Four-hour infusions of synthetic atrial natriuretic peptide in normal volunteers

Novel Therapies on the Horizon of Hypertension Management

BACKGROUND

The rates of uncontrolled hypertension, along with downstream cardiovascular outcomes, has been worsening in this country. Despite the plethora of antihypertensive medications on the market, the prevalence of resistant hypertension (RH) is estimated to be 13.7%. Therefore in addition to increased clinical education and focus on lifestyle management of hypertension and medication compliance, new therapies are needed to address this rise in hypertension.

METHODS

A systematic review of the available medical literature was performed to identify emerging treatment options for RH.

RESULTS

Six different pharmacologic classes and 2 procedural interventions were identified as being appropriate for review in this paper. The pharmacologic classes to be explored are non-steroidal mineralocorticoid receptor antagonists, aminopeptidase A inhibitors, dual endothelin antagonists, aldosterone synthetase inhibitors, atrial natriuretic peptide inhibitors, and attenuators of hepatic angiotensinogen. Discussion of procedural interventions to lower blood pressure will focus on renal denervation and devices that increase carotid baroreceptor activity.

CONCLUSIONS

Promising medication and procedural interventions are being developed and studied to expand our treatment arsenal for patients with uncontrolled essential hypertension and RH.

Natriuretic Peptides and Blood Pressure Homeostasis: Implications for MANP, a Novel Guanylyl Cyclase a Receptor Activator for Hypertension

The heart serves as an endocrine organ producing the hormones atrial natriuretic peptide (ANP) and b-type natriuretic peptide (BNP) which via the guanylyl cyclase A (GC-A) receptor and the second messenger cGMP participate in blood pressure homeostasis under physiologic conditions. Genetic models of the ANP gene or the GCA receptor together with genomic medicine have solidified the concept that both cardiac hormones are fundamental for blood pressure homeostasis and when deficient or disrupted they may contribute to human hypertension. Advances in peptide engineering have led to novel peptide therapeutics including the ANP-analog MANP for human hypertension. Most importantly a first in human study of MANP in essential hypertension has demonstrated its unique properties of aldosterone suppression and blood pressure reduction. Physiology and pharmacology ultimately lead us to innovative peptide-based therapeutics to reduce the burden of cardiovascular disease.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.

Blood pressure and urinary sodium excretion in relation to 16 genetic polymorphisms in the natriuretic peptide system in Chinese

We systematically investigated the association between single nucleotide polymorphisms (SNPs) in the natriuretic peptide system (NPPA, NPPB, NPPC, NPRA, NPRC, and Corin genes) and blood pressure in a Chinese population. The study population was recruited from a mountainous area 500 km south of Shanghai from 2003 to 2009. Using the ABI SNapShot method, we first genotyped 951 subjects enrolled in 2005 for 16 SNPs and then the remaining 1355 subjects as validation for 5 SNPs selected from the primary study. Overall, the association of the studied genetic polymorphisms with blood pressure and urinary excretion of cations was weak or non-significant. However, in the primary study, there was significant (Pint = 0.003) interaction between the rs198358 polymorphism and age in relation to diastolic blood pressure. After adjustment for covariates, diastolic blood pressure was significantly higher in the G allele carriers than AA homozygotes in 176 subjects aged 60 years or older (77.8 ± 1.72 vs 73.9 ± 1.54 mmHg, P = 0.001). In the primary combined with validation studies, this interaction remained statistically significant (Pint = 0.02). The odds ratio of hypertension for carrying the G allele versus AA homozygotes was 1.25 (95% CI: 1.03-1.52; P = 0.03) in all subjects, and 0.85 (0.51-1.41; P = 0.53), 1.30 (0.98-1.73; P = 0.06), and 1.45 (0.95-2.22; P = 0.08) in the subjects younger than 40 years, 40-59 years, and 60 years or older, respectively. Some of the genetic polymorphisms in the natriuretic peptide system might be associated with blood pressure. However, not only the size, but also the direction of the association may change with age.

Natriuretic peptides: an update on bioactivity, potential therapeutic use, and implication in cardiovascular diseases

The natriuretic peptide system includes three known peptides: atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). They contribute to the regulation of cardiovascular homeostasis through diuretic, natriuretic, and vasodilatory properties. Among them, ANP has received particular attention because of its effects on blood pressure regulation and cardiac function. Although the potential for its therapeutic application in the treatment of hypertension and heart failure has been evaluated in several experimental and clinical investigations, no pharmacological approach directly targeted at modulation of ANP levels has ever reached the stage of being incorporated into clinical practice. Recently, ANP has also received attention as being a possible cardiovascular risk factor, particularly in the context of hypertension, stroke, obesity, and metabolic syndrome. Abnormalities in either peptide levels or peptide structure are thought to underlie its implied role in mediating cardiovascular diseases. Meanwhile, BNP has emerged as a relevant marker of left ventricular (LV) dysfunction and as a useful predictor of future outcome in patients with heart failure. This review deals with the major relevant findings related to the cardiovascular and metabolic effects of natriuretic peptides, to their potential therapeutic use, and to their role in mediating cardiovascular diseases.

Natriuretic peptides and therapeutic applications

Since the discovery of atrial natriuretic factor by de Bold et al., there has been tremendous progress in our understanding of the physiologic, diagnostic and therapeutic roles of the natriuretic peptides (NPs) in health and disease. Natriuretic peptides are endogenous hormones that are released by the heart in response to myocardial stretch and overload. Three mammalian NPs have been identified and characterized, including atrial natriuretic peptide (ANP or atrial natriuretic factor), B-type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). In addition, Dendroaspis natriuretic peptide (DNP) has been isolated from the venom of Dendroaspis angusticeps (the green mamba snake), and urodilatin from human urine. These peptides are structurally similar and they consist of a 17-amino-acid core ring and a cysteine bridge. Both ANP and BNP bind to natriuretic peptide receptor A (NPR-A) that are expressed in the heart and other organs. Activation of NPR-A generates an increase in cyclic guanosine monophosphate, which mediates natriuresis, inhibition of renin and aldosterone, as well as vasorelaxant, anti-fibrotic, anti-hypertrophic, and lusitropic effects. The NP system thus serves as an important compensatory mechanism against neurohumoral activation in heart failure. This provides a strong rationale for the use of exogenous NPs in the management of acutely decompensated heart failure. In this article, the therapeutic applications of NPs in the acute heart failure syndromes are reviewed. Emerging therapeutic agents and areas for future research are discussed.

Caffeine decreases the expression of Na+/K+-ATPase and the type 3 Na+/H+ exchanger in rat kidney

1. The aim of the present study was to explore the mechanisms underlying the renal effects of caffeine. 2. Male Sprague-Dawley rats were treated with caffeine, consisting of a single oral bolus (0.2%, 20 mL/kg) followed by supplementation in drinking water (0.2%) for 1 day. Rats treated the same but given water without caffeine served as controls. 3. The expression of alpha1- and beta1-subunits of Na+/K+-ATPase, the type 3 Na+/H+ exchanger (NHE3) and aquaporin-1 was determined in the kidney by western blot analysis. 4. To explore possible involvement of local humoral mediators, the tissue expression of nitric oxide synthase (NOS) proteins was determined by western blot analysis and the expression of atrial natriuretic peptide (ANP) mRNA was determined by semiquantitative reverse transcription-polymerase chain reaction. 5. Following treatment with caffeine, the expression of alpha1- and beta1-subunits of Na+/K+-ATPase, as well as that of NHE3, was decreased. Accordingly, the catalytic activity of Na+/K+-ATPase was decreased. In contrast, the expression of aquaporin-1 was not altered significantly. 6. The expression of the endothelial isoform of NOS was increased, along with tissue nitrite/nitrate levels. The expression of ANP mRNA was increased. 7. It is suggested that caffeine decreases Na+/K+-ATPase and NHE3 activities and increases nitric oxide and ANP activities in the kidney.

Cardiovascular, endocrine, and renal effects of urodilatin in normal humans

Effects of urodilatin (5, 10, 20, and 40 ng. kg-1. min-1) infused over 2 h on separate study days were studied in eight normal subjects with use of a randomized, double-blind protocol. All doses decreased renal plasma flow (hippurate clearance, 13-37%) and increased fractional Li+ clearance (7-22%) and urinary Na+ excretion (by 30, 76, 136, and 99% at 5, 10, 20, and 40 ng. kg-1. min-1, respectively). Glomerular filtration rate did not increase significantly with any dose. The two lowest doses decreased cardiac output (7 and 16%) and stroke volume (10 and 20%) without changing mean arterial blood pressure and heart rate. The two highest doses elicited larger decreases in stroke volume (17 and 21%) but also decreased blood pressure (6 and 14%) and increased heart rate (15 and 38%), such that cardiac output remained unchanged. Hematocrit and plasma protein concentration increased with the three highest doses. The renin-angiotensin-aldosterone system was inhibited by the three lowest doses but activated by the hypotensive dose of 40 ng. kg-1. min-1. Plasma vasopressin increased by factors of up to 5 during infusion of the three highest doses. Atrial natriuretic peptide immunoreactivity (including urodilatin) and plasma cGMP increased dose dependently. The urinary excretion rate of albumin was elevated up to 15-fold (37 +/- 17 micrograms/min). Use of a newly developed assay revealed that baseline urinary urodilatin excretion rate was low (<10 pg/min) and that fractional excretion of urodilatin remained below 0.1%. The results indicate that even moderately natriuretic doses of urodilatin exert protracted effects on systemic hemodynamic, endocrine, and renal functions, including decreases in cardiac output and renal blood flow, without changes in arterial pressure or glomerular filtration rate, and that filtered urodilatin is almost completely removed by the renal tubules.

Atrial natriuretic peptide and arginine-vasopressin secretion in patients with active renal stone disease

The pathogenesis of active renal stone disease (ARSD) is still not fully elucidated. In the present study the role of atrial natriuretic peptide (ANP) and arginine-vasopressin (AVP) as potential pathogenetic factors in ARSD were examined. Thirty patients with ARSD and 21 healthy subjects (HS) were examined both under bed rest (BR) and head-out water immersion (WI) conditions. Serum concentrations of electrolytes (Na, Ca, Mg), ANP and AVP were assessed before (0'), and after 60 and 120 minutes of BR or WI, respectively. Urinary excretions of Na, Ca, Mg, and oxalates were also estimated during BR and WI. Patients with ARSD showed higher basal plasma levels of ANP and a greater response of ANP secretion, but a lower suppression of plasma AVP to WI induced hypervolaemia as compared with the controls. In addition, in patients with ARSD the physiological relationship between plasma AVP concentration and urinary excretion of Ca and Mg (positive correlation), between plasma ANP level and urinary excretion of Ca and Mg (negative correlation), and between plasma ANP and AVP concentration (negative correlation), respectively, were absent. In addition, patients with ARSD showed a positive correlation between plasma ANP and urinary oxalate excretion. From the results obtained in this study we conclude that both AVP and ANP may be involved in the pathogenesis of ARSD.

Hemodynamic and renal excretory effects of human brain natriuretic peptide infusion in patients with congestive heart failure. A double-blind, placebo-controlled, randomized crossover trial

BACKGROUND

The pharmacological effects of infusion of human brain natriuretic peptide (hBNP) in patients with severe congestive heart failure have not been characterized previously.

METHODS AND RESULTS

Twenty patients with severe congestive heart failure were randomized in a double-blind, placebo-controlled, crossover trial to receive incremental 90-minute infusions of hBNP (0.003, 0.01, 0.03, and 0.1 microgram/kg per minute) or placebo on 2 consecutive days. At the highest completed dose of the hBNP, mean pulmonary artery pressure decreased from 38.3 +/- 1.6 to 25.9 +/- 1.7 mm Hg; mean pulmonary capillary wedge pressure decreased from 25.1 +/- 1.1 to 13.2 +/- 1.3 mm Hg; mean right atrial pressure decreased from 10.9 +/- 1 to 4.8 +/- 1.0 mm Hg; mean arterial pressure decreased from 85.2 +/- 2.0 to 74.9 +/- 1.7 mm Hg; and cardiac index increased from 2.0 +/- 0.1 to 2.5 +/- 0.1 L/min per square meter (all P < .01 versus placebo). Urine volume and urine sodium excretion increased significantly during hBNP infusion when compared with placebo infusion (90 +/- 38 versus 67 +/- 27 mL/h and 2.6 +/- 2.4 versus 1.4 +/- 1.2 mEq/h, respectively, both P < .05 versus placebo), whereas creatinine clearance and urinary potassium excretion did not change.

CONCLUSIONS

Infusion of incremental doses of hBNP is associated with favorable hemodynamic and natriuretic effects in patients with severe congestive heart failure.

Influence of atrial natriuretic factor on spontaneous baroreflex sensitivity for heart rate in humans

Our objective in these experiments was to evaluate the effects of atrial natriuretic factor on the gain of the spontaneous baroreceptor-heart rate reflex in humans. On two separate study days, we gave either atrial natriuretic factor during supine rest (16 nmol over 3 minutes, then 16 pmol/kg per minute) or saline (as vehicle) to nine healthy men (age, 23 +/- 1 years; mean +/- SEM) according to a random, double-blind design. Beat-by-beat RR interval and systolic pressure were recorded noninvasively. Sequences during which systolic pressure and the RR interval of the following beat changed in parallel (either increasing [Up] or decreasing [Down]) over at least three consecutive beats were identified and classified as baroreceptor-heart rate reflex sequences. Regression lines relating RR interval to the preceding systolic pressure were derived for each individual sequence. The mean value of the slopes of these regression lines was calculated to obtain the mean spontaneous baroreflex sensitivity for heart rate for each subject. Saline infusion did not change RR interval, systolic pressure, or number of baroreflex sequences nor the slope of the mean spontaneous baroreflex sensitivity for heart rate or slopes of Up or Down sequences. Atrial natriuretic factor, at a dose that lowers central venous pressure, did not affect systolic pressure, respiratory rate, or the number of baroreflex sequences but reduced RR interval from 952 +/- 35 to 930 +/- 40 ms (P < .04) and the mean slope of spontaneous baroreflex sensitivity for heart rate from 32.7 +/- 4.8 to 23.1 +/- 2.8 ms.mm Hg-1 (P < .04).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced renal hemodynamic response to atrial natriuretic peptide in elderly volunteers

Aging is associated with decreased ability to excrete salt and water, thus increasing the susceptibility to volume overload in older individuals. Meanwhile, plasma levels of atrial natriuretic peptide (ANP) increase progressively with age for unknown reasons. We compared the natriuretic and renal hemodynamic responses to low-dose ANP infusion in an elderly group of volunteers (mean age, 74 years) with those of a group of younger subjects (mean age, 29 years). A significant reduction below baseline values in effective renal plasma flow occurred in the young group after the 2-hour peptide infusion (657 +/- 125 v 476 +/- 92 mL/min [mean +/- 1 SD]) when compared with the elderly group (two-way analysis of variance; P < 0.02). A concomitant increase in renal vascular resistance was noted in the young group only during the same period (6,631 +/- 1,384 v 9,136 +/- 2,126 dyn s cm2 x 10(6)). This increase was also significantly higher than that in the elderly group (analysis of variance; P < 0.02). Both groups demonstrated similar natriuretic responses. Absolute sodium excretion had increased significantly above baseline values in both young and elderly subjects at the end of the 2-hour peptide infusion (111 +/- 25 mumol/min to 183 +/- 33 mumol/min v 107 +/- 23 mumol/min to 198 +/- 56 mumol/min) and remained elevated until 1 hour postinfusion. We conclude that the elderly subjects in our study demonstrated a diminished renal hemodynamic response to infusion of ANP while preserving a natriuretic response similar to that found in the younger subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurohormonal inhibition and hemodynamic unloading during prolonged inhibition of ANF degradation in patients with severe chronic heart failure

BACKGROUND

The purpose of this study was to investigate the therapeutic potential of prolonged inhibition of atrial natriuretic factor (ANF) degradation in patients with severe chronic heart failure.

METHODS AND RESULTS

The effects of repeated doses of the endopeptidase inhibitor candoxatrilat (150 mg i.v.) were examined over a 24-hour period in patients with severe chronic heart failure (New York Heart Association class III-IV). Plasma alpha-hANF(99-126) was elevated at baseline (235 +/- 59 pg/ml), increased 2.5-fold at 2 hours after the first dose, and remained significantly elevated throughout the 24-hour protocol. In contrast, pro-hANF(31-67) decreased from 3,151 +/- 616 to 2,072 +/- 362 pg/ml (p less than 0.05). Cardiac index (CI) increased only transiently after the first dose of candoxatrilat (CI, 2.11 +/- 0.2 to 2.67 +/- 0.28 l/min/m2, p less than 0.05). Sodium excretion increased sixfold (p less than 0.05) 2 hours after the first dose of candoxatrilat and remained significantly elevated throughout the protocol. Degree of natriuresis and diuresis in response to candoxatrilat was closely related to baseline cardiac output. Glomerular filtration rate and volume excretion did not change significantly. Pulmonary capillary wedge pressure fell from 23 +/- 3 to 18 +/- 3 mm Hg (p less than 0.05) and remained below baseline throughout the 24 hours. Arterial pressure, heart rate, and total peripheral resistance did not change significantly during the 24-hour period. Urinary cGMP excretion increased fivefold (p less than 0.05), whereas urinary ANF immunoreactivity and plasma cGMP levels remained unchanged. Excretion of prostacyclin metabolite 6-keto-PGF-1 alpha increased 3.3-fold (p less than 0.05). Plasma norepinephrine and epinephrine levels decreased significantly after candoxatrilat and remained suppressed over the 24-hour period. There was also a transient reduction in plasma vasopressin, aldosterone levels, and plasma renin activity. Hematocrit, total protein content, and plasma albumin concentrations did not change, indicating that no fluid shift into the extravascular space had occurred.

CONCLUSIONS

1) The inhibition of ANF degradation causes sustained drop in left and right atrial pressures that appears to be mediated by an inhibition of neurohumoral activity; 2) concomitant inhibition of bradykinin breakdown (which in turn stimulates renal prostacyclin synthesis) contributes to natriuresis; 3) the close correlation between renal response and baseline cardiac index indicates that an inadequate renal perfusion secondary to low cardiac output diminishes the efficacy of this treatment modality. This spectrum of action would be advantageous for a first-line diuretic agent early in the course of disease rather than in patients with advanced chronic heart failure.

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.

Atrial natriuretic peptide inhibits the aldosterone response to metoclopramide in patients with glomerular disease and essential hypertension

1. We examined the effects of metoclopramide (MCP: 10 mg i.v.) on plasma atrial natriuretic peptide (ANP) and aldosterone concentrations (PAC) and the effect of ANP on MCP-induced PAC in four patients with primary glomerular diseases and seven patients with essential hypertension. 2. MCP injection caused no significant changes in plasma ANP. MCP produced a marked increase in PAC without a significant change in plasma renin activity. 3. The increase in PAC induced by MCP injection was markedly attenuated when preceded by the infusion of ANP (25 ng/kg per min). 4. These results suggest that the dopaminergic D2 mechanism is not involved in the regulation of ANP secretion and that ANP modulates the dopaminergic regulation of aldosterone secretion.

Mechanisms involved in the response to prolonged infusion of atrial natriuretic factor in patients with chronic heart failure

We examined the mechanisms involved in the cardiovascular and renal response to prolonged infusion of atrial natriuretic factor (ANF) in patients with chronic heart failure. ANF infusion was titrated to produce a 30% decrease in pulmonary capillary wedge pressure or a 20% increase in cardiac output, and this dose (average, 75 +/- 4 ng/kg/min) was then administered for 20 hours. The short-term response to ANF included significant reductions in central filling pressures, increases in cardiac output, modest increases in diuresis and glomerular filtration rates, significant reduction in plasma aldosterone levels, and a 3.6-fold increase in plasma cyclic GMP levels. During prolonged infusion, plasma cGMP levels and cardiac output gradually returned to baseline. Similarly, the initially increased diuretic effects were completely abolished during prolonged ANF infusion, although plasma alpha-hANF levels remained consistently elevated above baseline values (control, 198 +/- 38; titration, 2,760 +/- 596; 20 hours, 3,499 +/- 659 pg/ml). Four hours after beginning the ANF infusion, marked increases in hematocrit levels were noted (42.5 +/- 1.0% versus 45.3 +/- 1.4%, control and infusion, respectively, p less than 0.05); during this time, no change in total plasma protein concentration occurred, indicating extravascular shift of fluid and plasma proteins. No evidence was noted for activation of vasoconstrictor hormones during prolonged ANF infusion, although mean arterial pressure was significantly reduced throughout the infusion period. Plasma pro-ANF (31-67) levels, determined as a marker for endogenous ANF secretion, were significantly suppressed as were the reductions of central filling pressures. After ANF discontinuation, heart rate and pulmonary capillary wedge pressure increased significantly above baseline values without evidence for sympathetic stimulation. We conclude that 1) prolonged infusion of ANF causes only transient increases in plasma cGMP levels but a sustained reduction of the cardiac release of ANF and that 2) the beneficial hemodynamic effects of ANF, that is, unloading of the ventricles, may be associated with or, in part, may be secondary to a shift of plasma constituents into the extravascular space. The latter may limit the therapeutic potential of ANF for long-term treatment.

Attenuated forearm vasodilative response to intra-arterial atrial natriuretic peptide in patients with heart failure

It has been shown that renal responses to atrial natriuretic peptide (ANP) are markedly attenuated in patients with heart failure. This study aimed to determine if vasodilative response to ANP is altered in patients with heart failure. In patients with heart failure (n = 7) and age-matched normal subjects (n = 7), forearm blood flow was measured using a strain-gauge plethysmograph during intra-arterial infusion of alpha-human ANP (50, 100, 200, and 400 ng/min) or nitroglycerin (100, 200, 400, and 600 ng/min). Forearm vasodilatation evoked with intra-arterial alpha-human ANP in patients with heart failure was considerably less (p less than 0.01) than that in normal subjects. In contrast, nitroglycerin produced comparable forearm vasodilatation in the two groups. Plasma ANP and cyclic guanosine monophosphate (GMP) levels at rest were higher in patients with heart failure than in normal subjects (p less than 0.05 for both), but the increases in plasma ANP and cyclic GMP in the venous effluents during intra-arterial ANP infusion did not differ between the two groups. These results indicate that the direct vasodilative effect of ANP on forearm vessels was attenuated in patients with heart failure as compared with that in normal subjects. The mechanisms responsible for this alteration are not clear but might involve mechanisms other than down-regulation of the ANP receptors because the increases in venous plasma cyclic GMP caused by intra-arterial ANP were comparable between patients with heart failure and normal subjects.

Sympathoinhibitory effects of atrial natriuretic factor in normal humans

In rats, atrial natriuretic factor (ANF) reduces sympathetic nerve activity (SNA) reflexively by sensitizing cardiac mechanoreceptors with inhibitory vagal afferents. We performed three series of experiments in 26 normal young men to document whether ANF inhibits SNA in humans and if so, to determine potential mechanisms for this phenomenon. First, we recorded muscle SNA before and during brief infusions of ANF, vehicle (saline solution), and sodium nitroprusside, titrated to achieve reductions similar to those produced by ANF in diastolic pressure and central venous pressure, and we also assessed the effect of ANF on sympathetic nerve responses to a cold pressor test (CPT). Second, we determined the effect of ANF on Doppler-derived measurements of cardiac output and responses to hypotensive (-40 mm Hg) lower-body negative pressure (LBNP) and its sudden cessation. Third, we applied nonhypotensive (-15 mm Hg) LBNP to selectively unload cardiopulmonary baroreceptors, and we released LBNP to stimulate these inhibitory afferents during sequential infusions of nitroglycerin, vehicle (saline solution), and ANF. Our key findings were that 1) reductions in arterial and central venous pressures during ANF infusion were not accompanied by anticipated reflex increases in muscle SNA; 2) ANF blunted the increase in SNA with CPT; 3) ANF increased stroke volume and cardiac output; and 4) sympathoneural responses to both the application and the sudden cessation of nonhypotensive LBNP were attenuated, not augmented, by ANF. Changes in plasma norepinephrine concentrations reflected these sympathetic nerve responses to ANF. These results do not support the concept that ANF inhibits sympathetic outflow reflexively in humans by increasing discharge from cardiac mechanoreceptors with inhibitory vagal afferents but are consistent with either a central or a ganglionic sympathoinhibitory action of ANF. ANF could facilitate hypotension and natriuresis in humans by attenuating the reflex sympathetic response to baroreceptor deactivation.

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)

Low dose atrial natriuretic factor in primary aldosteronism: renal, hemodynamic, and vascular effects

Whether atrial natriuretic factor (ANF) plays a physiological role in primary aldosteronism has yet to be determined. In the present study, the renal, hemodynamic, humoral, and vascular effects of a synthetic (WY-47663) human analogue were studied in five water-loaded (15 ml H2O/kg) patients with adenomatous primary aldosteronism, a salt-sensitive, low renin, volume-expanded syndrome. ANF was infused for 3 hours at a low rate (0.005 micrograms/kg/min), which approximately doubled circulating immunoreactive ANF. Glomerular filtration rate and renal blood flow (inulin and para-aminohippurate clearance) remained stable, but sodium excretion increased significantly suggesting a dissociation between renal hemodynamics and natriuresis as well as a direct inhibitory effect on tubular sodium reabsorption by ANF. Intra-arterial diastolic blood pressure, heart rate, forearm blood flow (plethysmographic method), and arterial plasma norepinephrine did not change, but systolic blood pressure declined and hematocrit rose suggesting plasma volume contraction by ANF. Plasma aldosterone levels were unchanged indicating a loss of ANF-mediated aldosterone inhibition, possibly related to qualitative or quantitative alterations of ANF receptors in tumoral adrenal tissue. Infusion of the analogue into the brachial artery was at a rate of 0.005 micrograms/dl forearm tissue/min x 30 minutes, which also doubled local immunoreactive venous ANF concentrations and vasodilated forearm arterioles. These data suggest a physiological role for ANF in modulating body fluid volume even in human primary aldosteronism.

Antihypertensive effect of a 5-day infusion of atrial natriuretic factor in humans

Atrial natriuretic factor was infused in a low dose (0.2 microgram/min) during 5 days in six patients with essential hypertension. Atrial natriuretic factor infusion caused plasma levels of atrial natriuretic factor to increase from 49 +/- 10 to 106 +/- 19 pg/ml. Within 4 hours after the start of the atrial natriuretic factor infusion, urinary sodium excretion increased in all subjects. Sodium balance was regained after 24 hours with a net loss of 72.3 +/- 14.6 mmol. However, systolic as well as diastolic blood pressure started to decrease gradually in all subjects only after 12 hours of atrial natriuretic factor infusion, reaching a stable level after 36 hours with a decrease of 11.5 +/- 1.5% and 10.3 +/- 0.8%, respectively. Heart rate increased in parallel by 12.6 +/- 3.1%. Hematocrit rose 7.1 +/- 2.3%. After cessation of atrial natriuretic factor infusion, plasma atrial natriuretic factor levels, sodium balance, and hematocrit returned to baseline within 24 hours, whereas blood pressure slowly returned toward baseline values over 3 days. These data show that chronic atrial natriuretic factor infusion in patients with essential hypertension causes a negative sodium balance and a rise in hematocrit, followed by a smooth decrease in blood pressure with a rise in heart rate until a new equilibrium is reached after approximately 2 days. Thus, atrial natriuretic factor in low doses appears intimately involved in the regulation of sodium balance and blood pressure in humans. Moreover, these data suggest that atrial natriuretic factor-like substances will eventually become useful antihypertensive drugs.

Relationship between renal sympathetic activity and diuretic effects of atrial natriuretic peptide (ANP) in the rat

The effects of various adrenergic agonists and antagonists on the diuretic/natriuretic effects of rANP (103-125) were investigated in conscious and anaesthetized normotensive rats. Pharmacological sympathetic inhibition by reserpine completely inhibited the diuretic/natriuretic effects of ANP. However, surgical renal nerve denervation did not influence the renal response to ANP. Further studies using various pharmacological agents which interfere with adrenergic activity revealed that the diuretic mechanism of action differed between conscious and anaesthetized animals. In the anaesthetized group only, dopamine (D1) blockade reduced ANP-induced diuresis. In the conscious as well as anaesthetized rats, however, pre-synaptic dopamine (D2) stimulation and alpha 2-adrenergic receptor blockade effectively inhibited the renal response to ANP. The results of this study are compatible with the notion that ANP acts indirectly within the kidney via interaction with dopamine-containing neuronal or non-neuronal structures in the kidney.

Responsiveness of atrial natriuretic factor to reduction in right atrial pressure in patients with chronic congestive heart failure

In patients with congestive heart failure, atrial natriuretic factor may serve as a counter-regulatory hormone, offsetting the vasoconstrictive and volume-retentive effects of the sympathetic nervous system, the renin-angiotensin-aldosterone system and vasopressin. Indeed, the plasma levels of atrial natriuretic factor and the vasoconstrictor hormones are often simultaneously elevated in these patients. It is not known, however, whether atrial natriuretic factor remains responsive to sudden reductions in atrial pressure in patients with chronic heart failure, or is unresponsive like the vasoconstrictor systems. To examine this issue, the plasma concentrations of atrial natriuretic factor and the vasoconstrictor hormones were measured in 20 normal subjects and 12 patients with chronic congestive heart failure during incremental lower body negative pressure, an intervention that lowers atrial pressure. In the normal subjects, incremental lower body negative pressure at -10, -20 and -40 mm Hg decreased central venous pressure and pulse pressure. At maximal lower body negative pressure, plasma atrial natriuretic factor levels decreased from 51 +/- 5 to 27 +/- 3 pg/ml (p less than 0.01), whereas increases occurred in plasma levels of norepinephrine (194 +/- 11 to 385 +/- 70 pg/ml, p less than 0.01), renin activity (1.4 +/- 0.2 to 3.9 +/- 0.1 ng/ml per h, p less than 0.01) and vasopressin (1.3 +/- 0.1 to 6.4 +/- 2.4 pg/ml, p less than 0.05). In the patients with congestive heart failure, lower body negative pressure also reduced central venous pressure. Baseline plasma atrial natriuretic factor levels were markedly elevated, averaging 438 +/- 138 pg/ml, and decreased to 317 +/- 87 pg/ml at maximal lower body negative pressure (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Atrial natriuretic peptide in congestive heart failure in the dog: plasma levels, cyclic guanosine monophosphate, ultrastructure of atrial myoendocrine cells, and hemodynamic, hormonal, and renal effects

In an animal preparation of congestive heart failure in the dog, during the development of cardiac failure due to rapid right ventricular pacing we observed significant decreases in cardiac output and arterial pressure and increases in pulmonary arterial and right atrial pressure. We also observed a related increase in right atrial pressure and increases in plasma levels of atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (c-GMP). Ultrastructure changes in the atrial myoendocrine cells indicated extreme stimulation of the secretory apparatus of ANP. The response of hemodynamic, renal, and hormonal variables was investigated after incremental infusions (0.01, 0.03, 0.1, 0.3, and 0.06 microgram/kg/min) of exogenous ANP. In healthy animals ANP significantly decreased mean arterial pressure, cardiac output, stroke volume, and right atrial pressure without changing heart rate or peripheral vascular resistance. As expected, we found a striking increase in urine flow and urinary excretion of sodium, chloride, magnesium and calcium and a smaller increase in potassium excretion. ANP suppressed renin secretion, and increased renal plasma flow, glomerular filtration rate, and filtration fraction. In dogs with heart failure ANP caused a small reduction in mean arterial pressure. No effect was seen on other hemodynamic variables or plasma renin concentration. The excretory effects on the kidneys were completely absent, and smaller increases in glomerular filtration rate and filtration fraction were observed. We found no difference between healthy dogs and animals with heart failure with respect to the secretion of c-GMP during ANP infusions in relation to the plasma levels of ANP. This suggests an intracellular defect that prevents the mediation of the hormonal signal into biological action in the presence of heart failure.

Antihypertensive and hypotensive effects of atrial natriuretic factor in men

Synthetic atrial natriuretic factor (ANF) was administered in ascending doses (0.03, 0.20, 0.45 microgram/kg/min) to eight mildly essential hypertensive men on high (200 mEq/day) or low (10 mEq/day) sodium diets. Responses of blood pressure, heart rate, urinary volume and electrolyte excretion, renin, and aldosterone were measured. For the entire group, ANF lowered blood pressure and increased heart rate during the 0.20 and 0.45 microgram/kg/min infusions, and the antihypertensive effect of the peptide persisted for at least 2 hours after the infusions ended. Four patients (2 at 0.20 microgram/kg/min and 2 at 0.45 microgram/kg/min) experienced sudden bradycardia and hypotension at the end of or shortly after completion of ANF infusion. Renal excretion of water, sodium, chloride, calcium, and phosphorus increased in a dose-dependent fashion in response to infused ANF. Patients on the 200 mEq/day sodium diet had greater increases in urinary volume (11.1 +/- 2.8 vs 3.0 +/- 2.0 ml/min; p less than 0.05), sodium (870 +/- 134 vs 303 +/- 27 microEq/min; p less than 0.05), and chloride (801 +/- 135 vs 176 +/- 75 microEq/min; p less than 0.02) compared with patients on the low sodium diet. The apparent direct suppressive effect of a 0.03 microgram/kg/min infusion of ANF on renin and aldosterone levels was overcome at higher doses by counterregulation provoked by the depressor action. Renin was slightly (-12%) suppressed during the 0.03 microgram/kg/min infusion of ANF but increased at the 0.20 (+50%) and 0.45 microgram/kg/min (+90%; p less than 0.03) rates. Aldosterone declined significantly during the 0.03 microgram/kg/min infusion (-45%; p less than 0.01) of ANF but not during the two higher dose infusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Attenuation of reflex forearm vasoconstriction by alpha-human atrial natriuretic peptide in men

This study examined whether atrial natriuretic peptide (ANP) modulates reflex forearm vasoconstriction in humans. Synthetic alpha-human ANP (alpha-hANP) was infused at a rate of 0.03 microgram/kg/min in 8 healthy men (mean age 23 +/- 0.7 years, mean +/- SEM). The alpha-hANP decreased systolic blood pressure and central venous pressure (CVP) but did not significantly alter resting heart rate and forearm vascular resistance (FVR). The magnitudes of reflex increases in FVR during lower body negative pressure (LBNP) at -110, -20, and -40 mm Hg were less during infusion of alpha-ANP than those magnitudes during infusion of saline solution. The slope of the regression line relating changes in CVP and those in FVR was less during infusion of alpha-hANP than the slope during infusion of saline solution. Forearm vascular responses to intra-arterial infusion of norepinephrine at doses of 100, 200, and 500 ng/min did not significantly differ during infusion of alpha-hANP and saline solution. These results suggest that alpha-hANP attenuates cardiopulmonary baroreflex control of FVR in normal men.