title: Direct stimulatory effects of insulin-like growth factor-I on Leydig cell steroidogenesis in primary culture.
abstract: Insulin-like growth factor-I (IGF-I) in concentration as low as 10 ng/ml significantly increased basal testosterone formation and 100 ng/ml of IGF-I increased testosterone production more than two fold in primary cultures of purified mature Leydig cells. IGF-I also markedly potentiated hCG-induced testosterone formation in a dose-dependent manner. Furthermore, IGF-I enhanced 8-bromo cyclic AMP induced steroidogenesis and hCG-stimulated cyclic AMP formation. The binding of 125I-IGF-I to purified Leydig cells was linear with a binding affinity of 0.56 +/- 0.07 X 10(9) M-1 and a capacity of 167 +/- 10.2 fmol/mg protein. Insulin and multiplication-stimulating activity were less potent than IGF-I in competing the binding of 125I-IGF-I to purified Leydig cells. This suggests that Leydig cells contain specific type I IGF receptor and IGF-I could modulate Leydig cell steroidogenesis.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D007985:Leydig Cells / Q000187:drug effects*; D008297:Male; D051381:Rats; D013002:Somatomedins / Q000494:pharmacology*; D013739:Testosterone / Q000096:biosynthesis; D014168:Transferrin / Q000494:pharmacology
chemical_list: D006063:Chorionic Gonadotropin; D013002:Somatomedins; D014168:Transferrin; D013739:Testosterone; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I