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Increased Orderliness of Growth Hormone (GH) Secretion in GH-Deficient Adults with Low Serum Insulin-Like Growth Factor I

Research Centre for Endocrinology and Metabolism (J.S., B.-Å.B., G.J.), Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden; General Clinical Research Center, Department of Medicine, University of Virginia Health Sciences Center (J.D.V.), Charlottesville, Virginia 22908; and Salem Veterans Affairs Medical Center (A.I.), Salem, Virginia 24153

Address all correspondence and requests for reprints to: Johan Svensson, M.D., Research Centre for Endocrinology and Metabolism, Gröna Stråket 8, Sahlgrenska University Hospital, SE-413 45 Göteborg, Sweden. E-mail: . johan.svensson{at}medic.gu.se

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.

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