It was hoped that simultaneous record of the contractions of the stomach pouch and of the main stomach would throw some light on the relative importance of the tonus of the vagi, the condition of the blood, and the physiological state of the gastric motor mechanisms in the genesis of the hunger contractions. The Pavlov operation leaves the vagi connections with the stomach pouch at least partially intact, so that if the hunger contractions are normally initiated by efferent vagi impulses we might expect a close parallel between the rate and intensity of the contractions in the two stomachs. The character of the blood flowing to the two stomachs is necessarily the same. The amount of local nervous co-ordination between the two stomachs depends on the extent of the intact myenteric plexus and muscularis. The operation severs by far the greater amount of these neuromuscular connections. This may diminish the local nervous co-ordination and thus permit the development of different physiological states of the motor mechanisms in the two stomachs. The work was done on two young and vigorous dogs. Relatively large stomach pouches were made according to the method of Pavlov. In Dog I the muscularis joining the two stomachs was left intact for a distance of 6 cm. These figures were verified by post-mortem examination at the end of the experiment.
Simultaneous records of the hunger contractions in the two stomachs were taken while the dogs were lying quietly and comfortably in the lap of an attendant. The balloon was passed into the main stomach via the esophagus. The balloon used for the stomach pouch was much smaller than that used for the main stomach.
Dog I, having the 6 cm. of intact muscularis and myenteric nerve plexus uniting the two stomachs, showed a fairly close parallel of the tonus and the hunger contractions of the main stomach and the stomach pouch. When the tonus of the stomach was so great that the type III contractions (or incomplete tetanus) were present, the synchrony appeared complete. The two stomachs gave contractions of the same strength and rapidity. The contraction and relaxation phases of the individual contractions show also a fair degree of correspondence.
When the gastric tonus is weaker, so that the stomach exhibits the slower and stronger contractions of type II, the parallel between the stomachs is still in evidence, but it is less complete. That is to say, the contractions may appear simultaneously and be of corresponding strength, they may appear simultaneously and be very unequal in strength, or there may be considerable lack of synchrony both in the beginning and in the duration of the contractions of the two stomachs. At times the pouch would give two separate and strong contractions during a single but more protracted contraction of the main stomach. When the contractions are still slower, or of type I, the co-ordination between the two stomachs is more nearly perfect,
Dog II, with only 3 cm. of intact muscularis and myenteric plexus uniting the two stomachs, exhibited no synchrony between the two stomachs at any time. The main stomach would be quiescent, while the pouch showed vigorous hunger contractions, or vice versa. But more frequently both stomachs exhibited hunger rhythm at the same time, but without any synchrony in the rate and the strength of the contractions.
The Pavlov operation necessarily severs a considerable portion of the vagi connection with the pouch. But it is well known that at least half of the vagus influence can be eliminated by section of one vagus without any appreciable disturbance of the gastric tonus. In general the hunger rhythm of the pouch in Dog II resembled that of the stomach of dogs with section of both vagi. In this animal (Dog II) the amount of vagi connections with the motor mechanism of the pouch was not sufficient to maintain the normal tonus. It is also evident that the 3 cm. bridge of myenteric plexus was also insufficient for local co-ordination of the two stomachs.
In Dog II, therefore, the two stomachs differed in the quantity of innervation. The other obvious differences between the main stomach and the pouch, such as the presence of saliva, the occasional presence of intestinal juice and bile, gases and food d6bris, hair, etc., were common for Dogs I and II. These conditions were not sufficient to create inco-ordination through differences in the physiological state of the motor mechanisms when the connecting bridge of myenteric plexus was 6 cm. in length. The fact that in Dog II the pouch would show the hunger contractions during complete quiescence of.the main stomach and vice versa seems to show that the physiological state of the gastric motor mechanism and not the character of the blood is the primary factor in the genesis of these contractions. The main stomach and the pouch were supplied with the same blood. The character of the cb-ordination of the two stomachs in Dog I indicates that the hunger contractions are not normally caused by periodic impulses from the brain via the vagi. If such were the case there should have been a closer synchrony of the contraction and relaxation phases in the main stomach and the pouch. A primary vagi innervation of the contractions would not permit a contraction in the pouch with no contraction in the main stomach, the beginning of the pouch contraction during the relaxation phase of the main stomach, or two distinct and strong contractions of the pouch during a single contraction of the main stomach. These results are readily explainable on the ba,sis of local genesis of the contractions and some impairment of the myenteric connections between the two parts. Under these conditions the physiological state of the motor mechanism of the two stomachs would not be exactly alike, and in consequence there will be some interference with, or inhibition of, the excitation wave at the isthmus joining the two parts, as well as in the two stomachs themselves. Thus the excitation wave from the main stomach may pass the myenteric bridge unimpeded, but may reach the pouch during the refractory phase of the latter, and thus produce little or no effect. And a similar interference may obtain in the case of the excitation waves from the stomach pouch. Since most of the myenteric plexus joining the two parts of the stomach is severed in the Pavlov operation, the local co-ordinating mechanism is obviously imparied, although not completely destroyed. And if we assume a peripheral origin of the hunger contractions, this must lead to a certain degree of independent activity of stomach and pouch. The results demanded by this assumption of a peripheral stimulus or local automatism initiating the hunger contractions are those actually found in Dog I, that is, impaired synchrony of the two parts. As we have seen, the synchrony of the two stomachs is more nearly perfect the slower the contractions. When the contractions come at longer intervals there is less chance for interference with the excitation wave in the region of the myenteric isthmus and of collision, so to speak, with the refractory state. The parallel in the activity of the two stomachs during type III contractions may be only apparent or a parallel of the tonus only, for when the tonus reaches a certain degree the contractions appear at their maximum rapidity. Hence if the main stomach and the pouch have equally strong tonus they will exhibit an equal number of contractions per unit of time, even without any physiological co-ordination of the excitation waves between the two stomachs.
Blood from starving animals and animals in pancreatic diabetes transfused into normal animals acts as a temporary stimulus to the gastric hunger mechanism.
Excessive hemorrhage is followed by a temporary augmentation of the gastric hunger contractions.
Prolonged starvation, pancreatic diabetes, and possibly excessive hemorrhage result in some change in the blood that acts as a stimulus to the gastric hunger mechanism.
The character of the parallel between the hunger contractions of the main stomach and of the stomach pouch supports the view that these contractions are caused primarily by a gastric automatism and not by motor impulses via vagi nerves.
When the muscularis and myenteric isthmus joining the main and the accessory stomachs is relatively narrow, the two stomachs exhibit complete independence of the hunger contractions, even to the point of vigorous activity of the one during quiescence of the other. This fact points to a local automatism as a primary factor rather than the. condition of the blood, as the character of the blood flowing to the main stomach and the stomach pouch is necessarily the same.