(From the Physiological Laboratory, Cambridge.)

Transcription

1 THE INNERVATION OF THE PYLORIC SPHINCTER OF THE RAT. BY M. NAKANISHI. (From the Physiological Laboratory, Cambridge.) WHILST numerous observations have been made on the behaviour of the pyloric region of the stomach, few have been made on the effect of nerve stimulation on the pyloric sphincter as distinguished from the rest of the pyloric region. Openchowski('), in experiments in which some part of the central nervous system was stimulated, came to the conclusion that the thoracic nerves as far as the 10th sent inhibitory and motor fibres to the pyloric region inclusive of the sphincter: the inhibitory fibres being more numerous than the motor in the dog and less numerous than the motor in the rabbit. Elliott(2) briefly mentions that the pyloric sphincter of the rabbit is contracted by adrenaline and also by stimulation of the splanchnic nerve, but that the contraction is weak. Smith(3) in the course of observations on strips of the stomach removed from the body found that adrenaline caused slight contraction of the pyloric sphincter in a few instances, but that in most cases no reaction could be obtained. I have investigated the behaviour of the sphincter in rats by the following method. The rats were anaesthetised with urethane and kept warm by a bag containing hot water. A small glass tube was introduced into the stomach through the cesophagus and tied in the cesophagus. The tube was connected with Mariotte's bottle containing warm Ringer's solution. The right side of the abdomen was incised and another larger glass was inserted into the duodenum for recording the flow of fluid from the stomach by a drop-recorder. The critical intragastric pressure which was sufficient to force fluid through the sphincter was at first about cm. water pressure. It varied during the experiment and tended to become higher in the case of the vagus stimulation. The observations were begun a few centimetres below the critical pressure, the sphincter then generally had periodic openings. For stimulation of the nerves I used induction shocks of such strength as to be felt fairly strongly on the tip of the tongue. Sometimes I used also a stimulus which was only felt feebly.

2 PYLORIC SPHINCTER 481 The vagus. The peripheral end of the vagus was stimulated (a) on the cesophagus a little below the diaphragm, (b) in the neck after giving atropine, (c) in the neck without giving atropine. In stimulating the nerve below the diaphragm the branch on the ventral surface of the cesophagus was taken. With a fairly strong stimulus, relaxation of the sphincter was constantly obtained. The degree of relaxation and its duration varied considerably in different experiments, and in any one experiment varied with successive stimuli. Fig. 1 is an example opfmarked relaxation when there is high initial tone; the cessation of the stimulus is followed by rhythmic contraction and II Fig. 1. Marked relaxation of the pyloric sphincter caused by fairly strong stimulation of the anterior vagus branch below the diaphragm. Upper line: drops of fluid from the stomaach. Middle line: stimulation of the nerve. Under line: time in seconds. Fig. 2. Contraction of the pyloric sphincter caused by weak stimulation of the anterior vagus branch below the diaphragm. relaxation, the duration of the relaxation gradually decreasing. Weaker -stimulation in all cases but one gave a similar but less effect. In the exception, there was contraction of the sphincter instead of relaxation (Fig. 2) showing the presence of motor as well as of inhibitory fibres in the vagus. In some cases, especially when the tone of the sphincter was low, and fluid was passing at short intervals through it, the primary increase of flow caused by stimulation was followed by a decrease, indicating the presence of motor fibres: this however was not a marked feature of the results. The greater the tone, the. longer was the latent period and the more obvious the effect of vagus stimulation. Figs. 3a, 3b show the effect of two stimuli of equal strength, the former at the beginning

3 482 M. NAKANISHI. of an experiment with low tone, the latter after numerous stimulations when the tone had increased. (Time in seconds in all figures.) Fig. 3. Relaxation of the pyloric sphincter caused by weak stimulation of the anterior vagus branch below the diaphragm: a, at the beginning of an experiment with low tone of the sphincter:-relatively short latent period before the relaxation: b, when the tone of the sphincter had increased after repeated stimulation of the nerve: long latent period and greater, though less lasting, relaxation. When atropine (1.5 mgrm.) was injected into the femoral vein and the peripheral end of the cervical vagus stimulated, the results were much the same as those described above. So far as the experiments went, the after-contraction of the sphincter was greater (Fig. 4) with fairly strong stimulation. Weaker stimulation once, but only once, caused trifling Fig. 4. Relaxation and after-contraction of the sphincter caused by fairly strong stimulation of the vagus nerve in the neck after atropine injection. preliminary contraction. Stimulation of the vagus in the neck when atropine was not injected gave results not distinguishable with certainty from those obtained after atropine injection. The splanchniw nerve. The left splanchnic nerve was exposed and cut in the abdomen. Since the nerve is small in the rat, it was taken with a little fatty tissue surrounding it. Stimulation of the nerve caused con-

4 PYLORIC SPHINCTER 483 traction of the sphincter (Fig. 5). The effects were not due to setting free of adrenaline, for contraction was obtained by stimulating the Fig. 5. Contraction and after-relaxation of the sphincter caused by stimulating the left splanchnic nerve. splanchnic nerve after extirpation of the suprarenal glands. The contraction was usually followed by relaxation; this varied in character, sometimes being irregularly rhythmic, sometimes being fairly regular and slight. It may be mentioned that in one case the splanchnic was mechanically stimulated by traction and this had the same effect as electrical stimulation. The preceding results show that in the rat stimulation of the vagus has usually a predominant inhibitory effect and the splanchnic usually a predominant motor effect. The effect of adrenaline was then tried. Effect of adrenaline. In the first place this was applied locally. A small piece of cotton wool soaked in 0-1 p.c. adrenaline was placed on the outer surface of the pyloric sphincter. The effect was like that produced by Fig. 6. Contraction of the pyloric sphincter caused by local application of adrenaline. Middle line: placing and taking off of the cotton-wool soaked in adrenaline. Fig. 7. Contraction of the sphincter caused by intravenous injection of adrenaline. x, injection of adrenaline. stimulating the splanchnic nerve, but the contraction, though it took some time to produce, was greater (Fig. 6). In the example given the

5 484 M. NAKANISHI. contraction was followed by rhythmic dilatation. of adrenaline had a similar effect (Fig. 7). Intravenous injection SUMMARY. The experiments show that the predominant effect of the vagus is inhibition of the pyloric sphincter and that of the sympathetic is contraction, i.e. the predominant effects of the two systems of nerves are antagonistic. But it is clear that the vagus has also some motor fibres for the sphincter; these, no doubt, are brought into play in vomiting. The evidence that the sympathetic contains some inhibitory fibres for the sphincter is less satisfactory; since inhibition on stimulating the splanchnic nerve was only obtained as a secondary effect after a preliminary contraction. Adrenaline, as in so many other cases, produces an effect broadly similar to that caused by sympathetic stimulation. I am greatly indebted to Prof. Langley for his kind advice and suggestion during the course of my work. REFERENCES. (1) Openchowski. Arch. f. (Anat. u.) Physiol. s (2) Elliott. This Journ. 32. pp. 420 and (3) M. I. Smith. Amer. Journ. Physiol. 46. p CBBIRDGE: PRINTED BY W. LEWIS AT THE UNIVERSITY PRESS