Study of properties of high and low affinity binding sites in beta-adrenoceptors

研究了-肾上腺素能部分激动剂对-肾上腺素受体高、低亲和力结合位点的立体选择性。我们的研究结果表明，β -肾上腺素受体的高亲和力结合位点比低亲和力结合位点在豚鼠盲肠带绦虫中具有更强的立体选择性。贝福诺尔和卡替洛尔的s(-)-异构体对s(-)-异丙肾上腺素的pa_2值（由各浓度响应曲线随环AMP水平升高的位移计算）显著大于豚鼠盲肠带虫的R(+)-异构体，而s(-)-异构体对兔纤毛体的pa_2值不显著大于R(+)-异构体。结合实验测定的pki值与环AMP水平升高的pa_2值吻合较好。这些结果表明，β -肾上腺素受体在豚鼠盲肠带绦虫体内的高亲和力结合位点可能能够区分R（+）和S(-)-异构体之间的立体选择性，而在兔纤毛体中，两种对映体之间没有立体选择性。

The stereoselectivities of beta-adrenergic partial agonists for the high and low affinity binding sites of beta-adrenoceptors were studied. Our results suggest that the high affinity binding site of beta-adrenoceptors is more stereoselective than the low affinity binding site in the guinea-pig taenia caecum. The pA_2-Values of the s(-)-isomers of befunolol and carteolol against S(-)-isoprenaline, which were calculated from the shift of each concentration-response curve in increasing cyclic AMP levels, were significantly larger than those of the R(+)-isomers in the guinea-pig taenia caecum, while the pA_2-values of the S(-)-isomers were not significantly larger than those of the R(+)-isomers in the rabbit ciliary body. The pki-values determined from the binding experiments were in good agreement with the pA_2-values from the increases in cyclic AMP levels. These results suggest that the high affinity binding site of beta-adrenoceptors in the guinea-pig taenia caecum may be able to discriminate stereoselecticity between the R(+)-and S(-)-isomers, while in the rabbit ciliary body there is no stereoselectivity between the two enantiomers.