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

Atrial natriuretic peptide attenuates high glucose-activated transforming growth factor-beta, Smad and collagen synthesis in renal proximal tubular cells

Atrial natriuretic peptide, besides its role in the regulation of volume homeostasis, has been noted to exert cytoprotective effects in several cell types from hypoxia. The present study was performed to explore the effect of ANP on high glucose-activated transforming growth factor-beta1 (TGF-beta1), Smad and collagen synthesis in renal proximal epithelial cells. Cultured NRK-52E cells were divided into five groups: (1) normal glucose (5.5 mM), (2) high glucose (35 mM), (3) D-mannitol (29.5 mM), (4) high glucose plus ANP (10(-6)-10(-9) M), and (5) high glucose plus ANP (10(-6) M) and guanylate cyclase inhibitor LY83583 (10(-7) M) groups. Messenger RNA levels of TGF-beta1, Smad2, and collagens were measured by RT-PCR. ELISA, immunocytochemistry and Western blotting were used to detect protein levels of TGF-beta1, Smad2, phospho-Smad 2/3 and collagen type 1. We found high glucose to significantly increase mRNA levels of TGF-beta1, Smad 2, collagen types I and III and protein levels of TGF-beta1, phospho-Smad 2/3 and collagen type 1, but mannitol did not affect their expression. The addition of ANP significantly attenuated high glucose-enhanced mRNA and protein levels of TGF-beta1, Smad and collagens. LY83583 blocked the influence of ANP on high glucose-activated TGF-beta1, Smad and collagen synthesis. This is the first study to demonstrate that activation of TGF-beta1, Smad and collagen synthesis stimulated by high glucose can also be inhibited by exogenous ANP in renal tubular epithelial cells.

Nucleoside composition of Heloderma venoms

Venoms of Heloderma horridum and Heloderma suspectum were analyzed for the possible presence of purine and pyrimidine nucleosides. Adenosine, cytidine, guanosine, hypoxanthine, inosine, and uridine were found in mug quantities. These amounts are much smaller than those seen in many elapid or viperine venoms, but greater and more varied than those found in crotaline venoms. While their contribution to the hypotension induced by Heloderma venoms may be minor, venom nucleosides nonetheless act in concert with kallikreins/hemorrhagins, alkaline phosphomonoesterase, 5'-nucleotidase, helodermin, helospectins, helothermine, and serotonin. The use of nucleosides as toxins is therefore a generalized squamate strategy, rather than the exclusive province of snakes. Both Heloderma venoms were found to be devoid of NADase and phosphodiesterase activities. Enzymes to release endogenous purines in the prey, are not significant components of Heloderma venoms.

Muscarinic activity modulated by C-type natriuretic peptide in gastric smooth muscles of guinea-pig stomach

Natriuretic peptides (NPs) are a cyclic guanosine monophosphate (cGMP) generation system like nitric oxide (NO) and play an inhibitory regulation in gastrointestinal motility but the effect of NPs on muscarinic activity is still unclear. This study was designed to investigate effect of C-type natriuretic peptide (CNP) on muscarinic control of gastric motility and its ion channel mechanism. The spontaneous contraction of gastric smooth muscle strip was recorded by using physiograph in guinea-pig. Membrane currents and potential were recorded by using whole-cell patch-clamp technique. CNP significantly inhibited muscarinic M receptor agonist carbachol (Cch)-induced contractions of gastric smooth muscle strips and dramatically hyperpolarized Cch-induced depolarization of membrane potential in gastric single smooth muscle cell. Muscarinic currents induced by both Cch and GTPgammaS, a G-protein agonist were significantly suppressed by CNP. 8-Br-cGMP mimicked the effect of CNP on Cch-induced muscarinic currents, and the peak holding current was decreased from -200.66+/-54.35 pA of control to -67.35+/-24.82 pA. LY83583, a guanylate cyclase nonspecific inhibitor, significantly weakened the inhibitory effect of CNP on muscarinic current while zaprinast, a cGMP sensitive phosphoesterase inhibitor, potentiated the inhibitory effect of CNP on muscarinic current. cGMP production was dramatically enhanced by CNP and this effect was suppressed by LY83583 in gastric smooth muscle. These results suggest that CNP modulates muscarinic activity via CNP-NPR-particulate guanylate cyclase (pGC)-cGMP pathway in guinea-pig.

Presence of C-type natriuretic peptide (CNP) in guinea pig caecum: role and mechanisms of CNP in circular smooth muscle relaxation

The distribution and role of C-type natriuretic peptide (CNP) in the gastrointestinal tract are still unclear. This study was designed to investigate the distribution of CNP in guinea pig caecum and the inhibitory mechanisms of CNP in caecal circular smooth muscle cells. CNP immunoreactivity was recognized in smooth muscle cells, myenteric and submucosal neurons of the caecum by immunohistochemistry. CNP mRNA expression was demonstrated in both freshly dispersed and cultured smooth muscle cells by reverse-transcription polymerase chain reaction. CNP inhibited 1 nmol L(-1) cholecystokinin octapeptide (CCK-8)-induced smooth muscle cell contraction in a dose-dependent manner, with an IC(50) value of 0.24 nmol L(-1), and significantly stimulated the production of intracellular cyclic guanosine monophosphate. Furthermore, inhibitors of both soluble and particulate guanylate cyclase (GC) partially but significantly inhibited CNP-induced relaxation. This is the first report demonstrating that CNP localizes in gastrointestinal smooth muscle cells and the enteric nervous system. These results suggest that CNP acts locally through neural and autocrine pathways to modulate colonic motility via both particulate and soluble GC systems. These two pathways appear to be through natriuretic peptide receptor (NPR)-B, which has particulate GC domain, and NPR-C, which activates soluble GC, judging from previous findings that NPR-A is not expressed in these cells.

Interaction between brain natriuretic peptide and atrial natriuretic peptide in caecal circular smooth muscle cells

Guinea pig caecal circular smooth muscle cells were used to determine whether brain natriuretic peptide (BNP) can inhibit the contractile response produced by cholecystokinin-octapeptide (CCK-8). In addition, we examined the effect of an inhibitor of cAMP-dependent protein kinase, an inhibitor of particulate or soluble guanylate cyclase, an atrial natriuretic peptide (ANP) antagonist (ANP 1-11), and selective receptor protection on the BNP-induced relaxation of these muscle cells. The effect of BNP on cAMP formation was also examined. BNP inhibited the contractile response produced by CCK-8 in a dose-response manner, with an IC50 value of 8.5 nM, and stimulated the production of cAMP. The inhibitor of cAMP-dependent protein kinase and the inhibitor of soluble guanylate cyclase significantly inhibited the relaxation produced by BNP. In contrast, the inhibitor of particulate guanylate cyclase did not have any significant effect on the relaxation produced by BNP. ANP 1-11 significantly but partially inhibited the relaxation produced by BNP. The muscle cells where CCK-8 and ANP binding sites were protected completely preserved the inhibitory response to ANP, but partially preserved the inhibitory response to BNP. The muscle cells where CCK-8 and BNP binding sites were protected completely preserved the inhibitory response to both ANP and BNP. This study demonstrates that BNP induces relaxation of these muscle cells via both ANP binding sites coupled to soluble guanylate cyclase and distinct BNP binding sites coupled to adenylate cyclase.

Regulation of aortic atrial natriuretic factor and angiotensinogen in experimental hypertension

We investigated the relation between atrial natriuretic factor (ANF) gene expression and the status of the renin-angiotensin system (RAS) in aortic tissue in rats made hypertensive by either aortic banding or by deoxycorticosterone acetate (DOCA)-salt administration. These experimental models of hypertension are known to have differences in terms of the status of RAS. ANF messenger RNA (mRNA) levels were measured in aortic tissue by using a newly developed quantitative competitive reverse transcription polymerase chain reaction (QC-RT-PCR) technique. Changes in the proportions of alpha1 and alpha2 isoforms of Na+K+-adenosine triphosphatase (ATPase) mRNA levels were used as indicators of aortic hypertrophy. Treatment with DOCA alone, salt alone, or DOCA-salt for 5 weeks increased aortic-weight/body-weight ratio and aortic angiotensinogen mRNA levels, but did not change alpha1 or alpha2 Na+K+-ATPase mRNA levels. Aortic ANF mRNA levels had a tendency to increase after treatment with DOCA, salt, or DOCA-salt, but this change did not reach statistical significance. Suprarenal aortic banding for 6 weeks or 12 weeks increased aortic-weight/body-weight ratio (12 weeks), decreased alpha2 Na+K+-ATPase and angiotensinogen mRNA levels, but did not affect alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. Treatment with ramipril, an angiotensin-converting enzyme (ACE) inhibitor was carried out for 6 weeks just after aortic banding (prevention experiment) or after 6 weeks in rats that were banded for the previous 6 weeks (regression experiment). High-dose ramipril (1 mg/kg)--a treatment known to inhibit both tissue and circulating RAS--normalized aortic-weight/body-weight ratio, and also normalized alpha2 Na+K+-ATPase mRNA levels. Aortic angiotensinogen mRNA levels of banded rats treated with high-dose ramipril was higher than those of the normal control, sham operated, and banded rats. Treatment with high-dose ramipril did not affect alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. Low-dose ramipril (10 microg/kg)--a treatment that selectively inhibits tissue RAS--normalized aortic-weight/body-weight ratio but did not normalize alpha2 Na+K+-ATPase mRNA levels (regression experiment) or angiotensinogen mRNA levels (prevention experiment) and did not change either alpha1 Na+K+-ATPase mRNA levels or ANF mRNA levels. The results suggest that, in contrast to previous findings in heart and kidney, the regulation of ANF mRNA levels in aortic tissue is largely independent of pressure load, volume load, and plasma or tissue RAS. It is suggested that any antihypertrophic actions of ANF may be mediated by the increased circulating ANF levels and its interaction with its receptor or through CNP.

Role of nitric oxide in the physiopathology of pain

Many painful disorders, including joint dysfunctions such as rheumatoid arthritis (RA) or temporomandibular joint disorders (TMD), are associated with hyperthermia of the overlying skin. The same is true of certain intractable chronic pain conditions, such as chronic orofacial pain, which may be associated with TMD. We suggest that this skin hyperthermia, caused by regional vasodilation, is induced by extravascular nitric oxide (NO). Extravascular NO can be produced in the affected joint by osteoblasts, chondrocytes, and macrophages, by mechanical stimulation of endothelial cells, or by stimulated neurons. In view of a strong correlation between pain and skin hyperthermia in these disorders, and the evidence that NO enhances the sensitivity of peripheral nociceptors, we also suggest that at least this kind of pain is associated with excessive local level of NO. This hypothesis can be verified by dynamic area telethermometry, assessing the effect of NO on the sympathetic nervous function. This mechanism, which is in line with the general role of NO as a mediator between different organ systems, also may be relevant to any pain associated with enhanced immune response. Clinical implications of the proposed mechanism are discussed.

PMA and ionomycin differently affect atrial natriuretic peptide stimulated cyclic GMP production in rat mesangial cells

How 4 beta-phorbol 12-myristate 13-acetate (PMA) and ionomycin (Io), a calcium ionophore, affect on the atrial natriuretic peptide (ANP) stimulated cyclic-3',5'-guanosine monophosphate (cGMP) production in cultured rat mesangial cells was examined. Cultured mesangial cells were prepared by isolated glomeruli from Sprague Dawley rats employing the sieving method and were used between the 3rd and 15th passage for experiments. cGMP and protein contents were measured by radioimmunoassay and Lowry method. Incubations with effectors were carried out either in the presence or absence of 0.5 mM 1-methyl-3-isobutyl-xanthine (MIX). The intracellular concentration of calcium ([Ca2+]i) was determined by using the Fura-2 method. Pretreatment with PMA, an activator of protein kinase C (PKC), attenuated ANP stimulated cGMP production in a time- and dose-dependent fashion, while alpha PDD (an inactive analog of PMA) did not inhibit cGMP production. PMA inhibition was reversed by addition of staurosporine, a protein kinase C inhibitor. Io attenuated ANP stimulated cGMP production in the absence but not in the presence of MIX. These findings suggested that PMA acts on ANP receptor or guanylate cyclase via activation of PKC in rat mesangial cells. Io may inhibit ANP stimulated cGMP production via activation of cyclic nucleotide phosphodiesterase.

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.