Induction of Vasoactive Intestinal Peptide Gene Expression and Prolactin Secretion by Insulin-Like Growth Factor I in Rat Pituitary Cells: Evidence for an Autoparacrine Regulatory System*

The effects of recombinant human insulin-like growth factor I (IGF-I) on both vasoactive intestinal peptide (VIP) and PRL production and gene expression were studied using rat anterior pituitary cell cultures grown in serum-free defined medium. We also examined whether pituitary VIP could be involved in the PRL response to IGF-I and hence in a paracrine regulatory system. Exposure of cultured anterior pituitary cells to IGF-I (2.6 nM) for 3 h caused a significant decrease in both VIP content and media PRL. Treatment with IGF-I (from 0.65-5.2 nM) for 48 h increased VIP production and VIP messenger RNA (mRNA) accumulation, whereas only an increase in media and intracellular PRL content without changes in mRNA was observed. In all these experiments, IGF-I led to a decrease in both GH secretion and expression. Immunoglobulins G purified from VIP antiserum inhibited IGF-I-induced PRL release without affecting intracellular and mRNA levels. The inhibition of both GH secretion and gene expression induced by IGF-...