Figure 1.

Hypothalamic pituitary control of GH secretion. Hypothalamic GHRH and somatostatin, which traverse the portal vein, somatotroph-specific transcription factors, and negative feedback control of IGF-I all participate in regulatory GH synthesis and secretion. Accurate measurement of pulsatile GH secretion requires ultrasensitive assays. Prop-1, prophet of Pit-1; GHS, GH secretagogs (eg, ghrelin); SRIF, somatostatin. [Reproduced from S. Melmed: Medical progress: acromegaly. N Engl J Med. 2006;355:2558–2573 (81), with permission. © Massachusetts Medical Society.]