HS-142-1, a novel nonpeptide atrial natriuretic peptide (ANP) antagonist, blocks ANP-induced renal responses through a specific interaction with guanylyl cyclase-linked receptors

The Natriuretic Peptide System: A Single Entity, Pleiotropic Effects

In the modern scientific landscape, natriuretic peptides are a complex and interesting network of molecules playing pleiotropic effects on many organs and tissues, ensuring the maintenance of homeostasis mainly in the cardiovascular system and regulating the water-salt balance. The characterization of their receptors, the understanding of the molecular mechanisms through which they exert their action, and the discovery of new peptides in the last period have made it possible to increasingly feature the physiological and pathophysiological role of the members of this family, also allowing to hypothesize the possible settings for using these molecules for therapeutic purposes. This literature review traces the history of the discovery and characterization of the key players among the natriuretic peptides, the scientific trials performed to ascertain their physiological role, and the applications of this knowledge in the clinical field, leaving a glimpse of new and exciting possibilities for their use in the treatment of diseases.

Deciphering vascular endothelial cell growth factor/vascular permeability factor signaling to vascular permeability. Inhibition by atrial natriuretic peptide

Vascular endothelial cell growth factor (VEGF) was originally described as a potent vascular permeability factor (VPF) that importantly contributes to vascular pathobiology. The signaling pathways that underlie VEGF/VPF-induced permeability are not well defined. Furthermore, endogenous vascular peptides that regulate this important VPF function are currently unknown. We report here that VPF significantly enhances permeability in aortic endothelial cells via a linked signaling pathway, sequentially involving Src, ERK, JNK, and phosphatidylinositol 3-kinase/AKT. This leads to the serine/threonine phosphorylation and redistribution of actin and the tight junction (TJ) proteins, zona occludens-1 and occludin, and the loss of the endothelial cell barrier architecture. Atrial natriuretic peptide (ANP) inhibited VPF signaling, TJ protein phosphorylation and localization, and VPF-induced permeability. This involved both guanylate cyclase and natriuretic peptide clearance receptors. In vivo, transgenic mice that overexpress ANP showed significantly less VPF-induced kinase activation and vascular permeability compared with non-transgenic littermates. Thus, ANP acts as an anti-permeability factor by inhibiting the signaling functions of VPF that we define here and by preserving the endothelial cell TJ functional morphology.

Brain natriuretic peptide: role in cardiovascular and volume homeostasis

The identification of natriuretic peptides as key regulators of natriuresis and vasodilatation, and the appreciation that their secretion is under the control of cardiac hemodynamic and neurohumoral factors, has caused wide interest. The natriuretic peptides are structurally similar, but genetically distinct peptides that have diverse actions on cardiovascular, renal, and endocrine homeostasis. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are of myocardial cell origin, while cardiac natriuretic peptide (CNP) is of endothelial origin. ANP and BNP bind to the natriuretic peptide receptor (NPR-A) which, via 3' 5'-cyclic guanosine monophosphate (cGMP), mediates natriuresis, vasodialation, renin inhibition, and antimitogenic properties. CNP lacks natriuretic action but possesses vasodilating and growth inhibiting effects via the guanyl cyclase linked natriuretic peptide-B (NPR-B) receptor. All three peptides are cleared by natriuretic peptide-C receptor (NPR-C) and degraded by neutral endopeptidase, both of which are widely expressed in kidney, lung, and vascular wall. Recently, a fourth member of the natriuretic peptide, dendroaspsis natriuretic peptide (DNP) has been reported to be present in human plasma and atrial myocardium.

L-NAME enhances responses to atrial natriuretic peptide in the pulmonary vascular bed of the cat

This study investigated the hypothesis that atrial natriuretic peptide (ANP) responses are mediated by particulate guanylate cyclase in the pulmonary vascular bed of the cat. When tone in the pulmonary vascular bed was raised to a high steady level with the thromboxane mimic U-46619, injections of ANP caused dose-related decreases in lobar arterial pressure. After administration of HS-142-1, an ANP-A- and ANP-B-receptor antagonist, vasodilator responses to ANP were reduced. The nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) enhanced ANP vasodilator responses, suggesting that inhibition of NO modulates ANP responses. L-NAME administration with constant 8-bromo-cGMP infusion attenuated the increased vasodilator response to ANP, suggesting that supersensitivity to ANP occurs upstream to activation of a cGMP-dependent protein kinase. In pulmonary arterial rings, ANP produced concentration-related vasorelaxant responses with and without endothelium. Methylene blue, L-NAME, or N(omega)-monomethyl-L-arginine did not alter ANP vasorelaxant responses. These data show that ANP supersensitivity observed in the intact pulmonary vascular bed is not seen in isolated pulmonary arterial segments, suggesting that it may only occur in resistance vessel elements. These results suggest that ANP responses occur through activation of ANP-A and/or -B receptors in an endothelium-independent manner and are modulated by NO in resistance vessel elements in the pulmonary vascular bed of the cat.

Natriuretic peptides suppress vascular endothelial cell growth factor signaling to angiogenesis

Vascular endothelial cell growth factor (VEGF) is essential for angiogenesis. Atrial natriuretic peptide (ANP) inhibits the production of VEGF, but whether this important vascular peptide also inter- rupts VEGF signaling to angiogenesis is unknown. In cultured bovine aortic endothelial cells, VEGF significantly stimulated extracellular signal-regulated protein kinase activity and phosphorylation, which was inhibited 60% by coincubation with ANP or a natriuretic peptide clearance receptor specific ligand (NPRC), C-type NAP-(4-23) [C-ANP-(4-23)]. VEGF also stimulated c-Jun N-terminal kinase (JNK) and p38 activities/phosphorylation that were prevented by the two natriuretic peptides (NP). A specific NP guanylate cyclase (GC) receptor antagonist, HS-142-1, blocked the actions of ANP [but not those of C-ANP-(4-23)], supporting the involvement of both GC and NPRC receptors. VEGF and expression of constituitively active JNK each stimulated the synthesis of cyclin D1 and increased the activity of the cyclin-dependent kinase-4, which was inhibited 55% by ANP. VEGF induced endothelial cell proliferation and migration, which was significantly blocked by NP or by expressing a dominant negative JNK-1. VEGF stimulated human microvascular endothelial cells to form capillary tubes, which was significantly inhibited by expressing dominant negative JNK-1 and by NP. Therefore, VEGF induction of critical steps in angiogenesis is enhanced through JNK activation. The actions are significantly prevented by NP, which act through both the NPRC and GC receptors to block growth factor signaling. Thus, NP are candidate antiangiogenesis factors that inhibit both the synthesis and function of VEGF.

Increased activity of guanosine 3'-5'-cyclic monophosphate phosphodiesterase in the renal tissue of cirrhotic rats with ascites

A possible defect of guanosine 3'-5'-cyclic monophosphate (cGMP) content in the renal tissue caused by an increased activity of cGMP phosphodiesterase (PDE) has, so far, not been evaluated in the pathogenesis of renal resistance to endogenous natriuretic peptides (ENP) in cirrhosis with ascites. To test this hypothesis the activity of cGMP-PDE and the concentration of cGMP were evaluated in vitro in the renal tissue of 10 control rats and 10 cirrhotic rats with ascites before and after the intravenous (IV) administration of Zaprinast (Sigma, St. Louis, MO), a specific cGMP-PDE inhibitor (30 microgram/kg/min). Moreover, the effects of the intravenous administration of Zaprinast (15 microgram/kg/min and 30 microgram/kg/min) on renal plasma flow (RPF), glomerular filtration rate (GFR), and urinary sodium excretion (U(Na)V) were evaluated in 10 conscious control rats and 10 conscious cirrhotic rats with ascites. The effects of Zaprinast on plasma renin activity (PRA) was also evaluated in 10 control rats and in 10 cirrhotic rats with ascites. Finally, the effect of Zaprinast on RPF, GFR, and U(Na)V were evaluated in 10 cirrhotic rats after the IV administration of the ENP-receptor antagonist, HS-142-1. The renal content of cGMP was reduced in cirrhotic rats because of increased activity of cGMP-PDE. Zaprinast inhibited cGMP-PDE activity and increased the renal content of cGMP in these animals. The inhibition of cGMP-PDE was associated with an increase in RPF, GFR, and U(Na)V and a reduction in PRA. HS-142-1 prevented any renal effect of Zaprinast in cirrhotic rats. In conclusion, an increased activity of the cGMP-PDE in renal tissue contributes to the renal resistance to ENP in cirrhosis with ascites.

Renal function in high-output heart failure in rats: role of endogenous natriuretic peptides

The physiologic and pathophysiologic importance of natriuretic peptides (NP) has been imperfectly defined. The diminished renal responses to exogenous atrial NP in heart failure have led to the perception that the endogenous NP system might be less effective and thus contribute to renal sodium retention in heart failure. This study tests the hypothesis that in experimental heart failure, the renal responses to an acute volume load are still dependent on the NP system. The specific antagonist HS-142-1 was used to block the effects of NP in a model of high-output heart failure induced by an aortocaval shunt. Plasma cGMP levels and renal cGMP excretion were significantly lower in shunted and sham-operated rats receiving HS-142-1, compared with vehicle-treated controls, indicating effective blockade of guanylate cyclase-coupled receptors. Baseline sodium excretion and urine flow rate were lower in HS-142-1-treated sham-operated rats (15.2+/-1.1 microl/min versus 27.5+/-3.1 microl/min with vehicle, P < 0.001) and in HS-142-1-treated shunted rats (8.1+/-1.3 microl/min versus 19.9+/-2.3 microl/min with vehicle, P < 0.001). After an acute volume load, the diuretic and natriuretic responses were attenuated by HS-142-1 in control and shunted rats. The renal responses were reduced by HS-142-1 to a significantly greater extent in shunted rats than in control rats. HS-142-1 did not induce any significant systemic hemodynamic changes in either group, nor did it alter renal blood flow. However, the GFR in HS-142-1-treated shunted rats was lower than that in vehicle-treated shunted rats, both at baseline (0.6+/-0.3 ml/min versus 2.1+/-0.4 ml/min with vehicle, P < 0.05) and after an acute volume load (1.2+/-0.4 ml/min versus 2.6+/-0.4 ml/min with vehicle, P = 0.01), whereas no such effect was observed in control rats. These data indicate that the maintenance of basal renal function and the responses to acute volume loading are dependent on the NP system. The NP seem to be of particular importance for the maintenance of GFR in this model of experimental heart failure. These observations provide new insights into the importance of the renal NP system in heart failure.

Glomerular mesangial cells: electrophysiology and regulation of contraction

Mesangial cells are smooth muscle-like pericytes that abut and surround the filtration capillaries within the glomerulus. Studies of the fine ultrastructure of the glomerulus show that the mesangial cell and the capillary basement membrane form a biomechanical unit capable of regulating filtration surface area as well as intraglomerular blood volume. Structural and functional studies suggest that mesangial cells regulate filtration rate in both a static and dynamic fashion. Mesangial excitability enables a homeostatic intraglomerular stretch reflex that integrates an increase in filtration pressure with a reduction in capillary surface area. In addition, mesangial tone is regulated by diverse vasoactive hormones. Agonists, such as angiotensin II, contract mesangial cells through a signal transduction pathway that releases intracellular stores of Ca2+, which subsequently activate nonselective cation channels and Cl- channels to depolarize the plasma membrane. The change in membrane potential activates voltage-gated Ca2+ channels, allowing Ca2+ cell entry and further activation of depolarizing conductances. Contraction and entry of cell Ca2+ are inhibited only when Ca2+-activated K+ channels (BK(Ca)) are activated and the membrane is hyperpolarized toward the K+ equilibrium potential. The mesangial BK(Ca) is a weak regulator of contraction in unstimulated cells; however, the gain of the feedback is increased by atrial natriuretic peptide, nitric oxide, and the second messenger cGMP, which activates protein kinase G and decreases both the voltage and Ca2+ activation thresholds of BK(Ca) independent of sensitivity. This enables BK(Ca) to more effectively counter membrane depolarization and voltage-gated Ca2+ influx. After hyperpolarizing the membrane, BK(Ca) rapidly inactivates because of dephosphorylation by protein phosphatase 2A. Regulation of ion channels has been linked casually to hyperfiltration during early stages of diabetes mellitus. Determining the signaling pathways controlling the electrophysiology of glomerular mesangial cells is important for understanding how glomerular filtration rate is regulated in health and disease.

Atrial natriuretic peptide inhibits endothelin-1-induced activation of JNK in glomerular mesangial cells

Atrial natriuretic peptide (ANP) has been shown to counteract various actions of endothelin-1 (ET-1) in mesangial cells. We have reported that both extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) are activated by ET-1 and ET-1-induced activation of ERK is inhibited by ANP. To further clarify the action of ANP, we examined the effect of ANP on ET-1-induced activation of JNK. ANP inhibited ET-1-induced activation of JNK in a dose-dependent manner. This inhibitory effect of ANP was reversed by HS-142-1, an antagonist for biological receptors of ANP, while C-ANP, an analog specific to clearance receptors of ANP, failed to inhibit ET-1-induced activation of JNK. 8-Bromo-cGMP and sodium nitroprusside were also able to inhibit ET-1-induced activation of JNK, suggesting cGMP-dependent action of ANP. In contrast, ANP failed to inhibit interleukin-1 beta (IL-1 beta)-induced activation of JNK. Since an increase in intracellular calcium ([Ca2+]i) was shown to be necessary for ET-1-induced activation of JNK in mesangial cells, we measured [Ca2+]i using fura-2. ANP attenuated the ET-1-induced increase in [Ca2+]i in concentrations enough to inhibit ET-1-induced activation of JNK. Finally, ANP was able to inhibit ET-1-, but not IL-1 beta-induced increase in DNA-binding activity of AP-1 by gel shift assay. These results indicate that ANP is able to inhibit ET-1-induced activation of AP-1 by inhibiting both ERK and JNK, suggesting that ANP might be able to counteract the expression of AP-1-dependent genes induced by ET-1.

Role of guanylyl cyclase receptors for CNP in salt secretion by shark rectal gland

The role of C-type natriuretic peptide (CNP) and its guanylyl cyclase-linked receptors in mediating salt secretion by the rectal gland of the spiny dogfish shark (Squalus acanthias) was investigated using HS-142-1, a competitive inhibitor of the binding of natriuretic peptides to their guanylyl cyclase receptors. CNP binds to receptors and activates guanylyl cyclase in rectal gland membranes in a way that is inhibited by HS-142-1. Guanylyl cyclase activation in rectal gland membranes is far more sensitive to CNP than to atrial natriuretic peptide, whereas the reverse is true for membranes derived from mammalian (rabbit) renal collecting duct cells. HS-142-1 inhibited the stimulatory effect of CNP on ouabain-inhibitable oxygen consumption by rectal gland tubules. In explanted rectal glands continuously perfused with blood from intact donor sharks, HS-142-1 inhibited the increase in salt secretion normally provoked by infusing isotonic saline solutions into the donor animal. These results strongly support the view that CNP released into the systemic circulation in response to volume expansion mediates the secretion of chloride by the rectal gland via receptors linked to guanylyl cyclase.

Differential regulation of natriuretic peptide receptors on ciliary body epithelial cells

Atrionatriuretic peptide (ANP) lowers intraocular pressure in the eyes of humans and rabbits. We examined the effects of natriuretic peptides on cGMP formation and 125I-labelled-ANP binding to cultured cells derived from ciliary body epithelium, the site of aqueous humour formation in the eye. ANP, brain natriuretic peptide (BNP) and C-natriuretic peptide (CNP) at 1 microM stimulated cGMP formation 8.2(+/-1.2)-fold, 4.8(+/-0.6)-fold and 87.3(+/-12.1)-fold respectively. 125I-ANP bound to intact cells at a single site, with a dissociation constant KD=0.30+/-0.01 nM. BNP was as effective as ANP in displacing 125I-ANP, whereas CNP displaced label with a slightly higher IC50. 125I-ANP binding was displaced >95% by c-ANP, a specific ligand for natriuretic peptide C receptors (NPR-C). Cross-linking of 125I-ANP to cells labelled predominantly a protein of Mr 62000. These data suggest that 125I-ANP binding was primarily to NPR-C, whereas cGMP stimulation occurred primarily via natriuretic peptide B receptors (NPR-B). Vasopressin and histamine, both activators of the inositol phosphate/diacylglycerol phosphate pathway in non-pigmented ciliary epithelial cells, inhibited CNP stimulation of guanylate cyclase (NPR-B) and 125I-ANP binding (NPR-C) by 30-38%. Inhibition was mimicked by PMA, dioctanoylglycerol and phorbol didecanoate, whereas 4alpha phorbol didecanoate had no effect. Staurosporine and bisindolylmaleimide both blocked inhibition of 125I-ANP binding and cGMP formation by PMA. These results suggest that protein kinase C (PKC) down-regulates both NPR-B and NPR-C. PKC down-regulation of NPR-B varied inversely with CNP concentration. Inhibition by 1 microM PMA was 30.6(+/-4.0)% with 500 nM CNP, but 83.4(+/-8.8)% with 10 nM CNP, indicating that increasing CNP could partially overcome inhibition by PMA. Since extracellular CNP levels were not affected by PKC activation, the effect of PKC on NPR-B is best explained as a reduction in NPR-B affinity for CNP. NPR-C measured as 125I-ANP binding was likewise reduced 36.4(+/-5.1)% by exposure to PMA. In contrast with NPR-B inhibition, however, inhibition of NPR-C was due largely to a reduction in the number of receptor binding sites per cell rather than a reduction in receptor affinity for ligand. The data therefore suggest that both NPR-B and NPR-C are down-regulated by PKC, but that the mechanisms of down-regulation of the two receptors are different.

Atrial natriuretic peptide accelerates proliferation of chick embryonic cardiomyocytes in vitro

The developing embryonic heart has been reported to contain significant levels of atrial natriuretic peptide (ANP). In this study, the role of ANP in cardiac development was evaluated using cultured cardiomyocytes isolated from chick embryos. We analyzed the effect of ANP on cell number, DNA synthesis, total RNA level, the expression of cell-cycle-specific and sarcomeric proteins, and levels of lactate dehydrogenase and creatine phosphokinase. ANP increased overall DNA synthesis (measured by BrdU incorporation, P < 0.01) and enhanced cell proliferation. Morphologically, the development of the cardiomyocyte network was distinctly enhanced in the ANP-treated cells. Cellular RNA content was elevated; likewise, myosin and tropomyosin biosynthesis was significantly greater in ANP-treated cells. In addition, expression of G1/S-specific protein increased, whereas G2/M-specific protein remained unchanged by ANP treatment. An antibody against ANP and a specific ANP receptor antagonist, HS-142-1, antagonized and/or attenuated the action of ANP on both cell proliferation and protein biosynthesis. These results indicate that ANP accelerates myocardial cell proliferation by enhancing entry into S phase and by increasing DNA synthesis during S phase specifically through receptor mediated pathway. The in vitro effects of ANP on myocardial cell proliferation, together with the elevated levels of ANP seen in vivo during normal heart formation, suggest a possible autocrine function of ANP in embryonic cardiac development.

Atrial-natriuretic-peptide receptors in glomerular cryosections of renal malignant and spontaneously hypertensive rats

ANP-receptors affinities (KD) and capacities (Bmax) were assayed in cryosections of glomeruli from 'malignant' hypertensive rats (2K-1C) and spontaneously hypertensive rats (PHR). Plasma ANP concentration was twofold higher in 2K-1C (P < 0.05) and PHR (P < 0.02) than in the respective controls, KD and Bmax for rANP99-126 and ANP103-123 did not differ. ANP mediated cGAMP release in 2K-1C rats was also unaffected. ANP-C glomerular receptors (i.e. displacement of tracer binding with ANP103-123) were not down-regulated and had unchanged peptide binding affinity in either kidney of rats with 'malignant' hypertension and in PHR. The difference between Bmax for rANP99-126 and Bmax for rANP103-123 (ANP-A receptor binding) indicates moderate up-regulation of ANP-A receptors in the clipped, and down-regulation in the contralateral kidney of 2K-1C (2K-1C, right vs. left, P < 0.05). Since [ANP]pl, and also Bmax and KD for ANP were similar in both hypertension models investigated, changes of the [ANP]pl/ANP-receptor system can not completely explain the marked natriuresis of rats with 'malignant' hypertension.

Prevention of glomerular hyperfiltration in rats with streptozotocin-induced diabetes by an atrial natriuretic peptide receptor antagonist

The contribution of atrial natriuretic peptide (ANP) to the development of glomerular hyperfiltration in diabetes was investigated by examining the effects of HS-142-1, a non-peptide antagonist of biological receptors for ANP, on glomerular filtration rate (GFR) and renal plasma flow (RPF) in rats with streptozotocin-induced diabetes. Three to four weeks after streptozotocin injection, the plasma concentration of ANP, urinary cyclic GMP excretion rate, GFR, and RPF were significantly higher in diabetic rats than in control rats. The increase in GFR and RPF in diabetic rats was significantly reduced, in a dose-dependent manner, by a single intravenous injection of HS-142-1; the maximal effect was apparent at a dose of 10 mg per kg of body weight. Continuous subcutaneous administration of HS-142-1 with an osmotic minipump for 3 to 4 weeks, beginning 2 days after streptozotocin injection, prevented the increases in urinary cyclic GMP excretion rate, GFR, and RPF observed in untreated diabetic rats. These results highlight the importance of ANP in the development of diabetic glomerular hyperfiltration and indicate that this condition can be prevented by continuous inhibition of the action of ANP.

Atrial natriuretic factor significantly contributes to the mineralocorticoid escape phenomenon. Evidence for a guanylate cyclase-mediated pathway

The mechanism underlying the mineralocorticoid escape phenomenon remains unknown. To assess the possible contribution of natriuretic peptides to mineralocorticoid escape, rats were injected with 5 mg deoxycorticosterone acetate for 3 d. Plasma atrial natriuretic factor (ANF) rose to twice basal levels and atrial ANF content decreased significantly by 24 h of treatment. This coincided with renal escape and with a significant increase in urinary cGMP excretion. Plasma ANF remained elevated and atrial ANF content continued to decline by 48 and 72 h while atrial ANF mRNA levels increased significantly only at 72 h. Plasma brain natriuretic peptide did not increase during escape although atrial brain natriuretic peptide mRNA levels increased significantly. Chronically administered HS-142-1 (HS), a specific antagonist of the guanylate cyclase-coupled natriuretic peptide receptors, significantly and dose-dependently impaired the escape phenomenon. The highest dose of HS completely suppressed the increase in urinary cGMP. Despite the continued suppression, partial escape was observed by the end of the observation period. HS alone influenced neither plasma nor tissue or urine parameters. These findings show that despite activation of atrial ANF, blockade of the guanylate cyclase-coupled natriuretic peptide receptors impairs the ability of the kidney to escape the Na+ retaining effect of excess mineralocorticoid in a dose-dependent fashion. Later-acting, unknown mechanisms eventually come into play to mediate the escape phenomenon through a guanylate cyclase-independent pathway. Therefore, ANF of cardiac origin appears to be a major factor initiating mineralocorticoid escape through a guanylate cyclase-dependent pathway.

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.

Renal effects of natriuretic peptide receptor blockade in cirrhotic rats with ascites

The aim of this study was to assess the effect of HS-142-1, a recently discovered specific antagonist of endogenous natriuretic peptides, on systemic hemodynamics, renal function, and the renin-aldosterone system in rats with cirrhosis and ascites. The study consisted of three protocols, each including 10 conscious control rats and 10 conscious rats with carbon-tetrachloride-induced cirrhosis with ascites. In protocol 1, HS-142-1 administration (by intravenous bolus of 20 mg.kg-1.body weight in all protocols) was not associated with significant changes in mean arterial pressure, heart rate, cardiac output or total peripheral resistance in the two groups of animals. In protocol 2, HS-142-1 induced a significant reduction in glomerular filtration rate (from 4.2 +/- 0.5 to 2.6 +/- 0.3 ml/min, p < 0.025) in control animals. A decrease in renal plasma flow and an increase in renal vascular resistance also occurred, but these changes were not statistically significant. In cirrhotic rats, HS-142-1 resulted in a significant decrease in renal plasma flow (from 10.9 +/- 0.7 to 4.3 +/- 0.6 ml/min, p < 0.001) and a significant increase in renal vascular resistance (from 6.0 +/- 0.6 to 16.3 +/- 2.7 mm Hg.min.ml-1, p < 0.025). Glomerular filtration rate decreased more in cirrhotic rats with ascites than in control rats (from 3.8 +/- 0.3 to 1.3 +/- 0.2 ml/min, p < 0.001). Changes in urine flow rate and urinary sodium excretion rate paralleled those of glomerular filtration rate in both groups of animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiorenal and neurohumoral effects of endogenous atrial natriuretic peptide in dogs with severe congestive heart failure using a specific antagonist for guanylate cyclase-coupled receptors

BACKGROUND

To elucidate the extent of the compensatory role of endogenous atrial natriuretic peptide (ANP) in severe congestive heart failure (CHF), we examined the changes in hemodynamics and neuroendocrine and renal functions after incremental administration of an ANP antagonist, HS-142-1 (HS), in dogs with CHF.

METHODS AND RESULTS

We assessed the effects of HS on the suppression of plasma and urinary cGMP levels as a marker of endogenous ANP activity in dogs without CHF. Bolus injections of 0.3 and 1.0 mg/kg HS reduced plasma cGMP levels to 77% and 60% and urinary cGMP excretion to 78% and 61% of the relevant control levels, respectively. Then the study was performed in dogs with CHF induced by chronic rapid ventricular pacing, and the plasma ANP level was sixfold higher than that in the controls. Hemodynamic, hormonal, and renal variables were determined both before and after subsequent incremental administration (0.3, 1.0, and 3.0 mg/kg every 30 minutes) of HS. HS lowered the plasma and urinary cGMP levels dose dependently to 32% and 37% of the control levels, respectively. Mean arterial, pulmonary capillary wedge, and right atrial pressures and cardiac output did not change significantly. However, plasma renin activity, aldosterone level, and norepinephrine level increased rapidly to 226%, 179%, and 252% of the control values, respectively. Urine flow rate and urinary sodium excretion were significantly inhibited, with no concomitant change in glomerular filtration rate or renal plasma flow.

CONCLUSIONS

These findings suggest that endogenous ANP contributes to the suppression of the activation of the renin-aldosterone system and sympathetic nervous activity and body fluid retention but that the vasodilative action of this peptide is attenuated in advanced CHF.

Cardiovascular and renal functional effects of an antagonist of the guanylyl cyclase-linked ANF receptor

A selective antagonist for the cGMP-linked ANF receptor was used to assess inhibition of cardiovascular and renal actions of atrial natriuretic factor (ANF). Two groups of anesthetized rats were injected with antagonist or vehicle, respectively, prior to an infusion of ANF. A third group received neither antagonist injection nor ANF infusion and served as a time control. Compared to ANF infusion alone, prior antagonist administration was associated with significant reduction of both the hypotension and hemoconcentration following peptide infusion, although significant residual effects were still present. Glomerular filtration rates during ANF infusion were significantly lower in the antagonist group. The increases in urinary salt and water excretion were also partially blocked by the antagonist. Microcatheterization studies showed significant partial reversal of ANF-induced inhibition of sodium chloride and water reabsorption in the medullary collecting duct. We conclude that the antagonist is an effective specific blocker of the cardiovascular, renal hemodynamic, and tubular effects of ANF, providing a useful new tool to elucidate the regulatory roles of this peptide hormone system.

Role of endogenous atrial natriuretic peptide in DOCA-salt hypertensive rats. Effects of a novel nonpeptide antagonist for atrial natriuretic peptide receptor

BACKGROUND

To explore roles of endogenous atrial natriuretic peptide (ANP) in blood pressure and volume regulation, we examined the effects of a newly developed ANP antagonist, HS-142-1 (HS) in deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

METHODS AND RESULTS

We examined 1) the effects of HS on ANP- or brain natriuretic peptide (BNP)-induced reductions in renal vascular resistance (RVR) of rat isolated perfused kidneys, 2) the effects of HS on cyclic GMP (cGMP) production in rat cultured vascular smooth muscle cells pretreated with ANP or BNP, and 3) the renal and systemic effects of HS in DOCA-salt-treated rats and control rats. We found that 1) HS dose-dependently reversed ANP- or BNP-induced decreases in RVR; 2) ANP or BNP at 100 nM caused an eightfold increase in cGMP production. These increases in cGMP were inhibited by HS in a dose-dependent fashion, and 300 micrograms/ml HS decreased cGMP to the control level. HS alone did not influence RVR or cGMP production; and 3) DOCA-salt rats showed higher plasma concentrations of ANP (198 versus 75 pg/ml) and BNP (23.7 versus 2.7 pg/ml, each p < 0.01) than the control rats. Bolus administration of 8 mg/kg HS elevated blood pressure by 8% (p < 0.01). This rise in blood pressure was attributed to an increase in systemic vascular resistance (+14%, p < 0.05). Conversely, urinary excretion of sodium (-41%), glomerular filtration rate (-27%), and plasma (-77%) and urinary cGMP (-69%, each p < 0.01) were decreased by administration of 8 mg/kg HS. These effects were dose dependent in DOCA-salt rats but slight or negligible in the control rats.

CONCLUSIONS

These results suggest that endogenous ANP and BNP may be involved in the regulation of blood pressure and body fluid volume in DOCA-salt rats in which ANP and BNP secretion is augmented.

HS-142-1, a novel antagonist for natriuretic peptides, has no effect on the third member of membrane bound guanylate cyclases (GC-C) in T84 cells

HS-142-1, a novel non-peptide antagonist for natriuretic peptides, exerts antagonistic actions almost equally on two similar guanylate cyclase-linked natriuretic peptide receptors (GC-A and GC-B), but has little or no effect on the binding of natriuretic peptides to a membrane protein, the so-called "clearance receptor", which binds all natriuretic peptides. The third mammalian form of membrane bound guanylate cyclases (GC-C) was identified not as a natriuretic peptide receptor, but as a receptor for heat-stable enterotoxins (STa). In this study, we examined effects of HS-142-1 on GC-C (STaR) in T84 cells and showed that HS-142-1 exerts neither agonistic nor antagonistic activity for GC-C, indicating that HS-142-1 is not a common antagonist for a family of membrane bound guanylate cyclase receptors, but a specific antagonist for the guanylate cyclase-linked natriuretic peptide receptors.

Stable expression of natriuretic peptide receptors: Effects of HS-142-1, a non-peptide ANP antagonist

We established clonal cell lines stably expressing each of two subtypes of membrane bound guanylate cyclases (GC-A and GC-B), which are known as natriuretic peptide receptors. Using these cell lines, we showed that GC-A is an ANP/BNP receptor, whereas GC-B is a specific receptor for CNP. Effects of HS-142-1, a novel non-peptide ANP antagonist, on GC-A and GC-B were examined by using these cells. In cells expressing either GC-A or GC-B, HS-142-1 inhibited cGMP production elicited by ANP or CNP with IC50 values of 1.8 micrograms/ml and 1.5 micrograms/ml, respectively, and also competitively blocked specific binding of the natriuretic peptides with IC50 values of 2.2 micrograms/ml and 3.3 micrograms/ml, respectively. These results indicate that HS-142-1 is a potent antagonist of CNP as well as ANP. We also showed that CNP suppressed the growth of cells expressing GC-B by 22% and that HS-142-1 blocked the antiproliferative action of CNP.