Dynamic characteristics of the growth hormone (GH) axis are determined in part by developmental age, including fetal, neonatal, childhood, pubertal, young-adult and older-adult stages of life. The growth-promoting pituitary-dependent GH axis mediates soft-tissue and skeletal growth in puberty, and maintains body composition within relatively narrow bounds in puberty and adulthood. The hypothalamo-pituitary unit comprises a unique neuroendocrine interface, in which intermittent brain signals are delivered via a finite portal microvasculature to the multicellular anterior pituitary gland. The GHRH receptor is a GTP-dependent adenylyl cyclase-activating protein, with sequence homology to secretin and vasoactive intestinal polypeptide (VIP) receptors. The prototypical endogenous GHS is ghrelin, a 28-amino acid acylated peptide, which requires an octanoyl group esterified to serine in N-terminal position 3 for maximal receptor activation. Other fatty acyl groups can also confer bioactivity. Low pulsatile GH secretion in aged individuals may be reversed acutely by simultaneous administration of GHRH, GHS and L-arginine.
|Original language||English (US)|
|Title of host publication||Handbook of Neuroendocrinology|
|Number of pages||21|
|State||Published - Dec 1 2012|
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