Endocrine Abstracts

OBJECTIVE: To quantify the extent of change in total body water (TBW) and nature of its relationship with changes in body composition, measured by direct methods, during physiological GH replacement in severely GHD adults.

METHODS: Thirty (16 female, age range 17-65 years) severely GHD adults were studied. Patients with diabetes insipidus, cardiovascular or renal disease requiring diuretic therapy were excluded. Patients with other pituitary deficits had received stable conventional replacement for at least six months.

Serum IGF-I, body composition assessed by DEXA, and TBW by deuterium dilution were studied at baseline and after 3 and 6 months of GH replacement.

RESULTS: Median age-adjusted IGF-I SDS increased from -3.40 (-6.40 to -1.60) to -0.2 (-1.88 to 0.775), (p<0.0001) at 6 months (median daily GH dose of 0.364mg); LBM increased from (baseline) 47 ± 1.96kg to 49.51 ± 2.04kg (p=0.0008), fat mass (FM) decreased from (baseline) 27.99 ± 2.21kg to 27.16 ± 2.38kg (p=0.0004), and there was a non-significant median increase in TBW of 1.7kg (p=0.08).

At baseline, 3 and 6 months a highly significant linear correlation between LBM and TBW was demonstrated, baseline; r=0.92, p<0.0001, 3 months; r=0.91, p<0.0001, 6 months; r=0.91, p<0.0001. Hydration fraction of LBM was 0.721 (0.699-0.782) at baseline, 0.714 (0.697-0.762) at 3 months and 0.715 (0.694-0.788) at 6 months (p=0.87). A positive correlation was demonstrated between percentage change in LBM and TBW (r=0.395, p=0.038) and a negative correlation between percentage change in FM and TBW (r=-0.39, p=0.042). At 6 months IGF-I SDS correlated positively with LBM (r=0.49, p=0.01), and showed a trend towards a positive correlation with TBW (r=0.37, p=0.055).

CONCLUSIONS: The effects of GHD on TBW reflect reduction in LBM. Physiological GH replacement increases LBM and TBW proportionately. Direct methods of measurement therefore caution against previously reported discordance between body composition and TBW changes in GHD adults.