人外周血林巴细胞松果体素受体鉴定及意义

为证明免疫组织上是否存在松果体素受体（ＭＲ）。以＾１２５Ｉ－松果体系（Ｍ）为配体，应用放射配体结合法检测４０例健康人外周血淋巴细胞＾１２５Ｉ－Ｍ特异结合位点。结果：①＾１３５Ｉ－Ｍ特异结合最大结合容量（Ｂｍａｘ）为０．３６±０．１０ｆｍｏｌ／１０＾６细胞（２１７±６０位点／细胞）；平衡解离常数（Ｋｄ）为７９±１３ｐｍｏｌ／Ｌ；②动力学分析显示Ｋ１＝（１．２４±０．３１）×１０＾－７Ｌ·ｍｉｎ＾－１     

介绍一种大鼠脑中γ-氨基丁酸受体的检测方法

目的：介绍一种大鼠脑中γ－ 氨基丁酸受体的快速简便的检测方法。方法：用３Ｈ－ ＧＡＢＡ 为配体来检测大鼠脑神经末梢微囊中的ＧＡＢＡ受体。检测ＧＡＢＡ受体的合适条件是１．０ ×１０－３ｍｏｌ／Ｌ的脑膜蛋白在３７℃下反应３０ ｍｉｎ。结果：大鼠脑中存在ＧＡＢＡ受体,Ｋｄ＝ （９７．３±５．８） ×１０－９ｍｏｌ／Ｌ,Ｂｍａｘ ＝０．１０６１ ×１０－９ｍｏｌ／ｇ 蛋白±０．０１０３×１０ －９ｍｏｌ／ｇ 蛋白,属低亲和力受体。结论：用３Ｈ－ ＧＡＢＡ可以检测大鼠脑中的ＧＡＢＡ受体。     

有机磷毒剂对人脑谷氨酸受体的作用

本工作采用放射性配体结合实验方法，用健康意外死亡的人大脑额叶皮层突触膜作为受体源，３Ｈ－谷氨酸和３Ｈ－ＭＫ８０１作为标记配体在体外研究了人脑皮层ＮＭＤＡ受体的特性及有机磷毒剂对受体结合的影响。人大脑皮层膜与３Ｈ－谷氨酸有一特异性的可饱合性结合。特异性结合表现为单一结合位点，ＫＤ值和Ｂｍａｘ值分别为１０３ｎｍｏｌ／Ｌ和１．６７ｐｍｏｌ／ｍｇ蛋白。谷氨酸受体激动剂对人大脑皮层与谷氨酸结合的抑制强度依次为Ｌ－Ｇｌｕ＞ＤＬ－Ｇｌｕ＞ＫＡ＞ＮＭＤＡ＞Ｄ－Ｇｌｕ。谷氨酸受体亚型拮抗剂ＡＰ５和ＤＮＱＸ（１μｍ…     

介绍一种大鼠脑中γ—氨基丁酸受体的检测方法

目的：介绍一种大鼠脑中γ＝氨基丁酸本的快速简便的检测方法。方法：用＾３Ｈ－ＧＡＢＡ为配体来检测大鼠脑神经末梢微囊中的ＧＡＢＡ受体。检测ＧＡＢＡ受体的合适条件是１．０×１０＾－３ｍｏｌ／Ｌ的脑膜蛋白在３７℃下反应３０ｍｉｎ。结果：大鼠脑中存在ＧＡＢＡ受体,Ｋｄ＝（９７．３±５．８）×１０＾－９ｍｏｌ／ｇ蛋白±０．０１０３×１０＾－９ｍｏｌ／ｇ蛋白,属低亲和力受体。结论：用＾３Ｈ－ＧＡＢＡ可以检测大鼠     

大鼠感染性脑水肿时NMDA受体的变化

测定百日咳菌液（ＢＰ）所致大鼠感染性脑水肿（ＩＢＥ）对３ＨＭＫ８０１与大脑皮层神经细胞特异结合的影响。从大鼠左颈总动脉注入ＢＰ，制备ＩＢＥ模型。雄性ＳＤ大鼠随机分３组：①对照组（ＮＳ，ｎ＝１１）；②ＩＢＥ组（ＢＰ，ｎ＝１２）；③ＭＫ８０１＋ＢＰ预处理组（ＭＫ８０１，ｎ＝４）。０２ｍｌ／ｋｇ体重生理盐水或ＢＰ注入左颈总动脉作为ＮＳ或ＢＰ组；每天腹腔注射０５ｍｇＭＫ８０１／ｋｇ体重，共２天，然后注入ＢＰ为ＭＫ８０１组。注射ＢＰ２４小时后断头取脑。Ｎ甲基Ｄ天冬氨酸（ＮＭＤＡ）受体与３ＨＭＫ８０１的特异结合用放射配体结合分析法测定，Ｓｃａｔｃｈａｒｄ作图。结果，ＮＳ及ＢＰ组的Ｂｍａｘ分别为０６２３±００８２和０６０６±００８７ｐｍｏｌ／ｍｇ蛋白质（ｔ＝０４８，Ｐ＞００５），Ｋｄ分别为４３１±４２和３０５±３０μｍｏｌ／Ｌ（ｔ＝７８，Ｐ＜００５）。ＭＫ８０１预处理减少ＮＭＤＡ受体的特异结合。表明在此脑水肿模型中ＮＭＤＡ受体总数未发生变化，但亲和力明显增高，其增高能被预先腹腔注入的ＭＫ８０１抑制。     

人外周血淋巴细胞松果体素受体鉴定及意义

为证明免疫组织上是否存在松果体素受体（ＭＲ）。以１２５Ｉ松果体素（Ｍ）为配体，应用放射配体结合法检测４０例健康人外周血淋巴细胞１２５ＩＭ特异结合位点。结果：①１２５ＩＭ特异结合最大结合容量（Ｂｍａｘ）为０３６±０１０ｆｍｏｌ／１０６细胞（２１７±６０位点／细胞）；平衡解离常数（Ｋｄ）为７９±１３ｐｍｏｌ／Ｌ；②动力学分析显示Ｋ１＝（１２４±０３１）×１０－７Ｌ·ｍｉｎ－１·ｍｏｌ－１，Ｋ－１＝（４８±１１）×１０－３／ｍｉｎ；③特异性分析表明对Ｍ高度特异性；④亚细胞分布：特异结合部位以细胞核含量最高。结果表明人淋巴细胞存在ＭＲ，该特异结合位点具低结合容量、高亲和力、可饱和性及可逆性结合特点，对Ｍ高度特异性，符合特异结合位点的基本条件；也表明淋巴细胞是Ｍ作用的靶组织，提示Ｍ对免疫的兴奋作用可能是其与免疫组织上ＭＲ的直接作用所致。     

剂量辐射刺激小鼠骨髓细胞G-CSF受体表达

利用＾１２５Ｉ标记的Ｇ－ＣＳＦ（＾１２５Ｉ－Ｇ－ＣＳＦ）检测小鼠骨髓细胞表面Ｇ－ＣＳＦ受体表达，发现＾１２５Ｉ－Ｇ－ＣＳＦ与其受体的结合在３７℃，６０分钟内完成，３×１０＾６骨髓细胞表面的最大结合量（Ｂｍａｘ）为１５．１ｐｍｏｌ，解离常数（Ｋｄ）７８．６ｐｍｏｌ，推算细胞表面Ｇ－ＣＳＦ受体数为３１００个左右；小剂量辐射（５０－２５０ｍＧｙ）照射小鼠后４８小时，检测骨髓细胞表面Ｇ－ＣＳＦ受体数，发…     

γ—^32P标记反义核苷酸对HBV基因表达的封闭效应

人工构建特异性互补于ＨＢＶ基因ｍＲＮＡ ＳＰⅡ增强子区的１５－聚反义代脱氧核苷酸并和γ－＾３２Ｐ进行末端标记，以２μｍｏｌ／Ｌ剂量作用于ＨＢＶ基因转染的ＨｅｐＧ２细胞培养２４ｈ及４８ｈ后检测掺入２．２．１５细胞的１５－Ｓ－ａｓＯＮ分别为６９．４ｎｍｏｌ／Ｌ和７５．８ｎｍｏｌ／Ｌ；对ＨＢｓＡｇ的抑制率分别为５０％和７０％；斑点杂交检测ＨＢＶ ＤＮＡ，结果表明实验组与对照组与对照组无显著性差异。     

原发性高血压病患者左室重量与外周血淋巴细胞β受体密度的相关性研究

为研究高血压病（ＥＨ）患者左室重量与外周血淋巴细胞β受体密度的关系,采用超声心动图与３Ｈ－双氢阿普洛尔（３Ｈ－ＤＨＡ）放射性配基结合分析法,检测７０例ＥＨ男性患者左室重量指数（ＬＶＭＩ）与外周血淋巴细胞β受体最大结合容量（βｍａｘ）。结果显示：①ＬＶＭＩ＞１２５ｇ／ｍ２患者βｍａｘ为（６０３±１０１）ｆｍｏｌ／１０７细胞,分别高于ＬＶＭＩ＜１２５ｇ／ｍ２患者［（４１１±１０３）ｆｍｏｌ／１０７细胞,Ｐ＜０．０１］和正常人［（３６７±１１０）ｆｍｏｌ／１０７细胞,Ｐ＜０．００１］;②随着ＬＶＭＩ的增加,外周血淋巴细胞βｍａｘ呈现进行性上行调节（二者相关系数ｒ＝０．４４,Ｐ＜０．０１）。表明高血压病患者左室重量的增加与外周血淋巴细胞β受体密度的上行性调节具有相关关系。可能与高血压病理状态下机体内源性儿茶酚胺系统的激活,使β受体对其细胞生物活化效应的中介作用增强有关。     

吗啡受体显像剂7α—o—IA—DPA的合成

设计、合成了一种新的吗啡受体显像剂。选用吗啡拮抗剂特培洛啡（ＤＰＮ），经乙酰化选择性保护苯环３位－ＯＨ，将乙烯锡烷作为弥补基引入ＤＰＮ分子７α支链淑醇基因位置，采用碘代锡烷标记法一步合成碘烷ＤＰＮ（７α－ｏ－ＩＡ－ＤＰＮ）。其标记标准达９０％，比活度为８０ＴＢｑ／ｍｍｏｌ，放化纯度大于９５％。体外吗啡受体结合分析表明其具有很高的亲和力（Ｋｉ＝０．４ｎｍｏｌ／Ｌ）。结果表明：新合成的碘标记吗啡配体适     

In vivo measurement of D2 receptor density and affinity for 18F-(3-N-methyl)benperidol in the rat striatum with a PET system for small laboratory animals.

A recent investigation showed that intracerebral radioactivity concentrations can reliably be quantified in vivo with a small-animal PET device. The purpose of the current study was to investigate the binding characteristics of the D(2) receptor radioligand (18)F-(3-N-methyl)benperidol ((18)FMB) in rat striatum by determining receptor density (B(max)) and affinity (K(d)) in vivo. For validation, K(d) and B(max) additionally were determined in vitro using storage phosphor autoradiography. METHODS: Striatal radioactivity was measured with PET in 8 Sprague-Dawley rats after injection of (18)FMB in increasing specific activities. Free radioligand concentrations were estimated from cortical radioactivity concentrations and were subtracted from striatal radioactivity concentrations to obtain specific binding. In vitro saturation experiments were performed on 7 further rats according to the isotopic dilution method. Specific binding was determined by both subtraction of (18)FMB binding in the presence of raclopride and subtraction of cortical radioactivity concentrations from total radioligand binding. Saturation binding curves were obtained by plotting specifically bound radioligand concentrations against free radioligand concentrations and were evaluated with regression analysis. RESULTS: PET yielded a K(d) of 6.2 nmol/L and a B(max) of 16 fmol/mg for the striatal D(2) receptor. In vitro, K(d) and B(max) amounted to 4.4 nmol/L and 84.1 fmol/mg (subtraction of (18)FMB binding in the presence of raclopride), respectively, and 7.9 nmol/L and 70.1 fmol/mg (subtraction of cortical radioactivity concentrations), respectively. CONCLUSION: K(d) values measured with PET and autoradiography agreed and corresponded to inhibition constants obtained in previous in vitro studies. B(max) values lay within the same order of magnitude. The results of in vitro saturation binding analyses also agreed, irrespective of the mode of determination of free radioligand concentrations. Thus, B(max) and K(d) may be determined with PET in analogy to the evaluation of in vitro binding data by regression analysis of bound-versus-free ligand concentrations. Our results show that small-animal tomographs are valuable tools for the in vivo characterization of receptor radioligands as an alternative to autoradiography.     

眼镜蛇毒MP成分与大鼠大脑皮层及心肌M受体结合的亚型选择性研究

目的初步了解眼镜蛇毒MP成分与M受体结合的亚型选择性。方法制备大鼠大脑皮层组织和大鼠心肌组织两种M受体膜蛋白底物。采用放射配体结合法,分别测定眼镜蛇毒MP成分对[3H]QNB与这两种膜蛋白底物结合的抑制百分率和IC50值,分析MP与M受体结合的亚型选择性。结果 MP均能完全抑制[3H]QNB与这两种膜蛋白底物的结合。大鼠大脑皮层组中,MP的抑制行为呈两相式：第Ⅰ相的抑制率为25%,IC50=0.4 nmol·L-1;第Ⅱ相的抑制率为100%,IC50=248.8 nmol·L-1。心肌组MP的IC50值为22.1 nmol·L-1,约为皮层组第Ⅰ相的55倍、第Ⅱ相的1/10。结论 MP对M受体的结合具有亚型选择性。     

多巴胺受体显像半定量参数的探讨

目的探讨脑多巴胺受体显像中作为纹状体非特异性摄取的参照区。方法用大鼠体内研究资料，比较额叶皮质和小脑作为纹状体非特异性摄取参照区所获得的纹状体特异性结合１２５Ｉ（ｓ）（－）３碘２羟基６甲氧基Ｎ〔（１乙基）２吡咯烷基）甲基〕苯甲酰胺（ＩＢＺＭ）的结果。结果碘标记ＩＢＺＭ呈立体选择性和可逆性地与纹状体多巴胺Ｄ２受体结合。额叶皮质和小脑显示对配体的快速摄取和洗脱。当用小脑摄取作为纹状体非特异性摄取参照时，未能获得ＩＢＺＭ的饱和性，而用额叶皮质作为参照区时，可证实其可饱和性，Ｂｍａｘ＝４４ｐｍｏｌ／ｇ纹状体组织。Ｈａｌｏｐｅｒｉｄｏｌ的置换率和由大剂量ｓｐｉｐｅｒｏｎｅ或ｈａｌｏｐｅｒｉｄｏｌ竞争性抑制实验衍变而来的纹状体和其他脑区之间摄取差值百分率均提示：小脑摄取低估了纹状体的非特异性摄取，额叶皮质是一个合适的纹状体非特异性摄取参照区。结论在纹状体多巴胺Ｄ２受体显像中，特异性ＩＢＺＭ的结合和其他半定量参数的计算，最好选用额叶皮质作为非特异性结合参照区。     

Quantification of baboon cortical S2 serotonin receptors in vivo with 3-N-(2'-F18)fluoroethylspiperone and positron emission tomography

We used the ligand 3-N-(2'-F18)fluoroethylspiperone (FESP) and positron emission tomography (PET) to quantify in vivo serotonin S2 neuroreceptor density and affinity in the baboon frontal cortex. In the cortex, FESP binds specifically and exclusively to S2 receptors, and an equilibrium is reached when the rate of ligand-receptor association and dissociation become equal. Using multiple studies in the same baboon, an equilibrium (saturation) analysis approach provided a linear Hill plot with a slope of 1.02 (r2 = 0.988, P less than 0.0001), indicative of ligand binding to a single receptor class. Using serial PET scans, a dynamic approach was also used to quantify S2 receptors in the frontal cortex of the baboon, which provided an estimate of receptor density Bmax = 35.6 +/- 10.9 pmol/g. The rate constants corresponding to transport into and out of tissue were K1* = 0.2720 +/- 0.0299 mol/min.g and k2* = 0.0786 +/- 0.0315 min-1, respectively. The ligand-receptor dissociation constant was k4* = 0.0154 +/- 0.0109 min-1.     

The apparent positive cooperativity of in vivo [3H]PK-11195 binding in mouse fibrosarcoma

To evaluate the binding properties of peripheral benzodiazepine receptor (PBR) in mouse fibrosarcoma, [(3)H]PK-11195 binding, in vitro and in vivo, was investigated using either tissue dissection or autoradiographic method. The binding characteristics in fibrosarcoma were compared with those in the kidney. The results of an in vitro saturation study revealed that the maximal numbers of PBR binding sites (B(max)) in fibrosarcoma and in the kidney were almost the same (kidney: 5.2 pmol/mg protein; fibrosarcoma: 5.0 pmol/mg protein). On the other hand, the binding affinity (K(d)) in fibrosarcoma was lower than that in the kidney (kidney: 0.45 nM; fibrosarcoma: 1.34 nM). It is noteworthy that the in vivo binding of [(3)H]PK-11195 in fibrosarcoma increased with increasing doses of [(3)H]PK-11195 (in the dose range of 0.03-1 mg/kg), whereas that in the kidney decreased with competitive inhibition. The apparent positive cooperativity of [(3)H]PK-11195 binding in fibrosarcoma was only observed under in vivo conditions and might be possibly related to the incoordination of PBR subunits.     

Radiolabeling, biodistribution, and dosimetry of (123)I-mAb 14C5: a new mAb for radioimmunodetection of tumor growth and metastasis in vivo.

This study reports on the in vitro evaluation, biodistribution, and dosimetry of (123)I-labeled monoclonal antibody (mAb) 14C5, a new antibody-based agent proposed for radioimmunodetection of tumor growth and metastasis in vivo. METHODS: (123)I-mAb 14C5 was prepared by direct iodination and tested for stability in vitro. Binding assays were performed on human SK-BR-3 and HeLa carcinoma cells to investigate the antigen expression, antibody affinity, and kinetics of tracer binding. For the biodistribution and dosimetry study, 3- to 4-wk-old NMRI mice were injected intravenously with (123)I-mAb 14C5 (148.0 +/- 7.4 kBq per mouse) and killed at preset time intervals. Organs, blood, urine, and feces were counted for radioactivity uptake, and the data were expressed as the percentage injected dose per gram tissue (%ID/g tissue) or %ID. The MIRDOSE3.0 program was applied to extrapolate the estimated absorbed radiation doses for various organs to the human reference adult. RESULTS: (123)I-mAb 14C5 was obtained in radiochemical yields of 85.0% +/- 2.5% and radiochemical purities were >97%. The iodinated antibody demonstrated good in vitro stability with 93.6% +/- 0.1% of (123)I-mAb 14C5 remaining intact at 24 h after radiolabeling. (123)I-mAb 14C5 bound to SK-BR-3 cells (dissociation constant [K(d)] approximately 0.85 +/- 0.17 nmol/L) and HeLa cells (K(d) approximately 1.71 +/- 0.17 nmol/L) with nanomolar affinity and high specificity, whereas both cell types exhibited a high CA14C5 antigen expression (maximum number of binding sites [B(max)] = 40.6 +/- 5.2 and 57.1 +/- 9.6 pmol/L, respectively). In mice, (123)I-mAb 14C5 accumulated primarily in lungs (20.4 %ID/g), liver (15.1 %ID/g), and kidneys (11.1 %ID/g) within 5 min after injection. A delayed uptake was observed in stomach (12.8 %ID/g) and urinary bladder (8.7 %ID/g) at 3 and 6 h, respectively, after injection. Radioactivity clearance was predominantly urinary, with 44.9 +/- 4.5 %ID excreted during the initial 48 h after administration (cumulative amount). The highest absorbed radiation doses determined for the human reference adult were received by the urinary bladder wall (0.1200-0.1210 mGy/MBq), liver (0.0137-0.0274 mGy/MBq), uterus (0.0196-0.0207 mGy/MBq), and lower large intestine wall (0.0139-0.0258 mGy/MBq). The average effective dose resulting from a single (123)I-mAb 14C5 injection was estimated to be 0.017-0.022 mSv/MBq. CONCLUSION: (123)I-mAb 14C5 shows good in vitro biologic activity and favorable biodistribution properties for imaging carcinomas of different origin and provides an acceptable radiation dose to the patient.     

In vitro binding of [(11)C]raclopride with ultrahigh specific activity in rat brain determined by homogenate assay and autoradiography

OBJECTIVE: The aim of this study was to characterize the in vitro binding of [(11)C]raclopride with ultrahigh specific activity (SA) in the striatum and cerebral cortex of rat brain. METHODS: [(11)C]Raclopride, a dopamine D(2) receptor ligand, with an ultrahigh SA of 4880+/-2360 GBq/micromol (132+/-64 Ci/micromol, n=25) was synthesized. In vitro binding experiment was performed using brain homogenate assay and autoradiography (ARG). RESULTS: In vitro homogenate assay demonstrated that high SA [(11)C]raclopride (2520-6340 GBq/micromol; 68-171 Ci/micromol) had two-affinity (high and low) binding sites in the striatum and cerebral cortex of rat brain. In the striatum, K(d,high) and B(max,high) values were 0.005+/-0.002 nM and 0.19+/-0.04 fmol/mg tissue, respectively, while K(d,low) and B(max,low) values were 2.2+/-1.0 nM and 35.8+/-16.4 fmol/mg tissue, respectively. In the cerebral cortex, K(d,high) and B(max,high) values were 0.061+/-0.087 nM and 0.2+/-0.2 fmol/mg tissue, respectively, while K(d,low) and B(max,low) values were 2.5+/-3.2 nM and 5.5+/-4.8 fmol/mg tissue, respectively. On the other hand, only one binding site was found in the striatum and no binding site was identified in the cerebral cortex using low SA [(11)C]raclopride (44 GBq/micromol; 1.2 Ci/micromol). In vitro ARG for the rat brain using high SA [(11)C]raclopride (6212 GBq/micromol; 168 Ci/micromol) gave a coronal image of the striatum and cerebral cortex with a higher signal/noise ratio than using low SA [(11)C]raclopride (40 GBq/micromol; 1.1 Ci/micromol). CONCLUSION: Using ultrahigh SA [(11)C]raclopride for the in vitro homogenate assay, we succeeded in detecting two-affinity binding sites of [(11)C]raclopride, not only in the striatum but also in the cerebral cortex of rat brain.     

Effect of sabcomeline on muscarinic and dopamine receptor binding in intact mouse brain

Sabcomeline [(R-(Z)-(+)-alpha-(methoxyiamino)-1-azabicyclo[2.2.2]octane-3-acetonitrile)] is a potent and functionally selective muscarinic M1 receptor partial agonist. However, little is known of the binding properties of sabcomeline under in vivo conditions. In this study, muscarinic receptor occupancy by sabcomeline in mouse brain regions and heart was estimated using [3H]quinuclidinyl benzilate (QNB) and [3H]N-methylpiperidyl benzilate (NMPB) as radioligands. In the cerebral cortex, hippocampus, and striatum, the estimated IC50 value of sabcomeline for [3H]NMPB binding was almost 0.2 mg/kg. Sabcomeline was not a selective ligand to M1 receptors as compared with biperiden in vivo. In the cerebral cortex, maximum receptor occupancy was observed about 1 hr after intravenous injection of sabcomeline (0.3 mg/kg), and the binding availability of mACh receptors had almost returned to the control level by 3-4 hr. These findings indicated that the binding kinetics of sabcomeline is rather rapid in mouse brain. Examination of dopamine D2 receptor binding revealed that sabcomeline affected the kinetics of both [3H]raclopride and [3H]N-methylspiperone (NMSP) binding in the striatum. It significantly decreased the k3 and k4 of [3H]raclopride binding resulting in an increase in binding potential (BP = k3/k4 = Bmax/Kd) in sabcomeline-treated mice, and an approximately 15% decrease in k3 of [3H]NMSP binding was also observed. Although the mechanism is still unclear, sabcomeline altered dopamine D2 receptor affinity or availability by modulations via neural networks.     

Acute treatment with pentobarbital alters the kinetics of in vivo receptor binding in the mouse brain

The effect of pentobarbital, a sedative-hypnotic barbiturate, on the in vivo binding of benzodiazepine receptors in the mouse brain was investigated. Dose-related changes in the apparent binding of [3H]Ro15-1788 ([3H]flumazenil) in the cerebral cortex, cerebellum and pons-medulla were observed by pretreatment with pentobarbital. For quantification of the kinetic properties of the in vivo binding of [3H]Ro15-1788, time courses of radioactivity following its injection were examined, and kinetic analysis was performed using the compartment model. The time courses of radioactivity following injection of [3H]Ro15-1788 with 3 mg/kg Ro15-1788 were used as input function. In all regions studied, rate constants between input compartment and specific binding compartment were significantly decreased by pentobarbital. However, no significant alterations in the binding potential (BP=K3/K4) of benzodiazepine receptors by pentobarbital were observed in any of the regions. A saturation experiment indicated that the decrease in the input rate constant (K3), which includes both the association rate constant (k(on)) and the number of binding sites available (B(max)), was mainly due to decrease in k(on). These results suggest that apparent increases in binding at 20 min after tracer injection were due to the decrease in the association and dissociation rates of binding in vivo.     

Evaluation of cardiac beta-adrenoreceptors in the isolated perfused rat heart using (S)-11C-CGP12388.

(S)-(11)C-CGP12388 ((11)C-CGP12388) was recently developed as an in vivo PET tracer for the evaluation of cardiac beta-adrenergic receptors. The purpose of this study was to evaluate the myocardial kinetics of (11)C-CGP12388 using the perfused rat heart model. METHODS: Normal rat hearts were cannulated for retrograde perfusion according to the Langendorff method. Studies were performed using constant coronary flow rates of 12 mL/min (high flow: n = 6) and 6 mL/min (low flow: n = 6). Beta-adrenergic-blocking studies were also done using propranolol (blocking: n = 6). Two bolus injections of (11)C-CGP12388 were administered at a 25-min interval, and time-activity curves were measured using bismuth germanate detectors. The beta-adrenergic receptor density (B(max)) and total distribution volume (DV(tot)) were estimated using compartmental modeling. After the experiment, B(max) in vitro was measured for all hearts using (3)H-CGP12177, and the values were compared with the B(max) estimated in isolated hearts. RESULTS: DV(tot) was significantly lower in the blocking group than in the high-flow group (P < 0.01), and there was no significant difference in DV(tot) between the high- and the low-flow groups. B(max) values estimated from (11)C-CGP12388 kinetics were 5.05 +/- 0.90 pmol/g under the high-flow model and 5.20 +/- 0.63 pmol/g under the low-flow model. The B(max) results in isolated hearts correlated significantly with the measured in vitro B(max) values (r(2) = 0.69; P < 0.001). CONCLUSION: Beta-adrenoreceptor density in the isolated rat heart can be quantified using (11)C-CGP12388 and a 2-injection protocol. The binding of the tracer was flow independent, with low nonspecific binding. These results suggest that (11)C-CGP12388 is a promising PET tracer that may be applicable to human studies.