Motilin regulates interdigestive gastric blood flow in dogs

Roles of Endothelial Motilin Receptor and Its Signal Transduction Pathway in Motilin-Induced Left Gastric Artery Relaxation in Dogs

Background: Motilin increases left gastric artery (LGA) blood flow in dogs via the endothelial motilin receptor (MLNR). This article investigates the signaling pathways of endothelial MLNR.

Methods: Motilin-induced relaxation of LGA rings was assessed using wire myography. Nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) levels were measured using an NO assay kit and cGMP ELISA kit, respectively.

Results: Motilin concentration-dependently (EC₅₀=9.1±1.2×10⁻⁸M) relaxed LGA rings precontracted with U46619 (thromboxane A₂ receptor agonist). GM-109 (MLNR antagonist) significantly inhibited motilin-induced LGA relaxation and the production of NO and cGMP. N-ethylmaleimide (NEM; G-protein antagonist), U73122 [phospholipase C (PLC) inhibitor], and 2-aminoethyl diphenylborinate [2-APB; inositol trisphosphate (IP₃) blocker] partially or completely blocked vasorelaxation. In contrast, chelerythrine [protein kinase C (PKC) inhibitor] and H89 [protein kinase A (PKA) inhibitor] had no such effect. Low-calcium or calcium-free Krebs solutions also reduced vasorelaxation. N-nitro-L-arginine methyl ester [L-NAME; nitric oxide synthase (NOS) inhibitor] and ODQ [soluble guanylyl cyclase (sGC) inhibitor] completely abolished vasodilation and synthesis of NO and cGMP. Indomethacin (cyclooxygenase inhibitor), 18α-glycyrrhetinic acid [18α-GA; myoendothelial gap junction (MEGJ) inhibitor], and K⁺ channel inhibition through high K⁺ concentrations or tetraethylammonium (TEA-Cl; K_Ca channel blocker) partially decreased vasorelaxation, whereas glibenclamide (K_ATP channel blocker) had no such effect.

Conclusion: The current study suggests that motilin-induced LGA relaxation is dependent on endothelial MLNR through the G protein-PLC-IP₃ pathway and Ca²⁺ influx. The NOS-NO-sGC-cGMP pathway, prostacyclin, MEGJ, and K⁺ channels (especially K_Ca) are involved in endothelial-dependent relaxation of vascular smooth muscle (VSM) cells.

Differential expression of motilin receptors on the endothelium of dog gastrointestinal arteries and motilin-induced motilin receptor dependent relaxation of corresponding arteries

BACKGROUND

Motilin's role in the regulation of vascular tone and hemodynamic besides gastrointestinal motility is concerned. This study aimed to investigate the expression of motilin receptors in gastrointestinal arteries and motilin-induced relaxation.

MATERIAL AND METHODS

The expression of motilin receptors in the left gastric artery (LGA), superior mesenteric artery (SMA), and inferior mesenteric artery (IMA) of adult dogs (1.5-5 years old) were analyzed by immunochemistry, RT-PCR, and western blotting. Motilin's effects on the gastrointestinal arteries were evaluated in a multi-wire myograph system.

RESULTS

Immunohistochemical staining showed that motilin receptor was expressed on the membranes of endothelial cells with the fluorescence intensity LGA > SMA > IMA (P < 0.01). The motilin receptor's mRNA and protein expression levels shared the same distribution patterns as it in fluorescence intensity (P < 0.01). In isolated LGA preparations precontracted with U46619 (a thromboxaneA2 analog), motilin induced a concentration-dependent relaxation, and the EC₅₀ was 8.8 × 10^-8 ± 0.9 × 10^-8 M. Motilin-induced relaxation on the three arteries also shared the same pattern as it in fluorescence intensity (P < 0.01) and inhibited by denuded-endothelium and GM-109 (a motilin receptor antagonist) but not by atropine (a muscarinic receptor antagonist).

CONCLUSIONS

Motilin receptors are expressed differentially on the membranes of endothelial cells in dog gastrointestinal arteries with a significantly high expression in the LGA. Motilin-induced relaxation is endothelium- and motilin receptor-dependent. The motilin receptor expressed on the endothelial cell membrane of the LGA is the molecular basis for motilin regulating gastric blood flow under physiological conditions in dogs.

Motilin Comparative Study: Structure, Distribution, Receptors, and Gastrointestinal Motility

Motilin, produced in endocrine cells in the mucosa of the upper intestine, is an important regulator of gastrointestinal (GI) motility and mediates the phase III of interdigestive migrating motor complex (MMC) in the stomach of humans, dogs and house musk shrews through the specific motilin receptor (MLN-R). Motilin-induced MMC contributes to the maintenance of normal GI functions and transmits a hunger signal from the stomach to the brain. Motilin has been identified in various mammals, but the physiological roles of motilin in regulating GI motility in these mammals are well not understood due to inconsistencies between studies conducted on different species using a range of experimental conditions. Motilin orthologs have been identified in non-mammalian vertebrates, and the sequence of avian motilin is relatively close to that of mammals, but reptile, amphibian and fish motilins show distinctive different sequences. The MLN-R has also been identified in mammals and non-mammalian vertebrates, and can be divided into two main groups: mammal/bird/reptile/amphibian clade and fish clade. Almost 50 years have passed since discovery of motilin, here we reviewed the structure, distribution, receptor and the GI motility regulatory function of motilin in vertebrates from fish to mammals.

Expression of transforming growth factor β1 and its type I receptor in gastric cancer

AIM: To evaluate the significance of transforming growth factor-β1 (TGF-β1) and its β I type receptor (TGF-β R1) in the pathogenesis of gastric carcinoma.

METHODS: TGF-β1 and TGF-β R1 were detected by immunohistochemistry in and real-time PCR (RT-PCR) 50 cases of gastric carcinoma, 19 cases of atrophic gastritis and 18 cases of normal gastric mucosa.

RESULTS: Immunohistochemistry demonstrated that the positive expression rates of TGF-β1 and TGF-β R1 were significantly higher in gastric carcinoma (80.0% and 75.0%) than in normal gastric mucosa (33.3% and 27.8%) and atrophic gastritis (36.8% and 36.8%) (P < 0.01). The lower the differentiation of gastric carcinoma was, the higher the expression of TGF-β1 and TGF-β R1 was (r = 35.58, P < 0.01). Furthermore, the expression of TGF-β1 and TGF-β R1 mRNA was significantly higher in gastric carcinoma than in normal gastric mucosa and atrophic gastritis (TGF-β1: 4.20 ± 0.51 vs 9.15 ± 2.12, 8.22 ± 1.81; TGF-β R1: 1.28 ± 0.48 vs 5.55 ± 1.48, 4.19 ± 0.95).

CONCLUSION: High expression of TGF-β1 and TGF-β R1 is correlated with the development, biologic behavior and prognosis of gastric carcinoma.