Endocrine Abstracts

Growth hormone (GH) and leptin regulate body composition and leptin is elevated in adult growth hormone deficiency (AGHD), a syndrome characterised by increased adiposity. We have previously shown that GH replacement for 1 month reduces 24-h mean leptin concentration independent of changes in fat mass. The long tem effects of GHR on leptin have not been described.

24-h mean total leptin concentration was measured using half-hourly blood sampling, to account for circadian variations. Sampling was performed in 12 AGHD patients (6 men) before, then after 1 and 12 months of GH replacement (GHR) at a GH dose to maintain IGF-1within the 2 SD score of the age-related reference range. Body composition was estimated using bio-electrical impedance before then 1,3 and 12 months after GHR.

Target IGF-I was achieved within 3 months and maintained at 12 months (30.2plus/minus2.5micromol/liter) in all patients. Mean leptin correlated significantly (P <0.01) with fat mass and fat percentage. Leptin decreased from 2.05plus/minus0.04 nmol/liter to 1.65plus/minus0.03 nmol/liter at 1 month (Mean Difference (MD) 0.40 nmol/liter, CI 0.37 to 0.43, P <0.0001) and increased significantly to 2.04plus/minus0.04 nmol/liter from 1 month to 12 months (MD -0.39 nmol/liter, CI -0.43 to -0.36, P <0.0001) after GHR. The difference in leptin concentration prior to and after 12 months of GHR was not significant (MD 0.01 nmol/liter, CI -0.02 to 0.03). Fat mass decreased significantly from baseline (33.2 kg) to 3 months (31.3 kg, MD 1.9 kg, CI 0.6 to 3.2, P< 0.01) and this was preceded by the decrease in leptin. Fat mass increased between 3 and 12 months (32.0 kg, MD -0.6 kg, CI -2.4 to 1.2) but the difference between baseline and 12 months (MD 1.3 kg, CI -0.5 to 3.2) was not significant.

Fat mass changes follow changes in leptin during long term GHR and neither leptin nor fat mass are significantly different after 12 months of GHR despite initial significant reductions.