Characterization of atrial natriuretic peptide receptors in brain microvessel endothelial cells.

Atrial natriuretic peptide (ANP) binding and ANP-induced increases in cyclic guanosine monophosphate (cGMP) levels have been observed in brain microvessels (Chabrier et al., 1987; Steardo and Nathanson, 1987), suggesting that this fluid-regulating hormone may play a role in the fluid homeostasis of the brain. This study was initiated to characterize the ANP receptors in primary cultures of brain microvessel endothelial cells (BMECs). The apparent equilibrium dissociation constant, Kd, for ANP increased from 0.25 nM to 2.5 nM, and the number of ANP binding sites as determined by Scatchard analysis increased from 7,100 to 170,000 sites/cell between 2 and 10 days of culture following monolayer formation. Time- and concentration-dependent studies on the stimulation of cGMP levels by ANP indicated that guanylate cyclase-linked ANP receptors were present in BMECs. The relative abilities of ANP, brain natriuretic peptide (BNP), and a truncated analog of ANP containing amino acids 5-27 (ANP 5-27) to modulate the accumulation of cGMP was found to be ANP greater than BNP much greater than ANP 5-27. Affinity cross-linking with disuccinimidyl suberate and radiolabeled ANP followed by gel electrophoresis under reducing conditions demonstrated a single band corresponding to the 60-70 kD receptor, indicating the presence of the nonguanylate cyclase-linked ANP receptor. Radiolabeled ANP binding was examined in the presence of various concentrations of either ANP, BNP, or ANP 5-27 and suggested that a large proportion of the ANP receptors present in blood-brain barrier endothelial cells bind all of these ligands similarly. These data indicate both guanylate cyclase linked and nonguanylate cyclase linked receptors are present on BMECs and that a higher proportion of the nonguanylate cyclase linked receptors is expressed. This in vitro culture system may provide a valuable tool for the examination of ANP receptor expression and function in blood-brain barrier endothelial cells.     

Atrial natriuretic peptide, ANP(99-126), receptors in rat thymocytes and spleen cells

A single class of saturable, specific binding sites for the circulating form of atrial natriuretic peptides, ANP(99-126), was identified in rat thymus and spleen and in isolated thymocytes and spleen cells using quantitative autoradiographic techniques. In the thymus, the relative potency of ANP analogs to inhibit [125I] ANP(99-126) binding was ANP(99-126) = ANP(103-126) greater than ANP(111-126) greater than ANP(103-125). ANP(103-123) could not displace [125I]ANP(99-126) binding. Addition of ANP(99-126) stimulated the formation of cyclic GMP in isolated thymocytes and spleen cells in a dose-dependent manner. Our results indicate that immune cells have specific ANP receptors which could be coupled to guanylate cyclase activation and may play a role in the regulation of the immune response.     

Effect of saline infusion on kidney and collecting duct function in atrial natriuretic peptide (ANP) gene "knockout" mice.

Atrial natriuretic peptide (ANP) is thought to play a role in renal regulation of salt balance by reducing tubular reabsorption of sodium and chloride. Therefore, in the chronic absence of this hormone, a defect of salt excretion should be evident. We used an ANP gene deletion model to test this premise. F2 homozygous mutant mice (-/-) and their wild-type littermates (+/+) were fed an 8% NaCl diet prior to an acute infusion of isotonic saline. Arterial blood pressures, renal excretions of salt and water, as well as collecting duct transport of fluid and electrolytes were measured. Pressures were significantly higher in -/- compared with +/+ mice (139 +/- 4 vs. 101 +/- 2 mmHg; 1 mmHg = 133.3 Pa). There was no difference in glomerular filtration rate (-/- = 0.84 +/- 0.06; +/+ = 0.81 +/- 0.04 mL x min(-1) x g(-1) kidney weight). In the collecting duct, sodium and chloride reabsorptions were significantly higher in the -/- group than in the +/+ group. As a result, natriuresis and chloruresis were relatively reduced (U(Na)V: -/- = 8.6 +/- 1.1; +/+ = 14.0 +/- 1.1; U(Cl)V: -/- = 10.1 +/- 1.4; +/+ = 16.0 +/- 1.1 micromol x min(-1) x g(-1) kidney weight). We conclude that the absence of endogenous ANP activity in mice on a high-salt diet subjected to acute saline infusion causes inappropriately high reabsorption of sodium and chloride in the medullary collecting duct, resulting in a relative defect in renal excretory capacity for salt.     

Hypoxia reduces atrial natriuretic peptide clearance receptor gene expression in ANP knockout mice

We tested the hypotheses that hypoxic exposure is associated with exacerbated pulmonary hypertension and right ventricular (RV) enlargement, reduced atrial natriuretic peptide (ANP) clearance receptor (NPR-C) expression, and enhanced B-type natriuretic peptide (BNP) expression in the absence of ANP. Male wild-type [ANP(+/+)], heterozygous [ANP(+/-)], and homozygous [ANP(-/-)] mice were studied after a 5-wk hypoxic exposure (10% O(2)). Hypoxia increased RV ANP mRNA and plasma ANP levels only in ANP(+/+) and ANP(+/-) mice. Hypoxia-induced increases in RV pressure were significantly greater in ANP(-/-) than in ANP(+/+) or ANP(+/-) mice (104 +/- 17 vs. 45 +/- 10 and 63 +/- 7%, respectively) as were increases in RV mass (38 +/- 4 vs. 26 +/- 5 and 29 +/- 4%, respectively). NPR-C mRNA levels were greatly reduced in the kidney, lung, and brain by hypoxia in all three genotypes. RV BNP mRNA and lung and kidney cGMP levels were increased in hypoxic mice. These findings indicate that disrupted ANP expression worsens hypoxic pulmonary hypertension and RV enlargement but does not alter hypoxia-induced decreases in NPR-C and suggest that compensatory increases in BNP expression occur in the absence of ANP.     

Infusion of iso-rANP(1-45) or (17-45) increases plasma immunoreactive ANP and lowers plasma renin activity and aldosterone

We have reported that a second rat atrial natriuretic peptide, iso-rANP (1-45), as well as the putative ANP homologue, iso-rANP (17-45), elicited circulatory and renal responses in the rat similar to those found after administration of ANP. Iso-rANP also interacted with ANP to potentiate the observed biological activity in the rat. In the present studies in awake dogs, intravenous infusion of low doses (6.3-50 pmol.kg-1.min-1) of iso-rANP(1-45) and iso-rANP(17-45) increased plasma immunoreactive ANP and suppressed plasma renin activity (PRA) and aldosterone. Iso-rANP, like ring-deleted analogues of ANP, may have displaced ANP from ANP clearance receptors to increase plasma ANP concentration, since factors influencing myocardial ANP release were not changed. The effect of iso-rANP (1-45) and (17-45) in lowering PRA and plasma aldosterone may therefore have been indirect, via ANP stimulation of active guanylate cyclase-linked ANP receptors. However, an additional direct effect of iso-rANP on an active receptor cannot be excluded.     

Vasorelaxant effects of and receptors for atrial natriuretic peptides in the mesenteric artery and aorta of the rat

Vasorelaxant effects of different atrial natriuretic peptides (ANP) were measured on rat aortic strips and mesenteric artery rings. These results were compared with the potency of the same peptides to displace 125I-labelled ANP (101-126) on membrane preparations of aorta and of mesenteric vascular bed. In aortic strips and mesenteric artery rings precontracted with phenylephrine (3 X 10(-8) and 10(-6) M, respectively), the order of potency of ANP was as follows: ANP (99-126) greater than ANP (101-126) greater than ANP (103-126) = ANP (103-125) much greater than ANP (103-123). In the displacement binding assays, the order of potency of ANP peptides was similar to that of the relaxation experiments: ANP (99-126) = ANP (101-126) greater than ANP (103-126) = ANP (103-125) much greater than ANP (103-123). When the vessels were precontracted by a smaller concentration of phenylephrine (10(-7) M in mesenteric artery and 10(-8) M in aorta), the IC50 of ANP (101-126) was significantly lower than when the higher concentration of phenylephrine was used. These results show that ANP receptors in the mesenteric artery and in the aorta have similar structural requirements, according to the order of potency of different length ANP, both for binding and myotropic responses.     

Frog atrial natriuretic peptide and cGMP activate amiloride-sensitive Na<Superscript>+</Superscript> channels in urinary bladder cells of Japanese tree frog, <Emphasis Type="Italic">Hyla japonica</Emphasis>

In our previous study, it was suggested that ANP and cGMP may increase Na⁺ absorption in the urinary bladder of the Japanese tree frog, Hyla japonica. Thus, Na⁺ transport activated by ANP was investigated electrophysiologically by using a cell-attached patch-clamp technique in freshly isolated cells from the urinary bladder. A predominant channel expressed was a low conductance Na⁺ channel in the epithelial cells. The channel exhibited conductance for inward currents of 4.9 ± 0.2 pS, long open and closed times (c.a. 190 ms), and positive reversal potential. The channel activity was decreased under the pipette solution including 10⁻⁶ M amiloride. These characteristics were similar to those of amiloride-sensitive Na⁺ channels (ENaC). Addition of 10⁻⁹ M ANP activated and significantly increased the ENaC activity from 0.58 ± 0.09 to 1.47 ± 0.34. On the other hand, mean amplitudes and conductance of single channel did not change significantly after the addition of ANP. Addition of 10⁻⁵ M 8-Br-cGMP also activated the ENaC and significantly increased the channel activity from 0.56 ± 0.10 to 2.00 ± 0.33. The addition of ANP failed to activate the ENaC in the presence of 10⁻⁶ M amiloride. These results suggested that ANP and cGMP activate Na⁺ transport via ENaC in the epithelial cells of frog urinary bladder.     

Regulation of atrial natriuretic peptide secretion by cholinergic and PACAP neurons of the gastric antrum

Atrial natriuretic peptide (ANP) released from enterochromaffin cells helps regulate antral somatostatin secretion, but the mechanisms regulating ANP secretion are not known. We superfused rat antral segments with selective neural agonists/antagonists to identify the neural pathways regulating ANP secretion. The nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) stimulated ANP secretion; the effect was abolished by hexamethonium but doubled by atropine. Atropine's effect implied that DMPP activated concomitantly cholinergic neurons that inhibit and noncholinergic neurons that stimulate ANP secretion, the latter effect predominating. Methacholine inhibited ANP secretion. Neither bombesin nor vasoactive intestinal polypeptide stimulated ANP secretion, whereas pituitary adenylate cyclase-activating polypeptide (PACAP)-27, PACAP-38, and maxadilan [PACAP type 1 (PAC1) agonist] each stimulated ANP secretion. The PAC1 antagonist M65 1) abolished PACAP-27/38-stimulated ANP secretion; 2) inhibited basal ANP secretion by 28 +/- 5%, implying that endogenous PACAP stimulates ANP secretion; and 3) converted the ANP response to DMPP from 109 +/- 21% above to 40 +/- 5% below basal, unmasking the cholinergic component and indicating that DMPP activated PACAP neurons that stimulate ANP secretion. Combined atropine and M65 restored DMPP-stimulated ANP secretion to basal levels. ANP secretion in the antrum is thus regulated by intramural cholinergic and PACAP neurons; cholinergic neurons inhibit and PACAP neurons stimulate ANP secretion.     

Atrial natriuretic peptide negatively regulates follicle-stimulating hormone-induced porcine oocyte maturation and cumulus expansion via cGMP-dependent protein kinase pathway

This study examined the effect of atrial natriuretic peptide (ANP) on porcine cumulus-enclosed oocyte (CEO) maturation and cumulus expansion. ANP negatively regulated follicle-stimulating hormone (FSH)-stimulated germinal vesicle breakdown (GVBD; 90.1, 81.2 and 68.2% for FSH, FSH+10nM ANP and FSH+1 microM ANP, respectively), first polar body emission (PB1; 86.1, 75.3 and 53.3% for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) and cumulus expansion (CEI; 3.47, 3.16 and 2.43 for FSH, FSH+1 nM ANP and FSH+1 microM ANP, respectively) in a dose-dependent manner when CEOs were cultured in the maturation medium containing porcine follicular fluid (pFF). This negative effect showed a time-dependent manner after preincubation with 100 nM ANP for 5h (78.4% PB1), 10h (81.7% GVBD and 74.1% PB1), 20 h (78.5% GVBD and 68.9% PB1), and 44 h (75.3% GVBD and 60.5% PB1), respectively. ANP also significantly inhibited FSH-induced porcine oocyte GVBD (47.6% versus 83.8%) and PB1 emission (22.4% versus 45.2%) when CEOs were cultured in pFF-free maturation medium. cGMP analog 8-Br-cGMP (10 microM to 1mM) mimicked the effects of ANP on GVBD, PB1, and CEI. The negative effect of ANP was completely reversed by KT5823 (a specific inhibitor of cGMP-dependent protein kinase), while C-ANP-(4-23) (an analogue of ANP and specific binder for natriuretic peptide receptors-C) was ineffective in oocyte maturation. Neither ANP nor C-ANP-(4-23) had an effect on spontaneous porcine oocyte maturation and cumulus expansion. These results suggested that ANP negatively regulates FSH-activated porcine oocyte meiotic resumption, meiotic maturation and cumulus expansion. The function of ANP on porcine oocyte maturation is via the cGMP dependent protein kinase (PKG) pathway.     

Atrial natriuretic peptides in essential hypertension: basal plasma levels and relationship to sodium balance.

The identification of the atrial natriuretic peptides (ANP) as a new hormonal system has provided a new perspective on the mechanisms controlling renal sodium excretion and abnormalities in sodium homeostasis. The present article focuses on the potential importance of ANP (ANF 99-126) in essential hypertension with particular reference to circulating ANP levels and the relationship between the ANP and the renin-angiotensin system in the control of sodium balance and blood pressure. There is now considerable evidence demonstrating that a substantial proportion of patients with essential hypertension have raised circulating ANP levels. Given the known biological actions of ANP, these raised levels point to important compensatory mechanisms. This is further supported by studies during alterations in dietary sodium intake, as sodium restriction high-lighted important relationships between ANP and the renin angiotensin system. The potential importance of ANP in essential hypertension is strengthened by recent demonstration of natriuretic and antihypertensive actions associated with small increases in circulating ANP as induced by administration of exogenous ANP. Furthermore, the recent development of orally active inhibitors of ANP metabolism now provides a basis to determine the therapeutic importance of specific manipulation of endogenous ANP levels in patients with essential hypertension.     

Free and bound forms of atrial natriuretic peptide (ANP) in rat plasma: preferential increase of free ANP in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP)

Free and bound forms of atrial natriuretic peptide (ANP) in rat plasma were analysed by gel permeation chromatography combined with a radioimmunoassay (RIA) for rat ANP (rANP). Gel permeation chromatography showed two immunoreactive peaks in rat plasma, one corresponding to alpha-rANP, rANP(99-126), and the other eluted at a high molecular weight, clearly different from gamma-rANP, rANP(1-126). The chromatographic profile of rat plasma after incubation with synthetic alpha-rANP demonstrated that the high molecular immunoreactivity had ANP-binding capacity. This bound form of ANP was almost totally excluded following extraction procedure, therefore, the immunoreactive ANP (ir-ANP) measured with the extraction assay was mainly free ANP. On the other hand, direct RIA may detect not only the free but also the bound form of ANP. Using both direct RIA and the extraction method, bound forms of plasma ANP in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) were compared to normotensive Wistar Kyoto rats (WKY). Bound forms of plasma ANP in 20-week-old SHR and SHRSP were significantly higher than that in age-matched WKY. The ratio of free/bound form of plasma ANP in SHR and SHRSP also significantly increased compared to WKY, indicating a preferential increase in free ANP in the plasma of these hypertensive rats. These findings suggest that a bound form of ANP may be present in rat plasma and that it may play some pathophysiological role in the hypertension of SHR and SHRSP. Increased free ANP in plasma may indicate a compensatory increase in ANP release in these hypertensive rats.     

Distinct roles for L- and T-type Ca(2+) channels in regulation of atrial ANP release

Atrial secretion of atrial natriuretic peptide (ANP) has been shown to be regulated by atrial workload. Although modulating factors for the secretion of ANP have been reported, the role for intracellular Ca(2+) on the secretion of ANP has been controversial. The purpose of the present study was to define roles for L- and T-type Ca(2+) channels in the regulation of ANP secretion in perfused beating rabbit atria. BAY K 8644 (BAY K) increased atrial stroke volume and pulse pressure. BAY K suppressed ANP secretion and ANP concentration in terms of extracellular fluid (ECF) translocation concomitantly with an increase in atrial dynamics. BAY K shifted the relationship between ANP secretion and ECF translocation downward and rightward. These results indicate that BAY K inhibits myocytic release of ANP. In the continuous presence of BAY K, diltiazem reversed the effects of BAY K. Diltiazem alone increased ANP secretion and ANP concentration along with a decrease in atrial dynamics. Diltiazem shifted relationships between ANP secretion and atrial stroke volume or ECF translocation leftward. The T-type Ca(2+) channel inhibitor mibefradil decreased atrial dynamics. Mibefradil inhibited ANP secretion and ANP concentration in contrast with the L-type Ca(2+) channel inhibitor. These results suggest that activation of L- and T-type Ca(2+) channels elicits opposite effects on atrial myocytic release of ANP.     

Characterization of the molecular forms of ANP released by perfused neonatal rat heart

Although cultures of neonatal rat atria and ventricles have been widely used to study ANP biosynthesis and secretion, little is known regarding the circulating form of ANP in neonatal animals. To begin to address this issue, we have developed a method for perfusing isolated neonatal rat hearts. Reversed phase-HPLC analysis of the heart effluents coupled with ANP RIA demonstrated that the predominant form of ANP released was chromatographically identical to ANP(99-126). Size exclusion-HPLC confirmed that the secreted ANP was indistinguishable from ANP(99-126). This demonstrated that the neonatal rat heart can efficiently generate and secrete a peptide similar to the circulating form of ANP found in adult rats, and further justifies the use of neonatal rat atria as a source of primary cells for studies of ANP biosynthesis and secretion.     

Signaling cascade that mediates endothelial nitric oxide synthase activation induced by atrial natriuretic peptide

Atrial natriuretic peptide (ANP) induces activation of nitric oxide-synthase (NOS). Aims: to identify the isoform of NOS involved in ANP effects, to study whether ANP modifies NOS expression and to investigate the signaling pathways and receptors involved in NOS stimulation. NOS activation induced by ANP would be mediated by endothelial NOS (eNOS) since neuronal or inducible NOS inhibition did not alter ANP effect. The peptide induced no changes in eNOS protein expression. NOS activity stimulated by ANP, in the kidney, aorta and left ventricle, was partially abolished by the NPR-A/B antagonist, as well as PKG inhibition, but no difference in atria was observed. 8-Br-cGMP partially mimicked the effect of ANP on NOS in all tissues. NOS stimulation by ANP in atria disappeared when G protein was inhibited, but this effect was partial in the other tissues. Calmodulin antagonist abolished NOS stimulation via ANP. Inhibition of the PLC, PKC or PI3 kinase/Akt pathway failed to alter NOS activation induced by ANP. ANP would activate eNOS in the aorta, heart and kidney without modifying the expression of the enzyme. ANP would interact with NPR-C coupled via G proteins leading to the activation of Ca(2+)-calmodulin-dependent NOS in atria; while in ventricle, aorta and kidney, ANP could also interact with NPR-A/B, increasing cGMP, which in turns activates PKG to stimulate eNOS.     

The cellular localization of increased atrial natriuretic peptide mRNA and immunoreactivity in diabetic rat kidneys.

Increased intrarenal atrial natriuretic peptide (ANP) mRNA expression has been reported in several disorders. To further investigate the action of renal ANP, we need to elucidate the exact site of its alteration in diseased kidneys. ANP mRNA and ANP were detected by in situ hybridization and immunohistochemistry in the kidneys from five normal and five diabetic rats. Renal ANP mRNA in eight normal and nine diabetic rats was measured by RT-PCR with Southern blot hybridization. In normal and diabetic rats, the distribution of ANP mRNA and ANP-like peptide was mainly located in proximal, distal, and collecting tubules. However, diabetic rats had significant enhancement of ANP mRNA and ANP-immunoreactive staining in the proximal straight tubules, medullary thick ascending limbs, and medullary collecting ducts. ANP mRNA in the outer and inner medulla of nine diabetic rats increased 5.5-fold and 3.5-fold, but only 1.8-fold in the renal cortex. This preliminary study showed that ANP mRNA and ANP immunoreactivity in proximal straight tubules, medullary thick ascending limb, and medullary collecting ducts apparently increased in diabetic kidneys. These findings imply that ANP synthesis in these nephrons may involve in adaptations of renal function in diabetes.     

多串心钠素的纯化与活性测定

为获得纯化心钠素(ANP)单体,采用离子交换及疏水柱层析,纯化融合蛋白麦芽糖结合蛋白(MBP)-ANP和MBP-3ANP,用凝血因子Xa切割MBP-ANP后,经阳离子柱分离获得ANP单体.对ANP单体与BMP-3ANP进行生物学活性检测.1　材料与方法1.1　材料含心钠素多拷贝基因的重组表达质粒pMal-nANP...     

Long-term treatment with atrial natriuretic peptide inhibits ATP production and insulin secretion in rat pancreatic islets

Atrial natriuretic peptide (ANP) levels correlate with hyperglycemia in diabetes mellitus, but ANP effects on pancreatic islet β-cell insulin secretion are controversial. ANP was investigated for short- and long-term effects on insulin secretion and mechanisms regulating secretion in isolated rat pancreatic islets. A 3-h incubation with ANP did not affect basal or glucose-stimulated islet insulin secretion. However, 7-day culture of islets with 5.5 mM glucose and ANP (1 nM - 1 μM) markedly inhibited subsequent glucose (11 mM)-stimulated insulin secretion; total islet insulin content was not affected. Following ANP removal for 24 h, the islet insulin-secretory response to glucose was restored. The insulin-secretory response to other insulin secretagogues, including α-ketoisocaproic acid, forskolin, potassium chloride, and ionomycin were also markedly inhibited by chronic exposure to ANP. However, the combination of potassium chloride and α-ketoisocaproic acid was sufficient to overcome the inhibitory effects of ANP on insulin secretion. The glucose-stimulated increases in islet ATP levels and the ATP/ADP ratio were completely inhibited in ANP 7-day-treated islets vs. control; removal of ANP for 24 h partially restored the glucose response. ANP did not affect islet glycolysis. ANP significantly increased levels of islet activated hormone-sensitive lipase and the expression of uncoupling protein-2 and peroxisome proliferator-activated receptor-δ and -α. Although islet ANP-binding natriuretic peptide receptor-A levels were reduced to 60% of control after 7-day culture with ANP, the ANP-stimulated cGMP levels remained similar to control islet levels. Thus, long-term exposure to ANP inhibits glucose-stimulated insulin secretion and ATP generation in isolated islets.     

Central interaction of the brain atrial natriuretic polypeptide (ANP) system and the brain renin-angiotensin system in ANP secretion from heart--evidence for possible brain-heart axis

To elucidate the involvement of the brain renin-angiotensin system and the brain atrial natriuretic polypeptide (ANP) system in the regulation of ANP secretion from the heart, the effects of intracerebroventricular administration of angiotensin II and ANP on the plasma ANP level were examined in conscious unrestrained rats. The intracerebroventricular administration of angiotensin II at doses of 100 ng and 1 microgram significantly enhanced ANP secretion induced by volume-loading with 3-mL saline infusion (peak values of the plasma ANP level: control, 220 +/- 57 pg/mL; 100 ng angiotensin II, 1110 +/- 320 pg/mL, p less than 0.01; 1 microgram angiotensin II, 1055 +/- 60 pg/mL, p less than 0.01). The intracerebroventricular injection of angiotensin II at the same doses alone had no significant effect on the basal plasma ANP level. The enhancing effect of central angiotensin II on ANP secretion induced by volume-loading was significantly attenuated by pretreatment with the intravenous administration of the V1-receptor antagonist of vasopressin or with the intracerebroventricular administration of phentolamine. The intracerebroventricular administration of alpha-rANP(4-28) (5 micrograms) had no significant influence on the basal plasma ANP level; however, it significantly attenuated central angiotensin II potentiating effect of volume-loading induced ANP secretion. These results indicate that the brain renin-angiotensin system regulates ANP secretion via the stimulation of vasopressin secretion and (or) via the activation of the central alpha-adrenergic neural pathway, and that the brain ANP system interacts with the brain renin-angiotensin system in the central modulation of ANP secretion from the heart.(ABSTRACT TRUNCATED AT 250 WORDS)     

Pathophysiological significance and clinical application of ANP and BNP in patients with heart failure

Plasma levels of ANP and BNP increase in accordance with the severity of the heart failure. In severe cases, the amount of BNP secreted surpasses that of ANP. The main secretion site of BNP is the ventricles, and that of ANP is the atria. However, ANP is also secreted from the ventricles as heart failure advances, and thus the ventricles are important sites for both BNP and ANP. It is well known that myocardial stretch is a key factor in the stimulation of the secretion of ANP and BNP, although neurohumoral factors also play a role in the secretion mechanism. The major physiological effects of ANP and BNP are vasodilation, natriuresis, and inhibition of the renin-angiotensin-aldosterone (RAA) and the sympathetic nervous systems; all of which are supposed to suppress the progression of heart failure. The inhibitory action of ANP and BNP on the RAA system has been considered to be an extra-cardiac effect. We recently reported the activation of an angiotensin-converting enzyme and aldosterone production in failing human hearts. ANP and BNP, however, would inhibit aldosterone production, not only in the adrenal cortex but also in cardiac tissue. ANP, and especially BNP, are useful markers of the heart's status during treatment for heart failure. The infusion of synthetic ANP (hANP) or BNP (Nesiritide) is effective in the treatment of acute heart failure. In Japan, BNP occupies an important position in the diagnosis of chronic heart failure, as ANP does in the treatment of acute heart failure.     

Stimulation of atrial natriuretic peptide secretion and synthesis by Na-K-ATPase inhibitors

Ouabain has been reported to increase the secretion of ANP in vitro. In this study, we focused on whether this action is common in Na-K-ATPase inhibitors (ATPI) and whether ATPI simply increase the release of ANP or stimulate both its biosynthesis and release. The effects of ouabain and digoxin on secretion of ANP and accumulation of ANP mRNA were investigated in the rat cardiocyte superfusion system. Ouabain and digoxin increased the immunoreactive ANP (iANP) output into perfusate and accumulation of ANP mRNA significantly. These results suggest that ATPI may stimulate both ANP biosynthesis and release in vitro.