GASTROINTESTINAL ABSORPTION OF INSULIN-LIKE GROWTH-FACTOR IN THE MOUSE IN THE ABSENCE OF SALIVARY INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN

Based on previous observations of the presence of both insulin-like gr owth factors I and II (IGF-I and IGF-II) in murine saliva (Kerr er al. , Biochem Pharmacol 49: 1521-1531, 1995), the saliva from BALB/c and N on obese diabetic (NOD) mice was examined for the presence of insulin- like growth factor binding proteins (IGFBPs). Using a western-blot typ e ligand binding assay with I-125-labeled IGF-I, a series of binding p roteins with molecular masses (M(r)) between 25 and 45 kDa were detect ed in the sera, but not saliva, from both BALB/c and diabetic NOD mice . In the diabetic NOD mice, there were detectable changes in the conce ntrations of several of the IGFBPs relative to BALB/c mice. Using spec ific antibody to the binding proteins, one of these was identified as IGFBP-2. Gavage administration of [I-125]IGF-I indicated substantial u ptake from the gastrointestinal tract and significant tissue distribut ion. There was an increase in serum concentrations of radiolabeled IGF -I in diabetic NOD mice over that in BALB/c mice but less recovered fr om most of the tissues. Intact I-125-labeled IGF-I was extracted and p urified from various tissues, following gavage, and shown to retain bi ological activity. Thus, the uptake of biologically active IGFs from s aliva would appear to take place independently of specific binding pro teins. Copyright (C) 1996 Elsevier Science Inc.