Coronary blood flow control is impaired at rest and during exercise in conscious diabetic dogs

This study tested whether diabetes mellitus impairs coronary blood flow control sufficiently to alter the balance between myocardial oxygen delivery and metabolism. Dogs (n = 7) were instrumented with catheters in the aorta and coronary sinus, and with a flow transducer on the circumflex coronary artery. Coronary blood flow, myocardial oxygen consumption (MVO₂), heart rate and aortic pressure were measured at rest and during treadmill exercise before and after induction of diabetes with alloxan monohydrate (40 – 60 mg/kg). Arterial plasma glucose concentration increased from 4.6 ± 0.2 mM in non-diabetic, control dogs to 20.2 ± 2.3 mM one week after alloxan injection. In non-diabetic control dogs, exercise increased MVO₂ 3.1-fold, coronary blood flow 2.7-fold, and heart rate 2.4-fold. Coronary venous PO₂ decreased from 19.4 ± 0.6 mmHg at rest to 14.7 ± 0.7 mmHg during exercise. Diabetes significantly attenuated exercise coronary hyperemia and reduced coronary venous PO₂ at rest (15.6 ± 0.5 mmHg) and during exercise (12.6 ± 0.8 mmHg). Diabetes also significantly reduced myocardial oxygen delivery at each level of exercise. Acute hyperglycemia alone did not alter exercise-induced coronary vasodilation or reduce coronary venous PO₂. These findings demonstrate that experimental diabetes attenuates functional coronary hyperemia and impairs the balance between coronary blood flow and myocardial metabolism. However, this deleterious effect is not related to acute hyperglycemia but to the chronic disease process of diabetes mellitus. Received: 19 July 2001, Returned for 1. revision: 20 August 2001, 1. Revision received: 17 October 2001, Returned for 2. revision: 19 October 2001, 2. Revision received: 2 November 2001, Accepted: 5 November 2001     

Endogenous nitric oxide regulates right coronary blood flow during acute pulmonary hypertension in conscious dogs

This study investigated the role of nitric oxide (NO) in the control of right coronary (RC) blood flow at rest and during acute pulmonary hypertension. Experiments were performed in seven chronically instrumented, conscious dogs. NO synthesis was inhibited by systemic administration of N^ω-nitro-L-arginine (LNA, 35 mg/kg). Inflation of a balloon in the main pulmonary artery raised right ventricular (RV) peak systolic pressure from 34 ± 2 to 47 ± 3 mmHg before LNA and from 37 ± 2 to 47 ± 3 mmHg after LNA, but did not affect mean systemic arterial pressure. RV O₂ consumption (MVO₂) increased from 4.4 ± 0.7 to 6.1 ± 0.7 ml/min/100 g. 82 % of the elevated RV MVO₂ was provided by RC blood flow, which increased from 46 ± 7 to 61 ± 8 ml/min/100 g. After LNA, resting RV MVO₂ and RC flow fell. RC venous PO₂ fell, but RV lactate uptake was not altered. During pulmonary hypertension, the increase in RC blood flow was blunted by LNA, so that only 66 % of the elevated RV MVO₂ was supplied by increased RC flow. Analysis of O₂ supply variables as functions of RV MVO₂ further demonstrated a significant role of NO in regulating RC flow at rest and during moderate pulmonary hypertension. Conclusions NO is required for the RC hyperemic response to acute pulmonary hypertension as well as for normal resting RC blood flow. After blockade of NO synthesis, RV O₂ supply at rest and during pulmonary hypertension was sustained by increased RV O₂ extraction. Received: 2 April 2002, Returned for 1. revision: 17 April 2002, 1. Revision received: 13 May 2002, Returned for 2. revision: 29 May 2002, 2. Revision received: 5 June 2002, Accepted: 10 June 2002     

Nitric oxide synthases in vagal neurons are crucial for the regulation of heart rate in awake dogs

Nitric oxide synthase (NOS) inhibitors elicit bradycardias independent of the endothelium (e-NOS) or increases in blood pressure. Therefore, this bradycardia could be mediated by other NOS isoforms, most likely that of the nervous system (n-NOS). If so, heart rate variability (HRV) as a measure of vagal activity should be an indicator of the activity of n-NOS in vagal neurons. To test this, we studied the dose-effect relations of L-NAME (0.3 – 50 mg·kg⁻¹) on heart rate (HR), HRV and systemic vascular resistance (SVR) in seven awake dogs. HRV was analyzed in the time domain as standard deviation of the RR-intervals (SDNN) and in the frequency domain as power in the high (0.15 – 0.5 Hz) and low (0.04 – 0.15 Hz) frequency range. The effects of HR and SDNN reached their maxima at a dose of 3 mg·kg⁻¹ and had their ED₅₀ at 0.27 ± 0.03 mg·kg⁻¹ and 0.43 ± 0.1 mg·kg⁻¹, respectively, whereas SVR had its maximum at 10 mg·kg⁻¹ and ED₅₀ at 0.86 ± 0.11 mg·kg⁻¹ (p < 0.05). HF-power (vagal activity) predominated compared to LF-power (mainly sympathetic activity) during baseline as well as after L-NAME. The effects on HR and HRV were absent after ganglionic blockade (hexamethonium), whereas the effects on SVR remained unchanged. Thus, NO exerts a powerful restraining activity on vagal neurons and plays a key role in the adjustment of heart rate in awake resting animals with prevailing vagal activity. Received: 30 October 2000 / Returned for revision: 29 November 2000 / Revision received: 22 December 2000 / Accepted: 8 January 2001     

Blood flow heterogeneity in the heart

Local deposition density of microspheres is heterogeneous in histologically homogeneous myocardium under physiological conditions. The underlying biological heterogeneity must be distinguished from a methodological heterogeneity which depends preferentially on the number of microspheres injected, blood flow to a particular myocardial region and sample mass. As the variables space (spat), time (temp), and the method (meth) are independent of each other, the observed (obs) variability may be approximated using the coefficients of variation (CV) of the individual variables: CV_obs=(CV² _spat+CV² _temp+CV² _meth)^0.5. Studies in which these different variables have been quantified indicate that the largest fraction of the observed variability of microsphere deposition density is contributed by spatial flow heterogeneity which exists independent of the myocardial layer. Spatial flow heterogeneity increases with decreasing sample mass and decreasing mean flow. Fractal and autocorrelation analyses have shown that adjacent myocardial flows are spatially correlated and nonrandom. Local blood flow was shown to correlate with various metabolic and transport rates, while no differences were found between low and high flow regions with respect to several metabolic markers of tissue hypoxia. In conclusion, the evidence available to date indicates that 1) in histologically homogeneous myocardium there exists a spatial blood flow heterogeneity which 2) is temporally stable, 3) resolution dependent, 4) largely layer-independent, 5) nonrandom, and 6) related to local aerobic metabolism. Received: 1 July 1998, Returned for 1. revision: 12 August 1998, 1. Revision received: 28 August 1998, Accepted: 28 August 1998     

Microheterogeneity of myocardial blood flow

Myocardial blood flow exhibits the most marked heterogeneity at the microvascular level. Its within-layer spatial distribution can be described from subepi- to subendocardium with resolutions of 0.1 × 0.1 to 1 × 1 mm² by quantitative digital radiography based on the technique of desmethylimipramine deposition. In the subendocardium, flow heterogeneity is the highest, whereas local flow randomness is the lowest, showing the clustered pattern of high- or low-flow regions. The resolution-dependence of flow heterogeneity is characterized by its fractality, which holds consistently down to the microvascular level through the vascular structural transition from the treelike arteriolar to the non-treelike capillary network. Flow heterogeneity is adjustable in a transmurally different manner to local metabolic changes. The redistribution of flow is considered as a result of adaptive coordination of microperfusion between adjacent microcirculatory units, which are perfused by a single precapillary arteriole. Received: 28 February 2001, Returned for revision: 2 May 2001, Revision received: 31 May 2001, Accepted: 19 June 2001     

The mechanical and metabolic basis of myocardial blood flow heterogeneity

Precise measurements of regional myocardial blood flow heterogeneity had to be developed before one could seek causation for the heterogeneity. Deposition techniques (particles or molecular microspheres) are the most precise, but imaging techniques have begun to provide high enough resolution to allow in vivo studies. Assigning causation has been difficult. There is no apparent association with the regional concentrations of energy-related enzymes or substrates, but these are measures of status, not of metabolism. There is statistical correlation between flow and regional substrate uptake and utilization. Attribution of regional flow variation to vascular anatomy or to vasomotor control appears not to be causative on a long-term basis. The closest relationships appear to be with mechanical function, but one cannot say for sure whether this is related to ATP hydrolysis at the crossbridge or associated metabolic reactions such as calcium uptake by the sarcoplasmic reticulum. Received: 4 July 2001, Returned for revision: 21 August 2001, Revision received: 15 September 2001, Accepted: 17 September 2001     

Heterogeneity of metabolic parameters in the left ventricular myocardium and its relation to local blood flow

It is well established that myocardial blood flow is heterogeneous on the local level. During recent years comprehensive studies have been undertaken to assess the relation between myocardial metabolism and spatial blood flow heterogeneity. Based on the type of measurements two major groups of studies have been performed: enzyme activity and tissue metabolite level assessments. Enzyme activity measurements have provided only limited insight into the coupling of local metabolism and flow. This is probably due to the fact that, in addition to estimated V_max values, local substrate affinity (K_m values) and substrate concentrations affect the metabolite fluxes. However, the latter two variables remain normally unknown. In contrast, valuable insight has been obtained concerning flow-metabolism matching from tissue metabolite measurements, especially when connected with mathematical model analyses. The latter permitted the calculation of metabolic flux rates (e.g., production of oxidation water, citric acid cycle flux, glucose uptake, fatty acid uptake) or the translation of the metabolic indexes into physiologically meaningful local metabolite concentrations (e.g., free cytosolic adenosine). The bottom line of the studies reported to date is that the broad range of myocardial flows observed under resting control conditions correlates with local metabolism possibly affected by spatial differences in adrenergic stimulation. Thus, high flow samples exhibit a higher oxidative metabolism than low flow samples. As a result the flow threshold below which local myocardial ischemia ensues is higher in control high flow samples. The importance of these findings with respect to local flow-metabolism matching is underlined by the finding that the probability of developing an infarction following ischemia/reperfusion is related to the functional state of the myocardium under control conditions, i.e., the local level of flow-metabolism matching. Received: 12 April 2001, Returned for revision: 6 June 2001, Revision received: 5 July 2001, Accepted: 16 July 2001     

Measurement of coronary flow reserve and its role in patient care

Coronary anatomy and myocardial blood flow are major determinants of clinical symptomatology and survival in patients with coronary artery disease. While coronary anatomy has been successfully assessed by coronary angiography and intravascular ultrasound imaging, measurements of coronary blood flow are more difficult and their prognostic value has not been definitively evaluated. Measurements of coronary flow reserve (CFR), defined as maximal hyperemic flow divided by resting flow, have been used to assess the functional significance of coronary artery lesions. However, functional assessment of epicardial coronary lesions is limited by several factors, such as diffuse coronary artery disease, small-vessel disease, regional variations in myocardial flow, endothelial dysfunction, and left ventricular hypertrophy. CFR can be measured by several techniques, each one with distinct advantages and limitations, which are discussed in this review. An important distinction is between techniques that measure coronary blood flow (e.g., positron emission tomography) and those that measure blood flow velocity (e.g., Doppler catheters), from which coronary velocity reserve (CVR) is calculated. Although clinical CFR measurements have been possible for over fifteen years, their implementation in patient care has been slow due to several factors including the requirement for a sophisticated technology, the difficult interpretation of CFR results, and the limited knowledge of their prognostic value. While a normal CFR in patients with single vessel coronary disease is associated with a good prognosis, the converse has not been established, i.e., that there is a critical reduction in CFR that requires interventional treatment. A recent study (DEBATE) showed a decrease in the incidence of cardiac events at 6 months after coronary balloon angioplasty in patients with a post-procedural percent diameter stenosis <35% and CVR >2.5. The complex relation between coronary anatomy, myocardial perfusion, and patient outcome have enormous implications for both patient care and health costs, which need to be addressed in future prospective trials. Received: 20 October 1997, Returned for revision: 9 December 1997, Revision received: 9 April 1998, Accepted: 23 April 1998     

X-ray densitometry for the measurement of regional myocardial perfusion

The evaluation of regional myocardial blood flow (RMBF) during cardiac catheterization is of particular diagnostic interest. The purpose of this investigation was to validate x-ray densitometric parameters for the evaluation of RMBF. In five anesthetized dogs, arterial flow in the circumflex coronary artery was measured continuously with an electromagnetic flowmeter, and RMBF was determined by colored microspheres. Five different perfusion levels were created by mechanical obstruction of the coronary artery or by intravenous infusion of adenosine. At each steady-state perfusion level, digital subtraction coronary angiograms were obtained for densitometric analysis. Results documented a close correlation between the related time parameters 1/Mean Transit Time (1/MTT, r² = 0.969), and 1/Rise Time (1/RT, r² = 0.965) and RMBF over a wide range between 0.36 ml/(min · g) and 11.16 ml/(min · g). Maximum myocardial contrast density (Imax) also showed a good, but inverse correlation (r² = 0.889) with RMBF and, therefore, did not reflect vascular volume. Contrast medium Appearance Time (AT) showed no correlation to RMBF (r² = 0.017). Repeat densitometric measurements for different perfusion levels revealed a good reproducibility for MTT (accuracy: 0.001 s; precision: 0.447 s or 6.7%) and RT (accuracy: 0.014 s; precision: 0.202 s or 10.4%), while AT (accuracy: 0.072 s; precision: 0.420 s or 68.5%) and Imax (accuracy: 0.022 GL; precision: 1.197 GL or 44.5%) showed substantial variation. Myocardial perfusion reserve (MPR) calculated from RT (r² = 0.90) or MTT (r² = 0.94) showed better correlations to RMBF reserve than MPR calculated from AT (r² = 0.04). In conclusion, only 1/MTT and 1/RT showed a good reproducibility and a close correlation to RMBF. Therefore, only these parameters can be recommended for calculations of RMBF and its reserve under clinical conditions. Received: 2 November 1999, Returned for revision: 5 January 2000, Revision received: 1 February 2000, Accepted: 6 February 2000     

Coronary blood flow in chronic insulin-dependent diabetic dogs

Summary Diabetic patients appear to be at an increased risk for perioperative morbidity and mortality following coronary artery bypass grafting. Many have suggested that microangiopathy is a primary cause. Using radionuclide labelled microspheres, we measured the perfusion of the subendocardium, midmyocardium, subepicardium, and the subendocardium/subepicardium ratio in alloxan-induced diabetic and normal dogs. We found no statistical difference in the myocardial perfusion of dogs made diabetic for five months when compared to normal dogs. By using repeated measures two-factor analysis of variance-regression model, changing blood glucose levels had no effect on coronary blood flow in either the diabetic or normal dogs. This study was supported in part by Veterans Administration research funds, a Core Grant for Vision Research (P30 EY05722) from the National Eye Institute, Bethesda/MD, a recognition award from the Alcon Research Institute, and a generous gift from Dr. and Mrs. Harris Vernick.     

Assessing heterogeneous distribution of blood flow and metabolism in the heart

The literature is reviewed on methods to assess heterogeneity of blood flow, substrate uptake and oxidative end energy metabolism in the normal heart, and their interrelations. Even though the factors controlling matching on the regional level remain largely obscure, the evidence that heterogeneous blood flow partially correlates to indicators of metabolism in the normal heart is accumulating, particularly in face of a correlation between acetate metabolism indicative of regional O₂ consumption to microsphere blood flow. Moreover, the partial matching cannot be explained by vascular anatomical differences from one region to the other, since, although fractal theory can partially describe the branching patterns of the coronaries, vasodilation is similar among regions upon metabolic stimulation of the heart. It is dissimilar among regions, so that blood flow is redistributed, upon maximum vasodilation with adenosine or hypoxia, denoting regionally different maximum vessel diameter and flow reserve. However, regionally differing tissue composition could also contribute somewhat to regional differences in (the need for) blood flow. It is still unknown, because of technical limitations, how the foregoing measures relate to regional work load. Received: 2 April 2001, Returned for revision: 2 May 2001, Revision received: 31 May 2001, Accepted: 12 June 2001     

The blood perfused isolated heart: characterization of the model

We have characterized the aerobic blood-perfused isolated heart model evaluating the hemodynamics and metabolism of both the blood donor animal and the isolated organ. Anaesthesia of the blood donor with sodium pentobarbital (30 mg/kg) increases arterial concentration of non esterified fatty acids (NEFA) from 80 ± 6 to 452 ± 70 μM; p < 0.01. Injection of 1.000 U/kg heparin causes a second significant increase from 452 ± 70 to 1012 ± 104 μM; p < 0.01. Insertion of the perfusion circuit, without the isolated heart, causes a reduction in blood pressure of the blood donor and a significant increase in norepinephrine from 277 ± 44 to 634 ± 130 pg/ml; p < 0.05. Two hours of aerobic perfusion of the isolated heart inserted in the perfusion circuit, decreases arterial pressure of the blood donor with a concomitant increase of plasma norepinephrine from 475 ± 150 to 841 ± 159 pg/ml; p k< 0.05. Developed pressure, oxygen consumption, glucose and NEFA uptake of the isolated heart remain constant during two hours of aerobic perfusion, NEFA being the preferred substrate. Tissue content of high energy phosphates at the end of the perfusion is high and similar to that observed “in vivo”. Despite this, there is a release of lactate and CPK from the isolated heart. We conclude that: 1) the model allows accurate measurement of hemodynamics and metabolism of both the isolated heart and the blood donor animal; 2) the perfusion procedure modifies the substrates concentration of the blood donor animal which, in turn, results in the preferential NEFA utilization of the isolated heart. These changes do not affect the functional parameters of the perfused heart. Received: 15 May 1997, Returned for 1. revision: 9 June 1997, 1. revision received: 31 July 1998, Returned for 2. revision: 6 August 1998, 2. revision received: 3 February 1999, Accepted: 3 February 1999     

The relationship between regional blood flow and contractile function in normal, ischemic, and reperfused myocardium

During normoperfusion, both myocardial blood flow and contractile function are heterogeneously distributed throughout the left ventricle, in that midwall segment shortening is higher at the apex than at the base of the left ventricle, and greater in the anterior than in the posterior wall. Also, transmural heterogeneity of myocardial deformation exists with greater segment shortening and wall thickening occurring in inner than in outer myocardial layers. A transmural heterogeneity of myocardial blood flow – with greater inner as compared to outer wall perfusion – exists which is not simply related to temporal fluctuations since the heterogeneous flow pattern is stable over at least a few minutes. While an increase in myocardial contractile function will lead to a metabolically mediated increase in regional coronary perfusion within or above the autoregulatory range does not increase regional myocardial contractile function. During hypoperfusion, the reduction in subendocardial blood flow is more pronounced than that in subepicardial blood flow, and contractile function in the inner myocardial layers ceases more rapidly than in the outer myocardial layers. The reduced regional myocardial contractile function is closely matched to the reduced regional myocardial blood flow; however, such a coupling between reduced flow and function is lost when ischemia is prolonged for several hours in that function for a given flow is further reduced. During reperfusion, regional myocardial contractile function remains depressed for a prolonged period of time, depending on the severity, duration, and location of the preceding ischemic episode, while regional myocardial blood flow is restored to almost normal. Recovery of contractile function in the outer myocardial layers is faster than in the inner myocardial layers. Received: 30 April 1998, Accepted: 28 May 1998     

Transmural myocardial blood flow distribution in hypertrophic cardiomyopathy and effect of treatment

Verapamil alleviates symptoms in patients with hypertrophic cardiomyopathy (HCM), but the underlying mechanism of improvement remains speculative. Baseline and dipyridamole myocardial blood flow (MBF) were measured in 15 HCM patients (14 men, 42±10 years), before and after 4 weeks of verapamil SR 480 mg daily, using ¹⁵O labelled water and positron emission tomography (PET). Subendocardial (endo) and subpericardial (epi) MBF was measured in the septum (thickness 25.4±5.8 mm). Pre-treatment baseline whole heart MBF was 1.02±0.28 ml/min/g and 1.01±0.30 ml/min/g on treatment (p=ns). Dipyridamole MBF was 1.39±0.31 ml/min/g off treatment and 1.23±0.34 ml/min/g on treatment (p=ns). Coronary flow reserve (dipyridamole/resting MBF) was 1.45±0.52 and 1.30±0.51, respectively (p=ns). At baseline, the septal endo/epi MBF ratio was uniform off and on treatment (1.13±0.18 vs 1.18±0.21, p=ns). Before treatment, the endo/epi ratio following dipyridamole decreased to 0.93±0.24 (p<0.01 vs baseline) and 5/15 (33%) patients had a ratio <0.8 which would suggest subendocardial underperfusion. During treatment, the endo/epi ratio following dipyridamole was no more different from baseline (1.06±0.24, p=ns vs baseline) and 2/14 (14%) patients had an endo/epi <0.8. PET can be successfully used to determine transmural MBF in vivo in patients with hypertrophied ventricles. Despite symptomatic improvement, high dose verapamil therapy does not increase total MBF in patients with HCM but may improve septal transmural MBF distribution during dipyridamole in some patients. Received: 8 April 1998, Returned for revision: 6 May 1998, Revision received: 8 July 1998, Accepted: 2 September 1998     

Nifedipine limits infarct size via NO-dependent mechanisms in dogs

Objectives Amlodipine increases NO levels in coronary vessels and aorta via bradykinin-dependent mechanisms in vitro. We have previously reported that nifedipine increases cardiac NO levels in the ischemic canine hearts, suggesting that nifedipine may also have protective effects against ischemia and reperfusion injury, because the enhancement of NO production limits infarct size. We tested whether nifedipine limits infarct size via NO-dependent mechanisms. Methods In open chest dogs, the left anterior descending coronary artery was perfused with blood through a bypass tube and occluded for 90 min followed by 6 hours of reperfusion. Infarct size was assessed at 6 hours of reperfusion. Nifedipine of 3 or 6 μg/kg/min was infused into the bypass tube between 10 min prior to the onset of ischemia and 60 min of reperfusion. Results Neither systemic blood pressure nor heart rate changed during infusion of nifedipine. Infarct size was reduced by the administration of nifedipine (3 or 6 μg/kg/min) compared with the untreated condition (25.6 plusmn; 2.6 and 19.1 ± 3.5 vs. 43.4 ± 5.6 %, respectively), which was completely blunted by L-NAME (45.0 ± 3.6 and 45.4 ± 4.2 vs. 47.9 ± 3.9 % in the nifedipine (3 or 6 μg/kg/min) with L-NAME groups vs. the L-NAME group). Myeloperoxidase activity of the myocardium increased after 6 hours of reperfusion, which was attenuated by nifedipine. The limitation of infarct size and the attenuation in myeloperoxidase activity were completely blunted by L-NAME. There were no significant differences in collateral blood flow at 45 min of ischemia between each group. Conclusions We conclude that the Ca channel blocker, nifedipine, limits infarct size via NO-dependent mechanisms. Received: 21 September 2000, Returned for 1. revision: 9 October 2000, 1. Revision received: 17 January 2001, Returned for 2. revision: 5 February 2001, 2. Revision received: 13 February 2001, Accepted: 14 February 2001     

Myocardial ischemia and reperfusion reduce the levels of cyclic ADP-ribose in rat myocardium

Cyclic ADP-ribose (cADPR) is a novel Ca²⁺-mobilizing second messenger in mammalian cells including cardiomyocytes. It is unknown whether myocardial ischemia and reperfusion affect the metabolism of cADPR in the myocardium. The present study therefore examined the effects of myocardial ischemia and reperfusion on the concentrations of myocardial cADPR using high-performance liquid chromatography. Basal levels of cADPR in rat myocardium were 5.3 ± 1.8 nmol· mg⁻¹ protein. Myocardial ischemia for 30 min significantly decreased cADPR concentrations to 2.1 ± 0.4 nmol·mg⁻¹ protein. During reperfusion, cADPR was maintained at ischemic levels. The activity of ADP-ribosyl cyclase was expressed as the conversion rate of nicotinamide guanine dinucleotide (NGD⁺) to cyclic GDP-ribose. Myocardial ischemia and reperfusion did not alter the activity of ADP-ribosyl cyclase. However, cADPR hydrolase activity, as measured by the conversion rate of cADPR to ADP-ribose, was significantly elevated by ischemia and reperfusion. To determine the mechanism resulting in the enhancement of cADPR hydrolase activity, we examined the effects of changes in ADP, ATP, pH, and PO₂ on the conversion rate of cADPR to ADPR. Alterations of ADP, ATP, or pH in myocardial tissue had no effect on the degradation of cADPR, whereas a decrease in tissue PO₂ markedly increased the hydrolysis of cADPR. These results suggest that myocardial ischemia and reperfusion decrease cADPR in the myocardium by increasing its hydrolysis. Tissue hypoxia may be one of the important mechanisms to activate cADPR hydrolase. Received: 24 July 2001/Returned for 1. revision: 20 August 2001/1. Revision received: 25 October 2001/Returned for 2. revision: 20 November 2001/2. Revision received: 12 December 2001/Accepted: 2 January 2002     

Angiotensin inhibition and coronary autoregulation in a canine model of LV hypertrophy

In humans with hypertension and LV hypertrophy, beneficial effects of angiotensin inhibition may be associated with preserved autoregulatory capacity. We studied the effect of acute angiotensin converting enzyme (ACE) inhibition on coronary autoregulatory pressure-flow relations and transmural distribution of blood flow in sham and LV hypertrophy dogs. Heart/body weight ratio increased (p = 0.001) from 5.5 ± 0.7 in sham to 6.9 ± 0.5 in LV hypertrophy dogs. The lower coronary pressure limit (LPL) on the pressure-flow relation was 47 ± 2 mmHg in sham and 57 ± 6 mmHg (p = 0.001) in LV hypertrophy dogs; after acute ACE-inhibition the LPL was reduced to 40 ± 5 mmHg and 49 ± 6 mmHg (p = 0.001), respectively. Transmural distribution of blood flow was preserved at the LPL in both groups before and after acute ACE-inhibition. Concomitant blockade of prostaglandin and nitric oxide release and bradykinin catabolism had no additional effects on the LPL and distribution of blood flow. After acute ACE-inhibition in LV hypertrophy dogs, distribution of blood flow across the LV wall was preserved and subendocardial vascular reserve was maintained even though the LPL was significantly lower. Preservation of autoregulatory capacity by ACE inhibitors contributes to beneficial outcome in patients with hypertension and LV hypertrophy. Received: 2 October 2001, Returned for 1. revision: 17 October 2001, 1. Revision received: 20 December 2001, Returned for 2. revision: 2 January 2002, 2. Revision received: 14 January 2002, Accepted: 17 January 2002     

Cardiomyocyte apoptosis in acute and chronic conditions

Myocytes can die by necrosis or by apoptosis and the characteristics of both kinds of cell death are so typical that a differentiation can be made by histological and molecular-biological methods using electron microscopy, dUTP labeling with fluorescence or peroxidase stainig (TUNEL) and the DNA laddering method. However, the problem of quantification of apoptotic cells has not been completely solved because of lack of standardization as well as uncritical use and interpretation of the TUNEL method. Equally, quantification of apoptotic cells is not optimal until now because of three reasons: methodological (overinterpretation of results, no differentiation between myocytes and non-myocytes), experimental (global or regional acute ischemia, chronic conditions such as heart failure or hibernating myocardium), and interpretation (unknown time period for the completion of apoptosis). This problem is reflected in the large differences in incidence of apoptosis reported. Our own data show that in dog myocardium made globally ischemic for 90 min, 8% of the myocytes showed a positive staining for apoptosis (TUNEL method) after 6 h of reperfusion. Despite these results the question of reperfusion injury and the influence of apoptosis still remains open, because it can not be excluded until now that the apoptotic process is initiated during the ischemic period. Studies in hibernating myocardium and chronic heart failure show a similar situation, because of a wide variation of numbers of apoptotic cells and the limited possibility to investigate human tissue. There is no doubt that apoptosis plays an important role in chronic pathophysiological situations such as heart failure and hibernating myocardium but the importance of apoptosis in the acute situation of ischemia/reperfusion still has to be clarified.     

The expression of heat shock protein 60 in myocardium of patients with chronic atrial fibrillation

Objective Cardiomyocytes respond to stress with the expression of different heat shock proteins (HSP). HSP60 is induced by various stress factors. The aim of this study was to investigate the expression of HSP60 in human atrial fibrillation (AF). Method Right atrial samples from 14 patients undergoing elective cardiac surgery were excised and immediately frozen in liquid nitrogen. Eight patients had chronic AF and six patients were in sinus rhythm. The HSP60 protein level was determined by SDS-PAGE, Western blot and quantified by optical densitometry according to the immunoreactive bands of actin. Results In myocardial samples from patients with chronic AF, we found a more than 2.5-fold increase in HSP60 expression compared to atrial myocardium of patients in sinus rhythm. Conclusion This result indicates an up regulation of HSP60 in response to chronic atrial fibrillation Received: 31 October 2001, Returned for 1. revision: 20 Novemver 2001, 1. Revision received: 12 December 2001, Returned for 2. revision: 3 January 2002, 2. Revision received: 25 January 2002, Accepted: 6 February 2002     

Myocardial morphology and blood flow distribution in chronic volume-overload hypertrophy in dogs

Summary In this study we investigated myocardial structural alterations and regional myocardial blood flow in chronic volume-overload induced left ventricular hypertrophy in the dog. Moderate hypertrophy (28%) was produced by inserting a shunt between the left subclavian artery and the left atrial appendage in 7 dogs (LVH), while a sham operation was performed on 5 control dogs (C). At a paced heart rate of 100 beats/min there were no differences in blood-flow distribution to the subendocardium (ENDO) mid-myocardium (MYO) or subepicardium (EPI) or in ENDO/EPI ratios between the two groups of dogs. Following adenosine-induced coronary vasodilatation (1 mg/kg/min), there was a relative shift in blood flow away from the ENDO in the LVH dogs so that the ENDO/EPI ratio was reduced. Analysis of the microvascular bed and myocyte cross-sectional area in the same three regions of interest revealed a significant reduction in capillary density in the ENDO region of the hypertrophied hearts when compared to controls (LVH=2463±10, C=2773±75 caps/mm²) and a corresponding increase in myocardial cell cross-sectional area (LVH=262±10, C=233±36 m²). The reduction in capillary density in LVH may be explained on the basis of increased muscle growth without appropriate capillary proliferation indicating an inadequate neovascular response to this form of overload. The results also indicate that blood-flow distribution abnormalities may not be detected at resting flow with moderate LVH produced by volume overload.Work done during tenure as a Fellow of the Southeastern Pennsylvania Heart AssociationWork done during tenure as an established investigator of the American Heart AssociationSupported by USPHS NIH Grants No HL 19425 and HL 07198