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Migrating Motor Complex in Biological Sciences: Characterization, Animal Models and Disturbances

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Migrating Motor Complex in Biological Sciences: Characterization, Animal Models and Disturbances Indian Journal of Experimental Biology Vol. 47, April 2009, pp. 229-244 Review Article Migrating motor complex in biological sciences: Characterization, animal models and disturbances Krzysztof W. Romański Department of Animal Physiology, Faculty of Veterinary Medicine, Wrocław University of Environmental and Life Sciences, 31 Norwida str., 50-375 Wrocław, Poland The migrating motor complex (MMC) occurs in most mammals and birds and is organized during the fetal life. In some species, like ruminants and other herbivores, it is not abolished by feeding but its character and controlling mechanisms do not vary considerably from other animal species. However, the mechanisms controlling the MMC are complex and incompletely recognized. The central nervous system exerts rather modulatory effects upon the MMC and the role of the enteric nervous system in the initiation and propagation of the MMC is crucial. The hormones appear mainly to disrupt and convert the MMC cycle into the fed pattern. Several types of the disturbances of the MMC cycle and its phases have been described in various pathophysiological conditions. However, it can be more suitable to identify and describe the given MMC abnormality than to establish the rules of the MMC behavior in the course of the gastrointestinal diseases. Keywords: Migrating motor complex, Neurohormonal control, Non-ruminants, Ruminants In man and other monogastric species, during the allows to maintain the labile balance between the interdigestive period, also called the fasting state, the secretory and absorptive processes in the fasting state majority of previously ingested foods is already what in turn prevents accumulation of the digestive utilized in the stomach and small bowel. In normal juices and, in consequence, the arrival of conditions the interdigestive state can be simply gastrointestinal motor disturbances. The existence of defined as time period during which the stomach and some active contractions hampers the bacterial small intestine are almost empty. However, the overgrowth at least in the proximal small bowel and indigestible food remnants, bacteria and cellular aboral transport of chyme protects against the debris can still occur in the gastrointestinal lumen. It gastrointestinal mucosal damage and decreases the is also possible that in the fasting period small reflux frequency. During the interdigestive state these portions of fluid and foods are ingested. The secretion functions occur in the cyclic (interrupted) fashion. of the digestive juices, i.e. the gastric and pancreatic Mixing of the luminal content is less intense than after juice, bile and intestinal fluid, is incompletely feeding and well organized propulsion is adjusted to hampered during the interdigestive state in order to the amount of chyme stocked up inside the bowel. continue the digestive processes in the duodenum. Since these cycles move down along the bowel it was There are several physiological needs to sustain the proposed to call them the migrating motor complexes motor function in the interdigestive period. The motor (MMCs) or the interdigestive migrating motor function ensures mixing, transport, digestion, and complexes2 and the MMC concept is commonly in absorptive processes of the relatively small amounts use. The presence of the quiescent period in the MMC of luminal content during this period. The movements cycle allows muscle to rest and regeneration. Its active of the gastrointestinal wall facilitate the intramural phases ensure the physical smooth muscle exercise and blood and lymph flow, provide the smooth muscles exhibit some trophic and regulatory aspects. exercise, and probably also release a regulatory Thus the physiological role of the MMC warrants its 1 substances from the endocrine mucosal cells . This scientific interest. The MMC cycle can be included into ultradian rhythms and the rhythmic concept of _____________________ the gastrointestinal motility organization was Telephone: +48-71-3205422 3,4 Fax: +48-71-3281567 characterized . The historical background of the MMC 5 E-mail: [email protected] is already reported and hence not repeated here. 230 INDIAN J EXP BIOL, APRIL 2009 The aim of this communication is to present the Coordination of gastrointestinal functions during current knowledge on the interdigestive motility of interdigestive state the stomach and small intestine with special emphasis The interdigestive motility pattern can ensure the on the MMC, its control and possible disturbances digestive transport due to the coordination of principally addressed to the medical experimental and gastrointestinal contractions within the cycle and due clinical contributors. to the coordination of its function with other functions of the digestive system during the interdigestive state General characteristics of MMC in non-ruminants and ruminant species, and also The MMC cycle occurs in the majority of during the digestive state in ruminants. mammals and birds during the whole life4,6. In most Coordination of the gastrointestinal motility within monogastric animals the pattern is observed during the MMC—There are three basic levels of the interdigestive state but in ruminants it is not coordination of the gastrointestinal motility (MMC) in disrupted after feeding7. The MMC contains three the interdigestive state. First comprises the or four phases. During phase I the relative lack of relationship between the pacessetter potentials (slow contractions is present. In phase II, contraction waves) and the spike bursts. The frequency of the incidence gradually increases reaching the slow waves in the given gastrointestinal region maximum during phase III of the cycle. Phase IV of determines the frequency of the spike bursts and the MMC is not always observed. Species contractions during phase II, and especially during differences of the MMC are rather quantitative than phase III of the MMC when the incidence of the spike qualitative (Table 1) and the differences in cycle bursts and contractions are greatest. During phase II and phase duration are related to the species- of the MMC the presence of the slow waves facilitates specific features of the gastrointestinal tract. The the occurrence of the spike bursts and contractions in most precise identification criteria of MMC were response to weak stimuli, thus the gastrointestinal elaborated in man (Table 2). In pigs the MMC response to the given stimulus appears to be more arrival is related to the feeding frequency. In non- precise than without the slow waves8. The ruminant herbivores the interdigestive periods are intrasegmental coordination represents the second usually longer than in ruminant herbivores and level of coordination of the MMC cycles. This means duration of the MMC is longer. In herbivores the that within the given gastrointestinal shorter or longer MMC cycles accelerate the digestive transport segment the single spike bursts and contractions through the relatively long gastrointestinal tract. In (or their lack) behave in well-organized fashion9,10. In the myoelectrical recordings the organization of the the course of phase II of the MMC the series of MMC is similar to that in motor recordings. It contractions migrate along the bowel in well- occurs not only in the gastric region and in the organized fashion and their presence is apparently entire small bowel but is also observed in the related to the luminal stimuli. Similar situation is hindgut. Thus in mammals and birds the MMC during phase III. The mode of migration of the spike represents one of the main motility patterns. bursts in the small intestine is the best illustration of However, there are some methodological this physiological event. The third level comprises the difficulties in MMC recording (Table 3). intersegmental coordination of the MMC. This can be Table 1 — Species differences in the jejunal MMC recorded with an electromyographical method in fasted subjects Duration (min) MMC cycle Phase I Phase II Phase III Phase IV Ref. Man 122 – 172 20 – 90 35 – 135 2 – 11 133 Dog 90 – 114 13 – 72 15 – 74 5 – 7 2 – 4 134 Pig 75 – 80 10 – 20 ~ 50 ~ 5 7 Rat 13 – 21 4 – 7 5 – 7 4 – 5 135 Rabbit 136 – 153 5 – 10 ~ 90 – 120 5 – 30 0 – 20 136 Guinea pig 48 – 117 8 – 16 36 – 99 3 - 5 137 Sheep* 65 – 105 19 – 57 35 – 53 4 – 7 138,139 Gallus# 41 - 114 3 – 10 6 *in non-fasted animals, #in the proximal ileum ROMAŃSKI: MIGRATING MOTOR COMPLEX IN BIOLOGICAL SCIENCES 231 Table 2 —The applied criteria for identification of the MMC cycle and its phases in the human small intestine using the manometric techniques MMC cycle Phase I Phase II Phase III Phase IV Ref. 1. Cyclic arrival of Lack of motor Irregular Regular contractions more Short period of 140 the MMC activity contractions less than 10/min lasting over 2 declining phases than 10/min min and appeared sequentially activity after in both duodenal ports phase III 2. Not specified <1 contraction of 1-10 contractions Uninterrupted >2 min periods 141 ≥ 10 mm Hg per per min of irregular of regular phasic contractions min frequency and propagated distally at amplitude frequency 10-12 cpm 3. Cycle of phases Less than three Irregular Regular pressure waves at the 116 I-III while phase pressure waves contractile activity slow wave frequency lasting III is the most every 10 min before phase III for about 5 min, migrating distinctive aborally 4. Cycle containing Motor quiescence Motor activity Regular pressure waves, 10.5- 142 phase III period with below the phase III 14/min for at least 2 min contractions not frequency but more more than 2/10 than 2 min and preceded contractions/10 by phase III min 5. Cycle containing Motor quiescence Periods when phase ≥ 10 pressure waves per min 143 phases I – III <3 pressure waves I and phase III are for ≥ 2 min extending over per 10 min absent ≥ 4 sideholes (40 cm) 6. Phases I – III No contractions, More than 2 Rhythmic contractile activity 144 starting just after contractions per 10 with frequency 10-12 cpm the end of phase min but less than during 3 min, propagated III 10 per 1 min down and followed by phase I 7.
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