Hypothalamic control of GH secretion: pathophysiology and clinical implications.

GH is secreted episodically. Its pattern is regulated by the interplay of a releasing and a release-inhibiting hormone of hypothalamic origin. Modulation occurs by metabolic factors (glucose, free fatty acids, ketone bodies, amino acids). Altered GH secretion has been observed in states of metabolic derangement such as diabetes mellitus, malnutrition and obesity. Further modulation occurs by extrahypothalamic CNS structures. In man--but not in animals, including subhuman primates--sleep has an important effect on GH secretion. A defective GH secretory pattern has been found to occur in several states of sleep disturbance, such as sleep deprivation, narcolepsy, severe psychosocial derangement, the apallic syndrome. Other CNS influences on GH secretion are related to stress, emotional changes and psychiatric disturbances. The exact mechanisms by which most of these influences are relayed to the GH secretory apparatus of the hypothalamus remain yet to be investigated.