Dynamic changes of growth hormone-binding protein concentrations in normal men and patients with acromegaly: effects of short-term fasting.

Plasma concentrations of growth hormone (GH) and GH-binding protein (GHBP) were measured at hourly intervals in five healthy men and five patients with acromegaly during the fed state and after a 5-day fast. GHBP concentrations (both total and complexed with endogenous GH) were analyzed by the ligand-mediated immunofunctional assay (LIFA). Total GHBP was similar in both groups during the fed state (104.4 +/- 5.2 and 101.6 +/- 10.3 pmol/L), did not exhibit a diurnal rhythm, and was unchanged by fasting (91.9 +/- 5.4 and 109.9 +/- 10.5 pmol/L, respectively). However, the GHBP/GH complex concentration was significantly higher in acromegalics than in controls (41.0 +/- 2.8 v 18.0 +/- 2.2 pmol/L, respectively; P < .05), closely followed diurnal GH rhythm in normals, and was significantly correlated with mean 24-hour GH concentrations (r = .86, P < .01). We conclude that plasma concentrations of GHBP are stable throughout the day and are unchanged either by short-term calorie deprivation or by chronic exposure to high levels of endogenous GH. In contrast, GHBP/GH complex concentrations are altered both acutely and chronically by ambient GH.