Intracoronary intermedin 1-47 augments cardiac perfusion and function in anesthetized pigs: role of calcitonin receptors and beta-adrenoreceptor-mediated nitric oxide release

Intermedin1‑47 inhibits high phosphate‑induced vascular smooth muscle cell calcification by regulating Wnt/β‑catenin signaling

Vascular calcification is a major risk factor for cardiovascular disease and accounts for a large proportion of deaths from cardiovascular disease in patients with chronic kidney disease. The high incidence, rapid progression and irreversibility of vascular smooth muscle cell (VSMC) calcification in patients has attracted attention. In the present study, the effect of intermedin1‑47 (IMD1‑47), an important isoform of intermedin, was investigated on the calcification of rat cardiovascular VSMCs induced by high phosphate (HP). To stimulate osteoblast‑like differentiation and calcification in rat VSMCs, 10 mM β‑sodium glycerophosphate was used. The VSMCs were then treated with three doses of IMD1‑47 and the effects of IMD1‑47 on VSMC calcification, on the expression of osteogenic markers [osteoprotegerin, Runt‑related transcription factor 2 (Runx2) and osteopontin (OPN)] and on alkaline phosphatase (ALP) activity were assessed. HP treatment significantly enhanced the cellular calcium content of VSMCs, the expression of osteogenic markers, and ALP activity, while IMD1‑47 significantly reversed these effects in a dose‑dependent manner. The protein expression levels of Wnt1, Wnt3a and active β‑catenin were determined and it was found that IMD1‑47 significantly inhibited their expression. Following β‑catenin silencing, the protein expression levels Runx2 and OPN were increased compared with the IMD1‑47 treatment alone, indicating a role for the Wnt/β‑catenin pathway in the effects of IMD1‑47 on osteogenic markers. The present study suggested that IMD1‑47 inhibited HP‑induced VSMC calcification by regulating the Wnt/β‑catenin signaling pathway.

Intermedin facilitates hepatocellular carcinoma cell survival and invasion via ERK1/2-EGR1/DDIT3 signaling cascade

As one of the most malignant cancer types, hepatocellular carcinoma (HCC) is highly invasive and capable of metastasizing to distant organs. Intermedin (IMD), an endogenous peptide belonging to the calcitonin family, has been suggested playing important roles in cancer cell survival and invasion, including in HCC. However, how IMD affects the behavior of HCC cells and the underlying mechanisms have not been fully elucidated. Here, we show that IMD maintains an important homeostatic state by activating the ERK1/2-EGR1 (early growth response 1) signaling cascade, through which HCC cells acquire a highly invasive ability via significantly enhanced filopodia formation. The inhibition of IMD blocks the phosphorylation of ERK1/2, resulting in EGR1 downregulation and endoplasmic reticulum stress (ER) stress, which is evidenced by the upregulation of ER stress marker DDIT3 (DNA damage-inducible transcript 3). The high level of DDIT3 induces HCC cells into an ER-stress related apoptotic pathway. Along with our previous finding that IMD plays critical roles in the vascular remodeling process that improves tumor blood perfusion, IMD may facilitate the acquisition of increased invasive abilities and a survival benefit by HCC cells, and it is easier for HCC cells to obtain blood supply via the vascular remodeling activities of IMD. According to these results, blockade of IMD activity may have therapeutic potential in the treatment of HCC.

The Cardiopulmonary Effects of the Calcitonin Gene-related Peptide Family

Cardiopulmonary diseases are very common among the population. They are high-cost diseases and there are still no definitive treatments. The roles of members of the calcitonin-gene related-peptide (CGRP) family in treating cardiopulmonary diseases have been studied for many years and promising results obtained. Especially in recent years, two important members of the family, adrenomedullin and adrenomedullin2/intermedin, have been considered new treatment targets in cardiopulmonary diseases. In this review, the roles of CGRP family members in cardiopulmonary diseases are investigated based on the studies performed to date.

Adrenomedullin 2 increases cardiac sympathetic nerve activity in parallel to heart rate in normal conscious sheep

Both adrenomedullin 2 (AM2) and sympathetic nerve activity (SNA) have been shown to be involved in regulating cardiovascular activity, but whether any interaction between these two systems exists remains to be determined. In this study, we examine the effects of intravenous AM2 infusions on SNA directed toward the heart (cardiac SNA (CSNA)) in healthy sheep studied in the conscious state. In response to AM2, arterial pressure was reduced (P = 0.005) with both heart rate (P < 0.001) and cardiac output (P < 0.001) increased compared with vehicle control response. CSNA burst frequency (bursts/min) and burst area/min both increased during infusion of AM2 (both P < 0.001). However, correcting CSNA indices for concurrent heart rate changes resulted in CSNA burst incidence (bursts/100 beats) and burst area incidence (area/100 beats) being not significantly different between AM2 and control treatments. There were no significant differences demonstrated in plasma epinephrine or norepinephrine levels between the two study days. In conclusion, AM2 administered systemically to normal conscious sheep increases both CSNA and heart rate. However, correction for heart rate responses abrogates the rise in CSNA. It remains unclear whether AM2's primary effect is to act via the central nervous system to directly stimulate CSNA with resultant increase in heart rate, or to induce a rise in heart rate by other mechanisms.

Mechanism of adrenomedullin 2/intermedin mediated vasorelaxation in rat main pulmonary artery

Adrenomedullin 2/intermedin (AM2/IMD) is a member of calcitonin related gene peptide family and an important nitric oxide mediated vasorelaxant in various vascular beds. However, the mechanism of post receptor-interaction is not clear and may differ depending on tissue type and species. In this study, we aimed to investigate the exact mechanism and the role of BK_Ca and calcium channels on the vasorelaxant effect of AM2/IMD in rat PA. Changes in the AM2/IMD-mediated vasorelaxation were evaluated in the presence of various inhibitors. CGRP_(8-37) (10^-6 M), L-NAME (10^-4 M), ODQ (10^-5 M), SQ22536 (10^-4 M), H89 (10^-6 M), TEA (10^-2 M), iberiotoxin (3 × 10^-7 M), and verapamil (10^-5 M), all partly or completely inhibited the vasorelaxation. The relaxation was also abolished by removal of the endothelium, or in KCl precontracted PAs. AM2/IMD did not elicit vasorelaxation in the Ca²⁺-free conditions. However, the vasorelaxation was not inhibited with AM_(22-52) (10^-6 M), 4-AP (3 × 10^-3 M), glibenclamide (10^-5 M), apamin (3 × 10^-7 M), TRAM-34 (10^-5 M), and La⁺³ (10^-4 M). AM2/IMD -induced changes in intracellular calcium levels and isometric force were monitored simultaneously in fura-2-loaded, endothelium-intact PAs. The AM2/IMD-induced increase in intracellular Ca²⁺ concentration was inhibited in the presence of iberiotoxin and verapamil, whereas no change was observed with La³⁺ incubation. Our data suggest that the cAMP/PKA pathway is one of the important pathways AM2/IMD-induced vasorelaxation. AM2/IMD acts through activation of endothelial BK_Ca and subsequently causes hyperpolarization of the endothelial cell membrane. The hyperpolarization induces Ca²⁺ influx, which leads to NO production and subsequent vasorelaxation.

Intermedin Enlarges the Vascular Lumen by Inducing the Quiescent Endothelial Cell Proliferation

OBJECTIVE

Intermedin plays an important role in vascular remodeling and significantly improves blood perfusion, but the precise mechanism remains unclear. Herein, we aimed to define whether vascular lumen enlargement is responsible for the intermedin-increased blood perfusion and explore the underlying cellular and molecular mechanisms.

APPROACH AND RESULTS

To study the role of intermedin, we generated the IMD-KO (Adm2^-/-) mice using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat-associated 9) system. Intermedin significantly promoted vascular lumen enlargement in vitro (fibrin beads assay) and in vivo (murine retinas), which contributed to the improved blood perfusion in both physiological (retinal) and pathological (tumor) angiogenic models. We designed experiments to calculate the endothelial cell (EC) size and found that the lumen enlargement is because of EC proliferation but not because of a change in cell shape. ECs that construct vessel walls are considered quiescent cells because they are in a state of contact inhibition and show reduced responsiveness to VEGF (vascular endothelial growth factor). Using immunoprecipitation, Western blot assay, and fluorescent microscopy, we found that intermedin induced the formation of a signaling complex containing CRLR (calcitonin receptor-like receptor)/β-arr1 (β-arrestin1)/Src in ECs and promoted it internalizing into cytoplasm in a clathrin-dependent manner to activate downstream ERK1/2 (extracellular signal-regulated kinase 1/2). Importantly, this effect was not abrogated by cell-cell contacts of ECs. Through this mechanism, intermedin could reactivate the quiescent ECs to proliferate, resulting in continuous lumen expanding and a more effective blood perfusion.

CONCLUSIONS

Our findings suggest a novel mechanism that may explain how quiescent ECs overcome the contact inhibition and regain the ability to proliferate for continuous vascular lumen enlargement.

Adrenomedullin 2/intermedin: a putative drug candidate for treatment of cardiometabolic diseases

Adrenomedullin (ADM) 2/intermedin (IMD) is a short peptide that belongs to the CGRP superfamily. Although it shares receptors with CGRP, ADM and amylin, ADM2 has significant and unique functions in the cardiovascular system. In the past decade, the cardiovascular effect of ADM2 has been carefully analysed. In this review, progress in understanding the effects of ADM2 on the cardiovascular system and its protective role in cardiometabolic diseases are summarized.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Plasma Intermedin Level Indicates Severity and Treatment Efficacy of Septic Shock in Sprague-Dawley (SD) Rats

BACKGROUND The aim of this study was to investigate the value of plasma intermedin (IMD) in assessing severity and treatment efficacy of septic shock. MATERIAL AND METHODS Healthy male Sprague-Dawley (SD) rats were chosen and divided into a normal control group (n=15) and a shock model group (n=27) that received intravenous injection of lipopolysaccharide (LPS). Then, 3 specimens were taken from each group. The shock model group rats were divided into an LPS group and a treatment group with 12 rats each. The treatment group received intravenous injection of compound sodium lactate solution. Plasma IMD and IMD1-47 mRNA expressions were compared and analyzed. RESULTS Mean arterial pressure (MAP) was lower while white blood cell count and TNF-α were higher in the shock model group than in the normal control group (P<0.05). After 10 h and 20 h, the treatment group had lower plasma IMD and IMD1-47 mRNA expressions compared with the LPS group (P<0.05). Plasma IMD and IMD1-47 mRNA expressions in the LPS group after 20 h were significantly higher than after 10 h (P<0.05). IMD was positively correlated with interleukins (IL-3, IL-6, and IL-8), white blood cell count, and body temperature (all P<0.05), but were negatively correlated with systolic pressure (r=-0.8474, P=0.0040). CONCLUSIONS Plasma IMD level can effectively reflect the severity of septic shock and can be used as an important indicator of septic shock treatment effectiveness.

Monomeric adiponectin modulates nitric oxide release and calcium movements in porcine aortic endothelial cells in normal/high glucose conditions

AIMS

Perivascular adipose tissue can be involved in the process of cardiovascular pathology through the release of adipokines, namely adiponectins. Monomeric adiponectin has been shown to increase coronary blood flow in anesthetized pigs through increased nitric oxide (NO) release and the involvement of adiponectin receptor 1 (AdipoR1). The present study was therefore planned to examine the effects of monomeric adiponectin on NO release and Ca(2+) transients in porcine aortic endothelial cells (PAEs) in normal/high glucose conditions and the related mechanisms.

MAIN METHODS

PAEs were treated with monomeric adiponectin alone or in the presence of intracellular kinases blocker, AdipoR1 and Ca(2+)-ATPase pump inhibitors. The role of Na(+)/Ca(2+) exchanger was examined in experiments performed in zero Na(+) medium. NO release and intracellular Ca(2+) were measured through specific probes.

KEY FINDINGS

In PAE cultured in normal glucose conditions, monomeric adiponectin elevated NO production and [Ca(2+)]c. Similar effects were observed in high glucose conditions, although the response was lower and not transient. The Ca(2+) mobilized by monomeric adiponectin originated from an intracellular pool thapsigargin- and ATP-sensitive and from the extracellular space. Moreover, the effects of monomeric adiponectin were prevented by kinase blockers and AdipoR1 inhibitor. Finally, in normal glucose condition, a role for Na(+)/Ca(2+) exchanger and Ca(2+)-ATPase pump in restoring Ca(2+) was found.

SIGNIFICANCE

Our results add new information about the control of endothelial function elicited by monomeric adiponectin, which would be achieved by modulation of NO release and Ca(2+) transients. A signalling related to Akt, ERK1/2 and p38MAPK downstream AdipoR1 would be involved.

Intracoronary Des-Acyl Ghrelin Acutely Increases Cardiac Perfusion Through a Nitric Oxide-Related Mechanism in Female Anesthetized Pigs

Des-acyl ghrelin (DAG), the most abundant form of ghrelin in humans, has been found to reduce arterial blood pressure and prevent cardiac and endothelial cell apoptosis. Despite this, data regarding its direct effect on cardiac function and coronary blood flow, as well as the related involvement of autonomic nervous system and nitric oxide (NO), are scarce. We therefore examined these issues using both in vivo and in vitro studies. In 20 anesthetized pigs, intracoronary 100 pmol/mL DAG infusion with a constant heart rate and aortic blood pressure, increased coronary blood flow and NO release, whereas reducing coronary vascular resistances (P < .05). Dose responses to DAG were evaluated in five pigs. No effects on cardiac contractility/relaxation or myocardial oxygen consumption were observed. Moreover, whereas the blockade of muscarinic cholinoceptors (n = 5) or α- and β-adrenoceptors (n = 5 each) did not abolish the observed responses, NO synthase inhibition (n = 5) prevented the effects of DAG on coronary blood flow and NO release. In coronary artery endothelial cells, DAG dose dependently increased NO release through cAMP signaling and ERK1/2, Akt, and p38 MAPK involvement as well as the phosphorylation of endothelial NO synthase. In conclusion, in anesthetized pigs, DAG primarily increased cardiac perfusion through the involvement of NO release. Moreover, the phosphorylation of ERK1/2 and Akt appears to play roles in eliciting the observed NO production in coronary artery endothelial cells.

Prognostic Value of Plasma Intermedin Level in Patients With Non-ST-Segment Elevation Acute Coronary Syndrome

Intermedin (IMD), an autocrine/paracrine biologically active peptide, plays a critical role in maintaining vascular homeostasis. Recent research has shown that high plasma levels of IMD are associated with poor outcomes for patients with ST-segment elevation acute myocardial infarction. However, the prognostic utility of IMD levels in non-ST-segment elevation acute coronary syndrome (NSTE-ACS) has not yet been investigated. We hypothesized that the level of plasma IMD would have prognostic value in patients with NSTE-ACS. Plasma IMD was determined by radioimmunoassay in 132 NSTE-ACS patients on admission to hospital and 132 sex- and age-matched healthy-control subjects. Major adverse cardiovascular events (MACEs), including death, heart failure, hospitalization, and acute myocardial infarction, were noted during follow-up. In total, 23 patients suffered MACEs during the follow-up period (mean 227 ± 118 days, range 2-421 days). Median IMD levels were higher in NSTE-ACS patients than control [320.0 (250.9/384.6) vs. 227.2 (179.7/286.9) pg/mL, P <0.001]. The area under the receiver-operating characteristic curve for IMD and N-terminal pro-B-type brain natriuretic peptide (NT-proBNP) did not significantly differ (0.73 and 0.79, both P <0.001, respectively; P = 0.946). ROC curve analysis revealed a cut-off value for IMD at 340.7 pg/mL. Cox regression analysis with cardiovascular risk variables and NT-proBNP showed that the risk of MACEs increased by a factor of 12.96 (95% CI, 3.26-49.42; P <0.001) with high IMD levels (at the cut-off value). IMD has potential as a prognostic biomarker for predicting MACEs in patients with NSTE-ACS.

Effect of monomeric adiponectin on cardiac function and perfusion in anesthetized pig

Adiponectin, the most abundant adipokine released by adipose tissue, appears to play an important role in the regulation of vascular endothelial and cardiac function. To date, however, the physiological effects of human monomeric adiponectin on the coronary vasculature and myocardial systo-diastolic function, as well as on parasympathetic/sympathetic involvement and nitric oxide (NO) release, have not yet been investigated. Thus, we planned to determine the primary in vivo effects of human monomeric adiponectin on coronary blood flow and cardiac contractility/relaxation and the related role of autonomic nervous system, adiponectin receptors, and NO. In 30 anesthetized pigs, human monomeric adiponectin was infused into the left anterior descending coronary artery at constant heart rate and arterial blood pressure, and the effects on coronary blood flow, left ventricular systo-diastolic function, myocardial oxygen metabolism, and NO release were examined. The mechanisms of the observed hemodynamic responses were also analyzed by repeating the highest dose of human monomeric adiponectin infusion after autonomic nervous system and NO blockade, and after specific adiponectin 1 receptor antagonist administration. Intracoronary human monomeric adiponectin caused dose-related increases of coronary blood flow and cardiac function. Those effects were accompanied by increased coronary NO release and coronary adiponectin levels. Moreover, the vascular effects of the peptide were prevented by blockade of β2-adrenoceptors and NO synthase, whereas all effects of human monomeric adiponectin were prevented by adiponectin 1 receptor inhibitor. In conclusion, human monomeric adiponectin primarily increased coronary blood flow and cardiac systo-diastolic function through the involvement of specific receptors, β2-adrenoceptors, and NO release.

Intermedin modulates hypoxic pulmonary vascular remodeling by inhibiting pulmonary artery smooth muscle cell proliferation

BACKGROUND

Hypoxic pulmonary arterial hypertension (PAH) is a disabling disease with limited treatment options. Hypoxic pulmonary vascular remodeling is a major cause of hypoxic PAH. Pharmacological agents that can inhibit the remodeling process may have great therapeutic value.

OBJECTIVE

To examine the effect of intermedin (IMD), a new calcitonin gene-related peptide family of peptide, on hypoxic pulmonary vascular remodeling.

METHODS

Rats were exposed to normoxia or hypoxia (∼10% O(2)), or exposed to hypoxia and treated with IMD, administered by an implanted mini-osmotic pump (6.5 μg/rat/day), for 4 weeks. The effects of IMD infusion on the development of hypoxic PAH and right ventricle (RV) hypertrophy, on pulmonary vascular remodeling, on pulmonary artery smooth muscle cell (PASMC) proliferation and apoptosis, and on the activations of l-arginine nitric oxide (NO) pathway and endoplasmic reticulum stress apoptotic pathway were examined.

RESULTS

Rats exposed to hypoxia developed PAH and RV hypertrophy. IMD treatment alleviated PAH and prevented RV hypertrophy. IMD inhibited hypoxic pulmonary vascular remodeling as indicated by reduced wall thickness and increased lumen diameter of pulmonary arterioles, and decreased muscularization of distal pulmonary vasculature in hypoxia-exposed rats. IMD treatment inhibited PASMC proliferation and promoted PASMC apoptosis. IMD treatment increased tissue level of constitutive NO synthase activity and tissue NO content in lungs, and enhanced l-arginine uptake into pulmonary vascular tissues. IMD treatment increased cellular levels of glucose-regulated protein (GRP) 78 and GRP94, two major markers of endoplasmic reticulum (ER) stress, and increased caspase-12 expression, the ER stress-specific caspase, in lungs and cultured PASMCs.

CONCLUSIONS

These results demonstrate that IMD treatment attenuates hypoxic pulmonary vascular remodeling, and thereby hypoxic PAH mainly by inhibiting PASMC proliferation. Promotion of PASMC apoptosis may also contribute to the inhibitory effect of IMD. Activations l-arginine-NO pathway and of ER stress-specific apoptosis pathway could be the mechanisms mediating the anti-proliferative and pro-apoptotic effects of IMD.

In anesthetized pigs human chorionic gonadotropin increases myocardial perfusion and function through a β-adrenergic-related pathway and nitric oxide

Human chorionic gonadotropin (hCG) is not only responsible for numerous pregnancy-related processes, but can affect the cardiovascular system as well. So far, however, information about any direct effect elicited by hCG on cardiac function, perfusion, and the mechanisms involved has remained scarce. Therefore, the present study aimed to determine the primary in vivo effect of hCG on cardiac contractility and coronary blood flow and the involvement of autonomic nervous system and nitric oxide (NO). Moreover, in coronary endothelial cells (CEC), the intracellular pathways involved in the effects of hCG on NO release were also examined. In 25 anesthetized pigs, intracoronary 500 mU/ml hCG infusion at constant heart rate and aortic blood pressure increased coronary blood flow, maximum rate of change of left ventricular systolic pressure, segmental shortening, cardiac output, and coronary NO release (P < 0.0001). These hemodynamic responses were graded in a further five pigs. Moreover, while blockade of muscarinic cholinoceptors (n = 5) and of α-adrenoceptors (n = 5) did not abolish the observed responses, β1-adrenoceptors blocker (n = 5) prevented the effects of hCG on cardiac function. In addition, β2-adrenoceptors (n = 5) and NO synthase inhibition (n = 5) abolished the coronary response and the effect of hCG on NO release. In CEC, hCG induced the phosphorylation of endothelial NO synthase through cAMP/PKA signaling and ERK1/2, Akt, p38 MAPK involvement, which were activated as downstream effectors of β2-adrenoceptor stimulation. In conclusion, in anesthetized pigs, hCG primarily increased cardiac function and perfusion through the involvement of β-adrenoceptors and NO release. Moreover, cAMP/PKA-dependent kinases phosphorylation was found to play a role in eliciting the observed NO production in CEC.

Increased plasma levels of intermedin and brain natriuretic peptide associated with severity of coronary stenosis in acute coronary syndrome

Intermedin (IMD) is a newly discovered peptide with increased levels in plasma and cardiac tissue in mice with ischemia/reperfusion. Continuous administration of low dose IMD markedly elevated the mRNA abundance of myocardial BNP in rats. Plasma BNP levels may reflect the severity of degree of coronary stenosis in patients with acute coronary syndrome (ACS). However, the role of circulating IMD in coronary heart disease remains unclear. We aimed to examine the plasma content of IMD and brain natriuretic peptide (BNP) and its clinical significance in patients with ACS. We collected plasma samples from 41 patients with ACS and 31 controls and measured IMD and BNP levels by radioimmunoassay. The severity of coronary artery stenosis for patients with ACS was measured by coronary angiography. Plasma IMD and BNP levels were markedly higher in ACS patients than that in controls (P<0.05). The increased plasma IMD and BNP were positively correlated with degree of coronary stenosis in ACS patients (r=0.263 and r=0.238, respectively, both P<0.05). In addition, plasma levels of IMD were positively correlated with BNP levels.

The pharmacology of adrenomedullin 2/intermedin

Adrenomedullin 2 (AM2) or intermedin is a member of the calcitonin gene-related peptide (CGRP)/calcitonin family of peptides and was discovered in 2004. Unlike other members of this family, no unique receptor has yet been identified for it. It is extensively distributed throughout the body. It causes hypotension when given peripherally, but when given into the CNS, it increases blood pressure and causes sympathetic activation. It also increases prolactin release, is anti-diuretic and natriuretic and reduces food intake. Whilst its effects resemble those of AM, it is frequently more potent. Some characterization of AM2 has been done on molecularly defined receptors; the existing data suggest that it preferentially activates the AM(2) receptor formed from calcitonin receptor-like receptor and receptor activity modifying protein 3. On this complex, its potency is generally equivalent to that of AM. There is no known receptor-activity where it is more potent than AM. In tissues and in animals it is frequently antagonised by CGRP and AM antagonists; however, situations exist in which an AM2 response is maintained even in the presence of supramaximal concentrations of these antagonists. Thus, there is a partial mismatch between the pharmacology seen in tissues and that on cloned receptors. The only AM2 antagonists are peptide fragments, and these have limited selectivity. It remains unclear as to whether novel AM2 receptors exist or whether the mismatch in pharmacology can be explained by factors such as metabolism.

Intermedin elicits a negative inotropic effect in rat papillary muscles mediated by endothelial-derived nitric oxide

Intermedin (IMD) is a novel vasoactive peptide from the calcitonin gene-related peptide (CGRP) implicated in cardiac regulation, yet the contractile effects of IMD remain controversial, since previous studies in vivo and isolated cardiomyocytes documented contradictory results. We hypothesized cardiac endothelial cells involvement in IMD modulation of cardiac function as an explanation for these opposing observations. With this in mind, we investigated the direct action of increasing concentrations of IMD (10(-8) to 10(-6)M) on myocardial performance parameters in rat left ventricular (LV) papillary muscles with and without endocardial endothelium (EE) and in presence of receptor antagonists and intracellular pathways inhibitors. In LV papillary muscles with intact EE, IMD induced a concentration-dependent negative inotropic action (%decrease relative to baseline, at IMD concentration of 10(-6)M, active tension of 14 ± 4%, and maximum velocity of tension rise of 10 ± 4%). These effects were blunted by EE removal, AM receptor antagonist (AM(22-52)), and CGRP receptor antagonist (CGRP(8-37)). Additionally, nitric oxide (NO) synthase inhibition with N(G)-nitro-l-arginine (l-NAME) in muscles with and without EE and guanylyl cyclase inhibition with {1H-[1,2,4]oxadiazole-[4,4-a]-quinoxalin-1-one} not only blunted the negative inotropic action of IMD but also unmasked IMD-positive inotropic effect dependent on CGRP receptor PKA activation. Western blot quantification of phosphorylated cardiac troponin I (P-cTnI) in IMD-treated papillary muscles revealed a significant increase in P-cTnI when compared with untreated muscles, while in l-NAME-pretreated papillary muscles IMD failed to increase P-cTnI. Finally, we found that stimulation of both EE and microvascular endothelial cells with IMD significantly increased NO production by 40 ± 3 and 38 ± 3%, respectively, suggesting the role of cardiac endothelial cells in NO production upon IMD stimulation. Our findings establish IMD negative inotropic effect in isolated myocardium due to NO/cGMP pathway activation with concomitant thin myofilament desensitization by increase in cTnI phosphorylation and provide a coherent explanation for the previously reported contradictory results.

Inhibition of endoplasmic reticulum stress by intermedin(1-53) protects against myocardial injury through a PI3 kinase-Akt signaling pathway

Intermedin (IMD) is a novel member of the calcitonin/calcitonin gene-related peptide family. We aimed to explore whether the cardioprotective effect of IMD is mediated by inhibiting myocardial endoplasmic reticulum (sarcoplasmic reticulum) stress (ERS). In vitro, IMD(1-53) (10(-9), 10(-8), and 10(-7) mol/l) directly inhibited the upregulation of ERS markers such as glucose-regulated protein 78, CCAAT/enhancer binding protein homologous protein, and caspase-12 induced by the ERS inducers tunicamycin (Tm, 10 mg/ml) or dithiothreitol (DTT, 2 mmol/l) in cardiac tissue. IMD(1-53) also inhibited Tm- or DTT-induced upregulation of cleaved activating transcription factor 6 and 4. These inhibitory effects of IMD(1-53) were abolished by the IMD receptor antagonist IMD(17-47) (10(-6) mol/l) and phosphoinositide 3-kinase inhibitor LY294002 (10 μmol/l). However, preincubation with PD98059 (20 μmol/l), an extracellular signal-regulated protein kinase inhibitor, and H89 (10 μmol/l), a protein kinase A inhibitor, could not block the ERS-inhibiting effects of IMD(1-53). Furthermore, in an in vivo model of myocardium ischemia/reperfusion (I/R) in rats, administration of IMD(1-53) (20 nmol/kg, intravenously) greatly attenuated ERS and ameliorated myocardium impairment induced by I/R. IMD(1-53) could exert its cardioprotective effect by inhibiting myocardial ERS, which might be mediated by the phosphoinositide 3-kinase/Akt signaling pathway.

Rat intermedin1-47 does not improve functional recovery in postischemic hearts

Intermedin, a novel member of the calcitonin/calcitonin gene-related peptide family identified from vertebrate genomes, may directly affect cardiac function but current studies revealed no clear picture. The aims of our study were to compare direct contractile effects of intermedin on cardiomyocytes to that on the whole organ and to investigate whether intermedin improves postischemic recovery independent of an effect on acute reperfusion injury. Isolated adult rat ventricular cardiomyocytes were electrically paced and cell shortening was monitored as a readout associated to cardiac performance. Calcium transients were analyzed by Fura-2AM loading of these cells. Isolated rat hearts were investigated by Langendorff perfusion under nonischemic conditions and after 45-min no-flow ischemia followed up by 30-min reperfusion prior to drug testing. Intermedin caused a positive contractile effect on cardiomyocytes that was mediated by protein kinase A activation and accompanied by improved calcium transients. In contrast, intermedin reduced left ventricular developed pressure in Langendorff-perfused rat hearts. This negative inotropic effect was attenuated by inhibition of nitric oxide synthesis. In postischemic hearts (impaired nitric oxide synthesis), the negative inotropic effect was attenuated but no positive inotropic effect occurred. However, intermedin caused robust vasodilation in nonischemic and postischemic hearts. Our findings suggest that the peptide binds preferentially to vascular cells in the intact organ. The loss of nitric oxide induction in postischemic hearts attenuates a negative inotropic effect of intermedin but does not improve cardiac performance independent of acute reperfusion injury.

Intracoronary melatonin increases coronary blood flow and cardiac function through β-adrenoreceptors, MT1/MT2 receptors, and nitric oxide in anesthetized pigs

Melatonin is involved in the regulation of the cardiovascular system through the modulation of sympathetic function and the nitric oxide (NO)-related pathway and interaction with MT1/MT2 receptors. However, information regarding its direct actions on coronary blood flow and cardiac function is scarce. This study therefore determined the primary in vivo effect of melatonin on cardiac function and perfusion and the involvement of the autonomic nervous system, MT1/MT2 receptors, and NO. In 35 pigs, melatonin infused into the coronary artery at 70 pg for each mL/min of coronary blood flow while preventing changes in heart rate and arterial pressure increased coronary blood flow, dP/dt(max), segmental shortening, and cardiac output by about 12%, 14%, 8%, and 23% of control values (P < 0.05), respectively. These effects were accompanied by an increase in coronary NO release of about 46% (P < 0.05) of control values. The aforementioned responses were graded in a further five pigs. Moreover, the blockade of muscarinic cholinoreceptors (n = 5) and α-adrenoreceptors (n = 5) did not abolish the observed responses to melatonin. After β(1)-adrenoreceptors blocking (n = 5), melatonin failed to affect cardiac function, whereas β(2)-adrenoreceptors (n = 5) and NO synthase inhibition (n = 5) prevented the coronary response and the effect of melatonin on NO release. Finally, all effects were prevented by MT1/MT2 receptor inhibitors (n = 10). In conclusion, melatonin primarily increased coronary blood flow and cardiac function through the involvement of MT1/MT2 receptors, β-adrenoreceptors, and NO release. These findings add new information about the mechanisms through which melatonin physiologically modulates cardiovascular function and exerts cardioprotective effects.

Protective effect of intermedin on myocardial cell in a rat model of severe acute pancreatitis

Severe acute pancreatitis (SAP) is a common disease with a poor prognosis. Heart failure is one cause of SAP patient death. Intermedin (IMD) is a potent endogenous cardio-protective substance. Administration of exogenous IMD showed beneficial effects in cardiovascular diseases. The aim of this study was to investigate the myocardial damage in SAP and to determine the therapeutic potential of IMD for SAP. Using an SAP rat model, we examined endogenous IMD expression following SAP induction, and determined the effect of IMD on myocardial function, histological morphology, apoptosis-related gene expression, and prognosis. Our results indicated that the cardiac function and histological structure were significantly disrupted in SAP rats. Infusion of exogenous IMD significantly preserved cardiac function and ameliorated myocardial damage. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) revealed that myocardial apoptosis was extensively present in SAP rats, and IMD infusion led to increased expression of the prosurvival factor Bcl-2, but decreased pro-apoptotic factors Bax and caspase-3. In addition, IMD infusion also reversed the change of IMD receptor systems in SAP rat heart tissue. Furthermore, we found that IMD infusion greatly decreased mortality of SAP rats. In conclusion, administration of SAP produced therapeutic effects in SAP through modulating apoptotic and pro-survival gene expression, inhibiting myocardial apoptosis, preserving cardiac function, and a useful therapeutic agent for SAP, and provides us an insight for a clinical trial of IMD for treating human severe acute pancreatitis.

Intracoronary gastrin 17 increases cardiac perfusion and function through autonomic nervous system, CCK receptors, and nitric oxide in anesthetized pigs

The release of gastrointestinal hormones has been reported to modulate reflex cardiovascular responses caused by gastric distension, although the role played by gastrin 17 is as yet unknown. The present study was therefore planned to determine the primary in vivo effect of gastrin 17 on coronary blood flow and cardiac function and the involvement of autonomic nervous system, CCK1/2 receptors, and nitric oxide (NO). In 40 anesthetized pigs, gastrin 17 was infused into the left anterior descending coronary artery at constant heart rate and arterial blood pressure. In 35 of the 40 pigs, the mechanisms of the observed hemodynamic responses were analyzed by repeating gastrin 17 infusion after autonomic nervous system and NO blockade, and after specific CCK receptors agonists/antagonists administration. Intracoronary gastrin 17 administration caused dose-related increases of both coronary blood flow and cardiac function. The intracoronary co-administration of CCK33/pentagastrin and gastrin 17 potentiated the coronary effects observed when the above agents were given alone ( P <0.05). The potentiation of the cardiac response was observed only with the co-administration of pentagastrin and gastrin 17 ( P <0.05). Moreover, blockade of muscarinic cholinoceptors (intravenous atropine) and of α-adrenoceptors (intravenous phentolamine) did not abolish the hemodynamic responses to gastrin 17. The cardiac and vascular effects of the hormone were prevented by blockade of β-adrenoceptors (intravenous atenolol and butoxamine), CCK1/2 receptors (intracoronary lorglumide and CAM-1028), and NO synthase (intracoronary Nω-nitro-l-arginine methyl ester). In conclusion, gastrin 17 primarily increased coronary blood flow and cardiac function through the involvement of CCK receptors, β-adrenoceptors, and NO release.