Enhancement of glucose uptake in stunned myocardium: role of glucose transporter

This study quantifies the myocardial glucose uptake and clarifies the pathway of augmented glucose uptake in myocardium reperfused after a brief period of ischemia (stunned myocardium). The glucose uptake rate was determined from the time course of the sugar phosphate (SP) resonance in rat myocardium (d[SP]/dt) with 31P nuclear magnetic resonance after the substitution of glucose with its analog 2-deoxyglucose. The d[SP]/dt in stunned myocardium [1.03 +/- 0.05 (SE) micromol x g wet wt(-1) x min(-1); n = 8] increased significantly compared with nonischemic control myocardium (0.18 +/- 0.03 micromol x g wet wt(-1) x min(-1); n = 8; P < 0.0001), reaching the maximal stimulatory uptake rate during exposure to insulin (1.05 +/- 0.04 micromol x g wet wt(-1) x min(-1); n = 8). Twenty minutes after reperfusion, the d[SP]/dt was still augmented (0.41 +/- 0.05 micromol x g wet wt(-1) x min(-1); n = 5; P < 0.05 vs. control myocardium). To elucidate further the mechanism of augmented glucose uptake, N6-(L-2-phenylisopropyl)-adenosine (PIA; 100 micromol/l), a potent blocker of the glucose transporter, was administered to stunned hearts and, as a control, to insulin-stimulated hearts. PIA significantly and comparably inhibited the increase in d[SP]/dt in stunned myocardium (0.36 +/- 0.07 micromol x g wet wt(-1) x min(-1); n = 4; P < 0.0001 vs. without PIA) and in insulin-stimulated myocardium (0.38 +/- 0.02 micromol x g wet wt(-1) x min(-1); n = 4; P < 0.0001 vs. without PIA). These results indicate that the augmented glucose uptake in stunned myocardium is maintained by the glucose transporter, the amount of which is almost equal to that which can be maximally recruited by insulin.

Brain dopamine transporter in spontaneously hypertensive rats

The brain dopamine system plays an important role in the development of hypertension.

METHODS

The amounts of the dopamine transporter (DAT) and dopamine D1 and D2 receptors in the brain were assessed by in vitro autoradiography with the ligands [125I] beta-CIT, [125I]SCH23982 and [125I]iodospiperone, respectively. Changes in this transporter and the two receptors were evaluated in spontaneously hypertensive (SH) rats and control (Wistar-Kyoto) rats at the prehypertensive (2-wk-old, n = 5) and posthypertensive (15-wk-old, n = 5) stages.

RESULTS

The beta-CIT binding for the DAT was increased significantly in the caudate-putamen (CPu) of SH rats compared with that of Wistar-Kyoto (WKY) rats at both pre- and posthypertensive stages. In the evaluation of the lateral-to-medial CPu, the beta-CIT binding on the lateral side was significantly higher than that on the medial side in SH rats at 2 wk. The SCH23982 binding for D1 receptor was increased significantly in CPu at posthypertensive SH rats.

CONCLUSION

Increased DAT was found before the development of hypertension, and the increased DAT and D1 receptor were found at posthypertensive SH rats. The abnormal dopamine system contributes the development of hypertension, suggesting the possibility of diagnostic imaging for the essential hypertension.

Comparison of iodine-123-iomazenil SPECT and technetium-99m-HMPAO-SPECT in Alzheimer's disease

This study was designed to elucidate a central type of benzodiazepine (Bz) receptor distribution in patients with Alzheimer's disease using SPECT with [123I]iomazenil (IMZ).

METHODS

Eight patients with probable Alzheimer's disease were studied. Benzodiazepine receptor imaging was performed 15 min (early) and 180 min (delayed) after intravenous administration of 167 MBq IMZ, sequentially, using hexamethylpropylene amine oxime (HMPAO) SPECT to evaluate regional cerebral perfusion.

RESULTS

Early IMZ-SPECT depicted areas of reduced uptake in sites of decreased cerebral blood flow (CBF), but each area of decreased uptake was extended wider than the area of hypoperfusion. Delayed IMZ-SPECT images demonstrated a similar pattern of decreased area of CBF; the affected region in Bz receptor bindings, however, was clearer and broader compared with that in either HMPAO-SPECT or early IMZ-SPECT. In comparison with the uptakes for the normal cerebral hemisphere (ratio to the contralateral cerebellum) in patients with unilateral cerebral infarction as a control group (n = 4), the patients with Alzheimer's disease showed distinctive bilateral frontal or parietal defects (p < 0.05).

CONCLUSION

Brain SPECT using IMZ may be more sensitive than CBF images in patients with Alzheimer's disease.

Myocardial iodine-123-metaiodobenzylguanidine images and autonomic nerve activity in normal subjects

We studied the relationship between myocardial [123I]metaiodobenzylguanidine (MIBG) uptake and autonomic nerve activity in normal subjects.

METHODS

MIBG scintigraphy and power spectral analysis (PSA) of heart rate variability were performed simultaneously in 15 normal subjects. Anterior planar images and SPECT images were taken at five and two points after the injection of [123I]MIBG, respectively. In 10 of 15 subjects, 201TI myocardial SPECT was performed immediately after MIBG scintigraphy.

RESULTS

The heart/upper mediastinum MIBG uptake ratio in the planar image obtained at 240 min (r = 0.64, p < 0.01) and the washout rate of MIBG in the heart between 15 min and 240 min (r = 0.51, p < 0.05) showed significant correlation with the percentage of low frequency component of PSA (percent LF), an index of sympathetic nerve activity. Regional MIBG uptake in the inferior wall normalized by individual maximal uptake among all pixels was significantly correlated with the high frequency component of PSA, an index of parasympathetic nerve activity (r = -0.58, p < 0.05) and with mean R-R interval in a resting ECG (r = -0.82, p < 0.001) but did not correlate with percent LF, percent uptake of 201TI in the inferior wall or the liver/heart uptake ratio.

CONCLUSION

These results indicate that myocardial MIBG uptake correlates with sympathetic nerve activity in normal subjects. Our data indicate that heterogeneous MIBG distribution in the left ventricle is a physiologic rather than artifactual phenomenon and may be related to vagal tone rather than sympathetic nerve activity.

The effects of proteins on [Ca2+] measurement: different effects on fluorescent and NMR methods

Previous reports showed that the presence of proteins shifts the apparent dissociation constant (Kd) of a fluorescent dye indicator to Ca2+. To elucidate the sensitivity of Kd of an NMR-sensitive Ca2+ indicator, 5-fluoro-1,2-bis(2-amino-phenoxy)ethane N,N,N'N'-tetraacetic acid (5F-BAPTA) to proteins, and compare with that of a dye indicator, Fura-2, we measured Kd of Fura-2 or 5F-BAPTA using Ca-EGTA buffer with or without proteins. Aldolase (ALD) or bovine cardiac protein (BCP) extracted from bovine hearts was used at concentrations of 10, 25, or 50 mg/ml. ALD significantly increased the apparent Kd of Fura-2 to Ca2+ from 164.1 +/- 5.6 nM (mean +/- SE, N = 8) to 757.2 +/- 2.1 nM (n = 4, P < 0.05) at the concentration of 50 mg/ml. In contrast, Kd of 5F-BAPTA was not markedly changed by ALD (298.4 +/- 3. nM without ALD (n = 8), 385.1 +/- 2.7 nM (n = 4) with 50 mg/ml ALD). BCP (50 mg/ml) also significantly increased Kd of Fura-2 (928.5 +/- 3.3 nM, n = 4, P < 0.05), but did not change Kd of 5F-BAPTA (316.0 +/- 2.9 nM, n = 4). These results indicate that Kd of 5F-BAPTA is much less sensitive to the presence of proteins than Fura-2, and that 19F-NMR coupled with 5F-BAPTA is a more robust method to measure intracellular Ca2+ concentration than a fluorescent method with Fura-2.

Abnormal iodine-123-MIBG images in healthy volunteers

We have encountered two healthy volunteers with significant reductions of myocardial [123I]MIBG (metaiodobenzylguanidine) uptake and rapid clearance. In one of these subjects (a 31-yr-old man), we performed additional examinations to clarify the mechanism of the abnormal myocardial MIBG uptake. There was no abnormality on orthostatic test, maximal exercise test (bicycle ergometer) or in plasma norepinephrine concentration. Nevertheless, power spectral analysis (PSA) of heart rate variability revealed that the percent low frequency component (%LF), an index of sympathetic nerve activity, was increased. Furthermore, [123I]MIBG scintigraphy after oral administration of an alpha 2 agonist (guanabenz acetate; 4 mg) demonstrated that myocardial uptake and clearance of MIBG returned to normal, as did the %LF. These results suggest that reduced uptake and rapid clearance of myocardial MIBG in this subject was strongly related to the increased release of norepinephrine from sympathetic nerve terminals due to augmented sympathetic activity. This subject illustrated that unsuspected, subclinical variants of normal or abnormal sympathetic functions may pose a diagnostic pitfall in interpretating myocardial MIBG images.

Inhomogeneous disappearance of myofilament-related cytoskeletal proteins in stunned myocardium of guinea pig

The decrease in Ca2+ responsiveness of myofilaments in stunned myocardium implies that there may be structural changes in proteins composing the contractile machinery. To elucidate the lesion in stunned myocardium, isolated guinea pig hearts were subjected to global ischemia at 37 degrees C and reperfused. SDS-PAGE revealed that the contents of desmin, alpha-actinin, and spectrin decreased in the myofibrillar fraction isolated from hearts reperfused after 60-minute ischemia compared with nonischemic control hearts. To examine the change of cytoskeletal proteins in stunned myocardium, immunohistochemical studies with antibodies against these proteins were performed after 15 minutes of ischemia. In stunned myocardium, the staining was largely intact, but there were some lesions where desmin was not stained and alpha-actinin and spectrin were only weakly identified. The percentage of normally stained areas in the myocardium (percent stained area), quantified by image processing, was significantly lower in stunned myocardium (79.6 +/- 3.6%, mean +/- SEM) than in nonischemic control myocardium (96.5 +/- 0.7%). Percent recovery of developed pressure significantly correlated with percent stained area (r = .82, P < .001). In hearts subjected to 15-minute ischemia but not reperfused, or in hearts reperfused with Ca(2+)-free solution after 15-minute ischemia, staining by the antibodies remained intact, suggesting that the change of the cytoskeletal proteins is mediated by Ca2+ overload during reperfusion. In hearts treated with the protease inhibitor leupeptin (50 mumol/L) or calpain inhibitor I (100 mumol/L), both developed pressure and staining were well preserved. These results indicate that contractile dysfunction in stunned myocardium has a strong correlation with the disappearance of cytoskeletal proteins that may be mediated by a Ca(2+)-dependent intracellular protease activated during reperfusion. The disruption of cytoskeletal proteins is a possible mechanism for stunning, although it may be a secondary effect of protease activation.

Pharmacokinetics of radioiodinated fatty acid myocardial imaging agents in animal models and human studies

Since the oxidation of long chain fatty acids is the major pathway for energy production for the normoxic myocardium, the use of radiolabeled fatty acids for myocardial imaging continues to be a major area of both basic and clinical research. This paper focuses on a discussion of the kinetics of myocardial uptake of radioiodinated fatty acids, including planar and SPECT imaging of various iodine-123-labeled analogues, and data from animal and isolated heart studies, and where possible, comparison with results of clinical studies. Key examples include iodoalkyl-substituted straight chain fatty acids such as 17-IHDA (17-iodoheptadecanoic acid). These analogues are rapidly metabolized in the myocardium, resulting in release of free radioiodide, and can only be practically used for planar imaging. Terminal iodophenyl-substituted fatty acids illustrate a successful approach of stabilizing radioiodine to overcome the release of free iodide encountered with the straight-chain analogues. These analogues, exemplified by p-IPPA [15-(p-iodophenyl)pentadecanoic acid], are widely used in clinical practice. Although washout can be delayed by increase in the arterial lactate levels by mild exercise, SPECT imaging must still be carefully timed. In contrast to these examples, the ortho iodide-substituted IPPA isomer (ortho- instead of para-phenyl substitution of radioiodide) is a unique example which shows rapid myocardial washout in laboratory animals but nearly irreversible retention in humans. Introduction of methyl-branching is a major important approach which has been successfully used to alter tracer kinetics of radioiodinated fatty acids by increasing myocardial retention. A key example in this class of compounds is 3-(R,S)-BMIPP [15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid], an analogue of p-IPPA in which methyl-branching has been introduced into the beta-position of the carbon chain. Although tracer washout is significantly delayed with this structural perturbation, a large number of clinical studies have shown that slow myocardial washout is still observed. Detailed biochemical studies with radioiodinated 3-BMIPP have demonstrated that initial alpha-oxidation produces a metabolite that can then be catabolized by alpha-oxidation. An unexpected and important observation with the (123I]-3-(R,S)-BMIPP agent has been the mis-match between perfusion tracer distribution and the regional BMIPP distribution which has been widely observed in jeopardized, but viable myocardial regions. Another example in the methyl-branched series is DMIPP [15-(p-iodophenyl)- 3,3-dimethylpentadecanoic acid], which has very prolonged myocardial retention and slow washout kinetics although only animal studies have been reported with this agent. Still another more recent approach has been the synthesis and laboratory animal and human evaluation of analogues containing a phenylene bridge in the fatty acid chain. One example is 3-10 [13-(4'-iodophenyl)]-3-(p-phenylene)tridecanoic acid (PHIPA 3-10), which has also proven successful in delaying myocardial tracer washout. This paper focuses on a discussion of the effects of molecular structure on the myocardial uptake and release of these various radioiodinated fatty acid analogues.

A case of hypertensive-diabetic cardiomyopathy demonstrating left ventricular wall motion abnormality

We report a case of hypertensive-diabetic cardiomyopathy demonstrating left ventricular regional wall motion abnormality, with a normal coronary artery documented on coronary arteriography. Dipyridamole-infusion 201Tl scintigraphy demonstrated transient perfusion defects in the infero-posterior wall of the left ventricle, where reduced wall motion was demonstrated on contrast left ventriculography. Myocardial SPECT (single photon emission tomography) imaging with [123I] beta-methyliodophenylpentadecanoic acid (BMIPP) and 201Tl demonstrated reduced [123I]BMIPP uptake compared with 201Tl uptake in the infero-posterior wall of left ventricle. These results suggest that the impairment of myocardial free fatty acid metabolism is an etiologic or contributory factor for regional wall motion abnormality, together with small-vessel coronary artery disease, in this patient.

Ischemic and reperfused myocardium detected with technetium-99m-nitroimidazole

To evaluate the utility of 99mTc-labeled nitroimidazole (BMS) in the detection of ischemic or reperfused myocardium, we performed dual-tracer autoradiography with BMS and [125I]iodoantipyrine (IAP).

METHODS

In open-chest rats, the left coronary artery was ligated to produce 15- or 60-min ischemia followed by reperfusion or 60-min ischemia without reperfusion. BMS was injected just before ligation, 1 min before reperfusion or 15 min after reperfusion.

RESULTS

In the area at risk, regional myocardial blood flow (rMBF) evaluated by IAP recovered to the level in the nonischemic septum in all hearts, except in 60-min occlusion without reperfusion. In myocardium reperfused after 15-min ischemia (stunned), normalized BMS uptake (%BMS) in the area at risk was significantly increased only when BMS was injected before ischemia. When BMS was injected before 60-min ischemia or just before reperfusion, %BMS was significantly higher at the marginal zone of infarction than in the infarcted area. In contrast, %BMS was significantly lower in the infarcted area when BMS was injected during reperfusion. After 60 min of occlusion without reperfusion (permanent occlusion), rMBF in the area at risk was significantly decreased as was %BMS. In the peripheral zone of the area at risk, rMBF was significantly reduced, but %BMS was significantly increased.

CONCLUSION

BMS images stunned myocardium only when it is injected before ischemia, while it images the area at risk subjected to prolonged ischemia when it is injected up to the time of reperfusion. The infarcted area can be negatively visualized when BMS is injected after reperfusion.

Collateral channels that develop after an acute myocardial infarction prevent subsequent left ventricular dilation

OBJECTIVES

We sought to evaluate the effect of collateral channels that develop late after a first anterior myocardial infarction on left ventricular dilation and function.

BACKGROUND

Collateral channels in an infarct-related artery may develop long after occlusion of the artery. Well visualized collateral channels that appear immediately after a myocardial infarction reduce infarct size and preserve left ventricular function. However, the functional significance of collateral channels that develop late after myocardial infarction has not been evaluated in terms of left ventricular function.

METHODS

We studied 21 patients with a first anterior myocardial infarction and an infarct-related artery that remained totally occluded after reperfusion therapy and did not reopen within 1 month of infarction. No collateral channels were observed during the acute period. Patients were classified into two groups according to the extend of collateral formation 1 month after infarction: group C, patients with well developed collateral channels (n = 11), and group NC, patients with absent or poorly developed collateral channels (n = 10). Infarct size was determined by peak creatine kinase activity and thallium-201 single-photon emission computed tomography. Global and regional left ventricular function and left ventricular volumes were assessed by left ventriculography. These measurements were identical in both groups 1 month after infarction. Left ventricular function was reevaluated after 2.12 +/- 0.79 years (mean +/- SD).

RESULTS

There were no significant changes in global and regional left ventricular function between the two groups during the long-term follow-up period. However, the end-diastolic volume index of group NC increased from 71 +/- 14 to 85 +/- 19 ml/m2, whereas that of group C decreased from 64 +/- 18 to 59 +/- 12 ml/m2. This important change during the long-term follow-up period resulted in a significant difference (p = 0.0006) in the end-diastolic volume index between the groups 2 years after onset (p = 0.002), whereas 1 month after infarction the difference was not significant (p = 0.36). A similar pattern was observed for the end-systolic volume index (group C: 38 +/- 16 to 35 +/- 14 ml/m2; group NC: 45 +/- 12 to 58 +/- 18 ml/m2, p = 0.018). The power of the tests to detect the observed differences showing nonsignificant results ranged from 0.05 to 0.38, whereas the power of the tests indicating a significant difference in end-diastolic and end-systolic volume indexes was >0.88.

CONCLUSIONS

Collateral channels that develop after a myocardial infarction do not reduce the infarct size or prevent left ventricular dilation within 1 month of infarction. In contrast, such collateral channels prevent subsequent ventricular dilation and the deterioration of left ventricular function over 2 years. However, our results may have been biased because of the small number of patients.

Kinetics of radioiodinated species in subcellular fractions from rat hearts following administration of iodine-123-labelled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (123I-BMIPP)

It is recognized that iodine-123-labelled 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid (123I-BMIPP) slowly washes out of the myocardium. The mechanism for the washout was investigated in normal rat hearts by analyses of the subcellular distribution and lipid classes based on the BMIPP metabolism. Rat hearts were excised at 1-120 min after intravenous injection of 123I-BMIPP. After counting the radioactivity, the hearts were digested with Nagarse and homogenized, and then fractionated into the cytosolic, mitochondrial, microsomal and crude nuclear fractions by centrifugations. The radioactivity of each fraction was counted, and the lipid classes were analysed by radio-thin-layer chromatographic and high-performance liquid chromatographic methods. The heart uptake of 123I-BMIPP was maximal at 5 min (6.81%+/-0.36% ID/g), and 41% of the radioactivity disappeared within 120 min. The myocardial radioactivity was immediately distributed into the cytosolic, mitochondrial, microsomal and crude nuclear fractions. The distribution (%) of each fraction was almost identical from 5 min through 120 min. The cytosolic fraction was always the major site of radioactivity deposition (60%), and the time-activity curve of the cytosolic fraction paralleled that of the whole heart throughout the 120-min study period. In the cytosolic fraction, most of the radioactivity was incorporated into the triglyceride class, and the rest was present in the free fatty acid, phospholipid (phosphatidylcholine) and diglyceride classes. In the mitochondrial fraction, the radioactivity was mostly incorporated into the phospholipid class (phosphatidylethanolamine), followed by free fatty acids. The final metabolite of 123I-BMIPP, 123I-p-iodophenylacetic acid (123I-PIPA), initially appeared in the mitochondrial fraction as early as 1 min, and subsequently in the cytosolic fraction at 5 min. Another intermediary metabolite, 123I-p-iodophenyldodecanoic acid (123I-PIPC12), was found only in the mitochondrial fraction after 5 min. In conclusion, the slow washout kinetics of 123I-BMIPP from the myocardium mainly reflects the turnover rate of the triglyceride pool in the cytosol. The BMIPP metabolism, i.e. initial alpha-oxidation followed by subsequent cycles of beta-oxidation, was confirmed in vivo. The participation of the mitochondria in the metabolism was also proven.

Paradoxical uptake of F-18 fluorodeoxyglucose by successfully reperfused myocardium during the sub-acute phase in patients with acute myocardial infarction

The myocardial uptake of F-18 fluorodeoxyglucose (FDG) has been shown to indicate ischemia. To elucidate whether this is applicable to reperfused myocardium in patients with acute myocardial infarction (AMI), Tl-201 SPECT and F-18 FDG PET were performed in 10 patients with successfully recanalized AMI (male myocardial perfusion on the infarct-related area was classified, on the basis of Tl-201 images, into 2 groups (normal and defect) during the sub-acute phase, and into 3 grades (normal, redistribution (RD), and persistent defect) during the chronic phase (1 and 3 months after onset). Regional FDG uptake was calculated as FDG uptake in the region of interest normalized relative to that in a normal area. During the chronic phase, FDG accumulated only in the region of RD, indicating ischemia, but during the sub-acute phase, FDG accumulated mainly in the peri-infarct area. To elucidate whether the reperfused myocardium itself shows signs of accelerated glucose uptake, an experimental study was performed in rats. Glucose uptake in the isolated heart was measured by deoxyglucose and 31P-NMR spectroscopy, and was significantly increased after reperfusion compared with the pre-ischemic level. In conclusion, the enhancement of FDG uptake during the sub-acute phase was observed in successfully reperfused myocardium of patients with acute myocardial infarction. Such augmentation disappeared during the chronic phase. An experimental study in rats indicated that ischemia and reperfusion themselves augment glucose uptake. This mechanism may be responsible for the increase in FDG uptake of reperfused myocardium observed clinically.

A new approach for evaluation of left ventricular diastolic function: spatial and temporal analysis of left ventricular filling flow propagation by color M-mode Doppler echocardiography

OBJECTIVES

To evaluate left ventricular diastolic function and differentiate the pseudonormalized transmitral flow pattern from the normal pattern, the propagation of left ventricular early filling flow was assessed quantitatively using color M-mode Doppler echocardiography.

BACKGROUND

Because the propagation of left ventricular early filling flow is disturbed in the left ventricle with impaired relaxation, quantification of such alterations should provide useful indexes for the evaluation of left ventricular diastolic function.

METHODS

Study subjects were classified into three groups according to the ratio of early to late transmitral flow velocity (E/A ratio) and left ventricular ejection fraction: 29 subjects with an ejection fraction > or = 60% (control group); 34 with an ejection fraction < 60% and E/A ratio < 1 (group I); and 25 with ejection fraction < 60% and E/A ratio > or = 1 (group II). The propagation of peak early filling flow was visualized by changing the first aliasing limit of the color Doppler signals. The rate of propagation of peak early filling flow velocity was defined as the distance/time ratio between two sampling points: the point of the maximal velocity around the mitral orifice and the point in the mid-left ventricle at which the velocity decreased to 70% of its initial value. High fidelity manometer-tipped measurement was performed in 40 randomly selected subjects.

RESULTS

The rate of propagation decreased in groups I and II compared with that in the control group (33.8 +/- 13.8 [mean +/- SD] and 30.0 +/- 8.6 vs. 74.3 +/- 17.4 cm/s, p < 0.001, respectively) and correlated inversely with the time constant of left ventricular isovolumetric relaxation and the minimal first derivative of left ventricular pressure (peak negative dP/dt) (r = 0.82 and r = 0.72, respectively).

CONCLUSIONS

Spatial and temporal analysis of filling flow propagation by color M-mode Doppler echocardiography was free of pseudonormalization and correlated well with the invasive variables of left ventricular relaxation.

[Experience with mild exercise 123I-BMIPP myocardial imaging in two cases of ischemic heart disease]

During mild to moderate ischemia, glycolytic flux is enhanced and free fatty acid uptake is reduced in proportion to the reduction in mitochondrial metabolism. We considered that mild exercise may induce the reduction of 123I-BMIPP, reflecting myocardial fatty acid metabolism, in ischemic myocardium compared to normal myocardium. Therefore, mild exercise 123I-BMIPP myocardial imaging was carried out to detect myocardial ischemia in 2 cases of ischemic heart disease. Mild exercise was performed using a bicycle ergometer with 25-50 W loading. At seven minutes before cessation of exercise, 111 MBq of 123I-BMIPP was injected. Case 1 was a 12 year-old boy with Kawasaki's disease. The study showed a reduction of mild exercise 123I-BMIPP uptake in the anteroseptal wall. In contrast, stress 201T1 myocardial imaging did not show perfusion defect in the anteroseptal wall. Case 2 was a 64 year-old female with triple vessels disease. Mild exercise 123I-BMIPP myocardial imaging showed similar with those of stress 99mTc-sestamibi. We conclude that mild exercise 123I-BMIPP myocardial SPECT may be a sensitive method to detect myocardial ischemia.

Metabolism of iodine-123-BMIPP in perfused rat hearts

Increased clinical use of 123I-labeled 15-(p-iodophenyl)-3-(R,S)-methyl- pentadecanoic acid ([123I]BMIPP) revealed discordance between BMIPP uptake and that of perfusion agents, which was inexplicable due to the uncertainty of its myocardial metabolism. This study clarifies the metabolic fate of BMIPP and its relation to substrates in isolated rat hearts.

METHODS

Rat hearts were perfused with 5 mmole/liter HEPES buffer containing various energy substrates and 1% bovine serum albumin. The buffer was recirculated for 4 hr after bolus injection of [123I]BMIPP. Heart time-activity curves were monitored externally. After perfusion, the radioactivity in the heart and recirculated buffer was measured. The metabolites in the buffer were then extracted and analyzed by HPLC and TLC.

RESULTS

when 0.4 mmole/liter oleate was the energy substrate, more than eight radioactive BMIPP metabolites were detected. The metabolites in the coronary effluent depended on the energy substrate in the buffer. The radioactivity in the heart at the end of the perfusion period was significantly higher when 0.4 mmole/liter oleate (28.0% +/- 1.2% ID/g, mean +/- s.e.m.) or 10 mmole/liter glucose with 25 U/liter insulin (43.9% +/- 2.2% ID/g) were the substrates compared to when 5 mmole/liter acetate (8.5% +/- 0.4% ID/g) or 0.4 mmole/liter cold BMIPP (6.2% +/- 0.3% ID/g) were the substrates. The distribution of metabolites suggests that oleate stimulated both alpha and beta oxidations, whereas glucose with insulin inhibited both. Acetate also stimulated alpha oxidation but not beta oxidation. Cold BMIPP strongly inhibited both alpha- and beta-oxidations, and little alpha oxidation occurred compared to beta-oxidation.

CONCLUSION

These results suggest that [123I]BMIPP is metabolized in the myocardium and the metabolism is closely related to myocardial carbohydrate utilization.

Myocardial metabolism of 123I-BMIPP in patients with hypertrophic cardiomyopathy: assessment by radial long-axis SPET

To elucidate the metabolism of free fatty acid in the myocardium of hypertrophic cardiomyopathy (HCM), SPET was performed with 123I-15-(p-iodophenyl)-3-R,S-methylpentadecanoic acid (BMIPP), an analogue of free fatty acid, and with 201Tl in nine patients with HCM and eight healthy volunteers who acted as controls. For quantitative analysis of the apical area, a radial long-axis tomogram was reconstructed every 6 degrees after short-axis tomography. The relative regional uptake (RRU, %) in each segment was obtained by normalizing to the maximal value among all segments. The 3-h washout rate was calculated both for BMIPP and for 201Tl. The ratio of the RRU of BMIPP to that of 201Tl was significantly lower in the apical and antero-septal regions compared with other walls (P < 0.01) in the patients with HCM, whereas uptake of both BMIPP and 201Tl in the controls was homogeneous and there was a significant correlation between them. The coefficient of variation (CV) in all segments in the HCM patients was significantly higher (P < 0.01) than that of the controls both BMIPP and 201Tl, indicating inhomogeneous uptake of BMIPP in the HCM patients. The washout rate of BMIPP over 3 h was significantly higher in the patients with HCM (mean +/- S.D. 26.3 +/- 7.3%) than the controls (18.3 +/- 7.5%, P < 0.05). The ratio of segmental washout rate of BMIPP to that of 201Tl in the HCM patients was increased, especially in the septum and apex.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of beta-blockade on regional left ventricular function in patients with dilated cardiomyopathy

It has been reported that beta-blockade has beneficial effects on the cardiac function and prognosis of patients with congestive heart failure. However, the mechanism for these effects remained unclear. This study compared the use of an angiotensin-converting enzyme (ACE) inhibitor (enalapril, 2.5 to 5.0 mg/day, or delapril, 15 to 30 mg/day) alone with the effects of beta-blockade therapy (metoprolol, 40 to 60 mg/day) coupled with an ACE inhibitor on global and regional left ventricular (LV) function in patients with dilated cardiomyopathy. In 12 patients with dilated cardiomyopathy, the global LV ejection fraction (EF), regional EF (rEF), and regional ejection time (rET) were determined by sector analysis of the radionuclide ventriculogram before and after therapy (duration 14 +/- 9 months). The coefficients of variation of rEF and rET were calculated as indexes of the heterogeneity of regional LV systolic wall motion. EF increased significantly from 20% +/- 8% to 30% +/- 8% (p < 0.05) in patients who received beta-blockade and an ACE inhibitor (n = 5). Furthermore, the coefficients of variation of rET decreased from 27% +/- 13% to 16% +/- 7% (p < 0.05). In contrast, patients treated with an ACE inhibitor only (n = 7) showed no significant improvements in any of these parameters. These results suggest that, compared with an ACE inhibitor alone, beta-blockade improves global and regional LV function in dilated cardiomyopathy by synchronizing myocardial contraction.

[Serial assessment of MIBG scintigraphy in a case of DCM with heart failure improved by beta-blocker therapy]

We experienced a case of DCM (62-year-old man) improved by beta-blocker (Metoprolol) therapy and studied time course of MIBG scintigraphy. We measured cardiac functions by UCG and 99mTc cardiac pool imaging, and MIBG scintigraphy during 12 months of beta-blocker therapy. In planar images we measured washout rate (WR) in total myocardium and regional washout rate (rWR) in 6 segments of myocardium. Cardiac function improved after 3 months of therapy. The WR did not improve until 6 months, but improved after 9 months (Before: 35.1%, 3 months after: 34.6%, 6 months after: 33.6%, 9 months after: 27.6%, 12 months after: 25.4%). rWR in inferoapical segment first improved at 3 months (Before: 40.1%, 3 months after: 35.1%), whereas rWR in antero-apical segment improved after 6 months and that in anterior segment improved after 9 months. These results suggest that the improvement of cardiac sympathetic nerve function in DCM treated with beta-blocker was not identical in each myocardium region.

Effect of angina pectoris on myocardial protection in patients with reperfused anterior wall myocardial infarction: retrospective clinical evidence of "preconditioning"

OBJECTIVES

We examined whether angina pectoris occurring shortly before the onset of acute myocardial infarction can actually preserve postischemic left ventricular function in humans.

BACKGROUND

Experimental studies indicate that brief, transient episodes of ischemia render the heart very resistant to infarction from a subsequent sustained ischemic insult, an effect termed ischemic preconditioning. However, no clinical data are available concerning the implications of angina pectoris shortly before the onset of infarction in humans.

METHODS

We studied 84 patients with an acute anterior myocardial infarction. All patients had total occlusion of the proximal or medial portion of the left anterior descending coronary artery and achieved reflow within 6 h of onset. Patients were classified into three groups on the basis of duration of antecedent angina pectoris: group 1 = no angina (37 patients); group 2 = new angina pectoris occurring < or = 7 days of onset of infarction (22 patients); group 3 = angina pectoris beginning > 7 days before onset of infarction (25 patients). All patients underwent left ventriculography on the day of, and 28 days after, onset of infarction to determine ejection fraction and regional wall motion in the territory of the left anterior descending coronary artery by the centerline method.

RESULTS

Angiographic collateral flow grade was higher in group 3 than in groups 1 and 2 ([mean +/- SD] group 1 = 0.08 +/- 0.7, group 2 = 0.7 +/- 0.7, group 3 = 1.5 +/- 0.8). Although there were no differences in baseline ejection fraction and regional wall motion among the three groups, the degree of improvement was significantly greater in groups 2 and 3 than in group 1 (late minus baseline ejection fraction: group 1 = 0 +/- 8%, group 2 = 7 +/- 10% group 3 = 6 +/- 10% [p < 0.05 group 1 vs. groups 2 and 3]; late minus baseline regional wall motion: group 1 = 0.2 +/- 0.4, group 2 = 0.6 +/- 0.5, group 3 = 0.5 +/- 0.6 SD/chord [p < 0.05, group 1 vs. group 2]). When the study was limited to those patients with no or poor collateral flow (31 in group 1, 19 in group 2, 10 in group 3), only group 2 patients had a significant improvement in wall motion. Angina pectoris within 24 h before onset of infarction was more frequent in group 2 (82%) than group 3 (28%, p < 0.05).

CONCLUSIONS

Episodes of angina pectoris occurring shortly before the onset of infarction may preserve myocardial contractile function in reperfused myocardial infarction despite less support from collateral flow channels, although these are suggestive results in a limited number of patients.

Vagally mediated heart rate recovery after exercise is accelerated in athletes but blunted in patients with chronic heart failure

OBJECTIVES

Vagally mediated heart rate recovery after exercise was assessed in patients with chronic heart failure and in well trained athletes by analyzing the postexercise heart rate decay.

BACKGROUND

Vagal reactivation is an important cardiac deceleration mechanism after exercise. However, alterations of this mechanism under pathologic conditions have not been characterized because of the lack of a specific index.

METHODS

To find a vagally mediated component of heart rate recovery, the time constants of the beat-by-beat heart rate decay for the first 30 s (T30) and the first 120 s (T120) after exercise were obtained at six levels of exercise in eight normal volunteers: 1) at maximal exercise, 2) at anaerobic threshold, 3) at anaerobic threshold with propranolol administration, 4) at anaerobic threshold with atropine administration, 5) at anaerobic threshold with concomitant administration of both drugs, and 6) at 50% of anaerobic threshold. To investigate the effects of heart failure and endurance training on vagally mediated heart rate recovery, T30 and T120 at anaerobic threshold were obtained in 20 patients with chronic heart failure and in 9 cross-country skiers.

RESULTS

In normal volunteers, T30 and T120 were markedly prolonged by atropine administration, indicating that both time constants are mediated by vagal reactivation. Moreover, T30 was almost independent of the exercise intensity and sympathetic blockade, whereas T120 was affected by sympathetic nerve activity and exercise work load. These results indicate that T30 is mediated primarily by vagal reactivation, independent of sympathetic withdrawal, and is significantly smaller in athletes (p < 0.01) and significantly larger in patients with chronic heart failure (p < 0.01) than that in respective age-matched normal control subjects.

CONCLUSIONS

The T30 value could be a specific index for vagally mediated heart rate recovery. Vagally mediated heart rate recovery after exercise is accelerated in well trained athletes but blunted in patients with chronic heart failure.

Kinetics of a putative hypoxic tissue marker, technetium-99m-nitroimidazole (BMS181321), in normoxic, hypoxic, ischemic and stunned myocardium

This study focused on the kinetics of the newly developed 99mTc-nitroimidazole, propyleneamine oxime-1,2-nitroimidazole (BMS181321) in the different setting of myocardial perfusion states and oxygenation levels, and compared the kinetics of BMS181321 with those of other technetium analogues.

METHODS

The kinetics of BMS181321 were evaluated in isolated perfused rat hearts. Technetium-99m-hexamethylpropyleneamine oxime (HMPAO) and a non-nitroimidazole-containing analogue of BMS181321 (6-methyl propyleneamine oxime; PAO-6-Me) were used to compare their kinetics with those of BMS181321.

RESULTS

BMS181321 cleared quickly from normoxic hearts and the retention in the myocardium 10 min after injection was 0.84% +/- 0.04% ID/g wet wt (mean +/- s.e.m.). In contrast, BMS181321 was retained after reperfusion when it was injected before ischemia; the uptake in the myocardium 10 min after reperfusion was significantly greater than in controls (23.9% +/- 3.9% ID/g wt, p < 0.05).

CONCLUSIONS

These results indicate that 99mTc-BMS181321 is well trapped in ischemic myocardium and moderately trapped in hypoxic myocardium, but washed out quickly in stunned myocardium. The residence time influences the amount retained.

Split dose iodine-123-IMP SPECT: sequential quantitative regional cerebral blood flow change with pharmacological intervention

At least two quantitative rCBF measurements are needed to evaluate rCBF changes with pharmacological intervention. We have developed the split dose 123I-IMP SPECT method, which enables measurement of rCBF to be repeated in a short time.

METHODS

Thirty-one cerebrovascular disease patients were investigated to assess reproducibility and vasoreactivity to acetazolamide. During 44-min dynamic SPECT imaging, 123I-IMP injection and respective arterial sampling were performed twice at an interval of about 25 min. The rCBF values were calculated using a microsphere model in which the washout of 123I-IMP from the brain can be negligible in the first several minutes after injection. For the second rCBF measurement, the remaining activity due to the first 123I-IMP injection was estimated and subtracted from the total brain activity.

RESULTS

In ten patients, two consecutive resting mean rCBF values in the MCA territory (CBF1 and CBF2) had good correlation (CBF1 = 47.4 +/- 4.0 (ml/min/100 ml: mean +/- s.d.), CBF2 = 45.2 +/- 8.2, CBF2 = 0.900*CBF1 + 2.9, r = 0.915). In 11 patients with occlusive lesions in the unilateral ICA system, mean rCBF in the MCA territory was increased by only 27.7% +/- 14.0% in the affected side by a 1-g intravenous acetazolamide injection, while 44.5% +/- 12.3% increase was found in the nonaffected side. In 10 patients without a major arterial lesion, a 49.7% +/- 17.0% increase of rCBF was demonstrated.

CONCLUSIONS

This split dose method 123I-IMP SPECT can be useful to estimate vascular reserve.