Sarsasapogenin was extracted from the Chinese herb Zhimu and its pharmacological action was compared with ZM decoction （ZM） in "Hyperthyroid" mice. 125I-Pindoiol binding assay revealed that the maximum binding capacity （RT） of brain beta-adrenoceptors of the models was significantly higher than normal and that repeated oral administrations of either ZM or SAR reduced the elevated RT to nearly normal. The peak value of plasma cAMP after a single dose of isoproterenol （ISO） was also significantly higher in the models than in control. Again oral administrations of either ZM or SAR reduced the response of plasma cAMP to ISO to nearly normal. However

in vitro competitive binding assay indicated that neither SAR nor its succinyl derivative had any direct binding reaction with beta adrenoceptors. It is therefore concluded that SAR is an important component of Zhimu and the mechanism of its "Yin-tonic" action is probably a down-regulation of the beta-adrenoceptors rather than direct occupation of receptor binding sites.