Objective:To investigate the effects of thyroid motilin (MTL) on migrating motor complex (MMC) in fasting rats.Methods: The distribution and quantitative expression of motilin in the thyroids were detected by immunohistochemistry and radioimmunoassay.We also observed the effect of thyriod motilin on the MMC by recording the gastrointestinal motility in conscious rats.Results: Tail vein injection of MTL increased MMC in antrum and duodenum in a dose-dependent manner,as manifested by increased contraction frequency and amplitude (P<0.05,P<0.01).However,the contraction frequency and amplitude were significantly decreased after injection of MTL-R antagonist GM109(P<0.05).GM109 could obviously block the promoting effect of MTL on MMC.Removing left thyroid significantly increased MMC cycle,contraction amplitude,and decreased contraction frequency(P<0.05). Injection of anti-MTL serum into the thyroids could significantly promote MMC and increase the frequency and amplitude of contraction (P<0.05).Immunohistochemistry demonstrated that motilin immunoreactive (MTL-IR) cells,together with calcitonin (CT),were observed in the thyroids,indicating the expression of MTL in thyroid C-cells.Radioimmunoassay analyses displayed that MTL level in the duodenal mucosa was 128.02 and 100.57 times those in the antrum and thyroid,respectively.Conclusion: MTL is expressed in the thyroid C-cell and participates in the regulation of MMC.