Resting metabolic rate, body composition and related hormonal parameters in growth hormone-deficient adults before and after growth hormone replacement therapy

Department of Endocrinology, University Hospital Utrecht, The Netherlands.

The resting metabolic rate (RMR), and body composition were assessed in 30 growth hormone-deficient (GHD) adults before and after 3 and 6 months of replacement therapy with recombinant human growth hormone (rhGH). In addition, insulin-like growth factor I (IGF-I), IGF binding proteins (IGFBPs) and plasma insulin were measured at baseline and at 6 months in relation to RMR. During 6 months of rhGH replacement therapy, body fat decreased from 18.2 +/- 1.5 (mean +/- SEM) to 14.3 +/- 1.6 kg (p < 0.0001), whereas fat-free mass (FFM) increased from 53.5 +/- 3.3 to 56.3 +/- 3.6 kg (p < 0.0001), RMR increased from 1246 +/- 92 to 1539 +/- 102 kcal/24 h (p < 0.0001) and RMR per kilogram of FFM increased from 23.2 +/- 0.6 to 27.4 +/- 0.5 (p < 0.0001). When RMR data were adjusted for the differences in FFM, it appeared that apart from the increase in FFM, other factors may play a role in the increase in RMR. During rhGH replacement therapy, IGF-I (p < 0.0001) and IGFBP-3 (p = 0.003) levels increased, whereas IGFBP-1 levels decreased significantly (p = 0.004). The FFM explained for about 80% of the variance in RMR. In addition, waist/hip ratio and plasma IGF-I contributed significantly to the explained variance of RMR. This study shows that in GHD adults FFM is the main determinant of RMR and that, next to the increase in FFM, changes in metabolic and hormonal parameters contribute to the increase in RMR during rhGH replacement therapy.

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