Coronary hemodynamics and myocardial metabolism during and after pacing stress in normal humans

Current understanding of the contribution of lactate to the cardiovascular system and its therapeutic relevance

Research during the past decades has yielded numerous insights into the presence and function of lactate in the body. Lactate is primarily produced via glycolysis and plays special roles in the regulation of tissues and organs, particularly in the cardiovascular system. In addition to being a net consumer of lactate, the heart is also the organ in the body with the greatest lactate consumption. Furthermore, lactate maintains cardiovascular homeostasis through energy supply and signal regulation under physiological conditions. Lactate also affects the occurrence, development, and prognosis of various cardiovascular diseases. We will highlight how lactate regulates the cardiovascular system under physiological and pathological conditions based on evidence from recent studies. We aim to provide a better understanding of the relationship between lactate and cardiovascular health and provide new ideas for preventing and treating cardiovascular diseases. Additionally, we will summarize current developments in treatments targeting lactate metabolism, transport, and signaling, including their role in cardiovascular diseases.

[Clinical and prognostic effect of repeated ten-day courses of low-intensity laser exposure in patients with coronary heart disease]

The deterioration in the prognosis of coronary heart disease (CHD) is due to the influence of numerous pathophysiological factors, which is almost impossible to handle with only medication. Positive results obtained after one course of laser therapy (LT) in patients with angina pectoris substantiate the possibility of prolonging the effect when using repeated courses of low-intensity laser exposure.

PURPOSE OF THE STUDY

To assess the clinical and prognostic value of repeated courses of low-intensity LT in patients with CHD for 24 months.

MATERIAL AND METHODS

The study involved 40 men (mean age 56.6±8.2 years) with exertional angina pectoris with high (0-I functional class - 40%) and lower (II-III functional class - 60%) exercise tolerance (according to the classification of the Canadian Heart Association). Duration of the study was 24 months. All patients underwent 10-day courses of skin LT in the infrared radiation range every 6 months. Initially and after each course of LT, a bicycle ergometer test was performed with an assessment of the threshold values of blood pressure (BP), double product (DP=systolic BP×heart rate) and the ratio of DP to load power (DP/W). The blood levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) were studied after each course of LT.

RESULTS

Patients had an improvement in their well-being during LT: a decrease in the number of angina attacks, the need for nitroglycerin, antianginal and antihypertensive drugs. A statistically significant increase in exercise tolerance by 33.2-40.1% was revealed since 1 month after each course of LT, according to the results of stress tests. At the same time, the threshold values of blood pressure remained at the initial level, which was regarded as a manifestation of the hypotensive effect. The decrease in the DP/W index by 18.2-29.6% compared with the initial data indicates the energy economization of cardiac activity. LT was accompanied by a statistically significant decrease in blood cholesterol from 6.15±1.26 to 4.84±1.28-5.25±1.53 mmol/l and LDL-C from 4.70±1.16 to 3, 29±1.26-3.96 mmol/l.

CONCLUSION

Long-term clinical and preventive effect, good tolerability, availability, absence of side effects substantiate the possibility of widespread use of repeated courses of laser exposure in coronary heart disease.

PPAR control of metabolism and cardiovascular functions

Peroxisome proliferator-activated receptor-α (PPARα), PPARδ and PPARγ are transcription factors that regulate gene expression following ligand activation. PPARα increases cellular fatty acid uptake, esterification and trafficking, and regulates lipoprotein metabolism genes. PPARδ stimulates lipid and glucose utilization by increasing mitochondrial function and fatty acid desaturation pathways. By contrast, PPARγ promotes fatty acid uptake, triglyceride formation and storage in lipid droplets, thereby increasing insulin sensitivity and glucose metabolism. PPARs also exert antiatherogenic and anti-inflammatory effects on the vascular wall and immune cells. Clinically, PPARγ activation by glitazones and PPARα activation by fibrates reduce insulin resistance and dyslipidaemia, respectively. PPARs are also physiological master switches in the heart, steering cardiac energy metabolism in cardiomyocytes, thereby affecting pathological heart failure and diabetic cardiomyopathy. Novel PPAR agonists in clinical development are providing new opportunities in the management of metabolic and cardiovascular diseases.

Mitochondrial membrane transporters and metabolic switch in heart failure

Mitochondrial dysfunction is widely recognized as a major factor for the progression of cardiac failure. Mitochondrial uptake of metabolic substrates and their utilization for ATP synthesis, electron transport chain activity, reactive oxygen species levels, ion homeostasis, mitochondrial biogenesis, and dynamics as well as levels of reactive oxygen species in the mitochondria are key factors which regulate mitochondrial function in the normal heart. Alterations in these functions contribute to adverse outcomes in heart failure. Iron imbalance and oxidative stress are also major factors for the evolution of cardiac hypertrophy, heart failure, and aging-associated pathological changes in the heart. Mitochondrial ATP-binding cassette (ABC) transporters have a key role in regulating iron metabolism and maintenance of redox status in cells. Deficiency of mitochondrial ABC transporters is associated with an impaired mitochondrial electron transport chain complex activity, iron overload, and increased levels of reactive oxygen species, all of which can result in mitochondrial dysfunction. In this review, we discuss the role of mitochondrial ABC transporters in mitochondrial metabolism and metabolic switch, alterations in the functioning of ABC transporters in heart failure, and mitochondrial ABC transporters as possible targets for therapeutic intervention in cardiac failure.

Improved workflow for mass spectrometry-based metabolomics analysis of the heart

MS-based metabolomics methods are powerful techniques to map the complex and interconnected metabolic pathways of the heart; however, normalization of metabolite abundance to sample input in heart tissues remains a technical challenge. Herein, we describe an improved GC-MS-based metabolomics workflow that uses insoluble protein-derived glutamate for the normalization of metabolites within each sample and includes normalization to protein-derived amino acids to reduce biological variation and detect small metabolic changes. Moreover, glycogen is measured within the metabolomics workflow. We applied this workflow to study heart metabolism by first comparing two different methods of heart removal: the Langendorff heart method (reverse aortic perfusion) and in situ freezing of mouse heart with a modified tissue freeze-clamp approach. We then used the in situ freezing method to study the effects of acute β-adrenergic receptor stimulation (through isoproterenol (ISO) treatment) on heart metabolism. Using our workflow and within minutes, ISO reduced the levels of metabolites involved in glycogen metabolism, glycolysis, and the Krebs cycle, but the levels of pentose phosphate pathway metabolites and of many free amino acids remained unchanged. This observation was coupled to a 6-fold increase in phosphorylated adenosine nucleotide abundance. These results support the notion that ISO acutely accelerates oxidative metabolism of glucose to meet the ATP demand required to support increased heart rate and cardiac output. In summary, our MS-based metabolomics workflow enables improved quantification of cardiac metabolites and may also be compatible with other methods such as LC or capillary electrophoresis.

Diabetic cardiomyopathy: Pathophysiology, theories and evidence to date

The prevalence of type 2 diabetes (T2D) has increased worldwide and doubled over the last two decades. It features among the top 10 causes of mortality and morbidity in the world. Cardiovascular disease is the leading cause of complications in diabetes and within this, heart failure has been shown to be the leading cause of emergency admissions in the United Kingdom. There are many hypotheses and well-evidenced mechanisms by which diabetic cardiomyopathy as an entity develops. This review aims to give an overview of these mechanisms, with particular emphasis on metabolic inflexibility. T2D is associated with inefficient substrate utilisation, an inability to increase glucose metabolism and dependence on fatty acid oxidation within the diabetic heart resulting in mitochondrial uncoupling, glucotoxicity, lipotoxicity and initially subclinical cardiac dysfunction and finally in overt heart failure. The review also gives a concise update on developments within clinical imaging, specifically cardiac magnetic resonance studies to characterise and phenotype early cardiac dysfunction in T2D. A better understanding of the pathophysiology involved provides a platform for targeted therapy in diabetes to prevent the development of early heart failure with preserved ejection fraction.

Lactate metabolism: historical context, prior misinterpretations, and current understanding

Lactate (La^-) has long been at the center of controversy in research, clinical, and athletic settings. Since its discovery in 1780, La^- has often been erroneously viewed as simply a hypoxic waste product with multiple deleterious effects. Not until the 1980s, with the introduction of the cell-to-cell lactate shuttle did a paradigm shift in our understanding of the role of La^- in metabolism begin. The evidence for La^- as a major player in the coordination of whole-body metabolism has since grown rapidly. La^- is a readily combusted fuel that is shuttled throughout the body, and it is a potent signal for angiogenesis irrespective of oxygen tension. Despite this, many fundamental discoveries about La^- are still working their way into mainstream research, clinical care, and practice. The purpose of this review is to synthesize current understanding of La^- metabolism via an appraisal of its robust experimental history, particularly in exercise physiology. That La^- production increases during dysoxia is beyond debate, but this condition is the exception rather than the rule. Fluctuations in blood [La^-] in health and disease are not typically due to low oxygen tension, a principle first demonstrated with exercise and now understood to varying degrees across disciplines. From its role in coordinating whole-body metabolism as a fuel to its role as a signaling molecule in tumors, the study of La^- metabolism continues to expand and holds potential for multiple clinical applications. This review highlights La^-'s central role in metabolism and amplifies our understanding of past research.

Abnormal Glucose Tolerance Is Associated with a Reduced Myocardial Metabolic Flexibility in Patients with Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is characterized by a metabolic shift from fat to carbohydrates and failure to increase myocardial glucose uptake in response to workload increments. We verified whether this pattern is influenced by an abnormal glucose tolerance (AGT). In 10 patients with DCM, 5 with normal glucose tolerance (DCM-NGT) and 5 with AGT (DCM-AGT), and 5 non-DCM subjects with AGT (N-AGT), we measured coronary blood flow and arteriovenous differences of oxygen and metabolites during Rest, Pacing (at 130 b/min), and Recovery. Myocardial lactate exchange and oleate oxidation were also measured. At Rest, DCM patients showed a reduced nonesterified fatty acids (NEFA) myocardial uptake, while glucose utilization increased only in DCM-AGT. In response to Pacing, glucose uptake promptly rose in N-AGT (from 72 ± 21 to 234 ± 73 nmol/min/g, p < 0.05), did not change in DCM-AGT, and slowly increased in DCM-NGT. DCM-AGT sustained the extra workload by increasing NEFA oxidation (from 1.3 ± 0.2 to 2.9 ± 0.1 μmol/min/gO2 equivalents, p < 0.05), while DCM-NGT showed a delayed increase in glucose uptake. Substrate oxidation rates paralleled the metabolites data. The presence of AGT in patients with DCM exacerbates both the shift from fat to carbohydrates in resting myocardial metabolism and the reduced myocardial metabolic flexibility in response to an increased workload. This trial is registered with ClinicalTrial.gov NCT02440217.

β2-adrenergic stress evaluation of coronary endothelial-dependent vasodilator function in mice using (11)C-acetate micro-PET imaging of myocardial blood flow and oxidative metabolism

Background

Endothelial dysfunction is associated with vascular risk factors such as dyslipidemia, hypertension, and diabetes, leading to coronary atherosclerosis. Sympathetic stress using cold-pressor testing (CPT) has been used to measure coronary endothelial function in humans with positron emission tomography (PET) myocardial blood flow (MBF) imaging, but is not practical in small animal models. This study characterized coronary vasomotor function in mice with [¹¹C]acetate micro-PET measurements of nitric-oxide-mediated endothelial flow reserve (EFR_NOM) (adrenergic-stress/rest MBF) and myocardial oxygen consumption (MVO₂) using salbutamol β₂-adrenergic-activation.

Methods

[¹¹C]acetate PET MBF was performed at rest + salbutamol (SB 0.2, 1.0 μg/kg/min) and norepinephrine (NE 3.2 μg/kg/min) stress to measure an index of MBF response. β-adrenergic specificity of NE was evaluated by pretreatment with α-adrenergic-antagonist phentolamine (PHE), and β₂-selectivity was assessed using SB.

Results

Adjusting for changes in heart rate × systolic blood pressure product (RPP), the same stress/rest MBF ratio of 1.4 was measured using low-dose SB and NE in normal mice (equivalent to human CPT response). The MBF response was correlated with changes in MVO₂ (p = 0.02). Nitric oxide synthase (NOS)-inhibited mice (N^g-nitro-L-arginine methyl ester (L-NAME) pretreatment and endothelial nitric oxide synthase (eNOS) knockout) were used to assess the EFR_NOM, in which the low-dose SB- and NE-stress MBF responses were completely blocked (p = 0.02). With high-dose SB-stress, the MBF ratio was reduced by 0.4 following NOS inhibition (p = 0.03).

Conclusions

Low-dose salbutamol β₂-adrenergic-stress [¹¹C]acetate micro-PET imaging can be used to measure coronary-specific EFR_NOM in mice and may be suitable for assessment of endothelial dysfunction in small animal models of disease and evaluation of new therapies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-014-0068-9) contains supplementary material, which is available to authorized users.

Reduced coronary flow reserve in patients with primary hyperparathyroidism: a study by G-SPECT myocardial perfusion imaging

PURPOSE

The mechanisms underlying increased cardiovascular risk in primary hyperparathyroidism (pHPT) have not been fully defined. Recently, this issue has become the subject of renewed interest due to the increasing evidence that the endothelium and vascular wall are targets for parathyroid hormone (PTH). The aim of this study was to measure regional coronary flow reserve (CFR) to determine whether the vascular damage induced by pHPT extends to affect the coronary microvascular function.

METHODS

A total of 22 pHPT patients without a history of coronary artery disease and 7 age-matched control subjects were recruited. Dipyridamole myocardial blood flow (MBF) was assessed using 99mTc-sestamibi by measuring first-transit counts in the pulmonary artery and myocardial count rate from G-SPECT images. Baseline MBF was estimated 2 h later according to the same procedure. Regional CFR was defined as the ratio between dipyridamole and baseline MBF using a 17-segment left ventricular model.

RESULTS

Three pHPT patients showed reversible perfusion defects and were excluded from the analysis. In the remaining 19, CFR was significantly lower with respect to the control subjects (1.88±0.64 vs. 3.36±0.66, respectively; p<0.01). Moreover, patients studied for more than 28 months from pHPT diagnosis showed lower CFR values than the others (1.42±0.18 vs. 2.25±0.64, respectively; p<0.01). Consequently, the time from diagnosis to the nuclear study showed a reasonable correlation with the degree of CFR impairment (Spearman's rho -0.667, p<0.02).

CONCLUSION

pHPT is associated with a significant dysfunction of the coronary microcirculation. This disorder might contribute to the high cardiovascular risk of conditions characterized by chronic elevations in serum PTH levels.

Coronary microvascular resistance: methods for its quantification in humans

Coronary microvascular dysfunction is a topic that has recently gained considerable interest in the medical community owing to the growing awareness that microvascular dysfunction occurs in a number of myocardial disease states and has important prognostic implications. With this growing awareness, comes the desire to accurately assess the functional capacity of the coronary microcirculation for diagnostic purposes as well as to monitor the effects of therapeutic interventions that are targeted at reversing the extent of coronary microvascular dysfunction. Measurements of coronary microvascular resistance play a pivotal role in achieving that goal and several invasive and noninvasive methods have been developed for its quantification. This review is intended to provide an update pertaining to the methodology of these different imaging techniques, including the discussion of their strengths and weaknesses.

Myocardial glucose and lactate metabolism during rest and atrial pacing in humans

There is minimal in vivo data in humans evaluating myocardial substrate utilization during increased heart work. This study was performed to determine the balance of myocardial glucose and lactate metabolism during rest and increased heart work induced by atrial pacing in seven healthy men and women (age, 49.7 +/- 3.9 years; body mass index, 23.4 +/- 1.1 kg m(-2), maximum oxygen consumption, 35.5 +/- 3.0 ml kg(-1) min(-1), ejection fraction, 68 +/- 3%). After 3 days of dietary control, catheters were placed in coronary sinus, femoral arterial and venous, and peripheral venous blood vessels. Subjects received a primed continuous infusion of [3,3,3-(2)H]lactate and [6,6-(2)H]glucose throughout the study. Arterial and coronary sinus blood sampling and measurements of coronary sinus blood flow were made during rest and atrial pacing at approximately 111 beats min(-1). Myocardial oxygen consumption increased (P = 0.04) from rest to atrial pacing. Net glucose uptake increased (P = 0.04) from rest to atrial pacing with unchanged fractional extraction (rest: 9.1 +/- 2.7%, atrial pacing 9.8 +/- 2.9%). The percentage of whole body glucose disposal from myocardial uptake also increased from rest to atrial pacing. Isotopically measured lactate uptake also increased significantly from rest to atrial pacing with no significant differences in fractional extraction. The myocardium released lactate throughout the experiment, which increased significantly from rest and atrial pacing (P < 0.05). The heart accounted for a significantly greater percentage of whole body lactate disposal during atrial pacing (15.0 +/- 4.4%) compared to rest (4.9 +/- 0.9%, P = 0.03). These data suggest: (1) in the absence of ischaemia the myocardium is constantly taking up and releasing lactate at rest which increases during atrial pacing, and (2) when arterial substrate delivery is unchanged, increased myocardial work is accomplished with similar proportions of glucose and lactate utilization in healthy humans in vivo.

Myocardial FFA metabolism during rest and atrial pacing in humans

There is limited in vivo data in humans evaluating myocardial fat utilization during increased heart work. This study was done to determine myocardial free fatty acid (FFA) metabolism during rest and atrial pacing, which increases cardiac work without changing arterial substrate concentration. We studied seven healthy men and women (age = 49.7 +/- 3.9 yr, BMI = 23.4 +/- 1.1 kg/m(2), Vo(2max) = 35.5 +/- 3.0 ml.kg(-1).min(-1), ejection fraction = 68 +/- 3%). After 3 days of dietary control, coronary sinus, femoral arterial and venous, and peripheral venous catheters were placed. Subjects received [(13)C]bicarbonate followed by a continuous infusion of [1-(13)C]palmitate through the end of the study. Arterial and coronary sinus blood sampling and measurements of resting coronary sinus blood flow were made during rest and atrial pacing to 120 beats/min. MVo(2) increased (P < 0.05) from rest to atrial pacing. Coronary sinus FFA concentration was significantly lower than arterial through rest and atrial pacing (P = 0.007). Isotopically measured myocardial palmitate uptake increased significantly from rest to atrial pacing (P = 0.03). Approximately one-third of palmitate delivery was extracted by the myocardium during rest and atrial pacing. Myocardial V(13)CO(2) production and palmitate oxidation increased significantly from rest (P < 0.01) to atrial pacing. Net glycerol balance was significantly greater than zero during rest (P = 0.04) but not different from zero during atrial pacing (P = 0.13). These data suggest that myocardial lipid uptake and oxidation increase with greater heart work during atrial pacing, with a similar relative proportion of fat oxidation to total myocardial energy expenditure.

Impaired myocardial metabolic reserve and substrate selection flexibility during stress in patients with idiopathic dilated cardiomyopathy

Under resting conditions, the failing heart shifts fuel use toward greater glucose and lower free fatty acid (FFA) oxidation. We hypothesized that chronic metabolic abnormalities in patients with dilated cardiomyopathy (DCM) are associated with the absence of the normal increase in myocardial glucose uptake and maintenance of cardiac mechanical efficiency in response to pacing stress. In 10 DCM patients and 6 control subjects, we measured coronary flow by intravascular ultrasonometry and sampled arterial and coronary sinus blood. Myocardial metabolism was determined at baseline, during atrial pacing at 130 beats/min, and at 15 min of recovery by infusion of [(3)H]oleate and [(13)C]lactate and measurement of transmyocardial arteriovenous differences of oxygen and metabolites. At baseline, DCM patients showed depressed coronary flow, reduced uptake and oxidation of FFA, and preferential utilization of carbohydrates. During pacing, glucose uptake increased by 106% in control subjects but did not change from baseline in DCM patients. Lactate release increased by 122% in DCM patients but not in control subjects. Cardiac mechanical efficiency in DCM patients was not different compared with control subjects at baseline but was 34% lower during stress. Fatty acid uptake and oxidation did not change with pacing in either group. Our results show that in DCM there is preferential utilization of carbohydrates, which is associated with reduced flow and oxygen consumption at rest and an impaired ability to increase glucose uptake during stress. These metabolic abnormalities might contribute to progressive cardiac deterioration and represent a target for therapeutic strategies aimed at modulating cardiac substrate utilization.

Myocardial pre-synaptic sympathetic function correlates with glucose uptake in the failing human heart

PURPOSE

We have previously shown that the myocardium of patients with heart failure (HF) is insulin resistant. Chronic beta-adrenergic stimulation has been implicated in insulin resistance in cultured cardiomyocytes in vitro, where sustained noradrenaline stimulation inhibited insulin-modulated glucose uptake. As the failing heart is characterized by increased sympathetic drive, we hypothesized that there is a correlation between pre-synaptic sympathetic function and insulin sensitivity in the myocardium of patients with HF.

METHODS

Eight patients (aged 67 +/- 7 years) with coronary artery disease and left ventricular dysfunction (ejection fraction 44 +/- 10%) underwent function and viability assessment with cardiovascular magnetic resonance. Myocardial glucose utilization (MGU) was measured using positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG). Pre-synaptic noradrenaline re-uptake was measured by calculating [(11)C]meta-hydroxy-ephedrine (HED) volume of distribution (V (d)) with PET. Two groups of healthy volunteers served as controls for the FDG (n = 8, aged 52 +/- 4 years, p < 0.01 vs patients) and HED (n = 8, aged 40 +/- 6 years, p < 0.01 vs patients) data.

RESULTS

MGU in patients was reduced in both normal remote (0.44 +/- 0.14 micromol.min(-1).g(-1)) and dysfunctional (0.49 +/- 0.14 micromol.min(-1).g(-1)) segments compared with controls (0.61 +/- 0.7 micromol.min(-1).g(-1); p < 0.001 vs both). HED V (d) was reduced in dysfunctional segments of patients (38.9 +/- 21.2 ml.g(-1)) compared with normal segments (52.2 +/- 19.6 ml.g(-1)) and compared with controls (62.7 +/- 11.3 ml.g(-1)). In patients, regional MGU was correlated with HED V (d).

CONCLUSION

The results of this study provide novel evidence of a correlation between cardiac sympathetic function and insulin sensitivity, which may represent one of the mechanisms contributing to insulin resistance in failing human hearts.

Comparison of myocardial blood flow and coronary flow reserve during dobutamine and adenosine stress: Implications for pharmacologic stress testing in coronary artery disease

BACKGROUND

Mechanistic differences between pharmacologic stressors may offer different clinical benefits. Therefore the effects of dobutamine and adenosine on absolute myocardial blood flow (MBF) and coronary flow reserve (CFR) were compared.

METHODS AND RESULTS

We divided 36 patients (mean age, 61 +/- 8 years) with coronary artery disease into 2 groups based on stenosis severity as follows: greater than 50% but less than 75% (n = 16) and greater than 75% (n = 20). In addition, 18 normal volunteers (mean age, 46 +/- 7 years) served as control subjects. Groups of equal sizes received either dobutamine or adenosine. MBF at rest and peak MBF were measured by use of positron emission tomography in territories subtended by the stenosis (ischemic) and remote myocardium (remote), whereas left ventricular MBF was used in control subjects. CFR was calculated as peak MBF divided by MBF at rest. CFR was significantly greater with adenosine than with dobutamine stress in control subjects and remote CFR. Ischemic CFR was blunted to a similar degree with each stressor. Therefore adenosine achieved flow heterogeneity across all coronary stenosis severities greater than 50%. However, dobutamine achieved flow heterogeneity only in the presence of a severe coronary stenosis greater than 75% despite provoking a greater ischemic stimulus.

CONCLUSION

Adenosine stress demonstrated a higher sensitivity and dobutamine demonstrated a higher specificity with quantitative perfusion imaging. Therefore adenosine is superior for diagnostic perfusion imaging, whereas dobutamine is better suited in combination with visual imaging and in the functional assessment of a known coronary stenosis.

Dobutamine-induced hyperaemia inversely correlates with coronary artery stenosis severity and highlights dissociation between myocardial blood flow and oxygen consumption

OBJECTIVES

To compare the relationship between dobutamine myocardial blood flow (MBF), rate-pressure product (RPP) and stenosis severity in patients with coronary artery disease (CAD).

METHODS

27 patients with single-vessel CAD were allocated to three groups based on stenosis severity: group 1, 50-69% (n = 9); group 2, 70-89% (n = 9); and group 3, >or= 90% (n = 9). Nine normal volunteers served as controls. Resting and dobutamine MBF were measured by positron emission tomography in the territory subtended by the stenosis (Isc) and remote myocardium (Rem). Mean left ventricular MBF was used for controls.

RESULTS

In group 1, mean dobutamine MBF-Isc (2.48 (SD 0.48 ml/min/g)) and dobutamine MBF-Rem (2.70 (0.50) ml/min/g, NS) were comparable. In groups 2 and 3, dobutamine MBF-Isc (1.91 (0.44) and 1.22 (0.21) ml/min/g) was significantly lower than dobutamine MBF-Rem (2.27 (0.28) and 1.98 (0.25) ml/min/g, p < 0.02 and p < 0.005, respectively). An inverse relation between dobutamine MBF and stenosis severity existed both in Isc (r = 0.79, p < 0.001) and in Rem territories (r = 0.71, p < 0.001). For any given RPP, dobutamine MBF was greater in controls than in Rem (p < 0.05), which in turn was greater than in Isc (p < 0.05).

CONCLUSION

Dobutamine MBF inversely correlated with stenosis severity and achieved significant flow heterogeneity for coronary stenoses > 70%. Dobutamine MBF and RPP were dissociated in both Isc and Rem segments in patients compared with controls.

Effects of insulin on left ventricular function during dynamic exercise in overweight and obese subjects

AIMS

We designed this study in order to determine the effect of insulin on cardiac function in overweight and obese subjects during exercise.

METHODS AND RESULTS

The cardiac function of 62 normal glucose tolerant subjects, aged 30-40 and divided into normal weight (group 1, n=22, BMI 20-24.9 kg/m(2)), overweight (group 2, n=20, BMI 25-29.9 kg/m(2)), and obesity (group 3, n=20, BMI 30-35 kg/m(2)) was evaluated at rest and during dynamic exercise through angiocardioscintigraphy, when on hyperinsulinaemic euglycaemic clamp (test A) and when on normal saline infusion (test B). Left ventricular function at rest was statistically greater (P<0.05) in both tests in overweight and obese subjects compared with normal weight controls, with no statistical difference (P=0.057) within groups between insulin and normal saline infusion. During exercise, cardiac function improved in all the subjects in both tests. The increase was lower in overweight and obese patients, even if statistically significant only in obese vs. control subjects in both tests (P<0.05). Insulin sensitivity showed a significant correlation (P< or =0.001) with left ventricular ejection fraction (LVEF) at rest and with change in LVEF during clamp.

CONCLUSION

Our findings suggest a metabolic pathogenesis for the impaired LV function in obesity.

Myocardial and skeletal muscle glucose uptake during exercise in humans

The purpose of this study was to investigate the effects of exercise on myocardial glucose uptake and whether the pattern of glucose uptake is the same as in skeletal muscle. Glucose uptake was measured using positron emission tomography (PET) and 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG). Twelve healthy men were studied during rest, while 14 subjects were studied after 35 min of bicycle exercise corresponding to 30, 55 and 75 % of maximal oxygen consumption (*VO2,max)) on three separate days. [(18)F]FDG was injected 10 min after the start of exercise and exercise continued for a further 25 min. Myocardial and skeletal muscle PET scanning was commenced directly after the completion of the exercise bout. As compared to the resting state, exercise doubled myocardial glucose uptake at the 30 % (P = 0.056) and 55 % intensity levels (P < 0.05), while at the 75 % intensity level glucose uptake was reduced significantly compared to the lower exercise intensities. There was no significant difference between the highest intensity level and the resting state (P = 0.18). At rest and during low-intensity exercise, myocardial glucose uptake was inversely associated with circulating levels of free fatty acids. However, during higher exercise intensities when plasma lactate concentrations increased significantly, this association disappeared. In contrast to myocardial responses, skeletal muscle glucose uptake rose in parallel with exercise intensity from rest to 30 % and then 55 % *VO2,max) (P < 0.001) and tended to increase further at the intensity of 75 % *VO2,max) (P = 0.065). In conclusion, these results demonstrate that myocardial glucose uptake is increased during mild- and moderate-intensity exercise, but is decreased during high-intensity exercise. This finding suggests that the increased myocardial energy that is needed during high-intensity exercise is supplied by substrates other than glucose.

Insulin action on heart and skeletal muscle glucose uptake in essential hypertension

Essential hypertension is characterized by skeletal muscle insulin resistance but it is unknown whether insulin resistance also affects heart glucose uptake. We quantitated whole body (euglycemic insulin clamp) and heart and skeletal muscle (positron emission tomography and 18F-fluoro-2-deoxy-D-glucose) glucose uptake rates in 10 mild essential hypertensive (age 33 +/- 1 yr, body mass index 23.7 +/- 0.8 kg/m2, blood pressure 146 +/- 3/97 +/- 3 mmHg, VO2max 37 +/- 3 ml/kg per min) and 14 normal subjects (29 +/- 2 yr, 22.5 +/- 0.5 kg/m2, 118 +/- 4/69 +/- 3 mmHg, 43 +/- 2 ml/kg per min). Left ventricular mass was similar in the hypertensive (155 +/- 15 g) and the normotensive (164 +/- 13 g) subjects. In the hypertensives, both whole body (28 +/- 3 vs 44 +/- 3 mumol/kg per min, P < 0.01) and femoral (64 +/- 11 vs 94 +/- 8 mumol/kg muscle per min, P < 0.05) glucose uptake rates were decreased compared to the controls. In contrast, heart glucose uptake was 33% increased in the hypertensives (939 +/- 51 vs 707 +/- 46 mumol/kg muscle per min, P < 0.005), and correlated with systolic blood pressure (r = 0.66, P < 0.001) and the minute work index (r = 0.48, P < 0.05). We conclude that insulin-stimulated glucose uptake is decreased in skeletal muscle but increased in proportion to cardiac work in essential hypertension. The increase in heart glucose uptake in mild essential hypertensives with a normal left ventricular mass may reflect increased oxygen consumption and represent an early signal which precedes the development of left ventricular hypertrophy.

Different alterations in the insulin-stimulated glucose uptake in the athlete's heart and skeletal muscle

Physical training increases skeletal muscle insulin sensitivity. Since training also causes functional and structural changes in the myocardium, we compared glucose uptake rates in the heart and skeletal muscles of trained and untrained individuals. Seven male endurance athletes (VO2max 72 +/- 2 ml/kg/min) and seven sedentary subjects matched for characteristics other than VO2max (43 +/- 2 ml/kg/min) were studied. Whole body glucose uptake was determined with a 2-h euglycemic hyperinsulinemic clamp, and regional glucose uptake in femoral and arm muscles, and myocardium using 18F-fluoro-2-deoxy-D-glucose and positron emission tomography. Glucose uptake in the athletes was increased by 68% in whole body (P < 0.0001), by 99% in the femoral muscles (P < 0.01), and by 62% in arm muscles (P = 0.06), but it was decreased by 33% in the heart muscle (P < 0.05) as compared with the sedentary subjects. The total glucose uptake rate in the heart was similar in the athletes and control subjects. Left ventricular mass in the athletes was 79% greater (P < 0.001) and the meridional wall stress smaller (P < 0.001) as estimated by echocardiography. VO2max correlated directly with left ventricular mass (r = 0.87, P < 0.001) and inversely with left ventricular wall stress (r = -0.86, P < 0.001). Myocardial glucose uptake correlated directly with the rate-pressure product (r = 0.75, P < 0.02) and inversely with left ventricular mass (r = -0.60, P < 0.05) or with the whole body glucose disposal (r = -0.68, P < 0.01). Thus, in athletes, (a) insulin-stimulated glucose uptake is enhanced in the whole body and skeletal muscles, (b) whereas myocardial glucose uptake per muscle mass is reduced possibly due to decreased wall stress and energy requirements or the use of alternative fuels, or both.

Myocardial ischaemia and ventricular arrhythmias precipitated by physiological concentrations of adrenaline in patients with coronary heart disease

The clinical and haemodynamic effects of adrenaline infusion (30 ng kg-1 min-1) producing plasma adrenaline concentrations in the range seen during acute myocardial infarction and of placebo were investigated in a crossover design in 14 patients with stable coronary heart disease. Adrenaline infusion resulted in electrocardiographic evidence of myocardial ischaemia (greater than or equal to 1 mm (0.1 mV) horizontal or downsloping ST segment depression) in 10 patients and angina in four, although the mean (SEM) increase in heart rate was modest (14 (2) beats/min) and mean coronary vascular resistance fell from 1.56 (0.21) to 1.16 (0.14) mm Hg min ml-1 (p less than 0.005). New or increasingly frequent or complex ventricular arrhythmias occurred in five patients. Placebo infusion had no effect on the variables measured. Supine bicycle exercise during infusion of the saline placebo was associated with a similar degree of ST segment depression (0.9 (0.2) mm) as adrenaline infusion at rest (0.9 (0.1) mm) but exercise performed during adrenaline infusion (10 patients) resulted in more pronounced ST segment depression (1.9 (0.3) mm) (p less than 0.005) than either intervention alone. Angina occurred in three of 11 patients during control exercise and in six of 10 during the combination of adrenaline infusion and exercise. Such potentially adverse consequences of low dose adrenaline infusion in patients with stable coronary heart disease are consistent with the suggestion that adrenal activation is detrimental during acute myocardial infarction, being both arrhythmogenic and proischaemic.