Histone Deacetylase 1 Depletion Activates Human Cardiac Mesenchymal Stromal Cell Proangiogenic Paracrine Signaling Through a Mechanism Requiring Enhanced Basic Fibroblast Growth Factor Synthesis and Secretion.

BACKGROUND: Cardiac mesenchymal cell (CMC) administration improves cardiac function in animal models of heart failure. Although the precise mechanisms remain unclear, transdifferentiation and paracrine signaling are suggested to underlie their cardiac reparative effects. We have shown that histone deacetylase 1 (HDAC1) inhibition enhances CMC cardiomyogenic lineage commitment. Here, we investigated the impact of HDAC1 on CMC cytokine secretion and associated paracrine-mediated activities on endothelial cell function. METHODS AND RESULTS: CMCs were transduced with shRNA constructs targeting HDAC1 (shHDAC1) or nontarget (shNT) control. Cytokine arrays were used to assess the expression of secreted proteins in conditioned medium (CM) from shHDAC1 or shNT-transduced CMCs. In vitro functional assays for cell proliferation, protection from oxidative stress, cell migration, and tube formation were performed on human endothelial cells incubated with CM from the various treatment conditions. CM from shHDAC1-transduced CMCs contained more cytokines involved in cell growth/differentiation and more efficiently promoted endothelial cell proliferation and tube formation compared with CM from shNT. After evaluating key cytokines previously implicated in cell-therapy-mediated cardiac repair, we found that basic fibroblast growth factor was significantly upregulated in shHDAC1-transduced CMCs. Furthermore, shRNA-mediated knockdown of basic fibroblast growth factor in HDAC1-depleted CMCs inhibited the effects of shHDAC1 CM in promoting endothelial proliferation and tube formation-indicating that HDAC1 depletion activates CMC proangiogenic paracrine signaling in a basic fibroblast growth factor-dependent manner. CONCLUSIONS: These results reveal a hitherto unknown role for HDAC1 in the modulation of CMC cytokine secretion and implicate the targeted inhibition of HDAC1 in CMCs as a means to enhance paracrine-mediated neovascularization in cardiac cell therapy applications.

Hypoxia exposure and B-type natriuretic peptide release from Langendorff heart of rats.

AIM: We studied whether available oxygen without induced mechanical stretch regulates the release of the biologically active B-type natriuretic peptide (BNP) from Langendorff heart. METHODS: Rat hearts were isolated and perfused with a physiological Krebs-Henseleit solution at a constant hydrostatic pressure in Langendorff set-up. The basal O2 level of perfusate (24.4 ± 0.04 mg L-1 ) was gradually lowered to 3.0 ± 0.01 mg L-1 over 20 min using N2 gas (n = 7). BNP and O2 level were measured from coronary flow. During control perfusions (n = 5), the O2 concentration was kept at 26.6 ± 0.3 mg L-1 . RESULTS: A low oxygen concentration in the perfusate was associated with a significant increase in BNP release (F = 40.4, P < 0.001). Heart rate decreased when the oxygen concentration in the perfusate reached 9.1 ± 0.02 mg L-1 and continued to fall in lower oxygen concentrations (F = 14.8, P < 0.001). There was also a significant but inverse correlation between BNP and oxygen in the coronary flow (R2  = 0.27, P < 0.001). CONCLUSION: In the spontaneously beating Langendorff rat heart, a decreasing concentration of oxygen in the ingoing perfusion increased the secretion of BNP. The effect of oxygen was independent of mechanical stretch of the heart as it occurred even when the heart rate decreased but the pressure conditions remained constant. The difference in the oxygen capacitance of blood and Krebs-Henseleit solution appears to be a major factor affecting secretion of BNP, which is correlated with the oxygen tension of myocardial cells and affected both by the oxygen concentration and capacitance of solution perfusing the heart and by the coronary flow.

Osteocrin, a peptide secreted from the heart and other tissues, contributes to cranial osteogenesis and chondrogenesis in zebrafish.

The heart is an endocrine organ, as cardiomyocytes (CMs) secrete natriuretic peptide (NP) hormones. Since the discovery of NPs, no other peptide hormones that affect remote organs have been identified from the heart. We identified osteocrin (Ostn) as an osteogenesis/chondrogenesis regulatory hormone secreted from CMs in zebrafish. ostn mutant larvae exhibit impaired membranous and chondral bone formation. The impaired bones were recovered by CM-specific overexpression of OSTN. We analyzed the parasphenoid (ps) as a representative of membranous bones. In the shortened ps of ostn morphants, nuclear Yap1/Wwtr1-dependent transcription was increased, suggesting that Ostn might induce the nuclear export of Yap1/Wwtr1 in osteoblasts. Although OSTN is proposed to bind to NPR3 (clearance receptor for NPs) to enhance the binding of NPs to NPR1 or NPR2, OSTN enhanced C-type NP (CNP)-dependent nuclear export of YAP1/WWTR1 of cultured mouse osteoblasts stimulated with saturable CNP. OSTN might therefore activate unidentified receptors that augment protein kinase G signaling mediated by a CNP-NPR2 signaling axis. These data demonstrate that Ostn secreted from the heart contributes to bone formation as an endocrine hormone.

Yohimbine promotes cardiac NE release and prevents LPS-induced cardiac dysfunction via blockade of presynaptic α2A-adrenergic receptor.

Myocardial depression is an important contributor to mortality in sepsis. We have recently demonstrated that α2-adrenoceptor (AR) antagonist, yohimbine (YHB), attenuates lipopolysaccharide (LPS)-induced myocardial depression. However, the mechanisms for this action of YHB are unclear. Here, we demonstrated that YHB decreased nitric oxide (NO) and tumor necrosis factor-alpha (TNF-α) levels in the myocardium and plasma, attenuated cardiac and hepatic dysfunction, but not kidney and lung injuries in endotoxemic mice. Immunohistochemical analysis revealed that cardiac α2A-AR was mostly located in sympathetic nerve presynaptic membrane; YHB decreased cardiac α2A-AR level and promoted cardiac norepinephrine (NE) release in endotoxemic mice. Reserpine that exhausted cardiac NE without markedly decreasing plasma NE level abrogated the inhibitory effects of YHB on cardiac TNF-α and iNOS expression as well as cardiac dysfunction, but not the suppressive effects of YHB on plasma TNF-α and NO elevation in LPS-challenged mice. Furthermore, both reserpine and YHB significantly inhibited LPS-induced myocardial apoptosis. α1-AR, ß2-AR, but not ß1-AR antagonists reversed the inhibitory effect of YHB on LPS-stimulated myocardial apoptosis. However, ß1-AR antagonist attenuated LPS-caused cardiomyocyte apoptosis, partly abolished the protective effect of YHB on the left ventricular ejection fraction in endotoxemic mice. Altogether, these findings indicate that YHB attenuates LPS-induced cardiac dysfunction, at least in part, through blocking presynaptic α2A-AR and thus increasing cardiac NE release. YHB-elevated cardiac NE improves cardiac function via suppressing cardiac iNOS and TNF-α expression, activating ß1-AR and inhibiting cardiomyocyte apoptosis through α1- and ß2-AR in endotoxemic mice. However, cardiac ß1-AR activation promotes LPS-induced cardiomyocyte apoptosis.

[Where and when natriuretic peptides are secreted in the heart].

This review presents recent data on the structure, synthesis, and secretion of cardiac natriuretic peptides. It is known that these hormones have a broad spectrum of activity, but they remain the least studied and poorly understood link in the regulation of the water-salt homeostasis. Emphasis is placed on the problem of ontogenetic formation of the heart secretory activity during embryogenesis. We discuss the available scarce and scattered information on the paracrine and autocrine effects of the peptides on intercellular interactions, and on the division, growth and differentiation of the heart cells. These issues are hardly addressed in Russian literature.

Sex differences in postischemic cardiac dysfunction and norepinephrine overflow in rat heart: the role of estrogen against myocardial ischemia-reperfusion damage via an NO-mediated mechanism.

The purpose of this study is to elucidate the relationship between sex difference and norepinephrine (NE) release in the pathogenesis of myocardial ischemia/reperfusion (I/R) injury. Isolated male and female rat hearts were subjected to 40-minute global ischemia followed by 30-minute reperfusion. Compared with male hearts, I/R-induced cardiac dysfunction, such as decreased left ventricular developed pressure and dP/dtmax and increased left ventricular end diastolic pressure, was significantly attenuated in female hearts. An excessive NE overflow in the coronary effluent from the postischemic heart in females was much less than that in males. These sex differences were abolished by ovariectomy, but in vivo treatment with 17ß-estradiol recovered it. This ameliorating effect of 17ß-estradiol was not observed in the presence of nitric oxide (NO) synthase inhibitor N-nitro-L-arginine. When NOx (NO2/NO3) levels in the coronary effluent after onset of reperfusion were measured, reversed correlated relationships between NOx production and I/R-induced cardiac dysfunction, and NE overflow, were observed. These findings suggest that sex differences in the postischemic cardiac dysfunction are closely related to the NE overflow from the postischemic heart and that estrogen plays a key role in the cardioprotective effect against I/R injury in female rats, by suppressing NE release via the enhancement of NO production.

A polysaccharides MDG-1 augments survival in the ischemic heart by inducing S1P release and S1P1 expression.

Ophiopogon japonicus is a traditional Chinese medicine used to treat cardiovascular disease. Recent studies have confirmed the anti-ischemic properties of a water-soluble ß-D-fructan (MDG-1) from O. japonicus. The sphingosine 1-phosphate (S1P) signaling pathway is involved in its cytoprotective effects. Herein, we explore the role of the S1P signaling pathway in the anti-ischemic effect of MDG-1 and assess one possible mechanism by which it induces S1P release and sphingosine 1-phosphate receptor 1 (S1P(1)) expression in human microvascular endothelial cells (HMEC-1) and cardiomyocytes. Our evidence demonstrates that MDG-1 promotes sphingosine kinase (SPHK) activity in HMEC-1 cells. An analytical method for measuring the mass of S1P using ESI/MS/MS was developed and we found that MDG-1 increases intracellular S1P levels. Meanwhile, MDG-1 is protective during hypoxia and ischemia through mechanisms that require S1P(1) receptor activation, which was confirmed both in oxygen glucose deprivation (OGD) and coronary artery ligation models by using transfection of cloned human S1P(1) receptor and RNA interference. These data indicate that the increase of intracellular S1P generation, particularly by activation of the SPHK enzyme, coupled with the autocrine and paracrine stimulation of cell surface S1P receptors, is a potential mechanism in the anti-ischemic and cell protective effect of MDG-1.

Polymerized human placenta hemoglobin given before ischemia protects rat heart from ischemia reperfusion injury.

This study was to investigate whether polymerized human placenta hemoglobin (PolyPHb) given before ischemia protects in vivo rat heart function against ischemia/reperfusion (I/R) injury. Forty-five male Sprague-Dawley rats were randomly divided (n = 15 per group) into a sham group, control group (pretreatment with Lactated Ringer's solution), or PolyPHb group (pretreatment with 0.1 gHb/kg PolyPHb). Rat hearts were subjected to 30-min ischemia by occlusion of left anterior descending, followed by 2-hr reperfusion. As compared to the control group, PolyPHb preserved cardiac function and reduced cardiac troponin-I release and histopathological changes. Therefore, PolyPHb pretreatment provided a profound cardioprotective effect on the in vivo rat heart.

PTH-receptors regulate norepinephrine release in human heart and kidney.

Recent data suggests that chronic renal failure and hyperparathyroidism are associated with sympathetic overactivity. Since peptide hormones are known to modulate norepinephrine (NE) release by activating prejunctional receptors, this study investigates whether parathyroid hormone fragment (1-34) (hPTH(1-34)) increases neuronal NE release in human heart and kidney. Using specific PTH-receptor agonists and antagonists, this study furthermore highlights functional differences between PTH1 and PTH2 receptors. Human atrial and renal tissues were incubated with [(3)H]-NE and superfused. Three electrical stimulations (5Hz, 1min) induced a stable [(3)H]-NE release which was taken as an index of endogenous NE release. RT-PCR with specific primers for PTH1- and PTH2-receptor was performed in heart and kidney. hPTH(1-34) (0.01-0.1µmol/L) and a stable analog of its second messenger cAMP (8-bromo-cAMP) increased [(3)H]-NE release in human atria. This facilitatory effect of PTH was also observed in human renal cortex. The PTH1-receptor antagonist (D-Trp(12), Tyr(34))-pTH-(7-34) (0.5µmol/L) abolished the effect of hPTH(1-34). This data was verified using isolated perfused mouse kidneys. Tuberoinfundibular peptide of 39 residues (TIP-39) (0.1nmol/L-0.1µmol/L) decreased [(3)H]-NE release in atria. PTH1- and PTH2-receptor expressions were demonstrated in human heart and kidney. Moreover, a splice variant of the PTH2-receptor was detected in human kidney. In conclusion, PTH is able to facilitate NE release in human atria and renal cortex by activation of PTH1-receptors. The highly increased PTH levels that can be observed in chronic renal failure might be one contributor for the elevated sympathetic nerve activity and the associated cardiovascular mortality in patients with end stage renal disease.

Langendorff heart: a model system to study cardiovascular effects of engineered nanoparticles.

Engineered nanoparticles (ENPs) are produced and used in increasing quantities for industrial products, food, and drugs. The fate of ENPs after usage and impact on health is less known. Especially as air pollution, suspended nanoparticles have raised some attention, causing diseases of the lung and cardiovascular system. Human health risks may arise from inhalation of ENPs with associated inflammation, dispersion in the body, and exposure of vulnerable organs (e.g., heart, brain) and tissues with associated toxicity. However, underlying mechanisms are largely unknown. Furthermore future use of ENPs in therapeutic applications is being researched. Therefore knowledge about potential cardiovascular risks due to exposure to ENPs is highly demanded, but there are no established biological testing models yet. Therefore, we established the isolated beating heart (Langendorff heart) as a model system to study cardiovascular effects of ENPs. This model enables observation and analysis of electrophysiological parameters over a minimal time period of 4 h without influence by systemic effects and allows the determination of stimulated release of substances under influence of ENPs. We found a significant dose and material dependent increase in heart rate accompanied by arrhythmia evoked by ENPs made of flame soot (Printex 90), spark discharge generated soot, anatas (TiO(2)), and silicon dioxide (SiO(2)). However, flame derived SiO(2) (Aerosil) and monodisperse polystyrene lattices exhibited no effects. The increase in heart rate is assigned to catecholamine release from adrenergic nerve endings within the heart. We propose the isolated Langendorff heart and its electrophysiological characterization as a suitable test model for studying cardiovascular ENP toxicity.

Angiotensin-(1-7) attenuates hyposmolarity-induced ANP secretion via the Na+-K+ pump.

The alteration in osmolarity challenges cell volume regulation, a vital element for cell survival. Hyposmolarity causes an increase in cell volume. Recently, it has been reported that the renin-angiotensin system (RAS) plays a role in cell volume regulation. We investigated the effect of angiotensin-(1-7) [Ang-(1-7)] on hyposmolarity-induced atrial natriuretic peptide (ANP) secretion in normal and diabetic (DM) rat atria and modulation of the effect of Ang-(1-7) by the Na(+)-K(+) pump. Using isolated control rat atria, we observed that perfusion of hyposmotic solution into the atria increased ANP secretion. When Ang-(1-7) [0.1 microM or 1 microM] was perfused in a hyposmolar solution, it decreased the hyposmolarity-induced ANP secretion in a dose-dependent manner. This effect of Ang-(1-7) could be mediated by the Na(+)-K(+) pump, since ouabain, an Na(+)-K(+) pump inhibitor, significantly decreased the effect of Ang-(1-7) on hyposmolarity-induced ANP secretion. In contrast, N(omega) Nitro-l-arginine methyl ester hydrochloride (l-NAME) did not modify the effect of Ang-(1-7) on the hyposmolarity-induced ANP secretion. Interestingly, the ANP secretion was increased robustly by the perfusion of the hyposmolar solution in the DM atria, as compared to the control atria. However, the inhibitory effect of Ang-(1-7) on the hyposmolarity-induced ANP secretion was not observed in the DM atria. In the DM atria, atrial contractility was significantly increased. Taken together, we concluded that Ang-(1-7) attenuated hyposmolarity-induced ANP secretion via the Na(+)-K(+) pump and a lack of Ang-(1-7) response in DM atria may partly relate to change in Na(+)-K(+) pump activity.

cAMP produced by pituitary adenylate cyclase-activating polypeptide 27 inhibits atrial natriuretic peptide secretion in rabbit beating atria.

The aim of the present study was to determine the effects of increased cAMP levels in response to pituitary adenylate cyclase-activating polypeptide 27 (PACAP27) on atrial atrial natriuretic peptide (ANP) secretion in rabbit atria. A perfused beating atrial model was used in the present study and cAMP efflux and ANP levels in atrial perfusates were measured by radioimmnoassay. At 100 nmol/L, PACAP27 increased cAMP production, which resulted in subsequent inhibition of ANP secretion. Nicardipine (1.0 micromol/L), an L-type Ca2+ channel blocker, attenuated inhibition of ANP secretion by PACAP27. Staurosporine (1.0 micromol/L), a non-specific protein kinase inhibitor, and H-89 (1.0 micromol/L), a cAMP-dependent protein kinase A (PKA) inhibitor, completely blocked the inhibition of ANP secretion in response to PACAP27 but had no effect on PACAP27-induced increases in cAMP. In conclusion, the results suggest that increased cAMP levels in response to PACAP27 negatively regulate ANP secretion via the adenylate cyclase-cAMP-PKA signalling pathway in rabbit atria and that L-type Ca2+ channels may be involved, in part, in the regulation of ANP secretion by cAMP.

Direct cardiac actions of erythropoietin (EPO): effects on cardiac contractility, BNP secretion and ischaemia/reperfusion injury.

EPO (erythropoietin) has recently been shown to have protective actions upon the myocardium; however, the direct effects of EPO upon cardiac contractile and secretory functions are unknown and the signalling mechanisms are not well defined. In the present study, we provide the first evidence of direct cardiac contractile actions of EPO. In isolated perfused Sprague-Dawley rat hearts, a 30 min infusion of EPO significantly increased contractility in a dose-dependent fashion (maximal change 18+/-2% with 1 unit/ml EPO; P<0.005 compared with vehicle). Perfusate ET-1 (endothelin-1) increased transiently during EPO infusion, and the ET(A/)ET(B) antagonist bosentan abolished the inotropic response to EPO. BNP (B-type natriuretic peptide) secretion (28+/-8%; P<0.05) and nuclear transcription factor GATA-4 DNA-binding activity (51%; P<0.05) were both significantly increased by EPO and blocked by bosentan. In a model of global ischaemic injury, delivery of 1 unit/ml EPO during reperfusion significantly attenuated creatine kinase release (28+/-12%; P<0.05) and significantly improved contractile recovery (P<0.001), independent of ET(A) blockade. Apoptotic indices [assessed by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling)/cleaved caspase-3-positive cells] were significantly decreased (P<0.01) by 1 unit/ml EPO during reperfusion alone, coincident with significantly increased phosphorylation of myocardial JAK2 (Janus kinase 2) and STAT3 (signal transducer and activator of transcription 3). Thus EPO directly enhances cardiac contractility and BNP secretion and alleviates ischemia/reperfusion injury via ET-1-dependent and -independent mechanisms respectively.

The protective effect of prior ischemia reperfusion adenosine A1 or A3 receptor activation in the normal and hypertrophied heart.

OBJECTIVES: The increased susceptibility to ischemic injury of hypertrophied hearts has long been recognized. The purpose of this study was to investigate the effects of pre-ischemic pharmacological preconditioning (PC) with adenosine A(1) or A(3) receptor activation, on the recovery of the isolated myocardium post cardioplegic ischemia. In addition, we examined the p38 MAPK activation in this process. MATERIALS AND METHODS: WKY and SHR hearts were subjected to two different modes of treatment. (1) In the perfusion mode- (the first window of PC) isolated rat hearts were perfused for 10 min with Krebs Henseleit solution and then A(1) receptor agonist (CCPA) or A(3) receptor agonist (Cl-IB-MECA), 10 nM for 20 min, followed by 30 min of warm cardioplegic ischemia and 30 min of reperfusion. (2) In the injection mode (the second window of PC) 100 microg/kg CCPA or Cl-IB-MECA, were administered 24 h before the experiment. Isolated hearts were perfused for 30 min with KH and then subjected to the same protocol as described above. RESULTS: Recovery of hemodynamic parameters was always better in the normal vs. hypertrophied hearts. CCPA improved recovery of left ventricular developed pressure, coronary flow and ATP levels of the hearts (normal and hypertrophied) in both modes of treatment. Cl-IB-MECA was partially beneficial especially in the injected mode. Increased phosphorylation of p38 MAPK relative to baseline, in both early (perfused) and late (injected) modes of treatment especially in the WKY hearts, is demonstrated. CONCLUSION: CCPA in both modes of treatment and Cl-IB-MECA, especially in the injected mode, were beneficial in protecting the normal and hypertrophied perfused isolated rat heart subjected to normothermic cardioplegic ischemia. This protection was partially related to the increased phosphorylation of p38 MAPK.

Thyrotropin-releasing hormone in rat heart: effect of swelling, angiotensin II and renin gene.

AIM: This study was performed to examine thyrotropin-releasing hormone (TRH) secretion and regulation in rat heart. METHODS: Expression of prepro-TRH gene in left atrium and left ventricle was studied by RT-PCR. TRH secretion from slices of left auricle and left ventricle in response to cell swelling (induced by hypotonic medium or ethanol in isosmotic medium), angiotensin II and losartan and their combinations was studied. RESULTS: RT-PCR revealed two times higher prepro-TRH expression in left auricle than left ventricle. In transgenic rats with extra copy of mouse renin gene a marked increase of prepro-TRH expression in the heart was noted but the relative difference between left atrium and left ventricle persisted. The swelling stimulated TRH release from both left auricle and left ventricle and this stimulation could not be inhibited by bumetanide. Angiotensin II (10 nmol L-1) added into medium significantly decreased basal secretion of TRH. The inhibiting effect of Angiotensin II was prevented by 1 micromol L-1 losartan, an angiotensin II AT1 receptor blocker. When angiotensin II and hypotonicity were applied simultaneously, swelling-induced secretion persisted. CONCLUSION: TRH secretion from heart slices has attributes of regulated secretion--depending on the stimulus it could be either stimulated or inhibited. Renin positively affects prepro-TRH expression in the heart. Angiotensin II inhibits TRH secretion from heart tissue by a mechanism involving AT1 receptors. Swelling-induced TRH secretion overrides inhibitory effect of angiotensin II. Swelling could be a useful tool when natural or pharmacological secretagogue is unknown. Peptides and proteins released by swelling could be mediators of local and remote ischaemic preconditioning protecting from subsequent ischaemia.

Plasma cardiotrophin-1 is elevated in human hypertension and stimulated by ventricular stretch.

OBJECTIVE: Cardiotrophin-1 (CT-1) is an interleukin-6-related cytokine with known hypertrophic and protective actions upon cardiac myocytes. We provide here the first report of cardiac tissue and plasma levels of CT-1 in human and experimental hypertension, demonstrate cardiac CT-1 secretion stimulated by ventricular stretch, and characterise molecular forms of CT-1 in tissue and plasma. METHODS: CT-1 levels in human and rat plasma and in rat cardiac tissue extracts were determined by specific radioimmunoassay (RIA). Cardiac CT-1 secretion during ventricular stretch was studied in isolated, perfused hearts. Molecular forms of CT-1 were identified using RIA coupled with high performance liquid chromatography (HPLC). Results are given as mean+/-SEM. RESULTS: Plasma levels of CT-1 in patients with untreated hypertension (UTH, 606+/-18 pmol/L, n=24) were significantly higher than those in age-and BMI-matched normotensive volunteers (NT, 546+/-12 pmol/L, n=31, P<0.01 vs. UTH). CT-1 levels in matched patients with treated hypertension (THT, 618+/-10 pmol/L, n=35) were similar to those in UTH patients, but higher than in NT controls (P<0.01). Plasma CT-1 demonstrated a weak but significant correlation with systolic blood pressure in all patients (r=0.241, P<0.05, n=90). In contrast, CT-1 levels in male, 40-week-old, NT-WKY rats (1295+/-98 pmol/L) were significantly higher than those in matched UTH-SHR (937+/-31 pmol/L, P<0.01). In both WKY and SHR rats, atrial tissue concentrations of CT-1 were 8-fold higher than ventricular levels. Left ventricular tissue CT-1 protein concentrations were significantly higher in 40-week-old SHR compared with age-matched WKY (SHR 12.6+/-0.5 fmol/g vs. WKY 9.5+/-0.8 fmol/g, P<0.01). Ventricular stretch of Langendorff perfused, isolated WKY/SHR hearts resulted in significant, acute release of CT-1 and BNP. HPLC coupled with specific RIA revealed CT-1 in human/rat plasma, isolated rat heart perfusate, and rat heart tissue extracts to consist of complex, high molecular weight forms. CONCLUSIONS: This is the first report to show increased levels of plasma CT-1 in hypertensive disease. CT-1 is a unique cardiac cytokine whose release is stimulated by ventricular stretch. The atrium contains the highest levels of the protein. The stored and circulating molecular form of CT-1 is complex, which may modulate its in vivo role in cardiovascular disease.

Relaxin modulates fibroblast function, collagen production, and matrix metalloproteinase-2 expression by cardiac fibroblasts.

Cardiac fibrosis is a hallmark of heart disease and involves recruitment, proliferation, and differentiation of extracellular matrix-producing fibroblasts, leading to overproduction of collagen within the myocardium. In this study, the effects of relaxin in inhibiting these processes were investigated. We used neonatal rat atrial and ventricular fibroblasts, which respond to pro-fibrotic stimuli (i.e., transforming growth factor-beta and angiotensin II) and naturally express the relaxin receptor LGR7. Relaxin significantly inhibited TGF-beta- and angiotensin II-mediated fibroblast function and collagen production over a 72-h period, while increasing MMP-2 expression and activity in the presence of both profibrotic factors (all P < .05). These studies demonstrate that relaxin may have therapeutic potential in diseased states characterized by cardiac fibrosis.