Binding Characteristics of ^<125>I-Iodocyanopindolol to β-Adrenergic Receptors : Biphasic Scatchard Plts. II. : Effects of Selective Antagonists(Pharmacological)

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The characteristics of the high- and low-affinity binding sites for ^<125>I-iodocyanopindolol (^<125>I-ICYP) in rat cerebral cortex membrane were examined. The Scatchard plots of 〜<125>I-ICYP binding were biphasic in the absence of antagonists as well as in the presence of non-selective antagonists (d-, dl- and l-propranolol) and selective antagonists. Two of the latter (atenolol and practolol) are β_1-selective antagonists and two others (butoxamine and ICI-118551) are β_2-selective antagonists. The β_2-selective antagonists showed more potent action on the high-affinity sites than on the low-affinity sites, while the β_1-selective antagonists had a more potent effect on the low-affinity sites. These results were consistent with those obtained from pharmacological experiments, and suggest that the high- and low-affinity sites in the biphasic Scatchard plots correspond to β_2- and β_1-adrenoceptors, respectively. By means of this approach, the relative percentages of the two receptor subtypes in rat brain (cerebral cortex), lung, heart, and spleen were calculated (ratios of β_1:β_2-adrenoceptors) to be brain 89:11, lung 28:72, heart 92:8, and spleen 59:41. The absolute capacities of β-adrenoceptors per g wet weight in these tissues were 10-14pmol/g tissue except for heart (approx. 2.4pmol/g tissue).
公益社団法人日本薬学会の論文
1987-08-25