Inverse correlation between insulin-like growth factor (IGF)-binding protein-5 and IGF-I and II during postnatal development of the anterior pituitary gland.

BACKGROUND The insulin-like growth factor (IGF) system is important for pituitary development and control, with each member of this axis having a specific temporal and spatial expression. Because IGF-binding protein-5 (IGFBP-5) is one of the most highly expressed binding proteins in the anterior pituitary (AP), it might be of special importance in this gland. OBJECTIVE The purpose of this study was to examine the temporal relationship between the expression of the IGFs and IGFBP-5 in the AP during postnatal development. DESIGN AND METHODS Quantitative reverse transcription polymerase chain reaction was used to study the mRNA levels of these proteins in the AP of male and female rats at 10, 20, 30, 40 and 60 days of age. RESULTS The highest mRNA levels of IGF-I and II occurred at 10 and 20 days of age with a dramatic decrease at 30 days (p < 0.0001). IGF-I, but not IGF-II, mRNA levels increased again during adulthood (60 days). The pattern of IGFBP-5 mRNA was inversely expressed, with maximum values occurring at 40 days. IGF-I mRNA levels were higher in males at 10 days, but higher in females at 20 days. The expression of IGF-II was higher in males both at 10 and 20 days. IGFBP-5 gene expression was higher in females at 40 days. CONCLUSION The dramatic changes in the expression of IGF-I, IGF-II and IGFBP-5 throughout postnatal development suggest that these factors play important roles in the development of this gland and that their actions are highly interrelated.