Blocking action of berberine on alpha2 and alpha1 adrenoceptors in rat vas deferens and anococcygeus muscle

Chonidine produced an inhibition of the electrical stimulation-evoked contraction of the prostatic portion of the rat vas deferens. Berberine and yohimbine suppressed markedly the effect of clonidine. However, washing away the clonidine by Kreb’s solution produced a slow recovery of the responses. Both berberine an d yohimbine shifted clonidine cumulative dose-response curve rightward parallelly without decreasing the maximal response in rat vas deferens. The pA2 values of berberine and yohimbine were 5.3 and 7.8, respectively. The contractile response to phenylephrine was competitively inhibited by berberine and prazosin in anococcygeus muscle from the same rat. The pA2 values of berberine and prazosin were 6.4 ad 8.5, respectively. The results indicate that berberine possessed competitive alpha1 and alpha2 blocking action as prazosin and yohimbine and its selective ratio (alpha1/alpha2) was 8. As compared with these 2 drugs, the selectivity of berberine was much poorer. pD2 values were 8.8 for clonidine and 5.6 for phenylephrine.