Motilin-related immunoreactivity in mammalian adenohypophysis

Motilin, a gut peptide recently demonstrated in the mammalian brain and anterior pituitary, was localized immunocytochemically in rat, guinea pig, and human anterior pituitary glands with two antisera to synthetic porcine motilin. Adjacent sections of normal glands were immunostained for motilin, growth hormone, and prolactin reactivity. Motilin reactivity was consistently seen in somatotrophic regions of the mammalian glands and in many instances was colocalized in individual somatotrophs traced in adjacent sections stained for growth hormone. There was no motilin activity discerned in prolactin-secreting regions of the gland. These studies reinforce the close relationship of motilin or a motilin-like peptide with growth hormone in normal somatotrophs. Further anatomical and in vitro studies with tumor material will be useful in elucidating the physiological relationship of motilin to growth hormone.