ORIGINAL ARTICLE 
Annals of Nuclear Medicine Vol. 13, No. 2,89-93,1999 
Washout rate of 123I-metaiodobenzylguanidine increased by posture change or exercise in normal volunteers 
Takashi YANO, Hiroshi YAMABE and Mitsuhiro YOKOYAMA 
First Department of Internal Medicine,Kobe University School of Medicine 
123I-metaiodobenzylguanidine (MIBG) imaging detects sympathetic nerve function in the heart. The present study was conducted to clarify whether posture change or exercise affects 123I-MIBG kinetics in normal volunteers. Seven subjects underwent three 123I-MIBG studies, i.e., supine protocol, sitting protocol and exercise protocol. Planar 123I-MIBG images were obtained at 15 minutes, 1 hour and 4 hours after injection of 123I-MIBG. The washout rate (WR) from 15 minutes to 1 hour in the supine position in all subjects was similar for all three protocols, whereas the WR from 1 hour to 4 hours was significantly augmented in the sitting protocol and the exercise protocol as compared to the supine protocol (p < 0.05 and p < 0.01). The serum concentration of noradrenaline was significantly increased from the baseline to the 4 hour sampling in the sitting protocol and the exercise protocol (both p < 0.01 ), but was not altered in the supine protocol. The WR from 1 hour to 4 hours significantly correlated with the noradrenaline concentration in 4 hour sampling (r = 0.59, p < 0.01 ). It also significantly correlated with an increase in the noradrenaline concentration from the baseline to the 4 hour sampling (r = 0.53, p < 0.05). It is concluded that posture change or exercise affects the WR of 123I-MIBG in normal healthy subjects. 
Key words: sympathetic nerve, upright position, supine position, noradrenaline 
INTRODUCTION 
THERE IS INCREASING EVIDENCE that 123I-MIBG scintigraphy detects cardiac sympathetic function in various heart diseases.1-4 Sympathetic activation is linked to the severity of heart failure and indicates the patients' prognosis.5,6 123I-MIBG scintigraphy is useful in evaluating patients with heart failure 7-10 But no attention has been paid to posture or physical activity during 123I-MIBG scintigraphy, in spite of the fact that posture change or exercise affects the activity of autonomic nerves.11,12 It is important to clarify whether posture change or exercise alters 123I-MIBG kinetics or not. The present study was conducted with normal volunteers. 
Received September 9, 1998, revision accepted January 11, 1999. 
For reprint contact: Takashi Yano, M.D., Department of Internal Medicine, Shinko Kakogawa Hospital, 797-295 , Isshiki, Kakogawa-cho. Kakogawa 675-0115. JAPAN. 
MATERIALS AND METHODS 
Subjects 
Seven healthy volunteers were studied. All were males. Their age was 29 to 44 years (36 +- 5 years). None of them had any symptoms of cardiac disease, coronary risk factors, or taking medicines. The purpose and details of the study were explained, and Informed consent was obtained from each subject. The study protocol was approved by the Institutional Research Committee of the Kobe University School of Medicine. 
Study Design 
All subjects underwent three study protocols in random order: supine, sitting and exercise protocols. Figure 1 shows an outline of the protocols. In the supine protocol, subjects were in the supine position throughout the examination. They strictly maintained the supine position except when they went to the toilet. 123I-MIBG images were obtained at 15 minutes, 1 hour and 4 hours after the injection. In the sitting protocol, the subjects were in the supine position before injection of 123I-MIBG until the imaging 1 hours later, then they were in the sitting position until the imaging at 4 hours. In this protocol, patients did not leave the chair except when they went to the toilet. In the exercise protocol, the subjects were in the supine position before the injection of 123I-MIBG until the imaging at 1 hour, then they exercised intermittently three times for 30 minutes and rested in the sitting position at intervals. The subjects underwent a bicycle exercise on an electrically braked instrument (Colival-400, Load Co. Ltd., Holland). The exercise load was set to maintain the heart rate at 120 beats per minute in each subject. None of the protocol subjects took meals. Blood sampling for measurement of serum noradrenaline was performed through an indwelling catheter before the injection of 123I-MIBG and before 4 hour imaging. Noradrenaline was measured with a fully automated catecholamine analyzer (HLC, Toso Co. Ltd., Japan). 
123I-MIBG Scintigraphy 
Potassium iodide (300 mg daily) was given orally to block the uptake of 123I-MIBG by the thyroid gland on the day before the 123I-MIBG injection. Each subject was given 111 MBq 123I-MIBG via an antecubital vein in the supine position in all protocols. Anterior planar cardiac images were acquired 15 minutes (15 minute image), 1 hour (1 hour image) and 4 hours (4 hour image) post-injection with a standard field gamma camera equipped with a medium energy collimator. The energy window was set at 159 keV +- 20%. Data acquisition time was 5 minutes for each imaging in the supine condition. All data were recorded by a computer (Scintipac 2400, Shimadzu Medical System, Japan) for display and quantitative analysis. The analysis was performed with raw data. The myocardial 123I-MIBG uptake and washout rate (WR) were measured as follows. Regions of interest delineating the upper mediastinum and global heart were selected. The size of the region of interest on the mediastinum was 5 x 5 pixels with a 64 x 64 matrix size. Myocardial uptake was assessed by calculating the heart/mediastinum count ratio (H/M ratio), defined as (the global heart counts per pixel)/ (the mediastinum counts per pixel). The WR was calculated as, for example that from 15 minutes to 1 hour, {(15 minute heart counts -15 minute mediastinum counts) - ( 1 hour heart counts -1 hour mediastinum counts)}/(15 minute heart counts - 15 minute mediastinum counts). WR (1 hour to 4 hours) and WR (15 minutes to 4 hours) were calculated in a similar manner. The decay correction of 123I was not accounted for. 
Statistical Analysis 
The difference between protocols in parameters was analyzed by paired t-test. A p value less than 0.05 was regarded as significant. 
RESULTS 
Results of 123I-MIBG Analysis Table 1 shows a summary of the results. There were no significant differences among the three protocols in the H/M ratios of all the 15 minute, 1 hour and 4 hour images (Table 1). The WR (15 minute to 1 hour) was similar for all three protocols, but the WRs ( 1 hour to 4 hours) in the sitting protocol and the exercise protocol were significantly greater than in the supine protocol (p < 0.05 and p < 0.01), as shown in Figure 2. Similarly, the WR (15 minutes to 4 hours) in the sitting protocol and the exercise protocol were also significantly greater than in the supine protocol (p < 0.05 and p < 0.01). 
Quantitative analysis was also employed for the upper mediastinum counts. The WR of the upper mediastinum was significantly faster than that of the myocardium (p < 0.001 ). Among the three protocols the WRs of the upper mediastinum were not significantly different, but the WR (1 hr to 4 hr) increased from the supine to the sitting, and to the exercise protocol, though it was not significant (36.13 +- 2.92% vs. 37.55 +- 4.26% vs. 39.50 +- 3.22%, p = 0.09: supine vs. exercise). 
Change in Serum Noradrenaline Concentration 
In the supine protocol, the serum concentration of noradrenaline did not significantly change from the baseline to the sampling at 4 hours (Table 1), but in the sitting protocol and the exercise protocol, the serum concentration of noradrenaline was significantly increased from the baseline to the sampling at 4 hours (both p < 0.01 ). Correlation of 123I-MlBG with Noradrenaline 
The serum noradrenaline concentration at the baseline did not significantly correlate with any parameters of 123I-MIBG analysis, but the serum noradrenaline concentration at 4 hour sampling significantly correlated with WR (1 hour to 4 hours) of 123I-MIBG (r = 0.59, p < 0.01) as shown in Figure 3. In addition, the increase in the serum noradrenaline concentration from the baseline to the sampling at 4 hours also significantly correlated with the WR (1 hour to 4 hours) of 123I-MIBG (r = 0.53, p < 0.05). 
DISCUSSION 
The present study demonstrated that the WR of 123I-MIBG scintigraphy was significantly altered by a transient sympathetic activation caused by posture change or exercise in normal healthy subjects. 
123I-MIBG scintigraphy is a very useful method for detecting the functional state of the cardiac sympathetic nerve in heart diseases, but the characteristics of 123I-MIBG in physiological conditions has not been fully investigated. In the present study, we hypothesized that a transient change in autonomic nerve activity caused by posture change or exercise affects a quantitative marker of 123I-MIBG scintigraphy. To elucidate the hypothesis healthy volunteers were enrolled, and WR analysis based on planar 123I-MIBG images obtained at 15 minutes, 1 hour and 4 hours was employed. The kinetics of 123I-MIBG at nerve endings is similar to that of noradrenaline, but 123I-MIBG is different from noradrenaline as to degradation by monoamine oxidase or catechol-o-methyltransferase. Noradrenaline is actively transported into nerve endings by an uptake-1 mechanism and stays in the storage vesicles. After release via exocytosis rapid re-uptake happens. Such kinetics suggests that a scintigraphlcally documented cardiac 123I-MIBG up-take reflects the density of sympathetic nerve endings and the amount of noradrenaline in them.13 On the other hand, spillover of noradrenaline from the nerve endings is determined by the release and reuptake rate.14,15 Noradrenaline release is augmented by sympathetic activation, and the re-uptake rate is high in normal subjects.14,16,17 Since the WR of 123I-MIBG is analogous to noradrenaline spillover, it is a function of sympathetic activation in normal subjects. A change in the physiological state induced by a posture change or by exercise can cause sympathetic activation. Studies of heart rate variation have shown that a low/high ratio of spectral power is related to sympathetic/parasympathetic balance during upright tilt,11,12 but there has been no evidence that such a physiological change can alter the kinetics of 123I-MIBG. 
In our study, the WR of 123I-MIBG from 15 minutes to 1 hour in which period the subjects were in the supine position in all protocols did not differ among the three protocols, whereas the WRS at from 1 hour to 4 hours of the sitting protocol and the exercise protocol were significantly faster than that of the supine protocol. In this period; from 1 hour to 4 hours, the subjects were in the supine position, the sitting position or performed intermittent exercises. The latter two procedures caused a significant increase in the serum level of noradrenaline measured at the 4 hour sampling. In addition, the WR ( 1 hour to 4 hour) significantly correlated with the serum level of noradrenaline at the 4 hour sampling and also with its increase from baseline. These results suggested that a posture change from the supine position to the sitting position or exercise activated the sympathetic nerve, and they augmented the WR of 123I-MIBG simultaneously. There was no difference between supine protocol and other protocols in the H/M ratio of the 4 hour imaging. This was unexpected because an increased WR could result in a reduced 123I-MIBG accumulation in the 4 hour image. The WR of upper mediastinum, a background factor, tended to increase from the supine to the sitting, and to the exercise protocol. This may be one of the reasons for no significant difference in the H/M ratio at 4 hours. 
Sympathetic activity can be evaluated by heart rate variation.18 There have been several reports supporting a significant correlation between 123I-MIBG scintigraphy and heart rate variation.2-4 The low/high ratio in power analysis is changed by an upright tilt, which suggests a change in the sympathetic/parasympathetic balance,11,l2 but it is not known whether 123I-MIBG scintigraphy is affected by posture change or exercise. An increase in serum noradrenaline, a marker of activated sympathetic nerve, was significantly correlated with the WR of 123I-MIBG in our results. The WR of 123I-MIBG is an integration of 123I-MIBG release and faulty re-uptake at nerve endings. It means a spillover into blood, because 123I-MIBG is not degraded by monoamine oxidase or cat-echol-o-methyltransferase. [3H]-labeled noradrenaline studies14,15 have suggested that re-uptake of noradrenaline is decreased in patients with heart failure compared to normal controls, which agrees with an increased WR of 123I-MIBG in patients with heart failure.1 During exercise, noradrenaline spillover is reported to increase in normal humans,19 which agrees with our results. A variety of 123I-MIBG findings have been reported in normal subjects. Age, gender and hypoxia are factors modifying 123I-MIBG kinetics.20-24 Morozumi et al.21 demonstrated that 123I-MIBG accumulation can be abnormal in normal volunteers and is corrected by alpha-2 agonist. This report suggests the 123I-MIBG kinetics is a function of physiological states even in normal subjects and agrees with the findings of our study. 
Study Limitation 
In the present study we did not analyze the regional kinetics of 123I-MIBG. It is well known that the inferoposterior region has less 123I-MIBG uptake than the anterior region. A report on heart rate variation suggested that the 123I-MIBG in the inferior wall is more likely to reflect parasympathetic activity than sympathetic activity.2 Para-sympathetic withdrawal may be the first step in a reaction to posture change or exercise. The regional 123I-MIBG kinetics and comparison with heart rate variation remains an unsolved issue in our study. 
Clinical Implication 
Quantitative analysis of 123I-MIBG kinetics has been reported to be a valuable marker in determining the prognosis of patients with heart failure.9,10 It has never been noticed to control posture and a physical activity during examination, so that the reported quantitative analysis values possibly included a variation caused by physical activity during examination. Patients with heart failure have an augmented noradrenaline spillover 14 which may cause an unexpectedly fast washout of 123I-MIBG under active conditions of a patient. We therefore propose to keep the posture being supine during examination. Controlling the posture and patient's activity promises more valrdlty in 123I-MIBG scintigraphy. 
CONCLUSION 
The WR of 123I-MIBG is fastened by upright posture or exercise in normal healthy subjects. It is important to control the patient's posture and activity in 123I-MIBG scintigraphy. 
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