releasing factor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of several hormones secreted by the hypothalamus that stimulate the anterior part of the pituitary gland to release certain hormones.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a substance produced by the hypothalamus that is capable of accelerating the secretion of a given hormone by the anterior pituitary gland
• noun 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