Growth Hormone/IGF-I Axis
Growth hormone (GH) is secreted by somatotropic cells of the anterior pituitary gland under the stimulation control of hypothalamic factor GH Releasing Hormone (GHRH). GH acts directly and indirectly through Insulin-like Growth Factor-1 (IGF-1). Together GH and IGF promote mammalian growth and influence regulation of metabolism. In addition, the GH/IGF-1 axis has been shown to actively regulate lifespan in worms, flies and mice. However, it remains to be determined if the GH/IGF-1 axis has an equal influence on human longevity. Secretion of human GH progressively declines with age and is paralleled by decreased levels of IGF-1. GH/IGF-1 exert potent effects on the central nervous system, modulating plasticity and function. Age-related depletion of GH/IGF-1 has been associated with increased vulnerability to the development of cognitive and sleep disorders.