Radioligand binding assay of receptors with 1251 - iodopindolol revealed that Zhimu can siginificantly inhibit the increase of mouse heart β - adrenoceptors induced by T3. The kinetic parameters were calculated from the data of heart β- adrenoceptor binding sites determined at various periods after irreversible blocking of the preexisting β- adrenoceptors. Zhimu can decrease the production rate and degradation rate constant of hyperthyroid mice by 48 % and 35% respectively. These results indicate that Zhimu can decrease the production rate more potently than the degradation rate of heart β - adrenoceptors in hyperthyroid mice

and hence can make the number

of receptor binding sites approach normal.