THE RATIO BETWEEN SERUM LEVELS OF INSULIN-LIKE GROWTH-FACTOR (IGF)-I AND THE IGF BINDING-PROTEINS (IGFBP-1, IGFBP-2 AND IGFBP-3) DECREASES WITH AGE IN HEALTHY-ADULTS AND IS INCREASED IN ACROMEGALIC PATIENTS

OBJECTIVE Several in-vitro studies have suggested that the biological actions of IGF-I can be modified by the presence of specific IGF binding proteins. In man, the 24-hour serum levels of IGF-I and IGFBP-3 remain constant, but short-term changes in the IGF-I/IGFBP-3 ratio have been described following GH administration. Serum levels of IGF-I and IGFBP-3 decrease with age in normal adults and are elevated in active acromegaly due to excessive GH secretion. However, the individual ratios between serum levels of IGF-I and IGFBP-3 in acromegalic and healthy adults have not been described previously.