The circumstances and the timing of the discovery of growth hormone-releasing hormone (GHRH) encouraged early clinical studies of its effects in humans and influenced the direction of the first work. Because the structure of GHRH was derived from human tissue—tumors overproducing GHRH (1,2)—it was known with confidence that an authentic replica would be biologically active in man, and the first studies in human subjects could be planned with some knowledge of its physiological activities and potency. Because of extensive earlier studies with the hypothalamic releasing factors whose discovery had preceded that of GHRH—thyrotropin-releasing hormone (TRH), gonadotropin-releasing hormone (GnRH), corticotropin-releasing hormone (CRH), and the GH-inhibiting peptide somatostatin (somatotropin-release inhibiting factor, or SRIF)—there were ample precedents for clinical protocols to evaluate potential diagnostic and therapeutic uses. Studies of both of these types of applications began immediately upon the availability of sufficient quantities of synthetic GHRH.
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