title: Increased orderliness of growth hormone (GH) secretion in GH-deficient adults with low serum insulin-like growth factor I.
abstract: Available studies suggest that a proportion of GH-deficient (GHD) adults maintain serum IGF-I concentrations within the age- and sex-matched normal range. The basis for this distinction is not known. In this study 24-h GH profiles (sampling every 30 min) were appraised in five GHD adults with low serum IGF-I concentrations (<2 SD of the age- and sex-matched normal range), five GHD adults with normal serum IGF-I levels (within +/-2 SD), and five healthy subjects. Serial GH concentrations, measured using a chemiluminescence assay, were analyzed by deconvolution and approximate entropy (ApEn; regularity) analyses. The apparent half-duration of GH secretory bursts was longer in both GHD groups than in the healthy controls, as determined by deconvolution analysis (P < 0.05 each). The GH burst frequency was higher, the interburst interval was shorter, and the GH burst amplitude was lower in GHD adults with normal serum IGF-I than in healthy controls (P < 0.05, P < 0.05, and P < 0.01, respectively). The percentage of total daily GH secretion that was pulsatile was also reduced in the GHD adults with normal serum IGF-I compared with the other two groups (P < 0.05 and P < 0.05, respectively). In contrast, ApEn ratios were lower in the GHD adults with low serum IGF-I than in the GHD adults with normal IGF-I and controls (P < 0.01 and P < 0.05, respectively). Serum IGF-I concentrations correlated positively with ApEn ratios in the total study population (n = 15) and in the GHD adults (n = 10). In conclusion, 24-h patterns of GH release differed in GHD adults with low vs. normal serum IGF-I concentrations. GHD adults with low IGF-I levels maintain low ApEn ratios (denoting greater relative orderliness of GH secretion), whereas GHD patients with normal IGF-I values generate a high frequency, low amplitude GH output. The foregoing contrasts point to distinct neuroendocrine features of the GH-deficient state of adults, which can be related to concurrent IGF-I production.
authors.affiliation: Research Centre for Endocrinology and Metabolism, Gröna Stråket 8, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. johan.svensson@medic.gu.se
authors.forename: Johan
authors.initials: J
authors.lastname: Svensson
authors.forename: Johannes D
authors.initials: JD
authors.lastname: Veldhuis
authors.forename: Ali
authors.initials: A
authors.lastname: Iranmanesh
authors.forename: Bengt-Ake
authors.initials: BA
authors.lastname: Bengtsson
authors.forename: Gudmundur
authors.initials: G
authors.lastname: Johannsson
mesh_terms: D000328:Adult; D019277:Entropy; D005260:Female; D019382:Human Growth Hormone / Q000172:deficiency* / Q000378:metabolism*; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008661:Metabolism, Inborn Errors / Q000378:metabolism*; D008875:Middle Aged; D009994:Osmolar Concentration; D012016:Reference Values
chemical_list: D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I