Growth hormone-releasing hormone: Clinical perspectives revisited

Growth hormone-releasing hormone (GHRH) is limited as a diagnostic tool in both growth hormone (GH) deficiency and acromegaly. However, the combination of GHRH with other secretagogues, ie, arginine and/or GH-releasing peptides, is a good alternative to the insulin tolerance test for the diagnosis of GH deficiency. Choosing appropriate cutoff values for peak GH serum levels gives these tests 95% specificity and sensitivity to diagnose GH deficiency, especially in adults. Measurement of a GHRH serum level is still helpful in a patient with acromegaly suspected to have ectopic production of this peptide. GHRH may have more potential as a therapeutic agent. In children with GH deficiency, GHRH given as a subcutaneous injection twice daily stimulates linear growth with growth velocities comparable to GH therapy. The use of a GHRH antagonist may have some use in acromegaly but may be more useful as a cancer chemotherapeutic agent. A number of human tumors have been shown to have GHRH receptors and respond to GHRH with an increase in cellular proliferation. A GHRH antagonist is able to decrease the size of these tumors by 50% to 95%. The clinical use of GHRH may be greatly potentiated by novel preparations and delivery systems for this peptide.