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Effect of cinitapride in isolated ileum obtained from guinea-pigs treated with morphine
Gen. Pharmac. Vol, 22, No, 5, pp. 863-866, 1991 Printed in Great Britain.All rights reserved
0306-3623/91 $3.00+ 0.00 Copyright © 1991 PergamonPress plc
EFFECT OF CINITAPRIDE IN ISOLATED ILEUM OBTAINED FROM GUINEA-PIGS TREATED WITH MORPHINE M. I. COLADO,M. J. ALFARO,V. L. DEL VAL and M. I. MARTIN* Instituto de Farmacologia y Toxicologia, Departamento de Farmacologia, Facultad de Medicina, Universidad Complutense, 28040 Madrid, Spain [Tel. 3941479] (Received 2 January 1991)
Abstract--1. Cinitapride enhanced the contractile response induced by electrical stimulation in the guinea-pig myenteric plexus-longitudinal muscle strip preparations. 2. The contractile force was significantly increased in strips pretreated with morphine "in vitro" and in tolerant strips. 3. However when tissues were obtained from tolerant guinea-pigs and morphine was not added to the organ bath (morphine-abstinence), the cinitapride effect was significantly decreased. 4. Although further work is required to explain the changes in the effect of cinitapride after acute morphine treatment and in morphine tolerant tissues, the changes observed suggest that some of the cinitapride effects could be linked with the perypheral opioid system.
INTRODUCTION Cinitapride is a benzamide derivative that stimulates gastrointestinal motility. The pharmacological effects of this drug have been evaluated in guinea-pig ileum and its actions have been compared to those of metoclopramide. Cinitapride was more potent than metodopramide in enhancing the twitch response in electrically stimulated preparations (Massingham et al., 1985). The mechanism of action of both drugs appears to be similar and involves a prejunctional enhancement of acetylcholine release from intraneural cholinergic neurones (Bou et al., 1986; Massingham et al., 1985). Although the precise mechanism by which these drugs augment the gastrointestinal motility still require to be elucidated. It has been suggested that metoclopramide stimulates neuronal 5-hydroxytryptamine (5HT) receptors and thereby facilitates acetylcholine release (Kilbinger et al., 1982). Dopamine receptors (Costall et al., 1984; Fernandez and Massingham, 1985) or muscarinic presynaptic receptors (Mr) (Schuurkes et al., 1988) are not involved in the local stimulant effects of metoclopramide like drugs. Even more, the existence of 5HT prejunctional receptors and their involvement in the acetylcholine release has been demonstrated (Buchheit et aL, 1985). It has been suggested that serotonergic mechanisms are involved in opiate actions (Romandini et aL, 1986) and that morphine tolerance and abstinence could modify 5HT and 5-hydroxyindole 3-acetic acid levels in central nervous system (Ahtee et al., 1987; Rivot et al., 1988; Colado et al., 1989). In the present paper we study the relationship between cinitapride and opioid system in myenteric plexus-longitudinal muscle strips (MP-LM). It is well known that this preparation can be used as a model *To whom all correspondence should be addressed. op ~/s-o
to analyze the opioid activity and tolerance and dependence phenomena.
MATERIALS AND METHODS
Male guinea-pigs weighing 250-300 g and fasted 24 hr were used. The distal ileum was removed for experimentation and MP-LM strips were isolated as described previously (Ambache, 1954). MP-LM preparations were suspended under a tension of 1 g in an organ bath containing Krebs solution (NaC1 118, KCl 4.7, NaHCO3 250, MgCl2 1.2, NaH2PO4 1.0, CaCI2 2.6 and glucose I 1. l) at 34°C and gassed with a mixture of 95% 02 and 5% CO2. Electrical stimulation (0.3 Hz, 2 msec and supramaximal current) was applied by mean of two platinum ring electrodes after a stabilization period of 15 rain. Contractions were measured isometrically using Grass force transducers and were displayed on Grass recorders. In a series of experiences, tissues were obtained from morphine-tolerant guinea-pigs. The animals were made tolerant to morphine by s.c. injection of a slow release suspension containing a dose of 200 mg/kg of morphine (Contreras et al., 1988). Guinea-pigs were killed 5 days after morphine administration. The degree of tolerance in MP-LM strips was tested comparing the inhibitory effect of morphine (0.1, 0.2, 0.4, and 0.8 #M) in tissues obtained from control animals and from morphine-treated animals. To study the effects of cinitapride, the following sets of experiences were carried out: I. Effects on control tissues After accumulative administration of cinitapride (0.1, 0.3, 1 and 3 ~uM) to the organ bath, the percentage of increase of the contractile response induced by electrical stimulation was evaluated. In addition the effect of cinitapride (3/t M) on non-stimulated preparation was determined. In another series of experiments, the effect of cinitapride (3/~M) was studied 3 min after morphine administration to the organ bath.
863
864
M.I. COLADOet al.
2. Effects on morphine-tolerant tissues The effect of cinitapride (3 # M) was evaluated on tissues obtained from morphine-treated guinea-pigs in absence and presence of morphine (0.2 pM).
16 14 12
Statistical analysis Data were obtained from at least 8 experiments from 3 different animals and expressed as mean + SE. Differences between mean values were tested by Student's t-test or by Fisher's test. The difference between groups was judged to be significant when P < 0.05.
! N C R E
10
E
4
8
0.1
RESULTS
The inhibition of the contractile response induced by morphine administration was decreased in MPLM preparations obtained from morphine treated gulnea-pigs. The difference were statistically significant when compared with the inhibitory effect observed in preparations obtained from control animals (Fig. 1). The amplitude of electrically- evoked twitches did not differ between control tissues and those chronically treated with morphine. Effect o f cinitapride 1. Tissues from control animals. Cinitapride (3/~M) caused a contraction of the unstimulated guinea-pig ileum preparations. The force of these contractile responses amounted to 48 + 5.2% of the response of the tissues to acetylcholine (1 #M). The contractile response of the MP-LM strips induced by electrical stimulation was increased in a dose-dependent manner when cinitapride (0.1-3 # M) was cumulatively administered to the organ bath (Fig. 2). When morphine (0.2 #M) was added to the organ bath 3 min before cinitapride (3/z M) administration the increase of the contractile response was enhanced. When compared the increase in presence and absence of morphine, the difference was statistically significant (P < 0.001) (Fig. 3). 2. Tissues from morphine-treated animals. When MP-LM strips were obtained from tolerant guineapigs the effect of cinitapride (3 #M) was different in presence or absence of morphine. Statistically significant increase of the contractile response induced by electrical stimulation was found in the presence of morphine (tolerant-tissues). On the contrary, in the
0.3 1 CINITAPRIDE pM
3
Fig. 2. Effect of cinitapride on the contractile response induced by electrical stimulation. Each point is the mean of % increase of at least 8 preparations. Vertical bars show SEM. absence of morphine (abstinent-tissues) cinitapride decreased the contractile response. The difference was statistically significant when compared with control tissues (Fig. 3). DISCUSSION
It is well documented that cinitapride and other benzamides can increase the resting tension of intestinal smooth muscle as well as the contractile responses induced by electrical stimulation. Our results agree with the previous reports (Massingham et al., 1985; Bou et al., 1986); cinitapride elicited concentration-dependent increases in the contractile responses and in the resting tension. When MP-LM strips were treated in the organ bath with morphine or when they were obtained from morphine tolerant guinea-pigs an increased sensitivity to the cinitapride effect was observed. Massingham et al. (1985) have found that morphine addition to the organ bath reduced the cinitapride effect. These data were obtained in whole guinea-pig ileum but not in MP-LM strips, even more, the preparations were unstimulated. It is possible that the observed differences can be attributed to the experimental method. 140 120
100
.........,~:~,~~-~:~,: ~ ~i~~ I
1 O0 80 N l N H I B T
60
-'4-- CONTROL ~
~i!~~ ! ~
4O
TOLERANT
40
O N
0
~
~
- -
20 -20 0
0.1
0.~' 0.4 MORPHINE ~uM
0.8
Fig. I. Effect of morphine on the contractile response induced by electrical stimulation. Each point is the mean of the % inhibition of at least 8 preparations. Vertical bars show SEM. ***P < 0.001 compared with control.
Fig. 3. Effect of cinitapride 3 #M on tissues obtained from naive guinea-pigs in absence of morphine (open column) in presence of morphine (strippled columns) and from morphine (solid columns). Each value is the mean of the % of increase of at least 8 preparations. Vertical bars represent SEM. *P < 0.05, **P < 0.01, ***P < 0.001 compared with control.
Cinitapride and morphine in ileum Our results show that: (1) after acute addition of morphine to the organ bath the cinitapride effect was enhanced; (2) in morphine-tolerant preparations this enhanced effect was partially reversed (tolerance?) and finally; (3) during withdrawal by deprivation of morphine, cinitapride decreased the force of the contractile response. Further work is required to define the precise mechanism of action of cinitapride, nevertheless it has been demonstrated (Costall et al., 1984; Fernandez and Massingham, 1985; Schuurkes et al., 1988) that this drug facilitates the cholinergic transmission through a prejunctional mechanism. It has been suggested that the effect of the benzamide derivates in guinea-pig ileum could be mediated by activation of the presynaptic 5HT receptors and, thereby, facilitation of the acetylcholine release. Moreover, interactions with other presynaptic receptors has been rejected (Schuurkes et al., 1988; Kilbinger et al., 1982). In guinea-pig ileum, 5HT receptor activation causes the release of substance P (SP) which subsequently release acetylcholine (Buchheit et al., 1985). In previous studies SP and 5HT (Gintzler, 1980; Tsou et al., 1985) have been implicated in gut dependence on opioids but conflicting results have been obtained. The results varied with the duration of contact of the preparation with opioids and with the manner of precipitation of withdrawal (Chahl, 1983). The involvement of 5HT and SP on the morphine withdrawal has been reported; nevertheless we have not found any information about 5HT receptors or SP release in morphine tolerant guinea-pig ileum. Therefore, although our results could suggest that the cinitapride effect may be attributed to adaptive supersensitivity to the 5HT or SP effects; additional studies are required to understand this cinitapride effect. In MP-LM preparations obtained from tolerant guinea-pigs withdrawal by either washout of opioids or addition of naloxone results in a contracture which was mediated by acetylcholine and SP (Chalh, 1983; Wang and Tsou, 1989). After acute withdrawal the attenuation of potassium induced SP release has been demonstrated and this effect has been attributed to the depletion of SP by withdrawal release (Wang and Tsou, 1989). The lack of effect of cinitapride in morphine deprivated MP-LM strips could be caused by the depletion of SP in these preparations. From these results we conclude that the effect of cinitapride in MP-LM may be related to the opioid system. The exact nature of this interaction remains to be determined.
SUMMARY
Cinitapride is a benzamide derivate that stimulates the gastrointestinal motility. The "in vitro" administration of this drug enhanced the contractile activity of the guinea-pig ileum. The contractile response induced by electrical stimulation was significantly increased in strips pretreatcd with morphine "/n
865
vitro" and in morphine tolerant strips. However when tissues were obtained from tolerant guinea-pigs and morphine was not added to the organ bath (morphine-abstinence) the cinitapride effect was significantly decreased. Although further work is required to explain the changes in the effect of cinitapride after morphine acute treatment and in morphine tolerant tissues, our results suggest that some of the effects of this drug could be related to the opioid system and the relationship between cinitapride and opioid system may be mediated by SP or 5HT.
REFERENCES
Ahtee L., Attila P., Lauhakangas V., Soikinen A. and Sipila J. (1987) The fall of homovanillic acid and 5-hydroxyindolacetic acid concentrations in brains of mice withdrawn from repeated morphine treatment and their restoration by acute morphine administration. J. Neurol. Transm. 68, 63-78.
Ambache N. (1954) Separation of the longitudinal muscle of the rabbit's ileum as a broat she.at. J. Physiol. CXXV, 53p. Bou J., Fernandez A. G., Janregui J. M. and Massingham R. (I 986) Involvement of enteric neurons in the response of guinea-pig ileum preparations to metoclopramide. Br. J. Pharmac. 88, 95-102. Buchheit K., Engel G., Mutschler E. and Richardson B. 0985) Study of the contractile effect of 5-hydroxytriptamine (5HT) in the isolated longitudinal muscle strip from guinea-pig ileum. Naunyn-Schrriiedeberg~ A r c h f Pharmac. 329, 36-41. Chahl L. A. (1983) Contracture of guinea-pig ileum on withdrawal of methionine 5-enkephalin is mediated by substance P. Br. J. Pharmac. 80, 741-749. Colado M. I., Lorenzo P. and Martin M. I. (1989) Nifedipinc reversal of decreased serotonin metabolite levels during morphine withdrawal. Archs Int. Pharmacodyn. Ther. 298, 61-67. Contreras E., Tamayo L. and Amigo M. (1988) Calcium channel antagonists increase morphine-induced analgesia and antagonize morphine tolerance. Eur. J. Pharmac. 148, 463-466. Costall B., Gunning S. J. and Naylor R. J. (1984) SCH 23390 can enhance field stimulation-induced contractions of longitudinal smooth muscle from guinea-pig stomach. J. Pharm. Pharmac. 36, 356. Fernandez A. G. and Massingham R. (1985) Peripheral receptor populations involved in the regulation of gastrointestinal motility and the pharmacological actions of metoclopramide-like drugs. Life Sci. 31, 1-14. Gintzler A. R. (1980) Substance P involvement in the expression of gut dependence on opiates. Brain Res. 182, 224-228. Kilbinger H., Kruel R., Pfeuffer-Friederich I. and Wessler I. (1982) The effects of metoclopramide on acetylcholine release and on smooth muscle response in the isolated guinea-pig ileum. Naunyn-Schmiedeberg' s Archs Pharmac. 319, 231-238. Massingham R., Bou J. and Roberts P. J. (1985) A comparison of the stimulatory effects of metoclopramide and cinitapride in the gninea-pig isolated ileum. J. Auton. Pharmac. 5, 41-43. Rivot J. P., Pointis D. and Besson J. M. (1988) Morphine increases 5HT metabolism in the nucleus raphe magnus: an in vivo study in freely moving rats using 5-hydroxyindole electrochemical detection. Brain Res. 446, 333-342. Romandini S., Pich E. M., Esposito E., Kruszewska A. Z. and Samauin R. (1986) The effect ofintracerebroventricular 5,7-dihydroxytryptamine on morphine analgesia is time-dependent. Life $ci. 38, 869-875.
866
M. I. COLAOO et al.
Schuurkes J. A. J., van Bergen P. J. E. and van Nueten J. M. (1988) Prejunctional muscarinic (Mi)-receptor interactions on guinea-pig ileum: lack of cisapride. Br. J. Pharmac. 92, 228-234. Tsou K., Wu S. X., Lu Y. A. and Way E. L. (1985) Block of the hyoscine-resistant opiate withdrawal contraeture of ileum by a new substance P antagonist: D-Argt, D-Phe 5,
D-Trp7.9, Leull: substance P. Eur. J. Pharmac. 110, 155-156. Wang F. S. and Tsou K. (1989) Substance P on IleucinlEnkephalin release in guinea-pig ileum during naloxone-precipitated morphine withdrawal. J. Pharmac. exp. Ther. 249(1), 329-332.
0306-3623/91 $3.00+ 0.00 Copyright © 1991 PergamonPress plc
EFFECT OF CINITAPRIDE IN ISOLATED ILEUM OBTAINED FROM GUINEA-PIGS TREATED WITH MORPHINE M. I. COLADO,M. J. ALFARO,V. L. DEL VAL and M. I. MARTIN* Instituto de Farmacologia y Toxicologia, Departamento de Farmacologia, Facultad de Medicina, Universidad Complutense, 28040 Madrid, Spain [Tel. 3941479] (Received 2 January 1991)
Abstract--1. Cinitapride enhanced the contractile response induced by electrical stimulation in the guinea-pig myenteric plexus-longitudinal muscle strip preparations. 2. The contractile force was significantly increased in strips pretreated with morphine "in vitro" and in tolerant strips. 3. However when tissues were obtained from tolerant guinea-pigs and morphine was not added to the organ bath (morphine-abstinence), the cinitapride effect was significantly decreased. 4. Although further work is required to explain the changes in the effect of cinitapride after acute morphine treatment and in morphine tolerant tissues, the changes observed suggest that some of the cinitapride effects could be linked with the perypheral opioid system.
INTRODUCTION Cinitapride is a benzamide derivative that stimulates gastrointestinal motility. The pharmacological effects of this drug have been evaluated in guinea-pig ileum and its actions have been compared to those of metoclopramide. Cinitapride was more potent than metodopramide in enhancing the twitch response in electrically stimulated preparations (Massingham et al., 1985). The mechanism of action of both drugs appears to be similar and involves a prejunctional enhancement of acetylcholine release from intraneural cholinergic neurones (Bou et al., 1986; Massingham et al., 1985). Although the precise mechanism by which these drugs augment the gastrointestinal motility still require to be elucidated. It has been suggested that metoclopramide stimulates neuronal 5-hydroxytryptamine (5HT) receptors and thereby facilitates acetylcholine release (Kilbinger et al., 1982). Dopamine receptors (Costall et al., 1984; Fernandez and Massingham, 1985) or muscarinic presynaptic receptors (Mr) (Schuurkes et al., 1988) are not involved in the local stimulant effects of metoclopramide like drugs. Even more, the existence of 5HT prejunctional receptors and their involvement in the acetylcholine release has been demonstrated (Buchheit et aL, 1985). It has been suggested that serotonergic mechanisms are involved in opiate actions (Romandini et aL, 1986) and that morphine tolerance and abstinence could modify 5HT and 5-hydroxyindole 3-acetic acid levels in central nervous system (Ahtee et al., 1987; Rivot et al., 1988; Colado et al., 1989). In the present paper we study the relationship between cinitapride and opioid system in myenteric plexus-longitudinal muscle strips (MP-LM). It is well known that this preparation can be used as a model *To whom all correspondence should be addressed. op ~/s-o
to analyze the opioid activity and tolerance and dependence phenomena.
MATERIALS AND METHODS
Male guinea-pigs weighing 250-300 g and fasted 24 hr were used. The distal ileum was removed for experimentation and MP-LM strips were isolated as described previously (Ambache, 1954). MP-LM preparations were suspended under a tension of 1 g in an organ bath containing Krebs solution (NaC1 118, KCl 4.7, NaHCO3 250, MgCl2 1.2, NaH2PO4 1.0, CaCI2 2.6 and glucose I 1. l) at 34°C and gassed with a mixture of 95% 02 and 5% CO2. Electrical stimulation (0.3 Hz, 2 msec and supramaximal current) was applied by mean of two platinum ring electrodes after a stabilization period of 15 rain. Contractions were measured isometrically using Grass force transducers and were displayed on Grass recorders. In a series of experiences, tissues were obtained from morphine-tolerant guinea-pigs. The animals were made tolerant to morphine by s.c. injection of a slow release suspension containing a dose of 200 mg/kg of morphine (Contreras et al., 1988). Guinea-pigs were killed 5 days after morphine administration. The degree of tolerance in MP-LM strips was tested comparing the inhibitory effect of morphine (0.1, 0.2, 0.4, and 0.8 #M) in tissues obtained from control animals and from morphine-treated animals. To study the effects of cinitapride, the following sets of experiences were carried out: I. Effects on control tissues After accumulative administration of cinitapride (0.1, 0.3, 1 and 3 ~uM) to the organ bath, the percentage of increase of the contractile response induced by electrical stimulation was evaluated. In addition the effect of cinitapride (3/t M) on non-stimulated preparation was determined. In another series of experiments, the effect of cinitapride (3/~M) was studied 3 min after morphine administration to the organ bath.
863
864
M.I. COLADOet al.
2. Effects on morphine-tolerant tissues The effect of cinitapride (3 # M) was evaluated on tissues obtained from morphine-treated guinea-pigs in absence and presence of morphine (0.2 pM).
16 14 12
Statistical analysis Data were obtained from at least 8 experiments from 3 different animals and expressed as mean + SE. Differences between mean values were tested by Student's t-test or by Fisher's test. The difference between groups was judged to be significant when P < 0.05.
! N C R E
10
E
4
8
0.1
RESULTS
The inhibition of the contractile response induced by morphine administration was decreased in MPLM preparations obtained from morphine treated gulnea-pigs. The difference were statistically significant when compared with the inhibitory effect observed in preparations obtained from control animals (Fig. 1). The amplitude of electrically- evoked twitches did not differ between control tissues and those chronically treated with morphine. Effect o f cinitapride 1. Tissues from control animals. Cinitapride (3/~M) caused a contraction of the unstimulated guinea-pig ileum preparations. The force of these contractile responses amounted to 48 + 5.2% of the response of the tissues to acetylcholine (1 #M). The contractile response of the MP-LM strips induced by electrical stimulation was increased in a dose-dependent manner when cinitapride (0.1-3 # M) was cumulatively administered to the organ bath (Fig. 2). When morphine (0.2 #M) was added to the organ bath 3 min before cinitapride (3/z M) administration the increase of the contractile response was enhanced. When compared the increase in presence and absence of morphine, the difference was statistically significant (P < 0.001) (Fig. 3). 2. Tissues from morphine-treated animals. When MP-LM strips were obtained from tolerant guineapigs the effect of cinitapride (3 #M) was different in presence or absence of morphine. Statistically significant increase of the contractile response induced by electrical stimulation was found in the presence of morphine (tolerant-tissues). On the contrary, in the
0.3 1 CINITAPRIDE pM
3
Fig. 2. Effect of cinitapride on the contractile response induced by electrical stimulation. Each point is the mean of % increase of at least 8 preparations. Vertical bars show SEM. absence of morphine (abstinent-tissues) cinitapride decreased the contractile response. The difference was statistically significant when compared with control tissues (Fig. 3). DISCUSSION
It is well documented that cinitapride and other benzamides can increase the resting tension of intestinal smooth muscle as well as the contractile responses induced by electrical stimulation. Our results agree with the previous reports (Massingham et al., 1985; Bou et al., 1986); cinitapride elicited concentration-dependent increases in the contractile responses and in the resting tension. When MP-LM strips were treated in the organ bath with morphine or when they were obtained from morphine tolerant guinea-pigs an increased sensitivity to the cinitapride effect was observed. Massingham et al. (1985) have found that morphine addition to the organ bath reduced the cinitapride effect. These data were obtained in whole guinea-pig ileum but not in MP-LM strips, even more, the preparations were unstimulated. It is possible that the observed differences can be attributed to the experimental method. 140 120
100
.........,~:~,~~-~:~,: ~ ~i~~ I
1 O0 80 N l N H I B T
60
-'4-- CONTROL ~
~i!~~ ! ~
4O
TOLERANT
40
O N
0
~
~
- -
20 -20 0
0.1
0.~' 0.4 MORPHINE ~uM
0.8
Fig. I. Effect of morphine on the contractile response induced by electrical stimulation. Each point is the mean of the % inhibition of at least 8 preparations. Vertical bars show SEM. ***P < 0.001 compared with control.
Fig. 3. Effect of cinitapride 3 #M on tissues obtained from naive guinea-pigs in absence of morphine (open column) in presence of morphine (strippled columns) and from morphine (solid columns). Each value is the mean of the % of increase of at least 8 preparations. Vertical bars represent SEM. *P < 0.05, **P < 0.01, ***P < 0.001 compared with control.
Cinitapride and morphine in ileum Our results show that: (1) after acute addition of morphine to the organ bath the cinitapride effect was enhanced; (2) in morphine-tolerant preparations this enhanced effect was partially reversed (tolerance?) and finally; (3) during withdrawal by deprivation of morphine, cinitapride decreased the force of the contractile response. Further work is required to define the precise mechanism of action of cinitapride, nevertheless it has been demonstrated (Costall et al., 1984; Fernandez and Massingham, 1985; Schuurkes et al., 1988) that this drug facilitates the cholinergic transmission through a prejunctional mechanism. It has been suggested that the effect of the benzamide derivates in guinea-pig ileum could be mediated by activation of the presynaptic 5HT receptors and, thereby, facilitation of the acetylcholine release. Moreover, interactions with other presynaptic receptors has been rejected (Schuurkes et al., 1988; Kilbinger et al., 1982). In guinea-pig ileum, 5HT receptor activation causes the release of substance P (SP) which subsequently release acetylcholine (Buchheit et al., 1985). In previous studies SP and 5HT (Gintzler, 1980; Tsou et al., 1985) have been implicated in gut dependence on opioids but conflicting results have been obtained. The results varied with the duration of contact of the preparation with opioids and with the manner of precipitation of withdrawal (Chahl, 1983). The involvement of 5HT and SP on the morphine withdrawal has been reported; nevertheless we have not found any information about 5HT receptors or SP release in morphine tolerant guinea-pig ileum. Therefore, although our results could suggest that the cinitapride effect may be attributed to adaptive supersensitivity to the 5HT or SP effects; additional studies are required to understand this cinitapride effect. In MP-LM preparations obtained from tolerant guinea-pigs withdrawal by either washout of opioids or addition of naloxone results in a contracture which was mediated by acetylcholine and SP (Chalh, 1983; Wang and Tsou, 1989). After acute withdrawal the attenuation of potassium induced SP release has been demonstrated and this effect has been attributed to the depletion of SP by withdrawal release (Wang and Tsou, 1989). The lack of effect of cinitapride in morphine deprivated MP-LM strips could be caused by the depletion of SP in these preparations. From these results we conclude that the effect of cinitapride in MP-LM may be related to the opioid system. The exact nature of this interaction remains to be determined.
SUMMARY
Cinitapride is a benzamide derivate that stimulates the gastrointestinal motility. The "in vitro" administration of this drug enhanced the contractile activity of the guinea-pig ileum. The contractile response induced by electrical stimulation was significantly increased in strips pretreatcd with morphine "/n
865
vitro" and in morphine tolerant strips. However when tissues were obtained from tolerant guinea-pigs and morphine was not added to the organ bath (morphine-abstinence) the cinitapride effect was significantly decreased. Although further work is required to explain the changes in the effect of cinitapride after morphine acute treatment and in morphine tolerant tissues, our results suggest that some of the effects of this drug could be related to the opioid system and the relationship between cinitapride and opioid system may be mediated by SP or 5HT.
REFERENCES
Ahtee L., Attila P., Lauhakangas V., Soikinen A. and Sipila J. (1987) The fall of homovanillic acid and 5-hydroxyindolacetic acid concentrations in brains of mice withdrawn from repeated morphine treatment and their restoration by acute morphine administration. J. Neurol. Transm. 68, 63-78.
Ambache N. (1954) Separation of the longitudinal muscle of the rabbit's ileum as a broat she.at. J. Physiol. CXXV, 53p. Bou J., Fernandez A. G., Janregui J. M. and Massingham R. (I 986) Involvement of enteric neurons in the response of guinea-pig ileum preparations to metoclopramide. Br. J. Pharmac. 88, 95-102. Buchheit K., Engel G., Mutschler E. and Richardson B. 0985) Study of the contractile effect of 5-hydroxytriptamine (5HT) in the isolated longitudinal muscle strip from guinea-pig ileum. Naunyn-Schrriiedeberg~ A r c h f Pharmac. 329, 36-41. Chahl L. A. (1983) Contracture of guinea-pig ileum on withdrawal of methionine 5-enkephalin is mediated by substance P. Br. J. Pharmac. 80, 741-749. Colado M. I., Lorenzo P. and Martin M. I. (1989) Nifedipinc reversal of decreased serotonin metabolite levels during morphine withdrawal. Archs Int. Pharmacodyn. Ther. 298, 61-67. Contreras E., Tamayo L. and Amigo M. (1988) Calcium channel antagonists increase morphine-induced analgesia and antagonize morphine tolerance. Eur. J. Pharmac. 148, 463-466. Costall B., Gunning S. J. and Naylor R. J. (1984) SCH 23390 can enhance field stimulation-induced contractions of longitudinal smooth muscle from guinea-pig stomach. J. Pharm. Pharmac. 36, 356. Fernandez A. G. and Massingham R. (1985) Peripheral receptor populations involved in the regulation of gastrointestinal motility and the pharmacological actions of metoclopramide-like drugs. Life Sci. 31, 1-14. Gintzler A. R. (1980) Substance P involvement in the expression of gut dependence on opiates. Brain Res. 182, 224-228. Kilbinger H., Kruel R., Pfeuffer-Friederich I. and Wessler I. (1982) The effects of metoclopramide on acetylcholine release and on smooth muscle response in the isolated guinea-pig ileum. Naunyn-Schmiedeberg' s Archs Pharmac. 319, 231-238. Massingham R., Bou J. and Roberts P. J. (1985) A comparison of the stimulatory effects of metoclopramide and cinitapride in the gninea-pig isolated ileum. J. Auton. Pharmac. 5, 41-43. Rivot J. P., Pointis D. and Besson J. M. (1988) Morphine increases 5HT metabolism in the nucleus raphe magnus: an in vivo study in freely moving rats using 5-hydroxyindole electrochemical detection. Brain Res. 446, 333-342. Romandini S., Pich E. M., Esposito E., Kruszewska A. Z. and Samauin R. (1986) The effect ofintracerebroventricular 5,7-dihydroxytryptamine on morphine analgesia is time-dependent. Life $ci. 38, 869-875.
866
M. I. COLAOO et al.
Schuurkes J. A. J., van Bergen P. J. E. and van Nueten J. M. (1988) Prejunctional muscarinic (Mi)-receptor interactions on guinea-pig ileum: lack of cisapride. Br. J. Pharmac. 92, 228-234. Tsou K., Wu S. X., Lu Y. A. and Way E. L. (1985) Block of the hyoscine-resistant opiate withdrawal contraeture of ileum by a new substance P antagonist: D-Argt, D-Phe 5,
D-Trp7.9, Leull: substance P. Eur. J. Pharmac. 110, 155-156. Wang F. S. and Tsou K. (1989) Substance P on IleucinlEnkephalin release in guinea-pig ileum during naloxone-precipitated morphine withdrawal. J. Pharmac. exp. Ther. 249(1), 329-332.