PRESERVED GROWTH-HORMONE (GH) SECRETION IN AGED AND VERY OLD SUBJECTSAFTER TESTING WITH THE COMBINED STIMULUS GH-RELEASING HORMONE PLUS GH-RELEASING HEXAPEPTIDE-6 - COMMENT

Either spontaneous or pharmacological stimulated GH secretion is reduc ed with advanced age. This observation is an added difficulty for the biochemical diagnosis of GH deficiency in adults. Furthermore, the com bined administration of saturating doses of GH-releasing hormone (GHRH ) plus GH-releasing hexapeptide (GHRP)-6 is nowadays the most effectiv e GH-releasing stimulus tested in a variety of settings related to alt ered somatotroph function. To understand whether the GH discharge elic ited by the combined stimulus declines with age, 26 normal subjects of both sexes, divided into 3 age groups [adults 19-40 yr; aged 46-65 yr ; and very old (75-96 yr) subjects] mere studied. They were administer ed iv, as bolus and in combination, 90 mu g GHRH plus 90 mu g GHRP-6. In the three groups, the combined administration of GHRH plus GHRP-6 e licited a GH area under the curve (mu g/L per 120-min) of 3,127 +/- 26 2, 3,409 +/- 573, and 4,655 +/- 737 for adults, aged, and very old sub jects, respectively (nonsignificant differences). The mean GH peak was 47.5 +/- 4.5 mu g/L for adults, 52.9 +/- 8.4 mu g/L for aged subjects , and 76.0 +/- 11.7 for very old subjects (nonsignificant differences) . Individually examined, there were no nonresponders to the combined s timulus, and all subjects (independently of age) showed a GH peak over 25 mu g/L (the lowest peak was 27.3 mu g/L, and the highest peak was 119.2 mu g/L). In conclusion, the GHRH plus GHRP-6-induced GH release is well preserved in aged and very old subjects, which suggests that t he GH secretory capability of the combined test is not reduced by age. This combined test may be useful for the diagnosis of GH-deficient st ates in adults.