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Shlomo Melmed
Published in Volume 119, Issue 11
J Clin Invest. 2009; 119(11):3189–3202 doi:10.1172/JCI39375
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Figure 2
Normal and disrupted GHRH–GH–IGF1 axis and molecular targets for therapy.

Pituitary somatotroph cell development and gene expression are determined by the POU1F1 transcription factor. Net GH secretion is determined by integration of hypothalamic, nutritional, hormonal, and intrapituitary signals. GH synthesis and secretion are induced by hypothalamic GHRH and gut-derived ghrelin. GHRH may also act as a coagonist for the ghrelin receptor (28). Hypothalamic SRIF suppresses GH secretion mainly by high-affinity binding to SSTR2 and SSTR5 receptor subtypes expressed on somatotrophs (90). SSTR ligands (SRLs) signal through SSTR2 and SSTR5 to control GH hypersecretion and shrink tumor mass. GH secretion patterns in a normal subject and in acromegaly are depicted in the insets showing secretory bursts (mainly at night) and daytime troughs. Insets modified with permission from Expert opinion on biological therapy (S41).