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KMID : 0365819680080010213
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Journal of Pusan Medical College
1968 Volume.8 No. 1 p.213 ~ p.223
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Biphasic action of acetylcholine and nicotine on the rabbit ileum
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Abstract
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Preparations of rabbit ileum supplied by the mesenteric vessels were made and perfused with Locke´s solution containing drugs, using the author´s special apparatus. The responses of the perfused ileum to drugs were studied.
1) Acetylcholine and nicotine in low concentration (10"?-r10"e g/ml) caused contraction of the perfused rabbit ileum. In high concentration(>10-s g/ml) they caused a biphasic reaction of initial inhibition followed by stimulation.
2) The"transient pre-inhibitory effect" of acetylcholine and nicotine on the perfused rabbit ileum was enhanced, but their excitatory effect was abolished, by atropine.
3) The transient pre-inhibitory effect of acetylcholine on the perfused rabbit ileum was abolished, but its excitatory effect was enhanced, by hexamethonium. Both the pre-inhibitory and excitatory effects of nicotine on the perfused ileum were abolished by hexamethonium.
4) The pre-inhibitory effect of acetylcholine and nicotine on the perfused ileum was usually not blocked by either kind of adrenergic blockade alone, but was blocked by a combination of the two.
5) In the perfused ileum from reserpinized rabbits, the pre-inhibitory effect of acetylcholine and nicotine did not appear.
6) From the results it could be deduced that there are two kinds of functionally distinct ganglion cells in the myenteric plexus, one set being excitatory and cholinergic, the other inhibitory and adrenergic.
7) It is, therefore, concluded that the transient pre-inhibitory effect of acetylcholine and nicotine, on
the perfused rabbit ileum depends upon the response of inhibitory ganglia, and that the excitatory effect of nicotine is due to ganglionic effect alone and that of acetylcholine to ganglionic and peripheral effect.
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