Myoelectric Activity of the Autotransplanted Canine Jejunoileum

Transcription

1 GASTROENTEROLOGY 1981;81: Myoelectric Activity of the Autotransplanted Canine Jejunoileum MICHAEL G. SARR and KEITH A. KELLY Department of Surgery and the Gastroenterology Unit, Mayo Medical School, Rochester, Minnesota Our aim was to determine the role of the extrinsic nerves in the regulation of the canine jejunoileal interdigestive myoelectric complex (IDMEC). In six dogs, the extrinsic nerves to the jejunoileum were completely divided by autotransplanting this segment of bowel. The proximal 75 cm of autotransplant were isolated as a modified Vella loop, while the remaining portion was left in situ. Electrodes were implanted on the duodenum and on the autotransplanted bowel for later recording of myoelectric activity. After 10 days, the conscious dogs were studied during fasting and after a meal of 200 g liver. During fasting, the IDMEC occurred not only in the innervated duodenum, but also in the autotransplanted segments of jejunoileum. However, the period of IDMEC was shorter in the autotransplanted segments (-1.5 h) than in the duodenum (-2.5 h), and a consistent temporal association of IDMEC between the three areas studied was not present. Moreover, feeding interrupted the IDMEC in the duodenum but not in the auto transplanted segments. We concluded that the extrinsic nerves to segments of jejunoileum were not necessary for the appearance of the IDMEC within such segments. However, extrinsic innervation and/or intrinsic myoneural or luminal continuity were necessary for temporal coordination of the IDMEC between segments of small intestine and for postprandial inhibition of the jejunoileal IDMEC. The myoelectric activity of the small intestine of the fasted dog follows a cyclical pattern, called the in- Received November 17, Accepted March 2, Address requests for reprints to: Keith A. Kelly, M.D., Department of Surgery, Mayo Medical School. Rochester, Minnesota Dr. Sarr's present address is: Department of Surgery, Johns Hopkins Hospital. Baltimore, Maryland This work was supported by USPHS NIH Grants AM18278 and AM07198 and the Mayo Foundation. This work was presented before the American Gastroenterological Association, Salt Lake City, Utah, May 20, by the American Gastroenterological Association /81/ $02.50 terdigestive myoelectric complex (IDMEC) (1) or the migrating myoelectric or motor complex (MMC) (2). The IDMEC has been divided into four consecutive phases. Phase I, which lasts min, is an interval of quiescence with few or no action potentials, hence few or no contractions. During phase II, an interval of similar duration, a progressively increasing number of intermittent action potentials occur. Phase II culminates abruptly in phase III, the "activity front", during which action potentials of large amplitude appear with every pacesetter potential. This phase lasts about 5 min. Finally, phase IV, a brief interval of intermittent action potentials, represents a transition from the intense activity of phase III to the quiescence of phase I. Each phase of the cycle appears first in the duodenum and migrates aborally reaching the terminal ileum about 2 h later, at which time another cycle appears in the duodenum. Thus, the period of one complete cycle of the IDMEC is about 2 h. Feeding interrupts the cycles and in their place induces a sustained pattern of intermittent action potentials. The duration of postprandial interruption of the IDMEC varies with the amount and type of nutrient ingested (3). The interdigestive cycles are likely controlled by a complex interplay of hormonal, neural, and intraluminal influences. Many gastrointestinal hormones alter or abolish the cyclical interdigestive pattern (4-10), while motilin initiates the IDMEC in the stomach and duodenum (11). However, the physiologic role played by motilin and other hormones acting alone or in combination is unknown. Autonomic innervation of the small intestine may also have a role in the control of IDMEC. Atropine, hexamethonium, and guanethidine given systemically each inhibit the IDMEC (12), while atropine, tetrodotoxin, and hexamethonium given into the local arterial circulation block propagation of the ID MEC through the infused segment (13). After vagotomy, the IDMEC persists, but cycles are more irregular, and occasional intervals appear during which the IDMEC is absent (14-18). Moreover, after

2 304 SARR AND KELLY GASTROENTEROLOGY Vol. 81, No. 2 either temporary (19) or permanent vagal interruption (14-18), a failure to interrupt the interdigestive pattern with feeding or to sustain the fed pattern has been observed. Division of the preganglionic splanchnic nerves (20) or excision of the superior and celiac mesenteric ganglia (21) lengthen the period and disturb the regularity of the IDMEC but do not abolish its presence. Other investigators have addressed the role of the nervous system by selectively interrupting intrinsic myoneural continuity and/or extrinsic innervation to segments of the small intestine. Construction of a thiry-vella segment of canine jejunum, which interrupted both intestinal luminal and intrinsic myoneural continuity with the more proximal bowel, failed to abolish the temporal association of the ID MEC between the isolated segment and the remaining small intestine (22-26). Extrinsic denervation alone, with preservation of both intestinal and intrinsic myoneural continuity, altered only the regularity of the IDMEC in the denervated segment (24). However, isolation of a jejunal segment (thus interrupting intestinal luminal and intrinsic myoneural continuity), in association with concomitant extrinsic denervation, has been reported by some investigators to abolish the IDMEC in the isolated segment (24,26); this has not been confirmed by others (27). Intraluminal influences may also be important in organizing the presence and sequential distal migration of the IDMEC. Aeberhardt et al. (27) found that segments of porcine jejunum, when fully autotransplanted in situ, eventually became temporally reintegrated into the orderly, sequential pattern of migration of IDMEC. The observation suggests that intraluminal factors or the regrowth of intrinsic neural connections may have a role in controlling the migration of the IDMEC. However, we have shown previously that luminal continuity is not essential for the complete and orderly migration of the IDMEC, provided that intrinsic and extrinsic innervation is preserved (28). Our current aims were to investigate the role of extrinsic nerves in controlling the initiation, aboral migration, and temporal organization of the IDMEC in the canine small intestine. We chose to study myoelectric activity after autotransplantation of the jejunoileum, a technique assuring complete division of the extrinsic neural connections of the transplanted segment. Furthermore, we determined the effects of feeding on the myoelectric activity of the autotransplanted segment. Methods Preparation of Animals Six healthy female mongrel dogs weighing kg were subjected to celiotomy using sterile technique. Autotransplantation of the jejunoileum was accomplished in two stages. In the first stage, the superior mesenteric artery and vein were isolated at a site immediately distal to the neurovascular arcades supplying the pancreas and the duodenum (Figure 1) (29). All neural, lymphatic, and connective tissues accompanying the superior mesenteric artery and vein were transected and ligated at the site. In addition, the jejunal mesentery was divided in radial fashion starting at the site and proceeding to the serosal surface of the bowel at the ligament of Treitz. In a similar fashion, the mesentery was also divided from the site to the serosal surface of the terminal ileum 5 cm proximal to the ileocecal junction. All vessels transected by these maneuvers were ligated. Next, the dogs were given heparin (100 U/kg) intravenously. Five minutes later, the isolated segments of mesenteric artery and vein were occluded proximally and distally with noncrushing vascular clamps, transected, and reanastomosed using a microvascular technique and 7-0 polypropylene suture. Vascular transection and reanastomosis were accomplished in min. Immediately upon release of the occlusive clamps, the bowel became pink, and contractions appeared. At this stage, the neurovascular continuity of the jejunoileum with the remainder of the gastrointestinal tract was maintained only via the integrity of the intestinal wall. In order to give support to the vascular anastomoses and thus avoid tension and kinking, the previously transected distal ileal mesentery was reapproximated and sewn to the transverse mesocolon. The abdomen was closed. No further heparin was given in the postoperative period. Five to 10 days later, the dogs were reoperated. The duodenal-jejunal junction and distal ileum were divided at the sites of previous mesenteric transection, thus completing the autotransplantation of the jejunoileum. The proximal 75 cm of the autotransplant were then isolated from the intestinal stream (Figure 1). The proximal end of the isolated segment was oversewn, and the distal end was brought to the skin as a jejunostomy. The flanged end of a metal cannula was placed in the lumen of the segment 5 cm distal to the proximal end, and the opposite end of the cannula was brought to the abdominal surface. Intestinal continuity was reestablished by end-to-end anastomosis of the distal cut end of the still innervated duodenum to the proximal cut end of the distal autotransplanted jejunum, and by end-to-end anastomosis of the terminal ileum at the site of ileal transection. Nine silver-silver chloride monopolar recording electrodes (30) were sewn to the serosal surface of the intestine at 15-cm intervals-three on the innervated duodenum starting 45 cm proximal to the duodenojejunal anastomosis, four on the isolated jejunalloop starting 15 cm from the oversewn proximal end, and two on the distal jejunum starting 15 cm distal to the duodenojejunal anastomosis. Every dog had diarrhea during fasting and after feeding for about 4 wk beginning immediately after the first operation; four of the six dogs developed formed stools thereafter. During the first few weeks, all dogs lost 5%-10% of their preoperative weight, after which their weight remained stable or returned to the preoperative value. Conduct of Experiments All dogs were allowed at least 10 days to recover after the second operation. By this time, their eating habits

3 August 1981 MYOELECTRIC ACTIVITY OF THE SMALL INTESTINE em Figure 1. Preparation of autotransplanted canine jejunoileum (hatched areas). The neurovascular pedicle to jejunoileum was transected, the vessels were reanastomosed, and the proximal jejunal and distal ileal mesenteries were divided (left). Five to ten days later, autotransplantation was completed by transection of the proximal jejunum and distal ileum (right), while the proximal jejunum was isolated and recording electrodes (E t to E,,) were implanted. had returned to normal. Experiments were conducted in fully conscious dogs fasted for at least 24 h. Dogs were placed in Pavlov slings where they rested quietly for the duration of the experiment. Myoelectric activity was recorded continuously with a Gould Brush recorder (model 481) using a monopolar technique, alternating current amplifiers, and a time constant of 1 s. Fasting experiments. Myoelectric activity was recorded in each of the six dogs on six or more occasions during the period between 10 days and 3 mo after the second operation. Recording sessions varied from 8 to 14 h, depending on the period and regularity of the IDMEC recorded from the duodenum. Fed experiments. Each of the six dogs was studied on four separate occasions after feeding a meal of 200 g of raw, diced pork liver. This meal is known to interrupt consistently the IDMEC in the innervated canine duodenum and jejunum (28). The meal was given min after recording the migration of phase III of the IDMEC along the duodenal electrodes. Recordings were continued for 5 h after feeding. Analysis of Data All records of myoelectric activity were analyzed by visual inspection. lnterdigestive myoelectric complex. The IDMEC was recognized by the four sequential phases of myoelectric activity defined by Code and Marlett (1). The period of the IDMEC was measured as the time elapsed from the start of one phase III until the start of the next consecutive phase III at that electrode. In each dog, the mean period of the IDMEC in the duodenum, in the jejunal loop, and in the distal in situ jejunum, was determined separately. In three of six dogs, prolonged intervals which lacked the characteristic IDMEC were noted intermittently in the duodenum, and thus, only periods of the IDMEC of <240 min were included when calculating the mean period. The mean duration of phase III at each electrode was calculated, as was the mean velocity of migration of phase III between electrodes in the duodenum, in the jejunal loop, and in the distal in situ jejunum. The start of phase III at each electrode served as the reference point from which to evaluate the migration of the IDMEC along the small intestine. In the intact canine small intestine, all duodenal IDMEC migrate distally in sequential fashion through the proximal jejunum (31). The velocity of distal migration of IDMEC is such that all or nearly all Phase I1Is would migrate from the duodenum through the proximal 75 cm of jejunum and into the distal jejunum in 20 min. In our experiments, the temporal assocation between the IDMEC in the duodenum and the IDMEC in the jejunal loop was expressed in two ways: first, as the percentage of phase Ills in the duodenal segment followed within 20 min by phase III in the jejunal loop; and second, as the percentage of phase Ills in the jejunalloop preceded by phase III in the duodenal segment within the preceding 20 min. Identical comparisons were made of the temporal association of the IDMEC between the duodenal segment and the distal in situ jejunum and between the jejunal loop and the distal in situ jejunum.

4 306 SARR AND KELLY GASTROENTEROLOGY Vol. 81, No. 2 «E3 EI IlmV E2 ~IMII.,.. ~"n.w~~~iii"i".".""jdml~~~~''''_~_~ii~~\' '~"-'I,,, _,"..... ~ r!!i' l'!'ir""w"l'l..). ~..,.",., ' 'r r1 1 ' '''',"",...' " 5 MIN. Figure 2. Recording of interdigestive myoelectric activity from the innervated duodenum of a dog with autotransplanted jejunoileum. A burst of intense action potentials occurs at electrode E, and migrates sequentially through electrodes E2 and E 3 Arrows denote end of burst. Effect of feeding on the IDMEC. After feeding. the mean intervals until reappearance of the IDMEC were determined separately in the duodenum, in the jejunal loop, and in the in situ distal jejunum. These intervals were measured as the time elapsed from the start of the last phase III in the duodenum before feeding until the first phase III after feeding in each region. Pacesetter potential. The frequencies of the pacesetter potentials were determined as the mean values over a 5-min interval. During fasting. at least two measurements were made at each electrode during phase I or phase II of each experiment. After feeding, four measurements were made at 30-min intervals beginning 30 min after feeding in each experiment. Mean values for each dog during fasting and after feeding were calculated. Statistical analysis. Comparison of mean values, when appropriate, was performed using Student's t-test for paired data. The temporal association of the IDMEC, which was determined between two separate regions of the small intestine, was compared with that which would have been expected by random association based on the period of the IDMEC in each region. Results Myoelectric Activity During Fasting During fasting. a cyclical pattern of myoelectric activity was recorded from the innervated duodenum. The pattern resembled closely the IDMEC of the intact canine small intestine as described by others (1.30,31). A similar pattern was also recorded from the autotransplanted jejunal loop and from the autotransplanted in situ jejunum in all six dogs. In each region. an interval of quiescence devoid of action potentials (phase I) was followed by an interval during which action potentials appeared intermittently with the pacesetter potentials (phase II). Phase II culminated abruptly in a 4- to 7-min interval during which each pacesetter potential was accompanied by a burst of action potentials (phase III). A short interval of intermittent action potentials (phase IV) usually followed before a return to the E4 E5 E7... ~.. I IlmV 5 MIN. Figure 3. Recording of interdigestive myoelectric activity from a canine autotransplanted, jejunal loop. A burst of intense action potentials occurs at electrode E4 and migrates sequentially through electrodes E5 and E 7 Arrows denote end of burst. Recording not made at E 6

5 August 1981 MYOELECTRIC ACTIVITY OF THE SMALL INTESTINE 307 Table 1. Phase III of the IDMEC in Canine Small Intestine Autotransplanted Isolated In situ Intact proximal distal duodenum jejunum jejunum Duration a (min) Veloeityb (em/min) 8.6 ± a Mean of 6 dogs; SEM :s 0.1. b Mean of 6 dogs; SEM :s 0.7 unless shown. quiescent interval (phase I). Phase III migrated sequentially in an aboral direction from one electrode to the next electrode in each of the intestinal regions (Figures 2 and 3). The duration and velocity of migration of these bursts of action potentials (Table 1) were similar to the values reported for phase III of the IDMEC in the intact canine small intestine (31). In two of six dogs, prolonged intervals (>4 h) of intermittent action potentials alternating with intervals of quiescence, but lacking migrating phase IIIlike activity, occurred during 25% to 50% of the recordings from the duodenal segment. In a third dog, the same prolonged intervals occurred, with phase III-like activity being recorded on only six occasions in 70 h of recording. Similar but shorter and less frequent «5% of recordings) intervals of intermittent activity and quiescence were recorded from the autotransplanted jejunal regions of these three dogs. In no dogs were we able to recognize a burst of action potentials occurring simultaneously at each electrode in the autotransplanted regions, as described in dogs after celiac and superior mesenteric ganglionectomy (21). Moreover, we did not record a regularly occurring, short series of action potentials appearing at 20-min intervals in our auto transplanted jejunal segments, as observed by Bueno et al. (24) in extrinsically denervated, subcutaneously isolated, canine jejunal segments. Temporal Association of IDMEC Although each intestinal region exhibited the IDMEC, the period of the IDMEC was longest in the duodenum, shortest in the autotransplanted jejunal loop, and intermediate in the autotransplanted in situ jejunum (Table 2). Phase III of the IDMEC appeared to migrate sequentially from the duodenum to the jejunal loop and then back to the in situ jejunum on <5% of the occasions. Moreover, no temporal association could be demonstrated between the duodenal IDMEC and the IDMEC in the autotransplanted jejunal loop (Table 3). A mean of only 13% of duodenal phase IIIs were followed within 20 min by phase III in the isolated loop. This incidence was no different than that expected by chance alone. For example, the mean period of the IDMEC in the loop was 90 min; thus, by a random association, a phase III in the loop would be expected to occur within 20 min of a duodenal phase III about 22% of the time. A similar lack of association was evident between the IDMEC of the autotransplanted loop and that of the distal in situ jejunum. In contrast, an association was found between the duodenal IDMEC and the IDMEC of the in situ distal jejunum. A mean of 60% of duodenal phase Ills were followed within 20 min by migrating phase III activity in the autotransplanted jejunum distal to the duodenojejunal anastomosis. This association did not become more frequent as the interval after autotransplantation increased up to 3 mo. Effect of Feeding on the IDMEC Feeding interrupted consistently the duodenal IDMEC for the duration of the experiment (5 h) in all dogs and induced a noncyclical pattern of intermittent action potentials. However, feeding did not interrupt the appearance of phase III in either the autotransplanted jejunal loop or in the auto transplanted in situ jejunum. Cyclical phase III activity almost always returned in both autotransplanted regions within 2-3 h and often within 30 min (Table 4). A short series of intermittent action potentials occurred regularly in the duodenal electrodes immediately after feeding, but no such response to feeding was observed in the autotransplanted regions. Frequency of Pacesetter Potentials During fasting, the mean frequency of the pacesetter potentials in the duodenum was 18.3 cycles/min, a value similar to that reported by others for the intact canine duodenum (30,31). The duodenal frequency increased about 0.5 cycles/min in five of six dogs after feeding (p < 0.05). The mean fre- Table 2. Period of IDMEC in Canine Small Intestine Period of eycle a (min) Autotransplanted Proximal In situ distal Dog (n) Duodenum (n) jejunal loop (n) jejunum ± ± 5 b ±8 c ± ±6 b ± ± ± 7 b ± 15 c ± ±9 b ± ± ± 8 b ± 6 c a Mean ± SEM. b Different from duodenum and from in situ distal jejunum. p < c Different from duodenum. p < 0.05.

6 308 SARR AND KELLY GASTROENTEROLOGY Vol. 81, No. 2 Table 3. Temporal Association Between Segments of Canine Small Bowel Duodenum and autotransplanted Autotransplanted jejunal loop Duodenum and autotransplanted jejunal loop and in situ distal jejunum in situ distal jejunum % Loop % Loop % Duodenal phase Ills phase IIIs phase IIIs preceded by followed by followed by duodenal distal jejunal Dog loop phase IIIs phase Ills phase IIIs % Duodenal % Distal % Distal jejunal phase Ills jejunal phase Ills followed by phase Ills preceded preceded by distal jejunal by duodenal loop phase IIIs phase Ills phase Ills P Value greater than that expected by random association. quency of the pacesetter potentials was 13.5 cycles/ min in the jejunal loop and 12.4 cycles/min in the in situ distal jejunum. In contrast to the duodenum, the jejunal frequency did not increase with feeding, but decreased 0.3 cycles/min to 0.4 cycles/min. Discussion Our experiments demonstrated the continued presence of the IDMEC in the autotransplanted canine jejunoileum. However, autotransplantation of the jejunoileum caused a complete disruption of the orderly, sequential migration of the IDMEC from the intact, innervated duodenum into the more distal autotransplanted jejunal segments. Moreover, feeding failed to cause a sustained inhibition of the IDMEC in the autotransplanted jejunum. Many of our observations confirm the findings of Thomas and Kelly (32) and Aeberhardt et al. (27). Thomas and Kelly (32) found that the autotransplanted fundal pouch from the canine stomach displayed a cyclical pattern of contractions that oc- Table 4. Reappearance of Phase III of IDMEC in Canine Small Intestine after Feeding Duration until reappearance of phase III (min) Autotransplanted Proximal In situ Dog Duodenum jejunal loop distal jejunum 1 > ± ± 23 b 2 > ± ± 28 3 >300 8O±4 b 4 > ± 27 b 97 ± 39 b 5 > ± 16 b 89 ± 14b 6 > ± 28 b >300 a Mean ± SEM, n = 4. b Values differ from those of duodenum after feeding (p < 0.05), but do not differ from those of jejunoileum in Table 2 (p > 0.05). curred concurrently with phase III of the IDMEC, as recorded from the duodenum. Aeberhardt et al. (27) recently demonstrated the presence of the IDMEC in autotransplanted segments of porcine jejunum. These studies showed that extrinsic innervation was not necessary for the occurrence of a cyclical, interdigestive motor activity in the canine proximal stomach or in the porcine jejunum. Our results differ from those of both Weisbrodt et al. (26) and Bueno et al. (24). Both groups of investigators found that isolated canine jejunal loops, when extrinsically denervated, no longer exhibited the ID MEC. Weisbrodt et al. (26) extrinsically denervated a Thiry-Vella loop in two dogs by transecting all visible nerves in the mesenteric arcade of the loop and by stripping the mesenteric vessels supplying the loop of all visible nerves. However, complete autotransplantation was not performed, and it remains possible that some nerves traveling in close association with the mesenteric vessels were left untouched. Bueno et al. (24) found that after extrinsic denervation of an in situ segment of canine jejunum, regular spiking activity (phase III of the IDMEC) continued to occur and migrate distally provided that intestinal continuity was maintained. In contrast, after subcutaneous isolation of a 50-cm jejunal loop and later transection of the supplying mesenteric arcade (in the effect completing autotransplantation), migrating bursts of action potentials resembling phase III of the IDMEC were not observed. However, in their experiments, propagated myoelectric activity would have been difficult to discern because only two electrodes were implanted on the subcutaneous jejunal loop. Furthermore, their method of autotransplantation of the intestinal segment to a subcutaneous position may have impaired greatly its blood supply and thus may have altered the function of its smooth muscle. Indeed, before extrinsic de nervation, a decrease in the frequency of phase III activity and a pattern of nearly continuous,

7 August 1981 MYOELECTRIC ACTIVITY OF THE SMALL INTESTINE 309 irregular action potentials were evident in the subcutaneous jejunal loop. This pattern of myoelectric activity was quite different from the myoelectric patterns of a true Thiry-Vella loop (25). The presence of the IDMEC in the auto transplanted canine jejunum challenges the hypothesis that the extrinsic nerves are necessary for the presence of the IDMEC and for its orderly aboral migration (25). Furthermore, in our experiments, neither flow of proximal intestinal content through the autotransplanted loop nor intrinsic myoneural continuity with the innervated duodenum was required for the maintenance of interdigestive myoelectric cycles. These observations suggest that both the initiation and the orderly aboral migration of the interdigestive cycles within a segment of jejunoileum must reside in the intrinsic neural plexi or, less likely, in a cyclical myogenic response. The period of the interdigestive cycles in the autotransplanted jejunum was shorter than the period of the cycles in the duodenum. This relative decrease in the period of the interdigestive cycles in the autotransplanted segments might represent a lack of inhibition normally mediated either by continuity of the intrinsic neural plexi or by the extrinsic nerves. Another interpretation is that the longer period of the IDMEC in the duodenum might represent a relative increase in the period of the duodenal cycles possible secondary to interruption of neural feedback from the jejunoileum. This interpretation might explain also the periods of absence of the duodenal IDMEC noted in several of the dogs. Although the IDMEC persisted in the isolated jejunal loop, its temporal association with the innervated duodenum and with the autotransplanted distal jejunum was disrupted completely. In contrast, the migration of the IDMEC from the duodenum to the autotransplanted distal jejunum was, in part, preserved. This observation suggests that continuity of intestinal flow, even after extrinsic denervation and interruption of intrinsic myoneural continuity, might have a role in the regulation of aboral migration of the IDMEC, possibly by acting via mechanoreceptors or other receptors in the bowel wall or via properties of the smooth muscle itself. Another interpretation, offered by Aeberhardt et a1. (27), is that the temporal association of motor patterns occurred because of the regeneration of the intrinsic neural plexi across the anastomosis. This remains unsubstantiated. Autotransplantation of the jejunoileum prevented the postprandial changes in jejunal myoelectric activity seen in the intact jejunum (28). The liver meal consistently interrupted the IDMEC in the duodenum and increased the frequency of the duodenal pacesetter potentials. However, in the autotrans- planted jejunal segments, feeding failed to sustain a postprandial interruption of the IDMEC and failed to increase the frequency of the pacesetter potentials. Feeding is known to interrupt the IDMEC in an extrinsically innervated Thiry-Vella loop of canine jejunum (25). The lack of prolonged postprandial inhibition of the IDMEC in autotransplanted jejunum implies that the extrinsic nerves must have a major role in the postprandial myoelectric response to feeding, while hormones have a lesser role. The extrinsic nerves might impart a direct neural inhibition or exert a permissive effect for the inhibitory action of certain hormones released with feeding (6-8). The failure of the pacesetter potentials of the autotransplanted jejunal segments to increase in frequency after feeding may have been secondary to interruption of the intrinsic myoneural continuity or to the effects of extrinsic de nervation. In conclusion, the extrinsic nerves to segments of canine jejunoileum were not necessary for the appearance of inter digestive myoelectric cycles within such segments. However, extrinsic innervation and/ or intrinsic myoneural or luminal continuity were necessary for temporal coordination between segments of small intestine and for postprandial inhibition of the jejunal interdigestive cycles. References 1. Code CF. Marlett JA. The interdigestive myo-electric complex of the stomach and small bowel of dogs. J Physiol (Lond) 1975;246: Vantrappen G. Janssens J. Hellemans J. Christofides N. Bloom S. Studies on the interdigestive (migrating) motor complex in man. In: Duthie HL. ed. Gastrointestinal motility in health and disease. Lancaster: MTP Press Ltd. 1978: DeWever I. Eeckhout C. Vantrappen G. Hellemans J. Disruptive effect of test meals on interdigestive motor complex in dogs. Am J Physiol 1978;235:E661-E Bueno L. Ruckebusch Y. Insulin and jejunal electrical activity in dogs and sheep. Am J Physiol 1976;230: Wingate DL. Pearce EA. Thomas PAt Boucher BJ. Glucagon stimulates intestinal myoelectric activity (abstr). Gastroenterology 1978;74: Mukhopadhyay SK. Thor PJ. Copeland EM. et al. Effect of cholecystokinin on myoelectric activity of small bowel of the dogs. Am J Physiol 1977;232:E44-E Weisbrodt NW. Copeland EM. Kearley RW. et al. Effects of pentagastrin on electrical activity of small intestine of the dog. Am J Physiol 1974;227: Mukhopadhyay AK. Johnson LR. Copeland EM. Weisbrodt NW. Effect of secretin on electrical activity of the small intestine. Am J Physiol 1975;229: Konturek SJ. Thor p. Krol R. et al. Influence of methionine-enkephalin and morphine on myoelectric activity of small bowel. Am J Physiol 1980;238:G Thor P. Krol R. Konturek SJ. et al. Effect of somatostatin on myoelectric activity of the small bowel. Am J Physiol 1978;235:E249-E Hoh Z. Aizawa I. Takeuchi S. Couch E. Hunger contractions

8 310 SARR AND KELLY GASTROENTEROLOGY Vol. 81, No. 2 and motilin. In: Vantrappen C, ed. Proceedings of the Fifth International Symposium on Gastrointestinal Motility. Herentals: Typoff Press, 1975: Ormsbee HS III, Telford GL, Mason GR. Required neural involvement in control of canine migrating motor complex. Am J PhysioI1979;237:E451-E Sarna SK, Stoddard C, Belbeck LW, McWade O. The intrinsic nervous control mechanisms for the propagation of migrating myoelectric complex (abstr). Gastroenterology 1980;78: Weisbrodt NW, Copeland EM, Moore EP, et al. Effect of vagotomy on electrical activity of the small intestind of the dog. Am J Physiol 1975;228: Reverdin N, Hutton N, Ling A, et al. The motor response to food: vagus dependent or independent (abstr). Gastroenterology 1979;76: Aeberhardt p, Bedi BS. Effects of proximal gastric vagotomy (PGV) followed by total vagotomy (TV) on postprandial and fasting myoelectric activity of the canine stomach and duodenum. Gut 1977;18: Marik F, Code CF. Control of interdigestive myoelectric activity in dogs by the vagus nerves and pentagastrin. Gastroenterology 1975;69: Ruckebusch y, Bueno L. Migrating myoelectric complex of the small intestine. Gastroenterology 1977;73: Diamant NE, Hall K. Mui H, EI-Sharkaway TY. Vagal control of the feeding motor pattern in the lower esophageal sphincter, stomach, and small intestine of dog. In: Christensen J, ed. Gastrointestinal motility. New York: Raven Press, 1980: Ruckebusch y, Bueno L. Electrical activity of the ovine jejunum and changes due to disturbances. Am J Dig Dis 1975; 20: Marlett JA, Code CF. Effects of celiac and superior mesenteric ganglionectomy on interdigestive myoelectric complex in dogs. Am J Physiol 1979;237:E432-E Pearce EA, Wingate OL. The role of the myenteric plexuses (abstr)? Gastroenterology 1979;76: Ormsbee HS III, Telford GL, Mason GR. Mechanism of propagation of canine migrating motor complex-a reappraisal (abstr). Gastroenterology 1979;76: Bueno L, Praddaude F, Ruckebusch Y. Progapation of electrical spike activity along the small intestine: intrinsic versus extrinsic neural influences. J Physiol 1979;292: Carlson GM, Bedi BS, Code CF. Mechanism of propagation of interdigestive myoelectric complex. Am J Physiol 1972; 222: Weisbrodt NW, Copeland EM, Thor PI, et al. Nervous and humoral factors which govern the fasted and fed patterns of intestinal myoelectric activity. In: Proceedings of the Fifth International Symposium on Gastrointestinal Motility. Vantrappen C, ed. Herentals: Typoff Press, 1974: Aeberhardt PF, Magnenat LO, Zimmerman WA. Nervous control of migratory myoelectric complex of the small bowel. Am J Physioi 1980;238:G102-G Sarr MG, Kelly KA, Phillips SF. Changes in canine jejunal absorption and transit during interdigestive and digestive motor.,states. Am J Physiol 1980;239:G167-G Lillehei RC, Goot B, Miller FA. The physiologic response of the small bowel of the dog to ischemia including prolonged in vitro preservation of the bowel with successful replacement and survival. Ann Surg 1959;150: Akwari OE, Kelly KA, Steinbach JH, Code CF. Electric pacing of intact and transected canine small intestine and its computer model. Am J Physiol 1975;229: Szurszewski JH. A migrating electric complex of the canine small intestine. Am J Physioi 1969;217: Thomas PA, Kelly KA. Hormonal control of interdigestive motor cycles of canine proximal stomach. Am J Physiol 1979;237:E192-E197.