. In view of this exquisite sensitivity to infused angiotensin, it may be that the small variations in endogenous plasma renin activity that have been observed in primary aldosteronism may be capable of evoking large changes in aldosterone secretion in patients with aldosterone-producing adenomas.

Plasma renin activity and renin-substrate concentration in patients with liver disease

Peripheral venous renin activity was determined by the method of Boucher in 15 patients with cirrhosis of the liver and ascites who were on an unrestricted sodium intake. Positive sodium balance was present in all subjects. Marked elevation of mean plasma renin activity (43 ng angiotensin II/min per liter, SD±38) was present. The mean plasma renin activity in 16 normal ambulatory subjects on an unrestricted sodium intake was 10.7 ng (SD±4.9) of angiotensin II/min per liter. The difference was highly significant, P < 0.01. A zero-order enzyme reaction occurred in all but 1 patient; the first-order enzyme reaction in this 1 patient suggests a low renin-substrate concentration in liver disease. The renin-substrate concentration was determined in 18 patients with liver disease (13 with cirrhosis and 5 with hepatitis) and in 10 normal subjects. The renin substrate was expressed in equivalents of angiotensin II formed/100 ml plasma. The mean renin substrate in 13 patients with cirrhosis and ascites was 17,193 ng (SD±6556); the normal mean renin substrate was 34,385 ng (SD ± 5,679), P < 0.01. The lowest renin substrate concentration was seen in 2 patients with severe hepatitis.

Further observations on renal transplants in man from cadaveric donors

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