Effects of Cinnamaldehyde on Smooth Muscle Preparations.

The effects of cinnamaldehyde (CNA), known as a transient receptor potential ankyrin 1 (TRPA1) agonist, on guinea-pig ileum and urinary bladder were studied in isolated organ experiments. Contractile effects were found to be present on both preparations. In the ileum, both cholinergic and purinergic (pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid tetrasodium salt-sensitive) mechanisms are involved; the TRPA1 antagonist A967079 (1 µmol/L) significantly reduced the response. The contractile response to CNA in the bladder, but not in the ileum, was significantly reduced by in vitro capsaicin desensitization. In the bladder A967079 or the TRPV1 antagonist, BCTC failed to reduce the response. A direct relaxation on the smooth muscle was detected in the precontracted ileum. In the precontracted urinary bladder, CNA also caused relaxation that was insensitive to capsaicin pretreatment. It is suggested that CNA excites the muscles of the bladder via activation of capsaicin-sensitive nerves; in the ileum, it may interact with TRPA1 located on tissue elements that initiate both purinergic and cholinergic mechanisms. The relaxant effects of CNA may be due to the direct inhibition of the smooth muscles.

Serotonin or the Mucosa Do Not Mediate the Motor Effect of Allyl Isothiocyanate in the Guinea-Pig Small Intestine.

BACKGROUND: Serotonin (5-hydroxytryptamine, 5-HT), originating from the enterochromaffin cells has been reported to mediate the contractile effect of the sensory stimulant and TRPA1 activator allyl isothiocyanate (AITC) in the guinea-pig small intestine [Nozawa et al: Proc Natl Acad Sci U S A 2009;106:3408-3413]. SUMMARY: In the present experiments, the nerve-mediated contraction of this preparation due to AITC was not inhibited by a combination of methysergide (broad-spectrum 5-HT antagonist; 0.3 µmol/l), Y 25130 (azasetron, 5-HT3 receptor antagonist; 1 µmol/l) and SB 204070 (5-HT4 receptor antagonist; 2 µmol/l) or by 5-HT receptor desensitization, that is, pretreatments that practically abolished contractions of similar size in response to exogenous 5-HT, without causing nonspecific effects. AITC also contracted longitudinal muscle-myenteric plexus preparations, an effect also fully resistant to the combination of 5-HT receptor antagonists. The pharmacology of AITC in strip preparations matched that in the whole ileum. Key Messages: It is concluded that neither endogenous 5-HT nor the gut mucosa contributes to the excitatory effect of AITC in the guinea-pig small intestine. The combination of 5-HT antagonists elaborated is suitable for studying the possible involvement of 5-HT in motor responses of the guinea-pig intestine.

The TRPA1 Activator Allyl Isothiocyanate (AITC) Contracts Human Jejunal Muscle: Pharmacological Analysis.

The contractile effect of AITC (300 µM) on human jejunal longitudinal strips was inhibited by the TRPA1 antagonist HC 030031 and atropine or scopolamine, but was insensitive to tetrodotoxin, purinoceptor antagonists or capsaicin desensitization. It is concluded that TRPA1 activation stimulates a cholinergic mechanism in a tetrodotoxin-resistant manner.

The contractile effect of anandamide in the guinea-pig small intestine is mediated by prostanoids but not TRPV1 receptors or capsaicin-sensitive nerves.

Although exogenous and endogenous cannabinoid receptor agonists have well-documented inhibitory effects on gastrointestinal motility, a TRPV1 receptor-mediated excitatory action of anandamide (arachidonoyl ethanolamide, AEA) in the guinea-pig ileum strip has also been described. We used in vitro capsaicin desensitization for assessing the possible participation of sensory neurons in the contractile effect of anandamide on the guinea-pig whole ileum, as well as autonomic drugs and a cyclooxygenase inhibitor for characterizing this response. Isolated organ experiments were used with isotonic recording. Contractions induced by anandamide (1 or 10 µM) were strongly inhibited by tetrodotoxin, indomethacin or atropine plus a tachykinin NK(1) receptor antagonist, but weakly to moderately reduced by atropine alone and partly diminished by the fatty acid amide hydrolase inhibitor URB 597. Neither capsaicin pre-treatment nor the TRPV1 receptor antagonist BCTC, the ganglionic blocking drug hexamethonium or cannabinoid (CB1 or CB2 ) receptor antagonists, influenced the effect of anandamide. It is concluded that the capsaicin-insensitive, neuronal excitatory effect of anandamide in the intestine is most probably mediated by cyclooxygenase products. Such a mechanism may also play a role at other sites in the mammalian body.

Unexpected insensitivity of the cholinergic motor responses to morphine in the human small intestine.

BACKGROUND/AIMS: morphine is known to inhibit cholinergic contractions of the guinea pig small intestine. This has been compared to the human small intestinal innervated longitudinal muscle in the current study. METHODS: cholinergic primary contractions of human small intestinal longitudinal strips were evoked by electrical field stimulation (EFS; 0.5- 5 Hz in the presence of purinergic and nitrergic blockers or 5 Hz without pretreatment) and recorded isotonically in organ bath experiments. Guinea pig small intestinal segments were also studied. RESULTS AND CONCLUSION: neurogenic cholinergic contractions of human preparations were unaffected by morphine (1, 2 or 10 micromol/l). Longitudinal contractions of the guinea pig ileum were concentration-dependently suppressed by morphine (0.1-10 micromol/l). It is concluded that myenteric neurons supplying the longitudinal muscle of the human small intestine are much less sensitive to morphine than those of the guinea pig.