Effect of atrial peptides on aldosterone production

Metabolic cues impact non-oscillatory intergeniculate leaflet and ventral lateral geniculate nucleus: standard versus high-fat diet comparative study

The intergeniculate leaflet and ventral lateral geniculate nucleus (IGL/VLG) are subcortical structures involved in entrainment of the brain's circadian system to photic and non-photic (e.g. metabolic and arousal) cues. Both receive information about environmental light from photoreceptors, exhibit infra-slow oscillations (ISO) in vivo, and connect to the master circadian clock. Although current evidence demonstrates that the IGL/VLG communicate metabolic information and are crucial for entrainment of circadian rhythms to time-restricted feeding, their sensitivity to food intake-related peptides has not been investigated yet. We examined the effect of metabolically relevant peptides on the spontaneous activity of IGL/VLG neurons. Using ex vivo and in vivo electrophysiological recordings as well as in situ hybridisation, we tested potential sensitivity of the IGL/VLG to anorexigenic and orexigenic peptides, such as cholecystokinin, glucagon-like peptide 1, oxyntomodulin, peptide YY, orexin A and ghrelin. We explored neuronal responses to these drugs during day and night, and in standard vs. high-fat diet conditions. We found that IGL/VLG neurons responded to all the substances tested, except peptide YY. Moreover, more neurons responded to anorexigenic drugs at night, while a high-fat diet affected the IGL/VLG sensitivity to orexigenic peptides. Interestingly, ISO neurons responded to light and orexin A, but did not respond to the other food intake-related peptides. In contrast, non-ISO cells were activated by metabolic peptides, with only some being responsive to light. Our results show for the first time that peptides involved in the body's energy homeostasis stimulate the thalamus and suggest functional separation of the IGL/VLG cells. KEY POINTS: The intergeniculate leaflet and ventral lateral geniculate nucleus (IGL/VLG) of the rodent thalamus process various signals and participate in circadian entrainment. In both structures, cells exhibiting infra-slow oscillatory activity as well as non-rhythmically firing neurons being observed. Here, we reveal that only one of these two groups of cells responds to anorexigenic (cholecystokinin, glucagon-like peptide 1 and oxyntomodulin) and orexigenic (ghrelin and orexin A) peptides. Neuronal responses vary depending on the time of day (day vs. night) and on the diet (standard vs. high-fat diet). Additionally, we visualised receptors to the tested peptides in the IGL/VLG using in situ hybridisation. Our results suggest that two electrophysiologically different subpopulations of IGL/VLG neurons are involved in two separate functions: one related to the body's energy homeostasis and one associated with the subcortical visual system.

MANP Activation Of The cGMP Inhibits Aldosterone Via PDE2 And CYP11B2 In H295R Cells And In Mice

BACKGROUND

Aldosterone is a critical pathological driver for cardiac and renal diseases. We recently discovered that mutant atrial natriuretic peptide (MANP), a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP in vivo. MANP and natriuretic peptide (NP)-augmenting therapy sacubitril/valsartan are under investigations for human hypertension treatment. Understanding the elusive mechanism of aldosterone inhibition by NPs remains to be a priority. Conflicting results were reported on the roles of the pGC-A (particulate guanylyl cyclase A receptor) and NP clearance receptor in aldosterone inhibition. Furthermore, the function of PKG (protein kinase G) and PDEs (phosphodiesterases) on aldosterone regulation are not clear.

METHODS

In the present study, we investigated the molecular mechanism of aldosterone regulation in a human adrenocortical cell line H295R and in mice.

RESULTS

We first provided evidence to show that pGC-A, not NP clearance receptor, mediates aldosterone inhibition. Next, we confirmed that MANP inhibits aldosterone via PDE2 (phosphodiesterase 2) not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer experiments. Further, the inhibitory effect is mediated by a reduction of intracellular Ca2+ levels. We then illustrated that MANP directly reduces aldosterone synthase CYP11B2 (cytochrome p450 family 11 subfamily b member 2) expression via PDE2. Last, in PDE2 knockout mice, consistent with in vitro findings, embryonic adrenal CYP11B2 is markedly increased.

CONCLUSIONS

Our results innovatively explore and expand the NP/pGC-A/3',5', cyclic guanosine monophosphate (cGMP)/PDE2 pathway for aldosterone inhibition by MANP in vitro and in vivo. In addition, our data also support the development of MANP as a novel ANP analog drug for aldosterone excess treatment.

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.

Aldosterone-Regulated Sodium Transport and Blood Pressure

Aldosterone is a major mineralocorticoid steroid hormone secreted by glomerulosa cells in the adrenal cortex. It regulates a variety of physiological responses including those to oxidative stress, inflammation, fluid disruption, and abnormal blood pressure through its actions on various tissues including the kidney, heart, and the central nervous system. Aldosterone synthesis is primarily regulated by angiotensin II, K⁺ concentration, and adrenocorticotrophic hormone. Elevated serum aldosterone levels increase blood pressure largely by increasing Na⁺ re-absorption in the kidney through regulating transcription and activity of the epithelial sodium channel (ENaC). This review focuses on the signaling pathways involved in aldosterone synthesis and its effects on Na⁺ reabsorption through ENaC.

First-in-Human Study of MANP: A Novel ANP (Atrial Natriuretic Peptide) Analog in Human Hypertension

[Figure: see text].

NO mediates the effect of the synthetic natriuretic peptide NPCdc on kidney and aorta in nephrectomised rats

NPCdc is a synthetic natriuretic peptide that was originally derived from another peptide, the NP2_Casca, isolated from Crotalus durissus cascavella venom. These molecules share 70% structural homology with natriuretic peptides obtained from different species, including humans. NP2_Casca induces vasorelaxation and increases nitric oxide levels independently of natriuretic peptide receptors A and B. This study aimed to investigate whether NPCdc-induced hypotension in control rats and rats with a reduced kidney mass is associated with effects on the glomerular filtration rate, NADPH oxidase activity and components downstream of natriuretic peptide receptor C (NPR-C). Anaesthetized Wistar rats that were subjected to a sham operation and 5/6 nephrectomy (5/6Nx) were infused with saline (vehicle) or NPCdc (7.5 μg/kg/min) for 70 min. The NPCdc treatment decreased the mean arterial pressure and NADPH oxidase activity while simultaneously increasing the glomerular filtration rate, fractional Na⁺ excretion and nitric oxide level. After 70 min, the levels of p-AKT ^Ser-473, p-eNOS ^Ser-1177, p-nNOS ^Ser-1417 and p-iNOS^Tyr-151 were not affected. However, p-ERK1/2 ^{Thr-202/Tyr-204} levels were altered. Thus, nitric oxide and components of NPR-C signalling mediate the effects of NPCdc. The results suggest a potential therapeutic application of this peptide for cardiorenal syndrome.

Neprilysin Inhibition and the Treatment of Heart Failure: Recent Steps in the Right Direction

Numerous investigators have attempted to target the natriuretic peptide system in the treatment of heart failure since it was first described over 30 years ago. The history of neprilysin inhibition as a treatment for heart failure has been characterized by numerous setbacks. Recently, the PARADIGM-HF trial has shown favorable results, which may bring neprilysin inhibition into the mainstream of clinical practice. This article will review the history of the natriuretic peptide system and the investigations into it as a target for heart failure treatment, culminating in the positive results of the PARADIGM-HF trial, as well as planned and potential future directions for research.

Therapeutic options of Angiotensin Receptor Neprilysin inhibitors (ARNis) in chronic heart failure with reduced ejection fraction: Beyond RAAS and sympathetic nervous system inhibition

In heart failure, in addition to the renin-angiotensin-aldosterone system and sympathetic nervous system, the natriuretic peptide (NP) system plays a fundamental role among compensating mechanisms. The NPs undergo rapid enzymatic degradation that limits their vasorelaxant, natriuretic, and diuretic actions. Degradation of NPs is partially due to the action of neprilysin, which is a membrane-bound endopeptidase found in many tissues. This article summarizes recent findings on a new natriuretic peptide-enhancing drug and their implication for future pharmacological treatment of patients suffering from heart failure with reduced ejection fraction.

Natriuretic peptides and cardio-renal disease

The natriuretic peptide (NP) system is an important endocrine, autocrine and paracrine system, consisting of a family of peptides which provide cardiac, renal and vascular effects that, through their beneficial physiological actions, play a key role in maintaining overall cardiovascular health. Traditionally, the pathophysiological origins of cardio-renal disease have been viewed as the domain of the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system (SNS), with inappropriate activation of both systems leading to deleterious changes in cardio-renal function and structure. Therapies designed to suppress the RAAS and the SNS have been routinely employed to address the consequences of cardio-renal disease. However, it is now becoming increasingly apparent that enhancing the beneficial physiological effects of the NP system may represent an attractive alternative therapeutic approach to counter the pathophysiological effects of disease. In particular, innovative therapeutic strategies aimed at enhancing the physiological benefits afforded by NPs while simultaneously suppressing the RAAS are generating increasing interest as potential treatment options for the management of cardio-renal disease.

Salinity-dependent in vitro effects of homologous natriuretic peptides on the pituitary-interrenal axis in eels

We examined the effects of atrial, B-type, ventricular and C-type natriuretic peptides (ANP, BNP, VNP and CNP1, 3, 4) on cortisol secretion from interrenal tissue in vitro in both freshwater (FW) and seawater (SW)-acclimated eels. We first localized the interrenal and chromaffin cells in the eel head kidney using cell specific markers (cholesterol side-chain cleavage enzyme (P450ssc) and tyrosine hydroxylase (TH), respectively) and established the in vitro incubation system for eel interrenal tissue. Unexpectedly, none of the NPs given alone to the interrenal tissue of FW and SW eels stimulated cortisol secretion. However, ANP and VNP, but not BNP and three CNPs, enhanced the steroidogenic action of ACTH in SW interrenal preparations, while CNP1 and CNP4, but not ANP, BNP, VNP and CNP3, potentiated the ACTH action in FW preparations. These salinity dependent effects of NPs are consistent with the previous in vivo study in the eel where endogenous ACTH can act with the injected NPs. 8-Br-cGMP also enhanced the ACTH action in both FW and SW eel preparations, suggesting that the NP actions were mediated by the guanylyl cyclase-coupled NP receptors (GC-A and B) that were localized in the eel interrenal. Further, ANP and CNP1 stimulated ACTH secretion from isolated pituitary glands of SW and/or FW eels. In summary, the present study revealed complex mechanisms of NP action on corticosteroidogenesis through the pituitary-interrenal axis in eels, thereby providing a deeper insight into the role of the NP family in the acclimation of this euryhaline teleost to diverse salinity environments.

A novel atrial natriuretic peptide based therapeutic in experimental angiotensin II mediated acute hypertension

M-atrial natriuretic peptide (ANP; M-ANP) is a novel next generation 40 amino acid peptide based on ANP, which is highly resistant to enzymatic degradation and has greater and more sustained beneficial actions compared with ANP. The current study was designed to advance our understanding of the therapeutic potential of M-ANP in a canine model of acute angiotensin II-induced hypertension with elevated cardiac filling pressures and aldosterone activation. We compare M-ANP with vehicle and equimolar human B-type natriuretic peptide, which possesses the most potent in vivo actions of the native natriuretic peptides. M-ANP significantly lowered mean arterial pressure and systemic vascular resistance. Importantly, despite a reduction in blood pressure, renal function was enhanced with significant increases in renal blood flow, glomerular filtration rate, diuresis, and natriuresis after M-ANP infusion. Although angiotensin II induced an acute increase in pulmonary capillary wedge pressure, M-ANP significantly lowered pulmonary capillary wedge pressure, pulmonary artery pressure, and right atrial pressure. Further, M-ANP significantly suppressed angiotensin II-induced activation of aldosterone. These cardiovascular and renal enhancing actions of M-ANP were accompanied by significant increases in plasma and urinary cGMP, the second messenger molecule of the natriuretic peptide system. When compared with human B-type natriuretic peptide, M-ANP had comparable cardiovascular actions but resulted in a greater natriuretic effect. These results suggest that M-ANP, which is more potent than ANP in normal canines, has potent blood pressure lowering and renal enhancing properties and may, therefore, serve as an ANP based therapeutic for acute hypertension.

Molecular classification of an elasmobranch angiotensin receptor: quantification of angiotensin receptor and natriuretic peptide receptor mRNAs in saltwater and freshwater populations of the Atlantic stingray

Among the most conserved osmoregulatory hormone systems in vertebrates are the renin-angiotensin system (RAS) and the natriuretic peptides (NPs). We examined the RAS and NP system in the euryhaline Atlantic stingray, Dasyatis sabina (Lesueur). To determine the relative sensitivity of target organs to these hormonal systems, we isolated cDNA sequences encoding the D. sabina angiotensin receptor (AT) and natriuretic peptide type-B receptor (NPR-B). We then determined the tissue-specific expression of their mRNAs in saltwater D. sabina from local Texas waters and an isolated freshwater population in Lake Monroe, Florida. AT mRNA was most abundant in interrenal tissue from both populations. NPR-B mRNA was most abundant in rectal gland tissue from both populations, and also highly abundant in the kidney of saltwater D. sabina. This study is the first to report the sequence of an elasmobranch angiotensin receptor, and phylogenetic analysis indicates that the D. sabina receptor is more similar to AT(1) vs. AT(2) proteins. This classification is further supported by molecular analysis of AT(1) and AT(2) proteins demonstrating conservation of AT(1)-specific amino acid residues and motifs in D. sabina AT. Molecular classification of the elasmobranch angiotensin receptor as an AT(1)-like protein provides fundamental insight into the evolution of the vertebrate RAS.

A human atrial natriuretic peptide gene mutation reveals a novel peptide with enhanced blood pressure-lowering, renal-enhancing, and aldosterone-suppressing actions

OBJECTIVES

We sought to determine the physiologic actions and potential therapeutic applications of mutant atrial natriuretic peptide (mANP).

BACKGROUND

The cardiac hormone atrial natriuretic peptide (ANP) is a 28-amino acid (AA) peptide that consists of a 17-AA ring structure together with a 6-AA N-terminus and a 5-AA C-terminus. In a targeted scan for sequence variants within the human ANP gene, a mutation was identified that results in a 40-AA peptide consisting of native ANP((1-28)) and a C-terminal extension of 12 AA. We have termed this peptide mutant ANP.

METHODS

In vitro 3',5'-cyclic guanosine monophosphate (cGMP) activation in response to mANP was studied in cultured human cardiac fibroblasts known to express natriuretic peptide receptor A. The cardiorenal and neurohumoral properties of mANP compared with ANP were assessed in vivo in normal dogs.

RESULTS

We observed an incremental in vitro cGMP dose response with increasing concentrations of mANP. In vivo with high-dose mANP (33 pmol/kg/min), we observed significantly greater plasma cGMP activation, diuretic, natriuretic, glomerular filtration rate enhancing, renin-angiotensin-aldosterone system inhibiting, cardiac unloading, and blood pressure lowering properties when compared with native ANP. Low-dose mANP (2 pmol/kg/min) has natriuretic and diuretic properties without altering systemic hemodynamics compared with no natriuretic or diuretic response with low-dose native ANP.

CONCLUSIONS

These studies establish that mANP activates cGMP in vitro and exerts greater and more sustained natriuretic, diuretic, glomerular filtration rate, and renal blood flow enhancing actions than native ANP in vivo.

Atrial natriuretic peptide production and natriuretic peptide receptors in the human uterus and their effect on myometrial relaxation

OBJECTIVE

The objective of the study was to identify the effect of atrial natriuretic peptide (ANP) on uterine contractility, production of ANP, and natriuretic peptide receptor (NPR) expression in human myometrial tissue.

STUDY DESIGN

In an institutional review board-approved study, gravid human myometrium was obtained from patients undergoing cesarean section. Uterine contractility was examined using isometric force tension studies. After regular uterine contractions were obtained with oxytocin, ANP was added in increasing concentrations. ANP concentration was measured from myometrial tissue using radioimmunoassay (RIA). Primary myometrial cell culture was performed and treated with nifedipine vs oxytocin. RIA was performed on these cells and the cell culture media. Western blot analysis was performed on uterine tissue samples for natriuretic peptide receptors.

RESULTS

With increasing concentration of ANP (starting at 3 pM), myometrial contraction frequency decreased. ANP was identified in primary cultured myometrial cells and cell culture media. Myometrial ANP concentration increased with advancing gestational age. The concentration of ANP decreased within myometrial cells treated with oxytocin. The amount of ANP in the cell culture media increased from cells treated with nifedipine. Western blot identified NPR-A, -B, and -C in myometrial tissue. NPR-A expression was significantly increased in preterm samples.

CONCLUSION

ANP has a dose dependent effect on uterine relaxation. ANP is present in human myometrial cells and appears to be secreted by myometrial cells. The concentration of ANP may vary with gestational age and modulators of uterine contractility. NPR-A, -B, and -C receptor proteins are present in myometrial tissue. NPR-A levels may correlate with gestational age.

Comparison of N-terminal pro-brain natriuretic peptide versus electrophysiologic study for predicting future outcomes in patients with an implantable cardioverter defibrillator after myocardial infarction

The aim of the study was to examine the predictive value of N-terminal pro-brain natriuretic peptide (NT-pro-BNP) versus electrophysiologic study in patients with implantable cardioverter-defibrillators (ICDs) after myocardial infarction (MI). We prospectively studied 99 consecutive patients with a history of MI who underwent ICD implantation for primary or secondary prevention of sudden cardiac death. An electrophysiologic study was performed in all patients. Venous blood samples for NT-pro-BNP measurement were obtained at the beginning of the study. The primary end point was ventricular tachycardia or ventricular fibrillation (VT/VF) and the secondary end point was a composite of death, hospitalization for heart failure, or MI. On multivariate Cox regression analysis, NT-pro-BNP level at or greater than median (497 ng/L) was the only significant predictor for VT/VF occurrence (p = 0.047). Along with amiodarone use (p = 0.001), NT-pro-BNP levels higher than median were also associated with a higher risk of composite clinical events (p = 0.036). Kaplan-Meier analysis showed that patients with NT-pro-BNP level at or greater than median had a higher risk of experiencing VT/VF and composite clinical events than patients with NT-pro-BNP levels less than median (log-rank p <0.05). In conclusion, assay of NT-pro-BNP, which is easy to perform and widely available, is superior to electrophysiologic study for prediction of future outcomes in predominantly secondary prophylactic ICD recipients after MI. In the era of primary prophylactic ICD implantation without preimplantation electrophysiologic study, higher NT-pro-BNP levels might help to improve risk-adjusted concomitant antiarrhythmic therapy and device selection.

B-type natriuretic peptide measurement in heart failure

Serum testing for the hormone B-type natriuretic peptide (BNP) may have clinical utility in congestive heart failure (CHF). This hormone is secreted predominantly by the left ventricular myocardium in patients with CHF. Measurement of serum BNP may improve diagnosis of CHF and may also help guide therapy in patients with CHF. The literature regarding the clinical utility of BNP measurement in CHF is reviewed.

B-type natriuretic peptide in cardiovascular disease

Natriuretic peptide hormones, a family of vasoactive peptides with many favourable physiological properties, have emerged as important candidates for development of diagnostic tools and therapeutic agents in cardiovascular disease. The rapid incorporation into clinical practice of bioassays to measure natriuretic peptide concentrations, and drugs that augment the biological actions of this system, show the potential for translational research to improve patient care. Here, we focus on the physiology of the natriuretic peptide system, measurement of circulating concentrations of B-type natriuretic peptide (BNP) and the N-terminal fragment of its prohormone (N-terminal BNP) to diagnose heart failure and left ventricular dysfunction, measurement of BNP and N-terminal BNP to assess prognosis in patients with cardiac abnormalities, and use of recombinant human BNP (nesiritide) and vasopeptidase inhibitors to treat heart failure.

Role of brain natriuretic peptide in the diagnosis and management of heart failure: current concepts

BACKGROUND

Progression of heart failure is related to ventricular remodeling, a process associated to neurohormonal activation. Brain natriuretic peptide (BNP), a member of the natriuretic peptide family, has recently emerged as an important neurohormone in the pathophysiology of heart failure.

METHODS

In this update, some of the recent advances on the role of BNP in heart failure are summarized. In particular, the role of BNP in diagnosis of heart disease, as a prognostic marker of cardiovascular events and as a possible guide to optimize heart failure therapy is discussed.

RESULTS

Recent results from 4,300 patients enrolled in the Valsartan Heart Failure Trial (Val-HeFT) confirmed that BNP is the strongest predictor of outcome in heart failure, when compared to other neurohormones and clinical markers. The current use of BNP in the screening and diagnosis of heart failure and its possible future roles are presented.

CONCLUSION

In recent years, there has been an impressive accumulation of data supporting an important role of BNP as a diagnostic and prognostic marker of heart failure. Development of rapid, accurate and affordable diagnostic methods will allow the routine monitoring of BNP in a wide spectrum of settings, from general practice to controlled clinical trials.

A review of vasopeptidase inhibitors: a new modality in the treatment of hypertension and chronic heart failure

Vasopeptidase inhibitors are a group of agents capable of inhibiting neutral endopeptidase and angiotensin-converting enzymes, which leads to potentiation of natriuretic peptide actions and suppression of the renin-angiotensin-aldosterone system. With this distinctively characteristic mechanism, these agents have emerged as a new drug class for management of hypertension and heart failure. Several vasopeptidase inhibitors are under clinical investigation. Omapatrilat is the most studied agent in this class. Clinical studies of omapatrilat in hypertension have consistently shown the agent's effectiveness in a variety of patient populations. In patients with heart failure, omapatrilat significantly improved neurohormonal and hemodynamic status. Long-term effects of omapatrilat in patients with heart failure recently were compared with those of conventional therapy in a large phase II trial. Results of the study appear promising. Large clinical trials are ongoing, and additional information regarding safety and efficacy from these studies may help define the place in therapy for this agent.

Hypothalamic atrial natriuretic peptide and secretion of oxytocin

Our study corroborated previous findings on the distribution of ANP and co-localization of ANP and OT in hypothalamic magnocellular neurons. We detected ANP/OT in smaller cells which apparently corresponded to parvocellular neurons and additionally a massive group of ANP immunoreactive fibers from periventricular regions to the median eminence, here closely associated with oxytocinergic fibers originated from PVN. ANP immunoneutralization did not change the basal OT level but blocked the OT secretion normally induced by osmotic stimulus. Thus, endogenous hypothalamic ANP seems necessary to stimulate OT release in the hyperosmolality condition.

Angiotensin II and aldosterone regulation

The circulating renin-angiotensin system is a major regulator of the secretion of the adrenocortical hormone, aldosterone. This renin-angiotensin aldosterone system is important in the control of salt and water balance and blood pressure. This review describes the historical background leading to the discovery of aldosterone in the 1950s and the recognition in the 1960s that angiotensin II was involved in its control. Although angiotensin II is important in the regulation of aldosterone secretion, its action is influenced by multiple other factors, especially potassium and atrial natriuretic peptide. In addition to the circulating renin-angiotensin system, a local renin-angiotensin system is present in the zona glomerulosa cell. This local system also appears to be involved in the regulation of aldosterone production. The mechanism by which angiotensin II stimulates the adrenal zona glomerulosa cell is described in some detail. Angiotensin II interacts with the angiotensin receptor (AT1) membrane receptor that is coupled to cellular second messengers. Specific AT1 receptor antagonists are now clinically used to block angiotensin II's action on various target organs, including the adrenal gland.

Natriuretic peptides: physiology, therapeutic potential, and risk stratification in ischemic heart disease

BACKGROUND

The natriuretic peptide family consists of four molecules that share significant amino acid sequence homologic characteristics and a looped motif. Atrial natriuretic peptide and brain natriuretic peptide are similar in their ability to promote natriuresis and diuresis, inhibit the renin-angiotensin-aldosterone axis, and act as vasodilators. Understanding of the actions of C-type natriuretic peptide and dendroaspis natriuretic peptide is incomplete, but these two new family members also act as vasodilators. Because of the rapid evolution of information about this peptide family, we reviewed the state of the art with respect to risk stratification and therapeutic ability.

METHODS

English-language papers were identified by a MEDLINE database search covering 1966 through 1997 and supplemented with bibliographic references and texts.

CONCLUSIONS

The natriuretic peptides are counterregulatory hormones with prognostically important levels. They are similarly upregulated in heart failure and counteract neurohormones that induce vasoconstriction and fluid retention. BNP may be the superior prognosticator for risk stratification after myocardial infarction and is independent of left ventricular ejection fraction. Lastly, experimental trials suggest that administration of exogenous natriuretic peptides or inhibitors of their catabolism to patients with ischemic heart disease may be clinically beneficial.

Natriuretic response to the combination of atrial natriuretic peptide and terlipressin in patients with cirrhosis and refractory ascites

BACKGROUND/AIMS

Refractory ascites, which occurs in certain patients with cirrhosis, is associated with a blunted natriuretic response to exogenous atrial natriuretic peptide (ANP). Since this blunting seems to be related to ANP-induced arterial hypotension, a vasoconstrictor, such as terlipressin (a vasopressin analogue), may restore natriuresis to exogenous ANP. Moreover, since cirrhosis-elicited vasodilation is thought to play a role in sodium retention, a vasoconstriction caused by terlipressin alone may lead to an increase in sodium excretion. This study aimed to evaluate the natriuretic response to either a combination of ANP with terlipressin or terlipressin alone in patients with cirrhosis and refractory ascites.

METHODS

Sixteen consecutive patients with cirrhosis and refractory ascites were randomly assigned to receive either a combination of terlipressin (1-2 mg, i.v. bolus) with ANP (35 ng/kg, i.v. bolus followed by 15 ng x kg(-1) x min(-1) for 60 min) (n=8) or terlipressin alone (1-2 mg, i.v. bolus) (n=8). Sodium excretion and urine output, systemic, splanchnic and renal hemodynamics and renal oxygen consumption were measured before and during treatments.

RESULTS

Combined therapy did not change arterial pressure but significantly increased urinary sodium excretion and urine output. These effects were associated with a significant increase in glomerular filtration rate and a decrease in renal oxygen consumption. Terlipressin alone significantly increased arterial pressure but did not change urinary sodium excretion or urine output. Moreover, terlipressin did not change either glomerular filtration rate or renal oxygen consumption.

CONCLUSIONS

The combination of exogenous ANP with terlipressin, but not terlipressin alone, increases sodium excretion in patients with cirrhosis and refractory ascites.

An ecdysiostatin from flies

A bioassay for compounds with ecdysiostatic activity ('ecdysiostatins') was developed in order to prove the existence of an ecdysiostatin in blowfly larvae. The factor eluted by HPLC like Neb-TMOF (trypsin modulating oostatic factor), a hexapeptide that inhibits ecdysone biosynthesis. The ecdysiostatic activity of Neb-TMOF is specific, related peptides were less active or inactive. TMOF inhibits ecdysone biosynthesis rather than its secretion. It increases the cAMP level of ring glands. Effectors that elevate the intracellular cAMP can mimic the inhibitory effect of the ecdysiostatin. This suggests that cAMP may control steroidogenesis in fly larvae by shutting ecdysone biosynthesis. Thus, the hexapeptide acts as a prothoracicostatic hormone (PTSH) that controls ecdysone biosynthesis.

Relation of left atrial volume and systolic function to the hormonal response in idiopathic dilated cardiomyopathy

We studied the relation of left atrial mechanical function to the hormonal response in 14 patients with idiopathic dilated cardiomyopathy. Left atrial volumes were echocardiographically measured at mitral valve opening (maximal), at onset of atrial systole (onset of the P wave of the electrocardiogram) and at mitral valve closure (minimal) from the apical 2- and 4-chamber views using the biplane area-length method. Left atrial systolic function was assessed with the left atrial active emptying fraction ([volume at onset of atrial systole-minimal]/[volume at onset of atrial systole]). Plasma renin activity, aldosterone and atrial natriuretic peptide plasma levels were determined using commercially available kits. Left atrial maximal volume was directly, and left atrial active emptying fraction was inversely related to plasma renin activity (r = 0.60, P = 0.02 and r = -0.59, P = 0.026, respectively), aldosterone (r = 0.61, P = 0.02 and r = -0.53, P = 0.048) and atrial natriuretic factor (r = 0.79, P = 0.0009 and r = -0.62, P = 0.01) plasma levels. Thus, increased left atrial size and depressed left atrial contractile performance are associated with increased hormonal response in idiopathic dilated cardiomyopathy.

Atrial natriuretic peptide concentrations in children with pulmonary hypertension: correlation with hemodynamic measurements

To define the relation between atrial natriuretic peptide (ANP) and hemodynamic parameters in children with pulmonary artery hypertension, we measured the ANP concentrations of the femoral vein, right atrium, pulmonary artery, left atrium and left ventricle, or femoral artery in 32 patients during right or left heart catheterization. There is a strong correlation among the ANP levels obtained from different locations (p < 0.001), and these ANP levels are positively correlated with pulmonary arterial pressures and pulmonary resistance. Patients were divided into two groups according to their pulmonary arterial pressure. The group with pulmonary arterial systolic pressure higher than 31 mmHg had higher ANP levels than the group with pulmonary arterial systolic pressure lower than 31 mmHg. When patients were grouped according to their pulmonary resistance, ANP levels in the group with pulmonary resistance over 2 U/m2 were higher than those in the group with pulmonary resistance lower than 2 U/m2. In this study ANP levels showed a correlation with the right ventricular systolic pressure. A correlation was not seen between ANP levels and the flow ratios or the presence of shunt. The results of our study suggest that ANP should be considered an important factor in pulmonary hypertension, independent of other factors.

Inhibition of ecdysone biosynthesis in flies by a hexapeptide isolated from vitellogenic ovaries

The only identified insect peptides known to be involved in controlling the biosynthesis of ecdysone, the steroid moulting hormone of arthropods, are the prothoracicotropic hormones (PTTH). These neuropeptides stimulate ecdysone biosynthesis. Recently, a hexapeptide (NPTNLH) with folliculostatic and trypsin modulating activity was isolated from vitellogenic ovaries of the fleshfly Neobellieria bullata. Here we report that the hexapeptide, when tested in vitro on the isolated ring gland of flies, inhibited ecdysone biosynthesis immediately and completely (EC50 = 5 nM). The hexapeptide is the first known factor with 'prothoracicostatic activity' and may form part of the endocrine system that controls ecdysone biosynthesis in vivo.

Plasma levels of atrial natriuretic peptide and hemodynamic function in cardiac disease

Plasma concentrations of atrial natriuretic peptide were measured in eight patients with cardiac disease but normal resting right atrial pressure, during cardiac catheterization. No patient had clinical evidence of overt heart failure. An increase in peptide concentrations was observed between the aorta or the peripheral vein and the pulmonary artery. A linear relation was found between peripheral vein and pulmonary artery peptide concentration. Mean pulmonary artery and capillary wedge pressure also correlated with the peptide levels. No correlation was observed between mean right atrial pressure and peptide concentration. These findings demonstrate that atrial natriuretic peptide release, even in the absence of cardiac failure, seems at least partly regulated by left atrial pressure. Finally, peripheral levels reflect the central concentrations of atrial natriuretic peptide.

Inhibition of the aldosterone-suppressant activity of atrial natriuretic factor by progesterone and pregnancy in rats

Angiotensin II (AII) caused concentration-dependent increase in aldosterone secretion by dispersed zona glomerulosa cells from non-ovariectomized (non-OVX) and ovariectomized (OVX) rats treated with the vehicle (peanut oil), beta-estradiol (0.1 mg/kg/d x 3) or progesterone (2 mg/kg/d x 3); this effect of AII was greater on cells from progesterone- than from estrogen-treated animals. In contrast, atrial natriuretic factor (ANF) was 100- to 1,000-fold less effective in suppressing AII-stimulated aldosterone production by cells from progesterone-treated (both non-OVX and OVX) and pregnant (17-20 day) rats than by cells from nonpregnant controls and estrogen-treated animals. To our knowledge, this is the first demonstration of an inhibition of an important action of ANF by another hormone and our data suggest that increased circulating levels of progesterone during pregnancy produce a relative refractoriness to the aldosterone-suppressant activity of ANF, which favors fluid/salt expansion.

Atrial natriuretic peptide in severe heart failure: response to controlled changes in atrial pressures during intravenous nitroglycerin therapy

Atrial natriuretic peptide (ANP) levels were measured in 17 patients with severe congestive heart failure (New York Heart Association functional class IV), and the response of the peptide was studied during changes in cardiac filling pressures induced by a 24-hour infusion of nitroglycerin. In the control state plasma ANP levels (687 +/- 551 pg/ml) were 10-fold normal. During the administration of nitroglycerin, natriuretic peptide levels decreased (p less than 0.005) with changes matching very closely the decreases in pulmonary arterial wedge and right atrial pressures, a 1% mean decrease in the peptide level for every 1.5 to 2% mean change in atrial filling pressures. In patients with hemodynamic tolerance to constant-dose nitroglycerin infusion, the resulting increase in atrial pressures was accompanied by an appropriate secondary increase in the plasma ANP level. During the 24-hour study period there was a direct linear relationship between both wedge (r = 0.93, p = 0.007) and right atrial (r = 0.93, p = 0.008) pressures and the plasma ANP level, with a zero-pressure ANP intercept near normal (69 pg/ml for wedge, 174 pg/ml for right atrial pressure). The findings were no different in a subgroup of five patients receiving simultaneous treatment with captopril, except that plasma renin activity was higher and the aldosterone level lower than in the control group by a factor of approximately 2.5. The close relationship and tracking of atrial pressure and natriuretic peptide curves suggested that the sensitivity of the atrial stretch response to changes in atrial filling pressures was maintained in severe congestive heart failure.

Atrial natriuretic peptide-induced inhibition of aldosterone secretion: a quest for mediator(s)

Atrial natriuretic peptide (ANP) inhibits aldosterone secretion evoked by its physiological secretagogues by a mechanism(s) likely to involve intracellular messengers. When one examines the results of various investigations so far, this premise, although not definitive yet, seems to be supported. Therefore a brief perspective on the cellular messengers of the various secretagogues is provided before the inquiry into the possible mechanism of action of ANP. The receptors of ANP in the adrenal cells have been identified and characterized. ANP inhibits adenylate cyclase in various tissues through an inhibitory G protein, which appears to explain in part the inhibitory effect of ANP on adrenocorticotropin-induced aldosterone secretion. However, there could be other possible effects of ANP as discussed. ANP probably inhibits aldosterone secretion evoked by angiotensin II and potassium by interfering with the appropriate changes in calcium flux and cell calcium concentration, concomitants of stimulation by these secretagogues. The potential modes of these effects are probed. The role of guanosine 3',5'-cyclic monophosphate, which is increased by receptor activation of guanylate cyclase by ANP and is thought to play a major role in the biological effects of ANP in some other tissues, remains controversial in the aldosterone-lowering effect of ANP, and this is also discussed extensively in this review.

Cardiovascular and hormonal responses to ANP infusion in the guinea-pig: effects of angiotensin-converting enzyme inhibition with perindopril

In the guinea-pig, perindopril inhibited plasma angiotensin converting enzyme (ACE) by 90% when given orally at 2 mg/kg/day during 10 days. Mean blood pressure and plasma aldosterone, cortisol and vasopressin concentrations were not modified by this treatment, while plasma renin activity (PRA) and plasma angiotensin I concentrations increased significantly. The same parameters were studied using a constant intravenous 30 min-infusion of atrial natriuretic peptide (ANP) (0.1 micrograms.kg-1min-1). This dose of ANP infused to anesthetized guinea-pigs induced a significant decrease in mean blood pressure (about -20%) in control and in perindopril treated animals. In ANP infused animals, plasma aldosterone and cortisol concentrations decreased similarly in both groups by about -50%, whereas plasma vasopressin concentrations increased in controls (+169%) but not in perindopril treated guinea-pigs. An increase in PRA and plasma angiotensin I concentrations was observed in both groups after the infusion of ANP. Thus, when ANP demonstrated an potent hypotensive effect a concomitant increase in PRA occurred. The rise observed in vasopressin concentration in control animals was probably mediated by angiotensin II. The fall in plasma aldosterone and cortisol concentrations observed after ANP infusion demonstrated a direct potent action of ANP at the adrenal levels.

Effects of atrial natriuretic factor on corticosteroid and catecholamine secretion by the adrenals of Xenopus laevis

The effects of atrial natriuretic factor (ANF) on the adreno-corticosteroid and catecholamine secretion of Xenopus laevis were studied in vitro and in vivo. In vitro, the effects of rANF(99-126), from 0.1 to 50 nM, on corticosteroid secretion was investigated using a perifusion system. The basal secretion of aldosterone but not corticosterone was dose dependently decreased. A prolonged perifusion with 1 nM rANF(99-126) alternated ACTH(1-28) stimulation of secretion of both corticosteroids. Only ANF analogues with intact disulfide bridges (rANF(99-126), hANF(99-126), Atriopeptin II, frogANF(21)), and an extract of Xenopus laevis hearts significantly inhibited aldosterone release; the N-terminal (99-109) and the C-terminal ANF(116-126) fragments had no effects. In vitro norepinephrine (NE) and epinephrine (E) were released but dopamine (D) was not detected. rANF(99-126) at concentrations up to 1 microM affected neither basal nor acetylcholine stimulated catecholamine secretion. In vivo, a single injection of 3 nmol rANF(99-126) per 100 g body weight was given and the serum concentrations of corticosterone, aldosterone, D, NE, and E were determined 1, 3, 6, 12, and 24 hr later. Both steroids decreased after 12 hr, whereas the catecholamine concentrations were not significantly changed. ANF is concluded to act on steroidogenic but not chromaffin cells in Xenopus laevis.

Regulation of adrenal atrial natriuretic hormone receptor subtypes

Regulation of atrial natriuretic hormone (ANH) receptor binding and aldosterone suppression was studied in isolated adrenal glomerulosa cells from rats fed a high-salt (HS) or low-salt (LS) diet for 3 days. In plasma of HS rats, aldosterone levels were 5 times lower and immunoreactive ANH two times higher than in LS rats. Competitive binding studies showed the same affinity for human atrial natriuretic hormone (hANH) in both pools of cells, but receptor density was 50% higher on LS cells. A linear ANH analog that binds to non-guanylate-cyclase-coupled receptors did not show increased binding to LS cells. Cyclic GMP production in response to hANH was identical in both groups. The aldosterone-inhibitory effect of hANH on both groups of basal and angiotensin II-stimulated cells was also identical. Thus a short-term high-salt diet causes decreased density of ANH receptors in glomerulosa cells without changing biological activity of ANH. These results suggest that dietary salt content changes the number of ANH receptors and that non-guanylate-cyclase-coupled receptors contain at least two classes of receptors.

Atrial natriuretic factor inhibits metoclopramide stimulated aldosterone release in man

1. Atrial natriuretic factor (ANF) has an inhibitory effect on angiotensin II and ACTH stimulated aldosterone secretion in man. The selectivity of this aldosterone suppressing effect of ANF is unclear in man. The present study investigated the effect of ANF on the increase in plasma aldosterone due to metoclopramide in man. 2. Eight normal male volunteers were studied on three occasions. Metoclopramide (10 mg slow i.v.) was given on all study days and each volunteer was randomised to receive 45 min infusion of either 5% D-glucose (placebo) or ANF (99-126) 3 or 15 pmol kg-1 min-1. 3. Metoclopramide increased plasma aldosterone to approximately 170% of baseline levels (P less than 0.01). Concomitant infusion of ANF 3 pmol kg-1 min-1 and 15 pmol kg-1 min-1 significantly attenuated this rise in plasma aldosterone to approximately 130% (P less than 0.05) and 110% (P less than 0.01) of baseline values respectively. 4. It is suggested, in the light of previous findings, that the inhibitory effect of ANF represents a non-selective action of ANF on aldosterone release.

Prolonged neutral endopeptidase inhibition in heart failure

We studied the hormonal, renal and hemodynamic effects of prolonged treatment with SCH 39370, a new neutral endopeptidase (NEP) inhibitor, in experimental congestive heart failure (CHF). Coronary-ligated CHF rats and sham-operated controls received vehicle or SCH 39370 30 mg/kg s.c. twice daily for six days. In rats with heart failure, SCH 39370 elevated the high plasma atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) levels 2-fold both initially and at the end of the experiment. Initially, water balance was more negative in SCH 39370-treated CHF rats than in those treated with vehicle. In all SCH 39370-treated rats, ANP, cGMP and electrolyte excretion and diuresis were pronounced for 6 h after injection but attenuated thereafter. Blood pressure and pulse remained unchanged. On reverse phase high performance liquid chromatography (HPLC), ANP-(99-126) appeared to be the only circulating form of ANP in rats with heart failure. Three forms have been discovered in patients with heart failure. HPLC revealed only intact ANP in plasma of rats with heart failure during SCH 39370 treatment. NEP inhibitors may provide a new tool for treating chronic heart failure.

Sites of action of angiotensin II, atrial natriuretic factor and guanabenz, on aldosterone biosynthesis

It is well known that atrial natriuretic factor (ANF) inhibits aldosterone biosynthesis. Recent studies showed that amiloride can also inhibit adrenal steroidogenesis. Since the antihypertensive agent, guanabenz, is structurally related to amiloride, we have examined its action on aldosterone biosynthesis. The aim of this work was to localize the sites of action of angiotensin II (AII) and of ANF on steroidogenesis and to compare the effects of guanabenz to ANF. Trilostane, an inhibitor of 3 beta-hydroxysteroid dehydrogenase was used to separately study the early and late pathways of aldosterone biosynthesis. The different steps of steroidogenesis are stimulated by AII. ANF inhibits the formation of pregnenolone, the steps between progesterone and deoxycorticosterone, deoxycorticosterone and corticosterone and finally, corticosterone and aldosterone with ED50 of 114 +/- 17, 199 +/- 90, 14 +/- 3 and 92 +/- 34 pM of ANF, respectively, and around 70% of inhibition. These steps are also inhibited by guanabenz with ED50 of 66 +/- 17 microM for the formation of pregnenolone, 1.6 +/- 1.3, 3.3 +/- 1.7 and 29 +/- 4 microM for the last 3 steps. The percentage of inhibition by guanabenz was at least 80% for all the steps except for progesterone to deoxycorticosterone which is less than 35%. These results indicate that the major site of action of both AII and ANF could be at the level of intracellular signal transduction for the activation of mitochondrial steroidogenic enzymes or for the transport of steroids to mitochondria. We also showed that guanabenz mimics the inhibitory effects of ANF. This study with guanabenz suggests that it might be a prototype for a new family of antihypertensive agents.

Interaction of atrial natriuretic factor and osmoregulatory hormones in the Pekin duck

This study examined the influence of plasma atrial natriuretic factor (ANF) on the osmoregulatory hormones arginine vasotocin (AVT), angiotensin II (AII), aldosterone, and corticosterone in the blood of conscious Pekin ducks. Synthetic chicken ANF was iv infused at a nonhypotensive, natriuretic, and diuretic dose of 100 ng.kg-1.min-1 in normally hydrated ducks and birds in which the circulating levels of AVT, AII, aldosterone, and corticosterone were elevated by 24-hr dehydration. In normally hydrated animals the effect of ANF was limited to a reduction (P less than 0.05) in the basal concentration of aldosterone; in dehydrated birds both AII and aldosterone levels were reduced (P less than 0.05). ANF infusion was consistently without effect on plasma AVT or corticosterone concentrations. The iv infusions of AII with or without simultaneous infusion of ANF showed that ANF inhibited (P less than 0.05) the aldosterone response to AII. Autoradiographic and membrane binding techniques indicated that there were both AII and ANF receptors in the subcapsular zone of the duck adrenal gland and that ANF had no affinity for the AII binding sites. The results demonstrate that ANF is capable of modulating the duck angiotensin-aldosterone system and suggest a role for this peptide in avian salt and fluid homeostasis.

Guanabenz-induced inhibition of aldosterone secretion from isolated rat adrenal glomerulosa cells

The authors examined the effects of the alpha 2-adrenergic agonist guanabenz and other alpha-adrenergic ligands on aldosterone secretion and cyclic nucleotide content in isolated rat adrenal glomerulosa cells. Guanabenz inhibited aldosterone secretion stimulated by potassium, angiotensin II (AII), and adrenocorticotropic hormone (ACTH), exhibiting IC50 values of 35 microM, 43 microM, and 58 microM for stimulation by 10 mM K+, 1 nM AII, and 10 pM ACTH, respectively. Guanabenz did not affect the cGMP content of purified adrenal glomerulosa cells but inhibited ACTH stimulation of cAMP accumulation. Guanabenz inhibition of ACTH-induced cAMP may represent a mechanism for inhibition of aldosterone secretion, however, guanabenz also inhibited aldosterone secretion stimulated by the cAMP analog dibutyryl cAMP. The effect of guanabenz on the early and late pathways of steroidogenesis was tested in the isolated rat glomerulosa cells using 25-OH cholesterol and steroid precursors to aldosterone. Guanabenz inhibited the steroidogenic response to 25-OH cholesterol stimulation of aldosterone secretion but induced a much smaller inhibition of the steroidogenic response to exogenous pregnenolone, progesterone, and 11-deoxycorticosterone. These results suggested that guanabenz inhibited aldosterone secretion primarily through inhibition of the early component of the steroidogenic pathway prior to pregnenolone formation. The effects of guanabenz were not mimicked by other alpha-adrenergic ligands suggesting that these effects of guanabenz were not mediated through activation of alpha-adrenergic receptors.

[Atrial natriuretic factor in men]

The atrial natriuretic peptide (ANP) is rapidly secreted in case of acute changes in atrial volume and heart rate. Its effects are mainly natriuretic and vasodilator. This hormone is of interest to the anaesthetist because induction of anaesthesia, epidural anaesthesia and administration of morphine all result in changes in ANP plasma concentration.