Insulin-like growth factors (IGFs) and IGF-binding proteins in the developing rhesus monkey

Rhesus monkeys follow a developmental pattern of serum insulin-like growth factor-I (IGF-I) levels similar to that found in humans. In these monkeys, serum IGF-I levels peak during puberty (2.5-4.5 yr of age in males). We have examined the developmental pattern of IGF-binding protein-1 (IGFBP-1), -2, and -3 in serum by Western ligand blotting, the levels of IGFBP-3, IGF-I, and IGF-II in serum by RIA, and the IGFBP mRNA levels of IGFBP-1, -2, and -3 in the livers of rhesus monkeys from fetal life through adulthood by Northern analysis. The pattern of the serum levels of the IGFBPs reflected the liver mRNA levels of the IGFBPs. The IGFBP-1 and IGFBP-2 liver mRNA and serum levels were highest in the fetus and first year of life and were very low after 4 yr of age. Conversely, the IGFBP-3 liver mRNA and serum levels were relatively low early in life and peaked during puberty. The serum levels of IGF-I and IGF-II were strongly correlated with the level of IGFBP-3. We conclude that the developmental pattern of IGFBPs in the rhesus monkey is similar to that in the human, and that serum IGFBP levels are probably regulated by the rate of IGFBP mRNA synthesis.