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Heart mass can be predicted from heart volume as measured from post-mortem computed tomography (PMCT), but with limited accuracy. Although related to heart mass, age, sex, and body dimensions have not been included in previous studies using heart volume to estimate heart mass. This study aimed to determine whether heart mass estimation can be improved when age, sex, and body dimensions are used as well as heart volume. Eighty-seven (24 female) adult post-mortem cases were investigated. Univariable predictors of heart mass were determined by Spearman correlation and simple linear regression. Stepwise linear regression was used to generate heart mass prediction equations. Heart mass estimate performance was tested using median mass comparison, linear regression, and Bland–Altman plots. Median heart mass (P = 0.0008) and heart volume (P = 0.008) were significantly greater in male relative to female cases. Alongside female sex and body surface area (BSA), heart mass was univariably associated with heart volume in all cases (R2 = 0.72) and in male (R2 = 0.70) and female cases (R2 = 0.64) when segregated. In multivariable regression, heart mass was independently associated with age and BSA (R2 adjusted = 0.46–0.54). Addition of heart volume improved multivariable heart mass prediction in the total cohort (R2 adjusted = 0.78), and in male (R2 adjusted = 0.74) and female (R2 adjusted = 0.74) cases. Heart mass estimated from multivariable models incorporating heart volume, age, sex, and BSA was more predictive of actual heart mass (R2 = 0.75–0.79) than models incorporating either age, sex, and BSA only (R2 = 0.48–0.57) or heart volume only (R2 = 0.64–0.73). Heart mass can be more accurately predicted from heart volume measured from PMCT when combined with the classical predictors, age, sex, and BSA.

Predictors of overall epicardial adipose tissue deposition have been found to vary between males and females. Whether similar sex differences exist in epicardial fat cell morphology is currently unknown. This study aimed to determine whether epicardial fat cell size is associated with different clinical measurements in males and females. Fat cell sizes were measured from epicardial, paracardial, and appendix adipose tissues of post-mortem cases (N= 118 total, 37 females). Epicardial, extra-pericardial, and visceral fat volumes were measured by computed tomography from a subset of cases (N= 70, 22 females). Correlation analyses and stepwise linear regression were performed to identify predictors of fat cell size in males and females. Median fat cell sizes in all depots did not differ between males and females. Body mass index (BMI) and age were independently predictive of epicardial, paracardial, and appendix fat cell sizes in males, but not in females. Epicardial and appendix fat cell sizes were associated with epicardial and visceral fat volumes, respectively, in males only. In females, paracardial fat cell size was associated with extra-pericardial fat volume, while appendix fat cell size was associated with BMI only. No predictors were associated with epicardial fat cell size in females at the univariable or multivariable levels. To conclude, no clinical measurements were useful surrogates of epicardial fat cell size in females, while BMI, age, and epicardial fat volume were independent, albeit weak, predictors in males only.

Long-chain acylcarnitines (LCACs) are known to directly alter cardiac contractility and electrophysiology. However, the acute effect of LCACs on human cardiac function is unknown. We aimed to determine the effect of LCAC 18:1, which has been associated with cardiovascular disease, on the contractility and arrhythmia susceptibility of human atrial myocardium. Additionally, we aimed to assess how LCAC 18:1 alters Ca2+ influx and spontaneous Ca2+ release in vitro. Human right atrial trabeculae (n = 32) stimulated at 1 Hz were treated with LCAC 18:1 at a range of concentrations (1-25 µM) for a 45-min period. Exposure to the LCAC induced a dose-dependent positive inotropic effect on myocardial contractility (maximal 1.5-fold increase vs. control). At the 25 µM dose (n = 8), this was paralleled by an enhanced propensity for spontaneous contractions (50% increase). Furthermore, all LCAC 18:1 effects on myocardial function were reversed following LCAC 18:1 washout. In fluo-4-AM-loaded HEK293 cells, LCAC 18:1 dose dependently increased cytosolic Ca2+ influx relative to vehicle controls and the short-chain acylcarnitine C3. In HEK293 cells expressing ryanodine receptor (RyR2), this increased Ca2+ influx was linked to an increased propensity for RyR2-mediated spontaneous Ca2+ release events. Our study is the first to show that LCAC 18:1 directly and acutely alters human myocardial function and in vitro Ca2+ handling. The metabolite promotes proarrhythmic muscle contractions and increases contractility. The exploratory findings in vitro suggest that LCAC 18:1 increases proarrhythmic RyR2-mediated spontaneous Ca2+ release propensity. The direct effects of metabolites on human myocardial function are essential to understand cardiometabolic dysfunction.NEW & NOTEWORTHY For the first time, the fatty acid metabolite, long-chain acylcarnitine 18:1, is shown to acutely increase the arrhythmia susceptibility and contractility of human atrial myocardium. In vitro, this was linked to an influx of Ca2+ and an enhanced propensity for spontaneous RyR2-mediated Ca2+ release.

Diabetes is associated with cardiac metabolic disturbances and increased heart failure risk. Plasma fructose levels are elevated in diabetic patients. A direct role for fructose involvement in diabetic heart pathology has not been investigated. The goals of this study were to clinically evaluate links between myocardial fructose and sorbitol (a polyol pathway fructose precursor) levels with evidence of cardiac dysfunction, and to experimentally assess the cardiomyocyte mechanisms involved in mediating the metabolic effects of elevated fructose. Fructose and sorbitol levels were increased in right atrial appendage tissues of type 2 diabetic patients (2.8- and 1.5-fold increase respectively). Elevated cardiac fructose levels were confirmed in type 2 diabetic rats. Diastolic dysfunction (increased E/e’, echocardiography) was significantly correlated with cardiac sorbitol levels. Elevated myocardial mRNA expression of the fructose-specific transporter, Glut5 (43% increase), and the key fructose-metabolizing enzyme, Fructokinase-A (50% increase) was observed in type 2 diabetic rats (Zucker diabetic fatty rat). In neonatal rat ventricular myocytes, fructose increased glycolytic capacity and cytosolic lipid inclusions (28% increase in lipid droplets/cell). This study provides the first evidence that elevated myocardial fructose and sorbitol are associated with diastolic dysfunction in diabetic patients. Experimental evidence suggests that fructose promotes the formation of cardiomyocyte cytosolic lipid inclusions, and may contribute to lipotoxicity in the diabetic heart.

The adipocytokine resistin is released from epicardial adipose tissue (EAT). Plasma resistin and EAT deposition are independently associated with atrial fibrillation. The EAT secretome enhances arrhythmia susceptibility and inotropy of human myocardium. Therefore, we aimed to determine the effect of resistin on the function of human myocardium and how resistin contributes to the proarrhythmic effect of EAT. EAT biopsies were obtained from 25 cardiac surgery patients. Resistin levels were measured by ELISA in 24-h EAT culture media ( n = 8). The secretome resistin concentrations increased over the culture period to a maximal level of 5.9 ± 1.2 ng/mL. Coculture with β-adrenergic agonists isoproterenol ( n = 4) and BRL37344 ( n = 13) had no effect on EAT resistin release. Addition of resistin (7, 12, 20 ng/mL) did not significantly increase the spontaneous contraction propensity of human atrial trabeculae ( n = 10) when given alone or in combination with isoproterenol. Resistin dose-dependently increased trabecula-developed force (maximal 2.9-fold increase, P < 0.0001), as well as the maximal rates of contraction (2.6-fold increase, P = 0.002) and relaxation (1.8-fold increase, P = 0.007). Additionally, the postrest potentiation capacity of human trabeculae was reduced at all resistin doses, suggesting that the inotropic effect induced by resistin might be due to altered sarcoplasmic reticulum Ca2+ handling. EAT resistin release is not modulated by common arrhythmia triggers. Furthermore, exogenous resistin does not promote arrhythmic behavior in human atrial trabeculae. Resistin does, however, induce an acute dose-dependent positive inotropic and lusitropic effect.

We aimed to investigate the correlation between epicardial adipose tissue (EAT) and body mass index (BMI) in different ethnic groups in New Zealand.The study included 205 individuals undergoing open heart surgery. Māori and Pacific groups were combined to increase statistical power. EAT was measured using 2D echocardiography.There were 164 New Zealand Europeans (NZE) and 41 Māori/Pacific participants. The mean (SD) age of the study group was 67.9 (10.1) years, 69.1 (9.5) for NZE and 63.5 (11.4) for Māori/Pacific. BMI was 29.6 (5.5) kg/m2 for NZE and 31.8 (6.2) for Māori/Pacific. EAT thickness was 6.2 (2.2) mm and 6.0 (1.8) mm for NZE and Māori/Pacific, respectively. Using univariate linear regression, BMI showed moderate correlation with EAT in NZE (R2=0.26, p0.001); however, there was no significant correlation between BMI and EAT in Māori/Pacific patients (R2=0.05, p=0.17). Using multivariate analysis, BMI remained a significant predictor of EAT thickness in NZE (R2 =0.27, p0.001).BMI was associated with EAT thickness in NZE patients, but not in Māori/Pacific patients. The same level of BMI can carry different connotations of risk in different ethnic groups, with BMI likely being an inconsistent measure of obesity in in Māori/Pacific patients.

Heart weight is routinely measured at postmortem examination and is critical to determine whether the heart is enlarged (ie, cardiomegaly). Cardiomegaly has the potential to cause sudden death by being electrically unstable, resulting in fatal arrhythmias. The majority of fatal cardiac arrhythmias is ventricular in origin and is assumed that ventricular size is disproportionately larger in cardiomegaly. This prospective study compared ventricular weight (VW) and total heart weight (THW) in 40 consecutive cases. The results, unexpectedly, showed that VW increases proportionally and linearly with THW in normal and enlarged hearts (THW, >500 g) and did not increase disproportionally with increased THW. The ratio of VW/THW did not have any significant correlation or difference with sex, height, weight, and cardiac causes of death but did have a negative correlation with age. Further studies are indicated to document the morphological changes when the heart enlarges, which may aid in understanding the pathophysiology of sudden death from cardiomegaly.

Purpose Increasing cohorts of patients present with diabetic cardiomyopathy, and with no targeted options, treatment often rely on generic pharmaceuticals such as β‐blockers. β‐blocker efficacy is heterogenous, with second generation β‐blocker metoprolol selectively inhibiting β1‐AR, while third generation β‐blocker carvedilol has α1‐AR inhibition, antioxidant, and anti‐apoptotic actions alongside nonselective β‐AR inhibition. These additional properties have led to the hypothesis that carvedilol may improve cardiac contractility in the diabetic heart to a greater extent than metoprolol. The present study aimed to compare the efficacy of metoprolol and carvedilol on myocardial function in animal models and cardiac tissue from patients with type 2 diabetes and preserved ejection fraction. Methods Echocardiographic examination of cardiac function and assessment of myocardial function in isolated trabeculae was carried out in patients with and without diabetes undergoing coronary artery bypass grafting (CABG) who were prescribed metoprolol or carvedilol. Equivalent measures were undertaken in Zucker Diabetic Fatty (ZDF) rats following 4 weeks treatment with metoprolol or carvedilol. Results Patients receiving carvedilol compared to metoprolol had no difference in cardiac function, and no difference was apparent in myocardial function between β‐blockers. Both β‐blockers similarly improved myocardial function in diabetic ZDF rats treated for 4 weeks, without significantly affecting in vivo cardiac function. Conclusions Metoprolol and carvedilol were found to have no effect on cardiac function in type 2 diabetes with preserved ejection fraction, and were similarly effective in preventing myocardial dysfunction in ZDF rats., In this manuscript, we present data comparing the effects of carvedilol and metoprolol on in vivo and in vitro cardiac function in both diabetic and non‐diabetic human patients, as well as in a rat model of type 2 diabetes (Zucker Diabetic Fatty rats). Our data demonstrate that both carvedilol and metoprolol are able to improve the contractility of cardiac muscle from diabetic humans and rats, as well as preserving cardiac function in both models. Importantly, we saw no extra improvement in individuals or animals that received carvedilol over those who received metoprolol, suggesting that any improvement in health outcomes provided by carvedilol (as seen in the COMET study) are not derived from differences in the contractile function of the cardiac muscle.

Acute myocardial infarction (MI) triggers an adverse increase in cardiac sympathetic nerve activity (SNA). Whereas β-adrenergic receptor (β-AR) blockers are routinely used for the management of MI, they may also counter β-AR-mediated vasodilation of coronary vessels. We have reported that ghrelin prevents sympathetic activation following MI. Whether ghrelin modulates coronary vascular tone following MI, either through the modulation of SNA or directly as a vasoactive mediator, has never been addressed. We used synchrotron microangiography to image coronary perfusion and vessel internal diameter (ID) in anesthetized Sprague-Dawley rats, before and then again 30 minutes after induction of an MI (left coronary artery ligation). Rats were injected with either saline or ghrelin (150 µg/kg, subcutaneously), immediately following the MI or sham surgery. Coronary angiograms were also recorded following β-AR blockade (propranolol, 2 mg/kg, intravenously). Finally, wire myography was used to assess the effect of ghrelin on vascular tone in isolated human internal mammary arteries (IMAs). Acute MI enhanced coronary perfusion to nonischemicregions through dilation of small arterioles (ID 50 to 250 µm) and microvessel recruitment, irrespective of ghrelin treatment. In ghrelin-treated rats, β-AR blockade did not alter the ischemia-induced vasodilation, yet in saline-treated rats, β-AR blockade abolished the vasodilation of small arterioles. Finally, ghrelin caused a dose-dependent vasodilation of IMA rings (preconstricted with phenylephrine). In summary, this study highlights ghrelin as a promising adjunct therapy that can be used in combination with routine β-AR blockade treatment for preserving coronary blood flow and cardiac performance in patients who suffer an acute MI.

Background Attenuated increases in ventricular stroke volume during exercise are common in type 2 diabetes and contribute to reduced aerobic capacity. The purpose of this study was to determine whether impaired ventricular filling or reduced systolic ejection were responsible for the attenuated stroke volume reserve in people with uncomplicated type 2 diabetes. Methods Peak aerobic capacity and total blood volume were measured in 17 people with diabetes and 16 non-diabetic controls with no evidence of cardiovascular disease. Left ventricular volumes and other systolic and diastolic functional parameters were measured with echocardiography at rest and during semi-recumbent cycle ergometry at 40 and 60% of maximal aerobic power and compared between groups. Results People with diabetes had reduced peak aerobic capacity and heart rate reserve, and worked at lower workloads than non-diabetic controls. Cardiac output, stroke volume and ejection fraction were not different at rest, but increased less in people with diabetes during exercise. Left ventricular end systolic volume was not different between groups in any condition but end diastolic volume, although not different at rest, was smaller in people with diabetes during exercise. Total blood volume was not different between the groups, and was only moderately associated with left ventricular volumes. Conclusions People with type 2 diabetes exhibit an attenuated increase in stroke volume during exercise attributed to an inability to maintain/increase left ventricular filling volumes at higher heart rates. This study is the first to determine the role of filling in the blunted cardiac reserve in adults with type 2 diabetes. Electronic supplementary material The online version of this article (10.1186/s12933-017-0644-1) contains supplementary material, which is available to authorized users.

Epicardial adipose tissue (EAT) deposition has a strong clinical association with atrial arrhythmias; however, whether a direct functional interaction exists between EAT and the myocardium to induce atrial arrhythmias is unknown. Therefore, we aimed to determine whether human EAT can be an acute trigger for arrhythmias in human atrial myocardium. Human trabeculae were obtained from right atrial appendages of patients who have had cardiac surgery ( n = 89). The propensity of spontaneous contractions (SCs) in the trabeculae (proxy for arrhythmias) was determined under physiological conditions and during known triggers of SCs (high Ca2+, β-adrenergic stimulation). To determine whether EAT could trigger SCs, trabeculae were exposed to superfusate of fresh human EAT, and medium of 24 h-cultured human EAT treated with β1/2 (isoproterenol) or β3 (BRL37344) adrenergic agonists. Without exposure to EAT, high Ca2+ and β1/2-adrenergic stimulation acutely triggered SCs in, respectively, 47% and 55% of the trabeculae that previously were not spontaneously active. Acute β3-adrenergic stimulation did not trigger SCs. Exposure of trabeculae to either superfusate of fresh human EAT or untreated medium of 24 h-cultured human EAT did not induce SCs; however, specific β3-adrenergic stimulation of EAT did trigger SCs in the trabeculae, either when applied to fresh (31%) or cultured (50%) EAT. Additionally, fresh EAT increased trabecular contraction and relaxation, whereas media of cultured EAT only increased function when treated with the β3-adrenergic agonist. An acute functional interaction between human EAT and human atrial myocardium exists that increases the propensity for atrial arrhythmias, which depends on β3-adrenergic rather than β1/2-adrenergic stimulation of EAT.

Type 2 diabetes is associated with reduced left ventricular reserve. It is unclear whether exercise training improves left ventricular function in people with type 2 diabetes.This study aimed to determine whether 3 months of high-intensity interval training (HIIT) improves left ventricular function during exercise in adults with type 2 diabetes.Participants performed a V˙O2peak test and received a DXA scan and total blood volume measurement at baseline. Left ventricular end-diastolic volume (LVEDV), left ventricular end-systolic volume (LVESV), and left ventricular stroke volume (LVSV) were then measured at rest and during low- and moderate-intensity semirecumbent exercise in adults with type 2 diabetes before and after 3 months of HIIT (n = 11) or no training (control) (n = 5). The effects of HIIT were determined using repeated-measures ANOVA.HIIT increased V˙O2peak by approximately 15% (P0.002) but did not change body composition or total blood volume. LVESV decreased and LVEDV and LVSV increased from rest to moderate-intensity exercise in both groups at baseline (all P0.01). Three months of HIIT increased LVEDV (P = 0.008) and LVSV (P = 0.02) at all conditions, but there was no difference in controls (all P0.05). HIIT augmented the reduction in LVESV from rest to moderate-intensity exercise (P0.04), but LVESV was unchanged in controls. Increased LVEDV explained 51% of the change in LVSV after HIIT intervention. Mitral inflow parameters and mitral annular velocities were unaffected by HIIT (all P0.05).HIIT training increased the LVSV response to exercise in adults with type 2 diabetes. These data suggest that HIIT can improve LV filling and emptying during exercise and reverse early cardiac consequences of type 2 diabetes.

What is the central question of this study? Are there specific contributions of βImpaired β-adrenoceptor (β-AR) responsiveness causes cardiac vulnerability in patients with type 2 diabetes, but the independent contributions of β

NEW FINDINGS What is the central question of the study? Is the reduced signalling of AMP-activated protein kinase (AMPK), a key regulator of energy homeostasis in the heart, responsible for the reduced β-adrenergic responsiveness of the heart in obesity? What is the main finding and its importance? Inhibition of AMPK in isolated hearts prevented the reduced cardiac β-adrenergic responsiveness of obese rats, which was accompanied by reduced phosphorylation of AMPK, a proxy of AMPK activity. This suggests a direct functional link between β-adrenergic responsiveness and AMPK signalling in the heart, and it suggests that AMPK might be an important target to restore the β-adrenergic responsiveness in the heart in obesity. ABSTRACT The obesity epidemic impacts heavily on cardiovascular health, in part owing to changes in cardiac metabolism. AMP-activated protein kinase (AMPK) is a key regulator of energy homeostasis in the heart and is regulated by β-adrenoceptors (β-ARs) in normal conditions. In obesity, chronic sympathetic overactivation leads to impaired cardiac β-AR responsiveness, although it is unclear whether AMPK signalling, downstream of β-ARs, contributes to this dysfunction. Therefore, we aimed to determine whether reduced AMPK signalling is responsible for the reduced β-AR responsiveness in obesity. In isolated hearts of lean and obese Zucker rats, we tested β-AR responsiveness to the β1 -AR agonist isoprenaline (ISO, 1 × 10-10 to 5 × 10-8 m) in the absence and presence of the AMPK inhibitor, compound C (CC, 10 μm). The β1 -AR expression and AMPK phosphorylation were assessed by Western blot. β-Adrenergic responsiveness was reduced in the hearts of obese rats (logEC50 of ISO-developed pressure dose-response curves: lean -8.53 ± 0.13 × 10x m versus obese -8.35 ± 0.10 × 10x m ; P

Background Calcium/calmodulin-dependent kinase II-delta (CaMKIIδ) activity is enhanced during hyperglycemia and has been shown to alter intracellular calcium handling in cardiomyocytes, ultimately leading to reduced cardiac performance. However, the effects of CaMKIIδ on cardiac contractility during type 2 diabetes are undefined. Methods We examined the expression and activation of CaMKIIδ in right atrial appendages from non-diabetic and type 2 diabetic patients (n = 7 patients per group) with preserved ejection fraction, and also in right ventricular tissue from Zucker Diabetic Fatty rats (ZDF) (n = 5–10 animals per group) during early diabetic cardiac dysfunction, using immunoblot. We also measured whole heart function of ZDF and control rats using echocardiography. Then we measured contraction and relaxation parameters of isolated trabeculae from ZDF to control rats in the presence and absence of CaMKII inhibitors. Results CaMKIIδ phosphorylation (at Thr287) was increased in both the diabetic human and animal tissue, indicating increased CaMKIIδ activation in the type 2 diabetic heart. Basal cardiac contractility and relaxation were impaired in the cardiac muscles from the diabetic rats, and CaMKII inhibition with KN93 partially restored contractility and relaxation. Autocamtide-2-related-inhibitor peptide (AIP), another CaMKII inhibitor that acts via a different mechanism than KN93, fully restored cardiac contractility and relaxation. Conclusions Our results indicate that CaMKIIδ plays a key role in modulating performance of the diabetic heart, and moreover, suggest a potential therapeutic role for CaMKII inhibitors in improving myocardial function during type 2 diabetes.

Background Diabetes promotes progressive loss of cardiac cells, which are replaced by a fibrotic matrix, resulting in the loss of cardiac function. In the current study we sought to identify if excessive autophagy plays a major role in inducing this progressive loss. Methods and results Immunofluorescence and western blotting analysis of the right atrial appendages collected from diabetic and non-diabetic patients undergoing coronary artery bypass graft surgery showed a marked increase in the level of autophagy in the diabetic heart, as evidenced by increased expression of autophagy marker LC3B-II and its mediator Beclin-1 and decreased expression of p62, which incorporates into autophagosomes to be efficiently degraded. Moreover, a marked activation of pro-apoptotic caspase-3 was observed. Electron microscopy showed increased autophagosomes in the diabetic heart. In vivo measurement of autophagic flux by choloroquine injection resulted in further enhancement of LC3B-II in the diabetic myocardium, confirming increased autophagic activity in the type-2 diabetic heart. Importantly, in-vitro genetic depletion of beclin-1 in high glucose treated adult rat cardiomyocytes markedly inhibited the level of autophagy and subsequent apoptotic cell death. Conclusions These findings demonstrate the pathological role of autophagy in the type-2 diabetic heart, opening up a potentially novel therapeutic avenue for the treatment of diabetic heart disease.

Epicardial adipose tissue (EAT) deposition has a strong association with aspects of metabolic dysfunction, including obesity. The size of the EAT adipocytes in relation to obesity, however, has rarely been researched. Therefore, to contextualise EAT within the broader framework of pathophysiological adipocyte size changes in obesity, we aimed to determine whether EAT adipocyte size is associated with body mass index (BMI).During routine post-mortem examination, adipose tissue biopsies were obtained from four depots of 43 cases, including EAT, as well as pericardial (PAT), appendix mesenteric (AAT), and clavicular subcutaneous (SAT) adipose tissues. Tissues were fixed, sectioned, and stained using haematoxylin and eosin. The size (measured as area) of each adipocyte imaged from the depots was analysed in relation to BMI.Mean size of EAT adipocytes was significantly smaller than that from SAT and AAT depots, while not differing from PAT adipocytes. BMI positively correlated with the size of adipocytes isolated from SAT (r=0.5893, P.0001), PAT (r=0.5854, P.0001), and AAT (r=0.5829, P.0001) depots, but not from EAT (r=0.1242, P=.4274), even after multivariate adjustment for age and sex.EAT adipocyte size is not associated with increased BMI despite significant associations within adipocytes from other adipose depots.

a Department of Physiology — HeartOtago, Otago School of Medical Sciences, University of Otago, Dunedin, New Zealand b Department of Cardiothoracic Surgery, Dunedin School of Medicine, Dunedin Hospital, Dunedin, New Zealand c Department of Medicine — HeartOtago, Dunedin School of Medicine, Dunedin Hospital, Dunedin, New Zealand d NIHR Oxford Biomedical Research Centre, John Radcliffe Hospital, Oxford, United Kingdom

What is the central question of the study? The sympathetic system regulates heart rate via β-adrenoceptors; this is impaired during diabetes. However, the specific β-adrenoceptor subtype contributions in heart rate regulation in diabetes in vivo are unknown. What is the main finding and its importance? Telemetric recordings in conscious non-diabetic and type 2 diabetic rats demonstrated that the β

Type 2 diabetes (T2D) is associated with reduced cardiac reserve and aerobic capacity. Altered myocardial autonomic nervous regulation has been demonstrated in humans with diabetes (indirectly) and animal models (directly). Purpose: This study aimed to determine the chronotopic and inotropic response of the type 2 diabetic heart to β-adrenergic stimulation. Methods: Eight people with uncomplicated T2D and seven matched controls performed a dual-energy x-ray absorptiometry scan and V˙O2peak test. Plasma catecholamines were determined at rest and during peak exercise. On a second visit, HR and left ventricular contractility were assessed using echocardiography during supine rest, parasympathetic blockade (atropine), and during incremental β-adrenergic stimulation (dobutamine). Results: V˙O2peak and HR reserve were lower in T2D (P < 0.05) as expected. Both groups increased norepinephrine comparably (P = 0.23) during peak exercise; however, epinephrine increased less in the T2D group (P < 0.05). The dobutamine dose required to achieve 85% of age-predicted maximal HR was 36% higher in CON (P < 0.05). Resting HR was higher (P < 0.01) and stroke volume indexed to fat free mass was smaller (P < 0.05) in T2D. During dobutamine infusion the response (% change) in HR, end-diastolic volumeFFM, stroke volume, ejection fraction, and cardiac output were not different between the groups. However, HR was higher (P < 0.01) and end-diastolic volume indexed to fat free mass (P < 0.01), stroke volumeFFM (P < 0.01), ejection fraction (P < 0.05), and stroke work (P < 0.01) were lower in T2D. Conclusions: Although the type 2 diabetic heart worked at smaller volumes, the HR and contractile response to β-adrenergic stimulation were unaffected by diabetes. The reduced cardiac reserve observed in uncomplicated T2D was not explained by impaired myocardial sympathetic responsiveness but may reflect changes in the loading conditions or function of the diabetic left ventricle.

Background Emerging evidence suggests that microRNAs (miRs) could be a potential biomarker to identify early molecular alterations in the heart. HDL are the major carriers for miRs into the circulation. This study tested whether changes in the level of HDL could affect the diagnostic sensitivity of miRs. Methods and results Peripheral blood samples were collected from 20 diabetic and 22 age and gender matched non-diabetic patients undergoing coronary artery bypass graft (CABG) surgery for ischemic heart disease (IHD). Total RNA was extracted from the separated plasma and stored in −80°C. Reverse transcription and amplification using specific primers against cardio-enriched miR-1, -34a, -126, -133, and -499 showed significant correlation between HDL levels and miR-1, -133 and -499. Importantly, normalization of miR levels with HDL showed a significant downregulation of miR-1, -133 and -499 in diabetic plasma, which was not observed before normalization with HDL levels. Conclusion Normalization of circulating miR levels with HDL increases the diagnostic sensitivity of circulating miRs.

Background Inhaled carbon monoxide (CO) appears to have beneficial effects on endotoxemia-induced impairment of hypoxic pulmonary vasoconstriction (HPV). This study aims to specify correct timing of CO application, it’s biochemical mechanisms and effects on inflammatory reactions. Methods Mice (C57BL/6; n = 86) received lipopolysaccharide (LPS, 30 mg/kg) intraperitoneally and subsequently breathed 50 ppm CO continuously during defined intervals of 3, 6, 12 or 18 h. Two control groups received saline intraperitoneally and additionally either air or CO, and one control group received LPS but breathed air only. In an isolated lung perfusion model vasoconstrictor response to hypoxia (FiO2 = 0.01) was quantified by measurements of pulmonary artery pressure. Pulmonary capillary pressure was estimated by double occlusion technique. Further, inflammatory plasma cytokines and lung tissue mRNA of nitric-oxide-synthase-2 (NOS-2) and heme oxygenase-1 (HO-1) were measured. Results HPV was impaired after LPS-challenge (p

Controlled studies of male and female subjects with type 2 diabetes mellitus (DM) of short duration (~3–5 years) show that DM reduces peakV˙O2(L·min−1and mL·kg−1·min−1) by an average of 12–15% and induces a greater slowing of the dynamic response of pulmonaryV˙O2during submaximal exercise. These effects occur in individuals less than 60 years of age but are reduced or absent in older males and are consistently associated with significant increases in the exercise pressor response despite normal resting blood pressure. This exaggerated pressor response, evidence of exertional hypertension in DM, is manifest during moderate submaximal exercise and coincides with a more constrained vasodilation in contracting muscles. Maximum vasodilation during contractions involving single muscle groups is reduced by DM, and the dynamic response of vasodilation during submaximal contractions is slowed. Such vascular constraint most likely contributes to exertional hypertension, impairs dynamic and peakV˙O2responses, and reduces exercise tolerance. There is a need to establish the effect of DM on dynamic aspects of vascular control in skeletal muscle during whole-body exercise and to clarify contributions of altered cardiovascular control and increased arterial stiffness to exertional hypertension.

Right ventricular (RV) pressure overload causes right ventricular hypertrophy in several types of pulmonary and congenital heart diseases. The associated cardiac dysfunction has generally been attributed to alterations in RV function. However, due to global neurohormonal adaptations and mechanical ventricular interaction left ventricular (LV) function could be affected as well.Therefore,LV function, RV function and their interaction were studied in rats with monocrotaline (MCT)-induced RV hypertrophy and control rats. MCT (30 mg/kg) was used to induce pulmonary hypertension, which resulted, after 28 days, in marked RV hypertrophy (RV-weight: control 220 +/- 15,MCT 437 +/- 34mg,p0.05). In Langendorff-perfused hearts with balloons inserted in both the LV and the RV, the diastolic pressure-volume relations showed increased stiffness, and relaxation was prolonged in the LV and RV in the MCT group compared to controls. In the MCT group, developed pressures were increased only in the RV. An increase of LV volume increased RV diastolic pressure to a similar extent in both groups. However, an increase in RV volume did not affect LV diastolic pressure in controls, but significantly increased LV diastolic pressure in the MCT group. LV and RV developed pressure-volume relations were not affected. Calculated circumferential end-diastolic wall stresses (sigma) were larger in the MCT group (LV-sigma: 0.55 +/- 0.02, RV-sigma: 1.94 +/- 0.30 kN/m(2), both p0.05 to control) compared to controls (LV-sigma: 0.34 +/- 0.06,RV-sigma: 1.23 +/- 0.46 kN/m2). In the MCT group, collagen content was increased in the LV, septum and RV compared to controls. In conclusion, structural changes of the RV and LV result in depressed LV diastolic function during RV hypertrophy.

Objective: In human heart failure β-adrenergic-mediated protein kinase A (PKA) activity is down-regulated, while protein kinase C (PKC) activity is up-regulated. PKC-mediated myofilament protein phosphorylation might be detrimental for contractile function in cardiomyopathy. This study was designed to reveal the effects of PKC on myofilament function in human myocardium under basal conditions and upon modulation of protein phosphorylation by PKA and phosphatases. Methods: Isometric force was measured at different [Ca 2+] in single permeabilized cardiomyocytes from non-failing and failing human left ventricular tissue. Basal phosphorylation of myofilament proteins and the influence of PKC, PKA, and phosphatase treatments were analyzed by one- and two-dimensional gel electrophoresis, Western immunoblotting, and ELISA. Results: Troponin I (TnI) phosphorylation at the PKA sites was decreased in failing compared to non-failing hearts and correlated well with myofilament Ca2+ sensitivity (pCa50). Incubation with the catalytic domain of PKC slightly decreased maximal force under basal conditions, but not following PKA and phosphatase pretreatments. PKC reduced Ca2+ sensitivity to a larger extent in failing (ΔpCa50 = 0.19 ± 0.03) than in non-failing (ΔpCa50 = 0.08 ± 0.01) cardiomyocytes. This shift was reduced, though still significant, when PKC was preceded by PKA, while PKA following PKC did not further decrease pCa 50. Protein analysis indicated that PKC phosphorylated PKA sites in human TnI and increased phosphorylation of troponin T, while myosin light chain phosphorylation remained unaltered. Conclusion: In human myocardium PKC-mediated myofilament protein phosphorylation only has a minor effect on maximal force development. The PKC-mediated decrease in Ca2+ sensitivity may serve to improve diastolic function in failing human myocardium in which PKA-mediated TnI phosphorylation is decreased.

Ischemic heart disease is more apparent in the subendocardial than in subepicardial layers. We investigated coronary pressure-flow relations in layers of the isolated rat left ventricle, using 15 microm microspheres during diastolic and systolic arrest in the vasodilated coronary circulation. A special cannula allowed for selective determination of left main stem pressure-flow relations. Arterio-venous shunt flow was derived from microspheres in the venous effluent. We quantitatively investigated the pressure-flow relations in diastolic arrest (n=8), systolic arrest at normal contractility (n=8) and low contractility (n=6). In all three groups normal and large ventricular volume was studied. In diastolic arrest, at a perfusion pressure of 90 mmHg, subendocardial flow is larger than subepicardial flow, i.e., the endo/epi ratio is approximately 1.2. In systolic arrest the endo/epi ratio is approximately 0.3, and subendocardial flow and subepicardial flow are approximately 12% and approximately 55% of their values during diastolic arrest. The endo/epi ratio in diastolic arrest decreases with increasing perfusion pressure, while in systole the ratio increases. The slope of the pressure-flow relations, i.e., inverse of resistance, changes by a factor of approximately 5.3 in the subendocardium and by a factor approximately 2.2 in the subepicardium from diastole to systole. Lowering contractility affects subendocardial flow more than subepicardial flow, but both contractility and ventricular volume changes have only a limited effect on both subendocardial and subepicardial flow. The resistance (inverse of slope) of the total left main stem pressure-flow relation changes by a factor of approximately 3.4 from diastolic to systolic arrest. The zero-flow pressure increases from diastole to systole. Thus, coronary perfusion flow in diastolic arrest is larger than systolic arrest, with the largest difference in the subendocardium, as a result of layer dependent increases in vascular resistance and intercept pressure. Shunt flow is larger in diastolic than in systolic arrest, and increases with perfusion pressure. We conclude that changes in contractility and ventricular volume have a smaller effect on pressure-flow relations than diastolic-systolic differences. A synthesis of models accounting for the effect of cardiac contraction on perfusion is suggested.

Diabetic patients have increased cardiac complications during surgery, possibly due to impaired autonomic regulation. Anesthesia lowers blood pressure and heart rate (HR), whereas surgical intervention has opposing effects. The interaction of anesthesia and surgical intervention on hemodynamics in diabetes is unknown, despite being a potential perioperative risk factor. We aimed to determine the effect of diabetes on the integrative interaction between hemodynamics, anesthesia, and surgical incision. Zucker type 2 diabetic rats (DM) and their nondiabetic littermates (ND) were implanted with an intravenous port for drug delivery, and a radiotelemeter to measure mean arterial blood pressure (MAP) and derive HR (total n = 50). Hemodynamic pharmacological responses were assessed under conscious, isoflurane anesthesia (~2–2.5%), and anesthesia–surgical conditions; the latter performed as a laparotomy. MAP was not different between groups under conscious conditions (ND 120 ± 6 vs. DM 131 ± 4 mmHg, P > 0.05). Anesthesia reduced MAP, but not differently in DM (ND −30 ± 6 vs. DM −38 ± 4 ΔmmHg, P > 0.05). Despite adequate anesthesia, surgical incision increased MAP, which tended to be less in DM (ND +21 ± 4 vs. DM +13 ± 2 ΔmmHg, P = 0.052). Anesthesia disrupted central baroreflex HR responses to sympathetic activation (sodium nitroprusside 10 μg·kg−1, ND conscious 83 ± 13 vs. anesthetized 16 ± 5 Δbpm; P

Background: Increasing numbers of type 2 diabetic and obese patients with enhanced rates of cardiovascular complications require surgical interventions, however they have a higher incidence of perioperative haemodynamic complications, which has been linked to adrenergic dysfunction. Therefore, we aimed to determine how α- and β-adrenoceptor (AR)-mediated haemodynamic responses are affected by isoflurane anaesthesia in experimental type 2 diabetes and obesity in vivo. Methods: Sixteen-week old male Zucker type 2 Diabetic Fatty (ZDF) rats, Zucker Obese rats and their lean counterparts (n = 7-9 per group) were instrumented with radio telemeters to record blood pressure and heart rate and with vascular access ports for non-invasive intravenous drug delivery in vivo. Haemodynamic effects of α-AR (phenylephrine; 1-100 μg.kg �1 )o rβ-AR (dobutamine; 2-120 μg.kg �1 ) stimulation were assessed under conscious and anaesthetised (isoflurane; 2%) conditions. Results: Vascular α-AR sensitivity was increased in both diabetic (non-diabetic 80±3 vs. diabetic 95±4 ΔmmHg at 100 μg.kg �1 ; p < 0.05) and obese (lean 65 ± 6 vs. obese 84 ± 6 ΔmmHg at 20 μg.kg �1 ; p < 0.05) conscious rats. Interestingly, anaesthesia exacerbated and prolonged the increased α -AR function in both diabetic and obese animals (non-diabetic 51 ± 1 vs. diabetic 68 ± 4 ΔmmHg, lean 61 ± 5 vs. obese 84 ± 2 ΔmmHg at 20 μg.kg �1 ; p < 0.05). Meanwhile, β-AR chronotropic sensitivity was reduced in conscious diabetic and obese rats (non-diabetic 58±7 vs. diabetic 27±8 Δbpm, lean 103± 12 vs. obese 61±9 Δbpm at 15 μg.kg �1 ; p

Elevated sympathetic nerve activity (SNA) coupled with dysregulated β-adrenoceptor (β-AR) signaling is postulated as a major driving force for cardiac dysfunction in patients with type 2 diabetes; however, cardiac SNA has never been assessed directly in diabetes. Our aim was to measure the sympathetic input to and the β-AR responsiveness of the heart in the type 2 diabetic heart. In vivo recording of SNA of the left efferent cardiac sympathetic branch of the stellate ganglion in Zucker diabetic fatty rats revealed an elevated resting cardiac SNA and doubled firing rate compared with nondiabetic rats. Ex vivo, in isolated denervated hearts, the intrinsic heart rate was markedly reduced. Contractile and relaxation responses to β-AR stimulation with dobutamine were compromised in externally paced diabetic hearts, but not in diabetic hearts allowed to regulate their own heart rate. Protein levels of left ventricular β1-AR and Gs (guanine nucleotide binding protein stimulatory) were reduced, whereas left ventricular and right atrial β2-AR and Gi (guanine nucleotide binding protein inhibitory regulatory) levels were increased. The elevated resting cardiac SNA in type 2 diabetes, combined with the reduced cardiac β-AR responsiveness, suggests that the maintenance of normal cardiovascular function requires elevated cardiac sympathetic input to compensate for changes in the intrinsic properties of the diabetic heart.

Rats were exposed to either a footshock stimulus (FS) or emotional stimulus (ES, forced perception of another rat receiving footshocks) during a daily 10-min session for 5 consecutive days. The consequences of FS and ES on their behavioural responsiveness were assessed at different post-stress intervals using a small open-field. FS induced a decrease in ambulation, rearing and sniffing and an increased immobility in the small open field. These effects were present in rats tested immediately after the last session and remained present for at least 15 days. In contrast, ES induced a transient decrease in ambulation and rearing immediately after the last session, but in the period from half an hour until at least 15 days after the stimulus experience, an increase in ambulation, rearing and sniffing was observed. Exposure to one footshock per session for 5 consecutive days or to 10 footshocks in a single session also resulted in a long-lasting reduction in ambulation and sniffing and an increase in immobility. The former regime did not influence the behavioural response of ES rats, but the latter resulted in an increase in ambulation, rearing and sniffing in ES rats. Naloxone (1 mg/kg s.c.) pretreatment antagonized the increased behavioural activity of the ES rats whereas the activity of control and FS animals was not affected, suggesting an involvement of endogenous opioid systems in the behavioural responses observed in ES rats. It is suggested that the behavioural responses of the ES and FS animals are regulated by different mechanisms.

Volatile anesthetics protect the heart against ischemia-reperfusion injury. As an adjunct to general anesthesia, local and regional application of bupivacaine is often used. However, systemic plasma levels of bupivacaine might be cardiodepressant and interfere with sevoflurane-induced cardioprotection. Effects of bupivacaine on sevoflurane-induced cardioprotection were assessed in isolated Langendorff-perfused rat hearts subjected to 35 min of global ischemia followed by 60 min reperfusion. Hearts (n=40) were randomized to different groups: 1. CONTROL; 2. Bupivacaine: addition of 0.125 or 1.0 μg/ml bupivacaine to the perfusate for 40 min prior to ischemia-reperfusion; 3. Sevoflurane: preconditioning induced by three times 5-min episodes of sevoflurane (2.5 vol.%) prior to ischemia-reperfusion; 4. Bupivacaine-sevoflurane: combined application of bupivacaine and sevoflurane. After ischemia-reperfusion, cardioprotection was assessed from infarct size and recovery of ventricular function, and phosphorylation levels of glycogen synthase kinase 3β (GSK3β) and 5'AMP activated protein kinase (AMPK) were determined. Infarct size was reduced in the sevoflurane and bupivacaine-sevoflurane groups (Sevo: 23±7% and Bupi-Sevo: 23±5% vs.59±6%, P0.05). In the bupivacaine group infarct size was reduced as well (34±3%). In the sevoflurane and bupivacaine-sevoflurane groups the recovery of left ventricular function (+dP/dt) was improved (Sevo: 59±2% and Bupi-Sevo: 59±2% vs.47±3%, P0.05), but not in the bupivacaine group (48±3%). AMPK and GSK3β phosphorylation were increased by sevoflurane but not by bupivacaine. Sevoflurane-induced cardioprotection was not affected by bupivacaine in the non-cardiotoxic range. Bupivacaine alone also reduced infarct size. Both anesthetics activated different signaling kinases, indicating the existence of different cardioprotective intracellular signaling cascades.

Background— 5′AMP-activated protein kinase (AMPK), a well-known regulator of cellular energy status, is also implicated in ischemic preconditioning leading to cardioprotection. We hypothesized that AMPK is involved in anesthetic-induced cardioprotection and that this activation is mediated by reactive oxygen species (ROS). Methods and Results— Isolated Langendorff-perfused rat hearts were subjected to 35 minutes of global ischemia (I) followed by 120 minutes of reperfusion (I/R). Hearts were assigned to a control group (Con) or a sevoflurane (Sevo) group receiving 3 times 5-minute episodes of sevoflurane (2.5vol%) before I/R. Phosphorylation of both AMPK and endothelial nitric oxide synthase (eNOS) were determined by Western blot analysis. Cardioprotection was assessed after I/R from recovery of left ventricular pressure and from infarct size (triphenyltetrazolium chloride staining). In the control group, ischemia resulted in a 2-fold increase in phosphorylation levels of AMPK (Con 0.13±0.01 versus Con-I 0.28±0.05, P P P >0.05), but almost doubled the increase in AMPK phosphorylation relative to control after ischemia (Sevo-I 0.48±0.09, P P Conclusions— Sevoflurane-induced AMPK activation protects the heart against ischemia and reperfusion injury and relies on upstream production of ROS.

Right heart failure in pulmonary arterial hypertension (PH) is associated with mechanical ventricular dyssynchrony, which leads to impaired right ventricular (RV) function and, by adverse diastolic interaction, to impaired left ventricular (LV) function as well. However, therapies aiming to restore synchrony by pacing are currently not available. In this proof-of-principle study, we determined the acute effects of RV pacing on ventricular dyssynchrony in PH. Chronic PH with right heart failure was induced in rats by injection of monocrotaline (80 mg/kg). To validate for PH-related ventricular dyssynchrony, rats (6 PH, 6 controls) were examined by cardiac magnetic resonance imaging (9.4 T), 23 days after monocrotaline or sham injection. In a second group (10 PH, 4 controls), the effects of RV pacing were studied in detail, using Langendorff-perfused heart preparations. In PH, septum bulging was observed, coinciding with a reversal of the transseptal pressure gradient, as observed in clinical PH. RV pacing improved RV systolic function, compared with unpaced condition (maximal first derivative of RV pressure: +8.5 ± 1.3%, P < 0.001). In addition, RV pacing markedly decreased the pressure-time integral of the transseptal pressure gradient when RV pressure exceeds LV pressure, an index of adverse diastolic interaction (−24 ± 9%, P < 0.01), and RV pacing was able to resynchronize time of RV and LV peak pressure (unpaced: 9.8 ± 1.2 ms vs. paced: 1.7 ± 2.0 ms, P < 0.001). Finally, RV pacing had no detrimental effects on LV function or coronary perfusion, and no LV preexcitation occurred. Taken together, we demonstrate that, in experimental PH, RV pacing improves RV function and diminishes adverse diastolic interaction. These findings provide a strong rationale for further in vivo explorations.

Background. We previously demonstrated the involvement of the Ca 2+-independent protein kinase C-δ (PKC-δ) isoform in sevoflurane-induced cardioprotection against ischaemia and reperfusion (I/R) injury. Since sevoflurane is known to modulate myocardial Ca2+- handling directly, in this study we investigated the role of the Ca 2+-dependent PKC-α isoform in sevoflurane-induced cardioprotective signalling in relation to reactive oxygen species (ROS), adenosine triphosphate-sensitive mitochondrial K+ (mitoK + ATP) channels, and PKC-δ. Methods. Preconditioned (15 min 3.8 vol% sevoflurane) isolated rat right ventricular trabeculae were subjected to I/R, consisting of 40 min superfusion with hypoxic, glucose-free buffer, followed by normoxic glucose-containing buffer for 60 min. After reperfusion, contractile recovery was expressed as percentage of force development before I/R. The role of PKC-α, ROS, mitoK+ ATP channels, and PKC-δ was established using the following pharmacological inhibitors: Go6976 (GO; 50 nM), n-(2-mercaptopropionyl)-glycine (MPG; 300 μM), 5-hydroxydecanoic acid sodium (5HD; 100 μM), and rottlerin (ROT; 1 μM). Results. Preconditioning of trabeculae with sevoflurane improved contractile recovery after I/R [65 (3)% (I/R + SEVO) vs 47 (3)% (I/R); n = 8; P < 0.05]. This cardioprotective effect was attenuated in trabeculae treated with GO [42 (4)% (I/R + SEVO + GO); P > 0.05 vs (I/R)]. In sevoflurane-treated trabeculae, PKC-α translocated towards mitochondria, as shown by immunofluorescent co-localization analysis. GO and MPG, but not 5HD or ROT, abolished this translocation.ConclusionsSevoflurane improves post-ischaemic contractile recovery via activation of PKC-α. ROS production, but not opening of mitoK+ ATP channels, precedes PKC-α translocation towards mitochondria. This study shows the involvement of Ca2+-dependent PKC-α in addition to the well-established role of Ca2+-independent PKC isoforms in sevoflurane-induced cardioprotection.

During ischemic heart diseases and when heart failure progresses depletion of myocardial energy stores occurs. d-Ribose (R) has been shown to improve cardiac function and energy status after ischemia. Folic acid (FA) is an essential cofactor in the formation of adenine nucleotides. Therefore, we assessed whether chronic R-FA administration during the development of hypertrophy resulted in an improved cardiac function and energy status. In Wistar rats ( n = 40) compensatory right ventricular (RV) hypertrophy was induced by monocrotaline (30 mg/kg; MCT), whereas saline served as control. Both groups received a daily oral dose of either 150 mg·kg−1·day−1dextrose (placebo) or R-FA (150 and 40 mg·kg−1·day−1, respectively). In Langendorff-perfused hearts, RV and left ventricular (LV) pressure development and collagen content as well as total RV adenine nucleotides (TAN), creatine content, and RV and LV collagen content were determined. In the control group R-FA had no effect. In the MCT-placebo group, TAN and creatine content were reduced, RV and LV diastolic pressure-volume relations were steeper, RV systolic pressures were elevated, RV and LV collagen content was increased, and RV-LV diastolic interaction was altered compared with controls. In the MCT-R-FA group, TAN, RV and LV diastolic stiffness, RV and LV collagen content, and RV-LV diastolic interaction were normalized to the values in the control group while creatine content remained depressed and RV systolic function remained elevated. In conclusion, the depression of energy status in compensated hypertrophic myocardium observed was partly prevented by chronic R-FA administration and accompanied by a preservation of diastolic function and collagen deposition.

Collagen degradation is suggested to be responsible for long-term contractile dysfunction in different cardiomyopathies, but the effects of acute and specific collagen type I removal (main type in the heart muscle) on tension have not been studied. We determined the diastolic and developed tension length relations in isometric contracting perfused rat papillary muscles (perfusion pressure 60 cmH2O) before and after acute and specific removal of small collagen struts with the use of purified collagenase type I. At 95% of the maximal length (95% Lmax), diastolic tension increased 20.4 ± 8.1% ( P < 0.05, n = 6) and developed tension increased 15.0 ± 6.7% after collagenase treatment compared with time controls. Treatment increased the diastolic muscle diameter by 7.1 ± 3.4% at 95% Lmax, whereas the change in diameter due to contraction was not changed. Diastolic coronary flow and normalized coronary arterial flow impediment did not change after collagenase treatment. Electron microscopy revealed that the number of small collagen struts, interconnecting myocytes, and capillaries was reduced to ∼32% after treatment. We conclude that removal of the small collagen struts by acute and specific collagen type I degradation increases diastolic and developed tension in perfused papillary muscle. We suggest that diastolic tension is increased due to edema, whereas developed tension is increased because the removal of the struts poses a lower lateral load on the cardiac myocytes, allowing more myocyte thickening.

An increase in coronary perfusion, transversal stretch of the myocardium, increases developed force (Fdev) (Gregg effect) through activation of stretch-activated ion channels (SACs). Lengthening of the muscle, longitudinal stretch of the myocardium, causes an immediate increase in Fdev followed by a slow Fdev increase (Anrep effect). In isometrically contracting perfused papillary muscles of Wistar rats, we investigated whether both effects were based on similar stretch-induced mechanisms by measuring Fdev and intracellular Ca2+ concentration ([Ca2+]i) after a muscle length increase from 85% to 95% L max (length at which maximal isometric force develops) at low and high coronary perfusion before and after inhibition of SACs with gadolinium (10 μmol/l Gd3+). The increase of Fdev and peak [Ca2+]i by the Gregg effect was of similar magnitude as the Anrep effect (from 3.5 ± 0.8 to 3.9 ± 1.2 mN/mm2 and from 3.0 ± 0.7% to 3.8 ± 0.9% normalized [Ca2+]i, means ± SE). SAC blockade completely blunted the increase of Fdev and peak [Ca2+]i by the Gregg effect; however, it did not affect the Anrep effect. The slow force response, but not the calcium response, was augmented by an increase in coronary perfusion. Therefore, increased coronary perfusion, transversal stretch of the myocardium, and muscle lengthening, longitudinal stretch of the myocardium, increase myocardial contraction in the rat through different stretch-triggered mechanisms.

The role of stretch-activated ion channels (SACs) in coronary perfusion-induced increase in cardiac contractility was investigated in isolated isometrically contracting perfused papillary muscles from Wistar rats. A brief increase in perfusion pressure (3–4 s, perfusion pulse, n = 7), 10 repetitive perfusion pulses ( n = 4), or a sustained increase in perfusion pressure (150–200 s, perfusion step, n = 7) increase developed force by 2.7 ± 1.1, 7.7 ± 2.2, and 8.3 ± 2.5 mN/mm2(means ± SE, P < 0.05), respectively. The increase in developed force after a perfusion pulse is transient, whereas developed force during a perfusion step remains increased by 5.1 ± 2.5 mN/mm2( P < 0.05) in the steady state. Inhibition of SACs by addition of gadolinium (10 μmol/l) or streptomycin (40 and 100 μmol/l) blunts the perfusion-induced increase in developed force. Incubation with 100 μmol/l Nω-nitro-l-arginine [nitric oxide (NO) synthase inhibition], 10 μmol/l sodium nitroprusside (NO donation) and 0.1 μmol/l verapamil (L-type Ca2+channel blockade) are without effect on the perfusion-induced increase of developed force. We conclude that brief, repetitive, or sustained increases in coronary perfusion augment cardiac contractility through activation of stretch-activated ion channels, whereas endothelial NO release and L-type Ca2+channels are not involved.

Coronary arterial inflow is impeded and venous outflow is increased as a result of the decrease in coronary vascular volume due to cardiac contraction. We evaluated whether cardiac contraction is influenced by interfering with the changes of the coronary vascular volume over the heart cycle. Length-tension relationships were determined in Tyrode-perfused rat papillary muscle and when coronary vascular volume changes were partly inhibited by filling it with congealed gelatin or perfusing it with a high viscosity dextran buffer. Also, myocyte thickening during contraction was reduced by placing a silicon tube around the muscle. Increasing perfusion pressure from 8 to 80 cmH2O, increased developed tension by ∼40%. When compared with the low perfusion state, developed tension of the gelatin-filled vasculature was reduced to 43 ± 6% at the muscle length where the muscle generates the largest developed tension ( n = 5, means ± SE). Dextran reduced developed tension to 73 ± 6% ( n = 6). The silicon tube, in low perfusion state, reduced the developed tension to 83 ± 7% ( n = 4) of control. Time-control and oxygen-lowering experiments show that the findings are based on mechanical effects. Thus interventions to prevent myocyte thickening reduce developed tension. We hypothesize that when myocyte thickening is prevented, intracellular pressure increases and counteracts the force produced by the contractile apparatus. We conclude that emptying of the coronary vasculature serves a physiological purpose by facilitating cardiomyocyte thickening thereby augmenting force development.

Background Diastolic dysfunction is a key factor in the development and pathology of cardiac dysfunction in diabetes, however the exact underlying mechanism remains unknown, especially in humans. We aimed to measure contraction, relaxation, expression of calcium-handling proteins and fibrosis in myocardium of diabetic patients with preserved systolic function. Methods Right atrial appendages from patients with type 2 diabetes mellitus (DM, n = 20) and non-diabetic patients (non-DM, n = 36), all with preserved ejection fraction and undergoing coronary artery bypass grafting (CABG), were collected. From appendages, small cardiac muscles, trabeculae, were isolated to measure basal and β-adrenergic stimulated myocardial function. Expression levels of calcium-handling proteins, sarcoplasmic reticulum Ca2+ ATPase (SERCA2a) and phospholamban (PLB), and of β1-adrenoreceptors were determined in tissue samples by Western blot. Collagen deposition was determined by picro-sirius red staining. Results In trabeculae from diabetic samples, contractile function was preserved, but relaxation was prolonged (Tau: 74 ± 13 ms vs. 93 ± 16 ms, non-DM vs. DM, p = 0.03). The expression of SERCA2a was increased in diabetic myocardial tissue (0.75 ± 0.09 vs. 1.23 ± 0.15, non-DM vs. DM, p = 0.007), whereas its endogenous inhibitor PLB was reduced (2.21 ± 0.45 vs. 0.42 ± 0.11, non-DM vs. DM, p = 0.01). Collagen deposition was increased in diabetic samples. Moreover, trabeculae from diabetic patients were unresponsive to β-adrenergic stimulation, despite no change in β1-adrenoreceptor expression levels. Conclusions Human type 2 diabetic atrial myocardium showed increased fibrosis without systolic dysfunction but with impaired relaxation, especially during β-adrenergic challenge. Interestingly, changes in calcium-handling protein expression suggests accelerated active calcium re-uptake, thus improved relaxation, indicating a compensatory calcium-handling mechanism in diabetes in an attempt to maintain diastolic function at rest despite impaired relaxation in the diabetic fibrotic atrial myocardium. Our study addresses important aspects of the underlying mechanisms of diabetes-associated diastolic dysfunction, which is crucial to developing new therapeutic treatments.