Heterogeneity of motilin immunoreactivity in mammalian tissue

Motilin is a 22 amino acid peptide first isolated and sequenced from porcine gut. The use of antisera directed to the synthetic porcine gut motilin sequence has produced conflicting results as to regional distribution and histological localization of motilin in mammalian brain and gut. Motilin immunoreactivity has been detected (by RIA) in brain regions where no immunostaining is discernible. Variations in the patterns of staining are also observed with different antisera. These discrepancies have been explained by postulating species-, tissue-, and region-specific variations in peptide immunoreactivity, and variable cross reactivities of the independent antisera with these forms. The use of cloned porcine cDNA encoding gut prepromotilin in Northern blot analysis of brain regions expressing motilin-like immunoreactivity has also failed to reveal a homologous message, questioning the true nature of the immunoreactive material in the brain. Physiological studies, however, have suggested central roles for motilin in a variety of CNS (feeding behavior, bladder control, cerebral and brain stem modulation, pituitary growth hormone release) and gastrointestinal (gastric emptying, intestinal motility) functions. The motilin immunoreactive material detected in brain may be encoded by a distinct non-homologous gene, and still share amino acid homologies with the motilin sequence. Molecular biological characterization of the cell systems which contain motilin and motilin-like immunoreactivity should allow a better definition of their roles in these tissues.