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Whereas insulin-like growth factor I (IGF-I) has been found in various body fluids from different species, the presence or absence of IGF and associated binding proteins (IGFBPs) in bile has not been clearly defined. Bile concentration of IGF-I was measured in this study and found to be highest in the neonate and lowest in adult rats [133 +/- 15.9, 79.4 +/- 10.5, 45.3 +/- 12.7 ng/ml (mean +/- SE) in 12-day-old, 33-day-old, and adult rats, respectively]. When bile delivery rates of IGF-I (i.e., the product of IGF-I concentration in bile and the biliary flow rate) were calculated, IGF-I delivery was highest in weanling rats (469 pg.h-1.g body wt-1). When expressed as amount of IGF-I in bile delivered per day, however, delivery rates rose from 0.2 micrograms/day in the suckling and remained constant at 1.6-1.7 micrograms/day in both weanling and adult animals. Bile samples exposed to a placental membrane IGF receptor preparation showed significant dose-dependent inhibition of binding of native IGF-I. Because no IGF binding proteins were identified by Western ligand blot or by Sephadex gel chromatography, the results suggest the presence of biologically significant quantities of bioactive IGF-I in bile. We speculate that IGF-I in bile may play an important role in the growth of the gastrointestinal tract, both in the suckling as well as later in life.

Insulin like growth factor (IGF) 1 and 2 which are present and actively synthesised in the wound fluid stimulate several cell types involved in the process of wound healing. To investigate the role of IGF-1 and 2 and in addition, the association between IGF and their carrier proteins, IGF binding proteins (IGFBP), we have used a newly established model for human wound healing in fresh biopsy material. Histological examination shows that IGF-1 stimulates efficient reepithelialisation of the wounds both alone and in the presence of recombinant IGFBP-1. In contrast, IGF-2 stimulates healing only when used in combination with IGFBP-1. These findings suggest that the two IGFs and their carrier proteins may function during different phases of wound healing and that both IGF-1 and 2 act as potent inducers of wound healing; this may have direct clinical implications.

The present report describes the mitogenic effect of recombinant IGF-2 on cultured human keratinocytes and fibroblasts compared to that of IGF-1. Furthermore, the modulating effect of a recently expressed recombinant form of placental-derived IGF-binding protein 1 (IGFBP-1) on IGF-induced proliferation was examined. A dose-dependent increase, up to 100%, in cell proliferation was seen in cultured human keratinocytes with IGF-2 and -1 and the proliferative response was comparable to the effect of epidermal growth factor (EGF). In human fibroblasts, IGF-1 stimulated DNA synthesis up to 300% for IGF-1 and up to 200% for IGF-2. The mitogenic effect of IGF-1 was enhanced by IGFBP-1 in both cell types. In contrast, the IGF-2-induced mitogenic effect was unperturbed. These findings indicate that the interaction between IGFs and their binding proteins may induce different responses depending upon the ligand and the target cell.

Binding and growth promoting effects of insulin, insulin analogues modified in the B chain, proinsulin, insulin-like growth factor-I and -II were studied in cultured rat aortic smooth muscle cells. Specific binding of 125I-insulin was 0.9 +/- 0.2% of total 125I-insulin added, and the IC50-value was estimated to 8.9 pmol/l. The insulin analogue B10 Asp tended to be more potent than insulin in displacing 125I-insulin, B28 Asp was equipotent, B9 Asp/B27 Glu was approximately 100 times less potent and insulin-like growth factor-I more than 1000 times less potent than insulin. Specific binding of 125I-insulin-like growth factor-I after 4 h incubation at 10 degrees C was five times higher than the specific binding of insulin (4.4 +/- 0.4% of total 125I-insulin-like growth factor-I added), and the IC50-value was 0.3 nmol/l. Insulin was approximately 500 times less potent than insulin-like growth factor-I in displacing 125I-insulin-like growth factor-I. The insulin analogue B10 Asp was slightly more potent and analogue B28 Asp was equipotent with insulin. Analogue B9 Asp/B27 Glu was ten times less potent and proinsulin was more than ten times less potent than insulin. The order of potency was similar for 3H-thymidine incorporation into DNA: insulin-like growth factor-I greater than B10 Asp greater than insulin-like growth factor-II greater than insulin greater than or equal to B28 Asp greater than B9 Asp/B27 Glu greater than proinsulin. The maximal effect of insulin-like growth factor-I on 3H-thymidine incorporation was 71 +/- 16% higher than the maximal effect of insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Two different insulin-like growth-factor (IGF)-binding proteins have been found in human blood, one of high molecular mass and dependent on growth hormone for synthesis, the other of low molecular mass and independent of growth hormone. The small IGF-binding protein is abundant in human amniotic fluid. Its amino acid sequence has now been determined by direct analysis of the protein and its proteolytic fragments. Also, by immunoscreening a partial cDNA clone was isolated from a human hepatoma cell line. The mature protein consists of 234 amino acids and is coded for by an mRNA of approximately 1700 nucleotides in length. The primary structure of the protein reveals 18 Cys residues in N-terminal and C-terminal clusters and an Arg-Gly-Asp peptide sequence, common to extracellular proteins binding to receptors of the integrin family. A protein-sequence polymorphism was detected at position Ile/Met-228, indicating possible allelic variation. The 3'-untranslated mRNA sequence has a high A + T content and shows five copies of an ATTTA sequence, which has been shown to be involved in the regulation of the stability of certain mRNAs coding for growth-regulating proteins.