Characterization of the contractile response induced by 5-methoxytryptamine in rat stomach fundus strips

doi:10.1016/S0014-2999(96)00777-7

European Journal of Pharmacology

Volume 318, Issues 2–3, 30 December 1996, Pages 403-409

https://doi.org/10.1016/S0014-2999(96)00777-7 Get rights and content

Abstract

This study examined effects of 5-methoxytryptamine (5-MOT), an agonist at 5-HT₄ and 5-HT_2B receptors, on the contractile response and acetylcholine release in rat stomach fundus strips. 5-MOT (10⁻⁹ − 10⁻⁵ M) produced a concentration-dependent increase in the contraction, while it evoked acetylcholine release in a ‘bell-shaped’ concentration-dependent manner. Atropine reduced 5-MOT (10⁻⁸ − 10⁻⁶ M)-induced contractions, but it had little effect on the contractions evoked by higher concentrations. 5-MOT-induced contraction and acetylcholine release were inhibited by SDZ 205–557 (2-methoxy-4-amino-5-chloro-benzoic acid 2-[diethylamino] ethyl ester), a 5-HT₄ receptor antagonist. In the presence of atropine, both SDZ 205–557 and yohimbine, a 5-HT_2B receptor antagonist, inhibited the contraction. In the presence of tetrodotoxin, the contraction was inhibited by yohimbine, but not by SDZ –557. These results suggest that the contractile action of 5-MOT in rat stomach fundus involves atropine-sensitive and atropine-resistant components. The sensitive contraction appears to be mediated through 5-HT₄ receptors located on cholinergic neurons, whereas the resistant contraction is mediated through 5-HT₄ receptors located on non-cholinergic neurons and through 5-HT_2B receptors.

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Released 5-HT activates intrinsic afferent neurons located on the terminals of myenteric neurons and GI smooth muscle cells (Prins et al., 2000), and the role of 5-HT in the gut is characterized by its interactions with various 5-HT receptors. Especially, the role and distribution of 5-HT4 receptors within the GI tract has been well-established in different species including human, mice, rats and guinea pig (Amemiya et al., 1996; Foxx-Orenstein et al., 1996; Takada et al., 1999; Tuo et al., 2004). The 5-HT4 receptor is positively coupled to Gs proteins, resulting in stimulation of adenylyl cyclase and increase in cellular cyclic AMP.
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Facilitation of acetylcholine (ACh) release by SK-951 ((-)4-amino-N-[2-(l-azabicyclo[3.3.0] octan-5-yl)ethyl]-5-chloro-2,3-dihydro-2-methylbenzo[b]furan-7-carboxamide hemifumarate), a benzofuran derivative, via the 5-hydroxytryptamine (5-HT)₄ receptor in guinea pig stomach was examined by in vitro receptor autoradiography and functional studies. [¹²⁵I]SB207710 binding was detected in the myenteric plexus of the gastric corpus. High densities of binding sites were observed in the myenteric plexus and a moderate density in the muscle layer. SK-951 inhibited the binding of [¹²⁵I]SB207710, a specific 5-HT₄-receptor ligand, as in the case of SB204070, a specific 5-HT₄-receptor antagonist, thus indicating the presence of 5-HT₄ receptors in guinea pig stomach. SK-951 as well as 5-HT enhanced the electrically stimulated twitch contractions of gastric corpus strips, which were sensitive to tetrodotoxin and atropine, and enhanced electrically stimulated release of ACh from corporal strips, which was tetrodotoxin-sensitive and Ca²⁺-dependent. The enhancements of twitch contractions and ACh release by SK-951 were antagonized by GR113808, a selective 5-HT₄-receptor antagonist. Thus, SK-951 binds to 5-HT₄ receptors of the guinea pig gastric corpus and may accelerate gastric motility due to facilitation of ACh release.
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Localization and function of 5-HT₄ receptors in the stomach were examined in mucosa-free preparations of antrum, corpus and fundus from guinea pig stomach by determination of acetylcholine release and in vitro receptor autoradiography. Specific [ $^{125} I$ ]SB207710, (1-n-butyl-4-piperidinyl) methyl-8-amino-7-iodo-1,4-benzodioxane-5-carboxylate, binding sites were detected in 3 regions of the stomach. High densities of binding were observed in the myenteric plexus of antrum and corpus, but not fundus. In mucosa-free preparations treated with 5-HT₁, 5-HT₂ and 5-HT₃ receptor antagonists, 5-HT (10⁻⁸–10⁻⁶ M) potentiated the electrically stimulated (0.5 Hz, 1 ms) outflow of [ $^{3} H$ ]acetylcholine from antrum and corpus strips preloaded with [ $^{3} H$ ]choline, but not from fundus strips, and the potentiation was antagonized by SB204070, (1-n-butyl-4-piperidinyl) methyl-8-amino-7-chloro-1,4-benzodioxane-5-carboxylate. Thus, 5-HT₄ receptors are located on myenteric cholinergic neurons in the antrum and corpus of guinea pig stomach and their activation evokes the release of acetylcholine.
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Functions and the presence of 5-hydroxytryptamine (5-HT) receptors in the fundus, corpus and antrum of the guinea pig stomach were examined by measuring contractile force and acetylcholine (ACh) release. Stimulation of the 5-HT₁ receptor caused tetrodotoxin (TTX)-insensitive relaxations in the preparations from 3 regions. Stimulation of the 5-HT₂ receptor caused TTX-insensitive contractions in the preparations of fundus and antrum. Stimulation of 5-HT₃ receptors caused contractions that were sensitive to TTX and atropine and enhanced the outflow of [³H]ACh from preparations of only antrum. Stimulation of 5-HT₄ receptors caused contractions of antral strips and decreased relaxations of corporal strips and enhanced the outflow of [³H]ACh from the preparations of both corpus and antrum. In the guinea pig stomach, the fundus possesses relaxant 5-HT₁ receptor < contractile 5-HT₂ receptors and caused the contractile response to 5-HT. The corpus possesses relaxant 5-HT₁ receptors and relaxant receptors other than 5-HTi, 5-HT₂, 5-HT₃ and 5-HT₄ receptors < contractile 5-HT₄ receptor, and therefore 5-HT caused relaxations. The antrum possesses relaxant 5-HT₁ receptor < contractile 5-HT₂, 5-HT₃ and 5-HT₄ receptors, and thus 5-HT caused contractions.

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Characterization of the contractile response induced by 5-methoxytryptamine in rat stomach fundus strips

Abstract

Eur. J. Pharmacol.

Trends Pharmacol. Sci.

Eur. J. Pharmacol.

Trends Pharmacol. Sci.

Pharmacol. Ther.

Neurosci. Lett.

5-Hydroxytryptamine4 receptors mediate relaxation of the rat oesophageal tunica muscularis mucosac

Naunyn-Schmiedeberg's Arch. Pharmacol.

Further characterization of 5-hydroxytryptamine receptors (putative 5-HT2B) in rat stomach fundus longitudinal muscle

Br. J. Pharmacol.

Stimulant effects of 5-hydroxytryptamine on guinea pig stomach preparations in vitro

Eur. J. Pharmacol.

Study of the contractile effect of 5-hydroxytryptamine (5-HT) in the isolated longitudinal muscle strip from guinea-pig ileum: evidence for two distinct release mechanisms

Naunyn-Schmiedeberg's Arch. Pharmacol.

The rat isolated stomach fundus strip, a model for 5-HT1c receptors

Br. J. Pharmacol.

SDZ 205–557, a selective, surmountable antagonist for 5-HT4 receptors in the isolated guinea pig ileum

Naunyn-Schmicdeberg's Arch. Pharmacol.

Characterization of 5-hydroxytryptamine receptors in rat stomach fundus

J. Pharmacol. Exp. Ther.

Contractile serotonergic receptor in rat stomach fundus

J. Pharmacol. Exp. Ther.

The sites of action of 5-hydroxytryptamine in nerve-muscle preparations from the guinea-pig small intestine and colon

Br. J. Pharmacol.

Pharmacological characterization of a neuronal receptor for 5-hydroxytryptamine in guinea pig ileum with properties similar to the 5-hydroxytryptamine4 receptor

J. Pharmacol. Exp. Ther.

Characterization of 5-HT3 and ‘atypical’ 5-HT receptors mediating guinea-pig ileal contractions in vitro

Br. J. Pharmacol.

5-Hydroxytryptamine₄ receptors mediate relaxation of the rat oesophageal tunica muscularis mucosac

Further characterization of 5-hydroxytryptamine receptors (putative 5-HT_2B) in rat stomach fundus longitudinal muscle

The rat isolated stomach fundus strip, a model for 5-HT_1c receptors

SDZ 205–557, a selective, surmountable antagonist for 5-HT₄ receptors in the isolated guinea pig ileum

Pharmacological characterization of a neuronal receptor for 5-hydroxytryptamine in guinea pig ileum with properties similar to the 5-hydroxytryptamine₄ receptor

Characterization of 5-HT₃ and ‘atypical’ 5-HT receptors mediating guinea-pig ileal contractions in vitro