WordNet sense 1 (a substance produced by the hypothalamus that is capable of accelerating the secretion of a given hormone by the anterior pituitary gland):

Rf, releasing hormone

WordNet sense 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):

Rh, hypothalamic releasing factor, hypothalamic releasing hormone