WordNet (r) 3.0 (2006):

releasing factor
    n 1: a substance produced by the hypothalamus that is capable of
         accelerating the secretion of a given hormone by the
         anterior pituitary gland [syn: releasing factor,
         releasing hormone, RF]
    2: any of several hormones produced in the hypothalamus and
       carried by a vein to the anterior pituitary gland where they
       stimulate the release of anterior pituitary hormones; each of
       these hormones causes the anterior pituitary to secrete a
       specific hormone [syn: releasing hormone, RH, releasing
       factor, hypothalamic releasing hormone, hypothalamic
       releasing factor]