Effect of low dose beta blockers on atrial and ventricular (B type) natriuretic factor in heart failure: a double blind, randomised comparison of metoprolol and a third generation vasodilating beta blocker

OBJECTIVES

This study examines the acute effects of two differing beta adrenergic blocking agents (metoprolol and a third generation vasodilating beta blocker) on plasma concentrations of atrial natriuretic factor (ANF), brain (ventricular) natriuretic factor (BNF), and haemodynamic variables in patients with heart failure.

SETTING

University teaching hospital.

METHODS

20 patients with impaired left ventricular systolic function [ejection fraction 32 (SEM 2.3)%] were randomised in a double blind manner to receive either oral metoprolol 6.25 mg twice daily or celiprolol 25 mg daily. Haemodynamic variables were evaluated by Swan-Ganz pulmonary artery catheter over 24 hours. ANF and BNF concentrations were measured at baseline, 5 h, and 24 h by radioimmunoassay.

RESULTS

At baseline ANF and BNF concentrations were considerably raised compared to the normal range. Treatment with metoprolol caused ANF to rise further to 147% of the basal level at 5 h (P = 0.017) and 112% at 24 h (P = 0.029). This was associated with a small but non-significant rise in pulmonary capillary wedge pressure. Cardiac output and systemic vascular resistance were unchanged at 24 h. In contrast, after celiprolol ANF fell to 90% of basal levels at 5 h and to 74% of basal level at 24 h (P = 0.019), associated with a small but non-significant fall in pulmonary capillary wedge pressure [-3.3 (2.7) mm Hg] and systemic vascular resistance, and rise in cardiac output from 3.2 (0.2) to 4.0 (0.4) l/min (P = 0.04). BNF concentrations rose to 112% of baseline at 5 h (P = 0.09) after metoprolol but fell slightly, to 91% of baseline values, after celiprolol (NS).

CONCLUSIONS

Metoprolol, even in very low doses (6.25 mg), produced a rise in ANF and BNF, although minimal haemodynamic changes were detected. In contrast, a vasodilating beta blocker was associated with a significant fall in ANF and BNF and a small rise in cardiac output. This study confirms both the advantages of vasodilating beta blockers over metoprolol for initial treatment of heart failure and the usefulness of ANF and BNF measurements for the assessment of drug effects in heart failure compared to traditional haemodynamic measurements.

Circulating concentrations and physiologic role of atrial natriuretic peptide during endotoxic shock in the rat

OBJECTIVES

To determine if there are changes in circulating concentrations of endogenous atrial natriuretic peptide and the physiologic role of this peptide in endotoxic shock.

DESIGN

A prospective, randomized, controlled animal trial.

SETTING

University research laboratory.

SUBJECTS

Anesthetized male Wistar rats, weighing 250 to 350 g.

INTERVENTIONS

Six rats received 1.5 mg/kg body weight of lipopolysaccharide alone. Five rats received 1.5 mg/kg of lipopolysaccharide and 200 microL/100 g body weight of rabbit anti-atrial natriuretic peptide serum. Another five rats received 1.5 mg/kg of lipopolysaccharide and normal rabbit serum in the same volume as the antiserum.

MEASUREMENTS AND MAIN RESULTS

Plasma concentrations of atrial natriuretic peptide, arginine vasopressin, and aldosterone were measured, and changes in hemodynamic parameters and renal function were monitored in rats with endotoxic shock after catheterization of the right jugular vein. Urine volume, urine sodium excretion, urinary potassium excretion, and urine 3', 5'-cyclic guanosine monophosphate (cGMP) excretion were measured at 12-hr intervals. The plasma atrial natriuretic peptide concentration was slightly but significantly lower 30 mins after the lipopolysaccharide injection (114.8 +/- 9.0 pg/mL at 0 hr, 75.6 +/- 6.2 pg/mL at 30 mins, p < .01) and then began to increase, peaking at 6 hrs (752.8 +/- 104.5 pg/mL, p < .01 vs. 0 time) and remaining at higher concentrations than before the preinjection value, up to 24 hrs. In contrast, acute spike-like increases of arginine vasopressin and aldosterone concentrations were observed 30 mins after the lipopolysaccharide injection, preceding the increase of the plasma atrial natriuretic peptide concentration. Measurements of urine volume and urine sodium excretion showed oliguria during the initial 12 hrs after the lipopolysaccharide injection, followed by diuresis and natriuresis during the subsequent 12 hrs. In addition, injection with anti-atrial natriuretic peptide serum in the diuretic phase 12 hrs after the lipopolysaccharide injection significantly inhibited the diuresis, natriuresis, and urine cGMP excretion in this model. Furthermore, the plasma aldosterone concentration 24 hrs after the lipopolysaccharide injection was significantly increased by the administration of the antisera.

CONCLUSIONS

These findings suggest that endogenous atrial natriuretic peptide increases in the acute phase of endotoxic shock and plays an important role in water and electrolyte balance by regulating diuresis.

Pulmonary hypertension. Response of vasoactive peptides to a nonionic contrast medium in patients undergoing pulmonary angiography

RATIONALE AND OBJECTIVES

The degree to which pulmonary angiography may contribute to serious complications in patients with pulmonary hypertension has not been clarified and remains a matter of debate. Accordingly, this study was designed (1) to detect the potential release of vasoactive peptides and (2) to investigate the hemodynamic response after administration of a nonionic contrast medium in patients with pulmonary hypertension undergoing pulmonary angiography. Allergy-mediating substances also were measured to monitor for possible anaphylactoid reactions.

METHODS

Pulmonary digital subtraction angiography was performed in 20 patients with pulmonary hypertension (mean pulmonary arterial pressure more than 20 mm Hg). Iopromide was administered as a total of 100 mL via a 7F catheter inserted from the right femoral vein. The injected volume and duration of injection (15 to 20 mL/sec) were kept constant. Hemodynamic parameters were continuously monitored, including electrocardiogram, heart rate, phasic and mean pulmonary arterial and peripheral arterial pressures. Blood samples were obtained before and after administration of contrast media to assay for the concentration of the following vasoactive peptides using radioimmunoassay techniques: renin, angiotensin-I-converting enzyme, angiotensin II, aldosterone, atrial natriuretic peptide, antidiuretic hormone, cyclic-guanosine monophosphate, and myoglobin, as well as allergy-mediating substances such as tryptase, eosinophil protein X, and eosinophil cationic protein.

RESULTS

Administration of iopromide caused significant increases in atrial natriuretic peptide (from 61.3 +/- 11.8 to 94.0 +/- 16.7) and antidiuretic hormone (from 6.6 +/- 1.9 to 12.3 +/- 3.1), whereas renin significantly decreased (from 3.0 +/- 0.6 to 1.3 +/- 0.5). After administration of contrast media, there were no significant changes in the other measured vasoactive peptides, allergy-mediating substances, and monitored cardiovascular parameters.

CONCLUSION

Administration of iopromide for pulmonary angiography in patients with pulmonary hypertension resulted in no appreciable hemodynamic alterations associated with the observed changes in atrial natriuretic peptide, antidiuretic hormone, and renin. No allergy-mediated reactions were observed in these patients.

Attenuation of atrial natriuretic peptide response to sodium loading after cardiac operation

To evaluate the role of cardiac operation and the atrial appendage in secretion of atrial natriuretic peptide in response to sodium loading, we studied 44 patients who underwent heart operations with (28 patients; group I) or without (16 patients; group II) right atrial appendectomy and 16 patients who underwent lobectomy (group III). Before and after operation 1 ml/kg of 10% NaCl was infused for 15 minutes. Blood samples were taken before NaCl infusion and immediately after infusion and at 60 minutes after infusion. There were no significant changes in hemodynamics or hematocrit level throughout the study. Plasma and urine sodium levels and the fractional excretion of sodium were significantly increased by sodium loading. Before operation, plasma mean atrial natriuretic peptide levels increased markedly in response to sodium infusion in all groups. After operation, this atrial natriuretic peptide response disappeared in groups I and II, but remained present in group III. Elution profiles of plasma atrial natriuretic peptide showed that the major peak coincided with alpha-atrial natriuretic peptide before sodium loading, whereas a beta-atrial natriuretic peptide peak appeared 60 minutes after sodium loading in all groups both before and after operation. The mean plasma arginine vasopressin levels were significantly increased by sodium loading both before and after operation in all groups. Sodium loading decreased the mean plasma aldosterone levels in all groups before operation, but did not after operation in groups I and II. Plasma renin activity and angiotensin II concentrations were not changed by sodium loading. We conclude that atrial natriuretic peptide response to sodium loading is attenuated by cardiac operation irrespective of right appendectomy, but not by lobectomy. Sodium loading augments secretion of beta-atrial natriuretic peptide even in reduced atrial natriuretic peptide response states after heart operations.

Atrial natriuretic peptide and antihypertensive action due to beta-blockade in essential hypertensive patients

The effects of beta-blocker treatment on hemodynamics were studied in relation to plasma atrial natriuretic peptide (ANP) levels in 17 outpatients with essential hypertension. Administration of propranolol for twelve weeks to untreated subjects resulted in a significant (P < 0.001) rise in plasma ANP levels (from 37.9 +/- 21.2 to 66.7 +/- 46.2 pg/mL, mean +/- SD). Systolic and diastolic blood pressures were significantly decreased (P < 0.05 and P < 0.01, respectively). Heart rate was also significantly decreased (P < 0.001). On the other hand, a significant reduction of cardiac index was detected (from 4.12 +/- 1.34 to 2.96 +/- 0.75 L/min/m2, P < 0.01) with chronic administration of propranolol, suggesting a reflection of decreased cardiac function. A significant negative correlation was observed between %changes in systolic blood pressure and %changes in plasma ANP (r = -0.594, P < 0.05). These results suggest that the increased plasma ANP levels may contribute to the antihypertensive effect with propranolol.

Influence of naloxone on muscle sympathetic nerve activity, systemic and calf haemodynamics and ambulatory blood pressure after exercise in mild essential hypertension

OBJECTIVE

To determine the effects of prior exercise and naloxone on haemodynamics, muscle sympathetic nerve activity, pituitary hormones and ambulatory blood pressure.

METHODS

We studied 14 mild hypertensive and 14 normotensive subjects on two days. After baseline measurements, subjects were randomly allocated to vehicle or naloxone (0.4 mg/kg) 30 min before 45 min treadmill exercise.

RESULTS

In both groups blood pressure, stroke volume, and calf and total peripheral resistances were lower 1 h after exercise, whereas sympathetic activity was unchanged. In normotensive subjects naloxone abolished this calf vasodilation without altering muscle sympathetic nerve activity, and attenuated these haemodynamic aftereffects of exercise, implying a peripheral opioidergic mechanism. Naloxone had no haemodynamic effect in hypertensive subjects. In normotensives there was an inverse relationship between changes in blood pressure and sympathetic activity after vehicle and exercise. This was transformed by naloxone into a positive relationship (r = 0.69, P < 0.02) similar to that observed in hypertensives after vehicle and exercise. Naloxone did not alter the latter positive relationship. Naloxone altered exercise-induced changes in prolactin and luteinizing hormone, but only in normotensive males. In both groups ambulatory blood pressures and heart rates over 2 h after subjects left the laboratory were higher than the values recorded at baseline or 1 h after exercise, and were unaffected by naloxone.

CONCLUSIONS

The depressor effect of exercise is due to peripheral vasodilation, occurs in the absence of sympathetic withdrawal and is short-lived. Endogenous opioids, activated by running, participate in the haemodynamic, sympathoneural and pituitary hormone aftereffects of exercise in normotensive subjects, whereas in hypertensives these aftereffects of exercise are achieved through non-opioidergic mechanisms. These observations are consistent with the concept that activation of endogenous opioid systems by exercise is impaired in mild hypertension.

Hormonal and renal responses to neutral endopeptidase inhibition in normal humans on a low and on a high sodium intake

Hormonal and renal effects of candoxatril, a neutral endopeptidase 24.11 inhibitor, were investigated in eight subjects equilibrated on a low sodium diet (10 mmol sodium per day) and a high sodium (350 mmol per day) diet. After candoxatril treatment, plasma ANP increased to a maximum at 2-4 h and declined to baseline within 24 h. The increases were relatively greater on the high sodium diet, which was also associated with increases in urinary sodium, with highest values at 4h. On the low sodium diet, the magnitude of the changes was significantly lower (24 h cumulative sodium excretion was 11.4 +/- 5.5 mmol on the low sodium diet and 73.1 +/- 25.6 mmol on the high sodium diet; P < 0.01). There were no significant effects on urinary potassium excretion, creatinine clearance or haematocrit. After candoxatril treatment there were reductions in PRA, especially on the low sodium diet. On either diet there were no effects on systemic blood pressure. These results demonstrate that dietary sodium intake is an important determinant of the renal and hormonal responses to neutral endopeptidase inhibition.

Atrial natriuretic peptide response to postural change and medication in familial dysautonomia

Circulating atrial natriuretic peptide (ANP) was assayed before and after postural change and exercise in 54 patients with familial dysautonomia (FD) and 20 controls. ANP levels were compared with blood pressure, heart rate, plasma catecholamines and parameters of renal function. Compared with controls supine FD subjects had elevated blood pressures, heart rates and ANP levels (39 +/- 4 pg/ml vs. 23 +/- 3 pg/ml, p < 0.01). With the erect posture and exercise in FD subjects, blood pressure fell below control values, with ANP lowered. In FD subjects, blood pressure was correlated with ANP levels when supine and when erect and with heart rate post exercise. In controls, ANP levels did not correlate with other parameters. In FD patients on metoclopramide, supine and erect blood pressure and ANP levels were higher. FD subjects treated with fludrocortisone, had elevated supine and erect noradrenaline (p < 0.05 and p = 0.06); and those on diazepam had lower erect and post exercise noradrenaline (p < 0.05), but ANP levels were similar. In conclusion, sympathetic denervation may increase FD patients' responsiveness to other regulators of cardiovascular integrity, such as ANP. In addition, circulating ANP and catecholamines in FD subjects appear to be influenced by commonly used medications, such as metoclopramide.

Atrial natriuretic peptide response to unilateral pulmonary artery occlusion

To test the hypothesis that neural mechanisms evoked by unilateral pulmonary artery occlusion (UPAO) affect the release of atrial natriuretic peptides (ANP) from the heart, hemodynamics and levels of plasma ANP and cyclic guanosine monophosphate (c-GMP) were studied in 11 patients with lung cancer. The UPAO induced a significant rise in heart rate by 5.3 percent, increased mean pulmonary artery pressure by 31 percent without affecting right atrial pressure, and decreased plasma ANP levels in the coronary sinus by 17.4 percent (p < 0.05) from 202.5 +/- 27.1 pg/ml to 167.2 +/- 27.4 pg/ml. Atropine sulfate (0.04 mg/kg) injection increased the heart rate by 38.2 percent (p < 0.01), reduced the stroke volume index by 25.1 percent, decreased coronary sinus ANP levels from 198.5 +/- 16.4 pg/ml to 124.8 +/- 19.6 pg/ml (p < 0.01), and decreased coronary sinus plasma c-GMP levels from 4.6 +/- 0.5 pmol/ml to 3.1 +/- 0.4 pmol/ml (p < 0.05). After atropine pretreatment, UPAO induced a significant (p < 0.05) increase of 34.8 percent in the coronary sinus ANP level. Thus, it is concluded that in UPAO, the secretion of ANP from the heart is modulated partly by the autonomic nervous system.

[The effect of endothelin on the hemodynamics and cardiac contractility in waking rats with normal and artificially elevated levels of atriopeptide in the blood]

The effects of endothelin (0.1 nMol/kg and 1 nMol/kg into the left ventricle) on hemodynamics and cardiac contractility were investigated in conscious and unrestrained, WKY rats before and during continuous infusion of atriopeptides (1 microgram/kg/min i.v.). Bolus injection on endothelin into the left ventricle caused a transient hypotension and tachycardia followed by a long-lasting increase in mean blood pressure (MBP) and bradycardia in intact rats. In the rats receiving constant atriopeptide infusions, the hypotensive phase of endothelin effects was augmented whereas the hypertensive phase was reduced. Endothelin doses dependently increased cardiac contractility parameters during the first 3 minutes after injection. The stimulation of cardiac function at this time resulted from reflex responses due to the rapid decrease in the MBP. These effects were followed by decreases in cardiac contractility indices. Infusion of atriopeptide led to a tendency to the positive inotropic action of and augmented the negative inotropic action of endothelin.

Secretion of atrial and brain natriuretic peptides from human cardiac atrial explants in culture: effect of dynorphin

We have previously developed a method for maintaining human cardiac explants in culture under serum-free conditions, for the assessment of cardiac endocrine function and myocardial growth factors. In order to assess the local role of dynorphin in the human heart, we studied the effects of dynorphin on the secretion of atrial natriuretic peptide and brain natriuretic peptide by human cardiac atrial explants. Dynorphin did not affect the basal secretion of brain natriuretic peptide, but clearly enhanced the release of atrial natriuretic peptide from the human cardiac explants in culture. The atrial content of brain natriuretic peptide was not significantly reduced, whereas the atrial content of atrial natriuretic peptide in cultured explants was reduced two-fold in the presence of dynorphin. These findings indicate that dynorphin may have a direct stimulatory effect on the release of atrial natriuretic peptide, but not brain natriuretic peptide, from human cardiac atria.

Relationship of renin, angiotensin II and atrial natriuretic factor to clinical status in the early post-infarct period in patients with left ventricular dysfunction

The vasoconstrictor and cardiotoxic effects of angiotensin II may be particularly harmful in the early post-infarct period, but could be partially offset by the release of atrial natriuretic factor. We studied the relationship of renin, angiotensin II and atrial natriuretic factor to clinical status in the first 72 h after infarction in 36 patients not requiring treatment with diuretics on clinical grounds. Since these patients were treated with streptokinase, 16 non-thrombolysed patients were included to control for the acute effects of streptokinase on plasma hormones. Streptokinase caused transient fluctuations in plasma renin and atrial natriuretic factor but did not limit the subsequent development of supranormal hormone levels. Streptokinase-treated patients were divided on the basis of the highest recorded Killip class. Activation of the renin angiotensin system occurred only in those patients in Killip class 2 (n = 11), was maximal at 24-72 h and was proportional to the extent of left ventricular dysfunction. Plasma levels of atrial natriuretic factor were elevated on admission, even in patients in Killip class 1 (n = 25), but declined within an hour before rising again to supranormal levels at 24-72 h. Cumulative release of renin and angiotensin II, but not atrial natriuretic factor, were significantly greater in patients in Killip class 2. Heart rate was greater in Killip class 2 at 24 and 72 h but there was no difference in mean arterial pressures. We conclude that the renin angiotensin system is activated in the early post-infarction phase, but only in patients in Killip class 2, possibly as a result of increased sympathetic activity and reduced renal perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma N-terminal atrial natriuretic peptide in acute myocardial infarction

Plasma atrial natriuretic peptide (ANP) and the N-terminal (NT) fragment of the 126-amino acid prohormone of ANP (proANP; NT-proANP) were correlated with clinical findings in 41 patients with acute myocardial infarction and in 19 patients with angina pectoris. On admission to the hospital, the 39 patients with nonfatal infarction who subsequently had overt heart failure (n = 8) had plasma NT-proANP (2374 +/- 1038 pmol/L) and ANP (54 +/- 43 pmol/L) concentrations that were higher (p < 0.01) than those in the patients who remained without or who presented with minor signs of failure. In contrast to the relatively stable NT-proANP levels, ANP decreased markedly during the first 24 hours in the patients who had any signs of failure. Hence the plasma levels of NT-proANP and ANP did not go hand in hand in acute myocardial infarction, and NT-proANP appeared to be a better marker of cardiac dysfunction than ANP.

Human cardiovascular response to sympathomimetic agents during head-down bed rest: the effect of dietary sodium

Changes in sympathoadrenal function and cardiovascular deconditioning have long been recognized as a feature of the physiological adaptation to microgravity. The deconditioning process, coupled with altered hydration status, is thought to significantly contribute to orthostatic intolerance upon return to Earth gravity. The cardiovascular response to stimulation by sympathomimetic agents before, during, and after exposure to simulated microgravity was determined in healthy volunteers equilibrated on normal or high sodium diets in order to further the understanding of the deconditioning process.

[Endothelin action on the arterial pressure and venous tonus in waking rats with normal and artificially enhanced levels of atriopeptide in the blood]

The effects of endothelin (0.1 and 1 nmol/kg into the left ventricle) on mean blood pressure (MAP), heart rate (HR), central venous pressure (CVP), and mean circulatory filling pressure (MCFP) were investigated in conscious and unrestrained WKY rats before and during continuous infusion of atriopeptide (1 mu mk/kg/min i.v.). In intact rats, bolus injection of endothelin into the left ventricle caused a transient hypotension followed by a long-term increase in MAP. In the rats receiving atriopeptide infusion constantly, the hypotensive phase of endothelin effects was augmented whereas the hypertensive phase was reduced. Low doses of endothelin did not affect CVP and MCFP while the highest dose given to intact rats and atriopeptide-treated rats caused small, but significant decreases in CVP and MCFP. Our results suggest that endothelin has small effects on total body's venous tone in contrast to its effectiveness by increasing blood pressure.

[Comparison of the effect of short-term treatment with nifedipine and verapamil on blood pressure, plasma atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) in patients with primary arterial hypertension I degree according to WHO]

The aim of the study was the comparison of the effect of seven day treatment with nifedipine (2 x 10 mg daily) and subsequently with verapamil (3 x 40 mg daily) on blood pressure, heart rate, plasma ANP, cGMP, renin activity (PRA), aldosterone (ALDO) concentrations in patients with primary hypertension. The material consisted of 12 untreated patients with primary arterial hypertension Io WHO. These results suggest that short-term treatment with nifedipine and subsequently with verapamil in patients with primary hypertension Io WHO not influence on plasma ANP, cGMP, PRA and ALDO in spite of blood pressure reduction and the changes in heart rate. It seems that ANP did not participate in hypotensive action of nifedipine and verapamil. No augmentation of urinary sodium excretion was found after short-term treatment with nifedipine or verapamil.

Metoclopramide does not affect renal function and atrial natriuretic peptide release in response to acute saline loading in conscious rats

It was previously shown in man that metoclopramide (MCP), a dopamine (DA)-2 receptor blocker, attenuates the natriuresis of water immersion. In the present study, we therefore investigated the effects of MCP on renal function and atrial natriuretic peptide (ANP) release in conscious rats. Under basal conditions MCP did not affect glomerular filtration rate (GFR) (7.4 +/- 1.7 ml/min/kg without and 7.8 +/- 0.6 ml/min/kg with MCP), urinary fractional excretion of Na (FENa) (0.3 +/- 0.1% without and 0.3 +/- 0.1% with MCP) and K (FEK) (20.6 +/- 1.4% without and 28.0 +/- 6.2% with MCP) or plasma ANP (37 +/- 5 pmol/l without and 31 +/- 6 pmol/l with MCP). During acute saline loading equal to a 10% rise in body weight, which significantly (p < 0.05) increased GFR, MCP again had no effects on GFR (8.8 +/- 1.8 ml/min/kg with vs. 9.7 +/- 2.5 ml/min/kg without MCP), FENa (24.5 +/- 6.9% with vs. 20.4 +/- 5.1% without MCP), FEK (52.5 +/- 6.9% with vs. 52.5 +/- 9.5% without MCP) and plasma ANP (89 +/- 8 pmol/l with vs. 91 +/- 9 pmol/l without MCP). These results indicate that DA does not modulate renal function or ANP release via DA-2 receptors under basal conditions nor in response to acute saline loading in conscious rats.

Cold and warm infusion of Ringer's acetate in healthy volunteers: the effects on haemodynamic parameters, transcapillary fluid balance, diuresis and atrial peptides

The effects of Ringer's acetate (RAc) infusion with different temperatures, 18 degrees C compared to 36 degrees C, were studied in 20 healthy volunteers. An infusion volume of 20% of the estimated extracellular volume was given over 45 min. Before and after the RAc infusion, interstitial colloid osmotic pressure and interstitial fluid hydrostatic pressure were measured on the lateral part of the thorax and in the lower leg. Blood sampling and pressure measurements were performed through a cannula placed in the left radial artery, and arterial oxygen saturation was measured by pulse oximetry. Atrial peptides ANF (99-126) and ANF (1-98) in plasma were measured as indicators of volume loading. Cold RAc infusion increased mean arterial pressure from 82 (s.d. +/- 7) to 96 (s.d. +/- 9) mmHg (10.9-12.8 kPa) at the end of the infusion with a simultaneous fall in heart rate. Warm RAc infusion gave no changes in blood pressure or heart rate. The arterial oxygen saturation during the infusion of cold RAc was higher than during warm RAc infusion. Cold infusion produced the expected haemodilution with a fall in erythrocyte volume fraction (EVF) from 0.39 (+/- 0.03) to 0.33 (+/- 0.03) and a fall in plasma colloid osmotic pressure (COPp) from 21.7 (+/- 1.1) mmHg to 15.0 (+/- 1.3) mmHg (2.9-2.0 kPa). Warm infusion induced a nearly identical haemodilution. Interstitial colloid osmotic pressure fell from 11.6 (+/- 2.3) mmHg to 8.9 (+/- 2.7) mmHg (1.5-1.2 kPa) after warm infusion while cold infusion gave no changes. The changes in interstitial fluid hydrostatic pressure were not significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide in heart failure

Atrial natriuretic peptide hormone of cardiac origin, which is released in response to atrial distension and serves to maintain sodium homeostasis and inhibit activation of the renin-angiotensin-aldosterone system. Congestive heart failure is a clinical syndrome characterized by increased cardiac volume and pressure overload with an inability to excrete a sodium load, which is associated with increased activity of systemic neurohumoral and local autocrine and paracrine mechanisms. Circulating atrial natriuretic peptide is greatly increased in congestive heart failure as a result of increased synthesis and release of this hormone. Atrial natriuretic peptide has emerged as an important diagnostic and prognostic serum marker in congestive heart failure. In early heart failure, it may play a key role in preserving the compensated state of asymptomatic left ventricular dysfunction. Despite increased circulating atrial natriuretic peptide in heart failure, the kidney retains sodium and is hyporesponsive to exogenous and endogenous atrial natriuretic peptide. The mechanism for the attenuated renal response is multifactorial and includes renal hypoperfusion, activation of the renin-angiotensin-aldosterone and sympathetic nervous systems. Therapeutic strategies to potentiate the biologic actions of atrial natriuretic peptide may prolong the asymptomatic phase and delay progression to overt congestive heart failure.

Effect of perindopril in rat cardiac volume overload

The aortocaval fistula is a classic model of pure cardiac volume overload in rats. This model is characterized by dilation of the ventricular cavities and eccentric cardiac hypertrophy. There are also changes in peripheral arterial flow: high flow in the proximal part of the aorta, upstream of the shunt, and low flow in the distal aorta, downstream of the shunt. The chronic effects of converting enzyme inhibition in this model of volume overload have not yet been measured. We tested the effect of blood pressure and flow on cardiac mass and aortic dilatory pathway in normotensive Wistar and spontaneously hypertensive rats (SHR) with an aortocaval fistula. One half of the sham-operated rats and the normotensive and hypertensive rats with aortocaval fistulas were treated for 1 month with perindopril (2 mg/kg by daily gavage). Urine and plasma were collected at death, the heart was weighed, and the proximal (thoracic) and distal (abdominal) aortas were quickly removed and frozen in liquid nitrogen for measurement of cyclic guanosine monophosphate (cGMP). Blood pressure was always higher in SHR than in Wistar rats, in sham-operated rats than in those with aortocaval fistulas, and in untreated than in perindopril-treated rats. Similarly, the heart weight/body weight ratio was higher in SHR than in Wistar rats, in those with aortocaval fistulas than in sham-operated rats, and in untreated than in Wistar rats, in those with aortocaval fistulas than in sham-operated rats, and in untreated than in perindopril-treated rats. The aortocaval fistula increased the plasma atrial natriuretic factor and perindopril reduced it.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pinacidil on renal haemodynamics, tubular function and plasma levels of angiotensin II, aldosterone and atrial natriuretic peptide in healthy man

The effects of pinacidil on renal haemodynamics, tubular function evaluated by the lithium clearance technique and the plasma levels of angiotensin II (Ang II), aldosterone (Aldo) and atrial natriuretic peptide (ANP) have been evaluated in 12 healthy volunteers given pinacidil 0.1 mg/kg IV in comparison with a placebo given to 13 different healthy volunteers. Pinacidil induced significant reductions in glomerular filtration rate (-5%), renal plasma flow (-12%), urine output (-35%), urinary sodium excretion (-20%), and the fractional excretion of sodium (-17%) and potassium (-29%). Lithium clearance and proximal and distal absolute and fractional reabsorption of sodium were not significantly changed. Ang II and Aldo were significantly increased (80% and 115%, respectively) and ANP was unchanged. The mean arterial blood pressure was not significantly changed by pinacidil, but the heart rate was increased (22%). It is concluded that bolus IV injection of pinacidil in healthy subjects reduced renal blood flow, urine volume and the urinary excretion of sodium and potassium, whereas segmental tubular function was unchanged. The increase in heart rate and activation of the renin-angiotensin-aldosterone system are most likely to be secondary to stimulation of the sympathetic nervous system caused by the vasodilator effect of pinacidil.

Effect of coffee on ambulatory blood pressure in patients with treated hypertension

Effects of caffeine on ambulatory blood pressure, heart rate, renin-angiotensin system, and ANP were studied in patients treated for mild to moderate hypertension in a randomized, double-blind, placebo-controlled, cross-over trial comparing 2 weeks of caffeine-free diet with 2 weeks of regular coffee use. Twenty-three patients (13 men; aged 28-74 years) with treated, mild to moderate essential hypertension and a regular intake of 3-4 cups of coffee daily completed the study. Mean 24-h, day- or night-time ambulatory blood pressure and heart rate were not different between regimens. Nor were there any effects on the renin-angiotensin system while ANP was significantly increased during caffeine intake. Compliance of the dietary regimen was excellent as assessed by serum caffeine concentration measurements. We conclude that habitual coffee drinking did not influence the 24-h blood pressure profiles or cardiovascular hormones in treated hypertensives.

Effect of intravenous glucagon infusion on renal haemodynamics and renal tubular handling of sodium in healthy humans

The effects of a 2-h intravenous infusion of glucagon 5 ng kg-1 min-1 or placebo on glomerular filtration rate (GFR), renal plasma flow (RPF), tubular sodium handling as judged by the lithium clearance method, and plasma concentrations of angiotensin II (AngII), aldosterone (Aldo), and atrial natriuretic factor (ANF) were investigated in two groups of healthy human volunteers, glucagon group (n = 10), and placebo group (n = 10). Glucagon infusion resulted in a maximal increase in plasma concentrations of glucagon of 400%. GFR increased 5.9% (range 1.3-12.4, p < 0.001) through the whole infusion period, whereas RPF only increased transiently during the first hour of infusion 6.5% (range 2.6-15.3, p < 0.05). Whereas filtered load of sodium increased significantly in response to glucagon infusion (p < 0.001), urinary sodium excretion was unchanged. Neither of these variables were affected by placebo. As judged from assessments of tubular sodium handling derived from the renal clearance of lithium, the increased filtered load of sodium resulted in an increase in the output of sodium from the proximal tubules of a similar magnitude, and an increase in absolute reabsorption of sodium in the distal tubules totally counterbalancing this increased input to the distal tubules. These alterations in tubular sodium handling did not involve Ang II, Aldo, or ANF. We conclude that an increase in plasma concentration of glucagon within the physiological range is capable of inducing a small and sustained increase in GFR, whereas RPF increases only transiently.(ABSTRACT TRUNCATED AT 250 WORDS)