Increase in plasma atrial natriuretic peptides during acute volume expansion in hypertensive man

Increased plasma levels of atrial natriuretic peptide (ANP) in patients with paroxysmal supraventricular tachyarrhythmias

Atrial natriuretic peptide (ANP) is a cardiac hormone originating from atrial cardiocytes. It seems to be involved in the regulatory control of circulating volume and vascular tone. Plasma immunoreactive atrial natriuretic peptide (IrANP) was investigated in 22 patients with paroxysmal supraventricular tachyarrhythmia (16 with atrial fibrillation, 4 with atrial flutter, one with a Wolf-Parkinson-White syndrome (WPW) and one with atrial tachycardia). During the aute attack, IrANP was significantly increased (125.3 +/- 11.4 pmol/l) compared to samples obtained during convalescence (55.9 +/- 4.7 pmol/l). Heart rate (HR) was 144 +/- 4.3 beats/min during the arrhythmia and 75 +/- 2.6 during convalescence. The reduction of IrANP in plasma from the acute attack of tachycardia to follow-up was significantly related to the reduction of HR (p less than 0.05). Irrespective of type of paroxysmal supraventricular tachyarrhythmia, 50% of the patients experienced polyuria during the attack. This symptom was more frequent in younger patients with a shorter duration of tachycardia. Polyuria patients had a higher HR during the attack of supraventricular tachycardia. Even though polyuria was not always found in the patients with the highest IrANP values, the symptom was associated with significantly higher concentrations of IrANP in plasma compared to the non-polyuria group. We conclude that IrANP is increased in plasma during acute attacks of paroxysmal supraventricular tachycardia. Furthermore, the polyuria frequently associated with this condition may partly be due to excess release of ANP from cardiac myocytes.

Changes in plasma atrial natriuretic peptide during exercise in healthy volunteers

Graded exercise was performed in three healthy volunteers. Plasma levels of immunoreactive atrial natriuretic peptide (iANP) were determined at different workloads. Unchanged or slightly decreased plasma levels of iANP were observed during light exercise, whereas at medium to high workloads a considerable increase in plasma levels of iANP was found. Factors responsible for the increase in plasma levels of iANP might include elevated right atrial pressure and increased plasma levels of epinephrine and norepinephrine.

Calcium antagonism in essential hypertension: effect on renal haemodynamics and microalbuminuria

Sixteen middle-aged men with primary hypertension were treated with the calcium antagonist isradipine over a 9-week period in a randomized, placebo-controlled, double-blind cross-over manner. At the end of the intervention period the urinary albumin excretion rate, systemic and renal haemodynamics, haemorheological properties of blood and plasma concentrations of atrial natriuretic peptide, noradrenaline and peripheral renin activity were determined. Treatment with isradipine resulted in a substantial reduction in blood pressure due to a reduction in peripheral resistance. The mean albumin excretion rate was not influenced by the isradipine treatment. In a multivariate analysis, changes in the urinary albumin excretion rate were only related to changes in blood pressure.

[Atrial natriuretic peptide and its significance for arterial hypertension]

Atrial natriuretic peptide is a recently discovered cardiac hormone with natriuretic, vasodilatory and hypotensive activities. The role of this hormone in the pathophysiology of hypertension is of particular interest. In contrast to an earlier concept, a deficiency of the atrial peptide could not be found in animal models of hypertension or in patients. ANP plasma levels were elevated in SHR with accelerated hypertension, in salt-sensitive Dahl rats, in rats with DOCA-salt-hypertension and in animals with renovascular hypertension. Elevated ANP levels under these conditions can be explained by an expansion of the intravascular volume or by an elevated atrial wall stretch induced by the hypertension itself. In patients with primary hypertension, plasma levels of the peptide are raised in some patients and are normal in others. Plasma ANP levels correlate with age, blood pressure and signs of left ventricular hypertrophy. A negative correlation is described between ANP and renin. Measurement of plasma ANP levels does not allow a differentiation between primary and secondary forms of hypertension. Elevated ANP levels are also found in primary hyperaldosteronism and in renal failure. Stimulation of ANP secretion by physical exercise and dietary salt loading is maintained in hypertension. Infusion of 1-28-hANP leads to a reduction in systemic arterial pressure in normotensives and hypertensives. The natriuresis induced by exogenous ANP is more pronounced in hypertensives. Stimulation of endogenous ANP secretion does not prevent the rise in blood pressure possibly due to a reduction in ANP receptors in target tissues.

Plasma vasopressin and atrial natriuretic factor during haemorrhage: influence of cardiac and aortic receptors

1. The changes in plasma concentrations of immunoreactive vasopressin (iVP) and atrial natriuretic factor (iANF) in response to haemorrhage (10-30% blood volume) were measured in 10 anaesthetized rabbits before and after cardiac receptor denervation (vagal nerve section). Carotid sinus pressure was maintained constant (60 mmHg) to eliminate any changing input from carotid baroreceptors. 2. Haemorrhage increased iVP before and after vagal nerve section indicating that withdrawal of input from aortic baroreceptors may have contributed to the increase in iVP. 3. Section of the vagus nerves attenuated the iVP response to haemorrhage. 4. There was no correlation between release of iVP and iANF. 5. Haemorrhage decreased iAF before and after vagal nerve section. Section of the vagus nerves increased iANF. Plasma iANF was highly correlated with atrial pressure and mean arterial pressure suggesting iANF release was secondary to changes in cardiac haemodynamics.

Atrial natriuretic factor in renal failure and posthemodialytic postural hypotension

Atrial natriuretic factor (ANF) levels were ten times normal in hemodialysis patients before dialysis. ANF was not cleared by the dialyzer membrane but plasma levels decreased 47% by the end of dialysis. Patients undergoing peritoneal dialysis had plasma ANF levels four times normal and had detectable ANF in their dialysate. Hemodialysis patients with a marked fall in BP after dialysis had higher ANF levels (P less than 0.05) and lower norepinephrine (NE) levels (P less than 0.05) associated with a failure to increase NE in response to dialysis. Elevated ANF levels are associated with postdialysis hypotension in hemodialysis patients.

Hemodynamic and renal effects of atrial natriuretic factor (99-126) in volume expanded sheep

The renal and hemodynamic effects of atrial natriuretic factor 99-126 (ANF) were examined in hypervolemic sheep and the results compared to responses previously observed in normal isovolemic sheep. Infusion of 500 ml dextran over 60 min increased blood pressure by 6 +/- 2 mmHg, associated with increases in cardiac output and stroke volume. No change was seen in heart rate nor total peripheral resistance. Subsequent infusion of ANF at 100 micrograms/h for 60 min reduced blood pressure by 6 +/- 1 mmHg and decreased stroke volume and cardiac output. There was no change in heart rate. Total peripheral resistance decreased slightly, to a similar degree to that seen after control infusion of 500 ml dextran. Moderate increases in urine volume, sodium and chloride excretion were seen after infusion of dextran and subsequent infusion of ANF markedly enhanced these renal effects. The renal changes produced by ANF in volume expanded sheep were significantly greater than those observed in normal sheep. Although normal sheep are more sensitive to the hemodynamic than to the renal effects of ANF, after dextran pretreatment there was enhancement of the renal responses with little change in the effects on blood pressure.

The endocrine system in space flight

Hormones are important effectors of the body's response to microgravity in the areas of fluid and electrolyte metabolism, erythropoiesis, and calcium metabolism. For many years antidiuretic hormone, cortisol and aldosterone have been considered the hormones most important for regulation of body fluid volume and blood levels of electrolytes, but they cannot account totally for losses of fluid and electrolytes during space flight. We have now measured atrial natriuretic factor (ANF), a hormone recently shown to regulate sodium and water excretion, in blood specimens obtained during flight. After 30 or 42 h of weightlessness, mean ANF was elevated. After 175 or 180 h, ANF had decreased by 59%, and it changed little between that time and soon after landing. There is probably an increase in ANF early inflight associated with the fluid shift, followed by a compensatory decrease in blood volume. Increased renal blood flow may cause the later ANF decrease. Erythropoietin (Ep), a hormone involved in the control of red blood cell production, was measured in blood samples taken during the first Spacelab mission and was significantly decreased on the second day of flight, suggesting also an increase in renal blood flow. Spacelab-2 investigators report that the active vitamin D metabolite 1 alpha, 25-dihydroxyvitamin D3 increased early in the flight, indicating that a stimulus for increased bone resorption occurs by 30 h after launch.

Acute volume loading, atrial natriuretic peptide release and cardiac function in healthy men. Effects of beta-blockade

Release of ANP is dependent on right atrial distension and pressure, which in turn are dependent on both venous return and left ventricular function. These two latter parameters are both modulated by beta-receptors. In the present study, the effects of selective beta-blockade vs non-selective beta-blockade on hypertonic volume expansion induced changes in ANP release and systemic hemodynamics were assessed in 8 healthy normotensive male volunteers. On placebo, infusion of hypertonic saline (1200 ml of 2.5% NaCl) caused an intravascular volume expansion of 10-11%, and small non-significant increases in cardiac performance (LVEDV, SV, or CI), but it provoked a 2-fold increase in plasma ANP. Beta-blockade by either atenolol or propranolol blunted the increase in cardiac volume load (reflected by LVEDV) as compared to placebo, but did not affect the ANP response to volume expansion. The increase in ANP correlated closely with the intravascular volume expansion on placebo and to a lesser extent on beta-blockade. In healthy men, therefore, intravascular volume expansion that caused only small changes in cardiac activity, resulted in clear increases in release of ANP. Inhibition of the increase in cardiac volume load by beta-blockade did not interfere with ANP increase, suggesting a role for extra-cardiac receptors in the release of ANP or a change in the pressure/volume relationship.

Plasma atrial natriuretic peptide response to volume expansion in the ovine fetus

Atrial natriuretic peptide is a potent diuretic and vasorelaxant peptide secreted from the cardiac atria of adult mammals in response to increased intravascular volume. In sheep, fetal plasma levels of atrial natriuretic peptide are significantly greater than maternal levels, but the factors that control fetal release of atrial natriuretic peptide have not been defined. The present studies were conducted to determine whether the fetus responds to increased intravascular volume by atrial natriuretic peptide secretion. The mean (+/- standard error of the mean) atrial natriuretic peptide of basal fetal plasma (115 +/- 24 pg/ml) in chronically catheterized ovine fetuses (131 +/- 1 days' gestation) was significantly greater than atrial natriuretic peptide levels of basal maternal plasma (56 +/- 12 pg/ml). In response to successive 30-minute intravenous infusions of 0.9% saline solution at 0.5 and 1.0 ml/kg/min, fetal plasma atrial natriuretic peptide significantly increased to a maximum of 409 +/- 72 pg/ml during the high-dose saline infusion and returned to 234 +/- 83 pg/ml during a 30-minute recovery period. The increase in fetal plasma atrial natriuretic peptide was significantly correlated with the volume of saline solution infused (r = 0.68). During the saline infusion, a significant increase in fetal blood volume and heart rate was noted. Fetal blood pressure, maternal plasma levels of atrial natriuretic peptide, and fetal and maternal plasma osmolality remained unchanged. Despite elevated basal levels of plasma atrial natriuretic peptide, the third-trimester ovine fetus responds to increases in intravascular volume with a further increase in atrial natriuretic peptide secretion.

Changes in plasma atrial natriuretic peptide--immunoreactivity in patients undergoing coronary artery bypass graft placements

Plasma atrial natriuretic peptide immunoreactivity (IrANP) was measured before, during, and after cardiopulmonary bypass for coronary artery bypass graft placement. Eight subjects scheduled for elective operation had in the premedicated preoperative state slightly elevated IrANP compared to controls. Neither induction of anesthesia with a high dose narcotic/non-depolarising relaxant/diazepam technique nor cardiopulmonary bypass changed IrANP significantly. Mixed venous and arterial IrANP increased immediately after discontinuing bypass, and remained elevated 1 h later. Because ANPs affect peripheral resistance as well as urinary sodium loss, the post-bypass elevations in these peptides may contribute to cardiovascular and diuretic effects after cardiopulmonary bypass.

Effects of chronic salt loading on plasma atrial natriuretic peptide (ANP) in the spontaneously hypertensive rat

Plasma concentrations of immunoreactive atrial natriuretic peptide (ANP) was measured in spontaneously hypertensive rats (SHR) during chronic salt loading (1.5% NaCl in drinking water). During the 3-week experimental period mean arterial blood pressure, heart rate, urinary sodium excretion and body weight was assessed in salt-loaded as well as in control rats. The sodium excretion was more than 10-fold increased in the rats on the high salt diet. The plasma ANP concentration was significantly increased only 24 h after the start of the high salt intake. Thereafter plasma ANP concentrations were not significantly different from values obtained in control rats. The blood pressure was significantly increased after 3 weeks on the high salt diet. At the end of the 3-week experimental period the rats were subjected to a 10 and 20% acute volume expansion with homologous whole blood. During this intervention the increase in plasma ANP concentrations was blunted in the high salt rats compared to the control group. It is concluded that during chronic salt loading in SHR there is an initial rise in plasma ANP levels and that other hormonal and neuronal systems are more important in the long term maintenance of fluid and electrolyte balance.