Stimulation of Chick Embryo Cartilage Sulfate and Thymidine Uptake: Comparison of Human Serum, Purified Somatomedins, and Other Growth Factors*

Publisher Website
Google Scholar
Abstract
The stimulation of SO4 and thymidine uptake into 10 day old embryonic chick cartilage by normal human serum partially purified somatomedins (Sm) A and B, homogeneous insulin-like growth factors (IGF) I and II and several other substances were compared. With the exception of epidermal growth factor, all growth factors (GF) were assayed in the absence of other protein. Pelvic rudiments were preincubated in buffer for 6 h and then incubated for 24 with the GF or serum with labels added for the final 6 h. Human serum enhanced cartilage uptake of thymidine and SO4. There was a dose-dependent stimulation of thymidine uptake by Sm A or B (0.05-1 .mu.g/ml) and IGF I or II (0.5-20 ng/ml). Unlike serum, neither Sm nor IGF increased SO4 uptake under these conditions. Bovine GH (10-500 ng/ml), albumin (100-1000 ng/ml), fibroblast GF (1-100 ng/ml) and epidermal GF (1-100 ng/ml) were inactive for thymidine and sulfate. When a shorter incubation was used (7 h), Sm A enhanced SO4 uptake and discrimination was increased by preincubation of the rudiments in buffer for 24 h. With this procedure, IGF I (0.5 ng/ml) was nearly equipotent to 5% serum. On a weight basis, IGF I was more active than either SM A or IGF II. Apparently, assay conditions are crucial for demonstration of Sm activity. Appropriate conditions may be different for isolated GF than for a complex medium such as serum. With certain protocols, the responsiveness of chick embryo cartilage may be qualitatively similar to that of hypophysectomized rat cartilage.