Localization of specific binding sites for atrial natriuretic factor in peripheral tissues of the guinea pig, rat, and human

Mechanisms that drive bone pain across the lifespan

Disorders of the skeleton are frequently accompanied by bone pain and a decline in the functional status of the patient. Bone pain occurs following a variety of injuries and diseases including bone fracture, osteoarthritis, low back pain, orthopedic surgery, fibrous dysplasia, rare bone diseases, sickle cell disease and bone cancer. In the past 2 decades, significant progress has been made in understanding the unique population of sensory and sympathetic nerves that innervate bone and the mechanisms that drive bone pain. Following physical injury of bone, mechanotranducers expressed by sensory nerve fibres that innervate bone are activated and sensitized so that even normally non-noxious loading or movement of bone is now being perceived as noxious. Injury of the bone also causes release of factors that; directly excite and sensitize sensory nerve fibres, upregulate proalgesic neurotransmitters, receptors and ion channels expressed by sensory neurons, induce ectopic sprouting of sensory and sympathetic nerve fibres resulting in a hyper-innervation of bone, and central sensitization in the brain that amplifies pain. Many of these mechanisms appear to be involved in driving both nonmalignant and malignant bone pain. Results from human clinical trials suggest that mechanism-based therapies that attenuate one type of bone pain are often effective in attenuating pain in other seemingly unrelated bone diseases. Understanding the specific mechanisms that drive bone pain in different diseases and developing mechanism-based therapies to control this pain has the potential to fundamentally change the quality of life and functional status of patients suffering from bone pain.

Atrial natriuretic peptide inhibits the spontaneous contractions of rabbit isolated ileum

The present study investigates the effects of atriopeptin II on spontaneous phasic contractions of rabbit isolated ileum. Atriopeptin II caused a significant and concentration-dependent decrease in ileum motor activity. This effect was mimicked by 8-Br-cGMP and it was not affected by pretreatment with tetrodotoxin. Verapamil significantly decreased ileum contractions; however, in the presence of this calcium blocker, atriopeptin II further reduced ileal motility. These findings demonstrate that atriopeptin II depresses the motility of rabbit ileum through a cGMP-dependent mechanism and suggest that neither ileal neural networks nor extracellular calcium are involved in this effect.

Role of natriuretic peptide signaling in modulating asthma and inflammation

Atrial natriuretic peptide (ANP), the C-terminal peptide comprising residues 99-126 of the pro-ANP hormone, has been studied for 3 decades for its cardiovascular effects. Recent reports suggest that it plays a significant role in modulation of the immune system. Immune cells, including macrophages, dendritic cells, and T lymphocytes, express receptors for ANP. ANP plays a significant role in shaping the early immune response to environmental antigens and may play a critical role in the interaction between cells of the innate and adaptive immune systems; it also appears to be involved in polarizing the immune response to allergens. Thus, ability to alter the magnitude of natriuretic peptide receptor A (NPRA) signaling could be exploited to develop therapeutics for several allergic diseases, including asthma. This report will review and critically evaluate the role of the ANP pathway in asthma and inflammation.

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.

Modification of Atrial Natriuretic Peptide Receptor Expression in the Rat Inner Ear

HYPOTHESIS

The purpose of this animal study was to confirm the presence of all three atrial natriuretic peptide (ANP) receptor subtypes in the rat inner ear and compare the expression of each receptor after inner ear injection of ANP, phosphate-buffered saline, or a solution containing ANP incubated with anti-ANP antibody (to block upregulation).

BACKGROUND

Receptors for ANP and related compounds have been localized in the inner ear of animals and humans. A previous study at this institution demonstrated the ability to up-regulate the expression of the three ANP receptors (ANP-A, ANP-B, ANP-C) in response to round window injection of ANP in the rat inner ear.

METHODS

After surgical exposure, the round window of female Lewis rats was injected with various concentrations of ANP, ANP plus anti-ANP antibody, or control. Animals were killed 24 hours after injection, inner ear tissues were harvested and homogenized, and RNA was isolated for reverse-transcription polymerase chain reaction.

RESULTS

Electrophoresis showed the presence of all three receptor subtypes with exposure to phosphate-buffered saline. Expression was significantly higher 24 hours after injection with the two concentrations of ANP. This increase was partially blocked with increasing relative concentrations of anti-ANP antibody.

CONCLUSIONS

These findings confirm the presence and responsiveness of ANP receptors in the rat inner ear. The ability to block up-regulation with the antibody provides a potential new research tool for manipulating the function of this hormone system in experimental models and, ultimately, in understanding the mechanisms of fluid homeostasis in the inner ear.

Atrial natriuretic peptide receptor upregulation in the rat inner ear

The purpose of this study was to further examine whether fluid homeostasis in the endolymphatic system could be regulated by a locally effective paracrine system involving atrial natriuretic peptides (ANPs) and their receptors. We assessed the biologic activity of the 3 ANP receptors (ANP-A, ANP-B, ANP-C) in the rat inner ear by measuring receptor upregulation after inner ear administration of ANPs. After appropriate anesthesia, female Lewis rats were injected with ANP via the round window. The animals were sacrificed 24 hours later, and RNA was isolated for reverse transcription-polymerase chain reaction (RT-PCR). Electrophoresis of RT-PCR products showed the presence of all 3 ANP receptor genes in both injected and control animals. Gene expression was significantly higher 24 hours after injection. These findings demonstrate that ANP receptors in the inner ear can be upregulated after injection of ANPs.

Up-regulation of 'clearance' receptors in patients with chronic heart failure: a possible explanation for the resistance to biological effects of cardiac natriuretic hormones

BACKGROUND

Three specific receptors for the cardiac natriuretic peptide system have been identified to date. Down-regulation of the biologically active binding sites (i.e. NPR-A and NPR-B) could explain the blunted response to cardiac natriuretic hormones observed in heart failure (HF), but not the increased metabolic clearance rate. Variations in the ratio between biological and clearance (NPR-C) receptors in target tissue may explain this increase.

AIM

The aim of this study was to investigate the regulation of NPR-C receptors on platelets, in patients with HF.

METHODS

Eighteen patients with HF (NYHA class: I-II, n=8; III-IV, n=10) and 18 age-matched healthy subjects were studied. The affinity constant (K(d)) and density (B(max)) of binding sites were derived by saturation assays on platelet suspensions using 125I-ANP as radioligand.

RESULTS

B(max) increased as a function of the severity of disease: 21.3+/-3.3 fmol/10(9) cells in class III-IV, 11.7+/-2.2 in class I-II, and 11.6+/-1.1 in controls, respectively (P=0.0179 for class III-IV vs. controls and P=0.0451 vs. NYHA I-II).

CONCLUSIONS

The increase in density of 'clearance' receptors in severe HF is theoretically consistent with the reduction in cardiac natriuretic peptide biological activity, as well as the increase in metabolic clearance rate. This suggests that clearance receptor blockade may be of potential therapeutic value in HF.

Natriuretic peptides receptors in human aldosterone-secreting adenomas

Atrial natriuretic peptide (ANP) and B-type or brain natriuretic peptide (BNP) inhibit aldosterone secretion in humans both in vitro and in vivo. Unresponsiveness of aldosterone-secreting adenomas (aldosteronomas) to ANP in vitro and in vivo, might be due to reduced expression of the biologically-active natriuretic peptide receptor type A (NPr-A) and/or increased expression of the clearance receptor for natriuretic peptides (NPr-C). Therefore, we have analyzed NPr gene expression and ANP binding sites in human adrenals and aldosteronomas. Using reverse transcription and polymerase chain reaction, we cloned and characterized cDNAs for NPr-A, NPr-C, and the receptor (NPr-B) for the C-type natriuretic peptide (CNP). Total RNA from three normal human adrenals (obtained at surgery from patients with renal cancer) and five aldosteronomas were used for Northern analysis. NPr-A mRNA (approximately 4 kb) and NPr-B mRNA (approximately 4 kb) were expressed without significant differences in adrenals and in aldosteronomas except in an aldosteronomas that contained only very low amounts of NPr mRNAs. The gene expression of NPr-C was barely detectable both in adrenals and in aldosteronomas. ANP binding sites were analyzed by autoradiography with 125I-labeled ligand in other six aldosteronomas. Only one of the adenomas analyzed showed ANP binding sites with density of granules similar to nonadenomatous glomerulosa, whereas the others had significantly reduced densities. In summary, aldosteronomas express the genes encoding for NPr but mainly NPr-A, similarly to control adrenals. On the contrary, the binding sites for ANP are greatly reduced in most aldosteronomas. A somatic mutation or a post-transcriptional defect that reduces ANP binding sites might be present in some aldosteronomas.

Type B and type C natriuretic peptide receptors modulate intraocular pressure in the rabbit eye

We investigated (1) the in vivo functional significance of the type B (ANP(B)) and type C (ANP(C)) natriuretic peptide receptors in the rabbit eye by evaluating the effect of intracameral administration of C-type natriuretic peptide (CNP) and C-ANP-(4-23) on intraocular pressure, and (2) the action of CNP on guanylate cyclase activity in the rabbit ciliary process membranes. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were also studied for comparison. We demonstrated that the natriuretic peptides decrease intraocular pressure and stimulate guanylate cyclase activity, CNP being the most potent. The duration of the effect of C-ANP-(4-23) on intraocular pressure reduction was almost 9-fold that of the BNP and 20-fold that of ANP and CNP effect. This ligand increased threefold the immunoreactive natriuretic peptides levels in aqueous humour. Our data demonstrate the presence of functional ANP(A) and ANP(B) receptors in the rabbit eye and that the ANP(C) receptor modulates the concentration of the natriuretic peptides in the aqueous humour.

Non-lysosomal cycling pathway for atrial natriuretic peptide activated by protein kinase C in human NPE cells

Atrial natriuretic peptide (ANP) stimulates aqueous humor formation in primates, but the membrane-bound receptors which mediate this effect have not been well studied in the eye. Endocytosis of [125I]ANP bound to natriuretic peptide C receptors was characterized in fetal human nonpigmented ciliary epithelial (NPE) cells. [125I]ANP which bound to cells at 4 degreesC was detected in the cell interior after a temperature shift to 37 degreesC. Appearance of ligand within the cell peaked at 5 min, and then declined towards zero over 20 min. The endocytosis inhibitor phenylarsine oxide blocked the appearance of internalized ligand, whereas the lysosomotropic drug chloroquine had no effect on internalization but blocked subsequent loss of internalized ligand. Chloroquine also blocked the accumulation of degraded ligand in the extracellular medium. Treatment with phorbol 12-myristate, 13-acetate accelerated the loss of internalized ligand from cells and increased the accumulation of ligand in the extracellular medium. Ligand in the medium was also increased by dioctanoylglycerol but not by 4alpha phorbol didecanoate, an isomer which does not activate protein kinase C. The protein kinase inhibitors staurosporine and bisindolylymaleimide blocked the increase in ligand. Phorbol ester-stimulated loss of internalized ligand occurred in the presence of chloroquine. TCA precipitation of ligand in the extracellular medium showed that both degraded and undegraded [125I]ANP were present. However, in the presence of chloroquine only, undegraded ANP was detected in the medium, and phorbol esters stimulated its rate of appearance by approximately 2 fold. A similar stimulation occurred when cells containing internalized ligand, but stripped of membrane-bound ligand, were exposed to phorbol esters. The data suggest that ANP bound to natriuretic peptide C receptors on NPE cells is endocytosed, and that protein kinase C activates a non-lysosomal pathway for ANP retroendocytosis in these cells.

Compared effects of natriuretic peptides on ovalbumin-induced asthmatic model

We compared the effects of natriuretic peptides on antigen-induced bronchoconstriction and airway microvascular leakage in sensitized guinea pigs. Anesthetized male guinea pigs, ventilated via a tracheal cannula, were placed in a plethysmograph to measure pulmonary mechanics for 10 min after challenge with 1 mg/kg of ovalbumin, and then Evans blue dye was extravasated into airway tissue in order to indicate and evaluate microvascular leakage. Three separate intravenous pretreatments using atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) significantly inhibited the ovalbumin-induced bronchoconstriction and microvascular leakage in a dose-dependent manner. These inhibitory effects were mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate. We showed that the rank order of inhibitory potencies, which were mediated by cyclic guanosine 3',5'-monophosphate, was BNP > or = ANP > or = CNP. These results gave us some clues for the clinical application of the natriuretic peptides.

Receptors for natriuretic peptides in adrenal chromaffin cells

Atrial, brain, and C-type natriuretic peptides of the atrial natriuretic peptide family are present in adrenal chromaffin cells, and are secreted with catecholamines by exocytosis. These peptides modulate the physiological functions of the cells such as synthesis and secretion of catecholamines in an autocrine manner interacting with natriuretic peptide receptors.

ANF system in the newborn piglet pulmonary vessels

The atrial natriuretic factor (ANF) induces diuresis, natriuresis, and vasodilation. Although it was originally found to be secreted from the atria, ANF synthesis has been demonstrated in other organs. The adult lung is not only the first target organ for ANF, but it also expresses the ANF gene and synthesizes, releases, and clears ANF from the circulation. We have shown the presence of ANF in human fetal lungs and also demonstrated that these lungs can release bioactive ANF. However, the role of the ANF system in the newborn lung is unknown. Therefore we studied the ANF system in pulmonary vessels (arteries and veins dissected from the hilum down to a 100-microm diameter), in isolated perfused lungs, and in the plasma from pulmonary artery and vein of 1- and 7-day-old piglets. High-performance liquid chromatography (HPLC) revealed the presence of both the mature peptide and the ANF prohormone in pulmonary vein microsomes, but in pulmonary arteries, only the mature form was identified. Furthermore, in the veins, the ANF content tended to be higher in 7- than in 1-day-olds. ANF caused a dose-dependent decrease in perfusion pressure (p < 0.05). In veins and arteries, most of the ANF receptors were of the type A guanylate cyclase as opposed to clearance receptors. Interestingly, the ANF receptors were fewer in veins, where synthesis takes place, than in arteries (p < 0.05). Significant circulating ANF plasma levels were measured by radioimmunoassay in both pulmonary artery and vein. However, there was no site difference in ANF plasma levels, suggesting that ANF is cleared and synthesized in the pulmonary vessels. In conclusion, the entire ANF system is present in the newborn piglet pulmonary vessels. The paucity of clearance receptors compared with functional receptors potentiates the role of ANF in the regulation of postnatal pulmonary vascular resistance.

Detection of mRNA encoding guanylate cyclase A/atrial natriuretic peptide receptor in the rat cochlea by competitive polymerase chain reaction and in situ hybridization

Expression of mRNA encoding guanylate cyclase A (GC-A)/atrial natriuretic peptide (ANP) receptor in the rat cochlea was examined by polymerase chain reaction (PCR) and in situ hybridization (ISH). After reverse-transcription, PCR amplification, subcloning, and sequencing, we found that GC-A mRNA with sequence identical to that previously cloned from the rat brain (Chinkers et al., 1989) was expressed in the rat spiral ligament as well as in the spiral ganglion. However, GC-A mRNA was not detected in the stria vascularis. Competitive PCR using internal standard DNAs indicated that the expression of GC-A in the cochlea occurred at a level approximately 16 times less than that measured in kidney cortex. ISH histochemistry using a 35S-labeled antisense riboprobe showed the highest level of expression of GC-A mRNA to be in oligodendrocytes of the cochlear nerve root. The results suggest that ANP may play a role in the cochlear nerve function.

Messenger RNAs encoding the natriuretic peptides and their receptors are expressed in the eye

The rates of secretion and removal of aqueous humour are major determinants of intraocular pressure (IOP). The natriuretic peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) are vasodilators with variable effects on electrolyte and water transport at sites such as the nephron. There is some evidence that they may also affect fluid balance in the eye. As a first step in understanding the function of these peptides in the eye, we have used the technique of cDNA amplification with the polymerase chain reaction to demonstrate the presence of mRNA transcripts encoding the three natriuretic peptide receptors (NPR-A, NPR-B and NPR-C) in the retina, choroid and ciliary process of the rat and rabbit eye. In addition we have observed a differential distribution of ANP, BNP and CNP mRNAs in ocular tissues suggesting that at least part of the natriuretic peptide immunoreactivity detected in the eye arises from local synthesis of peptide. Thus, the eye appears to be able to synthesize all the components of the natriuretic peptide system necessary to modulate IOP independently of changes in the plasma concentrations of these peptides.

Gene expression of natriuretic peptide receptors in myocardial cells

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are cardiac hormones that serve to unload the heart through their effects on the kidney and vasculature. Whether the heart itself represents a site of action for these peptides is currently the subject of debate. Although functional studies indicate that ANP has some effects on isolated myocytes, several studies have been unable to detect binding of the hormone to these cells. The present study demonstrates that the genes for all three natriuretic peptide receptor (NPR) subtypes, NPR-A, NPR-B, and NPR-C, are expressed in the rat heart. For microlocalization of the receptor mRNAs in myocytes and nonmyocytic cells, a combination of cell isolation and reverse transcription-polymerase chain reaction (RT-PCR) was used. Cardiac myocytes were isolated by enzymatic dissociation of rat ventricular tissue, purified by density gradient centrifugation, and collected as single cells under microscopic control. Analysis by RT-PCR revealed the presence of transcripts for NPR-A as well as NPR-B and NPR-C. However, cGMP generation in purified myocytes was stimulated only by ANP and BNP, which specifically bind to NPR-A, whereas C-type natriuretic peptide (CNP, an NPR-B agonist) was ineffective. Therefore, rat ventricular myocytes appear to produce predominantly NPR-A. The expression of NPR-B may be low or even absent. The mRNAs for all three NPRs were also found in cultures of fibroblasts from the rat heart. In contrast to the myocytes, large increases in cGMP were observed in response not only to ANP but also to CNP.

Effects of angiotensin, vasopressin and atrial natriuretic peptide on intraocular pressure in anesthetized rats

The effects of atrial natriuretic peptide (ANP), vasopressin (AVP) and angiotensin (ANG) on blood and intraocular pressures of pentobarbital anesthetized rats were evaluated following intravenous, intracerebroventricular or anterior chamber routes of administration. Central injections did not affect intraocular pressure. Equipressor intravenous infusions of ANG raised, whereas AVP decreased, intraocular pressure. Direct infusions of a balanced salt solution (0.175 microliter/min) raised intraocular pressure between 30 and 60 min. Adding ANG or ANP slightly reduced this solvent effect but AVP was markedly inhibitory. An AVP-V1 receptor antagonist reversed the blunting of the solvent-induced rise by the peptide, indicating receptor specificity. Acetazolamide pretreatment lowered intraocular pressure, but the solvent-induced rise in intraocular pressure and inhibition by AVP still occurred without altering the temporal pattern. Thus, these effects appear unrelated to aqueous humor synthesis rate. The data support the possibility of intraocular pressure regulation by peptides acting from the blood and aqueous humor.

Interaction between atrial natriuretic peptide and vasoactive intestinal peptide in guinea pig cecal smooth muscle

BACKGROUNDS & AIMS

The role of atrial natriuretic peptide (ANP) in gastrointestinal motility is still unclear. The aim of this study was to investigate the relationship between ANP and vasoactive intestinal peptide (VIP) in guinea pig cecal circular smooth muscle cells.

METHODS

The inhibition of 125I-ANP binding or 125I-VIP binding to cecal smooth muscle cells was assessed using unlabeled peptides (i.e., ANP, ANP fragments, VIP, secretin, and peptide histidine isoleucine); the effect of ANP, ANP fragments, and VIP on muscle contraction stimulated by 1 mumol/L carbachol was assessed; and the inhibitory effects of ANP 1-11 on VIP-induced relaxation, ANP 1-11 and VIP 10-28 (a VIP antagonist) on ANP-induced relaxation, and nitric oxide production inhibitors on ANP-induced relaxation were assessed.

RESULTS

The specific binding of 125I-ANP was inhibited completely by unlabeled ANP and VIP in a dose-dependent manner but only slightly inhibited by secretin and peptide histidine isoleucine. ANP 1-11 and C-atrial natriuretic factor inhibited the binding of 125I-ANP with a lower affinity than ANP. ANP only partly inhibited 125I-VIP binding. ANP and VIP inhibited 1 mumol/L carbachol-induced contraction in a dose-dependent manner. ANP 1-11 significantly inhibited VIP-induced relaxation. ANP 1-11, VIP 10-28, and NO production inhibitors completely inhibited ANP-induced relaxation.

CONCLUSIONS

The results of the study showed that ANP 1-11 antagonized ANP-induced relaxation and that ANP stimulated NO production and subsequently induced relaxation via a receptor to which VIP binds.

Atrial natriuretic peptide and its potential role in pharmacotherapy

Atrial natriuretic peptide (ANP) is a 28 amino-acid polypeptide secreted into the blood by atrial myocytes after atrial pressure and distension. Although its role in humans is not clear, it can produce a variety of physiologic effects including vasodilatation, natriuresis, and suppression of the renin-angiotensin-aldosterone axis. These actions are potentially useful in a variety of pathologic states such as hypertension and congestive heart failure, and diverse methods to augment the effects of ANP in these states have been devised. The results are exciting and, despite some problems, may lead to the pharmacologic use of enhancement of ANP actions in several clinical disorders.

Identification of renal natriuretic peptide receptor subpopulations by use of the non-peptide antagonist, HS-142-1

1. The renal actions of natriuretic peptides are dictated by the distribution of guanylyl cyclase-linked (NPRA and NPRB) and non-guanylyl cyclase-linked (NPRC) receptors. Natriuretic peptide receptors have previously been distinguished on the basis of their differential affinity for peptide fragments and analogues; however, most of the available ligands are not fully selective. We have used the specific guanylyl cyclase-linked receptor antagonist, HS-142-1, to investigate the differential distribution of natriuretic peptide receptor subtypes in the human, bovine and rat kidney. 2. Specific, high affinity 3-([125I]-iodotyrosyl)-rat-ANP-(1-28)([125I]-rANP1-28) binding sites were identified in all three species, localized to glomeruli, inner medulla, intrarenal arteries and regions in the outer medulla corresponding to vasa recta bundles. Binding sites were also identified in the smooth muscle lining of the hilar region in the bovine and rat kidney. 3. In the rat, [125I]-rANP1-28 binding was inhibited by unlabelled peptide sequences with a rank order of potency (rANP1-28 > pCNP1-22 > C-ANP4-23). The glomeruli exhibited a heterogeneous population of binding sites, C-ANP4-23 and pCNP1-22 producing a significantly better fit to a two component inhibition curve compared to the single component curve for rANP1-28. 4. Competitive inhibition experiments with the receptor selective ligands, C-ANP4-23 and HS-142-1, suggested that, like the rat, human and bovine glomeruli possessed a heterogeneous population of binding sites, whilst those in the inner medulla and intrarenal arteries of all three species represented a homogeneous population. Rat glomeruli exhibited a high proportion (>80%) of the NPRc receptor subtype whereas in human and bovine glomeruli this receptor represented less than 20% of the total population, the majority of binding sites being HS-142-1-sensitive.5. C-ANP4-23 exhibited a significantly higher inhibitory potency for binding sites in rat glomeruli compared to those in human and bovine kidney whilst HS-142-1 was significantly more potent in the rat and bovine kidney compared to man. No evidence was found to suggest the presence of a renal NPRBreceptor subtype.6. The relative density, affinity and proportion of natriuretic receptor subtypes in the kidney exhibit significant species differences. HS-142-1 may be a valuable tool in further elucidating the localization and function of these receptors, but heterogeneity between species should be considered when selecting experimental models.

Identification of immunoreactive atrial natriuretic peptide in the gallbladder and bile juice of rabbit, pig and human

The presence of immunoreactive atrial natriuretic peptide (irANP) in rabbit, pig and human gallbladders was investigated using radioimmunoassay and immunohistochemistry. Serial dilution curves of gallbladder tissue and bile juice extracts were paralleled to the standard curve of atriopeptin III. Gel filtration profiles of gallbladder tissue extracts showed a major peak corresponding to rat pro-ANP. The amounts of irANP in rabbit, pig and human gallbladders were 30.0 +/- 12.3 pg/mg (n = 7), 7.0 +/- 2.0 fg/mg (n = 7) and 17.7 +/- 2.0 fg/mg wet tissue (n = 8), respectively. Bile juice was also shown to contain irANP but with small molecular mass. The amounts of irANP in the rabbit, pig and human bile juice were 25.0 +/- 2.0 (n = 7) and 0.50 +/- 0.02 (n = 7), and 1.3 +/- 0.1 pg/ml (n = 8), respectively. The immunohistochemical staining of the rabbit gallbladder tissue revealed the presence of irANP in the luminal epithelium and smooth muscle layer. The amount of irANP was higher in the luminal epithelium than in the rest of the gallbladder tissue from rabbits (0.30 +/- 0.06 vs. 0.01 +/- 0.01 pg/microgram protein, P < 0.01). These findings suggest that ANP may be synthesized and stored in the gallbladder, and may have a role in the regulation of fluid balance and cystic motility.

Direct inhibitory effect of atrial natriuretic peptide on isolated caecal circular smooth muscle cells via soluble guanylate cyclase

Atrial natriuretic peptide (ANP) relaxes the vascular smooth muscle via particulate guanylate cyclase. Smooth muscle cells isolated from the caecal circular muscle layer of the guinea pig were used to examine the direct inhibitory effect of ANP on those cells. The role of adenylate cyclase, particulate guanylate cyclase, and soluble guanylate cyclase in the direct inhibitory effect of ANP on contraction of this muscle cell induced by carbachol was investigated. ANP inhibited the contractile response produced by 10(6)M carbachol in a concentration-dependent manner, with an IC50 value of 8nM. An inhibitor of adenylate cyclase (2',5'-dideoxyadenosine) and two inhibitors of particulate guanylate cyclase (HS-142-1, and PMA) had no significant effect on the relaxation produced by ANP. In contrast, an inhibitor of soluble guanylate cyclase (LY83583) significantly and completely inhibited the relaxation produced by ANP. This is the first report demonstrating the direct inhibitory action of ANP on the isolated caecal smooth muscle cells via soluble guanylate cyclase, which differs from the intracellular mechanism responsible for the relaxation of vascular smooth muscle produced by ANP.

Differential regulation of natriuretic peptide receptor messenger RNAs during the development of cardiac hypertrophy in the rat

The heart expresses the three natriuretic peptide receptors (NPR), namely NPR-A, NPR-B, and NPR-C. We have examined the temporal relationship between the expression of mRNA transcripts for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) and their receptors in the heart during the development of cardiac hypertrophy in the aortovenocaval fistula rat. Messenger RNAs were measured by cDNA amplification. Progressive cardiac hypertrophy was accompanied by increased ANP mRNA prevalence throughout the heart and increased BNP mRNA in the left atrium. The most striking observation was the gradual disappearance of NPR-C transcripts (the putative "clearance" receptor) in all chambers; this was in marked contrast to the increase in mRNA levels for NPR-A and NPR-B (the guanylyl cyclase-linked receptors). Our observations have important therapeutic implications if the transcript changes are mirrored at the receptor protein level because (a) the apparent down-regulation of NPR-C may enhance the local action of natriuretic peptides on the heart, and (b) the loss of NPR-C, particularly if it is widespread, may reduce the rate of elimination of the natriuretic peptides, restricting the therapeutic potential of specific NPR-C ligands designed to reduce peptide clearance.

Disposal of atrial natriuretic factor (ANF99-126) in patients with cirrhosis: effect of beta-adrenergic blockade

To test a possible effect of blood flow change on disposal of atrial natriuretic factor: ANF99-126 (ANF), we determined renal, azygos, hepatic and cubital venous, and arterial plasma concentrations of ANF in 18 patients with cirrhosis before and after ingestion of propranolol 80 mg. Arterial ANF was similar to that of controls (9.4 vs. 10.9 pmol l-1, NS) and was positively correlated to cardiac output (r = 0.49, p < 0.02) and to right atrial pressure (r = 0.44, p < 0.01). All the vascular beds examined extracted ANF significantly. The renal (n = 17), hepato-enteric (n = 16), and splanchnic superior collateral (azygos) beds (n = 13) had significantly higher extraction ratios (0.34-0.39) than that observed in the cubital vein (0.24, n = 15, p < 0.05). Arterial ANF showed no significant change (9.6-11.0 pmol l-1, NS) after reduction of cardiac output (-25%, p < 0.001) by propranolol. Only insignificant changes in ANF extraction and a small decrease in azygos and hepato-enteric clearance occurred during beta-adrenergic blockade. Our results show a substantial extraction of ANF in the kidney, in the splanchnic bed drained through superior portosystemic collaterals, and in the hepato-enteric bed. Only minor effects on ANF extraction were observed after reduction of the blood flow with propranolol.

Atrial natriuretic factor (ANF) does not affect ion transport in human intestine but does in porcine intestine

The aim of this study was to test whether atrial natriuretic factor (ANF) exerts any effect on human intestinal ion transport, and the porcine intestine was used as a positive control of ANF's effects. Tissues from human proximal (n = 6) and distal (n = 6) colons, and from distal ileum (n = 6) were mounted in Ussing chambers, and short circuit current (Isc) was measured subsequent to serosal application of ANF (10(-6) M), 8-Br-cyclic guanosine monophosphate (8-Br-cGMP) (10(-4) M), and theophylline (10(-2) M). ANF did not affect Isc whereas 8-Br-cGMP increased Isc by 28 (8-53), 16 (3-36), and 16 (5-41) microA cm-2 in the distal colon (DC), proximal colon (PC) and distal ileum (DI), respectively. Likewise, transepithelial potential difference (PD) became more negative by 5.0 (0.6-8.9), 2.5 (0.4-4.0) and 0.9 (0.3-2.3) mV in DC, PC, and DI, respectively, subsequent to addition of 8-Br-cGMP. Isc and PD were further increased by theophylline. Additional radio-isotope flux studies in human colon revealed that ANF did not affect electroneutral sodium and chloride transport either. For comparison, ANF (10(-6) M) was administered to large intestinal tissues from young pigs in which ANF induced a significant increase in Isc which was comparable to the 8-Br-cGMP response in humans. The porcine Isc response was partly inhibited by chloride-free solution on the serosal side, by serosal application of bumetanide (10(-4) M) and BaCl2 (10(-3) M), and mucosal application of the chloride-channel blocker diphenylamine-2-carboxylate (DPC) (10(-3) M). Mucosal amiloride (10(-5) M) pre-treatment reduced baseline Isc but did not affect the porcine intestinal Isc response to ANF. In vitro radio-autography demonstrated specific binding sites for ANF in porcine distal colon, whereas no apparent labelling was observed in human distal colon. These findings suggest that the lack of effect of ANF on sodium and chloride transport in human distal ileum and colon is probably due to lack of ANF receptors. In the porcine intestine, however, the Isc response induced by ANF seems to involve stimulation of electrogenic chloride secretion, whereas electrogenic sodium absorption seems unaffected.

Natriuretic peptide receptor mRNAs in the rat and human heart

Functional studies indicate that atrial natriuretic peptide (ANP), a member of the natriuretic peptide family, has direct effects on cardiac muscle cells. However, conventional ligand-binding studies designed to establish the presence of natriuretic peptide-binding sites in the heart have yielded conflicting results. There are discrepancies also between the latter and the receptor distribution predicted from the pattern of the mRNA transcripts localized by in situ hybridization. Here we have employed the technique of cDNA amplification with the polymerase chain reaction to confirm the presence of natriuretic peptide A, B, and C receptor mRNAs in rat and human cardiac tissue. In the rat heart, the distribution of the A and B receptor transcripts appears to be relatively homogeneous; in contrast, the C type mRNA is concentrated principally in the atria, with no difference between the left and right sides of the heart. A and B receptor DNA products were obtained after amplification of left, but not right, ventricular cDNA from the heart of a 16-yr-old male with cystic fibrosis; the yield of C receptor DNA was similar for both ventricles. If these mRNA transcripts are translated into functional receptors in the rat and human heart, ANP and the other natriuretic peptides may have direct effects on cardiac function, including regulation of natriuretic peptide release via a short feedback loop, modulation of contractility of the heart, or activation of cardiac reflexes.

Binding sites of atrial natriuretic peptide (ANP) in the mammalian cochlea and stimulation of cyclic GMP synthesis

The distribution of binding sites for atrial natriuretic peptide (ANP) has been examined in frozen sections of the guinea pig inner ear by means of autoradiography. The highest density was found in the stria vascularis of all cochlear turns. In membrane preparations of stria vascularis in vitro, the production of the second messenger cGMP was strongly stimulated by synthetic ANP in a dose dependent manner. Adenylate cyclase was neither stimulated nor inhibited by ANP, thus suggesting, that the binding sites coincide with an ANP receptor, which is coupled to guanylate cyclase but not negatively coupled to an adenylate cyclase molecule. The production of cyclic GMP could not be reduced by GDP-beta S, a strong inhibitor of the Gs protein. We conclude the existence of an ANP receptor-guanylate cyclase signal transfer system, similar to the beta 2 receptor-adenylate cyclase system in the inner ear, without coupling to a G protein. ANP might play a role in sodium and water regulation of the endolymph and might antagonize the action of vasopressin.

A gradient in expression of the Escherichia coli heat-stable enterotoxin receptor exists along the villus-to-crypt axis of rat small intestine

Binding of Escherichia coli heat-stable enterotoxin to its receptor is critical to the initiation of toxin-induced secretion and diarrheal disease; it is also likely, however, that this receptor binds an endogenous ligand. In order to characterize the expression of the heat-stable enterotoxin receptor in the small intestine, we isolated epithelial cells from villus tip to crypt in rat jejunum and ileum. Binding of radiolabeled toxin was maximal in the villus preparations and gradually decreased along the villus-to-crypt axis, paralleling the decline of sucrase activity. Northern blots of total RNA identified a single heat stable enterotoxin receptor transcript (3.8 kb), predominantly in the villus cell fractions. In situ hybridization demonstrated clear signal in the villus cells with no apparent signal in the crypt cells, lamina propria or muscularis. Expression of this receptor was greatest after enterocytes leave the proliferative cycle and enter villi. This pattern of gene and protein expression may reflect a role of this receptor in binding endogenous ligands which in turn may regulate intestinal ion flux along the villus-to-crypt axis.

Effects of atrial natriuretic factor (ANF) on intraocular pressure and aqueous humor flow in the cynomolgus monkey

Atrial natriuretic factor (ANF: human sequence) was examined for its effects on basal and terbutaline-stimulated aqueous humor flow, intraocular pressure (IOP) and uveoscleral outflow in cynomolgus monkeys under pentobarbital anesthesia. A dilution method with radioactively labeled albumin was used for the determination of aqueous humor flow. ANF was given by i.v. infusion or intracamerally. Intracameral administration of terbutaline increased the aqueous humor flow significantly; 1.10 +/- 0.05 microliter min-1 in the control eye and 1.69 +/- 0.06 microliter min-1 in the treated eye. I.v. infusion of ANF, 97 fmol kg-1 min-1, increased the aqueous humor flow by about 44% from basal values in the control eye. There was a small but not statistically significant increase on the terbutaline-treated side. The IOP was not changed by ANF at this dose. An ANF dose of 97 pmol kg-1 min-1 increased the aqueous humor flow by 51% in the control eye and by 19% in the terbutaline-treated eye. A further rise of about 8% in aqueous humor flow was registered on the control side when the infused ANF-dose was doubled. Doubling the dose also resulted in a decrease of the IOP by 1.3 +/- 0.3 mmHg on the control side and 2.2 +/- 0.4 mmHg on the terbutaline-stimulated side. Intracameral administration of ANF (81-162 pmol ml-1 perfusion fluid) increased the aqueous humor flow transiently by approximately 50% with a maximum after about 2 hr. The uveoscleral outflow tended to increase and IOP tended to decrease in the ANF-treated eye compared with the control. However, these effects were not statistically significant. These results suggest that ANF may be involved in the control of aqueous humor formation.

Presence of atrial natriuretic factor prohormone in enterochromaffin cells of the human large intestine

Atrial natriuretic factor is a hormone intimately involved in water and salt homeostasis. The heart constitutes the major but not exclusive site of synthesis of this hormone. Among other functions, the gastrointestinal tract has endocrine functions, plays an important role in volume regulation of the body, and seems to be a target organ for atrial natriuretic factor. Therefore, the presence of atrial natriuretic factor was investigated in the human gut. Immunoreactive atrial natriuretic factor was found in intraoperatively obtained samples of normal human colon. Acidic extracts of human large intestine contained about 0.4 pmol/g wet wt of atrial natriuretic factor. Analysis of atrial natriuretic factor immunoreactivity by gel-filtration and reverse-phase high-performance liquid chromatography showed that about 65% of the immunoreactivity corresponded to the atrial natriuretic factor phohormone and about 35% corresponded to the C-terminal ANF99-126. Immunohistochemistry showed atrial natriuretic factor prohormone location in enterochromaffin cells of the colon mucosa. Altogether, these findings show the presence of atrial natriuretic factor prohormone in enterochromaffin cells of the human large intestine and may suggest this organ as a site of atrial natriuretic factor synthesis in humans.

Differential regional expression of three natriuretic peptide receptor genes within primate tissues

The natriuretic peptide receptors are three homologous cell surface proteins, each with a single transmembrane domain. The atrial natriuretic peptide receptor type A (ANPRA) and the homologous receptor type B (ANPRB) are both membrane guanylyl cyclases that synthesize cyclic GMP as an intracellular second messenger. The third receptor in this family, the atrial natriuretic peptide receptor type C (ANPRC), is not coupled to cyclic GMP production. We report on the distribution of the ANPRA, ANPRB, and ANPRC mRNAs in rhesus monkey tissues assayed by in situ hybridization. ANPRA mRNA is most abundantly expressed in the kidney glomerulus, adrenal zona glomerulosa, pituitary, cerebellum, and endocardial endothelial cells of the right and left atrium and right ventricle. In contrast, abundant ANPRB expression appears to be confined to the adrenal medulla, pituitary, and cerebellum. ANPRC mRNA appeared to be expressed very differently than ANPRA and ANPRB. In the heart, ANPRC mRNA is expressed most prominently in endocardial endothelial cells of all four chambers but is also found throughout the myocardium only in the right atrium. These data identify major sites of natriuretic peptide receptor mRNA expression and suggest that there may be prominent cell type-specific differential distribution of these receptors in central and peripheral targets for the natriuretic peptides.

The effect of atrial natriuretic peptide on small intestinal contractility and transit

Isometric tension in response to ANF (10(-10) to 10(-4) M) was recorded from longitudinally and circularly oriented rat jejunal smooth muscle strips. Conscious, fasted rats received an IV infusion of 1.25 nmol ANF/100 g body weight in 0.5 ml normal saline and controls received saline alone. Five minutes later 10 muCi Na2 51CrO4 in 0.5 ml saline was instilled through a jejunostomy. Fifteen minutes later animals were sacrificed, and the gut divided into 8 equal segments of small intestine, cecum and remaining colon. The radioactivity of each segment was measured and a geometric center of transit determined for each group. ANF induced relaxation of longitudinally oriented strips (Tm = -72.3 +/- 10.7 mN/g, ED50 7.3 +/- 3.6 x 10(-8) M), and contraction of circularly oriented strips (Tm = 35.0 +/- 5.0 mN/g, ED50 1.3 +/- 1.0 x 10(-8) M). This response was unaffected by 10(-6) M tetrodotoxin. The geometric mean center of transit was significantly (p less than 0.001) further aboral in ANF-treated compared to control animals (intestinal segment 4.2 +/- 0.2 vs. 3.2 +/- 0.2).

Differential regional expression of three natriuretic peptide receptor genes within primate tissues

The natriuretic peptide receptors are three homologous cell surface proteins, each with a single transmembrane domain. The atrial natriuretic peptide receptor type A (ANPRA) and the homologous receptor type B (ANPRB) are both membrane guanylyl cyclases that synthesize cyclic GMP as an intracellular second messenger. The third receptor in this family, the atrial natriuretic peptide receptor type C (ANPRC), is not coupled to cyclic GMP production. We report on the distribution of the ANPRA, ANPRB, and ANPRC mRNAs in rhesus monkey tissues assayed by in situ hybridization. ANPRA mRNA is most abundantly expressed in the kidney glomerulus, adrenal zona glomerulosa, pituitary, cerebellum, and endocardial endothelial cells of the right and left atrium and right ventricle. In contrast, abundant ANPRB expression appears to be confined to the adrenal medulla, pituitary, and cerebellum. ANPRC mRNA appeared to be expressed very differently than ANPRA and ANPRB. In the heart, ANPRC mRNA is expressed most prominently in endocardial endothelial cells of all four chambers but is also found throughout the myocardium only in the right atrium. These data identify major sites of natriuretic peptide receptor mRNA expression and suggest that there may be prominent cell type-specific differential distribution of these receptors in central and peripheral targets for the natriuretic peptides.

Brain natriuretic peptide-immunoreactive nerves in the porcine eye

Using immunohistochemistry, brain natriuretic peptide (BNP)-like immunoreactive (-LI) nerves localize to the anterior segment of the porcine eye. BNP-LI nerve fibers are visualized mainly in the aqueous outflow pathway, ciliary processes and anterior ciliary muscle. A small number of immunoreactive nerve fibers occur in the anterior iris stroma and in relation to the iris muscles and in the cornea. Given the known ocular effects of atrial natriuretic peptide (ANP) and that BNP and ANP seem to share common receptors, these results suggest an ocular role for peptides of this class independent of delivery by the systemic circulation.

Discrimination and quantification of glomerular receptor subtypes for atrial natriuretic factor (ANF)

Binding sites for atrial natriuretic factor (ANF) were determined on isolated rat glomeruli as well as on glomerular membranes. To define optimal conditions, binding of ANF was investigated varying incubation time, temperature and protein concentration. Binding conditions were found to be best at 4 degrees C for 5 hours with 15 micrograms of glomerular protein. Saturation and affinity cross-linking experiments confirmed the presence of two distinct receptor subtypes-the B-receptor (130 kDa) and the C-receptor (65 kDa). Quantitative differentiation of both ANF binding sites was achieved by competitive displacement with two different unlabeled ANF ligands: a) rANF(99-126) (homologous displacement), b) des(18-22)rANF(4-23)NH2 (heterologous displacement). Intact glomeruli and glomerular membranes did not differ significantly in receptor density for the B-receptor (71 +/- 37 vs. 94 +/- 53 fmol/mg protein) or the C-receptor (976 +/- 282 vs. 966 +/- 167 fmol/mg protein) or in affinity constants for the B-receptor (43 +/- 36 vs. 52 +/- 44 pM) or the C-receptor (876 +/- 377 vs. 307 +/- 36 pM). Glomerular membranes compared to glomeruli showed less nonspecific binding and less intra-assay variation of measuring points done in triplicates. This method of selective displacement should allow to study the influence of various physiological and pathophysiological conditions on the binding properties of B- and C-receptors for ANF.

Atrial natriuretic factor mRNA and binding sites in the adrenal gland

The factor inhibiting aldosterone secretion produced by the adrenal medulla may be atrial natriuretic factor (ANF), since the latter abolishes aldosterone release in response to a number of secretagogues, including angiotensin II and K+. In this study we have shown that cells in the adrenal medulla contain ANF mRNA and therefore have the potential to synthesize this peptide. The presence of binding sites for ANF predominantly in the adrenal zona glomerulosa suggests that, if ANF is synthesized in the medulla and transferred to the cortex, it may affect mineralocorticoid status.

Autoradiographic localization of specific atrial natriuretic peptide binding sites on immunocytochemically identified cells in cultures from rat and guinea-pig hearts

Dissociated cell culture preparations from rat and guinea-pig atria and interatrial septum, and from rat ventricles were studied using a combined autoradiographic and immunocytochemical approach. Alpha-atrial natriuretic peptide (125I-ANP1-128) bindings sites were confined to subpopulations of identified non-neuronal cells in each type of culture preparation, and had distinct patterns of labelling. The density of ANP1-28 binding sites was substantially greater in guinea-pig cultures than in rat cultures and was least in rat ventricular cultures. ANP1-28-labelled subpopulations of S-100-like immunoreactive glial cells were only seen in guinea-pig cultures. Von Willebrand factor (vWF)-like immunoreactive endothelial cells and vWF-negative endothelioid cells expressed ANP1-28 binding sites in both the guinea-pig and rat atrial cultures, but were unlabelled in rat ventricular cultures. In contrast, labelled subpopulations of fibronectin-like immunoreactive fibroblasts were present in all of the three types of culture preparation studied. ANP-like immunoreactive myocytes were present in both atrial and ventricular cultures. These cells did not, however, express ANP1-28 binding sites.

Brain natriuretic peptide binding sites in rats: in vitro autoradiographic study

Brain natriuretic peptide (BNP) is a recently discovered family of natriuretic peptides highly homologous to atrial natriuretic factor (ANF). Quantitative in vitro autoradiography with a computerized microdensitometer demonstrated that the distribution of BNP binding sites is similar to the known distribution pattern of ANF binding sites in rat tissues. Analysis of saturation and competition curves disclosed that the maximal binding capacity for BNP-(Asp-81--Tyr-106) and ANF-(Ser-99--Tyr-126) is similar within the plexiform layer of the olfactory bulb, the choroid plexus, and the adrenal zona glomerulosa. Examination of the competition curves of BNP-(Asp-81--Tyr-106), ANF-(Ser-99--Tyr-126), and des-(Gln-116--Gly-120)ANF-(Asp-102--Cys-121)NH2 (C-ANF, a ligand highly specific for ANF-R2 receptors) for 125I-labeled BNP-(Asp-81--Tyr-106) and 125I-labeled ANF-(Ser-99--Tyr-126) binding revealed that ANF fully displaced 125I-BNP binding and, conversely, BNP completely displaced 125I-ANF binding in these tissues, whereas C-ANF partially displaced 125-BNP and 125-ANF binding. Angiotensin II, insulin, glucagon, and substance P had no influence on 125I-BNP binding in the above tissues. These results support the view that BNP and ANF share the same binding sites in rats.

Influence of atrial natriuretic peptide on mammalian large intestine

Atrial natriuretic peptide is distributed in a number of organs including the large intestine. Atrial natriuretic peptide has potent diuretic and natriuretic properties and appears to play a central role in fluid and electrolyte homeostasis by an action on the kidney. We examined the influence of atrial natriuretic peptide on mammalian colon because this organ is also intimately involved in homeostasis. Segments of the distal colons of male Sprague-Dawley rats were stripped of muscle layers and mounted in flux chambers. Atrial natriuretic peptide, when added to the serosal side of the mucosa, in concentrations ranging from 10(-8)-10(-5) M, caused a rapid, concentration-dependent increase in short-circuit current, transmucosal electrical potential difference, and conductance. The response to atrial natriuretic peptide was inhibited by (a) chloride-free solution on the serosal surface; (b) pretreatment of the tissues with the chloride channel blocker, diphenylamine-2-carboxylate (10(-3) M mucosally); (c) pretreatment with d,l-verapamil (10(-4) M mucosally and serosally); (d) calcium-free solution on the serosal surface; (e) pretreatment with tetrodotoxin (10(-7) M to serosal surface); and (f) pretreatment with atropine (10(-5) M serosally). However, the response to atrial natriuretic peptide was not influenced by pretreatment with amiloride (10(-4) M to mucosal and serosal surfaces) or piroxicam (10(-5) M serosally). Atrial natriuretic peptide did not elicit an increase in short-circuit current and potential difference across T84 cells derived from a human colonic carcinoma cell line, suggesting that the response to atrial natriuretic peptide is not due to a direct effect on colonocytes. These findings suggest that atrial natriuretic peptide acts by a calcium-mediated secretory mechanism involving cholinergic nerves and is likely to be involved in the endogenous neurohumoral regulation of ion transport in the mammalian colon.

Visualisation of specific binding sites for atrial natriuretic peptide on non-neuronal cells of cultured rat sympathetic ganglia

The distribution of atrial natriuretic peptide binding sites on cells in dissociated culture preparations of neonatal rat superior cervical ganglia and in explant cultures of rat thoracic sympathetic chain ganglia has been studied. The autoradiographic visualisation of atrial natriuretic peptide binding sites has been combined with the use of specific immunocytochemical markers for glial cells (antiserum to S-100 protein), fibroblasts (antiserum to fibronectin) and neurones (antiserum to protein gene product 9.5) in order to achieve unambiguous identification of the cell types in culture. Specific binding sites for rat 125I-atrial natriuretic peptide(1-28) were observed over subpopulations of fibronectin-like-immunoreactive fibroblasts and S-100-like-immunoreactive glia in the dissociated superior cervical ganglion cultures. However, only a subpopulation of fibronectin-like-immunoreactive fibroblasts possessed atrial natriuretic peptide binding sites in the explant culture preparations. No atrial natriuretic peptide-like-immunoreactive cells were present in either culture. The distribution of autoradiographic grains over individual cell surfaces in culture was uniform, but there were distinct differences in the density of labelling of single cells of the same type. This apparent variation in the number of binding sites on glial cells and fibroblasts in culture did not seem to be related to the morphology of the cells or the surrounding cell types. No sympathetic neurones were labelled with autoradiographic grains in either the dissociated or explant culture preparations. However, the presence of atrial natriuretic peptide binding sites on non-neuronal cells of sympathetic ganglia in culture may be linked to the relationship between atrial natriuretic peptide and the sympathetic nervous system.

Peptides and vasomotor mechanisms

The multiple and diverse roles played by neuropeptide Y, vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide and other biologically active peptides in the cardiovascular system are considered. A model of the vascular neuroeffector junction is described, which illustrates the interactions of peptidergic and nonpeptidergic transmitters that are possible at pre- and postjunctional sites. The effects of peptides on specific endothelial receptors are also described, which highlights the ability of these agents to act as dual regulators of vascular tone at both adventitial and intimal surfaces, following local release from nerves, or from endothelial cells themselves. Changes in expression of vascular neuropeptides that occur during development and aging in some disease situations and following nerve lesion are discussed.

Degradation and clearance of atrial natriuretic factors (ANF)

Atrial natriuretic factor, the first well defined natriuretic hormone is synthesized in the human heart as 151 aminoacid (AA) preprohormone and stored as 126 AA prohormone in atrial granules. Upon appropriate stimulation, the prohormone is cleaved into a 98 AA N-terminal fragment and a 28 AA C-terminal fragment, the biological active ANF(99-126), both circulating in plasma. Circulating ANF(99-126) is cleared by various organs, such as lung, liver and intestine, kidney and upper and lower limbs. Reported arterial-venous extraction ratios vary greatly, but are not much different between organs, the average extraction ratio being about 35%. Due to marked differences of organ blood flow, the contribution of various organs to total body ANF clearance differs considerably. Major mechanisms for ANF clearance are uptake by clearance receptors and degradation by an endoprotease (EC 3.4.24.11.). Clearance receptors, distinct from the receptors mediating the biological actions of ANF, have been demonstrated in various organs. Characterization of the ANF degrading enzyme activity has been performed in kidney tissue. Whether and how pathophysiological states affect ANF clearance is still poorly understood. Inhibition of clearance by ANF analogues binding to clearance receptors and by inhibitors of degrading peptidase can increase the biological action of circulating ANF. This may prove to be a therapeutic approach in diseases with smooth muscle contraction or volume overload.

Purification and properties of active atrial-natriuretic-peptide receptor (type C) from bovine lung

Atrial-natriuretic-peptide (ANP) receptor, previously identified as a 140 kDa protein with a disulphide-linked homodimeric structure, was purified from bovine lung by (NH4)2SO4 fractionation and affinity chromatography on ANP-Affi-Gel 10. The purified receptor had a binding capacity of 4.2 nmol of ANP/mg of protein and an affinity constant of 6.5 pM. The isoelectric point of the receptor was 5.8, consistent with the acidic nature of the protein (amino acid analysis revealed a predominance of glutamic acid and aspartic acid residues). Treatment with endoglycosidase H and glycopeptidase F revealed that the receptor has three complex types of oligosaccharide chains per 70 kDa subunit. Deglycosylation of the receptor did not affect its binding activity. Reduction with dithiothreitol and reoxidation by dialysis revealed a strong tendency of the receptor subunits to dimerize via disulphide cross-linking; however, carboxymethylation of the reduced receptor indicated that the intersubunit disulphide bond is not necessary for the ligand-binding activity.

Glomerular atrial natriuretic factor receptors in primary glomerulopathies: studies on human renal biopsies

Human renal biopsies are currently used to provide information about morphologic changes, chronicity of disease, patterns of inflammation, and immunoglobulin deposition. This practice has provided only limited insight into functional aberrations and has failed to provided information necessary for disease classification based on pathophysiology. To expand the potential of the renal biopsy in this regard and to determine whether differences in glomerular atrial natriuretic factor (ANF) binding exist in different forms of primary renal disease, quantitative autoradiography and 125I-human ANF (1-28) were used to determine the location and pharmacological characteristics of ANF binding sites in the normal human kidney. Specific ANF binding was highest in the glomeruli, but lower levels of specific binding were localized to the inner medulla and the interlobular arteries. ANF binding sites in the human kidney were found to be highly stable and similar in both location and pharmacology to those observed in experimental animals. As determined by saturation experiments, the equilibrium dissociation constants for glomeruli, inner medulla, and interlobular arteries were almost identical at 4.0 x 10(-11) mol/L. Competitive binding inhibition studies with unlabeled human ANF (1-28) demonstrated highly specific binding shared by the glomerulus, inner medulla, and interlobular artery, with apparent half-maximal inhibition concentrations of 9.2 x 10(-10) mol/L, 8.0 x -10 mol/L, and 8.2 x 10(-10) mol/L, respectively. Quantitation of specific binding of ANF to glomeruli in needle biopsy specimens of three primary glomerulopathies, ie, minimal-change disease, membranous nephropathy, and focal glomerulosclerosis, showed no differences among the groups. This study demonstrates the feasibility of studying receptor physiology on biopsy specimens of the human kidney and should allow renal diseases, particularly of glomerular origin, to be characterized according to differences in hormone binding and hormone responsiveness. The absence of significant differences in glomerular ANF binding in the primary glomerulopathies studied is consistent with other studies that have failed to delineate important pathophysiological differences in renal function and volume homeostasis in these disease states.

Inhibitory action of atrial natriuretic factor on cholinergic and nonadrenergic, noncholinergic neurotransmission in guinea pig small intestine

We studied the effect of synthetic rat atrial natriuretic factor (ANF) (Ser 99-Tyr 126) on the isolated guinea pig proximal ileum. This preparation contained about one-third of the endogenous tissue ANF content which, for the most part, comes from the blood. ANF inhibited, in a dose-dependent manner, cholinergic twitch contractions (EC50 = 4.2 nM), nonadrenergic, noncholinergic (NANC) primary and rebound contractions and histamine-induced sustained tonic contraction (but not carbachol induced contraction) of the longitudinal muscle. Ascending enteric reflex (AER) contractions of the circular muscle were inhibited though not dose-dependently. We suggest pre- and post-synaptic actions of sustained intestinal tissue and blood ANF levels which may play a role in regulating motor activity and muscle tone of the small intestine.