Growth hormone neuroregulation and the clinical relevance of somatostatin.

The hypothalamus controls GH secretion from the anterior pituitary using two peptides; somatostatin inhibits GH, but physiologically the most important appears to GHRF, the structure of which has recently been discovered by two groups. This exciting development has not only given us further insight into the control of GH secretion, but also posed interesting questions as to the cause of the abnormal GH responses to various stimuli seen in patients with acromegaly. The other hypothalamic peptide controlling GH secretion, somatostatin has been the subject of intensive research in the last ten years. It is widely distributed and has important physiological actions including those involved in GH secretion and its action as a hypothalamic hormone. The secretion and synthesis of these two hypothalamic hormones is in turn modulated by a number of neurotransmitters, the most important of which appears to be dopamine. Knowledge gained in these studies has enabled the development of useful tools in the diagnosis of growth hormone deficiency as well as the only effective medical treatment for acromegaly. Much remains to be learnt of the physiology of growth hormone releasing factor and as a result further patients will benefit in the future.