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

Abstract

BackgroundMotilin’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 MethodsThe 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. ResultsImmunohistochemical 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). ConclusionsMotilin 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.