Blocking action of berberine on various receptors in rat anococcygeus muscle

Abstract

The contractile responses of rat anococcygeus muscle to phenylephrine, acetylcholine and 5-hydroxytryptamine in relation to berberine and to their specific antagonists were studied separately.

The effects of phenylephrine and acetylcholine were blocked by berberine as well as by atropine. But the α-blocking action of atropine was exhibited only at high concentration.

The anococcygeus muscle response to phenylephrine was competitively inhibited by berberine with a PA₂ value of 6.4. The contraction induced by acetylcholine was competitively inhibited by atropine (PA₂=8.7), whereas berberine, which differs basically from atropine, shifted the dose-response curve for acetylcholine non-parallelly to the right with its maximal response reduced concomitantly. Its pD₂ value was 4.6. This suggests that the antagonistic action of berberine may be exerted non-specifically through a site beyond the M-cholinergic receptor.

Berberine also relaxed the contraction of anococcygeus muscle induced by 5-hydroxytryptamine.

The contractile responses to histamine and isoprenaline were seen only at high concentration. In addition, the response to isoprenaline was little affected by propranolol in our experiment.

Keywords

berberine / phenylephrine / acetylcholine / 5-hydroxytryptamine / histamine / isoprenaline / prazosin / propranolol / rat anococcygeus muscle

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