It has been generally understood that the intestinal tracts are under the control of the autonomic nerves; the parasympathetics are excitatory and the sympathetics inhibitory. However, it is recently reported that the actions of these autonomic nerves in the newborn animals are shown to be different from those in the adult animals in some species.
In order to elucidate the role of sympathetic innervation to the intestinal tracts, the effects of periarterial nerve stimulation were studied in the periarterial sympathetics-jejunum preparations of the chick and the effects of some autonomic drugs on the isolated muscle strips were a1so studied.
The results obtained were as follows;
1. The periarterial stimulation in the periarterial sympathetics-jejunum preparation elicited the responses of three patterns; 1) contraction followed by relaxation 2) contraction only 3) relaxation only. The excitatory response was most effective in the stimulus frequencies of 40 cps, whereas the inhibitory response was maximal in the stimulus frequencies of 30 cycle per second.
2. The excitatory response to the periarterial stimulation was not affected by the pretreatment with phenoxybenzamine, dibenamine, propranolol and atropine, whereas the inhibitory response was completely blacked by the pretreatment with phenokybezamine and propranolol.
3. In the periarterial sympathetics-jejunum preparation treated with reserpine, the periarterial stimulation evoked only contraction, and the contraction was not affected by the pretreatment with phenoxybenzamine, propranolol and atropine.
4. The administration of norepinehrine evoked a relaxation in the isolated jejunum muscle strips and the effect was completely blocked by the pretreatment with phenoxybenzamine.
5. The administration of isoproterenol produced a relaxation in the isolated jejunum muscle strips and the effect was not affected by pretreatment with phenoxybenzamine, whereas the effect was completely blocked by the pretreatment with propranolol.
6. The administration of acetylcholine produced a marked contraction in the isolated jeunum muscle strips and the effect was completely abolished by the pretreatment of atropine.
These experimental evidences indicate that the inhibitory response to the periarterial stimulation is due to adrenergic fibers and the excitatory response is due to neither adrenergic nor cholinergic component.
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