Corticotropin synthesis and secretion is under negative feedback regulation by glucocorticoids. In addition a hypothalamic factor inhibiting ACTH synthesis and secretion, named corticotropin release inhibiting factor (CRIF), has been postulated but not identified. Here we report that transient transfection of a rat prepro-TRH cDNA into the mouse anterior pituitary tumor cell line AtT-20 inhibits the synthesis and secretion of both basal and CRH-stimulated ACTH. Thus, CRIF appears to be encoded by the same precursor as TRH, suggesting a coordinated regulation of pituitary-adrenal and pituitary-thyroid functions.
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