Exaggerated response of adrenocorticotropic hormone to growth hormone-releasing peptide-2 test in Cushing's disease. Case report.

A 47-year-old woman presented with a pituitary microadenoma manifesting as typical Cushing's syndrome. The diagnosis was Cushing's disease based on the endocrinological findings. Plasma adrenocorticotropic hormone (ACTH) levels were greatly increased from 66 pg/ml to 2490 pg/ml (about 38-fold) in response to the administration of 100 μg human growth hormone-releasing peptide (GHRP)-2. GHRP receptor type 1a messenger ribonucleic acid was detected in the tumor. Therefore, GHRP-2 may stimulate ACTH via the GHRP receptor type 1a in pituitary ACTH-producing tumor. The GHRP-2 test, currently clinically available in Japan, may be a useful diagnostic tool for Cushing's disease.