Growth retardation is a major manifestation of Turner syndrome (TS). Since plasma growth hormone and somatomedin-C/insulin-like growth factor I (SM-C/IGF-I) levels are generally normal, growth failure has been ascribed to peripheral defects in SM-C/IGF-I receptors or action. We have measured the binding of [125I]SM-C/IGF-I to cultured fibroblast monolayers derived from patients with Turner syndrome and have evaluated SM-C/IGF-I stimulation of both [3H]thymidine incorporation and cell replication. When compared to fibroblasts from normal adults, newborns, and age-matched children, no significant differences were observed in specific binding of [125I]SM-C/IGF-I to fibroblast monolayers, and displacement curves demonstrated similar receptor affinities for all groups. Similarly, equivalent SM-C/IGF-I stimulation of [3H]thymidine incorporation was seen in both Turner and control fibroblasts. In the absence of serum SM-C/IGF-I, at a concentration of 10-25 ng/ml, stimulated thymidine incorporation 3.7-11.8-fold in Turner fibroblasts and 1.9-9.8-fold in control cells. In conbination with 1.0% human hypopituitary serum (HHS), SM-C/IGF-I stimulated thymidine incorporation 20-70-fold in all cell lines. Cell replication in both TS and control cells was increased 90% by the combination of SM-C/IGF-I + 0.05% HHS, and 140% by SM-C/IGF-I + 0.5% HHS + dexamethasone. We conclude that TS fibroblasts have normal SM-C/IGF-I receptors and sensitivity, and are capable of enhanced DNA synthesis and replication following SM-C/IGF-I stimulation.
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