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Johji Kato

Publications and source records attributed to Johji Kato.

29 records · Page 2Linked to original sources
PubMed2003

Chronic salt loading upregulates expression of adrenomedullin and its receptors in adrenal glands and kidneys of the rat.

The vasodilator peptide adrenomedullin (AM) elicits diuresis and natriuresis and inhibits aldosterone secretion. The aim of this study was to better understand the role of AM in maintaining water and electrolyte balance during chronic salt loading. Male Wistar rats were divided into a high salt (HS) group that received a diet containing 8% sodium chloride (NaCl) and a normal salt group that received a diet containing 0.4% NaCl. Plasma AM concentrations as well as expression of AM mRNA in the adrenal gland and kidney were then measured after 3, 7, 14, and 28 days. After 28 days, sodium and water excretion were significantly higher in HS rats than in control, although blood pressure and fluid volume were not significantly affected. Moreover, although plasma AM remained unchanged for up to 14 days, it was increased 2.5-fold in HS rats after 28 days on a high salt diet, and there were corresponding 3-fold and 1.5-fold increases in the levels of AM mRNA in the adrenal gland and kidney, respectively. At the same time, expression of calcitonin receptor-like receptor mRNA was significantly upregulated in both kidney and adrenal gland, as was expression of receptor activity-modify protein 1 (RAMP1) and RAMP2 mRNA in the adrenals and expression of RAMP3 in kidneys. Taken together, these results suggest that AM plays a role in the regulation of water and electrolyte balance in animals chronically ingesting high levels of salt.

Adrenal Glands↗
PubMed2003

Glycine-extended adrenomedullin exerts vasodilator effect through amidation in the rat aorta.

Human adrenomedullin (hAM) is an endogenous peptide that has potent vasodilator activity. Mature AM is biosynthesized from its intermediate form, glycine-extended AM (AM-gly), by carboxy-terminal amidation. AM-gly is generally considered to be biologically inactive but is a major molecular form in human and rat plasma. The present study demonstrated that recombinant human AM-gly (hAM-gly) elicits potent vasodilator effect on isolated rat aorta. In aortic rings, hAM-gly produced dose-dependent (0.1-100 nM) relaxation in phenylephrine-precontracted strips (pD(2) 8.4+/-0.5). The vasorelaxant potency of hAM-gly was comparable to that of hAM (pD(2) 8.6+/-0.2) but hAM-gly took a significantly (P<0.01) longer time to reach the maximal relaxation compared with hAM (T(max) 23+/-4 vs. 5+/-2 min). Vasorelaxant responses to hAM-gly were abolished by endothelial removal. N(omega)-nitro-L-arginine (L-NNA) and AM(22-52) significantly (P<0.01) reduced the vasodilator effect of hAM-gly. Furthermore, 4-phenyl-3-butenoic acid (PBA), an alpha-amidation enzyme inhibitor, significantly (P<0.05) inhibited the vasorelaxant responses to hAM-gly without any effect on the hAM-induced relaxation, suggesting the possible process of amidation in the rat aorta. We further clarified that the aorta has the ability to convert exogenous hAM-gly to mature hAM and the conversion is inhibited by PBA. These results suggest that the circulating AM-gly may play a role in regulating vascular tone and increased plasma AM-gly may be involved in the pathophysiology of cardiovascular diseases.

Adrenomedullin↗
PubMed2003

Regulation of production and secretion of adrenomedullin in the cardiovascular system.

Adrenomedullin (AM) has multi-functional properties, of which the vasodilatory hypotensive effect is the most characteristic. AM and its gene are ubiquitous in a variety of tissues and organs, in the cardiovascular system, as well as the adrenal medulla. AM secretion, especially in cardiovascular tissues, is regulated mainly by mechanical stressors such as shear stress, inflammatory cytokines such as interleukin (IL)-1, tumor necrosis factor (TNF), and lipopolysaccharide (LPS), hormones such as angiotensin (Ang) II and endothelin (ET)-1, and metabolic factors such as hypoxia, ischemia, or hyperglycemia. Elevation of plasma AM due to overproduction in response to one or more of these stimuli in pathological conditions may explain the raised plasma AM levels present in cardiovascular and renal diseases such as congestive heart failure, myocardial infarction, hypertension, chronic renal failure, stroke, diabetes mellitus, and septic shock. In addition to shear stress, stretching of cardiomyocytes may be another mechanical stimulus for AM synthesis and secretion. Our recent studies have shown the importance of aldosterone and additional hormonal factor on AM secretion in vascular wall.

Adrenomedullin↗
PubMed2003

Adrenomedullin: a possible autocrine or paracrine hormone in the cardiac ventricles.

Adrenomedullin (AM), a potent vasodilator peptide originally isolated from pheochromocytoma, is expressed in cardiovascular tissues such as those of the cardiac atria and ventricles. Cell culture experiments have shown that AM peptide is synthesized and secreted from cardiac myocytes and fibroblasts of neonatal rats. Humoral factors, such as angiotensin II (Ang II) and endothelin-1 (ET-1), and mechanical stress due to pressure and volume overload to the heart have been shown to be involved in AM expression of the myocardium in both in vitro and in vivo studies. The effects of AM on cardiomyocytes and cardiac fibroblasts have been examined in in vitro studies, with the result that AM was shown to exert inhibitory actions on myocyte hypertrophy and on proliferation and collagen production of cardiac fibroblasts in an autocrine or paracrine manner. In rats, experimental therapeutic intervention consisting of transfer of the AM gene or of recombinant AM appears to partly inhibit the progression of cardiac hypertrophy and remodeling. It has been shown that the calcitonin receptor-like receptor (CRLR) and receptor-activity-modifying protein (RAMP) act together to function as AM receptors, although in this regard there are a number of issues, including the cellular mechanism of AM actions, that remain to be addressed. In addition, the role of proadrenomedullin N-terminal 20 peptide (PAMP), which is derived from preproAM, is another topic for future experiments. Collectively, the research data accumulating in this area suggest that AM plays a role as an autocrine or paracrine hormone in the cardiac ventricles, and that AM might be utilized as a therapeutic tool in the treatment of hypertensive or ischemic heart disease.

Adrenomedullin↗
PubMed2003

The function of extracellular cysteines in the human adrenomedullin receptor.

When co-expressed with receptor activity-modifying protein (RAMP) 2, calcitonin receptor-like receptor (CRLR) functions as an adrenomedullin (AM) receptor (CRLR/RAMP2). In the present study, we examined the function of the cysteine (C) residues in the extracellular loops of human (h)CRLR (C212, C225 and C282) and in the extracellular domain of hRAMP2 (C68, C84, C99 and C131). Using site-directed mutagenesis, the cysteine residues were substituted, one at a time, with alanine (A). Co-expression in HEK293 cells of hRAMP2 with the hCRLR C212A or C282A mutant significantly reduced the 50% of effective concentration (EC50) for AM-evoked cyclic adenosine monophosphate (cAMP) production, despite full cell surface expression of the receptor heterodimer. Co-expression of the C225A mutant had no effect on [125I]AM binding or receptor signaling. These results suggest that the cysteine residues in the first (C212) and the second (C282) extracellular loops form a disulfide bond that is important for stabilizing the receptor in the correct conformation for ligand binding and activation. Cells expressing hCRLR with an hRAMP2 mutant (C68A, C84A, C99A or C131A) showed no specific AM binding or AM-stimulated cAMP accumulation. Though abundant in the intracellular compartment, these receptors were not detected at the cell surface, suggesting that all four cysteine residues are essential for efficient transport to the plasma membrane. Cysteine residues in the extracellular loops of hCRLR and in the extracellular domain of hRAMP2 thus appear to play distinct roles in the cell surface expression and function of the receptor heterodimer.

Calcitonin Receptor-Like Protein↗
PubMed2002

The calcitonin receptor-like receptor/receptor activity-modifying protein 1 heterodimer can function as a calcitonin gene-related peptide-(8-37)-sensitive adrenomedullin receptor.

The receptor activity-modifying protein (RAMP)/calcitonin receptor-like (CRL) receptor heterodimer is thought to function as a receptor for either a calcitonin gene-related peptide (CGRP) (CRL receptor/RAMP1) or adrenomedullin (CRL receptor/RAMP2 or -3), depending on the RAMP isoform present. We examined the receptor specificity of adrenomedullin-induced increases in cAMP in human embryonic kidney (HEK)293 cells coexpressing human CRL receptor and human RAMP1 or RAMP2. In cells expressing CRL receptor/RAMP1, adrenomedulin-induced increases in cAMP were comparable to those induced by alpha-CGRP, and the CGRP receptor antagonist alpha-CGRP-(8-37), but not the adrenomedullin receptor antagonist adrenomedullin-(22-52), blocked the adrenomedullin-evoked responses. Cells expressing CRL receptor/RAMP2 responded more selectively to adrenomedullin; in this case, the effect was blocked by adrenomedullin-(22-52) but not by alpha-CGRP-(8-37). Real-time quantitative polymerase chain reaction confirmed that cotransfection of CRL receptor and RAMP1 had no effect on the endogenous expression of RAMP2. Thus, CRL receptor/RAMP1 likely functions as an adrenomedullin receptor as well as a CGRP receptor, which may explain why many of the actions of adrenomedullin are potently antagonized by alpha-CGRP-(8-37).

Adrenomedullin↗
PubMed2002

Rat RAMP domains involved in adrenomedullin binding specificity.

When coexpressed with receptor activity-modifying protein (RAMP)2 or -3, calcitonin receptor-like receptor (CRLR) functions as an adrenomedullin (AM) receptor (CRLR/RAMP2 or -3). Coexpression of rat (r)CRLR with rRAMP deletion mutants in HEK293T cells revealed that deletion of residues 93-99 from rRAMP2 or residues 58-64 from rRAMP3 significantly inhibits high-affinity [125I]AM binding and AM-evoked cAMP production, despite full cell surface expression of the receptor heterodimer. Apparently, these two seven-residue segments are key determinants of high-affinity agonist binding to rAM receptors and of receptor functionality. Consequently, their deletion yields peptides that are able to serve as negative regulators of AM receptor function.

Adrenomedullin↗
PubMed2002

Beneficial effects of adrenomedullin on left ventricular remodeling after myocardial infarction in rats.

OBJECTIVE: We previously reported that plasma adrenomedullin (AM) levels increase in patients with acute myocardial infarction (MI) and AM inhibits growth of rat cardiac myocytes and fibroblasts. The aim of this study was to examine the effects of long-term administration of AM on left ventricular (LV) remodeling, hemodynamic and hormonal parameters in a rat model of MI. METHODS: Rats with MI induced by left coronary ligation were intravenously infused with 1.0 microg/h of recombinant human AM or saline by osmotic mini-pump. After infusion for 4 weeks, hemodynamic and hormonal studies were performed, and the myocyte size and collagen volume in non-infarct LV area were quantified morphometrically. RESULTS: When compared with the MI rats infused with saline, continuous infusion of AM reduced the heart weight/body weight (4.4+/-0.2 vs. 3.6+/-0.1 g/kg, P<0.01), myocyte size (922+/-23 vs. 868+/-10 microm(2), P<0.05) and collagen volume fraction of non-infarct LV area (7.6+/-0.8 vs. 4.8+/-0.5%, P<0.05), without affecting the infarct size. The AM infusion had no significant effect on the arterial pressure, but decreased the LV end-diastolic pressure (8.8+/-1.8 vs. 4.4+/-0.5 mmHg, P<0.05) in the MI rats. The plasma level of endogenous rat AM in the MI rats infused with human AM was reduced by 27% (P<0.05), with a slight reduction of plasma atrial natriuretic peptide, compared with the control. CONCLUSIONS: Continuous administration of AM had beneficial effects on LV remodeling and hemodynamics in MI rats, suggesting the possibility that this peptide could be a useful therapeutic tool for acute MI.

Adrenomedullin↗
PubMed2002

Aldosterone augments adrenomedullin production without stimulating pro-adrenomedullin N-terminal 20 peptide secretion in vascular smooth muscle cells.

OBJECTIVE: Both adrenomedullin (AM) and pro-adrenomedullin N-terminal 20 peptide (PAMP), processed from the same precursor of prepro-adrenomedullin (preproAM), have differential biological properties; AM dilates blood vessels and presumably affects the vascular remodeling, while PAMP inhibits catecholamine secretion. Since aldosterone has been shown to be involved in vascular remodeling, we examined the effects of aldosterone on AM and PAMP secretion and preproAM gene expression in human aortic vascular smooth muscle cells (VSMC). METHODS: AM and PAMP secreted from human VSMC incubated with aldosterone were measured by radioimmunoassay, and preproAM gene expression was evaluated by quantitative polymerase chain reaction. RESULTS: Cultured human VSMC secreted both AM and PAMP into the media, while the secretion rate of AM was much higher than that of PAMP. Aldosterone increased preproAM gene expression in the cultured VSMC in a dose-dependent fashion following incubation for 48 h, with a concomitant increase in AM secretion from the cells, but PAMP secretion remained unchanged. Aldosterone-stimulated AM secretion was significantly reduced by spironolactone. Reverse-phase high-performance liquid chromatography analyses showed that immunoreactive AM secreted from the VSMC untreated or treated with aldosterone emerged at the point of human AM(1-52)-NH2. CONCLUSIONS: AM production was stimulated by aldosterone in cultured human VSMC without an increase in PAMP secretion, suggesting a possible role of AM in modulating vascular remodeling by aldosterone.

Adrenomedullin↗
PubMed2002

Plasma levels of adrenomedullin and atrial and brain natriuretic peptides in the general population: their relations to age and pulse pressure.

Adrenomedullin (AM) and atrial and brain natriuretic peptides (ANP and BNP) exert vasodilator and natriuretic actions and are thought to share roles in counteracting the progression of hypertension or heart failure as circulating or locally-acting hormones. However, little data is available with regard to their roles in subjects who have no apparent cardiovascular diseases. The present study was carried out to identify the factors that affect plasma levels of AM, ANP and BNP in the general population. We measured the plasma levels of AM, ANP and BNP in 184 local residents who had a scheduled regular health checkup, and compared the findings with those for other clinical parameters. Univariate analyses showed that the plasma levels of AM, ANP and BNP were significantly correlated with age. The plasma levels of ANP and BNP were also significantly correlated with systolic blood pressure (SBP) and with pulse pressure (PP), an indicator of the stiffness of the great vessels. Multivariate analyses conducted using a stepwise method revealed that age was a significant, independent variable for the plasma levels of AM, ANP and BNP. In addition, PP was a significant factor for the plasma levels of ANP and BNP, while the plasma AM was significantly associated with body mass index (BMI). Thus, the plasma levels of AM, ANP and BNP all increased in association with aging, and those of ANP and BNP increased in association with PP, suggesting possible relationships between the plasma levels and age-related changes in the cardiovascular system.

Adrenomedullin↗