Regional expression of natriuretic peptide receptors during the formation of arterial neointima in the rabbit

Renal actions of dendroaspis natriuretic peptide in rabbits

Dendroaspis natriuretic peptide (DNP) is one of four members of the natriuretic peptide family sharing functional and structural properties. The purpose of the present study was to elucidate the physiological role of DNP on renal functions and its cellular mechanism in the rabbit kidney. DNP (5 μg/kg/min) infused intravenously increased urine volume and urinary excretion of electrolytes. These renal actions induced by DNP were more pronounced than those caused by atrial natriuretic peptide (ANP). We compared profiles of (125)I-ANP and (125)I-DNP by reverse-phase HPLC during incubation in rabbit plasma at 37°C for 1, 2, and 4h. While (125)I-ANP was quickly degraded within 1h, (125)I-DNP was still stable in plasma for 4h. DNP induced the greatest cyclic guanosine monophosphate (cGMP) production in the glomeruli in a dose-dependent manner, when compared to other renal structures including cortical tubules, outer medullary tubules, and inner medullary tubules. Affinity cross-linking analysis revealed NPR-A is selective receptor for DNP in glomeruli. Forskolin, a stimulator of adenylyl cyclase, significantly decreased cGMP production in the renal glomeruli but not in the renal medulla. In summary, DNP is a more effective activator of renal functions than ANP, possibly because of the degradation resistance of DNP against the endogenous peptidases in plasma or tissues. These findings suggest that DNP plays a pivotal role as a renal regulating peptide via specific natriuretic peptide receptors with a guanylyl cyclase domain.

Knockdown of natriuretic peptide receptor-A enhances receptor C expression and signalling in vascular smooth muscle cells

AIMS

Natriuretic peptide receptor-A (NPR-A) knockout mice exhibited an increased blood pressure that may also be attributed to the up-regulation of NPR-C and associated signalling; however, the interaction between the two receptors has not been investigated. In the present study, we investigated the effect of knockdown of NPR-A using NPR-A antisense (AS) on the expression of NPR-C and adenylyl cyclase (AC) signalling in A10 vascular smooth muscle cells (VSMC).

METHODS AND RESULTS

The receptor and G protein expression was determined by western blotting, and AC activity was determined by measuring [(32)P]cAMP formation from [α-(32)P]ATP. Treatment of A10 VSMC with NPR-A AS decreased NPR-A and enhanced NPR-C expression without altering the levels of angiotensin II AT1 and muscarinic M2 receptors. In addition, siRNA-NPR-A also resulted in the up-regulation of NPR-C. The re-expression of NPR-A in AS-treated cells reversed the enhanced expression of NPR-C to control levels. In addition, NPR-C-, AT1, and M2 receptor-mediated inhibition of AC and Giα protein expression was enhanced in AS-treated cells, whereas NPR-A-mediated cyclic GMP (cGMP) formation and Gsα-mediated stimulation of AC were significantly reduced. Pertussis toxin treatment attenuated the AS-induced enhanced inhibition of AC to control levels. Furthermore, the enhanced levels of NPR-C and Giα proteins were reversed to control levels by 8-bromo-cGMP (8Br-cGMP) and PD98059, an MEK inhibitor. In addition, 8Br-cGMP also attenuated AS-induced enhanced ERK1/2 phosphorylation to control levels.

CONCLUSION

These results demonstrate that knockdown of NPR-A up-regulates the expression of NPR-C, Giα proteins, and NPR-C-linked AC signalling and suggests a cross-talk between NPR-A and NPR-C.

Presence of dendroaspis natriuretic peptide and its binding to NPR-A receptor in rabbit kidney

Natriuretic peptides help to maintain sodium and fluid volume homeostasis in a healthy cardio-renal environment. Since the identification of Dendroaspis natriuretic peptide (DNP) as a new member of the natriuretic peptide family, DNP has been considered as an important regulator of natriuresis and dieresis. The present study was undertaken to investigate the presence of immunoreactive Dendroaspis natriuretic peptide (DNP) and its specific receptor in rabbit. DNP was detected in heart, kidney, liver, brain, and plasma by radioimmunoassay (RIA). DNP contents of cardiac atrium and ventricle, renal cortex and medulla, liver, and brain were 1.42 ± 0.15, 1.0 6 ± 0.08, 2.55 ± 0.21, 1.81 ± 0.16, 1.36 ± 0.22, and 0.69 ± 0.15 pg/mg of wet weight, respectively. The concentration of DNP in plasma was 235.44 ± 15.44 pg/ml. By quantitative in vitro receptor autoradiography, specific ¹²⁵I-DNP binding sites were revealed in glomeruli, interlobular artery, acuate artery, vasa recta bundle, and inner medulla of the kidney with an apparent dissociation constant (K(d)) of 0.29 ± 0.05, 0.36 ± 0.03, 0.84 ± 0.19, 1.18 ± 0.23, and 10.91 ± 1.59 nM, respectively. Basal rate of 3', 5'-cyclic guanosine monophosphate (cGMP) production by particulate guanylyl cyclase (GC) activation of glomerular membranes was basally 13.40 ± 1.70 pmol/mg protein/min. DNP caused an increment of cGMP production in similar magnitude to that caused by ANP, BNP, and urodilatin, while the production of cGMP by CNP was significantly lower than that by DNP. Our results show that plasma levels of DNP were higher when compared to other tissues. DNP produces cGMP via the NPR-A receptor subtype in the kidney, similarly to ANP and BNP, suggesting that plasma DNP could have similar functions as ANP and BNP.

C-type natriuretic peptide regulation of guanosine-3',5'-cyclic monophosphate production in human endothelial cells

In vascular smooth muscle cells, relaxant actions of guanosine--3',5'-cyclic monophosphate (cGMP) are well recognized, but there is increasing evidence that cGMP also plays regulatory roles in vascular endothelium. However, the autacoid and endocrine mechanisms controlling cGMP production in endothelium are not well understood. The objective of these studies was to examine the mechanisms of cGMP accumulation in human umbilical vein endothelial cells (HUVEC) in response to natriuretic peptides. Expression in HUVEC of natriuretic peptide receptors, particulate guanylyl cyclases (GC)-A and GC-B, was confirmed by RT-PCR and Western blot analysis. In the presence of the phosphodiesterase inhibitor IBMX 500 microM, 3 h incubation of HUVEC with B-type natriuretic peptide (BNP) (preferential GC-A agonist) or C-type natriuretic peptide (CNP) (preferential GC-B agonist) stimulated concentration-dependent increases in cGMP production. At 10 and 100 nM, we observed two to three-fold greater potency of CNP compared to BNP. In the absence of IBMX, CNP-stimulated cGMP accumulation was significantly less than cGMP accumulation in response to sodium nitroprusside 1 mM. This greater sensitivity of GC-B-derived cGMP to phosphodiesterases suggests compartmentalization of two pools of cGMP from particulate and soluble guanylyl cyclases. Although CNP 100 nM and 1 microM was observed to increase nitrite + nitrate (stable metabolites of NO) production in HUVEC two-fold above basal level, the soluble guanylyl cyclase inhibitor ODQ 10 microM did not significantly modify CNP-stimulated cGMP accumulation suggesting that endothelial actions of CNP may be NO-independent. In conclusion, these studies indicate functional signaling by natriuretic peptides in endothelial cells, supporting possible roles of these mediators in regulating endothelial cell function.

Natriuretic peptide receptor B signaling in the cardiovascular system: protection from cardiac hypertrophy

Natriuretic peptides (NP) represent a family of structurally homologous but genetically distinct peptide hormones involved in regulation of fluid and electrolyte balance, blood pressure, fat metabolism, cell proliferation, and long bone growth. Recent work suggests a role for natriuretic peptide receptor B (NPR-B) signaling in regulation of cardiac growth by either a direct effect on cardiomyocytes or by modulation of other signaling pathways including the autonomic nervous system. The research links NPR-B for the first time to a cardiac phenotype in vivo and underlines the importance of the NP in the cardiovascular system. This manuscript will focus on the role of NPR-B and its ligand C-type natriuretic peptide in cardiovascular physiology and disease and will evaluate these new findings in the context of the known function of this receptor, with a perspective on how future research might further elucidate NPR-B function.

Renal atrial natriuretic peptide receptors binding properties and function are resistant to DOCA-salt-induced hypertension in rats

Atrial natriuretic peptide receptor types A (NPR-A) and C (NPR-C) binding properties and functional characteristics in renal glomeruli have been investigated in deoxycorticosterone acetate (DOCA)-treated hypertensive Wistar-Kyoto (WKY) rats and their respective controls. We found that DOCA administration had no significant effect on the maximum binding capacity or the affinity of renal NPR-A and NPR-C. NPR-C is involved in the regulation of cAMP production. Our results indicate that the cAMP production by NPR-C is not altered in DOCA-induced hypertension, since ANP(1-28), CNP(1-22) and C-ANP, which specifically bind to NPR-C, show a similar inhibitory effect on cAMP production stimulated by the physiological agonist histamine in glomeruli from DOCA-treated rats and controls. Finally, we have found that DOCA-induced hypertension does not modify NPR-A or NPR-C expression in rat glomerular membranes. These findings indicate that NPR-A and NPR-C binding properties and NPR-C-mediated inhibition of cAMP generation remain unaltered in DOCA-treated rats.

C-Type natriuretic peptide and natriuretic peptide receptors are expressed by smooth muscle cells in the neointima after percutaneous coronary intervention

Understanding restenosis after percutaneous coronary intervention (PCI) remains a challenge. Neointimal proliferation is the main cause of restenosis. C-Type natriuretic peptide (CNP) plays a role in relaxation and growth inhibition of vascular smooth muscle cells (SMCs); the effects depend on the presence of specific natriuretic peptide receptors (NPRs) consisting of NPR-A, NPR-B, and NPR-C. To test the hypothesis that CNP and NPRs may be involved in restenosis, we immunohistochemically studied the expression of CNP and NPRs during the post-PCI healing process; 10 sites after PCI obtained at autopsy and 14 atherectomy specimens obtained from restenotic sites were investigated. Frozen sections were stained with antibodies against CNP, NPRs, SMCs, macrophages, and endothelial cells. Within 2 months after PCI, most neointimal SMCs expressed CNP and NPR-A. The expression of CNP and NPR-A in these neointimal SMCs decreased from 6 months onward. In contrast, NPR-C was strongly expressed in neointimal SMCs from 1 to 9 months after PCI. In atherectomy specimens, most neointimal SMCs showed weak positivity for CNP and NPR-A, but NPR-C was strongly expressed in the neointimal SMCs. These findings strongly suggest that a paracrine and autocrine system of CNP and NPRs may be important in controlling neointimal growth after PCI in humans.

C-type natriuretic peptide and guanylyl cyclase B receptor

Guanylyl cyclases (GC) are widely distributed enzymes that signal via the production of the second messenger cGMP. The particulate guanylyl cyclases share a similar topology: an extracellular ligand binding domain and intracellular regulatory kinase-homology and cyclase catalytic domains. The natriuretic peptide receptors GC-A and -B mediate the effects of a family of peptides, atrial, B- and C-type natriuretic peptide (ANP, BNP and CNP, respectively), with natriuretic, diuretic and vasorelaxant properties. ANP and BNP, through the activation of GC-A, act as endocrine hormones to regulate blood pressure and volume, and inhibit cardiac hypertrophy. CNP, on the other hand, acts in an autocrine/paracrine fashion to induce vasorelaxation and vascular remodeling, and to regulate bone growth through its cognate receptor GC-B. GC-B, like GC-A, is phosphorylated in the basal state, and undergoes both homologous and heterologous desensitization, reflected by dephosphorylation of specific sites in the kinase-homology domain. This review will examine the structure and function of GC-B, and summarize the physiological processes in which this receptor is thought to participate.

Atrial Natriuretic Peptide Preserves Endothelial Function during Intimal Hyperplasia

BACKGROUND

Atrial and C-type natriuretic peptides (ANP and CNP), acting through different receptors, have antiproliferative effects in vitro. Beneficial effects of CNP in vivo on early atherosclerosis have been described, but it is not known if ANP is antiproliferative in vivo. In the present study, the effects of chronic in vivo ANP were tested and compared with CNP on endothelial dysfunction and intimal thickening caused by peri-arterial collars.

METHODS

Non-occlusive collars were placed bilaterally around the common carotid arteries of rabbits. One collar was filled with saline vehicle. The contralateral collar was filled with ANP or CNP (1 or 10 microM, n = 5-7) with slow replacement of peptide via mini-pump (1 or 10 fmol/h).

RESULTS

After 7 days, endothelium-dependent vasorelaxation in saline-collared arteries was 33 +/- 3% of maximum [averaged over 0.03-1 muM acetylcholine (ACh)] compared to 64 +/- 2% in normal (uncollared) arteries (p < 0.05, n = 23). In vivo ANP restored the ACh relaxation to normal (e.g., 57 +/- 6%, 1 microM ANP), similar to effects seen with CNP in vivo. Endothelium-independent vasorelaxation of collared-vessels was not altered by either peptide. Intimal hyperplasia induced by the collars was not prevented by peri-arterial natriuretic peptides. In additional rabbits (n = 6), CNP (100 pmol/h) given directly into the lumen of collared carotid arteries for 7 days reduced neointima formation by 16 +/- 5% (p < 0.05), whereas ANP given intraluminally (100 pmol/h; n = 6) did not.

CONCLUSIONS

The more potent actions of CNP on vascular smooth muscle cell migration and proliferation (established in vitro) may explain differences between the peptides on intimal hyperplasia in vivo. The major hallmark of atherosclerosis and restenosis, endothelial dysfunction, was prevented by chronic, peri-arterial administration of ANP or CNP.

C-type natriuretic peptide in vascular physiology and disease

Natriuretic peptides play a critical role in coordination of fluid/electrolyte balance and vascular tone. The renal effects of circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are distinct from the paracrine effects of vascular C-type natriuretic peptide (CNP). CNP is widely expressed throughout the vasculature and is found in particularly high concentrations in the endothelium. Recent studies demonstrate that CNP is a novel endothelium-derived hyperpolarising factor (EDHF) that complements the actions of other endothelial vasorelaxant mediators such as nitric oxide (NO) and prostacyclin. Since several cardiovascular disorders are associated with dysfunction of natriuretic peptide activity, selective modulation of the natriuretic peptide pathways represents an important therapeutic target; whilst this has been exploited to some degree in terms of ANP/BNP, the therapeutic potential of CNP has yet to be tapped. This review focuses on recent findings on the actions and mechanism of locally produced endothelial-derived CNP in the cardiovascular system and highlights many potential avenues for therapeutic intervention, via modulation of CNP-signalling, in cardiovascular disease.

Water deprivation enhances the inhibitory effect of natriuretic peptides on cAMP synthesis in rat renal glomeruli

This study investigates the effect of water deprivation on the expression of atrial natiruretic peptide (ANP)(1-28) binding sites in rat kidney. Water deprivation increased the B(max) of glomerular binding sites for ANP(1-28) and C-type natriuretic peptide (CNP)(1-22) without modifying their affinity, an effect that was prevented in the presence of C-atrial natriuretic factor (C-ANF), suggesting that natriuretic peptide receptor-C (NPR-C) binding sites might be enhanced. Our results indicate that ANP(1-28), CNP(1-22), and C-ANF inhibit cAMP synthesis directly stimulated by forskolin or by the physiological agonists histamine and 5-hydroxytryptamine. The inhibitory effect was found to be significantly greater in water-deprived rats than in controls. Our observations suggest that this effect must be attributed to the 67-kDa NPR-C-like protein, because the 67- and 77-kDa NPR-C-like proteins show high and low affinities for CNP(1-22), respectively, and the enhanced inhibitory effect of CNP on cAMP generation in water-deprived rats was detected at subnanomolar concentrations. In addition, using affinity cross-linking studies we have observed that water deprivation increases the expression of the 67-kDa NPR-C-like protein, and HS-142, which binds to NPR-A and the 77-kDa NPR-C-like but not the 67-kDa protein, reduced ligand internalization without affecting cAMP inhibition by ANP(1-28). Finally, we have found that ligand binding to the 67-kDa NPR-C-like protein is reduced by GTPgammaS, suggesting that this receptor is associated with a G protein in renal glomeruli. The enhanced inhibitory role of natriuretic peptides on cAMP synthesis induced by water deprivation may influence glomerular function in the rat kidney.

Expression and control of C-type natriuretic peptide in rat vascular smooth muscle cells

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family mainly distributed in the central nervous system. CNP is also produced and secreted by the endothelium and inhibits vascular smooth muscle cell proliferation. We have reported that endothelial damage stimulates only transiently vascular smooth muscle cell proliferation in arteries due to the development of an autocrine neointimal system for CNP that modulates neointimal growth. The present study demonstrates the production and secretion of CNP in rat vascular smooth muscle cells in the absence of endothelium. In addition, these cells express atrial natriuretic peptide (ANP) and the natriuretic peptide receptors A, B, and C. The production and secretion of CNP in vascular smooth muscle cells is stimulated by transforming growth factor-beta, whereas basic fibroblast growth factor plays an inhibitory role. These data show that ANP and mainly CNP are coexpressed with the natriuretic peptide receptors in rat vascular smooth muscle cells. This provides evidence for a vascular natriuretic peptide autocrine system of physiological relevance in these cells.

Accentuation of ANP secretion to endothelin-1 in hypertrophied atria

To investigate modulation of ANP secretion by atrial hypertrophy, the secretion of ANP in response to stretch and endothelin-1 was studied using isolated perfused quiescent atria from rats treated with monocrotaline (MCT). Male Sprague-Dawley rats were given a single subcutaneous injection of 50 mg/kg MCT or saline and were sacrificed at 6 weeks. Rats with right heart hypertrophy showed an increase in ANP mRNA and decrease in tissue concentration of ANP in hypertrophied atria and a marked increase in plasma concentration of ANP. In isolated perfused hypertrophied right atria from MCT rats, changes in atrial volume induced by increased atrial pressure caused proportional increases in mechanically stimulated extracellular fluid (ECF) translocation and stretch-activated ANP secretion. Changes in atrial volume and mechanically stimulated ECF translocation in hypertrophied right atria were not different from those in control right atria. The stretch-activated ANP secretion was suppressed without significant difference in basal ANP secretion, as compared to control right atria. Therefore, the stretch-activated ANP secretion from hypertrophied right atria into the atrial lumen in relation to the ECF translocation (ANP concentration in the interstitium) was lower than that from control atria. A positive correlation between the stretch-activated ANP secretion in relation to the ECF translocation and tissue ANP content was found in control atria but not in hypertrophied atria. Endothelin-1 caused increases in stretch-activated ANP secretion in a dose-dependent manner, which were accentuated in hypertrophied right atria. Therefore, we suggest that atrial hypertrophy causes an attenuated response to stretch and accentuated response to endothelin-1 of ANP secretion.

Coronary endothelial function in health and disease

The endothelium participates in the control of coronary vascular tone and growth through the release of vasodilating and growth-inhibiting factors such as nitric oxide (NO) and C-type natriuretic peptide (CNP), and vasoconstricting and growth-promoting substances such as endothelin-1 (ET-1). Abnormalities in NO and/or CNP generation or actions have been demonstrated in various cardiovascular pathophysiological states, specifically atherosclerosis, congestive heart failure, hypertension and hypercholesterolaemia. Moreover, an increase in plasma ET-1 levels has also been reported in these disease states. When these observations are considered together, these states may be characterised by an attenuated release or action of NO and/or CNP, together with an augmented release of ET-1. Thus, an imbalance between these opposing factors may contribute to the alteration in vascular tone and the vascular remodelling characteristics of cardiovascular disease. The following article summarises the present knowledge of endothelial control of the coronary circulation and derangements associated with coronary endothelial dysfunction.

Natriuretic peptide system in the rat lacrimal gland

The presence and characteristics of the natriuretic peptides and their receptors in the rat exorbital lacrimal gland were investigated. Serial dilution curves of the gland extracts were parallel to the standard curves of synthetic atrial natriuretic peptide (ANP) or C-type natriuretic peptide (CNP). Immunoreactive ANP or CNP in the gland extracts co-eluted with authentic ANP or CNP, and their contents were 4.95 +/- 0.60 and 2.87 +/- 0.53 pg mg(-1)protein (quadruplicate), respectively. By immunohistochemistry, strong immunoreactivities of ANP and CNP were co-localized in the tubules and excretory ducts of the gland, and moderate immunoreactivities were found in the myoepithelial cells and acini. Productions of guanosine 3',5'-cyclic monophosphate by particulate guanylyl cyclase in the gland membranes were stimulated by natriuretic peptides in a dose-dependent manner, and that by CNP was larger than by ANP. Messenger RNAs for ANP, CNP and their receptors were detected by reverse transcription-polymerase chain reaction. These results indicate that natriuretic peptides and their specific receptors are found in the rat lacrimal gland. Therefore, it is suggested that natriuretic peptide system may play physiological roles in the rat lacrimal gland.

Molecular mechanism of cGMP-mediated smooth muscle relaxation

Contraction and relaxation of smooth muscle is a tightly regulated process involving numerous endogenous substances and their intracellular second messengers. We examine the key role of cyclic guanosine monophosphate (cGMP) in mediating smooth muscle relaxation. We briefly review the current art regarding cGMP generation and degradation, while focusing on the recent identification of the molecular mechanisms underlying cGMP-mediated smooth muscle relaxation. cGMP-induced SM relaxation is mediated mainly by cGMP-dependent protein kinase activation. It involves several molecular events culminating in a reduction in intracellular Ca(2+) concentration and a decrease in the sensitivity of the contractile system to Ca(2+). We propose that the cGMP-induced decrease in Ca(2+) sensitivity is a strategic way to achieve "active relaxation" of the smooth muscle. In summary, we present compelling evidence supporting a key role for cGMP as a mediator of smooth muscle relaxation in physiological and pharmacological settings.

Modulation of endocardial natriuretic peptide receptors in right ventricular hypertrophy

Natriuretic peptide (NP) receptors (NPRs) located at the endocardial endothelium are suggested to be involved in regulating myocardial contractility. However, the characteristics and modulation of NPRs in relation to cardiac failure are not well defined. This study examined the properties of NPRs in ventricular endocardium using quantitative receptor autoradiography, RT-PCR, Southern blot analysis, and activation of particulate guanylyl cyclase (GC) by NPs. In control rats, specific 125I-labeled rat atrial NP (rANP)(1-28) binding sites were localized in right (RV) and left ventricular (LV) endocardium. Binding affinities of 125I-rANP(1-28) were remarkably higher in RV than LV endocardium. Radioligand binding at these sites was mostly inhibited by des[Gln18,Ser19,Gly20,Leu21, Gly22]ANP(4-23), a specific NP clearance receptor ligand. mRNAs for all three recognized NPRs were detected in endocardial cells by RT-PCR and confirmed by Southern blot analysis. Production of cGMP by particulate GC in endocardial cell membranes was stimulated by NPs with a rank order of potency of C-type NP(1-22) >> brain NP (BNP)(1-26) > ANP(1-28). We also examined the modulation of these NPRs during cardiac hypertrophy induced by monocrotaline (MCT). In MCT-treated rats with pulmonary hypertension, specific (125)I-rANP(1-28) binding to hypertrophied RV endocardium almost disappeared and cGMP production by NPs was significantly decreased. In rats with pulmonary hypertension, plasma levels of ANP and BNP were increased by fivefold compared with controls. The results indicate that there is a differential distribution of NPRs in the cardiac chambers, with the most abundant binding sites in RV endocardium, that NPR-B is the predominant GC-coupled NPR in ventricular endocardium, and that endocardial NPRs are downregulated with ventricular hypertrophy. Downregulation of NPRs may be associated with an increment of endogenous NP production caused by mechanical overload in hypertrophied ventricle.

Localization of atrial natriuretic peptide receptors in the rat tongue and hard palate

Atrial natriuretic peptide (ANP) receptors were characterized in rat oral mucosa using quantitative in vitro autoradiography and activation of particulate guanylyl cyclase (GC) by natriuretic peptides. Competition-binding analysis performed by quantitative in vitro autoradiography demonstrated specific [125I]rANP(1-28) binding sites in the tongue and hard palate. The precise location of this binding was revealed on the basal and parabasal cells of the epithelia by microautoradiography. The dissociation constant (Kd) and maximal binding capacity (Bmax) of these sites were 3.34+/-1.35 nM and 2.71+/-2.21 fmol/mm2 on the epithelium of the tongue, and 4.09+/-1.52 nM and 3.45+/-3.01 fmol/mm2 on the epithelium of the hard palate, respectively. Receptor subtypes were characterized by competition with des [Gln18, Ser19, Gly20, Leu21, Gly22] ANP(4-23) (C-ANP), a specific ligand for the clearance receptor (NPR-C). These binding sites were displaced by C-ANP with inhibition constant (Ki) of 8.96+/-3.18 nM and Bmax of 2.89+/-2.45 fmol/mm2 on the epithelium of the tongue, and Ki of 9.12+/-2.71 nM and Bmax of 3.08+/-2.94 fmol/mm2 on the epithelium of the hard palate, respectively. Production of cyclic GMP by particulate GC in the epithelial membranes of the tongue and hard palate was stimulated by rANP(1-28), porcine brain natriuretic peptide (BNP)(1-26), and C-type natriuretic peptide (CNP)(1-22) in a dose-dependent manner. These results indicate that ANP-binding sites in the epithelium of the tongue and hard palate are mainly clearance receptors (NPR-C) but biological receptors (NPR-A and/or NPR-B) with GC activity are also present, and suggest that ANP may have a role in the proliferation of the oral epithelial cells, especially in the tongue and hard palate.

Presence and biological activity of C-type natriuretic peptide-dependent guanylate cyclase-coupled receptor in the penile corpus cavernosum

PURPOSE

To investigate the presence of C-type natriuretic peptide 1-22 (CNP)-dependent guanylyl cyclase (GC)-coupled receptor and its biological function in the penile erectile smooth muscle.

MATERIALS AND METHODS

Experiments have been done in rabbit and rat to detect cyclic GMP (cGMP) generation by the activation of particulate GC by natriuretic peptides (NPs) in cavernosal membrane, to localize precise receptor using a quantitative in vitro autoradiography of the snap frozen sections, to define natriuretic peptide receptor (NPR) mRNA using a reverse transcriptase-polymerase chain reaction (RT-PCR) technique and to monitor changes of erectile smooth muscle tone by NPs in the penile tissue strips.

RESULTS

Productions of cGMP by particulate GC in the corpus cavernosum membranes of rabbit and rat were stimulated by CNP, atrial natriuretic peptide 1-28 (ANP) and brain natriuretic peptide 1-26 (BNP) with a rank order of potency of CNP > BNP > ANP. HS-142-1, a selective antagonist for the GC-coupled NPR, inhibited the CNP-stimulated cGMP production in corpus cavernosal membrane of rabbit and rat. Specific 125I-(Tyr[0])-CNP bindings were localized in the corpus cavernosal smooth muscle of rabbit with Kd of 19.92+/-3.38 nM. and Bmax of 734.64+/-139.63 amol./mm2. B-subtype of NPR mRNA was detected in the penile corpus cavernosum of rat using RT-PCR technique. CNP relaxed the smooth muscle contracted by Nomega-nitro-L-arginine methylester (L-NAME).

CONCLUSIONS

These results suggest for the first time that CNP modulates the erectile smooth muscle tone of penis by predominant activation of B-subtype of NPR with augmentation of cGMP production via particulate GC.