Expression and regulation of insulin-like growth factor-binding protein-1, -2, -3, and -4 messenger ribonucleic acids in purified rat Leydig cells and their biological effects

The actions of insulin-like growth factor-I (IGF-I) are modified by binding proteins [IGF-binding proteins (IGFBPs)]. Previously, we reported that IGF-I enhances Leydig cell steroidogenesis and that IGF-I mRNA is expressed in Leydig cells. In the present study, we evaluated the expression and regulation of IGFBP-1, -2, -3, and -4 in purified rat Leydig cells and their biological effects. We found that none of the testicular crude interstitial cells, purified Leydig cells, or seminiferous tubules expressed IGFBP-1 mRNA. This indicated that IGFBP-1 mRNA is not expressed in the testis in detectable amounts. In contrast, large amounts of IGFBP-2 with a size of 1.8 kilobases (kb) were expressed in purified Leydig cells, and lesser amounts in crude interstitial cells. Small amounts of IGFBP-2 mRNA were expressed in seminiferous tubules, but none could be detected in liver. IGFBP-3 mRNA was predominantly expressed in purified Leydig cells, crude interstitial cells, and liver, while appreciable amounts were not f...