Body composition and energy expenditure in acromegaly.

To investigate whether GH is a regulator of body composition and energy metabolism in adult life, we have compared body composition and resting energy expenditure (REE) in a cross-sectional study in 20 acromegalic and 20 normal subjects, pair-matched for sex, age, height, and weight. In a longitudinal study, 8 acromegalic patients were also studied before and after 12 weeks of treatment [n = 6 during octreotide (100 micrograms, 3 times/day); n = 2 after pituitary surgery], and 7 patients were studied 12 weeks after withdrawal of octreotide. REE was measured by indirect calorimetry and fat mass and fat-free soft tissue mass (FFSTM) by dual energy x-ray absorptiometry. A subgroup of 12 matched pairs of subjects and 7 treated patients had measurement of extracellular water (ECW) by 24Na dilution, which when subtracted from FFSTM provided an estimate of body cell mass (BCM). Fat mass was significantly reduced (25.4 +/- 2.2 vs. 29.7 +/- 2.7 kg; P = 0.007) and FFSTM increased (53.3 +/- 2.2 vs. 49.2 +/- 2.3 kg; P = 0.003) in acromegaly with ECW (25.6 +/- 1.6 vs. 21.1 +/- 0.9 L; P = 0.0003), but not BCM, significantly elevated. Treatment of acromegaly increased fat mass and reduced FFSTM [change (delta), -1.3 +/- 0.4 kg; P = 0.004]; the latter reflected a significant fall in ECW (delta, -2.2 +/- 0.4 L; P = 0.002), but not BCM. The opposite effect on body composition occurred after treatment withdrawal. REE was increased in acromegaly (1682 +/- 49 vs. 1540 +/- 45 Cal/24 h; P = 0.02) and significantly related to insulin-like growth factor-I (P = 0.02). REE was significantly reduced (delta, -154 +/- 17 Cal/24 h; P = 0.0001) with treatment and increased after treatment withdrawal (P = 0.003). In acromegaly, there is a reversible 1) reduction in fat mass; 2) increase in FFSTM, accounted for by an increase in ECW, but not BCM; and 3) increase in REE, which is dependent on disease activity. We conclude from these observations in acromegaly that GH is a regulator of energy metabolism and body composition.