OBJECTIVE We examined the effects of different doses of GH on insulin-like growth factor I (IGF-I), IGF binding protein 3 (IGFBP-3), body composition, energy expenditure, and various metabolites in GH deficient adults, in order to approach a metabolically appropriate GH dosage in young GH deficient adults.
DESIGN Ten GH deficient patients (age 21–43) were studied after 4 weeks without GH followed by three consecutive 4-week periods, where the patients received in a fixed order GH 1,2 and 4 IU/m2 s.c. per day. At the end of each period the patients were hospitalized for a 24-hour examination.
RESULTS Mean 24-hour levels of GH (mIU/l) were 2.7±0.3 (0 GH), 7 2±0.9 (1), 10.8±1.5 (2) and 18.9±2.7 (4 IU/m2) (mean ±SEM) (P<0.01). Likewise, IGF-I levels increased dose dependently from 61 ± 21 to 206 ± 65, 260 ± 70 and 468 ± 171 /μg/l (P < 0 05); serum IGF-I in an age and sex matched control group was 248 ± 25 /μg/l. Corresponding serum IGFBP-3 levels also increased from 1860 ±239 to 3261 ±379, 3762 ±434 and 4384 ±652 /μg/l (P = 001) respectively. Significant increases in diurnal serum insulin levels after 4 IU/m2 were recorded, whereas plasma glucose levels remained unchanged. Lipid intermediates increased dose independently during GH administration. GH caused a significant increase in resting energy expenditure, whereas the respiratory exchange ratio was unaltered. Fat mass was increased without GH therapy and decreased during the study. Four patients made complaints during 4 IU/m2 GH administration, probably related to GH induced fluid retention.
CONCLUSION Based primarily on IGF-I and IGFBP-3 levels our data suggest that a GH replacement dose in young GH deficient adults in the order of 1–2 IU/m2 per day is adequate. This is a relatively low dose as compared to dose regimens in children and adolescents.