Natriuretic peptides stimulate steroidogenesis in the fetal rat testis

To study the regulation of fetal testicular steroidogenesis in the rat, we examined effects of members of the natriuretic peptide family, that is, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), on testosterone production of dispersed Leydig cells of rat fetuses at Embryonic Day (E) 18.5. All three peptides stimulated testosterone production, with significant effect at concentrations > or =1 x 10(-8) mol/L of ANP, > or =1 x 10(-9) mol/L of BNP, and > or =1 x 10(-6) mol/L of CNP. Likewise, receptors for all three peptides (i.e., NPR-A, NPR-B, and NPR-C) were expressed in the fetal testis as early as E15.5. The natriuretic peptides had no effect on cAMP production by fetal Leydig cells. When tested in combination with two other peptides previously shown to stimulate fetal testicular steroidogenesis, vasoactive intestinal peptide and pituitary adenylate cyclase-stimulating polypeptide (PACAP-27), the combined effects did not differ significantly from the maximum effect with any one of the peptides alone. In conclusion, our present findings provide both functional and molecular evidences for NPR-A, NPR-B, and NPR-C in the fetal testis. Because ANP has previously been detected in fetal plasma and we now demonstrate the expression of BNP and CNP in fetal testes, these findings indicate involvement of the natriuretic peptides in endocrine and paracrine regulation during the early phase of fetal testicular steroidogenesis at E15.5--19.5 (i.e., before the onset of pituitary LH secretion).     

Immunoreactive forms of natriuretic peptides in ovine brain: response to heart failure

In order to elucidate how brain natriuretic peptides (NPs) are affected by experimentally induced heart failure, we have measured the immunoreactive (IR) levels of the NP in extracts from 10 regions of ovine brain, including pituitary, and clarified their molecular forms using high performance liquid chromatography (HPLC). Using species-specific radioimmunoassay (RIA), atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were all detected in extracts taken from control animals and sheep that had undergone rapid ventricular pacing for 7 days to induce heart failure. CNP was the most abundant NP as assessed by specific RIA, and the pituitary contained the highest IR levels for all three NP. Compared with control animals, the pituitary content of BNP in animals with heart failure was reduced by 40% (control, 0.26±0.02 pmol/g wet weight versus heart failure 0.16±0.01; P<0.01, n=7). No other significant changes were observed. The molecular forms of ANP and CNP in whole brain extracts as assessed by HPLC were proANP and CNP22, CNP53 and proCNP, respectively. BNP in pituitary extracts was assessed to be primarily proBNP with a minor component of mature BNP26.     

Natriuretic peptides differentially attenuate thrombin-induced barrier dysfunction in pulmonary microvascular endothelial cells

Previous studies have described a protective effect of atrial natriuretic peptide (ANP) against agonist-induced permeability in endothelial cells derived from various vascular beds. In the current study, we assessed the effects of the three natriuretic peptides on thrombin-induced barrier dysfunction in rat lung microvascular endothelial cells (LMVEC). Both ANP and brain natriuretic peptide (BNP) attenuated the effect of thrombin on increased endothelial monolayer permeability and significantly enhanced the rate of barrier restoration. C-type natriuretic peptide (CNP) had no effect on the degree of thrombin-induced monolayer permeability, but did enhance the restoration of the endothelial barrier, similar to ANP and BNP. In contrast, the non-guanylyl cyclase-linked natriuretic peptide receptor specific ligand, cyclic-atrial natriuretic factor (c-ANF), delayed the rate of barrier restoration following exposure to thrombin. All three natriuretic peptides promoted cGMP production in the endothelial cells; however, 8-bromo-cGMP alone did not significantly affect thrombin modulation of endothelial barrier function. ANP and BNP, but not CNP or c-ANF, blunted thrombin-induced RhoA GTPase activation. We conclude that ANP and BNP protect against thrombin-induced barrier dysfunction in the pulmonary microcirculation by a cGMP-independent mechanism, possibly by attenuation of RhoA activation.     

Natriuretic peptides cause relaxation of human esophageal mucosal muscle

Natriuretic peptides have been demonstrated to cause relaxation of the human gallbladder muscle through interaction with natriuretic peptide receptor-B (NPR-B/NPR2). Effects of natriuretic peptides in the human esophageal muscle were unknown. To investigate the effects of natriuretic peptides in the human esophagus, we measured relaxation of muscularis mucosae strips isolated from the human esophagus caused by C-type natriuretic peptide (CNP), brain natriuretic peptide (BNP), atrial natriuretic peptide (ANP) and des[Gln(18), Ser(19), Gly(20), Leu(21), Gly(22)]ANP(4-23) amide (cANP(4-23)), a selective natriuretic peptide receptor-C (NPR-C) agonist. In endothelin-1 or carbachol-contracted mucosal muscle strips, CNP caused moderate, sustained and concentration-dependent relaxation. BNP caused a very mild relaxation whereas ANP and cANP(4-23) did not cause any relaxation. CNP was much more potent than BNP and ANP in causing relaxation. These suggest the existence of NPR-B mediating relaxation. The CNP-induced relaxation was not affected by tetrodotoxin or atropine in endothelin-1-contracted esophageal strips and not by tetrodotoxin in carbachol-contracted strips, indicating a direct effect of CNP on the human esophageal muscularis mucosae. Taken together, these results demonstrate that natriuretic peptides cause relaxation of the muscularis mucosae of the human esophagus and suggest that the relaxation is through interaction with NPR-B. Natriuretic peptides may play an important role in the control of human esophageal motility.     

C-type natriuretic peptide is a potent activator of guanylate cyclase in endothelial cells from brain microvessels.

An exposure of endothelial cells from rat brain microvessels to C-type natriuretic peptide (CNP) resulted in a rapid and large increase in cGMP formation. The action of CNP did not require inhibitors of phosphodiesterases to be observed and occurred at nanomolar concentrations. Other natriuretic peptides (ANP and BNP) also stimulated cGMP formation in endothelial cells from brain microvessels but with a potency that was at least 100 times less than that of CNP. In contrast, endothelial cells from the aorta showed large cGMP responses to low concentrations of ANP and BNP but were unresponsive to CNP up to concentrations as large as 100 nM. It is concluded that endothelial cells from brain microvessels and from aorta express different receptors subtypes for natriuretic peptides. Endothelial cells from brain microvessels express CNP specific ANPB receptors; aortic endothelial cells express ANP (and BNP) specific ANPA receptors. CNP may play an important role in the regulation of water and electrolyte movements across the blood brain barrier.     

Natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with natriuretic peptide receptor-B

Atrial natriuretic peptide (ANP) binding sites have been demonstrated in the guinea-pig gallbladder muscle with unclear function. To investigate effects of natriuretic peptides in the gallbladder, we measured relaxation of isolated human and guinea-pig gallbladder strips caused by natriuretic peptides, including C-type natriuretic peptide (CNP), brain natriuretic peptide (BNP) and ANP, as well as des[Gln18, Ser19, Gly20, Leu21, Gly22]ANP(4-23) amide (cANP(4-23)), a selective natriuretic peptide receptor-C (NPR-C) agonist. Results in the human gallbladder were similar to those in the guinea-pig gallbladder. CNP, BNP, ANP and cANP(4-23) alone did not cause contraction or relaxation in resting gallbladder strips. However, in carbachol or endothelin-1-contracted strips, CNP caused moderate, sustained and concentration-dependent relaxation. The relaxation was not affected by tetrodotoxin or atropine in endothelin-1-contracted gallbladder strips and not by tetrodotoxin in carbachol-contracted strips. These indicate a direct effect of CNP on the gallbladder muscle. The relative potencies for natriuretic peptides to cause relaxation were CNP>BNP> or = ANP. cANP(4-23) did not cause relaxation. These indicate the existence of the natriuretic peptide receptor-B (NPR-B) mediating the relaxation. Taken together, these results demonstrate that natriuretic peptides cause relaxation of human and guinea-pig gallbladder muscle through interaction with the natriuretic peptide receptor-B.     

ANP, BNP, and CNP enhance bradycardic responses to cardiopulmonary chemoreceptor activation in conscious sheep

We demonstrated previously that atrial natriuretic peptide (ANP) enhances reflex bradycardia to intravenous serotonin [5-hydroxytryptamine (5-HT)] (von Bezold-Jarisch reflex) in rats. To determine whether 1) ANP affects this cardiopulmonary vagal reflex in another species and 2) B-type (BNP) and C-type (CNP) natriuretic peptides share with ANP the ability to modulate this reflex, we used intravenous phenylbiguanide (PBG), a 5-HT(3) agonist, as the stimulus to evoke a von Bezold-Jarisch reflex (dose-related, reproducible bradycardia) in conscious adult sheep (n = 5). Three doses of PBG (13 +/- 3, 20 +/- 3, and 31 +/- 4 microg/kg) injected into the jugular vein caused reflex cardiac slowing of -7 +/- 1, -15 +/- 2, and -36 +/- 3 beats/min, respectively, under control conditions. These doses of PBG were repeated during infusions of ANP, BNP, or CNP (10 pmol. kg(-1). min(-1) iv), or vehicle (normal saline). Each of the natriuretic peptides significantly (P < 0.05) enhanced the sensitivity of bradycardic responses to PBG by 94 +/- 8% (ANP), 142 +/- 55% (BNP), and 61 +/- 16% (CNP). Thus not only did ANP sensitize cardiopulmonary chemoreceptor activation in a species with resting heart rate close to that in humans, but BNP and CNP also enhanced von Bezold-Jarisch reflex activity in conscious sheep.     

C-type natriuretic peptide receptor expression in pancreatic alpha cells

Atrial natriuretic peptide (ANP), brain type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) comprise a family of natriuretic peptides that mediate their biological effects through three natriuretic peptide receptor subtypes, NPR-A (ANP, BNP), NPR-B (CNP) and NPR-C (ANP, BNP, CNP). Several reports have provided evidence for the expression of ANP and specific binding sites for ANP in the pancreas. The purpose of this study was to identify the ANP receptor subtype and to localize its expression to a specific cell type in the human pancreas. NPR-C immunoreactivity, but neither ANP nor NPR-A, was detected in human islets by immunofluorescent staining. No immunostaining was observed in the exocrine pancreas or ductal structures. Double-staining revealed that NPR-C was expressed mainly in the glucagon-containing alpha cells. NPR-C mRNA and protein were detected in isolated human islets by RT-PCR and Western blot analysis, respectively. NPR-C expression was also detected by immunofluorescent staining in glucagonoma but not in insulinoma. ANP, as well as BNP and CNP, stimulated glucagon secretion from perifused human islets (1,111 ± 55% vs. basal [7.3 fmol/min]; P < 0.001). This response was mimicked by cANP(4–23), a selective agonist of NPR-C. In conclusion, the NPR-C receptor is expressed in normal and neoplastic human alpha cells. These findings suggest a role for natriuretic peptides in the regulation of glucagon secretion from human alpha cells.     

三种钠尿肽抑制大鼠肺动脉平滑肌细胞增殖效应的比较

本文比较了心房钠尿肽（ＡＮＰ）、Ｃ－型钠尿肽（ＣＮＰ）、血管钠肽（ＶＮＰ）抑制肺动脉平滑肌细胞（ＰＡＳＭＣｓ）增殖的效应。用蛋白激酶Ｃ激动剂佛波酯（ＰＭＡ）刺激体外培养大鼠ＰＡＳＭＣｓ的增殖,以总蛋白含量和ＭＴＴ比色ＯＤ值为指标,观察三种钠尿肽对ＰＭＡ刺激大鼠ＰＡＳＭＣｓ增殖的影响。结果表明,ＰＭＡ（１０＾－９－１０＾－７ｍｏｌ／Ｌ）显著升高（Ｐ＜０．０５）ＰＡＳＭＣｓ的总蛋白含量和ＭＴＴＯＤ值,     

Cardiac natriuretic peptides and pancreatic islet blood flow in anesthetized rats.

The aim of the study was to evaluate effects of cardiac natriuretic peptides on splanchnic circulation, especially to the pancreatic islets. Pentobarbital-anesthetized rats were infused intravenously (0.01 ml/min for 20 min) with saline, atrial natriuretic peptide (ANP; 0.25 or 0.5 microg/kg BW/min), brain natriuretic peptide (BNP; 0.5 microg/kg BW/min) or C-type natriuretic peptide (CNP; 0.5 or 2.0 microg/kg BW/min). Splanchnic blood perfusion was then measured with a microsphere technique. Mean arterial blood pressure was decreased by ANP and BNP, but not by CNP. The animals given the highest dose of ANP became markedly hypoglycemic, whilst no such effects were seen in any of the other groups of animals. Total pancreatic blood flow was decreased by the highest dose of CNP, whereas no change was seen after administration of the other peptides. Islet blood flow was increased by the highest dose of ANP. Neither BNP nor CNP affected islet blood flow. None of the natriuretic peptides influenced duodenal, colonic or arterial hepatic blood flow. It is concluded that cardiac natriuretic peptides exert only minor effects on splanchnic blood perfusion in anesthetized rats. However, islet blood perfusion may be influenced by ANP.     

Natriuretic peptides in cardiovascular diseases

The natriuretic peptide family comprises atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), dendroaspis natriuretic peptide (DNP), and urodilatin. The activities of natriuretic peptides and endothelins are strictly associated with each other. ANP and BNP inhibit endothelin-1 (ET-1) production. ET-1 stimulates natriuretic peptide synthesis. All natriuretic peptides are synthesized from polypeptide precursors. Changes in natriuretic peptides and endothelin release were observed in many cardiovascular diseases: e.g. chronic heart failure, left ventricular dysfunction and coronary artery disease.     

C-type natriuretic peptide (CNP): a new member of natriuretic peptide family identified in porcine brain

Two types of natriuretic peptide, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), very similar to each other in structure and in pharmacological effect, are known to be present in mammalian heart and brain. In our present survey for unidentified peptides in porcine brain extracts, we found a new peptide of 22 amino acid residues, eliciting a potent relaxant activity on chick rectum. The amino acid sequence determined for the peptide shows remarkable similarity to those of ANP and BNP, especially in the 17-residue sequences flanked by two cysteine residues. The peptide shows a pharmacological spectrum similar to ANP and BNP. Thus, the peptide was designated "C-type natriuretic peptide (CNP)", the third member to join the natriuretic peptide family. In contrast to ANP and BNP, CNP terminates in the second cysteine residue, lacking a further C-terminal extension.     

Dendroaspis natriuretic peptide is the most potent natriuretic peptide to cause relaxation of lower esophageal sphincter

Atrial natriuretic peptide (ANP) causes relaxation in the opossum lower esophageal sphincter. The effects of dendroaspis natriuretic peptide (DNP) and other natriuretic peptides in the lower esophageal sphincter were not known. We measured the relaxation of transverse strips from the guinea pig lower esophageal sphincter caused by DNP, ANP, brain natriuretic peptide (BNP), C-type natriuretic peptide (CNP), and a natriuretic peptide receptor-C agonist des[Gln(18), Ser(19), Gly(20), Leu(21), Gly(22)]ANP(4-23) amide (cANF(4-23)) in vitro. In resting strips of the guinea pig lower esophageal sphincter DNP and BNP caused marked relaxations. Furthermore, in both sarafotoxin S6c and carbachol-contracted lower esophageal sphincter strips, DNP caused marked and BNP caused moderate, concentration-dependent relaxations. ANP as well as CNP caused mild relaxations. In contrast, cANF(4-23) did not cause relaxation. The relative potencies for natriuretic peptides to cause relaxation were DNP>BNP>ANP>=CNP in both sarafotoxin S6c and carbachol-contracted lower esophageal sphincter strips. The DNP and BNP-induced relaxations were not affected by tetrodotoxin or atropine, suggesting that the natriuretic peptide-induced response was not neutrally mediated. In conclusion, these results demonstrate that natriuretic peptides cause the relaxation of the guinea pig lower esophageal sphincter. DNP is the most potent natriuretic peptide to cause lower esophageal sphincter relaxation, which might be mediated by natriuretic peptide receptor-A or a novel DNP-selective natriuretic peptide receptor.     

Natriuretic peptide receptors in cultured rat diencephalon

To characterize the type of cell expressing natriuretic peptide receptors in the brain and the nature of these receptors, we conducted studies in primary cultured glial and neuronal cells derived from fetal rat diencephalon. The glial predominant cultures (95% of total cells and glial fibrillary acidic protein positive) expressed nearly a 10-fold greater specific binding of the natriuretic peptides to cell surface receptors compared with the neuron-predominant cultures. Scatchard analysis of binding studies with 125I-atrial natriuretic peptide (ANP) and 125I-brain natriuretic peptide (BNP) revealed a single class of receptors with dissimilar affinities (0.25 +/- 0.09 and 0.74 +/- 0.07 nM, respectively, n = 3 experiments p less than 0.01) but similar numbers of binding sites for both peptides (93 and 88 fmol/mg of protein, respectively). Cross-linking of 125I-ANP and BNP to cultured glia followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography identified distinct bands at either approximate Mr 130,000, or 102,000 and 66,000, corresponding to two high molecular weight (B) receptors and one low molecular weight (C) receptor described in other tissues. Different subtypes of astrocytes appeared to express different B receptors. Binding and cross-linking of radiolabeled ANP or BNP were competitively inhibited equally by unlabeled ANP or BNP, indicating that ANP and BNP probably bind the same receptors. The glial cultures functionally expressed a receptor(s) with guanylate cyclase activity; BNP was less potent than ANP in stimulating cGMP at lower concentrations. These results indicate that both high and low molecular weight natriuretic peptide receptors are expressed in astrocyte-predominant cultures from the fetal diencephalon and suggest that glia participate in several actions of ANP which are probably mediated through this area of the brain.     

A Comparison of the Lipolytic Activity of Different Natriuretic Peptides on Human Adipocytes

Atrial natriuretic peptide (ANP) was recently shown to promote triacylglycerol hydrolysis in human white adipocytes both in vitro and in vivo through a cGMP-dependent pathway. The ANP-stimulated lipolytic effect is known to be specific to primates. In this study, we compared the lipolytic effect of different natriuretic peptides obtained from several species, including ANP from human, rat, chicken, frog, and eel, brain natriuretic peptide (BNP) from porcine and rat, C-type natriuretic peptide (CNP) from human, chicken, and frog, Dendroaspis natriuretic peptide (DNP), urodilatin, and des-[Gln¹⁸, Ser¹⁹, Gly²⁰, Leu²¹, Gly²²]-ANP (C-ANP), on human and rat adipocytes. We also compared the amount of intracellular cGMP produced in both human and rat adipocytes that were treated with natriuretic peptides. Among these NPs, rat ANP, as well as porcine and rat BNP, DNP and urodilatin showed the ability to elevate intracellular cGMP and to stimulate lipolysis as human ANP. No natriuretic peptide showed the ability to stimulate lipolysis in rat adipocytes, though some of them induced significant elevation of intracelluar cGMP concentrations. These results suggest that ANP and BNP from species close to human have the ability to induce lipolysis in human adipocytes. Jiahua Yu and Yeon Jun Jeong contributed equally.     

Distribution and characterization of immunoreactive porcine C-type natriuretic peptide.

C-type natriuretic peptide (CNP) is a new member of the natriuretic peptide family recently identified in porcine brain (1). We raised an antiserum against porcine CNP and set up a radioimmunoassay (RIA) for CNP. Using this RIA system, distribution of immunoreactive (ir-) CNP in porcine tissue was measured and compared with that of ir-atrial natriuretic peptide (ANP) and ir-brain natriuretic peptide (BNP). Tissue concentration of ir-CNP in brain was the highest of the three natriuretic peptides at about 0.79 pmol/g wet wt. CNP was present in medulla-pons in high concentration, with a significant concentration detected in cerebellum. In contrast, ir-CNP was not detected in peripheral tissue, including heart, in a significant concentration. These data demonstrated sharp contrasts in the distribution of the three natriuretic peptides, suggesting that CNP is a natriuretic peptide functioning in the central nervous system.     

Characterization of immunoreactive human C-type natriuretic peptide in brain and heart.

Amino acid sequence of human C-type natriuretic peptide (CNP) has recently been deduced to be identical to those of porcine and rat CNPs in the bioactive unit of C-terminal 22 residues (CNP-22) (1). Thus, tissue concentrations and molecular forms of immunoreactive (ir-) CNP in human brain and heart were determined or characterized using a radioimmunoassay established for porcine CNP. In human brain (hypothalamus and medullapons), ir-CNP was detected at a concentration of 1.04 pmol/g, being about 25 times or 70 times higher than ir-atrial (A-type) natriuretic peptide (ANP) or ir-brain (B-type) natriuretic peptide (BNP). CNP was present mainly as CNP-53, with CNP-22 as well as 13K CNP (presumed to be pro-CNP) as minor components. In heart, 1 approximately 5 pmol/g of ir-CNP was detected in both atrium and ventricle, but this ir-CNP was shown to be derived from crossreactivity of ANP. These results demonstrated that human CNP functions exclusively in the central nervous system in contrast to ANP and BNP which mainly function in the circulation system.     

Molecular cloning of natriuretic peptide receptor A from bullfrog (Rana catesbeiana) brain and its functional expression

A comparative study of natriuretic peptide receptor (NPR) was performed by cloning the NPR-A receptor subtype from the bullfrog (Rana catesbeiana) brain and analyzing its functional expression. Like other mammalian NPR-A receptors, the bullfrog NPR-A receptor consists of an extracellular ligand binding domain, a hydrophobic transmembrane domain, a kinase-like domain and a guanylate cyclase domain. Sequence comparison among the bullfrog and mammalian receptors revealed a relatively low ( approximately 45%) similarity in the extracellular domain compared to a very high similarity ( approximately 92%) in the cytoplasmic regulatory and catalytic domains. Expression of NPR-A mRNA was detected in various bullfrog tissues including the brain, heart, lung, kidney and liver; highest levels were observed in lung. Functional expression of the receptor in COS-7 cells revealed that frog atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) elicited cyclic guanosine 3'5'-monophosphate production by stimulating the receptor in a dose-dependent manner from 10(-10) M concentrations. Rat ANP was also effective in stimulating the frog receptor whereas rat BNP and porcine BNP were less responsive to the receptor. On the other hand, frog C-type natriuretic peptide (CNP) as well as porcine CNP stimulated the receptor only at high concentrations (10(-7) M). This clearly indicates that the bullfrog receptor is a counterpart of mammalian NPR-A, and is specific for ANP or BNP but not for CNP.     

Natriuretic peptides reduce plasminogen activator inhibitor-1 expression in human endothelial cells

Plasma concentrations of natriuretic peptides increase in some pathological conditions, but very little is known about the effect of these vasodilator peptides on the regulation of the blood coagulation system. The fundamental role in the regulation of fibrinolysis is played by plasminogen activator inhibitor type 1 (PAI-1). Recent studies demonstrate that natriuretic peptides can modulate PAI-1 expression in bovine aortic smooth muscle cells and rat aortic endothelial cells. In this report, we tested the effect of natriuretic peptides on PAI-1 expression in the human endothelial cell line (EA.hy 926). For this purpose, we treated the cell cultures with ANP, BNP and CNP, and modulation of PAI-1 synthesis was evaluated. We compared the effect of natriuretic peptides on synthesis and release of PAI-1 in unstimulated cells, and after activation with tumour necrosis factor alpha (TNFalpha). Natriuretic peptides abolished TNFalpha - induced upregulation of PAI-1 expression at both the PAI-1 mRNA and the antigen levels. The inhibitory efficiency was higher in the case of CNP when compared to that produced by ANP and BNP, particularly when TNFalpha-stimulated cells were used. We observed an inhibition of stimulatory effect of TNFalpha on PAI-1 expression also at the level of the PAI-1 promoter in cells transfected with a PAI-1 promoter fragment (+71 to -800). The PAI-1 promoter activity was markedly inhibited by C-type natriuretic peptide, already at a very low (0.001 micro M) concentration of the peptide.