title: Presence of insulinlike growth factor receptors and lack of insulin receptors on fetal bovine smooth muscle cells.
abstract: Previous investigations have demonstrated specific receptors and associated mitogenic actions for insulin and insulinlike growth factors I and II (IGF-I and II) in postnatal bovine aortic smooth muscle. Using fetal tissue we have observed different patterns of binding and action for these peptides. Smooth muscle cells isolated from near-term fetal bovine aortae were studied in early passage. Specific receptors for both IGF-I and IGF-II were identified. Specific binding averaged 5.7%/2.5 X 10(5) cells for IGF-I, and 16.2% for IGF-II, and 0.3% for insulin. High affinity Kd for both IGF receptors were nanomolar. IGF-II was fivefold less potent than IGF-I in displacing IGF-I binding. IGF-I showed no affinity for the IGF-II receptor. Insulin, at physiologic concentrations, was incapable of displacing either IGF-I or IGF-II binding. Cellular incorporation of [methyl-3H]thymidine was stimulated at the lowest dose of IGF-I tested, 0.5 ng/ml. IGF-II showed no effect up to 100 ng/ml, after which a sharp increase in incorporation was noted. Insulin had a similar effect only at concentrations greater than 0.5 micrograms/ml, with a maximal response noted at 5 to 10 micrograms/ml. Our results indicate that fetal bovine aortic smooth muscle cells have an abundance of IGF receptors but lack specific insulin receptors. In addition, IGF-II binding levels are three times higher than for IGF-I. These results are consistent with observations in other species, in which a predominance of IGF over insulin receptors has been demonstrated in fetal tissue, and provide further evidence for a role for the IGFs in embryonic cellular metabolism.
authors.affiliation: Department of Pediatrics, Stanford University, California 94305.
authors.forename: P D
authors.initials: PD
authors.lastname: Lee
authors.forename: R L
authors.initials: RL
authors.lastname: Hintz
authors.forename: R G
authors.initials: RG
authors.lastname: Rosenfeld
authors.forename: W E
authors.initials: WE
authors.lastname: Benitz
mesh_terms: D000818:Animals; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D005333:Fetus; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000032:analysis* / Q000196:embryology; D011972:Receptor, Insulin / Q000032:analysis*; D017451:Receptors, Somatomedin; D013936:Thymidine
chemical_list: D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D011972:Receptor, Insulin; D013936:Thymidine