GHRH is expressed and secreted from the hypothalamic
neurons of the arcuate nucleus (ARC). GHRH stimulates
the release of growth hormone (GH) in the anterior
pituitary. In 1982, three isoforms of GHRH(1–37, 1–40, 1–44 aa
residues) were initially isolated from human pancreatic
tumors that caused acromegaly, and the latter two were
found in the human hypothalamus. The aa sequence of
GHRH was also identified in various vertebrates from
rodents to fish, including a protochordate. In nonmammalian vertebrates, GHRH-like peptide (pituitary adenylate cyclase-activating polypeptide (PACAP)-related
peptide in mammals) was first isolated like GHRH,
although the GHRH-like peptide had less activity on
GH release. Later, actual GHRH, which was more phylogenetically and structurally similar to mammalian
GHRH and showed GH-releasing activity, was isolated
in nonmammalian vertebrates.
