In normal subjects the main form of circulating insulin-like growth factor (IGF) is the 150-kDa complex.This complex is formed by the IGF peptide, the acid-stable IGF-binding protein-3 (IGFBP-3), and the acid-labile subunit (ALS).Experimental and clinical data have demonstrated that ALS is primarily under the control of GH and plays a critical role in maintaining constant levels of circulating IGF-I.In this study we evaluated ALS, IGF-I, and IGFBP-1, -2, and -3 in 45 acromegalic patients in basal conditions and, in 37 of these, twice after surgical therapy compared with 100 age-and sex-matched control subjects to estimate their value as parameter of GH secretory state.The results demonstrated that in acromegaly before treatment all parameters (ALS, 523 Ϯ 26; IGF-I, 129 Ϯ 6; IGFBP-1, 0.7 Ϯ 0.1; IGFBP-3, 234 Ϯ 21; nmol/L; mean Ϯ SEM) but IGFBP-2 were significantly different (P Ͻ 0.0001) from those in healthy subjects (ALS, 281 Ϯ 4; IGF-I, 22 Ϯ 1; IGFBP-1, 1.6 Ϯ 0.1; IGFBP-3, 91 Ϯ 3).IGF-I was more sensitive (100%) than ALS (89%), and both were more predictive of disease status than IGFBP-3, in that 27% of the patients had IGFBP-3 levels within the normal range.Considering the ALS/ IGFBP-3 molar ratio, almost 55% of ALS circulated in a free form in active acromegaly.Before treatment, the IGF-I/IGFBPs (Ϫ1 ϩ Ϫ2 ϩ Ϫ3) molar ratio, which can be regarded as free, biologically active, IGF-I, was greatly increased (0.77 Ϯ 0.06; P Ͻ 0.0001) compared with that in control subjects (0.23 Ϯ 0.01).
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M. Arosio (2001) studied this question.