Growth hormone-releasing hormone (GHRH), also known as growth hormone-releasing factor (GRF or GHRF), is a 44-amino acidpeptide hormone produced in the arcuate nucleus of the hypothalamus. GHRH is released from neurosecretory nerve terminals of these arcuate neurons, and is carried by the hypothalamo-hypophysial portal circulation to the anterior pituitary gland where it stimulates growth hormone (GH) secretion. GHRH also stimulates the production of GH. GHRH is released in a pulsatile manner, stimulating similar pulsatile release of GH. In addition, GHRH also promotes slow-wave sleep directly (PMID 11924022).
The actions of GHRH are opposed by another hypothalamic hormone, somatostatin, also known as "growth hormone-inhibiting hormone" (GHIH). Somatostatin is released from neurosecretory nerve terminals of periventricular somatostatin neurons, and is carried by the hypothalamo-hypophysial portal circulation to the anterior pituitary where it inhibits GH secretion by hyperpolarising the somatotropes. Somatostatin and GHRH are secreted in alternation, giving rise to the markedly pulsatile secretion of GH.
The amino acid sequence of GHRH is:
Tyr - Ala - Asp - Ala - Ile - Phe - Thr - Asn - Ser - Tyr - Arg - Lys - Val - Leu - Gly - Glu - Leu - Ser - Ala - Arg - Lys - Leu - Leu - Gln - Asp - Ile - Met - Ser - Arg - Glu - Gln - Gly - Glu - Ser - Asn - Gln - Glu - Arg - Gly - Ala - Arg - Ala - Arg - LeuNH2