Psychoendocrinology and growth hormone: A review

(1) Growth hormone is a pituitary hormone which is very largely dependent on central nervous system regulation. Both inhibitory and excitatory hypothalamic hormones exist. Only the inhibitory hormone has been isolated and characterized. (2) In experimental animals, the regulation of growth hormone secretion has been shown to be dependent on afferent inputs to the hypothalamus from a variety of limbic and other brain areas including amygdala, septum, hippocampus and midbrain structures. (3) In man there is evidence for excitatory dopaminergic, noradrenergic and serotonergic neural mechanisms. (4) Growth hormone is primarily secreted in bursts of which there are approximately seven per day in the adult human male. Bursts can be either spontaneous or can be triggered by a variety of metabolic and stressful stimuli. Most of the effects of growth hormone appear to be mediated by another hormone, somatomedin, whose release is regulated by growth hormone. (5) Elevated levels of growth hormone are seen in a variety of conditions in which there are no direct psychological effects. Conversely, it is rather unlikely that there is a psychogenic origin for the hypersecretion of growth hormone seen in acromegaly. In response to physical or psychological stress, a rise in growth hormone is frequently seen which does not always correspond to adrenal activation (an accepted index of stress). GH can show a rise independent of cortisol and the reverse is also true. Conditions producing these divergent responses are only now beginning to be defined. (7) Elevation in growth hormone seen in anorexia nervosa is clearly related to nutritional status in that those patients with poor caloric intake have an elevated level which is reversed rapidly as the caloric intake increases. Reduced levels of growth hormone found in hypopituitarism or in single defects of pituitary function appear to produce no direct psychological effects. (8) In severe endogenomorphic depression, defective growth hormone responses to insulin hypoglycemia are seen in a high proportion of patients and frequently co-exist with the presence of growth hormone responses to TRH, a response which does not occur in normal subjects. These findings may be related to an underlying neurotransmitter abnormality. (9) In psychosocial deprivation, deficiency of growth hormone responses has also been reported which correlates with poor growth. It is important, however, to differentiate this condition from caloric deprivation in which there is inadequate food intake as many of such patients have elevated growth hormone resting levels.