[Motilin and motilin receptor].

Motilin, a 22 amino acid polypeptide, is known to play an important role in the initiation of phase III activity of the interdigestive migrating contractions (IMC) in the dog and man. The precursor of human motilin consists of 115 amino acids including a 25 amino acid signal peptide in direct linkage with the 22 amino acid motilin sequence and a 66 amino acid carboxy-terminal motilin-associated peptide (MAP). Northern blot analysis revealed that motilin mRNA is abundant in the duodenum. In vitro studies suggested that motilin acts directly on motilin receptors located on gastrointestinal smooth muscle cells in the rabbit, cat and man. On the contrary, in vivo studies suggested that motilin receptors are likely to be present in the nervous system. The cloning of motilin receptors is needed to clarify the detailed mechanism(s) of motilin's action.