IGFBP1 and hyperinsulinism: Moreover, hyperinsulinemia may increase the bioavailability of IGF-I and IGF-II through two mechanisms: (1) by inhibiting the synthesis of certain IGF-binding proteins, such as IGF-binding protein 1 (IGF-BP1) and IGF-binding protein 2 (IGF-BP2), (2) by increasing IGF-I hepatic production.