Growth hormone (GH) responses to the combined administration of GH-releasing hormone plus GH-releasing peptide 6 in adults with GH deficiency

Abstract

In recent years the health problems of adults with growth hormone deficiency (GHD) and the benefits of GH replacement therapy have received considerable attention. However, the reliability of conventional GH tests in the assessment of pituitary GH reserve in this group of patients is still controversial. In this study, we assessed GH secretion after the combined administration of GH-releasing hormone (GHRH) (1 microgram/kg iv) and GH-releasing peptide 6 (GHRP-6, 1 microgram/kg iv) in adult patients diagnosed with GHD by conventional GH testing, and correlate this response with insulin-like growth factor I levels. Twenty-one subjects (13 male, 8 female) with long-standing diagnosis of GHD aged 21-54 years were studied. In 13 subjects GH responses to GHRH plus GHRP-6 were markedly reduced (peak GH response < 10 mU/l), whereas in the remaining eight the response was greater (range 11-100 mU/l). In conclusion, our data show that combined administration of GHRH plus GHRP-6 elicited a significant increase in plasma GH levels in about 40% of patients diagnosed with GHD by conventional GH testing.