BLOCKING ACTION OF BERBERINE ON VARIOUS, RECEPTORS IN RAT ANOCOCCYGEUS MUSCLE

The contractile response of rat anococcygeus muscle to phenylephrine, acetylcholine and 5-hydrotryptamine were studied in relation to berberine and their specific antagonist separately.The effects of phenylephrine and acetycholine were blocked by atropine and berberine respectively. But the α-blocking action induced by atropine was exhibited only at high dose.The anococcygeus muscle response to phenylephrine was competitively inhibited by berberine with a pA₂ value of 6.4. The contraction induced by acetycholine was competitively inhibited by atropine (pA₂=8.7). Berberine, which differs characteristically 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.The contractile responses to histamine and isoprenaline was seen only at high concentration. In addition, the response to isoprenaline was little affected by propranolol in this preparation.