Inactivation of atrial natriuretic factor by the renal brush border

Atrial natriuretic factor (ANF), a 28-amino-acid peptide secreted from the mammalian heart, is known to be cleared rapidly from the circulation. In vitro and in vivo studies implicate the kidney as an important site for clearance and subsequent degradation of atrial natriuretic factor. We have observed that atrial natriuretic factor is inactivated rapidly by rabbit kidney brush-border membranes. The rate of degradation of ANF measured by the loss of bioactivity followed a similar time-course to the decrease in peptide peak area measured by high-performance liquid chromatography. Interestingly, inactivation of ANF produced only a single major degradation product, which was isolated and purified. Sequence analysis revealed that the product had the same sequence of amino acids as ANF with the Cys-7-Phe-8 bond cleaved and the disulfide bridge between Cys-7 and Cys-23 remaining intact. As the renal brush border contains an abundance of proteolytic activities, it is surprising that this peptide is cleaved primarily at a single peptide bond.     

The role of X-chromosome inactivation in female predisposition to autoimmunity

We propose that the phenomenon of X-chromosome inactivation in females may constitute a risk factor for loss of T-cell tolerance; specifically that skewed X-chromosome inactivation in the thymus may lead to inadequate thymic deletion. Using a DNA methylation assay, we have examined the X-chromosome inactivation patterns in peripheral blood from normal females (n = 30), female patients with a variety of autoimmune diseases (n = 167). No differences between patients and controls were observed. However, locally skewed X-chromosome inactivation may exist in the thymus, and therefore the underlying hypothesis remains to be disproved.     

中性肽链内切酶（CD10）生理功能研究进展

中性肽内切酶（Neutral Endopeptidase,NEF）,属于M13锌金属蛋白酶家族的一种Ⅱ型整合细胞膜糖蛋白,在许多组织中有广泛的表达。同时,NEP作为一种神经肽的降解酶,已经被发现广泛地存在于中枢神经系统以及外周各种组织中。NEP通过水解疏水性氨基酸侧链,使神经肽失活。而这些神经肽参与生命调节的多重代谢活动,对生命系统的正常有序运转有重要的作用。其中P物质为一种神经肽,是造血系统网络的成员之一,同时也可以诱发炎症反应,从而,NEP可以间接参与造血系统和呼吸系统的代谢活动。而心钠素是调节血压维护心肌功能的重要调节因子,NEP通过调节心钠素的浓度来调节血压,最终参与心血管系统的代谢。由于NEP具有广泛的组织特异性,决定了NEP在多个系统的调节中都具有重要意义。因此就NEP在造血系统,心血管系统和呼吸系统的功能做一综和评述。     

Ozone increases amino- and carboxy-terminal atrial natriuretic factor prohormone peptides in lung,heart, and circulation

Ozone can cause pulmonary edema and simultaneously decrease blood pressure. Atrial natriuretic peptides may mediate both of these effects in that they increase pulmonary capillary permeability resulting in edema formation and are potent vasodilating peptides. To examine this possibility, the lungs of Fischer 344 rats were exposed to ozone (0.5 ppm) for 8 hours which resulted in a three- to fourfold increase in atrial natriuretic peptides. Ozone also increased atrial natriuretic peptides in the heart two- to fivefold from 266 ± 25, 226 ± 22, and 288 ± 40 ng/g (room air) to 716 ± 26, 471 ± 14, and 1473 ± 235 ng/g recognized by the proANFs 1–30 and 31–67 and atrial natriuretic factor radioimmunoassays, respectively. Ozone also doubled the concentrations of proANFs 1–30, 31–67, and 1–98 and ANF in the circulation. This study demonstrates that ozone increases atrial natriuretic peptides within the heart, lung, and circulation, suggesting that atrial natriuretic peptides may mediate the decreased blood pressure and pulmonary edema observed with ozone exposure. Since the proANF 31–67 radioimmunoassay exclusively recognizes the ANF prohormone within the heart, this study further indicates that ozone can increase the synthesis of the ANF prohormone.     

中性肽链内切酶(CD10)生理功能研究进展

中性肽内切酶(Neutral Endopeptidase,NEP),属于M13锌金属蛋白酶家族的一种Ⅱ型整合细胞膜糖蛋白,在许多组织中有广泛的表达。同时,NEP作为一种神经肽的降解酶,已经被发现广泛地存在于中枢神经系统以及外周各种组织中。NEP通过水解疏水性氨基酸侧链,使神经肽失活。而这些神经肽参与生命调节的多重代谢活动,对生命系统的正常有序运转有重要的作用。其中P物质为一种神经肽,是造血系统网络的成员之一,同时也可以诱发炎症反应,从而,NEP可以间接参与造血系统和呼吸系统的代谢活动。而心钠素是调节血压维护心肌功能的重要调节因子,NEP通过调节心钠素的浓度来调节血压,最终参与心血管系统的代谢。由于NEP具有广泛的组织特异性,决定了NEP在多个系统的调节中都具有重要意义。因此就NEP在造血系统,心血管系统和呼吸系统的功能做一综和评述。     

急性缺血性脑卒中患者入院时血浆BNP水平与梗死部位关系

目的：分析急性缺血性脑卒中患者入院时血浆脑钠肽（BNP）水平与缺血性脑卒中梗死部位的关系。方法：随机入选88例急性缺血性脑卒中患者,按梗死部位,将其分为前循环病灶组（66名）和后循环病灶组（22名）两组进行比较。测定入院时血浆脑钠肽（BNP）水平进行比较。两组脑卒中病人的危险因素血糖、糖化血红蛋白、血脂全套,肝肾功能分析对比,并将急性缺血性脑卒中患者梗死部位相关的多个变量采用单因素logistic回归分析。结果：前循环病灶组血浆脑利钠肽水平的中位数是225.90 pg/mL,四分位数间距为596.00 pg/mL;后循环病灶组的中位数是750.95 pg/mL,四分位数间距为907.00 pg/mL。后循环病灶组血浆脑利钠肽水平要显著高于前循环病灶组血浆脑利钠肽水平,两个部位间入院时的脑利钠肽水平有统计学差异（P=0.004）。通过入院时脑利钠肽水平与缺血性脑卒中梗死部位的关系的ROC曲线,得出截点299.50 pg/mL。入院时血浆脑利钠肽水平≥299.50 pg/mL可以作为后循环病灶组的预测指标,其敏感性72.72%,特异性62.12%。结论：急性缺血性脑卒中患者入院时血浆BNP水平可作为急性期区别前后循环脑梗死的预测因子。     

Responses of vasoactive hormones in congestive cardiac failure

Congestive cardiac failure causes activation of various neurohumoral responses that increase total peripheral resistance and promote salt and water retention. These effects increase blood pressure and organ perfusion in the short term, but ultimately cause further cardiac decompensation by increasing ventricular afterload and cardiac work. The role of the renin-angiotensin-aldosterone system and the catecholamines is partially understood, and blockade of these systems as a treatment of heart failure is now established. The role of vasopressin in heart failure is more controversial, but there is now compelling evidence that vasopressin may have important vasoconstrictor actions in addition to its fluid retaining properties. Atrial natriuretic factor is a newly described cardiac hormone released from the atrium. Atrial natriuretic factor causes natriuresis, diuresis, vasodilatation, suppression of thirst, and suppression of both renin and aldosterone. These actions largely counteract the effects of the renin-angiotensin system and vasopressin. Plasma atrial natriuretic factor has been reported to be markedly elevated in human and experimental heart failure, and may act to limit the neurohumoral response to reduced cardiac output. This review summarizes our understanding of the vasoactive hormones and reports experimental evidence supporting a pathophysiological role for vasopressin and atrial natriuretic factor in congestive cardiac failure.     

The elucidation of the structure of atrial natriuretic factor, a new peptide hormone

The benchmark experiments of Adolfo de Bold and Harald Sonnenberg revealed that heart atria contained a substance or substances (atrial natriuretic factor) which when injected into rats caused a profound diuresis, natriuresis, and fall in blood pressure. Acid extraction and purification of atrial natriuretic factor resulted initially in the purification of a low molecular weight peptide containing a disulfide bond. This peptide was named cardionatrin I. Amino acid sequencing of less than 1 nmol of cardionatrin I revealed it to be a 28-residue peptide with the following structure: (sequence; see text) The position of the disulfide bond was verified by a radioactive method. From the sequence of complementary DNA for atrial natriuretic factor, the 28-residue peptide was shown to be the C-terminal portion of a larger protein called pro-atrial natriuretic factor. The discovery and characterization of atrial natriuretic factor substantiated the idea that the heart atria serve in an endocrine capacity.     

The effect of atrial natriuretic factor on force development in rat cardiac trabeculae

Studies in single cardiac muscle cells have demonstrated that atrial natriuretic factor decreases the L-type calcium current. Recent investigations in human atrial cells have also demonstrated that atrial natriuretic factor causes a voltage-dependent reduction in sodium channel activity and thus may reduce intracellular calcium via decreased activity of the sodium-calcium exchange mechanism. By reducing intracellular calcium, atrial natriuretic factor may have a negative inotropic effect on cardiac muscle. To characterize the effect of atrial natriuretic factor on the development of force, we studied the force-sarcomere length relationship in 11 right ventricular rat trabeculae, both before and after exposure of the muscles to increasing concentrations of atrial natriuretic factor. Sarcomere length was measured by laser diffraction techniques and controlled by a servomotor system. The addition of atrial natriuretic factor to the superfusion solution, at concentrations of 10(-9)-10(-7) M, increased stimulus threshold, reduced peak twitch force in a dose-dependent manner by 38% (maximum), and reduced time to peak twitch force by 15% (maximum). Incubation of muscle preparations with concentrations of atrial natriuretic factor below 10(-9) M had no effect on force generation. The negative inotropic effect of atrial natriuretic factor was associated with a change in the shape of the force-sarcomere length relationship, similar to a reduction of the extracellular calcium concentration. ANF (10(-7) M) had no effect on the rate of decay of force following post extra-systolic potentiation. These observations are consistent with the assumption that the negative inotropic effect of atrial natriuretic factor is mediated by reduction of calcium entry into the cardiac cell.     

Temporal (Circadian) and Functional Relationship Between Atrial Natriuretic Peptides and Blood Pressure

Long-acting natriuretic peptide, vessel dilator, and atrial natriuretic factor consisting of amino acids (a.a.) 1 to 30, 31 to 67, and 99 to 126 of the 126-a.a. atrial natriuretic factor (ANF) prohormone, respectively, circulate in humans and have potent vasodilatory properties. To determine if these atrial natriuretic peptides are directly related to blood pressure in clinically healthy normotensive humans, we obtained 24-h profiles of vessel dilator, long-acting natriuretic peptide, ANF, and blood pressure in 10 men in 1988 and 11 men in 1993 (seven men were studied twice) to compare circulating concentrations of atrial natriuretic peptides with naturally occurring changes in blood pressure. Overall, vessel dilator, long-acting natriuretic peptide, and ANF each had significant (p > 0.001) circadian rhythms, with peak concentrations late during sleep (at 04:00 h) being nearly twice their concentrations in the afternoon and evening. This high-amplitude circadian change allowed for the refinement of normal limits for ANF peptides by computing 3-hourly tolerance intervals (chronodesms) against which to compare time-specified single samples for normality. Systolic, diastolic, and mean arterial blood pressure also had significant circadian rhythms (p > 0.001) with peaks and troughs that were exactly opposite those of the ANF peptides. In addition to this inverse temporal relationship, there was a significant inverse correlation between absolute values for blood pressure and each ANF peptide (p > 0.001), implying a functional relationship. These data suggest that in addition to other well-established neurochemical factors, the ANF peptides (vessel dilator, long-acting natriuretic peptide, and ANF) are important for the maintenance of blood pressure and modulation of its circadian rhythm.     

Atrial granules contain an amino-terminal processing enzyme of atrial natriuretic factor

At least three enzymes have been identified in atrial tissue homogenates that are capable of processing pro-atrial natriuretic factor to active atrial peptides. The atrial peptides possess potent natriuretic, diuretic, vasorelaxant, and hemodynamic properties, and their existence has implicated the mammalian heart as an endocrine organ. We have purified and characterized a serine proteinase (Mr approximately equal to 70,000) associated with atrial granules that preferentially hydrolyzes the Arg-Ser bond in the synthetic substrates Gly-Pro-Arg-Ser-Leu-Arg, benzoyl-Gly-Pro-Arg-Ser-Leu-Arg, and benzoyl-Gly-Pro-Arg-Ser-Leu-Arg-Arg-2-naphthylamide, the Arg-2-naphthylamide bond in the substrate benzoyl-Gly-Pro-Arg-2-naphthylamide, and the Arg-Ser bond in a 31-residue substrate (Gly96-Tyr126 peptide) corresponding to residues Arg98-Ser99 in pro-atrial natriuretic factor. The Gly96-Tyr126 peptide contains the putative processing site in pro-atrial natriuretic factor and the sequence for the bioactive peptides. Our results indicate that the minimum processing site sequence is -Gly-Pro-Arg-Ser-Leu-Arg-Arg- and that the Ser99-Tyr126 natriuretic peptide is the predominant hydrolytic product. After prolonged incubation or at high enzyme concentrations, the Ser103-Tyr126 natriuretic peptide may also be formed. The Ser103-Arg125 natriuretic peptide was only a very minor product. The doublet of basic amino acids is not the primary processing site in pro-atrial natriuretic factor, but their presence may influence cleavage at the single Arg residue "upstream." Our findings are consistent with the idea that the pro-protein and the processing enzymes are packaged into the secretory granule and in response to the proper stimulus, the pro-protein is processed to the active peptides, probably during the process of secretion. The processing pathway of pro-atrial natriuretic factor is discussed.     

Natriuretic and depolarizing effects of a stable fly (Stomoxys calcitrans) factor on Malpighian tubules

A two-step HPLC purification procedure resulted in a factor from the stable fly that depolarizes the lumen-negative transepithelial voltage (V(t)) of the adult stable fly Malpighian tubule. When applied to tubules of the female mosquito, Aedes aegypti, this factor partially mimics the electrophysiological actions of the mosquito natriuretic factor (MNF). It also selectively increases active transepithelial Na transport by the mosquito Malpighian tubule. The blood meal causes a transient increase in hemolymph Na and Cl contents and hemolymph volume during the course of the 24-h post-feeding period. The level of a factor that is immunologically cross-reactive with the human atrial natriuretic peptide (ANP) increases more than 6-fold within 6h following a blood meal by the stable fly. The temporal pattern of the levels of the ANP-immunoreactive factor closely parallels the blood meal-induced rise and subsequent fall in hemolymph NaCl content and hemolymph volume, suggesting a functional correlation between the ANP-immunoreactive factor and the rate of NaCl and fluid loss from the hemolymph.     

Changes of regional blood flow induced by atrial natriuretic factor (ANF) in conscious rats

The effect of synthetic atrial natriuretic factor (ANF 101-126) has been studied on regional blood flow distribution. Microspheres (15 +/- 3 microns), labelled with either 113Sn or 57Co, were injected through an intraventricular cannula into conscious rats while a reference blood sample was withdrawn. Two minutes after the first microspheres injection either ANF or NaCl were injected. Five minutes later, the second microspheres injection was administered, and after two minutes the animals were sacrificed, and several tissues removed and counted. Percent of flow distribution, cardiac output and tissue blood flow were calculated by standard formulas. ANF produced a significant increase in absolute blood flow in lungs, heart, spleen, kidneys and testes. Total renal blood flow and total splanchnic blood flow were also increased in ANF-injected animals. No significant changes were observed in cardiac output. It is suggested that the natriuretic and hypotensive responses to ANF in vivo may be, at least partially, explained by its hemodynamic effects.     

Atrial natriuretic peptide clearance receptors in trout: effects of receptor inhibition in vivo.

Inactivation of circulating atrial natriuretic peptides (ANP) by specialized clearance (C) receptors has been characterized in mammals but has not been examined in fish. In the present study arterial blood pressure, urine flow, and urine electrolytes were measured in chronically cannulated rainbow trout, Oncorhynchus mykiss, during infusion of the specific C receptor inhibitor, SC-46542. C receptor inhibition decreased blood pressure and pulse pressure, increased heart rate and urine flow, but did not affect urinary electrolyte concentrations. These responses are consistent with those produced by exogenous ANP administration and indicate that: (1) trout possess C-type receptors capable of ANP inactivation, and (2) ANP-like molecules are continuously released and metabolized by trout in vivo. Phosphoramidon, an inhibitor of neutral endopeptidase, did not enhance the SC-46542 response, indicating that C receptors predominate in ANP inactivation in these fish.     

Renal responses to atrial natriuretic factor during converting enzyme inhibition

The effect of converting enzyme inhibitor (CEI) on the renal response to atrial natriuretic factor (ANF) was determined in the rat. In the absence of CEI, ANF produced rapid and significant increases in sodium, potassium, calcium, and urine excretions while blood pressure declined transiently. In the presence of CEI, ANF enhanced the excretion of sodium and potassium but not of calcium and urine. The activity of CEI was documented by observing that, in the presence of CEI, the elevation of blood pressure produced by angiotensin I was significantly attenuated. The potentiating effect of CEI on the natriuretic response to ANF supports the hypothesis that converting enzyme may be involved in the metabolism of ANF.     

Plasma atrial natriuretic factor concentrations and renal actions in the domestic fowl

Plasma atrial natriuretic factor concentrations in Rhode Island red hens averaged 72.1±6.9 pg·ml^-1, range 33.4–136.0 pg·ml^-1. The intravenous infusion of isotonic saline containing 3% dextran for 2 h produced no significant changes in plasma osmotic or electrolyte concentrations; however, haematocrit changes indicated vascular expansions of 14.4% after 1 h and 21.3% after 2 h and plasma atrial natriuretic factor concentrations were elevated by 190% and 257%, respectively. The intravenous infusion of chicken atrial natriuretic factor at rates of 10, 25, 50 and 100 ng·kg^-1·min^-1 for 20 min produced levels of plasma atrial natriuretic factor that were directly related to the infusion rate and which, in birds undergoing a steady-state diuresis/natriuresis driven by the intravenous infusion of isotonic saline at 1 ml·min^-1, produced dose-dependent increases of 19, 26, 38 and 55% in urine flow rate and of 8, 30, 49 and 77% in sodium excretion. Potassium excretion was significantly increased only at the two highest atrial natriuretic factor infusion rates. The observed correlation between plasma atrial natriuretic factor concentration and vascular volume together with the atrial natriuretic factor-induced modulation of renal salt and water elimination is consistent with the concept that in the chicken this peptide has a physiological role as a regulatory hormone in volume homeostasis.Abbreviations AII angiotensin II - ANF atrial natriuretic factor - AVT arginine vasotocin - BV blood volume - chANF chicken atrial natriuretic factor - CHE chicken heart extract - ECF extracellular fluid - EDTA ethylenediaminetetra-acetate - Hct haematocrit - i.v. intravenous - PCR plasma clearance rate - PRA plasma renin activity - RIA radioimmunoassay     

Cardiovascular investigations of an endogenous digoxin-like factor

A circulating factor with digoxin immunoreactivity has been demonstrated. Elevated levels of this substance appear to be present after volume expansion and salt loading, and in some forms of hypertension. The potentially causative role for this factor in hypertension can be demonstrated by the normalization of blood pressure after antidigoxin antibody infusions in low-renin and sodium-dependent hypertension. The possibility that renal excretory defects may be the initiating event to elevate endogenous digoxin is suggested by studies with normotensive humans and monkeys with renal disease. In the latter case cardiovascular deficits were noted that were analogous to those detected in renal hypertensive monkeys with elevated endogenous digoxin. Considered together, these results suggest the existence of a natriuretic and hypertensive substance that plays a role in body fluid homeostasis and blood pressure regulation.     

Renal hemodynamic and natriuretic effects of atrial natriuretic factor

In this article we review the renal hemodynamic and excretory actions of atrial natriuretic factor (ANF) and consider some of the mechanisms of its vascular and natriuretic effects. ANF leads to a marked, sustained, and parallel increase in whole-organ and superficial single-nephron glomerular filtration rate (GFR) while mean blood pressure is decreased and renal blood flow (RBF) is unchanged or even decreased. The increase in GFR is caused by an efferent arteriolar vasoconstriction or by a combination of afferent vasodilation and efferent vasoconstriction. ANF also leads to a decrease in the hypertonicity of the innermedullary interstitium. Together with the increase in GFR, this phenomenon accounts wholly or in great part for the ANF-induced natriuresis. The overall renal vascular effects of ANF are complex and may tentatively be conceptualized as a behavior of a functional partial agonist: slight vasoconstriction in vasodilated kidneys, no sustained effects on the vascular resistance in normal kidneys, and vasodilation in vasoconstricted kidneys. The vasoconstrictor effect of ANF may be direct or indirect and depends on extracellular calcium whereas the antagonist effect likely results from alterations in intracellular calcium homeostasis. The data raise the perspective that ANF is not only a powerful natriuretic substance but has the potential of being an important modulator of GFR and RBF in intact animals.     

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.     

Cellular mechanism of release of atrial natriuretic factor

Tissue extracts of rat heart atria contain a family of peptides with natriuretic and vasorelaxant properties. We have shown previously that this “atrial natriuretic factor” may be released in vitro from incubated atria by muscarinic cholinergic stimulation. Experiments reported here demonstrate that incubation with adrenalin or arginine vasopressin, but not with deamino-8-D-arginine vasopressin, also results in liberation of atrial natriuretic factor. Since the effective agonists have in common activation of the cellular polyphosphoinositide system with consequent production of inositol triphosphate, we suggest that inositol triphosphate is the second messenger of stimulus-secretion coupling in atrial cells.