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Central muscarinic control of the pattern of small intestinal motility in rats
Life Sciences, Vol. 40, pp. 1709-1715 Printed in the U.S.A.
Pergamon Journals
CENTRAL MUSCARINIC CONTROL OF THE PATTERN OF SMALL INTESTINAL MOTILITY IN RATS M.J. Fargeas, J. Fioramonti
and L. Bu~no
Station de Pharmacologie-Toxicologie, INRA 180 chemin de Tournefeuille, 31300 Toulouse, France (Received in final form February
5, 1987)
Summary The effects of central and peripheral administration of muscarin i c a g o n i s t s and a n t a g o n i s t s on s m a l l i n t e s t i n a l m o t i l i t y were examined In conscious rats chronically fitted with electrodes implanted in the duodeno-JeJunal wall and a cannula in a cerebral lateral ventricle. Intracerebroventricular (i.c.v.) administration of either atropine or pirenzepine at doses from i to i0 ug, 15 mln before a 3 and 6 g lab chow meal significantly reduced the duration of the postprandial disruption of the mi grating myoelectric complexes (MMC). The reduction was signlfl cantly greater for atropine, a mixed M1 and M2 muscarlnic receptor antagonist, than for pirenzepine, an antagonist with a h i g h affinity for M1 receptors. At a higher dose (i0 ~g) intra peritoneal (i.p.) administration of atropine or pirenzepine did not modify the postprandial disruption of MMC. Oxotremorine (10 ng) a M2 agonist, but not McNeil A343 (5 pg), a selective M1 agonlst, given i.c.v, in fasted rats disrupted for 1.5 h the MMC pattern. At the same doses given i.p. oxotremorine and Mc Nail A343 disrupted the MMC for 15 and 45 min respectively. We conclude that the postprandial changes in the small intestinal motility involve muscarlnlc receptors, mainly of M2 subtype, at the level of the central nervous system.
The control of gastrointestinal motility through muecarinic cholinergic receptors at the level of smooth muscle cells and myenteric neurons is well documented (I, 2). Central effects of acetylcholine and other cholinergic agonists on gastric acid secretion have been reported (3, 4). Central neuropeptiderglc (5) and adrenergic (6) mechanisms have been shown to modulate the motor profile of the small intestine. Except a work showing that cholinergic stimulation of certain areas of the brain affect colonic motility, suggesting the involvement of cholinergic transmission in the activation of excitatory and inhibitory hypothalamic neurons regulating digestive motility (7), no data was available on the cholinergic control of gastrointestinal motility at the level of the central nervous system. Two subtypes of muscarlnic receptors which correspond to M1 and M2 receptors initially described for the lower esophageal sphincter (8) have been evidenced in the rat brain (9). Autoradiographic studies in the rat brain have shown a differential anatomical localization of MI and M2 sites, adding evidence for a distinct functional role of these two receptor populations in brain function (9, I0, Ii). Pirenzeplne preferentially antagonizes the action of acetylcholine at M1 receptors, whereas atropine
Copyright
0024-3205/87 $3.00 + .00 (c) 1987 Pergamon Journals Ltd.
1710
Muscarinic Control of Intestinal Motility
Vol. 40, No. 17, 1987
acts at both receptors without apparent preference for the M1 or M2 subtypes (12). On the other hand cholinergic agonlsts such as McNeil A343 selectively stimulates M1 receptors (8) while oxotremorine is known for its high affinity for M2 sites (]i). According to the increase in parasympathetic activity after a meal (13) and the control of intestinal motility by the central nervous system (5), the present study was undertaken in the rat to establish whether central muscarini¢ receptors are involved in the postprandial changes of the intestinal motor pattern.
Methods Animal preparation Male Wistar rats weighing 350-~00 g, individually housed and fed with chow pellets, were used in these experiments. Under halothane anesthesia animals were prepared for long term electromyographic recordings of intestinal motility using a previously described technique (14). Nichrome wires electrodes (Microfil-Industrle, Renens, Switzerland), 80 pm in diameter and 60 cm in length, were implanted in the duodeno-jeJunum wall at 5, 20 and 40 cm from the pylorus. The electrodes wires were exteriorized on the back of the neck and protected by a glass tube attached to the skin. In addition rats were fitted with a small polyethylene catheter (PEI0) inserted into a lateral ventricle of the brain (15). Motility recording Electromyographic recordings began 5 days after surgery. The spiking activity was amplified by an electroencephalograph machine (Reega VIII, Alvar, Paris) and summated every 20 s by an integrator circuit and automatically plotted 24 h/day on the y axis of a potentlometric recorder with a paper speed of 6 cm/h (16). This "integrated" record permitted a clear determination of MMC and postprandial patterns of intestinal activity. Experimental procedure Experiments were performed at two days intervals in rats fasted for 15 hours with free access to water. In I0 rats, a meal of 3 g or 6 g of chow pellet was given at this time. Ingestion of the entire meal Was checked after one hour. Atropine (Sigma, St Louis, MO) or pirenzepine (a gift from Boerhinger-Ingelheim, Reims, France) was given 15 mln before the meal at doses from 1 to I0 ~g intracerebroventricularly (i.c.v.) or I0 pg intraperitoneally (i.p.). Cholinergic agonists were administered in 10 other rats also fasted from 15 hours but deprived of food for 5 supplementary hours. McNeil A343 (4-hydroxy-2-butymyl-trimethylammonium chloride, RBI, Wayland, MA) was administered i.c.v, and i.p. at a dose of 5 ug. Oxotremorine (Aldrich, Strasbourg, France) was administered i.c.v. (i0 ng) and i.p. (i0 and 100 ng). All drugs were dissolved in saline and administered i.c.v, in a 10 pl volume. Experiments and controls (saline, i0 ~I i.c.v.) were performed randomly once in each animal. Changes in motility pattern were appreciated by measuring the duration of MMC disruption after a meal or a drug administration and values expressed as mean + SD were compared using the paired "t" test.
Vol. 40, No. 17, 1987
Muscarinic Control of Intestinal Motility
1711
Results C o n t r o studies The myoelectrical activity of the small intestine in 15 h fasted rats was organized into migrating myoelectrlc complexes (MMC) which recurred at intervals of 12-15 min as previously described (14). Each MMC consisted of irregular spiking activity (phase 2) followed by a short (4-5 min) period of intense and regular spiking activity (phase 3). These phases of activity lasted 9-10 mln and were separated by a 3-5 min period of quiescence (phase 1). A meal of 3 g lab chow given to 15 h fasted rats receiving a i0 ul i.c.v, administration of saline 15 min before, immediately disrupted the MMCs and induced a pattern of irregular spiking for 168 + 34 min. Such a disruption lasted 263 + 50 min for a meal of 6 g. Effects of muscarinic antagonists on the postprandrial disruption of MMCs ICV administration of atropine or pirenzepine 15 min before the meal significantly (P < 0.001) reduced the duration of the postprandial disruption of MMCs (Fig. I and 2). For each drug the effects were doserelated (Fig. i). For each dose (I to 10 pg) and each meal (3 and 6 g) the duration of the postprandial pattern was significantly (P < 0.01) shorter after atropine than after pirenzeplne administration. After atropine given at i0 ~ g i.c.v., the postprandial disruption of MMCs was nearly abolished since it did not exceed 20 min for a 3 g meal and 30 min for a 6 g meal. However the duration, the amplitude and the frequency of the phases 3 of the MMCs was irregular for the 4-5 hrs after i.c.v, administration of atropine. Atropine or pirenzepine given i.p. at a dose of i0 ~g, 15 min before the meal, did not significantly (P > 0.05) modify the duration of the postprandial pattern induced by a 3 or 6 g meal (Fig. I). Effect of muscarinic agonists on the MMC pattern Oxotremorine i.c.v, administered at a dose of i0 ng in 15 h fasted rats immediately disrupted the MMC pattern which was replaced by a irregular spiking activity for 83 + 21 min (Fig. 3). Such a disruption was abollshed by a previous i.c.v, administration of atropine (I0 ~g) but not of pirenzeplne (i0 ~g). After pirenzeplne, oxotremorine (10 ng i.c.v.) induced a period of irregular activity lasting 71 + 24 min (n = 5). IP admlnistered at the same dose oxotremorine induced a short period of irregular activity which did not exceed 20 min. An i.p. dose of i00 ng was necessary to obtain a MMC disruption similar in duration (71 + 17 mln) to that observed after an i.c.v, administration of 10 ng. McNeil A343 i.c.v. injected at a dose of 5 ~g did not modify the MMC pattern (Fig. 3) while the same dose i.p. administered disrupted the MMCs for 43 + 13 mln (Table I).
TABLE I Duration (minutes) of the disruption of MMCs after administration of muscarinic agonists in fasted rats. Mean + S.E.M. (n = i0).
Route of Administration
Oxotremorine i0 ng 100 ng
i.c.v.
83 + 21
i.p.
16 Z 4
McNeil A343 5 pg 0
71 Z 17
43 ± ]3
1712
Muscarinic Control of Intestinal Motility
3g 3007, CONT
6 g
MEAL
ATROPINE
Vol. 40, No. 17, 1987
PlRENZEPINE
' CONT
MEAL
ATROPINE
PIRENZEPINE
z
n, hi
200 Q
z no. FQ. ~
IO0
u. 0
Q o
0 IP i0
--ICV1
I0
IP I0
ii ii, ii -ICVI ~0
I,D
iO
---ICV-I
5
IP
I0
I0
--ICV-I
5
I0
FIG. i Duration of the postprandial disruption of the MMC pattern after a 3 and 6 g meal of chow pellet in 15 hrs fasted rats receiving I0 pl of saline i.c.v. (control), plrenzepine or atropine i.c.v, and i.p. 15 min before the meal. Administrations of plrenzepine or atropine i.c.v. (I to 10 pg) but not i.p. (i0 ~g) significantly (*, P < 0.001) reduced the duration of the postprandial pattern of motility. This reduction was dose-related and greater for atropine than plrenzeplne.
Discussion The present study indicates that in the rat central muscarinlc receptors are probably involved In the disruption of the jejunal MMCs induced by a meal. It has been previously shown that some neuropeptides (17) or o~2 antagonists (6) were able to restore a MMC pattern when centrally administered one hour after a meal. As indicated by the effects of atropine i.c.v, administered at a dose of 10 ~g, this study shows for the first time that the postprandial disruption of the MMCs can be abolished by acting at the CNS level. As already indicated In dogs (18) the duration of the postprandial disruption was related to the amount of food eaten. For a given meal atropine or plrenzeplne induced a dose related effect and for a given dose their effects were related to the size of the meal. These relationships are in favour of a physiological involvement of central muscarinlc receptors in the postprandial changes in intestinal motility. The greater effect of atropine compared with that of plrenzeplne at the same dosage is in favour of an involvement of M2 rather than MI receptors although pharr0acoklnetlc considerations may explain the difference between the effects of the two drugs. M2 receptors which are characterized by a low afflnlt~ for plrenzeplne (12) are mainly found in thalamus, hypothalamus, midbraln and brainstem (ii), areas involved in the control of vegetative functions. In contrast MI receptors sites are mainly loca]ized in forebraln areas such as strlatum, hippocampus and cortex (ii). This
Vol. 40, NO. 17, 1987
Muscarinic Control of Intestinal Motility
1713
anatomical localization is also in favour of a central chollnergic control of intestinal motility through M2 receptors. The involvement of M2 rather than M1 receptors is reinforced by the lack of effect of McNeil A343, a selective M1 agonist (8) and the effect of oxotremorine, known for its high affinity for M2 sites (ii), which disrupted the MMC pattern when given i.c.v, in fasted rats. It can be postulated that oxotremorine acts at M1 receptors to disrupt the MMC pattern but the selective blockade of this effect by atropine but not plrenzlne plays in favour of an action at M2 receptors. However the lack of involvement of M1 receptors iS not demonstrated here because the dose of McNeil A343 used (5 pg) was perhaps too low to act at M1 sites. The use of higher doses could not permit to conclude to a specific central action since the 5 pg dose given peripherally was effective to disrupt MMCs. All the effects observed herein seem to be strictally centrally mediated since the doses of atropine or plrenzeplne active when centrally administered were ineffective when l.p. administered. Moreover pirenzepine is an hydrophilic compound which probably poorly crosses the blood brain barrier. On the other ha~d oxotremorlne induced only a slight effect when l.p. administered at a dose effective when centrally administered but oxotremorlne, well known for its convulsivant effects, easlly crosses the blood brain barrier.
JEJUNUM
Ii~C SALINE IO~ll Icvt
tMeal (31)
.
.
.
.
.
/
12~c
1
IllgICV I ATROPINE lug ICV
I Meal(3g)
li~C Ihour
FIG. 2 Integrated records of jejunal myoelectrlcal activity in the same rat receiving a 3 g meal preceded with an i.c.v, administration of saline (control), pirenzepine or atropine. Note the reduction of the duration of the postprandial disruption of the MMC pattern after i.c.v, pirenzepine or atropine.
1714
Muscarinic Control of Intestinal Motility
Vol. 40, No. 17, 1987
Muscarinic M2 receptors have been found also involved, but at the peripheral level, in the colonic motor response to eating in humans (19). Finally these data and our results showing a central action of M2 agonlsts and antagonists on intestinal motility, indicate that M2 receptors play probably an important role, at both central and peripheral levels, in the postprandial changes of digestive motility.
tOXOTREMORINE lOng ICV
t McNeil A 343 5 pg ICV
"
I hour
FIG. 3 Effect of oxotremorine and McNeil A343 on the jejunal MMC pattern on 15 h fasted rats. Oxotremorine given i.c.v, at a dose of I0 ng disrupted the MMCs for more than one hour while McNeil A343 at a dose of 5 ~g i.c.v, did not modify the MMC pattern.
References I.
2. 3. 4. 5. 6. 7. 8.
T.B. BOLTON, In : Smooth muscle : an assessment of current knowledge, E. Bulbrlng, A.F. Bradlng, A.W. Jones and T, Tomita (Eds.), Edward Arno]d Ltd, London, pp. 199-217 (1981). J.D. WOOD, In : Physiology of gastrointestin.al trac_~t, L.R. Johnson (Ed.), Raven Press, New York, pp. 1-38 (1981). S.V. ANICHKOV and L.L. GRECHISHKIN, Arch. Int. Pharmacodyn. 166 417422 (1967). T. ISHIKAWA, Y. OSUMI, M. FUJIWARA and M. NAGATA, Eur. J. Pharmacol. 80 331-336 (1982). L. BUENO and J.P. FERRE, Science 216 1427-1429 (1982). M.J. FARGEAS, J. FIORAMONTI and L. BUENO, Gastroenterology 91 14701475 (1986). R. BOOM, G. CHAVEZ-IBARRA, J.J. DEL VILLAR and R. HERNANDEZ-PEON, Int. J. Neuropharmacol. 4 169-175 (1965). R.K. GOYAL and S. RATTAN, Gastroenterology 74 598-619 (1978).
Vol. 40, No. 17, 1987
9. I0. ii. ]2. 13. 14. 15. 16. 17. 18. ]9.
Muscarinic Control of Intestinal Motility
1715
L.T. POTTER, D.D. FLYNN, H.E. HANCHETT, D.L. KALINOSKI, J. LUBERNAROD and D.C. MASH, TIPS Suppl. January 22-31 (1984). J.K. WAMSLEY, D.R. GEHLERT, W.R. ROESKE and H. YAMAMURA, Life Scl. 34 1395-1402 (1984). R. CORTES and J.M. PALACIOS, Brain Res. 362 227-238 (1986). R. HAMMER and A. GIACHEi ~ [Afe Sci. 3] 2991-2998 (1982). A.B. STEFFENS, J. VAN DER GUGTEN, J. GODEKE, P.G.M. LUITEN and J.H. STRUBBE, Physiol. Behav. 37 119-122 (]986). M. RUCKEBUSCH and J. FIORAMONTI, Gastroenterology 68 1500-1508 (1975). J.J. STEWART, N.W. WEISBRODT and T.F. BURKS, J. Pharmacol. Exp. Ther. 205 547-555 (1978). A. LATOUR, Ann. Rech. Vet. 4 347-353 (1973). L. BUENO, M.J. FARGEAS, J. FIORAMONTI and M.P. PRIMI, Gastroenterology 88 1888-1894 (1985). I. DE WEVER, C. EECKHOUT, G. VANTRAPPEN and J. HELLEMANS, Am. J. Physiol. 235 E661-E665 (1978). F. NARDUCCI, G. BASSOTTI, S. DANIOTTI, P. DEL SOLDATO, M.A. PELLI and A. MORELLI, Dig. Dis. Sci. 30 124-128 (1985).
Pergamon Journals
CENTRAL MUSCARINIC CONTROL OF THE PATTERN OF SMALL INTESTINAL MOTILITY IN RATS M.J. Fargeas, J. Fioramonti
and L. Bu~no
Station de Pharmacologie-Toxicologie, INRA 180 chemin de Tournefeuille, 31300 Toulouse, France (Received in final form February
5, 1987)
Summary The effects of central and peripheral administration of muscarin i c a g o n i s t s and a n t a g o n i s t s on s m a l l i n t e s t i n a l m o t i l i t y were examined In conscious rats chronically fitted with electrodes implanted in the duodeno-JeJunal wall and a cannula in a cerebral lateral ventricle. Intracerebroventricular (i.c.v.) administration of either atropine or pirenzepine at doses from i to i0 ug, 15 mln before a 3 and 6 g lab chow meal significantly reduced the duration of the postprandial disruption of the mi grating myoelectric complexes (MMC). The reduction was signlfl cantly greater for atropine, a mixed M1 and M2 muscarlnic receptor antagonist, than for pirenzepine, an antagonist with a h i g h affinity for M1 receptors. At a higher dose (i0 ~g) intra peritoneal (i.p.) administration of atropine or pirenzepine did not modify the postprandial disruption of MMC. Oxotremorine (10 ng) a M2 agonist, but not McNeil A343 (5 pg), a selective M1 agonlst, given i.c.v, in fasted rats disrupted for 1.5 h the MMC pattern. At the same doses given i.p. oxotremorine and Mc Nail A343 disrupted the MMC for 15 and 45 min respectively. We conclude that the postprandial changes in the small intestinal motility involve muscarlnlc receptors, mainly of M2 subtype, at the level of the central nervous system.
The control of gastrointestinal motility through muecarinic cholinergic receptors at the level of smooth muscle cells and myenteric neurons is well documented (I, 2). Central effects of acetylcholine and other cholinergic agonists on gastric acid secretion have been reported (3, 4). Central neuropeptiderglc (5) and adrenergic (6) mechanisms have been shown to modulate the motor profile of the small intestine. Except a work showing that cholinergic stimulation of certain areas of the brain affect colonic motility, suggesting the involvement of cholinergic transmission in the activation of excitatory and inhibitory hypothalamic neurons regulating digestive motility (7), no data was available on the cholinergic control of gastrointestinal motility at the level of the central nervous system. Two subtypes of muscarlnic receptors which correspond to M1 and M2 receptors initially described for the lower esophageal sphincter (8) have been evidenced in the rat brain (9). Autoradiographic studies in the rat brain have shown a differential anatomical localization of MI and M2 sites, adding evidence for a distinct functional role of these two receptor populations in brain function (9, I0, Ii). Pirenzeplne preferentially antagonizes the action of acetylcholine at M1 receptors, whereas atropine
Copyright
0024-3205/87 $3.00 + .00 (c) 1987 Pergamon Journals Ltd.
1710
Muscarinic Control of Intestinal Motility
Vol. 40, No. 17, 1987
acts at both receptors without apparent preference for the M1 or M2 subtypes (12). On the other hand cholinergic agonlsts such as McNeil A343 selectively stimulates M1 receptors (8) while oxotremorine is known for its high affinity for M2 sites (]i). According to the increase in parasympathetic activity after a meal (13) and the control of intestinal motility by the central nervous system (5), the present study was undertaken in the rat to establish whether central muscarini¢ receptors are involved in the postprandial changes of the intestinal motor pattern.
Methods Animal preparation Male Wistar rats weighing 350-~00 g, individually housed and fed with chow pellets, were used in these experiments. Under halothane anesthesia animals were prepared for long term electromyographic recordings of intestinal motility using a previously described technique (14). Nichrome wires electrodes (Microfil-Industrle, Renens, Switzerland), 80 pm in diameter and 60 cm in length, were implanted in the duodeno-jeJunum wall at 5, 20 and 40 cm from the pylorus. The electrodes wires were exteriorized on the back of the neck and protected by a glass tube attached to the skin. In addition rats were fitted with a small polyethylene catheter (PEI0) inserted into a lateral ventricle of the brain (15). Motility recording Electromyographic recordings began 5 days after surgery. The spiking activity was amplified by an electroencephalograph machine (Reega VIII, Alvar, Paris) and summated every 20 s by an integrator circuit and automatically plotted 24 h/day on the y axis of a potentlometric recorder with a paper speed of 6 cm/h (16). This "integrated" record permitted a clear determination of MMC and postprandial patterns of intestinal activity. Experimental procedure Experiments were performed at two days intervals in rats fasted for 15 hours with free access to water. In I0 rats, a meal of 3 g or 6 g of chow pellet was given at this time. Ingestion of the entire meal Was checked after one hour. Atropine (Sigma, St Louis, MO) or pirenzepine (a gift from Boerhinger-Ingelheim, Reims, France) was given 15 mln before the meal at doses from 1 to I0 ~g intracerebroventricularly (i.c.v.) or I0 pg intraperitoneally (i.p.). Cholinergic agonists were administered in 10 other rats also fasted from 15 hours but deprived of food for 5 supplementary hours. McNeil A343 (4-hydroxy-2-butymyl-trimethylammonium chloride, RBI, Wayland, MA) was administered i.c.v, and i.p. at a dose of 5 ug. Oxotremorine (Aldrich, Strasbourg, France) was administered i.c.v. (i0 ng) and i.p. (i0 and 100 ng). All drugs were dissolved in saline and administered i.c.v, in a 10 pl volume. Experiments and controls (saline, i0 ~I i.c.v.) were performed randomly once in each animal. Changes in motility pattern were appreciated by measuring the duration of MMC disruption after a meal or a drug administration and values expressed as mean + SD were compared using the paired "t" test.
Vol. 40, No. 17, 1987
Muscarinic Control of Intestinal Motility
1711
Results C o n t r o studies The myoelectrical activity of the small intestine in 15 h fasted rats was organized into migrating myoelectrlc complexes (MMC) which recurred at intervals of 12-15 min as previously described (14). Each MMC consisted of irregular spiking activity (phase 2) followed by a short (4-5 min) period of intense and regular spiking activity (phase 3). These phases of activity lasted 9-10 mln and were separated by a 3-5 min period of quiescence (phase 1). A meal of 3 g lab chow given to 15 h fasted rats receiving a i0 ul i.c.v, administration of saline 15 min before, immediately disrupted the MMCs and induced a pattern of irregular spiking for 168 + 34 min. Such a disruption lasted 263 + 50 min for a meal of 6 g. Effects of muscarinic antagonists on the postprandrial disruption of MMCs ICV administration of atropine or pirenzepine 15 min before the meal significantly (P < 0.001) reduced the duration of the postprandial disruption of MMCs (Fig. I and 2). For each drug the effects were doserelated (Fig. i). For each dose (I to 10 pg) and each meal (3 and 6 g) the duration of the postprandial pattern was significantly (P < 0.01) shorter after atropine than after pirenzeplne administration. After atropine given at i0 ~ g i.c.v., the postprandial disruption of MMCs was nearly abolished since it did not exceed 20 min for a 3 g meal and 30 min for a 6 g meal. However the duration, the amplitude and the frequency of the phases 3 of the MMCs was irregular for the 4-5 hrs after i.c.v, administration of atropine. Atropine or pirenzepine given i.p. at a dose of i0 ~g, 15 min before the meal, did not significantly (P > 0.05) modify the duration of the postprandial pattern induced by a 3 or 6 g meal (Fig. I). Effect of muscarinic agonists on the MMC pattern Oxotremorine i.c.v, administered at a dose of i0 ng in 15 h fasted rats immediately disrupted the MMC pattern which was replaced by a irregular spiking activity for 83 + 21 min (Fig. 3). Such a disruption was abollshed by a previous i.c.v, administration of atropine (I0 ~g) but not of pirenzeplne (i0 ~g). After pirenzeplne, oxotremorine (10 ng i.c.v.) induced a period of irregular activity lasting 71 + 24 min (n = 5). IP admlnistered at the same dose oxotremorine induced a short period of irregular activity which did not exceed 20 min. An i.p. dose of i00 ng was necessary to obtain a MMC disruption similar in duration (71 + 17 mln) to that observed after an i.c.v, administration of 10 ng. McNeil A343 i.c.v. injected at a dose of 5 ~g did not modify the MMC pattern (Fig. 3) while the same dose i.p. administered disrupted the MMCs for 43 + 13 mln (Table I).
TABLE I Duration (minutes) of the disruption of MMCs after administration of muscarinic agonists in fasted rats. Mean + S.E.M. (n = i0).
Route of Administration
Oxotremorine i0 ng 100 ng
i.c.v.
83 + 21
i.p.
16 Z 4
McNeil A343 5 pg 0
71 Z 17
43 ± ]3
1712
Muscarinic Control of Intestinal Motility
3g 3007, CONT
6 g
MEAL
ATROPINE
Vol. 40, No. 17, 1987
PlRENZEPINE
' CONT
MEAL
ATROPINE
PIRENZEPINE
z
n, hi
200 Q
z no. FQ. ~
IO0
u. 0
Q o
0 IP i0
--ICV1
I0
IP I0
ii ii, ii -ICVI ~0
I,D
iO
---ICV-I
5
IP
I0
I0
--ICV-I
5
I0
FIG. i Duration of the postprandial disruption of the MMC pattern after a 3 and 6 g meal of chow pellet in 15 hrs fasted rats receiving I0 pl of saline i.c.v. (control), plrenzepine or atropine i.c.v, and i.p. 15 min before the meal. Administrations of plrenzepine or atropine i.c.v. (I to 10 pg) but not i.p. (i0 ~g) significantly (*, P < 0.001) reduced the duration of the postprandial pattern of motility. This reduction was dose-related and greater for atropine than plrenzeplne.
Discussion The present study indicates that in the rat central muscarinlc receptors are probably involved In the disruption of the jejunal MMCs induced by a meal. It has been previously shown that some neuropeptides (17) or o~2 antagonists (6) were able to restore a MMC pattern when centrally administered one hour after a meal. As indicated by the effects of atropine i.c.v, administered at a dose of 10 ~g, this study shows for the first time that the postprandial disruption of the MMCs can be abolished by acting at the CNS level. As already indicated In dogs (18) the duration of the postprandial disruption was related to the amount of food eaten. For a given meal atropine or plrenzeplne induced a dose related effect and for a given dose their effects were related to the size of the meal. These relationships are in favour of a physiological involvement of central muscarinlc receptors in the postprandial changes in intestinal motility. The greater effect of atropine compared with that of plrenzeplne at the same dosage is in favour of an involvement of M2 rather than MI receptors although pharr0acoklnetlc considerations may explain the difference between the effects of the two drugs. M2 receptors which are characterized by a low afflnlt~ for plrenzeplne (12) are mainly found in thalamus, hypothalamus, midbraln and brainstem (ii), areas involved in the control of vegetative functions. In contrast MI receptors sites are mainly loca]ized in forebraln areas such as strlatum, hippocampus and cortex (ii). This
Vol. 40, NO. 17, 1987
Muscarinic Control of Intestinal Motility
1713
anatomical localization is also in favour of a central chollnergic control of intestinal motility through M2 receptors. The involvement of M2 rather than M1 receptors is reinforced by the lack of effect of McNeil A343, a selective M1 agonist (8) and the effect of oxotremorine, known for its high affinity for M2 sites (ii), which disrupted the MMC pattern when given i.c.v, in fasted rats. It can be postulated that oxotremorine acts at M1 receptors to disrupt the MMC pattern but the selective blockade of this effect by atropine but not plrenzlne plays in favour of an action at M2 receptors. However the lack of involvement of M1 receptors iS not demonstrated here because the dose of McNeil A343 used (5 pg) was perhaps too low to act at M1 sites. The use of higher doses could not permit to conclude to a specific central action since the 5 pg dose given peripherally was effective to disrupt MMCs. All the effects observed herein seem to be strictally centrally mediated since the doses of atropine or plrenzeplne active when centrally administered were ineffective when l.p. administered. Moreover pirenzepine is an hydrophilic compound which probably poorly crosses the blood brain barrier. On the other ha~d oxotremorlne induced only a slight effect when l.p. administered at a dose effective when centrally administered but oxotremorlne, well known for its convulsivant effects, easlly crosses the blood brain barrier.
JEJUNUM
Ii~C SALINE IO~ll Icvt
tMeal (31)
.
.
.
.
.
/
12~c
1
IllgICV I ATROPINE lug ICV
I Meal(3g)
li~C Ihour
FIG. 2 Integrated records of jejunal myoelectrlcal activity in the same rat receiving a 3 g meal preceded with an i.c.v, administration of saline (control), pirenzepine or atropine. Note the reduction of the duration of the postprandial disruption of the MMC pattern after i.c.v, pirenzepine or atropine.
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Muscarinic Control of Intestinal Motility
Vol. 40, No. 17, 1987
Muscarinic M2 receptors have been found also involved, but at the peripheral level, in the colonic motor response to eating in humans (19). Finally these data and our results showing a central action of M2 agonlsts and antagonists on intestinal motility, indicate that M2 receptors play probably an important role, at both central and peripheral levels, in the postprandial changes of digestive motility.
tOXOTREMORINE lOng ICV
t McNeil A 343 5 pg ICV
"
I hour
FIG. 3 Effect of oxotremorine and McNeil A343 on the jejunal MMC pattern on 15 h fasted rats. Oxotremorine given i.c.v, at a dose of I0 ng disrupted the MMCs for more than one hour while McNeil A343 at a dose of 5 ~g i.c.v, did not modify the MMC pattern.
References I.
2. 3. 4. 5. 6. 7. 8.
T.B. BOLTON, In : Smooth muscle : an assessment of current knowledge, E. Bulbrlng, A.F. Bradlng, A.W. Jones and T, Tomita (Eds.), Edward Arno]d Ltd, London, pp. 199-217 (1981). J.D. WOOD, In : Physiology of gastrointestin.al trac_~t, L.R. Johnson (Ed.), Raven Press, New York, pp. 1-38 (1981). S.V. ANICHKOV and L.L. GRECHISHKIN, Arch. Int. Pharmacodyn. 166 417422 (1967). T. ISHIKAWA, Y. OSUMI, M. FUJIWARA and M. NAGATA, Eur. J. Pharmacol. 80 331-336 (1982). L. BUENO and J.P. FERRE, Science 216 1427-1429 (1982). M.J. FARGEAS, J. FIORAMONTI and L. BUENO, Gastroenterology 91 14701475 (1986). R. BOOM, G. CHAVEZ-IBARRA, J.J. DEL VILLAR and R. HERNANDEZ-PEON, Int. J. Neuropharmacol. 4 169-175 (1965). R.K. GOYAL and S. RATTAN, Gastroenterology 74 598-619 (1978).
Vol. 40, No. 17, 1987
9. I0. ii. ]2. 13. 14. 15. 16. 17. 18. ]9.
Muscarinic Control of Intestinal Motility
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L.T. POTTER, D.D. FLYNN, H.E. HANCHETT, D.L. KALINOSKI, J. LUBERNAROD and D.C. MASH, TIPS Suppl. January 22-31 (1984). J.K. WAMSLEY, D.R. GEHLERT, W.R. ROESKE and H. YAMAMURA, Life Scl. 34 1395-1402 (1984). R. CORTES and J.M. PALACIOS, Brain Res. 362 227-238 (1986). R. HAMMER and A. GIACHEi ~ [Afe Sci. 3] 2991-2998 (1982). A.B. STEFFENS, J. VAN DER GUGTEN, J. GODEKE, P.G.M. LUITEN and J.H. STRUBBE, Physiol. Behav. 37 119-122 (]986). M. RUCKEBUSCH and J. FIORAMONTI, Gastroenterology 68 1500-1508 (1975). J.J. STEWART, N.W. WEISBRODT and T.F. BURKS, J. Pharmacol. Exp. Ther. 205 547-555 (1978). A. LATOUR, Ann. Rech. Vet. 4 347-353 (1973). L. BUENO, M.J. FARGEAS, J. FIORAMONTI and M.P. PRIMI, Gastroenterology 88 1888-1894 (1985). I. DE WEVER, C. EECKHOUT, G. VANTRAPPEN and J. HELLEMANS, Am. J. Physiol. 235 E661-E665 (1978). F. NARDUCCI, G. BASSOTTI, S. DANIOTTI, P. DEL SOLDATO, M.A. PELLI and A. MORELLI, Dig. Dis. Sci. 30 124-128 (1985).