Regulation of growth hormone secretion during normal conditions and in patients with acromegaly.

A present considered concept of growth hormone secretion is that the hormone is tonically inhibited by the hypothalamic tetradecapeptide somatostatin. The episodic fashion of GH secretion with 6-8 GH peaks per 24 hours and its modulation by light and sleep are probably governed by factors other than somatostain, one possibly being melatonin. Evidence for a GH-releasing factor also exists, causing a basal release pattern of GH in moderate hourly peaks. The regulotary peptides in their turn, and possibly the GH producing cell itself, are influenced by dopaminergic or noradrenergic neurons. GH secretion is also modulated in a not yet elucidated relation to serotonin activity. Furthermore, GH induced somatomedin may constitute a negative feed-back on the pituitary and/or hypothalamic level. In acromegaly and gigantism, conditions characterized by chronic hypersecretion of GH, the GH producing cells are less differentiated as indicated by their response with GH release to unphysiological stimuli as well as their cessation of GH release to stimuli that normally act as releasors of GH.