Atrial natriuretic factor in human pathophysiology

Contemporary Issues in the Pharmacologic Management of Acute Heart Failure

Acute heart failure is an evolving syndrome that continues to be defined by ongoing studies and registries. It is associated with significant morbidity and mortality and places a huge economic burden on health care systems. Improved understanding of the underlying pathophysiologic processes has prompted interest into understanding the implications of current and future pharmacologic management strategies beyond hemodynamics. Diuretics, vasodilators, and inotropes remain the mainstays of therapy with several new classes of agents on the horizon. Clinicians should understand the rationale for use and limitations of each therapy to maximize benefit and cost-effectiveness, while minimizing the potential for adverse outcomes.

Augmented response in plasma atrial natriuretic peptide to dynamic exercise in patients with congestive heart failure

Neurohormonal activation is present and neurohormonal responses to dynamic exercise are altered in patients with congestive heart failure (CHF). The aim of this study was to determine if the responses of atrial natriuretic peptide (ANP) normalized for peak oxygen consumption (peak VO2) to exercise are augmented in patients with CHF. Ventilatory and ANP responses were assessed in 28 patients with CHF (NYHA classes II: 16, III: 12), 17 patients in NYHA class I, and 14 normal subjects during symptom-limited cardiopulmonary exercise testing. Plasma ANP was measured at rest and immediately after peak exercise. The increase in ANP was divided by peak VO2 and this ratio [ANP-Exercise Ratio: (peak ANP-rest ANP)/peak VO2] was compared among the 3 groups. Peak VO2 (Normal, NYHA I, CHF: 29.9 +/- 1.7, 24.0 +/- 1.3, 17.4 +/- 0.8 ml/min per kg), anaerobic threshold and peak work rate were lower in patients with CHF. The resting ANP level was significantly higher in patients with CHF (Normal, NYHA I, CHF: 35.4 +/- 4.6, 42.9 +/- 5.8, 80.8 +/- 12.9 pg/ml). The ANP level increased during exercise in all 3 groups, and patients with CHF had a significantly higher ANP level than normal subjects and NYHA class I patients (Normal, NYHA I, CHF: 65.3 +/- 10.7, 75.9 +/- 14.4, 141.6 +/- 20.1 pg/ml). The ANP-Exercise Ratio in patients with CHF was significantly higher than those in normal subjects and NYHA class I patients (Normal, NYHA I, CHF: 0.96 +/- 0.26, 1.32 +/- 0.38, 3.59 +/- 0.72). These data suggest that patients with CHF but not those in NYHA class I have an augmented ANP response, as reflected by both absolute ANP levels and by the exercise ratio, which was normalized by the peak exercise level.

Catecholamines, renin-angiotensin-aldosterone system, and atrial natriuretic peptide at rest and during submaximal exercise in patients with congestive heart failure

The aim of this study was to determine the responses of plasma catecholamines, renin-angiotensin-aldosterone (RAA) activity, and plasma atrial natriuretic peptide (ANP) to exercise in patients with congestive heart failure (CHF). Cardiac and neurohormonal responses were assessed during submaximal treadmill exercise testing in 23 patients with CHF (New York Heart Association classes I-III) and 13 control subjects (without CHF). Plasma norepinephrine, epinephrine, renin activity (PRA), angiotensin II (ATII), aldosterone, and ANP were measured at rest and immediately after exercise. Exercise duration was shorter in patients with CHF (control, 10.4 +/- 0.9 minute; CHF, 6.2 +/- 0.7 minute; P < 0.01). Heart rate and blood pressure responses were similar except for the smaller peak heart rate (control, 145 +/- 5 beats per minute; CHF, 129 +/- 4 beats per minute; P < 0.05) and higher systolic blood pressure at recovery stage (control, 122 +/- 4 mm Hg; CHF, 142 +/- 4 mm Hg; P < 0.01) in patients with CHF. At rest, plasma norepinephrine levels were insignificantly higher in patients with CHF (control, 110 +/- 10 pg/mL; CHF, 170 +/- 26 pg/mL; P = 0.09), and ANP levels (control, 40 +/- 5 pg/mL; CHF, 94 +/- 17 pg/mL; P < 0.05) and PRA levels (control, 0.77 +/- 0.11 ng/mL/hr; CHF, 4.33 +/- 1.25 ng/mL/hr; P < 0.05) were significantly higher. There were no differences in peak norepinephrine, epinephrine, or ANP between the two groups. Angiotensin II and aldosterone levels were similar between the two groups, although, in patients with CHF, there was a trend toward higher levels of ATII while at rest (control, 12.4 +/- 1.4 pg/mL; CHF, 20.3 +/- 3.3 pg/mL; P = 0.08) and at peak (control, 20.5 +/- 1.8 pg/mL; CHF, 41.0 +/- 9.4 pg/mL; P = 0.10). Peak values of PRA, ATII, and aldosterone positively correlated with respective resting values of PRA (r = 0.88 ng/mL/hr, P < 0.01), ATII (r = 0.63 pg/mL, P < 0.01), and aldosterone (r = 0.99, P < 0.01). Peak norepinephrine and peak ANP also positively correlated with respective resting values of norepinephrine (r = 0.58 pg/mL, P < 0.05) and ANP (r = 0.94, P < 0.01). Analysis of these results showed that patients with CHF had significantly higher levels of PRA and ANP at rest, and a trend toward augmentation in RAA system activity during exercise with less exercise workload. Basal level of neurohormones seemed to be an important determinant for the degree of exercise-induced neurohormonal activation in patients with CHF.

Renal extraction of atrial natriuretic peptide in hypertensive patients with or without renal artery stenosis

The renin-angiotensin-aldosterone system plays a major role in renovascular hypertension, but the relationship between renin release and the renal fractional extraction of atrial natriuretic peptide (ANP) in this condition is not well defined. We measured ANP levels in the renal veins and aortas of 49 untreated hypertensive patients studied under standardized conditions immediately before renal angiography. Twenty-one patients had renal artery stenosis, 13 of which were unilateral and 8 bilateral. Five of the 13 patients with unilateral renal artery stenosis had an elevated renin ratio (> or = 1.5). Patients with renal artery stenosis were older (P < .01) and had higher systolic pressures (P < .05) than patients with essential hypertension. Arterial levels of ANP were significantly higher in patients with unilateral or bilateral renal artery stenosis than in patients with essential hypertension (P < .05). Patients with hypertension and left ventricular hypertrophy had significantly higher arterial ANP levels than those with no hypertrophy (40 versus 26 pmol/L, P < .05), but in patients with renal artery stenosis, arterial ANP levels were similar in those with or without hypertrophy. Renal venous ANP levels were significantly higher in stenotic than in normal kidneys. Moreover, in unilateral renal artery stenosis, stenotic kidneys of patients with an elevated renin ratio (stenotic kidney/contralateral kidney > or = 1.5) had a significantly higher renal venous ANP level than stenotic kidneys of patients with normal renin ratio (30 versus 17 pmol/L, P < .05). However, the median fractional extraction of ANP was similar, around 0.50 (range, 0 to 0,83), in normal kidneys of hypertensive patients and in stenotic and contralateral kidneys of patients with renal artery stenosis. A significant inverse correlation between arterial ANP and renal venous active plasma renin concentration was found for normal kidneys (r= -.62, P < .01) of hypertensive patients without hypertrophy. However, for stenotic kidneys, no such relationship was apparent. A significant correlation between arterial ANP and the arteriovenous difference of ANP (r = +.92, P < .001) was found. This relationship was similar for normal and stenotic kidneys. In conclusion, an inverse relationship between arterial ANP and renal venous active plasma renin concentration exists in normal kidneys of essential hypertensive patients without left ventricular hypertrophy. Furthermore, data of ANP extraction through normal and stenotic kidneys suggest that saturation of ANP extraction does not occur. Increased levels of ANP in renal artery stenosis are likely caused by enhanced cardiac secretion of this peptide.

Reduced renal extraction of atrial natriuretic peptide in primary aldosteronism

We investigated renal and peripheral forearm extraction of atrial natriuretic peptide in patients with primary aldosteronism to determine whether alterations in extraction may contribute to the elevated levels of circulating atrial natriuretic peptide observed in primary aldosteronism. We obtained simultaneous venous blood samples from the left renal vein and a peripheral vein and from the radial artery in 28 patients with primary aldosteronism and 10 patients with essential hypertension. Renal extraction of atrial natriuretic peptide was significantly (P < .001) reduced (40 +/- 2%) in primary aldosteronism compared with essential hypertensive patients (62 +/- 3%). Peripheral forearm extraction was also reduced (P < .01) in primary aldosteronism compared with essential hypertensive patients (24 +/- 3% versus 38 +/- 4%). These findings are consistent with widespread downregulation of atrial natriuretic peptide receptors in primary aldosteronism. Consistent with reports that marked reduction in glomerular filtration rate is required before the renal extraction of atrial natriuretic peptide is reduced, no significant relationship between renal extraction of atrial natriuretic peptide and plasma creatinine was seen in primary aldosteronism or essential hypertension. Although the major regulators of atrial natriuretic peptide secretion in primary aldosteronism are presumably alterations in arterial blood pressure and plasma volume, reduced renal and peripheral extraction of atrial natriuretic peptide in primary aldosteronism may also contribute significantly to the elevated circulating levels observed.

Potentiation of natriuretic peptides by neutral endopeptidase inhibitors

1. Inhibitors of neutral endopeptidase (NEP) EC 3.4.24.11 were developed to regulate endogenous levels of the natriuretic and vasodilatory hormone atrial natriuretic peptide (ANP). The selective NEP inhibitor SQ 28603 enhanced the increases in plasma ANP and urinary excretion of ANP, cyclic GMP and sodium stimulated by infusion of human ANP in conscious monkeys. SQ 28603 also potentiated the renal and depressor responses to rat brain natriuretic peptide (BNP) in conscious spontaneously hypertensive rats (SHR) and human BNP in conscious monkeys. Therefore, selective NEP inhibitors protected both natriuretic peptides from degradation in vivo and enhanced their biological activities. 2. Selective NEP inhibitors lowered blood pressure in conscious DOCA/salt hypertensive rats and SHR with antihypertensive activity similar to that of exogenous ANP. Furthermore, simultaneous treatment with an angiotensin converting enzyme (ACE) inhibitor enhanced the depressor activity of the NEP inhibitor in SHR. 3. SQ 28603 stimulated urinary excretion of cyclic GMP and sodium in a dose-related manner in conscious dogs with tachycardia-induced heart failure. Addition of the ACE inhibitor captopril significantly reduced blood pressure and systemic vascular resistance while sustaining sodium excretion and increasing cardiac output, glomerular filtration rate and renal blood flow. Therefore, combined NEP and ACE inhibition produced a unique haemodynamic and renal profile in dogs with pacing-induced heart failure. 4. The novel dual metalloprotease inhibitor BMS-182657 potentiated the renal responses to exogenous ANP and suppressed the pressor response to angiotensin I in conscious monkeys, indicating in vivo inhibition of both NEP and ACE.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide and plasma volume of dogs suffering from heart failure or dehydration

Studies in humans and experimental animal models suggest that volume overload increases and volume underload decreases release of atrial natriuretic peptide (ANP), a hormone intimately linked to water and electrolyte homeostasis. This relationship was examined in dogs suffering from heart failure or dehydration and the data presented here are in support of this general concept. Plasma ANP concentration in dogs with congestive heart failure (CHF) was elevated with the severity of the disease (NYHA classification, class II: 21.4 +/- 9.2 fmol ANP/ml; class III: 65.5 +/- 72.6; class IV: 119.7 +/- 87.1; healthy dogs: 13.9 +/- 7.5). The increment in plasma ANP concentration in cardiac patients was also positively correlated with the plasma volume. The blood volume of dogs with moderate and severe CHF was significantly (P < 0.05) elevated and a normotonic blood pressure prevailed. In contrast, dehydrated dogs tend to display reduced ANP plasma concentration (7.7 +/- 5.6 fmol/ml) as well as significantly lower plasma volume and reduced blood pressure (P < 0.05). In dogs with severe CHF, ANP precursor material is present in the blood, which is normally undetectable. These data further support the concept of a regulatory function of ANP in volume homeostasis of dogs.

Renal extraction of atrial natriuretic peptide in unilateral renal artery stenosis

1. Elevated peripheral atrial natriuretic peptide (ANP) levels were observed in 12 patients with unilateral renal artery stenosis (U-RAS). 2. Renal extraction of ANP was higher across the affected than the unaffected kidney in U-RAS, provided the glomerular filtration rate in the affected kidney was not severely reduced (> 12 mL/min). As ANP is a high clearance compound, reduced flow on the affected side may result in increased renal extraction of ANP. 3. When glomerular filtration rate (GFR) in the affected kidney was severely reduced (< 12 mL/min), renal extraction of ANP was also reduced, possibly contributing to increased circulating ANP levels in this subgroup. 4. Overall, renal extraction of ANP was inversely correlated to peripheral ANP levels in patients with U-RAS. This might be explained by progressive sodium retention as GFR falls leading to volume expansion and increased ANP secretion.

Protein kinase C-dependent prostaglandin production mediates angiotensin II-induced atrial-natriuretic peptide release

The respective roles of protein kinase C (PKC) and endogenous prostaglandin formation in angiotensin II (Ang II)-induced myocardial secretion of atrial natriuretic peptide (ANP) was studied in cultured, spontaneously beating, neonatal-rat cardiomyocytes. Incubation of cardiomyocytes with 0.1 microM Ang II led to a rapid but transient increase in particulate-bound PKC activity, a response accompanied by marked increases in cellular 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha) generation and ANP secretion. A role for PKC in Ang II-induced 6-oxo-PGF1 alpha formation and ANP secretion was apparent, insofar as both responses were suppressed in the presence of the PKC inhibitors staurosporine (1 microM) and CGP 41251 (1 microM), as well as in cells in which PKC had been previously down-regulated by pretreatment with phorbol diester. Furthermore, Ang II-induced 6-oxo-PGF1 alpha production was found to be strongly correlated with Ang II-induced ANP release (r = 0.87, P < 0.001, n = 6), indicating a role for prostacyclin (PGI2) in Ang II-induced ANP secretion in these cells. This hypothesis was confirmed by finding that both Ang II-induced 6-oxo-PGF1 alpha production and ANP release were abolished in the presence of the respective phospholipase A2 and cyclo-oxygenase inhibitors quinacrine (10 microM) and indomethacin (10 microM), whereas exogenously applied PGI2 (1 microM) and prostaglandin E2 (0.1 microM) mimicked Ang II-induced ANP secretion in this system. Taken together, these results suggest that Ang II induces ANP secretion in spontaneously beating rat cardiomyocytes via a PKC-dependent autocrine pathway involving a cyclo-oxygenase product and a yet-to-be-identified myocardial prostanoid receptor.

Effects of a small bolus dose of ANF in healthy volunteers and in patients with volume retaining disorders

Thirty-seven patients with volume-retaining disorders (liver cirrhosis with ascites, n = 8; heart failure NYHA III-IV, n = 12; endstage renal failure, n = 17) and twelve healthy age-matched controls were given a small dose (33 micrograms) of hANF (human atrial natriuretic factor). We tested the resulting hemodynamic and renal effects as well as the effect on plasma cyclic GMP levels and compared them with the properties of platelet ANF receptors. The ANF injection evoked an increase in cyclic GMP plasma levels of 19.3 +/- 2.2 nM in healthy controls. This increase tended to be smaller in the cirrhosis group (15.5 +/- 3.3 nM) and in the heart failure group (16.8 +/- 2.3 nM) than in the dialysis group (20.5 +/- 2.5 nM). The invasion rates of cyclic GMP were comparable in all groups, but the evasion rates increased more in the heart failure and endstage renal failure groups (27.9 +/- 7.7 min and 26.1 +/- 3.4 min, respectively) than in the cirrhosis and control groups (14.9 +/- 1.9 min and 14.2 +/- 1.9 min, respectively). Patients with endstage renal failure and congestive heart failure showed a smaller decrease in diastolic blood pressure than controls and patients with liver cirrhosis. Renal actions of ANF were diminished in cirrhosis and heart failure patients. Binding capacities of platelet ANF receptors were higher in the control group (12.2 +/- 1.5 receptors/cell) than in the patient groups (cirrhosis, 7.8 +/- 1.2; endstage renal failure, 8.0 +/- 0.9; heart insufficiency, 8.0 +/- 1.0 receptors/cell), with no differences among the patient groups. Binding affinities were not significantly different. Correlation analysis showed that the relationship between the actions of ANF and the increases in plasma cyclic GMP levels is loose and cannot predict the hemodynamic or renal effects of exogenous ANF in a given patient. Although the behavior of plasma cyclic GMP levels fails to predict the responsiveness of the body to ANF in a given patient, it does reflect the differences between the patient groups and the control group. In contrast, we found no correlation between the properties of platelet ANF receptors and ANF action.

Atrial natriuretic peptide levels in congestive heart failure in man before and during converting enzyme inhibition

1. To determine the response of plasma atrial natriuretic peptide (ANP) to treatment with an angiotensin converting enzyme (ACE) inhibitor in heart failure, seven patients (NYHA Functional Class III-IV) were studied before and after the addition of ramipril to maintenance digoxin and diuretic treatment. 2. Baseline arterial ANP levels were raised, but fell during ramipril treatment in parallel with changes in both haemodynamic recordings (arterial pressure, pulmonary artery diastolic pressure, and right atrial pressure) and hormone levels (angiotensin II and aldosterone). 3. Coronary sinus ANP, measured in three patients, was greater than concomitant arterial levels, and the coronary sinus ANP secretion rate was calculated to be between 15 and 119 pmol/min. 4. These results demonstrate that improvement in haemodynamic function during ACE inhibitor treatment is associated with a decline in elevated ANP levels, and support the concept that atrial stretch or pressure regulates the secretion of atrial peptides in man.

Effects of altitude on atrial natriuretic peptide: the Bicentennial Mount Everest Expedition

1. Overnight recumbent atrial natriuretic peptide levels were significantly elevated in all ten subjects of the Australian Bicentennial Mount Everest Expedition during the first week at 5400 m, during acclimatization. 2. Twenty-four hour urine volume and urine sodium increased markedly at altitude. 3. Plasma renin activity and plasma aldosterone levels decreased significantly at altitude. 4. No significant changes in plasma cortisol, plasma sodium or potassium, body temperature, systolic or diastolic blood pressure or heart rate were observed. 5. Although it was impossible to control or measure salt and water intake during the study, results suggest that atrial natriuretic peptide may be important in the reduction in renin and aldosterone levels and in the diuresis and natriuresis necessary to adapt to hypoxia at altitude.