Jing-Hui Yang

Protective effects of ghrelin on ischemia/reperfusion injury in the isolated rat heart.

Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor, has been reported to have beneficial effects on cardiac function. The authors used the Langendorff model of ischemia/reperfusion (I/R) injury in isolated rat heart to determine whether ghrelin exerts direct cardioprotective effects. Also, the capacity of ghrelin to bind to sarcolemmal membrane fractions before and after ischemia and reperfusion was examined. Compared with vehicle administration, administration of ghrelin (100–10,000 p M) during the reperfusion period resulted in improvement in coronary flow, heart rate, left ventricular systolic pressure, and left ventricular end-diastolic pressure. Ghrelin also enhanced the rates of left ventricular contraction and relaxation after ischemia following reperfusion. Administration of ghrelin during reperfusion reduced myocardial release of lactate dehydrogenase and myoglobin, indicating protection against cardiomyocyte injury. In addition, ghrelin attenuated the depletion of myocardial ATP resulting from ischemia and reperfusion. A receptor-binding assay demonstrated that maximum binding capacity of ghrelin to sarcolemmal membranes was significantly increased after ischemia and was further increased after I/R. However, Scatchard analysis showed that the affinity of ghrelin for its receptor was not altered. The authors have concluded that administration of ghrelin during reperfusion protects against myocardial I/R injury. The cardioprotective effects are independent of growth hormone release and likely involve binding to cardiovascular receptors, a process that is upregulated during I/R.

Cardiovascular effects of newly discovered peptide intermedin/adrenomedullin 2.

Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide (CGRP). The present study aimed to investigate the cardiovascular effects of IMDs (IMD1-47 and IMD8-47) in rats. Intravenous administration of 150 nmol IMDs continuously decreased mean arterial pressure and inhibited cardiac function. Administration with IMDs decreased left ventricular end-systolic pressure (LVESP) and maximal rate of left-ventricle pressure development (+/-LVdp/dt(max)), and elevated left ventricular end-diastolic pressure (LVEDP). Changes with IMD1-47 treatment were close to that with IMD8-47 (P>0.05). Perfusion of isolated rat hearts in vitro with IMD8-47 (10(-8) and 10(-7)mol/L) resulted in lower LVSP, by 40 and 56% (P<0.01); lower +LVdp/dt (max), by 33 and 47% (P<0.01); lower -LVdp/dt(max), by 25 and 39% (P<0.01); but higher coronary perfusion flow (CPF), by 25% (P<0.05) and 33% (P<0.01), respectively, than controls. However, both IMD8-47 and IMD1-47 (from 10(-13) to 10(-7)mol/L) relaxed preconstricted aortic rings in a dose-dependent manner. Intravenous administration of IMD1-47 and IMD8-47 (10(-7)mol/L) in vivo increased the cyclic adenosine monophosphate (cAMP) content by 68 and 150% (both P<0.01), respectively, in myocardia and 320 and 281% (both P<0.01), respectively, in aortas, compared with controls. Perfusion of isolated hearts with IMD1-47 and IMD8-47 (10(-7)mol/L) enhanced cAMP content by 24% (P<0.05) and 73% (P<0.01), respectively, compared with controls. IMDs inhibited 3H-Leucine incorporation in cardiomyocytes in a concentration-dependent manner. IMD1-47 and IMD8-47 (10(-7) and 10(-8)mol/L) decreased 3H-Leucine incorporation by 12-25% (P<0.01) and 14-18% (P<0.01), respectively. IMD mRNA was detected in cultured neonatal cardiomyocytes and isoproterenol-induced hypertrophic myocardia but not normal myocardia of adult rats. These results suggest that IMD might be a regulatory factor for cardiovascular function and myocardial hypertrophy as a cardiovascular active peptide.

Protective effects of intermedin/adrenomedullin2 on ischemia/reperfusion injury in isolated rat hearts.

Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide (CT/CGRP) family identified from human and other vertebrate tissues. Preprointermedin can generate a 47-amino acid mature peptide (IMD(1-47)) and a shorter 40-amino acid one (IMD(8-47)) by proteolytic cleavage. The present study was designed to determine the protective effect of IMD on cardiac ischemia/reperfusion (I/R) injury and its possible mechanism. Isolated rat hearts were perfused on a Langendorff apparatus and subjected to 45-min global ischemia and 30-min reperfusion. Cardiac function was measured. The release of myocardial protein and lactate dehydrogenase (LDH) and the formation of malondialdehyde (MDA) were assayed. Myocardial cAMP content was determined by radioimmunoassay (RIA). Cardiac I/R induced a marked inhibition of cardiac function and myocardial injury. Reperfusion with IMD significantly attenuated the I/R injury. Compared with I/R alone, perfusion with 10(-8)mol/L IMD(1-47) and IMD(8-47) induced a 36% and 33% increase in Delta left ventricular pressure (DeltaLVP), 30% and 28% in maximal rate of increase of LV pressure (+LVdP/dt max), and 34% and 31% in maximal rate of decrease of LV pressure (-LVdP/dt max), respectively (all P<0.01) but an approximately 58% and 51% decrease in LV diastolic pressure, respectively (P<0.01). In addition, perfusion with IMD markedly attenuated the leakage of LDH, total protein and myoglobin from myocardia compared with I/R alone. The contents of ventricular myocardia cAMP after reperfusion with 10(-8)mol/L IMD(1-47) and IMD(8-47) were 130% and 91% higher, respectively, than that with I/R alone (all P<0.01). However, formations of myocardial MDA were 52% and 50% lower than that with I/R alone (all P<0.01), respectively. Interestingly, the above IMD effects were similar to those of adrenomedullin (10(-8)mol/L). These results suggest that IMD, like adrenomedullin, exerts cardio-protective effects against myocardial I/R injury.

Intermedin 1–53 in central nervous system elevates arterial blood pressure in rats

Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide (CGRP) family identified from human and other vertebrate tissues. Preprointermedin can generate various mature peptides by proteolytic cleavage. Amino acid sequence analysis showed cleavage sites located between two basic amino acids at Arg93-Arg94 resulting in the production of prepro-IMD(95-147), namely IMD(1-53). The present study was designed to determine the effects of the IMD(1-53) fragment in the central nervous system (CNS) on mean arterial blood pressure and heart rate in normal rats and its possible mechanism. Rats were given doses of adrenomedullin (ADM) or IMD(1-53), intracerebroventricularly or intravenously, respectively, with continuous blood pressure and heart rate monitoring for 45min. Analysis with CGRP receptor antagonist CGRP(8-37), ADM receptor antagonist ADM(22-52), and anti-prepro-IMD antibody showed that 0.1, 0.5, and 1.0 nmol/kg IMD(1-53), caused a dose-dependent elevation in blood pressure, which was more prominent than the increase with equivalent IMD(1-47) or ADM. As well, IMD(1-53) caused a persistent increase in heart rate. The CNS action of IMD(1-53) could be blocked by ADM(22-52), CGRP(8-37), or prepro-IMD antibody. In contrast to the CNS action, intravenous administration of IMD(1-53) induced a depressor effect. These results suggest that IMD(1-53) is an important regulatory factor in mean arterial blood pressure and heart rate through its central and peripheral bioaction.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by aldosterone

Objective Aldosterone is involved in cardiovascular diseases such as hypertension and heart failure by inducing sodium retention and vascular remodeling, which is characterized by fibroblast proliferation and migration in adventitia. It is well known that aldosterone stimulates vascular smooth muscle cells and fibroblasts to produce and secrete adrenomedullin (ADM), a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We examined the effect of aldosterone on ADM production and secretion and its mRNA expression in rat aortic adventitia to study the paracrine/autocrine interaction between endogenous ADM and aldosterone. Methods ADM produced and secreted from adventitia stimulated by aldosterone in the absence or presence of spironolactone, RU486 or spironolactone together with RU486 were detected by radioimmunoassay, proliferation in adventitia cells was evaluated by the level of [3H]-thymine incorporation, and preproADM gene expression was measured by semi-quantitative reverse transcriptase polymerase chain reaction. Results Adventitial ADM secretion and mRNA expression stimulated by aldosterone were concentration-dependent as was the inhibitive effect of ADM on aldosterone-induced proliferation. The induction of aldosterone in ADM secretion was mediated by mineralocorticoid receptor. Antagonists of specific receptors of calcitonin gene-related peptide (CGRP) receptor type 1 and ADM both potentiated the proliferation effect induced by aldosterone; and thiorphan, an inhibitor of the enzyme for ADM degradation, inhibited the adventitial [3H]-thymine incorporation induced by aldosterone. ADM inhibited the activity of extracellular signal related kinase (ERK) stimulated by aldosterone. Conclusion Aldosterone stimulates adventitia to produce and secrete ADM, which in turn, antagonizes the aldosterone-induced proliferation in adventitia.

Effect of intermedin1-53 on angiotensin II-induced hypertrophy in neonatal rat ventricular myocytes.

Objectives: Intermedin (IMD) is coexpressed in the heart with its receptor, which suggests that it may have localized actions as a modulator of cardiac function. The present study was designed to observe the interaction between IMD and cardiac hypertrophy and the possible mechanism involved in the antihypertrophic effects of IMD1-53 in cultured neonatal ventricular myocytes. Methods: Myocyte hypertrophy was induced by treating the cells with angiotensin II, and the hypertrophic response was characterized by a significant increase in cell surface area, protein synthesis, and BNP mRNA expression. Results: Our results showed that angiotensin II led to an obvious decrease in the production, secretion, and mRNA expression of IMD and increase receptor activity modifying proteins 1, 3 mRNA expression. Moreover, IMD1-53 inhibited the angiotensin II-induced hypertrophic response and the effects of IMD1-53 were similar to those of equivalent-dose adrenomedullin and could been blocked by H89. Otherwise, in our study, IMD1-53 resulted in dose-dependent increases of cAMP production in cardiomyocytes. Conclusions: Thus, IMD and its receptor system are involved in cardiac hypertrophy, and like adrenomedullin, IMD1-53 exerts an antihypertrophic effect on neonatal cardiomyocytes and the effect can be mediated by the cAMP/PKA pathway.

Effects of adrenomedullin on cell proliferation in rat adventitia induced by lysophosphatidic acid

Lysophosphatidic acid (LPA) is a bioactive phospholipid having growth factor-like activity on fibroblasts and is involved in cardiovascular diseases such as hypertension and heart failure by inducing vascular remodeling, characterized by fibroblast proliferation and migration in adventitia. Among various bioactive factors that LPA works with, adrenomedullin (ADM) is a multiple functional peptide with an important cytoprotective effect against cardiovascular damage. We studied rat aortic adventitia to explore the possible paracrine/autocrine interaction between endogenous ADM and LPA. LPA stimulation of the adventitia to secrete ADM and express its mRNA was concentration dependent. ADM inhibited LPA-induced proliferation in adventitial cells and attenuated the activity of mitogen-activated protein kinase (MAPK) stimulated by LPA. In contrast, treatment with specific antagonists of the ADM receptor potentiated the LPA-induced proliferation in adventitial cells. We concluded that LPA stimulates the adventitia to produce and secrete ADM, which in turn regulates the vascular biological effects of LPA.