Plasma N-terminal pro-brain natriuretic peptide and adrenomedullin: prognostic utility and prediction of benefit from carvedilol in chronic ischemic left ventricular dysfunction. Australia-New Zealand Heart Failure Group.

OBJECTIVES: We sought to assess plasma concentrations of the amino (N)-terminal portion of pro-brain natriuretic peptide (N-BNP) and adrenomedullin for prediction of adverse outcomes and responses to treatment in 297 patients with ischemic left ventricular (LV) dysfunction who were randomly assigned to receive carvedilol or placebo. BACKGROUND: Although neurohormonal status has known prognostic significance in heart failure, the predictive power of either N-BNP or adrenomedullin in chronic ischemic LV dysfunction has not been previously reported. METHODS: Plasma N-BNP and adrenomedullin were measured in 297 patients with chronic ischemic (LV) dysfunction before randomization to carvedilol or placebo, added to established treatment with a converting enzyme inhibitor and loop diuretic (with or without digoxin). The patients' clinical outcomes, induding mortality and heart failure events, were recorded for 18 months. RESULTS: Above-median N-BNP and adrenomedullin levels conferred increased risks (all p < 0.001) of mortality (risk ratios [95% confidence intervals]: 4.67 [2-10.9] and 3.92 [1.76-8.7], respectively) and hospital admission with heart failure (4.7 [2.2-10.3] and 2.4 [1.3-4.5], respectively). Both of these predicted death or heart failure independent of age, New York Heart Association functional class, LV ejection fraction, previous myocardial infarction or previous admission with heart failure. Carvedilol reduced the risk of death or heart failure in patients with above-median levels of N-BNP or adrenomedullin, or both, to rates not significantly different from those observed in patients with levels below the median value. CONCLUSIONS: In patients with established ischemic LV dysfunction, plasma N-BNP and adrenomedullin are independent predictors of mortality and heart failure. Carvedilol reduced mortality and heart failure in patients with higher pre-treatment plasma N-BNP and adrenomedullin.

Atrial natriuretic factor in hypertension: bioactivity at normal plasma levels.

To ascertain whether small shifts in plasma atrial natriuretic factor (ANF) exerted biological effects in hypertension, we studied the renal, hemodynamic, and hormonal effects of ANF [human ANF-(99-126)] infused at a dose (0.75 pmol/kg/min for 3 hours) that would induce changes in plasma ANF confined to the normal, resting range, in a group of six young men with uncomplicated, mild essential hypertension. During ANF infusions, the patients excreted 11.8 +/- 2.0 mmol (mean +/- SEM) sodium more than during the time-matched placebo phase natriuresis (p less than 0.001, mean increase of 53% above placebo values). Urinary excretion of cyclic guanosine monophosphate rose to more than double (212%, p less than 0.001) placebo values. Plasma renin activity (0.4 +/- 0.05 vs. 0.9 +/- 0.12 nmol/l/hr, p less than 0.0001) and aldosterone concentrations (102 +/- 4 vs. 184 +/- 47 pmol/l, p less than 0.05) were clearly suppressed during administration of ANF. Plasma norepinephrine also fell significantly below placebo values (268 +/- 17 vs. 439 +/- 35 pg/ml, p less than 0.05). Urine volume, the excretion of electrolytes other than sodium, hematocrit, effective renal plasma flow, glomerular filtration rate, and filtration fraction were unaffected by ANF. Similarly, plasma concentrations of epinephrine, arginine vasopressin, adrenocorticotropic hormone, and cortisol were unchanged. Blood pressure and heart rate were unchanged. Minor perturbations in plasma ANF concentrations exert clear biological effects in patients with mild essential hypertension. These data suggest that such minor shifts in plasma ANF are of physiological relevance in mild hypertension and probably contribute to volume homeostasis in this condition.

Radioimmunoassay and characterization of atrial natriuretic peptide in human plasma.

A RIA for alpha-human atrial natriuretic peptide (alpha hANP) in plasma was developed and used to study the immunoreactive components secreted by the heart and circulating in peripheral venous plasma. The assay used [125I]diiodotyrosyl-alpha hANP, purified by high pressure liquid chromatography (HPLC), and a C-terminal-specific antiserum purchased from Peninsula Laboratories. Serial dilution curves of coronary sinus plasma samples were parallel with the standard curve, but significant nonparallelism was found in peripheral plasma samples of low immunoreactivity. When plasma was extracted using C-18 Sep-Pak cartridges, serial dilution curves from both coronary sinus and peripheral plasma samples were parallel to the standard curve. Although values for plasma samples assayed before and after extraction agreed closely (r = 0.99; n = 76), immunoreactive ANP in unextracted plasma was consistently greater (70-79 pmol/liter) than in extracts of plasma, suggesting non-specific interference by a component in plasma when assayed without extraction. Mean plasma immunoreactive ANP in 19 normal subjects consuming a normal salt intake was 14 +/- 1 (+/- SE) pmol/liter. In 5 normal men, increasing dietary sodium intake from 10 to 200 mmol sodium/day was associated with a 2-fold increment in ANP levels, and similar changes accompanied acute sodium loading using iv saline. Elevated values were found in patients with congestive heart failure (mean, 58 pmol/liter; range, 0-200; n = 9), chronic renal failure (mean, 118 pmol/liter; range, 30-290; n = 8), and primary aldosteronism (range, 32-90 pmol/liter; n = 3). HPLC and gel chromatographic analysis of the immunoreactive material found in coronary sinus plasma extracts showed that a large amount of the material eluted in the position of alpha hANP. A smaller quantity of immunoreactive material with a mol wt of about 1600 was also identified. Peripheral venous plasma extracts also contained several immunoreactive components, the largest amount of which corresponded to alpha hANP. The pattern of immunoreactive components in peripheral venous plasma, as identified by both gel chromotography and HPLC, was similar to that in coronary sinus plasma drawn during an active phase of hormone secretion. These findings indicate that the heart secretes alpha hANP or a closely similar peptide which is also present in peripheral venous plasma. Plasma immunoreactive ANP is responsive to sodium loading in normal man and is elevated in patients with hypervolemic disorders.

Atrial natriuretic peptide in humans. Production and clearance by various tissues.

Although it is assumed that the human heart secretes atrial peptides, direct proof is not available. We therefore measured immunoreactive atrial natriuretic peptide levels in coronary sinus blood and simultaneously in femoral arterial and venous blood from patients before and during stepwise incremental atrial pacing of up to 200 beats per minute. Since the fate of circulating atrial peptides is unknown, we also measured immunoreactive atrial natriuretic peptide concentrations in arterial and venous blood across the liver, kidney, lower limb, and lung in patients undergoing cardiological investigation. Peptide levels in coronary sinus blood were higher than in samples from the femoral artery or vein. As the heart rate was accelerated by atrial pacing, peptide concentrations increased in coronary sinus blood and to a lesser extent in peripheral samples. Whereas the levels in venous blood draining the liver, kidney, and lower limb were approximately 50% of those in arterial blood, concentrations were similar in samples drawn simultaneously from the pulmonary artery and the aorta. These results show that the human heart produces immunoreactive atrial natriuretic peptide and that secretion increases with atrial tachycardia. The liver, kidney, and lower limb remove the peptide from arterial blood, but there is little change in its concentration during circulation of blood through the lungs.

Effect of physiological levels of atrial natriuretic peptide on hormone secretion: inhibition of angiotensin-induced aldosterone secretion and renin release in normal man.

Large doses of atrial natriuretic peptide (ANP) inhibit renin and aldosterone secretion in normal man, but the effect of physiological levels is unknown. We, therefore, studied the effect of a low infusion rate of alpha-human ANP (alpha hANP; 0.5 microgram/min for 180 min) on the plasma corticosteroid response to graded physiological doses of angiotensin II (0.5, 1.0, 2.0, and 4.0 ng/kg X min, each for 30 min) and ACTH (6.25, 12.5, 25, and 50 mIU, each for 30 min) in six normal men eating a low salt diet (10 mmol sodium and 100 mmol potassium daily). The angiotensin II and ACTH infusions were given from 0900-1100 h on separate days, during which randomized infusions of placebo or alpha hANP were given from 0800-1100 h according to a single blind protocol. Plasma immunoreactive ANP levels were less than 10 pmol/L on the placebo day compared to 30-50 pmol/L during the alpha hANP infusions, and were not altered by either ACTH or angiotensin II. Compared with the control observations, there was no significant change in arterial pressure or heart rate during either the alpha hANP or angiotensin II infusions. ACTH infusions evoked an incremental response in plasma aldosterone and cortisol, and the dose-response relationship was unaltered by alpha hANP. In contrast, while an incremental and significant increase in plasma aldosterone in response to angiotensin II occurred with the placebo infusion, no significant increase occurred in response to angiotensin during the alpha hANP infusion. The slope of the angiotensin II/aldosterone regression line was significantly less during all alpha hANP infusions compared to that during the placebo infusion (P less than 0.02). In addition, on the ACTH infusion day significant suppression of both PRA (P less than 0.05) and plasma angiotensin II (P less than 0.008) occurred during the alpha hANP infusion compared to that during the placebo infusion, whereas PRA was equally suppressed by angiotensin II in the presence or absence of alpha hANP. alpha hANP also increased urine volume [176 +/- 31 (+/- SEM) vs. 113 +/- 19 mL/mmol creatinine with placebo; P less than 0.03] and sodium excretion (2.14 +/- 0.48 vs. 0.58 +/- 0.22 mmol/mmol creatinine with placebo; P less than 0.004) on the ACTH infusion days. With angiotensin II, urine volume was also significantly increased by alpha hANP (150 +/- 27 vs. 81 +/- 15 mL/mmol creatinine with placebo; P less than 0.03), and urine sodium excretion doubled.(ABSTRACT TRUNCATED AT 400 WORDS)

Plasma brain natriuretic peptide and endopeptidase 24.11 inhibition in hypertension.

In contrast to the wealth of information available concerning the response of plasma atrial natriuretic peptide to changes in pressure and volume status and to inhibition of endopeptidase 24.11, very little is known of possible concomitant effects on brain natriuretic peptide. The effects of change in posture, pressor infusions of angiotensin II, or inhibition of endopeptidase 24.11 were documented in two groups of patients with essential hypertension receiving one of two orally active inhibitors (SCH 42495 or UK 79300) in double-blind, placebo-controlled, random-order crossover studies. Sustained (4 days) inhibition of endopeptidase 24.11 with either inhibitor significantly enhanced plasma atrial natriuretic peptide (P < .05, both groups) but suppressed plasma brain natriuretic peptide (P < .01, both groups) in association with significant falls in arterial pressure (P < .05, both groups). Assumption of the recumbent posture increased plasma atrial natriuretic peptide (20 +/- 5 vs 13 +/- 3 pmol/L, P < .05), whereas brain natriuretic peptide was unchanged (7 +/- 0.3 vs 7 +/- 0.4 pmol/L, NS). Pressor infusions of angiotensin II increased plasma levels of both atrial natriuretic peptide and brain natriuretic peptide (33 +/- 11 vs 17 +/- 4 pmol/L, P < .05, and 7.5 +/- 0.6 vs 5.5 +/- 0.4 pmol/L, P < .05, respectively). In contrast to atrial natriuretic peptide, brain natriuretic peptide probably is primarily regulated by left ventricular load rather than by atrial distending pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal, endocrine, and hemodynamic effects of human brain natriuretic peptide in normal man.

Brain Natriuretic Peptide (BNP) is a recently identified hormone which is secreted by the human heart and circulates in plasma. To determine the effects of pathophysiological levels of human BNP (hBNP), we have studied the integrated renal, hormonal, and hemodynamic response in six normal men receiving 2-h infusions of synthetic hBNP (2.0 pmol/kg.min) or placebo in random order. Steady state levels of hBNP (20-30 pmol/L), achieved at 90-120 min, were similar to levels observed in mild heart failure. Compared to placebo infusions, hBNP induced a greater than 2-fold increase in sodium excretion (P = 0.014) and suppressed plasma aldosterone (P < 0.004) to levels less than 50% of placebo values. These changes were associated with an increase in both plasma (P = 0.028) and urine excretion (P < 0.004) of cGMP. Effects on blood pressure were not statistically significant but increases in both heart rate (P < 0.0001) and plasma albumin (P = 0.007) after cessation of hBNP infusions indicate significant hemodynamic effects of hBNP. High MCR (5.8 +/- 0.7 L/min) yet slow disappearance rate (mean t1/2 22.6 min) indicate that hBNP has a large volume of distribution in humans. These studies show that hBNP, at plasma levels observed in patients with mild heart failure, has potentially important natriuretic, endocrine, and hemodynamic effects which are similar to those observed with comparable infusion rates of ANF.

Assay of brain natriuretic peptide (BNP) in human plasma: evidence for high molecular weight BNP as a major plasma component in heart failure.

A RIA for human brain natriuretic peptide (BNP) was developed. Both BNP and atrial natriuretic peptide (ANP) were extracted from human plasma with Vycor glass powder (71% recovery for BNP). The assay had a minimum detection limit of 0.45 fmol/tube and an IC50 of 9 fmol/tube. The within-assay coefficients of variation were 11.4% at 4 pmol/L and 3.2% at 22 pmol/L, and the between-assay coefficient of variation was 11% at 24 pmol/L. There was no significant loss of immunoreactive (IR)-BNP in plasma samples stored at -80 C for 4 weeks. Low rates of labeled BNP and IR-BNP degradation occurred in EDTA plasma incubated at 37 C. The mean venous plasma IR-BNP (6.3 +/- 0.3 pmol/L) in normal subjects (n = 48) was significantly lower than plasma ANP (8.4 +/- 0.6 pmol/L). In contrast to ANP, IR-BNP did not increase when normotensive or hypertensive subjects changed from erect to supine posture. Markedly elevated levels were found in patients with congestive heart failure (mean IR-BNP, 87 +/- 11 pmol/L; ANP, 87 +/- 12 pmol/L; n = 35), recent myocardial infarction (mean IR-BNP, 60 +/- 9 pmol/L; ANP, 33 +/- 6 pmol/L; n = 7), and chronic renal failure. High pressure liquid chromatography of plasma extracts from heart failure subjects revealed both high (mol wt, 10,000) and low (mol wt, 4,000) mol wt IR-BNP. High mol wt BNP was the major component (mean ratio, 1.9:1) and was linearly correlated with low mol wt BNP (r = 0.99). HPLC of plasma extracts from three normal subjects receiving constant infusions of human BNP (2 pmol/kg.min) showed a single major peak eluting in the position of hBNP-32, with no evidence of high mol wt material. These results show that whereas marked elevations in BNP occur in circulatory disorders, a major (> 50%) and consistent contribution to immunoreactivity is due to precursor forms. Further, compared to ANP, there is no IR-BNP response to supine posture in normal and hypertensive subjects.

Predicting surgically remedial primary aldosteronism: role of adrenal scanning, posture testing, and adrenal vein sampling.

Distinguishing surgically remedial forms from other causes of primary aldosteronism (PA) may be difficult, and it is made more challenging by the earlier detection of milder disease. The technical demands of bilateral adrenal vein sampling (AVS)-increasingly advocated for localizing a unilateral autonomous lesion (UAL)- and lack of agreed criteria for establishing unilateral autonomy, add further to the diagnostic challenge. This retrospective review of 49 hypokalemic patients with unequivocal PA (41 with surgically proven and remedial UAL, eight patients with bilateral adrenal hyperplasia) analyzes the value of computerized tomography adrenal scanning (n = 32), 4 h erect posture testing (n = 42), and AVS (n = 27) in predicting and lateralizing a surgically remedial lesion. A fall in plasma aldosterone during 4 h erect posture (positive test) occurred in 63% of patients with UAL and in none with bilateral adrenal hyperplasia. A positive posture test or computerized tomography adrenal scan (single focal macroadenoma) both had high positive predictive value (100% and 89% respectively), but low sensitivity for diagnosis of UAL. AVS, undertaken during low dose ACTH stimulation, localized the UAL in all cases (positive predictive value 100%) where the aldosterone/cortisol ratio of blood drawn from the uninvolved gland was less than that of peripheral blood (contralateral ratio <1). Biochemical severity, reflected by overnight supine plasma aldosterone, was strongly correlated with the degree of contralateral gland suppression (n = 16, r = 0.79, P < 0.001). Importantly, the AVS findings show that when bilateral access is not possible, UAL can be successfully lateralized when only one adrenal vein (the contralateral) is accessed, or the ipsilateral vein is sampled in subjects whose posture test was positive. In this series of patients with overt (hypokalemic) PA, preoperative testing successfully identified a surgically remedial lesion in 39 of 41 cases. Confirmation of the recommended diagnostic approach must now await larger prospective studies.

Effect of posture on clearance of atrial natriuretic peptide from plasma.

The effect of posture on plasma atrial natriuretic peptide (ANP) levels during a constant iv infusion of the 28-amino acid polypeptide was investigated in 8 normal men. alpha-Human ANP was infused at a constant rate of 0.5 micrograms/min (162 pmol/min) while the men were supine, then erect, and finally when supine again. Plasma ANP levels rose from 10.9 +/- 1.6 (+/- SEM) to 33.3 +/- 2.4 pmol/L after 60 min of constant infusion with the men in the supine position. On standing, plasma ANP increased further to 40.6 +/- 3.4 pmol/L, then fell to 32.2 +/- 2.7 pmol/L with resumption of supine posture. The calculated MCR of ANP fell from a mean of 7.7 to 5.7 L/min on standing, but rose again to 7.6 L/min upon lying down. We conclude that body posture has a significant effect on the rate of clearance of ANP from plasma.

Differing biological effects of equimolar atrial and brain natriuretic peptide infusions in normal man.

Atrial natriuretic peptide (ANP) and Brain natriuretic peptide (BNP) are cardiac hormones with similar actions and potency in humans yet with distinctly different effects on plasma cyclic guanosine monophosphate (cGMP). Because most biological actions of natriuretic peptides are thought to be mediated by the guanylate cyclase (G-C) receptors via cGMP, we have compared the biological and G-C-stimulating effects of equimolar infusions of ANP and BNP (2 pmol/kg.min), or vehicle control, on renal, hormonal and hemodynamic function in 8 normal subjects. In addition, the modulating effects of ANP and BNP on the biological actions of infused angiotension II (AngII) were studied. During ANP infusions, plasma ANP concentration increased from 8.8 +/- 0.7 pmol/L to 34 +/- 3 pmol/L at 120 min. Similar increments in plasma BNP occurred during BNP infusions (7.3 +/- 0.6 pmol/L preinfusion, 37 +/- 1 pmol/L at 120 min). Increase in plasma cGMP during ANP infusions was 4-fold that observed during BNP infusions yet natriuresis, contraction in plasma volume, and inhibition of plasma aldosterone were comparable. By contrast, ANP (but not BNP) significantly inhibited the plasma aldosterone response to AngII (P < 0.001). The pressor response to AngII was unaltered by ANP or BNP. Thus, at plasma ANP/BNP levels observed in mild heart failure, ANP is more potent than BNP in inhibiting the aldosterone response to AngII. Comparable natriuresis and inhibition of basal aldosterone is seen, despite much less stimulation of plasma cGMP by BNP, suggesting a different mechanism of hormone action-possibly via non-G-C receptor pathways.

Brain natriuretic peptide and neutral endopeptidase inhibition in left ventricular impairment.

Brain natriuretic peptide (BNP) is increased in left ventricular impairment and neutral endopeptidase (NEP) is involved in its metabolism. In random order, eight patients with left ventricular impairment received placebo, a 4-h infusion of human BNP (3.0 pmol/kg min), a single oral dose of NEP inhibitor (SCH 42495, 300 mg), and combined BNP and SCH 42495. Plasma BNP, cGMP, and cortisol were significantly increased by all three treatments (P < 0.05-P < 0.001). Combined treatment had a synergistic effect on plasma cGMP. The metabolic clearance rate of exogenous BNP was reduced (25%) by NEP inhibition. Endogenous plasma ANP was augmented more than BNP by NEP inhibition. Plasma aldosterone, unchanged during infusions, rose markedly after BNP and after the combined treatment (P < 0.05 for both). Urine sodium excretion, increased by NEP inhibition (P < 0.05) and by BNP (P = 0.05), was unchanged during combined treatment. Urine cGMP excretion was increased, whereas blood pressure was reduced by all active treatments (P < 0.05-0.01 for all). Heart rate increased only with combined treatment (P = 0.007). Plasma renin activity, norepinephrine, and cardiac output were unaffected. BNP infusion and NEP inhibition both induced significant hemodynamic and renal responses. The augmented hypotensive effect of combined treatments, and consequent fall in renal perfusion pressure, may underly the observed blunting of the natriuretic response that occurred despite greater than additive increments in plasma BNP, ANP, and cGMP.

EC 24.11 inhibition in man alters clearance of atrial natriuretic peptide.

Metabolic clearance and the biological effects of exogenous human atrial natriuretic factor (ANF) were assessed in two groups each of eight normal volunteers receiving 2-h iv infusions of ANF (2.5 pmol/kg.min) on the fifth day of dosing with the orally active inhibitor of endopeptidase 24.11, candoxatril (25 mg every 12 h in group 1 and 100 mg every 12 h in group 2), and placebo in balanced randomized, double blind, placebo-controlled, cross-over experiments. Although 4 days of pretreatment with the endopeptidase inhibitor did not affect basal plasma ANF, candoxatril enhanced mean ANF-induced increases in plasma ANF by 27 pmol/L (P = NS) and 42 pmol/L (P less than 0.002) in groups 1 and 2, respectively. Calculated MCRs for ANF were significantly reduced by both doses of candoxatril [group 1, 2.5 +/- 0.4 vs. 4.3 +/- 0.6 L/min (P less than 0.01); group 2, 2.3 +/- 0.4 vs. 5.6 +/- 0.8 L/min (P less than 0.001)]. ANF significantly enhanced urinary sodium excretion above preinfusion values in both study phases in both groups. Candoxatril significantly further augmented natriuresis in group 2 (P less than 0.01), but not group 1. Inulin clearance was minimally enhanced, and para-aminohippuran clearance was slightly decreased by candoxatril in both groups. Neither effect alone was statistically significant, but derived renal filtration fractions were significantly enhanced in both groups [group 1, 15.5 +/- 0.5% vs. 13.9 +/- 0.6% (P less than 0.01); group 2, 19.3 +/- 1.9% vs. 18.0 +/- 2.7% (P less than 0.01)]. Basal and stimulated cGMP concentrations in both plasma and urine were significantly enhanced by candoxatril in the two groups (P less than 0.001 and P less than 0.01, respectively, for combined data). Urinary ANF immunoreactivity was significantly enhanced by candoxatril in both groups (P less than 0.05 and P less than 0.01 in groups 1 and 2, respectively), with a more pronounced effect evident at the higher dose (P less than 0.01). These results show that chronic pretreatment with an endopeptidase inhibitor in normal man causes a dose-related reduction in the metabolic clearance of exogenous ANF, amplifies cGMP, and increases renal filtration and the natriuretic responses to infused ANF.

Bioactivity and metabolism of C-type natriuretic peptide in normal man.

C-Type natriuretic peptide (CNP) is a recently identified member of the natriuretic peptide family with potent vasodepressor activity in experimental animals. Specific CNP receptors and gene transcripts have been identified in human vascular tissues, but the bioactivity and metabolism of CNP in humans are unknown. Accordingly, we have studied the renal, hormonal, and hemodynamic responses in nine normal men (seated, nonfasting) receiving a morning infusion (2 h) of synthetic human CNP-22 (5 pmol/kg.min) or placebo in single blind, random order. To determine the vasodepressor action, the effect of a second identical (afternoon) infusion on the pressor and hormone responses to angiotensin-II (2, 4, and 8 ng/kg.min each for 30 min) was also studied. In the morning infusion, plasma CNP increased from undetectable baseline levels to plateau levels (mean, 60 +/- 6 pmol/L) at 30-120 min. The mean MCR was 4.8 +/- 0.7 L/min, and the t 1/2 (plasma) was 2.6 min. Compared with the effects of placebo, there were significant increases in plasma cGMP (P = 0.001) and plasma atrial natriuretic peptide (ANP; P = 0.02) and a significant decrease in plasma aldosterone (P = 0.007). No significant hemodynamic action or natriuresis was observed. During coinfusion of angiotensin-II, the expected pressor and aldosterone responses were not significantly altered by CNP. In contrast to atrial and brain natriuretic peptide, short term infusion of CNP in humans, achieving supraphysiological levels in plasma, are not vasodepressor or natriuretic. Increases in plasma ANP and plasma cGMP and inhibition of aldosterone may be due in part to competitive displacement by CNP of ANP in common degradative pathways.

Hemodynamic and hormonal effects of neutral endopeptidase inhibitor SCH 39370 in sheep.

Whole body clearance of atrial natriuretic factor is due to both receptor uptake and enzymatic degradation initiated by neutral endopeptidase 24.11. The effects of neutral endopeptidase inhibition have been studied in seven sodium-replete sheep using SCH 39370, a specific and potent inhibitor of neutral endopeptidase, in the presence or absence of exogenous hormone [rat ANF-(101-126), 2.4 pmol/kg/min for 2 hours]. SCH 39370 alone (2.5 mg/kg bolus) increased plasma atrial natriuretic factor and plasma cyclic GMP levels, lowered arterial pressure for periods beyond changes in plasma atrial natriuretic factor or cyclic GMP, and suppressed both plasma aldosterone and cortisol levels when compared with vehicle injections. The effects of SCH 39370 were similar to or exceeded those of atrial natriuretic factor infusions, which induced significantly greater increases in plasma atrial natriuretic factor (p = 0.01). Neither agent alone was natriuretic. When SCH 39370 and atrial natriuretic factor were given together, plasma cyclic GMP but not atrial natriuretic factor levels were increased (p = 0.013) compared with atrial natriuretic factor infusion alone, and the half-life was prolonged (p = 0.002) in the presence of SCH 39370. The hypotensive response was greater than that induced by atrial natriuretic factor alone (p = 0.03) but not different from SCH 39370 alone. Inhibitory effects of SCH 39370 on aldosterone levels were similar in the presence of absence of exogenous atrial natriuretic factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal, hemodynamic, and hormonal responses to atrial natriuretic peptide infusions in normal man, and effect of sodium intake.

The effect of 60-min constant iv infusions of alpha-human atrial natriuretic peptide (alpha hANP; 200 micrograms), sufficient to increase the steady state venous plasma alpha hANP concentration to levels found in patients with some circulatory disorders, was studied in six normal men equilibrated on a high sodium diet (200 mmol daily) and again when equilibrated on a low sodium intake (10 mmol daily). In each instance, the responses to alpha hANP were compared to those to control infusions given on the preceding day. The mean steady state plasma immunoreactive ANP concentration during the infusions was 320 pmol/liter and was the same during both diets. Thus, the MCR of alpha hANP was unaffected by major changes in sodium intake. Compared to control day observations, infusions of alpha hANP induced a more than 3-fold increase in sodium excretion and at least a 2-fold increase in urine volume and calcium and magnesium excretion in subjects ingesting 200 mmol sodium daily. During the low sodium diet, alpha hANP was still diuretic and induced comparable magnesium excretion, but the natriuresis was only 11% of that during the high salt diet. No significant changes in blood pressure or heart rate occurred during alpha hANP infusions during either diet, although during both diets there was a significant rise in plasma norepinephrine (P less than 0.02), which persisted well beyond the disappearance of immunoreactive ANP from plasma. Despite this sympathetic activation, renin and aldosterone production was reduced by alpha hANP. During low salt intake, alpha hANP significantly decreased PRA (mean pretreatment, 1.79; posttreatment, 1.25 nmol/liter/h; P less than 0.03), angiotensin II (mean pretreatment, 49; posttreatment, 28 pmol/liter; P less than 0.008), and plasma aldosterone (mean pretreatment, 554; posttreatment 307 pmol/liter; P less than 0.007), whereas values during control infusions did not change. Similar percent decreases in PRA and aldosterone also occurred during the high salt diet. Plasma cortisol and arginine vasopressin did not change during the alpha hANP infusions on either diet. We conclude that steady state levels of alpha hANP in plasma, similar to those in patients with some circulatory disorders, significantly increase sodium excretion and inhibit all elements of the renin-angiotensin-aldosterone system. The natriuretic, but not the hormonal or chronotropic, effects of alpha hANP are reduced by sodium depletion in normal man.

Endopeptidase 24.11 inhibition by SCH 42495 in essential hypertension.

The detailed integrated renal, hormonal, and hemodynamic effects of acute (first dose) and established (4 days) inhibition of endopeptidase 24.11 by SCH 42495 (200 mg, every 12 hours) were documented in eight patients with essential hypertension in a double-blind, balanced random-order, crossover study. SCH 42495 suppressed plasma endopeptidase activity (> 90%, P < .001) for the duration of the dosing period. Initially, plasma atrial natriuretic factor levels increased markedly (+123%, P < .01) and remained elevated, although to a lesser extent (+34%, P < .01), with established enzyme inhibition. Cyclic guanosine monophosphate in both plasma and urine remained elevated throughout the treatment period. Significant augmentation of sodium excretion in excess of placebo values (96 +/- 27 mmol sodium, P < .001) was established in the initial 24 hours of dosing but later became attenuated, with a mild antinatriuresis (P < .01) in the latter 3 days of treatment. Blood pressure, heart rate, the renin-angiotensin-aldosterone system, and plasma norepinephrine levels were all initially (first dose) unchanged. With established enzyme inhibition (day 4), however, blood pressure was significantly lower (mean 24-hour values, 9.3 +/- 3/-3.8 +/- 1 mm Hg, P < .05 for both systolic and diastolic pressures) than matched placebo values, whereas heart rate was higher (2.7 +/- 1 beats per minute, P < .01). Mean 24-hour values of plasma renin activity (+33%, P < .05), aldosterone (+36%, P < .05), and norepinephrine (+40%, P < .001) were all clearly increased above placebo values with established enzyme inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic, hormonal, and renal effects of short-term adrenomedullin infusion in healthy volunteers.

The actions of adrenomedullin (ADM), a 52-amino acid peptide, are not well defined in man. We, therefore, studied eight normal volunteers aged 1832 yr in a placebo-controlled crossover study. On the 2 study days, subjects received, in random order, ADM in "low" and "high" dose (2.9 pmol/kg x min and 5.8 pmol/kg x min for 2 h each) or vehicle (hemaccel) infusion on day 4 of a metabolic diet (Na+ 80 mmol/day, K+ 100 mmol/day). Achieved plasma ADM levels were in the pathophysiological range, and plasma cAMP values rose 5 pmol/L during the higher dose. Compared with time-matched vehicle infusion, high-dose ADM increased peak heart rate by 10 beats per minute (P < 0.05) and lowered diastolic (by 5 mm Hg, P < 0.01) blood pressure. Cardiac output increased in both phases of ADM (low dose, 7.6 L/min; high dose, 10.2 L/min; vehicle, 6 L/min; P < 0.05 for both). Despite a 2-fold rise in PRA during high-dose ADM (P < 0.01), aldosterone levels were unaltered. Norepinephrine levels increased by 50% during high-dose ADM (P < 0.001), but epinephrine levels were unchanged. Plasma PRL levels increased during high-dose ADM (P = 0.014). ADM had no significant effect on urine volume and sodium excretion. Infusion of ADM to achieve pathophysiological plasma levels produced significant hemodynamic effects, stimulated renin but inhibited the aldosterone response to endogenous angiotensin II, and activated the sympathetic system and PRL without altering urine sodium excretion in normal subjects.

Ouabain is not detectable in human plasma.

An enzyme-linked immunosorbent assay is described for the measurement of ouabain in human plasma. This assay is specific for ouabain, strophanthidin, and ouabagenin, with other steroids, including digoxin and vasopressor hormones, exhibiting negligible cross-reactivity. Assay sensitivity was 0.06 nmol/L if 1 mL plasma was extracted and less than 0.005 nmol/L when 20 mL plasma was analyzed. Extracted plasma samples showed ouabainlike immunoreactivity that diluted in parallel with the ouabain standard curve. Repeated extraction and assay of single plasma samples, however, did not produce consistent results in the assay. Increased specificity was obtained by high-performance liquid chromatography of sample extracts before assay. When high-performance liquid chromatographic profiles of plasma spiked with ouabain standard or following bolus intravenous injections of ouabain into normal human volunteers were compared with profiles of unspiked plasma, there was no support for the immunoreactive material in the latter samples being ouabain. We propose that if ouabain is present in the human circulation, its concentration is less than 0.005 nmol/L.

The effects of pathophysiological increments in brain natriuretic peptide in left ventricular systolic dysfunction.

Plasma levels of brain natriuretic peptide (BNP) are raised in patients with left ventricular impairment and may play a role in the adaptation to left ventricular impairment. Manipulation of BNP levels may have therapeutic potential. The effects of BNP have not been well studied in patients with left ventricular impairment. We studied the effects of low-dose BNP infusion, reproducing the increment in plasma BNP seen with progression from mild to severe heart failure in patients with impaired left ventricular systolic function. BNP was infused in a placebo-controlled, single-blind, crossover design at a rate of 3.3 pmol x kg(-1) x min(-1) over 4 hours to 8 patients with a history of congestive heart failure and persistent impairment of left ventricular systolic function (left ventricular ejection fraction <35%). Endocrine, renal, and hemodynamic effects were measured. Compared with time-matched placebo-control, BNP infusion decreased mean systemic arterial pressure (peak decrease, 17.1 mm Hg; P=.04), mean pulmonary artery pressure (peak decrease, 6.1 mm Hg; P=.007), mean pulmonary capillary wedge pressure (peak decrease, 5.5 mm Hg; P=.04), and systemic vascular resistance (peak decrease, 1400 dyne s(-1) cm(-5); P=.015), but cardiac output and heart rate were unchanged. Urinary volume and urinary excretion of sodium and potassium were not altered. BNP infusion increased plasma cGMP (2.3-fold change, P=.002). Plasma atrial natriuretic peptide levels were increased for the first hour of BNP infusion (peak increase, 11.5 pmol/L; P=.005). Plasma aldosterone levels were unchanged during but increased over time-matched control levels after the end of the BNP infusion (peak increase, 90 pmol/L; P=.02). Plasma renin activity and cortisol and catecholamine levels were unchanged. Low-dose infusion of BNP causes favorable hemodynamic changes and relative neurohormonal suppression but has attenuated renal effects in patients with impaired left ventricular systolic function.