Blocking action of berberine on α₂- and α₁-adrenoceptors in rat vas deferens and anococcygeus muscle

Abstract

Clonidine produced an inhibition of the electrical stimulationevoked 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 Krebs’ solution produced a slow recovery of the responses.

Both berberine and 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 and 8.5 respectively.

The results indicate that berberine possesses competitive α₁ and α₂ blocking action like prazosin and yohimbine, and its selective ratio (α₁/α₂) 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.

Keywords

berberine / prazosin / yohimbine / phenylephrine / clonidine / anococcygeus muscle / vas deferens / drug dose-response relationship

References

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