GH secretion is controlled by complex hypothalamic and peripheral factors. GH-releasing hormone (GHRH) is a 44-amino-acid hypothalamic peptide that stimulates GH synthesis and release. Ghre- lin, an octanoylated gastric-derived peptide, and synthetic agonists of the GHS-R induce GHRH and also directly stimulate GH release. Somatostatin (somatotropin-release inhibiting factor [SRIF]) is synthe- sized in the medial preoptic area of the hypothalamus and inhibits GH secretion. GHRH is secreted in discrete spikes that elicit GH pulses, whereas SRIF sets basal GH secretory tone. SRIF also is expressed in many extrahypothalamic tissues, including the central nervous system (CNS), gastrointestinal tract, and pancreas, where it also acts to inhibit islet hormone secretion