SEARCH

SEARCH BY CITATION

Keywords:

  • Intestinal motility;
  • cannabinoid receptors;
  • inflammatory bowel disease;
  • antidiarrhoeal drugs;
  • small intestine

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  • We have evaluated the effect of cannabinoid drugs, administered intraperitoneally (i.p.) or intracerebroventricularly (i.c.v.) on upper gastrointestinal transit in control and in croton oil-treated mice.

  • The cannabinoid agonists, WIN 55,212-2 (2–239 nmol mouse−1) and cannabinol (24–4027 nmol mouse−1), decreased while the CB1 antagonist SR141716A (2–539 nmol mouse−1) increased transit in control mice. WIN 55,212-2, cannabinol and SR141716A had lower ED50 values when administered i.c.v., than when administered i.p. The CB2 antagonist SR144528 (52 nmol mouse−1, i.p.) was without effect.

  • During croton oil (0.01 ml mouse−1, p.o.)-induced diarrhoea, the ED50 values of i.p.-injected WIN 55,212-2 and cannabinol (but not SR141716A) were significantly decreased (compared to control mice). However, the ED50 values of WIN 55,212-2 were similar after i.p. or i.c.v. administration.

  • The inhibitory effects of WIN 55,212-2 and cannabinol were counteracted by SR141716A (16 nmol mouse−1, i.p.) but not by SR144528 (52 nmol mouse−1, i.p.) both in control and croton-oil treated mice.

  • Ganglionic blockade with hexamethonium (69 nmol mouse−1, i.p.) did not modify the inhibitory effect of i.p.-injected cannabinoid agonists either in control or in croton-oil treated mice.

  • The lower ED50 values of cannabinoid drugs after i.c.v. administration suggest a central (CB1) site of action. However, a peripheral site of action is suggested by the lack of effect of hexamethonium. In addition, croton oil-induced diarrhoea enhances the effect of cannabinoid agonists by a peripheral mechanism.

British Journal of Pharmacology (2000) 129, 1627–1632; doi:10.1038/sj.bjp.0703265


Abbreviations:
CO

croton oil

Δ9-THC

Δ9-tetrahydrocannabinol

Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Preparations of Cannabis sativa have been used medicinally for over 4000 years for the treatment of a variety of disorders, including migraine, muscle spasm, seizures, glaucoma, pain, nausea and diarrhoea (Felder & Glass, 1998). In 1964 Δ9-tetrahydrocannabinol (Δ9-THC) was isolated, which was later shown to be responsible for many of the pharmacological actions of Cannabis preparations (Mechoulam et al., 1998). With regard to the gastrointestinal tract, Dewey et al. (1972) were the first to report that Δ9-THC reduced the rate of passage of a charcoal meal in the mouse small intestine and these findings were confirmed by others (Chesher et al., 1973; Jackson et al., 1976; Shook & Burks, 1989).

Understanding of the mechanism by which Δ9-THC exerts its pharmacological actions has seen considerable progress in the last ten years following the discovery of two distinct cannabinoid receptors, named CB1, (expressed mainly by central and peripheral neurons) and CB2 (that occur mainly in immune cells) (Matsuda et al., 1990; Munro et al., 1993; Pertwee, 1998). The discovery of these receptors has led to the demonstration that there are endogenous agonists for these receptors, namely anandamide and 2-arachidonylglycerol (Devane et al., 1992; Stella et al., 1997), the latter found in the intestine of the dog (Mechoullam et al., 1995).

The myenteric plexus of the guinea-pig intestine contains CB1-, but not CB2-like cannabinoid receptor mRNA (Griffin et al., 1997). Activation of prejunctional CB1 receptors produces inhibition of excitatory transmission (Pertwee et al., 1996; Izzo et al., 1998) in the isolated guinea-pig ileum and these inhibitory effects are associated with a decrease in acetylcholine release from enteric nerves (Coutts & Pertwee, 1997). However, a preliminary report indicates that cannabinoid agonists potentiate electrically-induced contractions in the porcine ileum and this effect is mediated by CB2 receptors (Albasan et al., 1999).

The involvement of CB1 receptors in intestinal motility has been confirmed also in vivo. Indeed, the endogenous cannabinoid agonist anandamide (Calignano et al., 1997) and the synthetic cannabinoid agonist WIN 55,212-2 (Colombo et al., 1998; Izzo et al., 1999a) inhibited, whilst the CB1 receptor antagonist, SR141716A increased gastrointestinal transit in mice. However, in these studies, cannabinoid drugs were administered intraperitoneally or subcutaneously and therefore it was not clear if cannabinoids were acting at central or peripheral cannabinoid receptors. In addition, there are no data in the literature concerning the effects of cannabinoid drugs in the control of upper gastrointestinal motility during pathophysiological states.

The present study, therefore, has two objectives: (i) to compare the effect of cannabinoid drugs on intestinal motility after intracerebroventricular and intraperitoneal administration and (ii) to evaluate the effect of cannabinoid agonists on intestinal motility during experimental diarrhoea. In order to achieve this experimental condition, we have used croton oil, a well-known cathartic agent (Pol et al., 1996). The cannabinoid drugs used were: the natural agonist cannabinol (Petitet et al., 1998) and the synthetic agonist WIN 55,212-2 (Compton et al., 1992), the CB1 receptor antagonist SR141716A (Rinaldi-Carmona et al., 1995) and the CB2 receptor antagonist SR144528 (Rinaldi-Carmona et al., 1998).

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Animals

Male ICR mice (Harlan Italy, Corezzana, MI) (24–26 g) were used after 1 week of acclimation (temperature 23±2°C; humidity 60%). Food was withheld 3 h before experiments but there was free access to drinking water.

Upper gastrointestinal transit

Gastrointestinal transit was measured in control mice or 3 h after treatment with croton oil (0.01 ml mouse−1). At this time, 0.1 ml of a black marker (10% charcoal suspension in 5% gum arabic) was administered orally to assess upper gastrointestinal transit as previously described (Pol et al., 1996; Izzo et al., 1999a). After 20 min the mice were killed by asphyxiation with CO2 and the gastrointestinal tract removed. The distance travelled by the marker was measured and expressed as a percentage of the total length of the small intestine from pylorus to caecum (Izzo et al., 1999a).

The cannabinoid agonists WIN 55,212-2 (2–239 nmol mouse−1), cannabinol (24–4027 nmol mouse−1), the CB1 receptor antagonist SR141716A (2–539 nmol mouse−1), the CB2 receptor antagonist SR144528 (52 nmol mouse−1) or vehicle (DMSO, 4–8 μl mouse−1) were given intraperitoneally (i.p.) or intracerebroventricularly (i.c.v.) 20 min before charcoal administration. In some experiments SR141716A (16 nmol mouse−1=0.3 mg kg−1), SR144528 (52 nmol mouse −1=1 mg kg−1) or hexamethonium (69 nmol mouse −1=1 mg kg−1) were given (i.p.) 10 min before the cannabinoid agonists. The doses of hexamethonium and SR144528 were selected on the basis of previous published work (Schirgi-Degen & Beubler, 1995; Rinaldi-Carmona et al., 1998)

Intracerebroventricular injections

Intracerebroventricular injections were performed as described by Haley & McCormick (1957)). Mice were briefly anaesthetized with enflurane and the drugs were delivered in a volume of 4 μl, using a Hamilton microlitre syringe fitted with 26-gauge needle.

Drugs

Drugs used were: WIN 55,212-2 mesylate (Tocris Cookson, Bristol, U.K.), hexamethonium bromide and cannabinol (SIGMA, Milan, Italy). SR141716A [(N-piperidin-l-yl)-5-(4-chlorophenyl)-1-2,4-dichlorophenyl) - 4 -methyl-lH-pyrazole-3-carboxamide hydrochloride and SR144528 (N-[-1S-endo-1,3,3-trimethyl bicyclo [2.2.1] heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl) - pyrazole - 3 - carboxamide-3-carboxamide) were a gift from Dr Madaleine Mossé and Dr Francis Barth (SANOFI-Recherche, Montpellier, France). Cannabinoid drugs were dissolved in DMSO, while hexamethonium was dissolved in saline.

Statistics

Data are mean±s.e.mean. To determine statistical significance, Student's t-test for unpaired data or one-way analysis of variance followed by Tukey–Kramer multiple comparisons test was used. A P-value less than 0.05 was considered significant. ED50 (dose which produced a 50% variation of gastrointestinal transit) and Emax (maximal effect) values were calculated using the computer program of Tallarida & Murray (1986).

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

Effect of cannabinoid drugs on upper gastrointestinal transit in control mice

The effect of i.p.- or i.c.v.- injected WIN 55,212-2 (2–239 nmol mouse−1) and cannabinol (24–4027 nmol mouse−1) on percentage inhibition of upper gastrointestinal transit are presented in Figure 1. Both WIN 55,212-2 and cannabinol produce a dose-dependent inhibition of gastrointestinal transit. However, the ED50 values after i.p. or i.c.v. administration were statistically different. The ED50 and Emax values of cannabinoid drugs are shown in Table 1.

image

Figure 1. Dose related inhibition of upper gastrointestinal transit by WIN 55,212-2 and cannabinol after i.p. or i.c.v. administration in control mice. Each point represents the mean±s.e.mean of 10–13 animals for each experimental group. *P<0.05, **P<0.01 and ***P<0.001 vs corresponding control.

Download figure to PowerPoint

Table 1. ED50±s.e.mean and Emax±s.e.mean of cannabinoid drugs after i.p. or i.c.v. administration in control mice and in mice receiving croton oil (0.01 ml mouse−1, orally)Thumbnail image of

The CB1 receptor antagonist SR141716A (16 nmol mouse−1, i.p.), but not the CB2 receptor antagonist SR144528 (52 nmol mouse−1, i.p.) counteracted the inhibitory effect of WIN 55,212-2 (5 nmol mouse−1, i.c.v. or 50 nmol mouse−1, i.p.) and cannabinol (201 nmol mouse−1, i.c.v. or 2010 nmol mouse−1, i.p.) after both i.c.v. (Figure 2) and i.p. (Figure 3) routes of administration. Hexamethonium (69 nmol mouse−1, i.p.) abolished the effect of both WIN 55,212-2 and cannabinol after i.c.v. (Figure 2) but not after i.p. (Figure 3) administration.

image

Figure 2. Effect of WIN 55,212-2 (5 nmol mouse−1 i.c.v) and cannabinol (201 nmol mouse, i.c.v.) on upper gastrointestinal transit alone or in mice treated with SR141716A (16 nmol mouse−1, i.p.) or SR144528 (52 nmol mouse−1, i.p.) or hexamethonium (69 nmol mouse−1, i.p.). Results are mean±s.e.mean of 8–11 animals for each experimental group. *P<0.01 vs control and #P<0.05 vs WIN 55,212-2 (or cannabinol).

Download figure to PowerPoint

image

Figure 3. Effect of WIN 55,212-2 (50 nmol mouse−1, i.p.) and cannabinol (2010 nmol mouse−1, i.p.) on upper gastrointestinal transit alone or in mice treated with SR141716A (16 nmol mouse−1, i.p.) or SR144528 (52 nmol mouse−1, i.p.) or hexamethonium (69 nmol mouse−1, i.p.). Results are mean±s.e.mean of 8–11 animals for each experimental group. **P<0.01 vs control and #P<0.01 vs WIN 55,212-2 (or cannabinol).

Download figure to PowerPoint

SR 14176A (i.p. or i.c.v.), per se, dose-dependently increased upper gastrointestinal transit (Figure 4a). However, the ED50 value after i.c.v. administration was significantly (P<0.01) lower than the ED50 after i.p. administration (Table 1). At a dose of 16 nmol mouse−1, SR141716A (i.c.v.) significantly (P<0.05) increased intestinal motility (Figure 4a) and this effect was significantly (P<0.05) counteracted by hexamethonium (69 nmol mouse−1 i.p.) (per cent increase of SR141716A: 44±3; per cent increase of SR141716A in the presence of hexamethonium; 1±3, n=10).

image

Figure 4. Dose-related increase of upper gastrointestinal transit by SR141716A in control mice (a) or mice treated with croton oil (0.01 ml mouse−1, orally) (b). Results are mean±s.e.mean of 10–12 animals for each experimental group. *P<0.05 and **P<0.01 vs corresponding control.

Download figure to PowerPoint

The CB2 receptor antagonist SR144528 (52 nmol mouse−1, i.p.), given alone, did not significantly modify gastrointestinal transit (control 47±4%; SR144528 48±2%, n=10, P>0.2). Hexamethonium (69 nmol mouse−1 i.p.) did not significantly modify gastrointestinal transit (17±8% increase, n=12). DMSO (4 μl mouse−1 i.c.v. or 4–8 μl mouse−1 i.p.) had no effect on the response under study (data not shown).

Effect of cannabinoid drugs on upper gastrointestinal transit during croton oil-induced diarrhoea

Oral administration of croton oil produced diarrhoea which was associated with a significant increase in gastrointestinal transit (per cent transit: control 46±2; croton oil, 56±2, P<0.01, n=24). Both WIN 55,212-2 (2–239 nmol mouse−1, i.p.) and cannabinol (24–4027 nmol mouse−1, i.p.) produced a dose-related inhibition of transit (Figure 5) and both agonists had a lower ED50 value compared to the corresponding i.p. treatment in control mice (Table 1). In croton oil-treated animals, WIN 55,212-2 (i.p.) and cannabinol (i.p.) had a significant inhibitory effect with threshold doses of 5 nmol mouse−1 and 80 nmol mouse−1 doses respectively whilst in control mice, significant inhibitory effects were achieved at doses of 14 nmol mouse−1 (WIN 55,212-2) and 2010 nmol mouse−1 (cannabinol) respectively (Figure 5).

image

Figure 5. Dose-related inhibition of upper gastrointestinal transit by WIN 55,212-2 (i.p.) and cannabinol (i.p.) in control mice or in mice receiving croton oil (0.01 ml mouse−1, orally). Results are mean±s.e.mean of 10–12 animals for each experimental group. *P<0.05, **P<0.01 and ***P<0.001 vs corresponding control.

Download figure to PowerPoint

Administered i.c.v. WIN 55,212-2 (2–239 nmol mouse−1) also decreased intestinal motility, but the ED50 value (74±10 nmol mouse−1) was not statistically different from the ED50 value (68±5 nmol mouse−1) after i.p. administration (Table 1).

The inhibitory effect of i.p.-injected WIN 55,212-2 (14 nmol mouse−1) or cannabinol (805 nmol mouse−1) was reduced by the CB1 receptor antagonist SR141716A (16 nmol mouse−1, i.p.) but not by the CB2 receptor antagonist SR144528 (52 nmol mouse−1, i.p.) or by the ganglion blocker hexamethonium (69 nmol mouse−1, i.p.) (Figure 6).

image

Figure 6. Upper gastrointestinal transit in mice with diarrhoea induced by croton oil (0.01 ml mouse−1, orally): effect of WIN 55,212-2 (14 nmol mouse−1, i.p.) and cannabinol (805 nmol mouse−1, i.p.) alone or in mice treated with SR141716A (16 nmol mouse−1, i.p.) or SR144528 (52 nmol mouse−1, i.p.) or hexamethonium (69 nmol mouse−1, i.p.). Results are mean±s.e.mean of 8–11 animals for each experimental group. @P<0.05 vs control, **P<0.01 and ***P<0.001 vs croton oil and #P<0.01 vs croton oil+WIN 55,212-2 (or croton oil+cannabinol).

Download figure to PowerPoint

Figure 4b shows the potentiating effect of SR141716A (2–539 nmol mouse, i.p.) in mice treated with croton oil. The ED50 value (418±32 nmol mouse−1) was not statistically different from the corresponding ED50 value in control animals (375±31 nmol mouse−1). By contrast, SR144528 (52 nmol mouse−1, i.p.) or hexamethonium (69 nmol mouse−1, i.p.) did not modify gastrointestinal transit (per cent transit: croton oil: 58±6, croton oil+SR144528 61±5, croton oil+hexamethonium 68±4, n=6, P>0.2).

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

The role of cannabinoid receptors in control mice

It is now well known that cannabinoid agonists can reduce intestinal motility through activation of CB1 receptors. Indeed activation of CB1 receptors can mediate, (i) inhibition of electrically-evoked contractions in the isolated guinea-pig (Pertwee et al., 1996; Izzo et al., 1998) and human ileum (Croci et al., 1998), (ii) inhibition of fast and slow synaptic transmission in guinea-pig myenteric nerves (Lopez-Redondo et al., 1997), (iii) inhibition of electrically-evoked acetylcholine release from myenteric nerves (Coutts & Pertwee, 1997) and (iv) reduction of peristalsis efficiency in the isolated guinea-pig ileum (Heinemann et al., 1999; Izzo et al., 2000). These findings are in keeping with the presence of CB1, but not CB2-like receptor messenger RNA in the myenteric plexus of the guinea-pig small intestine (Griffin et al., 1997). Consistent with these in vitro findings, it has been shown that cannabinoid agonists reduced intestinal motility in mice (Calignano et al., 1997; Colombo et al., 1998; Izzo et al., 1999a) and rats (Izzo et al., 1999c) and this effect was counteracted by SR141716A, a specific CB1 antagonist. However, whether the effect of cannabinoid drugs in vivo is mediated via a central or a peripheral site of action was not demonstrated in these studies. Indeed the CB1 receptor is located within both the central nervous system (Matsuda et al., 1990) and within the enteric nervous system (Griffin et al., 1997).

In the present study we have shown that the synthetic cannabinoid agonist WIN 55,212-2 and the natural cannabinoid agonist cannabinol produced a dose-related inhibition of upper gastrointestinal transit when administered i.p. or i.c.v. The inhibitory effect of cannabinoid agonists was abolished by SR141716A, a specific CB1 antagonist, but not by SR144528, a CB2 receptor antagonist, indicating an involvement of CB1 but not CB2 receptors.

The ED50 values of WIN 55,212-2 and cannabinol after i.c.v. administration were significantly lower than the corresponding ED50 values after i.p. administration. The low doses that were needed to inhibit transit after i.c.v. injection implies that cannabinoid agonists may inhibit intestinal motility through activation of central CB1 receptors. However, the effect of i.p.-injected cannabinoid agonists was not modified by the ganglion blocker hexamethonium. These results probably indicate that the effect of i.p.-injected cannabinoid agonists is mediated by peripheral CB1 cannabinoid receptors.

Although some reports indicate that the CB1 receptor antagonist SR141716A does not affect intestinal motility in the isolated human ileum (Croci et al., 1998) and gastric emptying in the rat (Izzo et al., 1999b), other studies indicate that intestinal motility could be tonically inhibited by the endogenous cannabinoid system. Indeed SR141716A increased electrically-induced contractions in the isolated guinea-pig ileum (Pertwee et al., 1996; Izzo et al., 1998) and intestinal motility and defaecation in the mouse (Colombo et al., 1998; Izzo et al., 1999a). The observation that SR141716A, per se, increased intestinal motility does not necessary imply that endogenous cannabinoids are involved in the control of intestinal motility in view of the inverse agonist properties of SR141716A at human recombinant CB1 (Landsman et al., 1997) and both CB1 and CB2 receptors (MacLennan et al., 1998).

In the present study, we have shown that SR141716A (i.c.v. or i.p.) produced a dose-dependent increase in upper gastrointestinal transit. The ED50 value after i.c.v. administration was significantly lower than the ED50 value after i.p. administration, suggesting a central site of action of SR141716A. The most likely explanation of these results is that the endogenous cannabinoid system, within the central nervous system, can inhibit intestinal motility through activation of CB1 receptors. In a recent study, we have shown that SR141716A (i.p.)-induced changes in intestinal motility are not modified by the ganglionic blocker hexamethonium (Izzo et al., 1999a), suggesting a peripheral site of action of i.p.-injected SR141716A.

Effect of cannabinoid drugs during croton oil-induced diarrhoea

Croton oil is a well known irritant that has been widely used to produce experimental inflammation in different tissues, especially skin and mucosa, and induces diarrhoea associated with intestinal inflammation in the mouse small intestine (Pol et al., 1996). According to Pol et al., (1996), we have shown that croton oil increases upper gastrointestinal transit 3 h after oral administration. The cannabinoid agonists WIN 55,212-2 and cannabinol blocked the increase in intestinal motility induced by croton oil; in addition, the ED50 values of i.p.-injected WIN 55,212-2 and cannabinol were significantly decreased (compared to control mice). However, during croton oil-induced diarrhoea the ED50 value of WIN 55,212-2 was similar after i.p. or i.c.v. treatment and ganglionic blockade with hexamethonium did not alter the inhibitory effect of i.p.-injected cannabinoids.

Taken together, these results indicate that the enhanced effect of cannabinoid agonists are mediated by peripheral receptors. By contrast, using the castor oil test, we have recently shown that cannabinoid agonists possess either weak or no antidiarrhoeal activity in the rat (Izzo et al., 1999c). The use of a different cathartic (castor oil vs croton oil), different species (rat vs mouse) and different region of the gut (whole gut vs upper gastrointestinal tract) could explain this discrepancy. Consistent with this hypothesis, Shook & Burks (1989) showed that Δ9-THC produced a greater inhibition of small intestinal transit than large bowel transit.

In line with the result obtained in control mice and those reported in the isolated guinea-pig ileum (Pertwee et al., 1996; Izzo et al., 1998), the antitransit response of cannabinoid agonists involves CB1, but not CB2 receptors, as the inhibitory effect of both WIN 55,212-2 and cannabinol were reduced by SR141716A, but not SR144528. Administration of SR141716A (i.p.), per se, increased intestinal motility in control mice and those given croton oil with a similar ED50 value, thus indicating that during the experimental diarrhoea the endogenous cannabinoid system is activated as in control animals. By contrast, SR144524, a specific CB2 receptor antagonist, at doses previously shown to bind the CB2 receptor in the rat spleen (Rinaldi-Carmona et al., 1998), failed to modify the inhibitory effect of both WIN 55,212-2 and cannabinol and did not modify, per se, intestinal motility during the diarrhoea induced by croton oil. Thus, a role for CB2 receptors in modulating intestinal motility during experimental diarrhoea seems unlikely.

Conclusions

Our results suggest that both central and peripheral CB1 receptors can modulate upper gastrointestinal motility. However, the effect of systemic (i.p.) cannabinoid drugs is probably mediated by peripheral receptors. Diarrhoea induced by the irritant croton oil enhances the inhibitory effect of cannabinoid agonists by a peripheral mechanism, while CB2 receptors are not involved in the control of intestinal motility, either in physiological or in pathophysiological states. Thus, selective non-psychotropic CB1 agonists could represent novel drugs to treat motility disorders associated with inflammatory diarrhoea.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References

This work was supported by Cofinanziamento Murst 1999 and Enrico and Enrica Sovena Foundation (Roma). The Authors are grateful to Drs Antonio Calignano and Carla Cicala for their help. SR141716A and SR144528 were a kind gift from SANOFI (Montpellier, France).

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Methods
  5. Results
  6. Discussion
  7. Acknowledgments
  8. References
  • ALBASAN, H., SOLDANI, G. & BROWN, D.R. (1999). Synthetic cannabinoids potentiate electrically-induced contractions in porcine ileum in vitro. Pharm. Res., 39, (Supplement) 5.
  • CALIGNANO, A., LA RANA, G., MAKRIAYANNIS, A., LIN, S.Y., BELTRAMO, M. & PIOMELLI, D. (1997). Inhibition of intestinal motility by anandamide, an endogenous cannabinoid. Eur. J. Pharmacol., 340, R7R8.
  • CHESHER, G.B., DAHL, C.J., EVERNGHAM, M., JACKSON, D.M., MARCHANT-WILLIAMS, H. & STARMER, G.A. (1973). The effect of cannabinoids on intestinal motility and their antinociceptive effect in mice. Br. J. Pharmacol., 49, 588594.
  • COLOMBO, G., AGABIO, R., LOBINA, C., REALI, R. & GESSA, G.L. (1998). Cannabinoid modulation of intestinal propulsion in mice. Eur. J. Pharmacol., 344, 6769.
  • COMPTON, D.R., GOLD, L.H., WARD, S.J., BALSTER, R.L. & MARTIN, B.R. (1992). Aminoalkylindole analogs: cannabimimetic activity of a class of compounds structurally distinct from Δ9-tetrahydrocannabinol. J. Pharmacol. Exp. Ther., 263, 11181126.
  • COUTTS, A.A. & PERTWEE, R.G. (1997). Inhibition by cannabinoid receptor agonists of acetylcholine release from the guinea-pig myenteric plexus. Br. J. Pharmacol., 121, 15571566.
  • CROCI, T., MANARA, L., AUREGGI, G., GUAGNINI, F., RINALDI-CARMONA, M., MAFFRAND, J.P., LE FUR, G., MUKENGE, S. & FERLA, G. (1998). In vitro functional evidence of neuronal cannabinoid CB1 receptors in human ileum. Br. J. Pharmacol., 125, 13931396.
  • DEVANE, W.A., HANUS, L., BREUER, A., PERTWEE, R.G., STEVENSON, L.A., GRIFFIN, G., GIBSON, D., MANDELBAUM, A., ETINGER, A. & MECHOULAM, R. (1992). Isolation and structure of a brain constituent that binds to the cannabinoid receptor. Science, 277, 119131.
  • DEWEY, W.L., HARRIS, L.S. & KENNEDY, J.S. (1972). Some pharmacological and toxicological effects of 1-trans-8 and 1-trans-9tetrahydrocannabinol in laboratory rodents. Arch. Int. Pharmacod. Ther., 196, 133145.
  • FELDER, C.C. & GLASS, M. (1998). Cannabinoid receptors and their endogenous agonists. Annu. Rev. Pharmacol. Toxicol., 38, 179200.
  • GRIFFIN, G., FERNANDO, S.R., ROSS, R.A., MCKAY, N.G., ASHFORD, M.L.J., SHIRE, D., HUFFMAN, J.W., YU, S., LAINTON, J.A.H. & PERTWEE, R.G. (1997). Evidence for the presence of CB2-like cannabinoid receptors on peripheral nerve terminals. Eur. J. Pharmacol., 339, 5361.
  • HALEY, T.J. & MCCROMICK, W.G. (1957). Pharmacological effects produced by intracerebral injection of drugs in the conscious mouse. Br. J. Pharmacol., 12, 1215.
  • HEINEMANN, A., SHAHBAZIAN, A. & HOLZER, P. (1999). Cannabinoid inhibition of guinea-pig intestinal peristalsis via inhibition of excitatory and activation of inhibitory neural pathways. Neuropharmacology, 38, 12891297.
  • IZZO, A.A., MASCOLO, N., BORRELLI, F. & CAPASSO, F. (1998). Excitatory transmission to the circular muscle of the guinea-pig ileum: evidence for the involvement of cannabinoid CB1 receptor. Br. J. Pharmacol., 124, 13631368.
  • IZZO, A.A., MASCOLO, N., BORRELLI, F. & CAPASSO, F. (1999a). Defaecation, intestinal fluid accumulation and motility in rodents: implications of cannabinoid CB1 receptors. Naunyn-Schmiedeberg's Arch. Pharmacol., 359, 6570.
  • IZZO, A.A., MASCOLO, N., CAPASSO, R., GERMANO', M.P., DE PASQUALE, R. & CAPASSO, F. (1999b). Inhibitory effect of cannabinoid agonists on gastric emptying in the rat. Naunyn-Schmiedeberg's Arch. Pharmacol., 360, 221223.
  • IZZO, A.A., MASCOLO, N., PINTO, L., CAPASSO, R. & CAPASSO, F. (1999c). The role of cannabinoid receptors in intestinal motility, defaecation and diarrhoea in rats. Eur. J. Pharmacol., 384, 3742.
  • IZZO, A.A., MASCOLO, N., TONINI, M. & CAPASSO, F. (2000). Modulation of peristalsis by cannabinoid CB1 ligands in the isolated guinea-pig ileum. Br. J. Pharmacol., 129, 984990.
  • JACKSON, D.M., MALOR, R., CHESHER, G.B., STARMER, G.A., WELBURN, P.J. & BAILEY, R. (1976). The interaction between prostaglandin E1 and delta9-tetrahydrocannabinol on intestinal motility and on the abdominal constriction response in the mouse. Psychopharmacology, 47, 187193.
  • LANDSMAN, R.S., BURKEY, T.H., CONSROE, P., ROESKE, W.R. & YAMAMURA, H.I. (1997). SR141716A is an inverse agonist at the human cannabinoid CB1 receptors. Eur. J. Pharmacol., 334, R1R2.
  • LOPEZ-REDONDO, F., LEES, G.M. & PERTWEE, R.G. (1997). Effects of cannabinoid receptor ligands on electrophysiological properties of myenteric neurones of the guinea-pig ileum. Br. J. Pharmacol., 122, 330384.
  • MACLENNAN, S.L., REYNEN, P.H., KWAN, J. & BONHAUS, D.W. (1998). Evidence for inverse agonism of SR141716A at human recombinant cannabinoid CB1 and CB2 receptors. Br J. Pharmacol., 124, 619622.
  • MATSUDA, L.A., LOLAIT, S.J., BROWNSTEIN, B.J., YOUNG, A.C. & BONNER, T.L. (1990). Structure of a cannabinoid receptor and functional expression of the cloned cDNA. Nature, 346, 561564.
  • MECHOULAM, R., BEN-SHABAT, S., HANUS, L., LIGUMSKY, M., KAMINSKI, N.E., SCHATZ, A.R., GOPHER, A., ALMOG, S., MARTIN, B.R., COMPTON, D.R., PERTWEE, R.G., GRIFFIN, G., BAYEWITCH, M., BARG, J. & VOGEL, Z. (1995). Identification of an endogenous 2-monogliceride, present in canine gut, that binds to a cannabinoid receptor. Biochem. Pharmacol., 50, 8390.
  • MECHOULAM, R., FRIDE, E. & DI MARZO, V. (1998). Endocannabinoids. Eur. J. Pharmacol., 359, 118.
  • MUNRO, S., THOMAS, K.L. & ABU-SHAAR, M. (1993). Molecular characterization of a peripheral receptor for cannabinoids. Nature, 365, 6165.
  • PERTWEE, R.G. (1998). Pharmacological, physiological and clinical implications of the discovery of cannabinoid receptors. Biochem. Soc. Trans., 26, 267272.
  • PERTWEE, R.G., FERNANDO, S.R., NASH, J.E. & COUTTS, A.A. (1996). Further evidence for the presence of cannabinoid CB1 receptors in guinea-pig small intestine. Br. J. Pharmacol., 118, 21992205.
  • PETITET, F., JEANTAUD, B., REIBAUD, M., IMPERATO, A. & DUBROEUCQ, M.C. (1998). Complex pharmacology of natural cannabinoids: evidence for partial agonist activity of Δ9-tetrahydrocannabinol and antagonist activity of cannabidiol on rat brain cannabinoid receptors. Life Sci., 63, PL1PL6.
  • POL, O., VALLE, L., FERRER, I. & PUIG, M. (1996). The inhibitory effects of α2-adrenoceptor agonists on gastrointestinal transit during croton oil-induced intestinal inflammation. Br. J. Pharmacol., 119, 16491655.
  • RINALDI-CARMONA, M., BARTH, F., HEAULME, M., ALFONSO, R., SHIRE, D., CONGY, C., SOBRIE', P., BRELIERE, J.-C. & LE FUR, G. (1995). Biochemical and pharmacological characterization of SR141716A, the first potent and selective brain cannabinoid receptor antagonist. Life Sci., 56, 19411947.
  • RINALDI-CARMONA, M., BARTH, F., MILLAN, J., DEROCQ, J.M., CASELLAS, P., CONGY, C., OUSTRIC, D., SARRAN, M., BOUABOULA, M., CALANDRA, B., PORTIER, M., SHIRE, D., BRELIERE, J.C. & LE FUR, G. (1998). SR144528, the first potent and selective antagonist of the CB2 cannabinoid receptors. J. Pharmacol. Exp. Ther., 284, 644650.
  • SCHIRGI-DEGEN, A. & BEUBLER, E. (1995). Significance of nitric oxide in the stimulation of intestinal fluid absorption in the rat jejunum in vivo. Br. J. Pharmacol., 114, 1318.
  • SHOOK, J.E. & BURKS, T.F. (1989). Psychoactive cannabinoids reduce gastrointestinal propulsion and motility in rodents. J. Pharmacol. Exp. Ther., 249, 444449.
  • STELLA, N., SCHWEITZER, P. & PIOMELLI, D. (1997). A second endogenous cannabinoid that modulates long-term potentiation. Nature, 388, 773778.
  • TALLARIDA, R.J. & MURRAY, R.B. (1986). Manual of Pharmacological Calculations with Computer Programs. New York: Springer-Verlag.