Diagnostic and therapeutic uses of growth hormone-releasing substances in adult and elderly subjects

The aim of this review is to answer two questions. The first question is: is there any alternative provocative test equal to, or even better than, the insulin-tolerance test (ITT), the so-called gold standard, for the diagnosis of growth hormone deficiency (GHD) in adults and the elderly? The answer is 'yes'. In fact, when combined with arginine or pyridostigmine, growth hormone-releasing hormone (GHRH) becomes one of the most potent and reproducible tests for distinguishing patients with severe GHD from normal subjects. Owing to its tolerability and its suitability for use in the elderly, the GHRH + arginine test is the best alternative choice and is at least as sensitive as the ITT provided that appropriate cut-off limits are given. The second question is: is there any therapeutic approach alternative to recombinant human growth hormone (rhGH) for adult and elderly patients with GHD and/or for the somatopause? At present, the answer is 'no'. Growth hormone (GH)-releasing substances need the functional integrity of somatotroph cells to induce the release of growth hormone. Probably only patients with childhood-onset, isolated GHD (frequently hypothalamic-dependent) could benefit from treatment with GHRH or growth hormone secretagogues (GHS). Whenever restoration of the activity of the GH/insulin-like growth factor-1 (IGF-1) axis in the elderly would be of use, GHRH and/or GH secretagogues would be good candidates. In fact, the existence of a considerable pool of releasable growth hormone has been demonstrated in the elderly.