Antihypertensive and hypotensive effects of atrial natriuretic factor in men

The Importance of Natriuretic Peptides in Cardiometabolic Diseases

The natriuretic peptide (NP) system is composed of 3 distinct peptides (atrial natriuretic peptide or ANP, B-type natriuretic peptide or BNP, and C-type natriuretic peptide or CNP) and 3 receptors (natriuretic peptide receptor-A or NPR-A or particulate guanynyl cyclase-A natriuretic peptide receptor-B or NPR-B or particulate guanynyl cyclase-B, and natriuretic peptide receptor-C or NPR-C or clearance receptor). ANP and BNP function as defense mechanisms against ventricular stress and the deleterious effects of volume and pressure overload on the heart. Although the role of NPs in cardiovascular homeostasis has been extensively studied and well established, much remains uncertain about the signaling pathways in pathological states like heart failure, a state of impaired natriuretic peptide function. Elevated levels of ANP and BNP in heart failure correlate with disease severity and have a prognostic value. Synthetic ANP and BNP have been studied for their therapeutic role in hypertension and heart failure, and promising trials are under way. In recent years, the expression of ANP and BNP in human adipocytes has come to light. Through their role in promotion of adipocyte browning, lipolysis, lipid oxidation, and modulation of adipokine secretion, they have emerged as key regulators of energy consumption and metabolism. NPR-A signaling in skeletal muscles and adipocytes is emerging as pivotal to the maintenance of long-term insulin sensitivity, which is disrupted in obesity and reduced glucose-tolerance states. Genetic variants in the genes encoding for ANP and BNP have been associated with a favorable cardiometabolic profile. In this review, we discuss several pathways that have been proposed to explain the role of NPs as endocrine networkers. There is much to be explored about the therapeutic role of NPs in improving metabolic milieu.

The multifaceted role of natriuretic peptides in metabolic syndrome

Due to globalization and sophisticated western and sedentary lifestyle, metabolic syndrome has emerged as a serious public health challenge. Obesity is significantly increasing worldwide because of increased high calorie food intake and decreased physical activity leading to hypertension, dyslipidemia, atherosclerosis, and insulin resistance. Thus, metabolic syndrome constitutes cardiovascular disease, type 2 diabetes, obesity, and nonalcoholic fatty liver disease (NAFLD) and recently some cancers are also considered to be associated with this syndrome. There is increasing evidence of the involvement of natriuretic peptides (NP) in the pathophysiology of metabolic diseases. The natriuretic peptides are cardiac hormones, which are produced in the cardiac atrium, ventricles of the heart and the endothelium. These peptides are involved in the homeostatic control of body water, sodium intake, potassium transport, lipolysis in adipocytes and regulates blood pressure. The three known natriuretic peptide hormones present in the natriuretic system are atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and c-type natriuretic peptide (CNP). These three peptides primarily function as endogenous ligands and mainly act via their membrane receptors such as natriuretic peptide receptor A (NPR-A), natriuretic peptide receptor B (NPR-B) and natriuretic peptide receptor C (NPR-C) and regulate various physiological and metabolic functions. This review will shed light on the structure and function of natriuretic peptides and their receptors and their role in the metabolic syndrome.

Effects of continuous infusion of low-dose human atrial natriuretic peptide (hANP) on the lungs during cardiac surgery

OBJECTIVE

The objective of this study was to determine the effects of a continuous infusion of low-dose hANP on the lungs during cardiac surgery in patients under cardiopulmonary bypass (CPB).

METHODS

We analyzed 30 consecutive cases of cardiac surgery performed at our hospital from 2007-2008. The patients were divided into a group that received hANP (hANP group) or a group that received saline and no hANP (N-hANP group). We measured various parameters before and after surgery using a PiCCO monitor.

RESULT

There were no differences in the preoperative characteristics between the groups, although urine volume during the operation was significantly greater in the hANP group. After surgery, there were no significant differences between the groups in cardiac output index (CI), global enddiastolic volume index (GEDVI), intrathoracic blood volume index (ITBI), pulmonary blood volume index (PBI), extravascular lung water index (ELWI) and pulmonary vascular permeability index (PVPI), total protein, and creatine. In contrast, interleukin-6 (IL-6) and renin were significantly lower, and albumin was significantly higher in the hANP group.

CONCLUSION

We found that low-dose hANP during open cardiac surgery inhibited the secretion and plasma activity of IL-6 and renin. Although there were no differences in lung circulatory parameters such as the amount of fluid in the pulmonary blood vessels between the two groups, we believe that the strong diuretic effect of hANP reduced third-space fluid retention caused by CPB.

Designer natriuretic peptides: a vision for the future of heart failure therapeutics

Despite recent pharmacological advances in heart failure therapy, mortality from acute decompensated heart failure remains high. Conventional therapies are often insufficient to address the complex interplay between structural, functional, neurohumoral, and renal mechanisms involved in the heart failure syndrome. The natriuretic peptide system, however, offers a unique pleiotropic strategy which could bridge this gap in heart failure therapy. Exogenous administration of native A-type and B-type natriuretic peptides has been met with both success and limitations, and despite the limitations, remains a worthwhile endeavor. Alternatively, synthetic modification to create “designer” chimeric peptides holds the possibility to extend both the application and therapeutic benefits possible with a natriuretic peptide based approach. Herein we describe the development of natriuretic peptide based heart failure therapies, including the design, rationale, and preliminary studies of the novel chimeric peptides CD-NP and CU-NP.

Central role of guanylyl cyclase in natriuretic peptide signaling in hypertension and metabolic syndrome

Studied for nearly 30 years for its ability to control many parameters, such as vascular smooth muscle cell relaxation, heart fibrosis, and kidney function, the natriuretic peptide (NP) system is now considered to be a key element in several other major metabolic pathways. After stimulation by NPs, natriuretic peptide receptors (NPR) convert GTP to the second messenger cGMP. In addition to its vasodilatory effects and natriuretic and diuretic functions, cGMP has been positively associated with fat cell function, apoptosis, and NPR expression/activity modulation. The NP system is also closely linked to metabolic syndrome (MetS) progression and obesity control. A new era is now on its way targeting the NP system to not only treat high blood pressure, but to also assist in the fight against the obesity pandemic. Here, we summarize recent data on the role of NPs in hypertension and MetS.

Experimental investigation of direct myocardial protective effect of atrial natriuretic peptide in cardiac surgery

OBJECTIVE

Human atrial natriuretic peptide has recently become known not only as a heart failure drug but also for myocardial protection. We investigated its direct myocardial protective effect on ischemia-reperfusion injury in cardiac surgery.

METHODS

Male pigs (35-45 kg) undergoing surgery with cardiopulmonary bypass, with 60-minute reperfusion after 30-minute cardioplegia, were grouped by timing of atrial natriuretic peptide administration: group C (n = 8), no atrial natriuretic peptide (cardioplegia only); group H1 (n = 8); 100-mug atrial natriuretic peptide administration after aortic crossclamping; group H2 (n = 8), administration before aortic declamping; and group H1 + H2 (n = 8), administration both after crossclamping and before declamping. Blood and myocardial cyclic guanosine monophosphate, calcium, and residual adenosine triphosphate levels were determined. Histologic investigation was conducted by electron and optical microscopy.

RESULTS

Atrial natriuretic peptide increased blood and myocardial cyclic guanosine monophosphate levels (P < .0001, P < .0001, P < .007 H1 + H2 vs C; P < .0014, P < .0007, P < .003 H1 vs C), decreased myocardial calcium (P < .0038 H1 + H2 vs C), and increased myocardial residual adenosine triphosphate. Electron microscopy revealed ischemic changes in mitochondria and nuclei in group C but not in treatment groups.

CONCLUSIONS

Ischemia-reperfusion injury was inhibited with equal effectiveness by atrial natriuretic peptide both during ischemia and immediately before reperfusion, acting directly on myocardium through cyclic guanosine monophosphate. Atrial natriuretic peptide may be useful as a supportive measure for patients with long aortic crossclamping time or difficulties in weaning from cardiopulmonary bypass.

Natriuretic peptides, their receptors, and cyclic guanosine monophosphate-dependent signaling functions

Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide, B-type natriuretic peptide, C-type natriuretic peptide, and possibly osteocrin/musclin. Three single membrane-spanning natriuretic peptide receptors (NPRs) have been identified. Two, NPR-A/GC-A/NPR1 and NPR-B/GC-B/NPR2, are transmembrane guanylyl cyclases, enzymes that catalyze the synthesis of cGMP. One, NPR-C/NPR3, lacks intrinsic enzymatic activity and controls the local concentrations of natriuretic peptides through constitutive receptor-mediated internalization and degradation. Single allele-inactivating mutations in the promoter of human NPR-A are associated with hypertension and heart failure, whereas homozygous inactivating mutations in human NPR-B cause a form of short-limbed dwarfism known as acromesomelic dysplasia type Maroteaux. The physiological effects of natriuretic peptides are elicited through three classes of cGMP binding proteins: cGMP-dependent protein kinases, cGMP-regulated phosphodiesterases, and cyclic nucleotide-gated ion channels. In this comprehensive review, the structure, function, regulation, and biological consequences of natriuretic peptides and their associated signaling proteins are described.

Combined inhibition of neutral endopeptidase and angiotensin-converting enzyme by sampatrilat in essential hypertension

BACKGROUND

The antihypertensive response to angiotensin-converting enzyme (ACE) inhibitors may be attenuated by a compensatory decrease in atrial natriuretic factor production. If so, inhibition of atrial natriuretic factor breakdown by neutral endopeptidase (NEP) may enhance the antihypertensive effects of ACE inhibition. We compared effects of the combined ACE-NEP inhibitor sampatrilat, lisinopril, and placebo on blood pressure, plasma ACE, and renin activity and urinary cyclic guanosine monophosphate (cGMP) of patients with hypertension.

METHODS AND RESULTS

After a 4-week placebo run-in period, 124 patients with a mean blood pressure of 162/102 mm Hg were randomized in a double-blind parallel-group design to 1 of 5 treatments, given once daily for 10 days: 50 mg, 100 mg, or 200 mg sampatrilat; 20 mg lisinopril; or placebo. The first dose of sampatrilat did not lower clinic or ambulatory blood pressure. Lisinopril had an immediate antihypertensive effect that differed significantly from all doses of sampatrilat. After 10 days of treatment, sampatrilat lowered clinic and ambulatory blood pressure significantly at all doses, with a trend toward a dose response for systolic ambulatory blood pressure. Sampatrilat inhibited plasma ACE in a dose-dependent fashion but significantly less so than lisinopril on days 1 and 10 of treatment. Lisinopril but not sampatrilat significantly increased plasma renin activity, whereas sampatrilat but not lisinopril significantly increased urinary cGMP excretion.

CONCLUSION

The increasing efficacy of sampatrilat compared with lisinopril over 10 days could not be attributed to an increase in plasma ACE inhibition, suggesting that the NEP inhibitor activity of sampatrilat may have contributed to its antihypertensive action. NEP inhibition may enhance the antihypertensive effect of ACE inhibition.

Quantification and predictors of plasma volume expansion from mannitol treatment

OBJECTIVE

To determine the effects of acute hypertonic mannitol infusion on intravascular volume expansion and to identify potential predictors of hypervolemia.

DESIGN

Measurements of plasma volume and volume regulatory hormones were performed in healthy volunteers before and over 90 min after acute infusion of 20% mannitol solution in a therapeutic dose of 0.5 g/kg body weight, equalling an average infusion volume of 180 ml.

SETTING

Clinical research unit in an 800-bed teaching hospital in the eastern part of Switzerland.

PARTICIPANTS

Eight normal male volunteers.

MEASUREMENTS AND RESULTS

Baseline plasma volume was determined by the indocyanine green dye dilution technique. Serial plasma protein measurements were performed after mannitol infusion to calculate intravascular volume changes. Mannitol administration resulted in a plasma expansion that persisted for more than 90 min and peaked at 112% of the baseline plasma volume 15 min after infusion. Concomitantly, an increase in systolic blood pressure and a fall in plasma sodium concentration occurred. Pharmacokinetic analyses of mannitol distribution and elimination revealed a close relation between plasma volume expansion and mannitol serum concentrations. While renin activity and aldosterone concentrations were suppressed proportionally to the intravascular volume increase, antidiuretic hormone was increased despite notable volume expansion and hyponatremia. Similarly, a rise in atrial natriuretic peptide was detected.

CONCLUSIONS

Therapeutic doses of hypertonic mannitol cause substantial plasma volume expansion, resulting in increased blood pressure. Plasma volume expansion is related to mannitol serum concentrations and mannitol clearance determines the time required to restore normovolemia. ADH and ANP are potentially aggravating factors of mannitol-induced hyponatremia.

Severe hypotension and bradycardia after continuous intravenous infusion of urodilatin (ANP 95-126) in a patient with congestive heart failure

The effects of a continuous i.v. infusion of urodilatin at a dose of 30 ng kg-1 min-1 were studied in a patient with congestive heart failure. After 30 min, urodilatin had induced a marked stimulation of plasma cyclic GMP concentrations. In parallel haematocrit increased. No significant diuresis and no change of invasive haemodynamics was observed. After 2 h the patient developed a profuse perspiration. Eighty minutes later he suffered from dizziness due to hypotension (blood pressure 80/40 mmHg) and a sudden bradycardia (50 bpm). Urodilatin was discontinued and symptoms were relieved by bed tilt and rapid infusion of isotonic saline solution. Mechanisms contributing to these adverse effects may be fluid extravasation to the third space and sympathoinhibitory effects known to occur with natriuretic peptide infusion.

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.

Sodium loads enhance the natriuretic responses to atrial natriuretic peptide and neutral endopeptidase inhibitors in conscious cynomolgus monkeys

1. The effects of sodium supplements on the renal responses to human atrial natriuretic peptide (hANP 99-126) and to the selective inhibitors of neutral endopeptidase 3.4.24.11 (NEP) SQ 28,603 and candoxatrilat were determined in conscious monkeys. 2. When the monkeys' diet was changed from 0.55% sodium to 1.1% sodium, the natriuretic response to 100 mumol/kg intravenous of SQ 28,603 increased from 665 +/- 64 to 1015 +/- 224 mu Eq/3 h. An acute oral load of 25 mEq sodium significantly increased the natriuresis stimulated by 300 mumol/kg, p.o., of SQ 28,603 from 700 +/- 332 mu Eq/3 h in normal monkey to 2437 +/- 841 mu Eq/3 h. Therefore, the non-human primate model was appropriate for investigating the effects of sodium loads on the urinary ANP and cGMP responses to exogenous ANP in the presence and absence of NEP inhibitors. 3. Graded intravenous infusions of saline increased basal urine volume and excretion of sodium and ANP. Salt supplements enhanced the diuretic, natriuretic and ANP responses to 0.3 nmol/kg intravenous of hANP 99-126 in monkeys treated with vehicle or 10 mumol/kg intravenous of candoxatrilat. The sodium and ANP excretions stimulated by hANP 99-126 were positively correlated with each other and with the calculated intravenous sodium load in the presence or absence of candoxatrilat. 4. SQ 28,603 and candoxatrilat (0.3 to 10 mumol/kg intravenous) each produced significant, dose-related potentiation of the natriuretic, cGMP and ANP responses to 0.3 nmol/kg intravenous of hANP 99-126 in monkeys receiving 5 mL/kg+0.2 mL/min saline. In addition, the highest dose of SQ 28,603 produced significant depressor activity. 5. In conclusion, the increased natriuretic activity of hANP 99-126 in sodium loaded monkeys was mediated, in part, by increased ANP delivery to the guanylate cyclase linked ANP receptors in the distal renal tubules.

Effects of atrial natriuretic peptide on left ventricular function in hypertension

Atrial natriuretic peptide (ANP) has natriuretic and vasodilator actions that lower arterial pressure and may be beneficial to hypertensive patients. To assess the effects of ANP on left ventricular function in patients with hypertension, we compared it with the pure vasodilator nitroprusside. Simultaneous left ventricular micromanometer pressure and radionuclide volume were obtained at baseline, during nitroprusside infusion, during a second baseline period, and during ANP infusion in 10 patients with hypertension. Mean arterial pressure fell during ANP and nitroprusside. Heart rate and plasma norepinephrine levels increased by similar amounts during the two agents, whereas cardiac index and stroke volume index were unchanged during both. Peak positive left ventricular dP/dt fell similarly during ANP and nitroprusside, but left ventricular dP/dt at a developed pressure of 40 mm Hg, a less load-dependent index of contractility, was unchanged during both. The relation between end-systolic pressure and volume during ANP infusion was not shifted leftward or rightward from that during nitroprusside infusion, indicating no inotropic effect. Both ANP and nitroprusside shortened at time constant of isovolumic relaxation calculated by the logarithmic method but did not change the time constant calculated by the derivative method. Peak filling rate was unchanged from baseline during both agents. ANP did not shift the end-diastolic pressure-volume point away from the relation constructed from baseline and nitroprusside points. We conclude that ANP has no direct effect on myocardial contractile or diastolic function in patients with hypertension.

Insulin blunts the natriuretic action of atrial natriuretic peptide in hypertension

Hyperinsulinemia and insulin resistance are implicated in the etiology of hypertension, but the mechanisms involved have not been established. The objectives of this study were to determine whether untreated essential hypertensive patients are more sensitive to the antinatriuretic action of insulin and more resistant to the counteracting natriuretic effect of atrial natriuretic peptide in contrast to age- and sex-matched normotensive control subjects. Urinary sodium excretion was measured at baseline, during hyperinsulinemic euglycemic clamp, and during coadministration of insulin and atrial natriuretic peptide. Baseline urinary sodium excretion was not significantly different in the normotensive subjects (415 +/- 47 mumol/min, n = 12) and hypertensive patients (381 +/- 18 mumol/min, n = 10); with the institution of insulin infusion, there was a similar and significant decline from baseline (P < .001) to 289 +/- 35 mumol/min in normotensive subjects and 235 +/- 17 mumol/min in hypertensive patients. Atrial natriuretic peptide was able to oppose the antinatriuretic action of insulin in normotensive subjects, increasing urinary sodium excretion significantly to a mean level of 352 +/- 31 mumol/min (P < .05), which did not differ significantly from baseline. In the hypertensive group, atrial natriuretic peptide infusion had no effect on urinary sodium excretion (238 +/- 18 mumol/min), and the difference from baseline remained highly significant (P < .001). The hypertensive patients were significantly less insulin sensitive than their normotensive counterparts, as reflected by a lower glucose utilization rate and higher mean baseline plasma insulin level (P < .05 for each).(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of atrial natriuretic factor (ANF)-like peptides in the brain and heart of the treefrog Hyla japonica: effect of weightlessness on the distribution of immunoreactive neurons and cardiocytes

The localization of atrial-natriuretic factor (ANF)-like immunoreactivity was investigated in the brain and heart of the treefrog Hyla japonica by the indirect immunofluorescence technique. Concurrently, the effect of weightlessness on the distribution of ANF-containing neurons and cardiocytes was studied in frogs that were sent into space for 9 days on the space station "MIR." In control animals, the amygdala contained the most prominent group of ANF-immunoreactive cells and fibers. ANF-positive neurons and nerve processes were also detected in other areas of the telencephalon such as the nucleus olfactorius, the pallium mediale, and the striatum. In "space frogs," the intensity of labeling of the amygdala and nucleus olfactorius was similar to that seen in control animals. In contrast, the pallium and the striatum of "space frogs" were totally devoid of positive cell bodies. In the diencephalon, of all animals, numerous ANF-immunoreactive perikarya and fibers were seen in the hypothalamus, the anterior thalamus, the infundibulum, and the median eminence. ANF-positive cell bodies were also noted in the lateral forebrain bundle of control frogs but were absent in "space frogs." The major difference between control and "space frogs" was observed in the posterior nuclei of the thalamus. In "space frogs," the nucleus posterocentralis thalami and the nucleus posterolateralis thalami exhibited large ANF-immunoreactive perikarya, while, in control frogs, these nuclei only contained scarce positive nerve fibers. In the mesencephalon, ANF-positive cell bodies and nerve processes were seen in the nucleus tegmenti mesencephali, the interpeduncular nucleus, and the nucleus cerebelli of all animals. However, stained perikarya were only observed in the nucleus reticularis isthmi of control frogs. In the heart, atrial cardiocytes exhibited intense ANF-like immunoreactivity. ANF-positive myocytes were also detected in the subpericardial region of the ventricle. The density and distribution of the staining were identical in the heart of control and "space frogs." These data support the concept that prolonged exposure to microgravity affects biosynthesis and/or release of ANF-related peptides in discrete regions of the amphibian brain.

Atrial natriuretic factor: its (patho)physiological significance in humans

The first human studies using relatively high-doses of ANF revealed similar effects as observed in the preceding animal reports, including effects on systemic vasculature (blood pressure fall, decrease in intravascular volume), renal vasculature (rise in GFR, fall in renal blood flow), renal electrolyte excretion (rises in many electrolytes), and changes in release of a number of different hormones. Whether all these changes are the result of direct ANF effects or secondary to a (single) primary event of the hormone remains to be determined. Certainly, it has been proven that more physiological doses of ANF fail to induce short-term changes in many of these parameters leaving only a rise in hematocrit, natriuresis and an inhibition of the RAAS as important detectable ANF effects in humans. This leads us to hypothesize that ANF is a "natriuretic" hormone with physiological significance. The primary function in humans is to regulate sodium homeostasis in response to changes in intravascular volume (cardiac atrial stretch). Induction of excess renal sodium excretion and extracellular volume shift appear to be the effector mechanisms. The exact mechanism of the natriuresis in humans still needs to be resolved. It appears however, that possibly a small rise in GFR, a reduction in proximal and distal tubular sodium reabsorption, as well as an ensuing medullary washout, are of importance. The pathophysiological role of ANF in human disease is unclear. One may find elevated plasma irANF levels and/or decreased responses to exogenous ANF in some disease states. Whether these findings are secondary to the disease state rather than the cause of the disease remains to be resolved. Therapeutic applications for ANF, or drugs that intervene in its production or receptor-binding, seem to be multiple. Most important could be the antihypertensive effect, although areas such as congestive heart failure, renal failure, liver cirrhosis and the nephrotic syndrome cannot be excluded. Although the data that have been gathered to date allowed us to draw some careful conclusions as to the (patho)physiological role of ANF, the exact place of ANF in sodium homeostatic control must still be better defined. To achieve this, we will need more carefully designed low-dose ANF infusion, as well as ANF-breakdown inhibitor studies. Even more promising, however, is the potential area of studies open to us when ANF-receptor (ant)agonists become available for human use.

Dietary sodium and inhibition of neutral endopeptidase 24.11 in essential hypertension

Basal atrial natriuretic peptide levels and the response to exogenous atrial natriuretic peptide are influenced by dietary sodium intake. In view of interest in the therapeutic potential of elevating plasma atrial natriuretic peptide by inhibition of neutral endopeptidase 24.11, we studied the renal and hormonal effects of 200 mg of the oral endopeptidase 24.11 inhibitor candoxatril in eight patients with untreated essential hypertension on high sodium (350 mmol/day) and low sodium (10 mmol/day) diets. With endopeptidase 24.11 inhibition, plasma atrial natriuretic peptide increased more than twofold on low and high sodium diets (p less than 0.05). Plasma N-terminal pro-atrial natriuretic peptide increased on the high sodium intake but was unaffected by candoxatril. Urinary sodium excretion increased threefold on the low sodium and sixfold on the high sodium diet (p less than 0.05). The absolute increase in urinary sodium excretion during the 24 hours after treatment compared with placebo was 18 +/- 8 mmol on the low sodium and 98 +/- 34 mmol on the high sodium diet (p less than 0.05). Plasma renin activity was suppressed by treatment on the low but not on the high sodium diet (p less than 0.05). Blood pressure did not change in the 6 hours after a single dose of candoxatril. These findings show that sodium intake is a major determinant of the response to endopeptidase 24.11 inhibition. The lack of effect on N-terminal pro-atrial natriuretic peptide suggests that candoxatril does not influence cardiac secretion of atrial natriuretic peptide or catabolism of N-terminal pro-atrial natriuretic peptide, and the latter does not appear to play a role in the response to candoxatril.

Effects of atrial natriuretic peptide on glomerular filtration rate in essential hypertension: a radionuclide study

A number of studies show that atrial natriuretic peptide (ANP) raises renal sodium excretion with a concomitant increase in glomerular filtration rate (GFR) in both experimental animals and normal humans. Studies using indirect evaluation of GFR have provided less consistent results in hypertensive patients. We studied the effects of intravenously administered (iv) alpha-human ANP on GFR in patients with hypertension by a radionuclide technique using technetium 99m diethylenetriaminepenta-acetic acid. In six patients (ANP group), GFR was determined under control conditions, during iv ANP (initial bolus of 0.5 micrograms/kg followed by a 21-min maintenance infusion at 0.05 micrograms.kg-1.min-1) and during a recovery phase. In six other patients (control group), GFR was determined under control conditions, during saline iv infusion and during recovery. The two groups did not differ with respect to age, sex, basal blood pressure, heart rate or GFR. In the ANP group, the infusion of the peptide induced a significant decrease of mean blood pressure (from 133 +/- 5 to 120 +/- 5 mmHg, P less than 0.01), no change in heart rate and a significant increase in GFR (from 104 +/- 4 to 125 +/- 5 ml/min, P less than 0.01). During recovery, blood pressure, heart rate and GFR were not different from the values recorded under control conditions. No changes in blood pressure, heart rate or GFR (from 106 +/- 5 to 108 +/- 5 ml/min, n.s.) were detected during saline infusion in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial peptides induce mast cell histamine release

Human atrial natriuretic peptide [ANF(1-28)] contains five arginine residues and carries an overall positive change of four. It was hypothesized that atrial peptides may induce mast cell histamine release. In vitro, three atrial peptides [ANF(1-28), (3-28) and (5-28)] were demonstrated to induce dose-dependent histamine release from isolated rat peritoneal mast cells. In vivo, ANF(3-28) produced a dose-dependent increase in rat skin permeability which was blocked by antagonists of histamine and serotonin. The results indicate atrial peptides are capable of inducing mast cell degranulation in a manner similar to that described for other positively charged peptides.

Atrial natriuretic factor as a vasodilator agent in hypertensive patients

To investigate the role of Atrial Natriuretic Factor (ANF) in modulating arteriolar tone in hypertension, a synthetic 25 AA human ANF-analogue (anaritide) was infused intraarterially in the forearm vascular bed of five patients with mild hypertension. A dose-dependent increase in blood flow (plethysmographic technique) was seen at rates covering a thousand-fold range (0.008, 0.08, 0.8, 8.0 micrograms/dl tissue/min x 15 minutes each). At the lowest infusion rate, the forearm blood flow increment was associated with changes in local venous ANF concentrations comparable with those reported during biological stimuli in hypertensive man and consistent with an ANF physiologic role in forearm arterioles of hypertensive patients. However, at local venous concentrations greater than 1000 pg/ml, ANF did not relax forearm vessels by more than about one-fourth of the total forearm vasodilator capacity (as assessed through a maximally active ischemic stimulus). These data confirm the low potency of ANF as an endogenous vasodilator, although vasodilator potency is not a necessary requirement for physiologic systems involved in the regulation of muscular vascular tone. Systemic arterial pressure, heart rate, and contralateral flow did not change during the study in spite of the markedly increased peripheral ANF levels recirculating from the local forearm administration. This behavior indicates that arteriolar vasodilation is apparently not the main mechanism of action of ANF on systemic hemodynamics in hypertensive patients.

Atrial natriuretic factor and autonomic nervous system function in man

To delineate a possible interaction of atrial natriuretic peptide ANF-(99-126) with autonomic nervous system function in humans, a spectrum of indices were assessed in 10 healthy young men during a 90 min iv administration of a) synthetic ANF-(99-126) 50 micrograms bolus followed by 0.025 micrograms.kg-1.min-1, b) the potent vasodilator sodium nitroprusside (SNP) 0.35 micrograms.kg-1. min-1, or c) vehicle 0.9% NaCl40 ml and 20% albumin 5 ml, in random sequence. Plasma immunoreactive ANF (irANF) rose from 32 to 1700 pg.ml-1 during the ANF-(99-126) infusion and was stable during SNP or vehicle. Infusion of ANF-(99-126) and SNP, but not vehicle, decreased diastolic blood pressure (BP) on average by -9 and -7.5%, respectively; systolic BP was largely unchanged. Heart rate (HR, + 15 and 12%) or plasma norepinephrine (NE) rose similarly during ANF-(99-126) and SNP infusions, and the systolic BP response to orthostasis was similar (-18 mmHg). The following autonomic indices did not differ significantly after the 3 infusions: responses of HR and NE to orthrostasis; reflex bradycardic response to phenylephrine (PE)-induced rise in systolic BP (+ 20 mmHg); responses of BP to hyperventilation, PE, or 3 min of sustained handgrip; and beat-to-beat variation (R-R interval) during deep breathing. The immediate orthostatic HR response (30/15 R-R interval ratio) fell similarly during infusion of ANF-(99-126) or nitroprusside. The findings indicate that in healthy men the function of the autonomic nervous system is not notably impaired by high circulating ANF levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolonged low dose infusion of atrial natriuretic factor in essential hypertension

The C-terminal fragment of atrial natriuretic factor (ANF) was infused intravenously at 0.5 pmol/kg/min during 12 hours in 6 patients with mild to moderate essential hypertension, and in 6 normotensive volunteers, all recumbent and well hydrated, under a daily intake of 200 and 120 mmoles of sodium and potassium, respectively. Plasma C-terminal ANF tended to increase during ANF and to decrease during vehicle infusions. Plasma concentrations of the N-terminal fragment of ANF decreased by 20 to 40% (p less than 0.05) during ANF and remained unchanged following vehicle infusion, suggesting that exogenous ANF reduces endogenous ANF secretion. ANF increased significantly plasma cyclic guanosine monophosphate (p less than 0.01) from 3.1 +/- 0.4 to 4.3 +/- 0.8 and from 2.8 +/- 0.4 to 5.1 +/- 0.5 nmol/L in controls and patients respectively. ANF reduced systolic diastolic blood pressure during the last 8 hours of the infusion, by about 5% (p = 0.055) in patients, but did not alter blood pressure in controls. Sodium excretion during ANF increased 42% vs vehicle (p less than 0.05), in the patients group and remained unchanged in controls. Hematocrit levels increased significantly in both groups with ANF infusion. We conclude that a prolonged infusion of ANF at a physiological rate causes a modest increase in plasma cyclic guanosine monophosphate, hemoconcentration, and reduces endogenous ANF secretion. It also stimulates diuresis and natriuresis and slightly reduces systolic blood pressure in patients with essential hypertension.

[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.

Low-dose infusion of atrial natriuretic factor in mild essential hypertension

Intra-arterial blood pressure, cardiac output, heart rate, right heart indexes, urinary electrolytes, and urinary volume were monitored in eight patients with untreated (WHO Class I) essential hypertension. The patients were given synthetic atrial natriuretic factor (ANF) (99-126 alpha-hANP) at 1 and 2 pmol/kg/min in series (phases 1 and 2, 2 hours each dose) or vehicle (hemaccel) in random order on two separate occasions while on their usual diet. Arterial plasma ANF levels increased significantly from basal and time-matched placebo values from 25 +/- 2 and 28 +/- 3 pmol/l to 50 +/- 4 and 83 +/- 9 pmol/l at the end of phases 1 and 2, respectively (p less than 0.001). After 30 minutes during phase 2, systolic blood pressure decreased significantly by 20 +/- 4 mm Hg (p less than 0.001) from basal and time-matched placebo values and remained significantly reduced (-17 +/- 4 mm Hg, p less than 0.001) by the end of the recovery period (2 hours after infusions were completed). Pulmonary systolic blood pressure decreased by 5 +/- 1 mm Hg (phase 2, p less than 0.05). Cardiac output decreased by 0.5 +/- 0.1 l/min below baseline at the end of phase 2 of ANF infusion, whereas it increased significantly (p less than 0.02) by 0.6 +/- 0.1 l/min during vehicle infusion. Systemic diastolic, pulmonary diastolic, right atrial, and wedge pressures were not significantly changed during ANF or vehicle infusions, nor were pulmonary vascular resistance or heart rate altered. Systemic vascular resistance did not change significantly during both infusions, whereas during recovery, systemic vascular resistance decreased significantly after ANF infusion was discontinued (p less than 0.05). Microhematocrit levels increased dose dependently during ANF. The maximum increase was observed at the end of phase 2 (+4.7 +/- 1.7%), whereas the microhematocrit level decreased to -2.4 +/- 0.6% with vehicle (p less than 0.001) at the end of phase 2. Urinary sodium excretion increased significantly (p less than 0.02) by the end of phase 2 under ANF infusion (+38 +/- 15%), whereas it decreased (-10 +/- 6%) under placebo infusion by the end of phase 2. Urinary magnesium excretion was significantly increased during ANF infusion from phase 1 (p less than 0.02), whereas urinary potassium levels, calcium levels, creatinine levels, volume, and glomerular filtration rate did not differ significantly between the two infusions. Plasma renin, angiotensin II, aldosterone, and catecholamine concentrations did not change significantly during ANF or vehicle infusions.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Harnessing the therapeutic potential of atrial natriuretic peptide

The biological actions of Atrial Natriuretic Peptide (ANP) make it potentially useful in the treatment of hypertension and heart failure. We review here the physiology of ANP, the effects of infusion in heart failure and hypertension and preliminary data suggesting that inhibition of endopeptidase 24.11, the enzyme degrading ANP, is an effective mechanism of raising circulating levels of endogenous ANP. Due to the rate of progress in this field we have restricted ourselves to recent work much of which is still available only in abstract form. For more complete accounts the reader is referred to recent reviews [9, 11, 14].

Effects of a bolus dose of atrial natriuretic factor in young and elderly volunteers

We assessed the haemodynamic and renal effects as well as the effects on plasma cGMP levels of a small i.v. dose (33 micrograms) of human atrial natriuretic factor (99-126; hANF) in two age groups of healthy volunteers. Binding properties of platelet ANF receptors were also measured. The elderly (four males, eight females, mean age 52.3 years) showed increased haemodynamic (decrease in blood pressure) and renal responses (diuresis, natriuresis, calciuresis) as well as greater increases in plasma cGMP levels and urinary cGMP excretion than the young subjects (four males, 12 females, mean age 26 years). Binding capacities and affinities of platelet ANF receptors were identical in both groups. These data indicate that the sensitivity to ANF increases with age and that this increased sensitivity is reflected in the reactivity of plasma cGMP levels but not in the properties of platelet ANF receptors. The data may be important for the therapeutic use of ANF, for the understanding of the physiological regulation of ANF action and may underline the necessity of using age-matched control subjects for clinical studies on the possible therapeutic effectiveness of ANF.

Cardiac and vascular effects of atrial natriuretic factor and sodium nitroprusside in healthy men

To assess the contribution of venous effects to the hemodynamic changes caused by atrial natriuretic factor (ANF), the cardiac and peripheral effects of ANF were compared with those induced by the venoarterial vasodilator sodium nitroprusside. On 3 different days, eight healthy subjects received 2-hour infusions of either ANF, sodium nitroprusside, or placebo, by a single-blind crossover design. ANF was administered at a rate of 15 ng/kg/min for hour 1 and 50 ng/kg/min for hour 2; each infusion rate was preceded by a 50-micrograms bolus. The lower ANF infusion rate increased plasma cGMP fourfold, but only modest cardiovascular effects (small decreases in left ventricular end-diastolic and end-systolic volumes) were noted. At the higher ANF infusion rate, left ventricular volumes and intravascular volume, as indirectly assessed by changes in hematocrit levels, decreased further, which resulted in decreases in stroke volume, cardiac index, and systolic blood pressure. No evidence for arterial vasodilation (no decrease in diastolic blood pressure, total peripheral resistance, or forearm resistance) was obtained, and no increase in sympathetic activity was noted. In contrast, sodium nitroprusside caused arterial vasodilation, an increase in cardiac index, and significant increases in sympathetic activity. We conclude that short-term increases in plasma ANF within the physiologic range primarily affect the venous vascular bed (by decreasing intravascular volume or by venodilation) without increasing sympathetic activity.

Renal response to infusion versus repeated bolus injections of atrial natriuretic factor in man

In 7 healthy humans consuming a 170 mmol sodium diet the effect of the mode of administration of atrial natriuretic factor (human ANF 99-126) on renal function has been investigated, using conventional clearance studies during maximal water diuresis. ANF was administered as four repeated bolus (0.4 microgram/kg) injections and, after a 2-day interval, as a one-hour infusion (0.02 microgram/kg/min) preceded by a 0.4 microgram/kg bolus injection. In the two experiments ANF caused comparable elevations in glomerular filtration rate, free water clearance, and lithium excretion. No change in blood pressure or heart rate was observed in either study, and plasma renin activity and aldosterone fell by a similar extent. As expected, the time course of plasma ANF concentrations was markedly different during the two studies. It is concluded that with those doses of ANF the changes in renal haemodynamics and sodium handling were essentially similar after bolus injections and a constant infusion.