PHYSIOLOGICAL SIGNIFICANCE OF THE CONTRACTIONS OF

Quarterly Journal of Experimental Physiology (1982) 67, 407-417Printed in Great Britain

PHYSIOLOGICAL SIGNIFICANCE OF THECONTRACTIONS OF THE RABBIT PROXIMAL COLON

HANS-JORG EHRLEIN, HELMUT REICHAND MARTINA SCHWINGER

Institute of Zoophysiology, University of Hohenheim, D-7000 Stuttgart 70, Federal Republic of Germany(RECEIVED FOR PUBLICATION 22 JULY 1981)

SUMMARY

In humans and in carnivores the motor activity of the colon was separated into various typesbased on records of the intraluminal pressure. However, little is actually known about thephysiological significance of the various pressure waves. The aim of the present investigationwas to clarify the basic pattern of colonic motility in a herbivorous species. Motility of theproximal colon was studied by strain gauge transducer records combined either with fluoroscopyor by direct visual observation in conscious and anaesthetized rabbits. In the proximal colonthree types of contractions were found: (1) high frequency repetitive contractions, (2) lowfrequency rises of the base line, and (3) monophasic progressive waves. The frequency of therepetitive contractions was 13 8 contractions/min at the oral site and 16 3 contractions/min atthe aboral site of the proximal colon. The mean duration of the repetitive contractions was3 2 + 1 s. They coincided with orally migrating (1-2 mm/s) shallow annular constrictions whichrepresented haustral activity. The low frequency rises of the base line (mean duration 131 + 47 s)were associated with aborally migrating (7 mm/min) deep annular constrictions representingsegmental activity. The monophasic progressive waves represented peristaltic contractions. Themean durations of the monophasic waves were 55 + 1 2 s (period of hard faeces formation),and 9 7+2 8 s (period of soft faeces formation), the average rates of progression were3 2 + 1 2 cm/s (period of hard faeces production), and 1 3 + 0 6 cm/s (period of soft faecesproduction). The results proved that the colonic motility ofrabbits consisted ofa complex motorpattern. The present classification was similar but not identical with that described in carnivoresand man. Further comparative studies on other mammals are necessary to decide whether themotor activity of the colon is comparable between various species.

INTRODUCTION

The anatomical structures of the colon differ widely in various species. In carnivores thecolon is short and without sacculations, whereas the colon of herbivores is sacculated. Thecolon of man is rather of the herbivorous than the carnivorous type.

In humans, most available information about the motor activity of the colon refers tothe sigmoid colon (Connell, 1968). The ascending, transverse and descending colon has beenstudied less intensively due to a deficiency of appropriate methods for investigating theseparts of the colon. Therefore, little is known about the motor activity of the proximal partsof the human colon.

In experimental studies, the motility of the colon has been investigated most commonlyin carnivores (dogs and cats). The motor activity of the colon is usually separated intovarious types based on records of the intraluminal pressure (Templeton & Lawson, 1931).However, little is actually known about their functional significance. Therefore, severalinvestigators have concluded that no adequate classification of the colonic motility exists(Connell, Texter & Vantrappen, 1965).

H.-J. EHRLEIN, H. REICH AND M. SCHWINGER

The present study was designed to clarify the physiological significance of the rabbitcolonic contractions and to examine the relationship between motility records and thetransit of the colonic contents. Motility of the proximal colon was studied by strain gaugetransducer records combined either with fluoroscopy or by direct visual observations inconscious and anaesthetized rabbits.The patterns of the motor activity of the colon are documented in a film (Ehrlein, 1981).

METHODS

DefinitionsThe colon of the rabbit can be divided into a proximal colon which is sacculated, and into a distal

colon which is narrower and devoid of sacculation. The oral part of the proximal colon (Fig. 1) whichhas three taeniae and three rows of haustra is called the 'triple haustrated colon', the following partwith one row of haustra and one taenia is the 'single haustrated colon'. The fusus coli which hasno haustra is attributed to the proximal colon because the motility patterns are the same as thoseof the single haustrated colon.

Animal preparation for chronic experimentsThe chronic experiments were carried out in seven domestic, cross-bred rabbits weighing 2 9-49 kg.

The animals were fed pelleted laboratory chow ad libitum supplemented with hay.Surgical procedures were performed under general anaesthesia. Following pre-medication with

xylazine 4 mg/kg body wt. ketamine 20 mg/kg body wt., and atropine sulphate 0-5 mg/kg body wt.,06-1 55% halothane inO2/N2O was administered by a semi-closed circuit and a face mask.The large intestine was exposed through a mid-line abdominal incision. Extraluminal strain gauge

transducers (type F 102, Hellige, Freiburg, F.R.G.) were sutured to the triple and single haustratedcolon and to the fusus coli at right angles to the longitudinal axis of the bowel (Fig. 1). The transducerswere prepared as previously described (Ehrlein, 1980 a). The dimensions of the finished transducerswere 5 x 9 mm.A polyethylene tube (i.d. 1 mm, o.d. 2 mm) coated with silicone and flanged with a silicone plate

was implanted into the middle of the triple haustrated colon for injection of contrast medium. Toprevent leakage, the incision of the bowel wall was covered with a small disc of polyvinyl alcoholsponge (Prosthex, Ramer Chemical Co. Ltd, Camberley). The disc was cemented to the tube withsilicone adhesive (SV4, Bayer Leverkusen, F.R.G.).The tube and the leads of the strain gauge transducers were carried under the skin from the mid-line

abdominal incision to the back where they were exteriorized. The incision of the skin was closed bya special plug which was prepared with polyvinyl alcohol sponge and silicone adhesive (Ehrlein,1980a). Once recovered from anaesthesia, the animals were fitted with jackets and plastic collars.

Experimental procedure. The experiments were begun when the animals had recovered from theoperation and when food intake and faeces production had normalized. The experiments were carriedout either between 4 a.m. and 7 a.m. (period of soft faeces formation) or between 10 a.m. and 6 p.m.(period of hard faeces production). The rabbits were restrained by a hammock in their normalposition. Each experiment lasted about 2 h. To record motility the strain gauge transducers wereconnected with Wheatstone bridges. The amplified signals were recorded with a multichannelrecorder (Hellige, Freiburg, F.R.G.). With seven rabbits 125 experiments were made.

Radiography. Contrast medium (Micropaque, Damancy, Slough) was slowly injected into thetriple haustrated colon through the implanted tube. The outline and the transit of the coloniccontents were observed fluoroscopically using an X-ray image intensifier video system (Siemens,Erlangen, F.R.G.). The motility records were continuously filmed with a television camera. The signalof this camera and the signal of the X-ray television camera were mixed so that the contractions seenfrom the tracings and the outline and flow of faecal contents could be observed simultaneously onthe monitor and stored on video tape. The advantages of this method have been described in a previouspaper (Ehrlein, 1980b). Drawings of characteristic motor patterns were prepared from videorecordings using still image play-back.

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SIGNIFICANCE OF COLONIC CONTRACTIONS

-*-Caecum Proximal colon

Triple haustrated colon + Single haustrated colon -4Fus. colil

-Tube

Fig. 1. Schematic diagram of the rabbit proximal colon and positions of strain gauge transducers and implantedtube in chronic experiments.

Sringe I nductive transducers

0^Site I Site 2A

P(l ure transducer Pressure transducer

Caecum Triple haustrated colon Single haustrated colon

Fig. 2. Positions of strain gauge transducers, open-ended catheters and inductive transducers in acute experiments.

Animal preparation for acute experimentsSix domestic, cross-bred rabbits weighing 3 0-5 3 kg were used in the acute experiments. The

animals were fed with pelleted food and hay ad libitum.The experiments were performed under general anaesthesia with 055% halothane in 02/N20 after

induction with xylazine 4 mg/kg body wt. and ketamine 20 mg/kg body wt. An endotracheal tube(Cole tube Chl6) was inserted.The caecum and the proximal colon were exposed by a mid-line abdominal incision. To prevent

desiccation and cooling, the exposed intestine was treated with infra-red rays, and saline solution wascontinuously dripped on the colon.Motor activities of the single haustrated colon were measured at two recording sites simultaneously

by strain gauge transducers and by intraluminal pressure (Fig. 2). Open-ended liquid-filled catheterswere inserted through small incisions in the caecum and in the distal part of the single haustratedcolon. The intraluminal pressure was recorded with pressure transducers (Statham P23 Db). Themovements of the haustra were recorded additionally with inductive transducers (Sachs, Freiburg,F.R.G.; Fig. 2).

Motility was stimulated either by intravenous infusion of carbachol 0 1-0.5 ,ug/kg. min over aperiod of 10-20 min or by injections of saline solution or mashed potatoes via a tube which wasinserted into the colon by an incision in the caecum (Fig. 2). Colonic motility was recorded over aperiod of 4-5 h. The movements of the triple and single haustrated colon were observed visually.Typical patterns of the motor activity were filmed with a 16 mm camera.

Analysis of motor activitiesThe duration of the high frequency repetitive contractions was analysed by a computer (Ehrlein

& Hiesinger, 1982). The duration of the base line fluctuations and the duration and rate ofpropagationof the monophasic progressive contractions were evaluated visually from the tracings in the chronicexperiments. The amplitudes of the strain gauge signals and of the intraluminal pressure waves weremeasured manually in the acute experiments and correlated with each other.

409

4H-J. EHRLEIN, H. REICH AND M. SCHWINGER

1 min

F. coli U

I h.c. *

3 h.c. U

Fig. 3. Typical patterns of colonic motility of conscious rabbits showing the three types of contractions: highfrequency repetitive contractions, low frequency rises of the base line, and monophasic progressive contractions(indicated by arrows). 1 h.c., single haustrated colon; 3 h.c., triple haustrated colon.

RESULTS

Three types of contractions were found at the distal part of the triple haustrated colon, atthe single haustrated colon, and at the fusus coli: (1) high frequency repetitive contractions,(2) low frequency rises of the base line, and (3) monophasic progressive contractions. Thehigh frequency repetitive contractions and the low frequency rises of the base line werecontinuously present in the conscious animals during the period of hard faeces production.In the anaesthetized animals the high frequency repetitive contractions and the lowfrequency rises of the base line occurred sometimes spontaneously; otherwise they wereevoked either by gradual distension of the bowel or by intravenous infusion of carbachol.The monophasic progressive contractions were never found in the acute experiments; inthe conscious animals they occurred during the periods both of hard and of soft faecesformation.

High frequency repetitive contractionsThe motor activity of the proximal colon of conscious rabbits consisted of repetitive

contractions which were superimposed on base line fluctuations (Fig. 3). They were foundat all recording sites of the proximal colon. The amplitudes of the repetitive contractionswere variable; they often increased and decreased in close relationship to the fluctuationsof the baseline. The analysis of 30084 repetitive contractions revealed a mean duration of3 2 + 1 s. The frequency of the repetitive contractions augmented from the oral towards theaboral parts of the proximal colon. The rates at the oral half of the single haustrated colonwere 1 3 8 + 1 6 contractions/min, at the distal half 14 8 + 0 5 contractions/min, and at thefusus coli 16-2 + 2-2 contractions/min. In simultaneous fluoroscopy it was observed that therepetitive contractions were regularly associated with rolling movements of the haustra.

410

Oily

t t


mmHg g 1 minRecording site 2mmHg 1 minA 2

Intraluminal 20 1pressure 10

Straingauge

of haustra

B

Fig. 4. A, records ofhigh frequency repetitive contractions in acute experiments. B, schematic drawing ofmigratingshallow rings of constriction associated with rolling movements of the haustra.

They produced mixing and a retrograde transfer of colonic contents. However, it could notbe clarified fluoroscopically in which way the haustral movements were produced.

In anaesthetized animals the visual observation of the exposed colon showed that themovements of the haustra were caused by shallow annular constrictions which occurredsimultaneously in a series with intervals of 4-8 mm between their troughs. The annularconstrictions of the triple haustrated colon travelled always retrograde towards thecaecum whereas the annular constrictions of the single haustrated colon moved eitherorally or aborally. The rate of progression was about 1-2 mm/s. When the annularconstrictions moved orally the aboral part of the haustra contracted while the oral partrelaxed. Thereby a rolling movement of the haustra was produced which seemed to beopposite to the movement of the annular constrictions (Fig. 4B). The simultaneousrecordings of the strain gauge, pressure and inductive transducers revealed that the annularconstrictions and the movements of the haustra were associated with high frequencyrepetitive contractions (Fig. 4A). In the acute experiments the frequency of the repetitivecontractions varied between 7 and 13 contractions/min, i.e. it was less in comparison tothe chronic experiments.The signals of the strain gauge transducers and of the intraluminal pressure showed a

close conformity on the tracings. The analysis of 1990 contractions revealed a linearrelationship between the amplitudes of the intraluminal pressure waves and of the straingauge transducer records. A low correlation coefficient (0-73), however, indicated that theamplitudes of both signals were often different.

Low frequency rises of the base lineSustained rises of the base line were found in both conscious and anaesthetized animals.

They were present at the end of the triple haustrated colon and at the single haustratedcolon (Fig. 3). When the conscious rabbits produced hard faeces the base line fluctuationsoccurred without interruption; only the amplitudes were variable. The fluctuations of thebase line were most pronounced and regular in sequence at the fusus coli. They were usually

41


I min

I h.c.

bl b2 b3 b4

Fig. 5. Relationship between rises of the base line and transit of radiopaque colonic contents in unanaesthetizedrabbits. The faecal boli (bl-b4) passed the recording site one after the other. When bolus bl reached therecording site the base line of the tracings decreased and the amplitudes of thesurmounted repetitive contractionswere reduced. When bolus b 1 moved aborally and a constricted segment of the bowel came to the recordingsite the base line of the tracing increased and the amplitudes of the surmounted repetitive contractionsaugmented. These events were repeated during the transit of the subsequent boli and segmental indentations.

surmounted by the high frequency repetitive contractions (Fig. 3). The analysis of 3028base line fluctuations showed a mean duration of 131 + 47 s; hence follows an average rateof 4-6 contractions/10 min.The simultaneous observation of the transducer records and either of the expo'sed

intestine or ofthe outline ofthe opaque colonic contents showed that the rises ofthe base linewere produced by deep annular, long-lasting constrictions which separated the faecal massinto single boli. In the unanaesthetized rabbits the deep segmental constrictions movedslowly aborally at the rate of about 7 mm/min pushing the boli ahead of them; thus onesegmental constriction and one bolus after the other passed the recording sites. Fig. 5 showsthe relationship between the contractions of the single haustrated colon and the transit ofradiopaque faecal boli in unanaesthetized rabbits.

Monophasic progressive contractionsThe third type ofcontractions consisted ofmonophasic waves which occurred successively

at two recording sites (Fig. 3). The amplitudes of these contractions were larger and theduration of each contraction was longer compared to those of the high frequency repetitivecontractions. The progressive contractions occurred sporadically; the mean rates of theiroccurrence were 0 5 contractions/h during the period of hard faeces production and 2-3contractions/h during the period of soft faeces formation. The duration of the monophasicwaves and their rates of progression were different between the periods of soft and hardfaeces formation. During the production of hard faeces the mean duration of twenty-sixidentified progressive contractions was 5 5 + 1 2 s, whereas during the production of softfaeces the mean duration of seventy identified progressive contractions was 9 7 + 2-8 s. Theaverage rates of progression were 3 2 + 1 -2 cm/s (period of hard faeces formation) and1 3 + 0-6 cm/s (period of soft faeces formation).The monophasic waves which occurred during the period of hard faeces formation were

usually induced when a gas bubble of the caecum was forced into the colon. Theyrepresented peristaltic contractions which propelled the gas rapidly through the proximalcolon. The faecal masses usually did not change their position. Sometimes, however, someof the faecal boli were also forced aborally over a few centimetres.

412


a ac3a4 ch

b -'lb

1 minFig. 6. Motility tracings of the single haustrated colon (left panel) and drawings of fluoroscopic pictures preparedfrom video recordings (right panel). A wave ofmass peristalsis moved over the single haustrated colon producingrapid transit of opaque colonic contents. On the tracings, large monophasic waves occurred successively at bothrecording sites (a and b).

The progressive waves which occurred during the period of soft faeces formationrepresented mass peristalsis (Fig. 6). A circular constriction passed along the bowelproducing a progressive obliteration of the colonic lumen. The contraction was associatedwith a progressive zone of relaxation (Fig. 6). Thereby the faecal mass was completelypropelled abroad ahead of the stripping wave. When the mass movement was finished thefaecal mass was again separated into several boli.

DISCUSSION

The classification of colonic intraluminal pressure waves into three types was introducedby Templeton & Lawson (1931) in dogs and has been applied later also to man (Adler,Atkinson & Ivy, 1941; Spriggs, Code, Bargen, Curtiss & Hightower, 1951; Posey & Bargen,1951; Code, Hightower & Morlock, 1952). Type I waves were generally described as simplewaves of short duration (about 5 s) and small amplitude (Fig. 7 B). They were often foundto be superimposed on type II and III waves. Type II waves were characterized by greateramplitude and longer duration (about 25 s) in comparison to type I waves. Type III waveswere described as complex waves consisting of a rise in base line and surmounted type I ortype II waves. In patients with ulcerative colitis a fourth type of contraction was found(Spriggs et al. 1951; Kern, Almy, Albot & Bogdonoff, 1951). The type IV waves weredescribed as monophasic contractions of large amplitudes which lasted 2-5 min with a meanduration of 2 2 min. The physiological significance of the various pressure waves is notexactly known (Chaudhary & Truelove, 1961; Truelove, 1966). Type I and type II wavesappeared to represent haustral activity, whereas type IV waves were regarded as representingpropulsive activity. Combined manometric and cineradiographic studies on humans oftenfailed to reveal a relationship between the pressure waves and the movements of the bowelwall (Gramiak, Ross & Olmsted, 1971).The present study has shown that the motor activity of the proximal colon of rabbits

can be separated into three types of contractions (Fig. 7 A). This classification was basedon two features: (1) on different waves of the motility records, and (2) on different patternsof contraction as seen by fluroscopy or direct visual observation of the exposed intestine.The present classification is similar but not exactly identical to that described in theliterature (Fig. 7B). To avoid confusion the various modes of contractions which werefound on the proximal colon of rabbits were characterized as high frequency repetitive

413


A BPresent results in rabbits Literature

High frequency Rolling movements Type I Type IIrepetitive contract. of haustra

- - sM~V~

Rises of Migrating segmental Type IIIbaseline constrictions

Monophasic Type IVprogressive waves Peristalsis

Fig. 7. Schematic representation of the various wave forms found in the proximal colon of rabbits in comparisonto the classification described in literature (Adler et al. 1941; Spriggs et al. 1951; Kern et al. 1951; Chaudhary& Truelove, 1961; Connell, 1968).

contractions, low frequency rises of the base line, and monophasic progressive contractionsinstead of type I, II and III waves.

High frequency repetitive contractionsThese contractions represented haustral activity. It consisted of shallow rings of

constrictions which occurred in a series with intervals of 4-8 mm between their troughs. Mostoften they travelled retrograde producing rolling movements of the haustra. Exactly thesame pattern of contractions was described as antiperistaltic waves in the proximal colonof cats, rats and guinea pigs (Elliott & Barclay-Smith, 1904; Cannon, 191 1; Hukuhara &Neya, 1968). Similar movements of the haustra were also found in the human colon andwere called 'interhaustral progression' (Ritchie, 1968). The repetitive contractions of theproximal colon of rabbits might be identical with type I waves.

Low frequency rises of the base lineA sustained rise of the base line represented segmental activity. It consisted of persistent

rings of constriction which migrated very slowly aborally. These contractions mightcorrespond to type III waves. However, type III waves were usually described as a complexwaveform consisting of base line changes with superimposed type I or type II waves. Thisclassification seems to be misleading since the complex waves are a combination of twoseparate features. The segmental constrictions found in rabbits are comparable with thosecontractions which were described in rats and guinea pigs as peristalsis (Hukuhara & Neya,1968) and in humans as 'serial multihaustral propulsion' (Ritchie, 1968) or as 'peristalticripples' (Ritchie, Truelove, Ardran & Tuckey, 1971). It is assumed that the segmental activityof the proximal colon is more pronounced in rabbits than in humans since these animalsproduce pelleted faeces.

414


Monophasic progressive contractionsThe progressive contractions of the colon produced on the tracings strong monophasic

waves which occurred successively at two recording sites. These contractions representedperistaltic waves. During the formation of hard faeces they were usually associated witha rapid transit of gas, whereas during the formation of soft faeces they produced adisplacement of the faecal masses over a long distance. The latter progressive contractionswere always preceded by a wave of relaxation and a disappearance of the segmentalconstrictions. The same events were described as characteristic features of the massperistalsis of humans (Holzknecht, 1909; Williams, 1967; Torsoli, Ramorino, Ammaturo,Capurso, Paoluzi & Anzini, 1971; Ritchie, 1972). In the studies on humans it was foundthat the colonic mass peristalsis was associated with strong monophasic pressure wavescorresponding to those found in rabbits (Spriggs et al. 1951; Kern et al. 1951; Hardcastle& Mann, 1968; Mann & Hardcastle, 1970; Torsoli et al. 1971). However, the duration ofthe pressure waves of the human colon (1-5 min) seems to be longer than that of the rabbitcolon (about 10 s), whereas the velocity of the mass peristalsis was higher in the rabbit colon(1.3 cm/s) than in the human colon (about 30 cm/min = 0 5 cm/s).'When the results of motility records are compared between various species it becomes

evident that the different patterns of motility are often described by the same terms.Migrating annular constrictions are usually called 'peristaltic waves', and local stationarycontractions are described as 'segmental activity'. However, the.contractile patterns ofvarious stationary or migrating waves can be completely different. The series oforad-movingshallow constrictions, which are called 'antiperistalsis ' (Cannon, 1911; Hukuhara & Neya,1968) and the aborad-moving stripping waves, which are called 'peristalsis', representdifferent patterns of motility producing different waves on the tracings. In the present studyin rabbits segmental activity was found to be a sustained annular indentation, whereas inhumans the occurrence of haustra and the movements of haustra- were often described as'segmental activity" (Connell, 1968; Ritchie, 1968). Therefore, it seems to be necessary tocreate new terms for the various motor patterns of the gastro-intestinal tract or to describethe various types of contractions in more detail instead of the use of general terms.Many investigators who recently studied the motility of the human colon have questioned

the usefulness of the classification of the colonic pressure events into types (Connell et al.1965; Connell, 1968; Bloom, Lo Presti & Farrar, 1968). Instead of classification, the colonicmotor activity was often divided into propulsive and non-propulsive waves or intosegmental and peristaltic activity. However, it must be noticed that most studies on themotility of the human colon refer to the sigmoid colon (Connell, 1968). The proximal partof the human colon has been studied less intensively since not enough appropriate methodshave been available. Fluoroscopic examinations are limited in humans because of thedangers of irradiation (Connell, 1968). Time-lapse cineradiography (Ritchie, 1968) mightbe helpful to study details of contractions, but it might be difficult to recognize the patternsof activity by means ofthis method. In studies ofthe intraluminal pressure by radiotelemetriccapsules, type I waves were scarcely found in the human colon; they were regarded asartifacts which originated outside the colon (Gramiak et al. 1971). In the presentexperiments, a strong correlation between the intraluminal pressure waves and therecordings of strain gauge transducers were found showing that both methods revealed thesame patterns of motor activity. The larger variation of the data, however, indicated thatthe amplitudes of contractions are different to some extent when different methods are used.In chronic experiments on rabbits, recordings of the intraluminal pressure sometimes failed

415


to indicate haustral activity of the triple haustrated colon. The same might happen in thehuman colon. Therefore, it cannot be decided whether the motility patterns of the colonof rabbits are similar to that of the human colon. To clarify this question furthercomparative studies on the colonic motility of other herbivores and omnivores arenecessary.

Our thanks are due to Mrs Ingeborg Ehrlein and to Mrs Margrit Hartmann for excellent technicalassistance.

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PHYSIOLOGICAL SIGNIFICANCE OF THE CONTRACTIONS OF