The membrane-enriched fraction from the rat brain was prepared by using the method previously described.8) In brief, after the removal of the rat brain, cerebral cortex was minced and homogenized with a glass homogenizer. The homogenate

The binding affinities of racemic derivatives of propranolol to ƒÀ-adrenoceptors were examined by means of radioligand binding assay to determine whether racemic propranolol shows biphasic binding to ,ƒÀ-adrenoceptors in a displacement experiment. Rat brain was used and the ƒÀadrenoceptor binding assay was carried out with 3H-dihydroalprenolol as the radioligand. A higher affinity of l-propranolol than of d-propranolol was observed and dand l-propranolol each gave a uniphasic curve. However, dl-propranolol showed a biphasic curve. Furthermore, a mixture of dand l-propranolol also showed a biphasic curve. These results imply that ƒÀ-adrenoceptors of rat brain may bind the dand l-isomers at distinct sites.