Novel biomarkers in patients with uncontrolled hypertension with and without kidney damage.

INTRODUCTION: Estimated glomerular filtration rate (eGFR) and urine albumin/creatinine ratio (ACR) are insensitive biomarkers for early detection of hypertension-mediated organ damage (HMOD). In this nationwide cross-sectional study, we assessed potential biomarkers for early HMOD in healthy persons and patients with hypertension. We hypothesised that plasma levels of biomarkers: (1) are different between healthy controls and patients with hypertension, (2): can classify patients with hypertension according to the degree of hypertension severity. DESIGN AND METHODS: Patients with hypertension prescribed ≥2 antihypertensive agents were selected from a multicentre study. Healthy controls were selected from an ongoing study of living kidney donor candidates. Uncontrolled hypertension was defined as systolic daytime ambulatory blood pressure ≥135 mmHg. Kidney HMOD was defined by ACR > 3.0 mg/mmol or eGFR < 60 mL/min/1.73 m2. Patients with hypertension were categorised into three groups: (1) controlled hypertension; (2) uncontrolled hypertension without kidney HMOD; (3) uncontrolled hypertension with kidney HMOD. Fifteen biomarkers were analysed using a Luminex bead-based immunoassay, and nine fell within the specified analytical range. RESULTS: Plasma levels of Interleukin 1 receptor antagonist (IL-1RA), neutrophil gelatinase-associated lipocalin (NGAL) and uromodulin were significantly different between healthy controls (n = 39) and patients with hypertension (n = 176). In regression models, with controlled hypertension (n = 55) as the reference category, none of the biomarkers were associated with uncontrolled hypertension without (n = 59) and with (n = 62) kidney HMOD. In models adjusted for cardiovascular risk factors and eGFR, osteopontin (OPN) was associated with uncontrolled hypertension without kidney HMOD (odds ratio (OR) 1.77 (1.05-2.98), p = 0.03), and regulated upon activation normal T-cell expressed and secreted (RANTES) with uncontrolled hypertension with kidney HMOD (OR 0.57 (0.34-0.95), p = 0.03). CONCLUSIONS: None of the biomarkers could differentiate our hypertension groups when established risk factors were considered. Plasma OPN may identify patients with uncontrolled hypertension at risk for kidney HMOD.

What is the context? In order to tailor individualised hypertension treatment, a risk assessment for cardiovascular disease (CVD) must be performed. This includes evaluation of established hypertension-mediated organ damage (HMOD), such as the presence of kidney damage and associated risk factors. Today, kidney function is assessed by blood and urine samples. However, today's blood and urine samples are not sensitive enough to capture kidney damage due to hypertension at a stage when prevention may be most effective.What is new? In this study, we evaluated plasma levels of biomarkers related to endothelial and kidney cell pathology, inflammation and fibrosis in healthy patients and patients with hypertension. We hypothesised that plasma levels of biomarkers could differentiate between different degrees of hypertension severity.Healthy controls had lower Interleukin 1 receptor antagonist (IL-1RA) and neutrophil gelatinase-associated lipocalin (NGAL) levels, but higher uromodulin compared to patients with hypertension. Except for osteopontin (OPN), all biomarkers showed significant trends in median biomarker levels across study groups. However, as hypertension severity increased, the median plasma OPN levels also rose. None of the biomarker could consistently differentiate the hypertension severity groups after considering established risk factors. However, OPN may be an early biomarker for kidney damage in hypertension.What is the impact? Biomarkers for early detection of organ damage in hypertension may guide targeted treatment. Plasma OPN may have potential to identify those at risk for hypertensive kidney damage. However, the studied biomarkers lack consistent discrimination across hypertension severity levels.

Cardiovascular rEmodelling in living kidNey donorS with reduced glomerular filtration rate: rationale and design of the CENS study.

Purpose: Until recently, it has been believed that donating a kidney not represents any risk for development of cardiovascular disease. However, a recent Norwegian epidemiological study suggests that kidney donors have an increased long-term risk of cardiovascular mortality. The pathophysiological mechanisms linking reduced kidney function to cardiovascular disease are not known. Living kidney donors are screened for cardiovascular morbidity before unilateral nephrectomy, and are left with mildly reduced glomerular filtration rate (GFR) after donation. Therefore, they represent an unique model for investigating the pathogenesis linking reduced GFR to cardiovascular disease and cardiovascular remodelling. We present the study design of Cardiovascular rEmodelling in living kidNey donorS with reduced glomerular filtration rate (CENS), which is an investigator-initiated prospective observational study on living kidney donors. The hypothesis is that living kidney donors develop cardiovascular remodelling due to a reduction of GFR.Materials and methods: 60 living kidney donors and 60 age and sex matched healthy controls will be recruited. The controls will be evaluated to fulfil the Norwegian transplantation protocol for living kidney donors. Investigations will be performed at baseline and after 1, 3, 6 and 10 years in both groups. The investigations include cardiac magnetic resonance imaging, echocardiography, bone density scan, flow mediated dilatation, laser Doppler flowmetry, nailfold capillaroscopy, office blood pressure, 24-h ambulatory blood pressure, heart rate variability and investigation of microbiota and biomarkers for inflammation, cardiovascular risk and the calcium-phosphate metabolism.Conclusions: The present study seeks to provide new insight in the pathophysiological mechanisms linking reduced kidney function to cardiovascular disease. In addition, we aim to enlighten predictors of adverse cardiovascular outcome in living kidney donors. The study is registered at Clinical-Trials.gov (identifier: NCT03729557).

The cardiac ventricular 5-HT4 receptor is functional in late foetal development and is reactivated in heart failure.

A positive inotropic responsiveness to serotonin, mediated by 5-HT(4) and 5-HT(2A) receptors, appears in the ventricle of rats with post-infarction congestive heart failure (HF) and pressure overload-induced hypertrophy. A hallmark of HF is a transition towards a foetal genotype which correlates with loss of cardiac functions. Thus, we wanted to investigate whether the foetal and neonatal cardiac ventricle displays serotonin responsiveness. Wistar rat hearts were collected day 3 and 1 before expected birth (days -3 and -1), as well as day 1, 3, 5 and 113 (age matched with Sham and HF) after birth. Hearts from post-infarction HF and sham-operated animals (Sham) were also collected. Heart tissue was examined for mRNA expression of 5-HT(4), 5-HT(2A) and 5-HT(2B) serotonin receptors, 5-HT transporter, atrial natriuretic peptide (ANP) and myosin heavy chain (MHC)-α and MHC-ß (real-time quantitative RT-PCR) as well as 5-HT-receptor-mediated increase in contractile function exvivo (electrical field stimulation of ventricular strips from foetal and neonatal rats and left ventricular papillary muscle from adult rats in organ bath). Both 5-HT(4) mRNA expression and functional responses were highest at day -3 and decreased gradually to day 5, with a further decrease to adult levels. In HF, receptor mRNA levels and functional responses reappeared, but to lower levels than in the foetal ventricle. The 5-HT(2A) and 5-HT(2B) receptor mRNA levels increased to a maximum immediately after birth, but of these, only the 5-HT(2A) receptor mediated a positive inotropic response. We suggest that the 5-HT(4) receptor is a representative of a foetal cardiac gene program, functional in late foetal development and reactivated in heart failure.

Attenuated fatigue in slow twitch skeletal muscle during isotonic exercise in rats with chronic heart failure.

During isometric contractions, slow twitch soleus muscles (SOL) from rats with chronic heart failure (chf) are more fatigable than those of sham animals. However, a muscle normally shortens during activity and fatigue development is highly task dependent. Therefore, we examined the development of skeletal muscle fatigue during shortening (isotonic) contractions in chf and sham-operated rats. Six weeks following coronary artery ligation, infarcted animals were classified as failing (chf) if left ventricle end diastolic pressure was >15 mmHg. During isoflurane anaesthesia, SOL with intact blood supply was stimulated (1s on 1s off) at 30 Hz for 15 min and allowed to shorten isotonically against a constant afterload. Muscle temperature was maintained at 37°C. In resting muscle, maximum isometric force (F(max)) and the concentrations of ATP and CrP were not different in the two groups. During stimulation, F(max) and the concentrations declined in parallel sham and chf. Fatigue, which was evident as reduced shortening during stimulation, was also not different in the two groups. The isometric force decline was fitted to a bi-exponential decay equation. Both time constants increased transiently and returned to initial values after approximately 200 s of the fatigue protocol. This resulted in a transient rise in baseline tension between stimulations, although this effect which was less prominent in chf than sham. Myosin light chain 2s phosphorylation declined in both groups after 100 s of isotonic contractions, and remained at this level throughout 15 min of stimulation. In spite of higher energy demand during isotonic than isometric contractions, both shortening capacity and rate of isometric force decline were as well or better preserved in fatigued SOL from chf rats than in sham. This observation is in striking contrast to previous reports which have employed isometric contractions to induce fatigue.

Moderate heart dysfunction in mice with inducible cardiomyocyte-specific excision of the Serca2 gene.

The sarco(endo)plasmic reticulum calcium ATPase 2 (SERCA2) transports Ca(2+) from cytosol into the sarcoplasmic reticulum (SR) of cardiomyocytes, thereby maintaining the store of releasable Ca(2+) necessary for contraction. Reduced SERCA function has been linked to heart failure, and loss of SERCA2 in the adult mammalian heart would be expected to cause immediate severe myocardial contractile dysfunction and death. We investigated heart function in adult mice with an inducible cardiomyocyte-specific excision of the Atp2a2 (Serca2) gene (SERCA2 KO). Seven weeks after induction of Serca2 gene excision, the mice displayed a substantial reduction in diastolic function with a 5-fold increase in the time constant of isovolumetric pressure decay (tau). However, already at 4 weeks following gene excision less than 5% SERCA2 protein was found in myocardial tissue. Surprisingly, heart function was only moderately impaired at this time point. Tissue Doppler imaging showed slightly reduced peak systolic tissue velocity and a less than 2-fold increase in tau was observed. The SR Ca(2+) content was dramatically reduced in cardiomyocytes from 4-week SERCA2 KO mice, and Ca(2+) transients were predominantly generated by enhanced Ca(2+) flux through L-type Ca(2+) channels and the Na(+)-Ca(2+) exchanger. Moreover, equivalent increases in cytosolic [Ca(2+)] in control and SERCA2 KO myocytes induced greater cell shortening in SERCA2 KO, suggesting enhanced myofilament responsiveness. Our data demonstrate that SR-independent Ca(2+) transport mechanisms temporarily can prevent major cardiac dysfunction despite a major reduction of SERCA2 in cardiomyocytes.

Slow contractions characterize failing rat hearts.

The reduced power of the failing heart can be ascribed to a combination of reduced force and slower contraction. We hypothesized that these two properties are due to different cellular mechanisms. We measured contraction parameters both in vivo and in isolated left ventricular (LV) cardiomyocytes from a rat model of post infarction congestive heart failure (CHF). ECG was measured simultaneously with echocardiography and LV pressure, respectively. Shortening and shortening velocity (SV) in isolated cardiomyocytes were measured during different stimulation protocols. LV end diastolic pressure (LVEDP) was 24.6 +/- 0.7 mmHg in CHF. LV systolic pressure was decreased by 20%, maximum rate of pressure development in the LV (+dP/dtmax) by 36% and time in systole increased by 20% in CHF compared to sham. Electrical remodelling occurred in CHF cells, which were depolarized and had prolonged action potentials (AP) compared to sham cells. Fractional shortening (FS) was increased in CHF compared to sham independent of stimulation protocol. Larger FS was accompanied by increased sarcoplasmic reticulum (SR) Ca2+ load and depended on the electrical remodelling. Time to peak contraction (TTP) was increased in CHF compared to sham cells, but in contrast to FS, TTP was only slightly affected when the cells were stimulated with sham APs and sham diastolic membrane potential (DMP). Contraction duration (corresponding to systolic duration) was 25% longer in CHF than in sham independent on stimulation protocol. We conclude that electrical remodelling affecting DMP and AP duration (APD) significantly affects the size of contraction, whereas the mechanism for slowing of contraction in CHF is different.

Altered Na+/Ca2+-exchanger activity due to downregulation of Na+/K+-ATPase alpha2-isoform in heart failure.

AIMS: The Na+/K+-ATPase (NKA) alpha2-isoform is preferentially located in the t-tubules of cardiomyocytes and is functionally coupled to the Na+/Ca(+-exchanger (NCX) and Ca2+ regulation through intracellular Na+ concentration ([Na+]i). We hypothesized that downregulation of the NKA alpha2-isoform during congestive heart failure (CHF) disturbs the link between Na+ and Ca2+, and thus the control of cardiomyocyte contraction. METHODS AND RESULTS: NKA isoform and t-tubule distributions were studied using immunocytochemistry, confocal and electron microscopy in a post-infarction rat model of CHF. Sham-operated rats served as controls. NKA and NCX currents (I NKA and I NCX) were measured and alpha2-isoform current (I NKA,alpha2) was separated from total I NKA using 0.3 microM ouabain. Detubulation of cardiomyocytes was performed to assess the presence of alpha2-isoforms in the t-tubules. In CHF, the t-tubule network had a disorganized appearance in both isolated cardiomyocytes and fixed tissue. This was associated with altered expression patterns of NKA alpha1- and alpha2-isoforms. I NKA,alpha2 density was reduced by 78% in CHF, in agreement with decreased protein expression (74%). When I NKA,alpha2 was blocked in Sham cardiomyocytes, contractile parameters converged with those observed in CHF. In Sham, abrupt activation of I NKA led to a decrease in I NCX, presumably due to local depletion of [Na+]i in the vicinity of NCX. This decrease was smaller when the alpha2-isoform was downregulated (CHF) or inhibited (ouabain), indicating that the alpha2-isoform is necessary to modulate local [Na+]i close to NCX. CONCLUSION: Downregulation of the alpha2-isoform causes attenuated control of NCX activity in CHF, reducing its capability to extrude Ca2+ from cardiomyocytes.

Serotonin responsiveness through 5-HT2A and 5-HT4 receptors is differentially regulated in hypertrophic and failing rat cardiac ventricle.

Cardiac ventricular responsiveness to serotonin appears in rat postinfarction congestive heart failure (CHF), mainly mediated by 5-HT(4) receptors in chronic dilated CHF and 5-HT(2A) receptors in acute CHF. To differentiate between the effects of left ventricular (LV) hypertrophy and failure on 5-HT(2A)- and 5-HT(4)-mediated inotropic serotonin response, male Wistar rats with increasing LV hypertrophy (AB1-3) and failure (ABHF) 6 weeks after banding of the ascending aorta were screened for contractile function in vivo (echocardiography) and ex vivo in LV papillary muscles, and mRNA expression level determined by RT-PCR. Both AB1-3 and ABHF displayed LV hypertrophy and remodelling. In ABHF, systolic LV and left atrial diameter increased and cardiac output decreased compared to AB3. Serotonin induced a positive inotropic response (PIR) in papillary muscles correlated with the degree of hypertrophy reaching a maximum in ABHF. Both 5-HT(2A) and 5-HT(4) receptors contributed to the PIR. The 5-HT(2A) contribution increased with increasing hypertrophy, and the 5-HT(4) contribution increased upon transition to heart failure. No 5-HT(2B)-mediated PIR was observed, consistent with increased 5-HT(2B) mRNA only in non-cardiomyocytes. The 5-HT(2A), 5-HT(2B) and 5-HT(4) mRNA levels increased in AB1-3 and increased further in ABHF compared to AB3, but did not correlate with degree of hypertrophy. 5-HT(2A) mRNA was also increased in LV of terminally failing human hearts. In conclusion, functional 5-HT(2A) and 5-HT(4) receptors are differentially induced in LV hypertrophy and failure. While the 5-HT(2A)-mediated PIR is linearly correlated with the degree of hypertrophy, the 5-HT(4)-mediated PIR seems to increase with LV dilatation, as also seen in postinfarction CHF.

Serotonin increases L-type Ca2+ current and SR Ca2+ content through 5-HT4 receptors in failing rat ventricular cardiomyocytes.

Rats with congestive heart failure (CHF) develop ventricular inotropic responsiveness to serotonin (5-HT), mediated through 5-HT(2A) and 5-HT(4) receptors. Human ventricle is similarly responsive to 5-HT through 5-HT(4) receptors. We studied isolated ventricular cardiomyocytes to clarify the effects of 5-HT on intracellular Ca(2+) handling. Left-ventricular cardiomyocytes were isolated from male Wistar rats 6 wk after induction of postinfarction CHF. Contractile function and Ca(2+) transients were measured in field-stimulated cardiomyocytes, and L-type Ca(2+) current (I(Ca,L)) and sarcoplasmic reticulum (SR) Ca(2+) content were measured in voltage-clamped cells. Protein phosphorylation was measured by Western blotting or phosphoprotein gel staining. 5-HT(4)- and 5-HT(2A)-receptor stimulation induced a positive inotropic response of 33 and 18% (both P < 0.05) and also increased the Ca(2+) transient (44 and 6%, respectively; both P < 0.05). I(Ca,L) and SR Ca(2+) content increased only after 5-HT(4)-receptor stimulation (57 and 65%; both P < 0.05). Phospholamban serine(16) (PLB-Ser(16)) and troponin I phosphorylation increased by 26 and 13% after 5-HT(4)-receptor stimulation (P < 0.05). 5-HT(2A)-receptor stimulation increased the action potential duration and did not significantly change the phosphorylation of PLB-Ser(16) or troponin I, but it increased myosin light chain 2 (MLC2) phosphorylation. In conclusion, the positive inotropic response to 5-HT(4) stimulation results from increased I(Ca,L) and increased phosphorylation of PLB-Ser(16), which increases the SR Ca(2+) content. 5-HT(4) stimulation is thus, like beta-adrenoceptor stimulation, possibly energetically unfavorable in CHF. 5-HT(2A)-receptor stimulation, previously studied in acute CHF, induces a positive inotropic response also in chronic CHF, probably mediated by MLC2 phosphorylation.

Expression of mRNA encoding G protein-coupled receptors involved in congestive heart failure--a quantitative RT-PCR study and the question of normalisation.

Congestive heart failure (CHF) induces changes in the neurohumoral system and gene expression in viable myocardium. Several of these genes encode G protein-coupled receptors (GPCRs) involved in mechanisms which compensate for impaired myocardial function. We used real-time quantitative RT-PCR (Q-RT-PCR) to investigate the expression of mRNA encoding 15 different GPCRs possibly involved in CHF, and the effect of normalisation to GAPDH mRNA (GAPDH) or 18S rRNA (18S). CHF was induced in rats by coronary artery ligation, with sham-operated controls (Sham). After 6 weeks, mRNA expression in viable left ventricular myocardium was determined using both 18S and GAPDH as the normalisation standard. An apparent 30% reduction in GAPDH mRNA levels vs. 18S in CHF compared to Sham, although not significant in itself, influenced the interpretation of regulation of other genes.Thus, levels of mRNA encoding receptors for angiotensin II (AT(1)), endothelin (ET(A), ET(B)) and the muscarinic acetylcholine (mACh) receptor M(1) increased significantly in CHF only when normalised to GAPDH. Levels of mRNA encoding the mACh receptors M(3) and M(4) and the serotonin receptors 5-HT(2A) and 5-HT(4) increased, whereas alpha(1D)-adrenoceptor mRNA decreased in CHF irrespective of the normalisation standard. No significant change was detected for M2 and M5 mACh receptors or alpha(1A)-, alpha(1B)-, beta(1)- or beta(2)-adrenoceptors. Q-RT-PCR is a sensitive and powerful method to monitor changes in GPCR mRNA expression in CHF. However, the normalisation standard used is important for the interpretation of mRNA regulation.

EC-coupling in normal and failing hearts.

Systolic heart failure may be due to too few cardiomyocytes, or to reduced contractile function of the heart cells. In the latter situation the myocardial function is impaired and this condition is called myocardial failure. The pathophysiological mechanism behind this cellular defect is not known, but Ca2+ handling is altered. Although the most important trigger of sarcoplasmatic reticulum (SR) Ca2+ release, the L-type Ca2+ current, seems to be unaltered, SR Ca2+ load is reduced in human heart failure. This could explain the reduced contractility observed in failing hearts. Three possible mechanisms have been suggested to explain the reduction in SR Ca2+ load. They are leak through the SR Ca2+ release channel (RyR), impaired SR Ca2+ ATPase (SERCA) function and increased Na+/Ca2+-exchanger (NCX) function. Leak through RyR is not consistently found. Increased NCX function is probably secondary to a change in Ca2+ handling, and thus not a primary mechanism, but blockade of the NCX might have therapeutic potential. Reduced SERCA function is probably a primary mechanism for the observed systolic dysfunction, and further insight is to be gained through studies in genetically modified models.

Dual serotonergic regulation of ventricular contractile force through 5-HT2A and 5-HT4 receptors induced in the acute failing heart.

Cardiac responsiveness to neurohumoral stimulation is altered in congestive heart failure (CHF). In chronic CHF, the left ventricle has become sensitive to serotonin because of appearance of Gs-coupled 5-HT4 receptors. Whether this also occurs in acute CHF is unknown. Serotonin responsiveness may develop gradually or represent an early response to the insult. Furthermore, serotonin receptor expression could vary with progression of the disease. Postinfarction CHF was induced in male Wistar rats by coronary artery ligation with nonligated sham-operated rats as control. Contractility was measured in left ventricular papillary muscles and mRNA quantified by real-time reverse-transcription PCR. Myosin light chain-2 phosphorylation was determined by charged gel electrophoresis and Western blotting. Ca2+ transients in CHF were measured in field stimulated fluo-4-loaded cardiomyocytes. A novel 5-HT2A receptor-mediated inotropic response was detected in acute failing ventricle, accompanied by increased 5-HT2A mRNA levels. Functionally, this receptor dominated over 5-HT4 receptors that were also induced. The 5-HT2A receptor-mediated inotropic response displayed a triphasic pattern, shaped by temporally different activation of Ca2+-calmodulin-dependent myosin light chain kinase, Rho-associated kinase and inhibitory protein kinase C, and was accompanied by increased myosin light chain-2 phosphorylation. Ca2+ transients were slightly decreased by 5-HT2A stimulation. The acute failing rat ventricle is, thus, dually regulated by serotonin through Gq-coupled 5-HT2A receptors and Gs-coupled 5-HT4 receptors.

Enhanced matrix metalloproteinase activity in skeletal muscles of rats with congestive heart failure.

Patients with congestive heart failure (CHF) are prone to increased skeletal muscle fatigue. Elevated circulatory concentrations of tumor necrosis factor (TNF)-alpha and monocyte chemoattractant protein-1, which may stimulate matrix metalloproteinase (MMP) activity and, thereby, contribute to skeletal muscle dysfunction, are frequently found in CHF. However, whether skeletal muscle MMP activity is altered in CHF is unknown. Hence, we have used a gelatinase assay to assess the activity of MMP and tissue inhibitors of MMP in single skeletal muscles of rats with CHF 6 wk after induction of myocardial infarction. Sham-operated (Sham) rats were used as controls. We also measured the gene expression and protein contents of MMP-2 and MMP-9 in skeletal muscles of these rats. Plasma MMP activity was nearly seven times higher (P < 0.05) in CHF than in Sham rats. Concomitantly, the MMP activity within single slow- and fast-twitch skeletal muscles of CHF rats increased two- to fourfold compared with Sham animals, whereas tissue inhibitor of MMP activity did not differ (P > 0.05). Preformed MMP-2 and MMP-9 were probably activated in CHF, because neither their gene expression nor protein levels were altered (P > 0.05). Serum concentrations of TNF-alpha and monocyte chemoattractant protein-1 remained unchanged (P > 0.05) between CHF and Sham rats during the 6-wk observation period. We conclude that development of CHF in rats enhances MMP activity, which in turn may distort the normal contractile function of skeletal muscle, thereby contributing to increased skeletal muscle fatigue.

Appearance of a ventricular 5-HT4 receptor-mediated inotropic response to serotonin in heart failure.

BACKGROUND: Current pharmacological treatment of congestive heart failure (CHF) addresses changes in neurohumoral stimulation or cardiac responsiveness to such stimulation. Yet, undiscovered neurohumoral changes, adaptive or maladaptive, may occur in CHF and suggest novel pharmacological treatment. Serotonin [5-hydroxytryptamine (5-HT)] enhances contractility and causes arrhythmias through 5-HT(4) receptors in human atrium and ventricle but not through rat ventricular 5-HT(4) receptors. OBJECTIVE: We investigated whether CHF could induce ventricular responsiveness to serotonin. METHODS: Postinfarction CHF was induced in male Wistar rats by coronary artery ligation. Contractility was measured in left ventricular papillary muscles 6 weeks after infarction. Messenger RNA was quantified by RT-PCR and cAMP by RIA. RESULTS: Serotonin caused positive inotropic (-logEC(50)=7.5) and lusitropic effects in CHF but not Sham papillary muscles. The inotropic effect of 10 muM serotonin in CHF (31.3+/-2.2%) was of similar size as the effect of 10 muM isoproterenol (34.0+/-1.7%). The effects of serotonin were antagonised by GR113808 (0.5-5 nM), consistent with mediation through 5-HT(4) receptors. This was further supported by positive inotropic effects of the 5-HT(4)-selective partial agonist RS67506. Carbachol blunted the serotonin responses and serotonin increased ventricular and cardiomyocyte cAMP, consistent with coupling to G(s) and adenylyl cyclase. Quantitative RT-PCR revealed fourfold increased 5-HT(4(b)) mRNA expression in CHF vs. Sham ventricles. CONCLUSION: Functional ventricular 5-HT(4) receptors are induced by myocardial infarction and CHF of the rat heart. We propose that they are a model for ventricular 5-HT(4) receptors of human failing heart and may play a pathophysiological role in heart failure.