Biological Activity and Mechanisms of Action of Somatocrinin, Growth Hormone Releasing Factor, on the Release of Growth Hormone in Vitro and its Antagonism by Somatostatin

The concept of a neurohumoral hypothalamic control of the adenohypophysis as originally formulated by G. W. Harris was later expanded to propose that there would be one hypothalamic substance (a releasing factor, as they were called later) involved for controlling the secretion of each pituitary hormone. The concept was ultimately validated with the isolation and characterization in 1969 of TRF, the thyrotropin releasing factor, known now also to release prolactin, and in 1971 of LRF, the luteinizing hormone releasing factor, known now also to release follicle stimulating hormone. Regarding the secretion of growth hormone, it has been known since the early 1960’s that hypothalamic lesions will inhibit body growth along with growth hormone secretion, and in 1964 Durben and Meites reported the presence of a growth hormone releasing factor in extracts of hypothalamic tissues. The search for the isolation and characterization of the growth hormone releasing factor has been on ever since, with no satisfactory results, despite earlier claims to the contrary.