The serum half-life of somatomedin activity: evidence for growth hormone dependence.
The serum half-life of somatomedin (SM) activity has been measured following the intravenous injection of SM activity into hypophysectomized rats. A [3H]thymidine incorporation assay in chick embryo fibroblasts (CEFs) has been utilized to measure SM activity. Cell cycle analysis data obtained with the flow microfluorometer shows that the [3H]thymidine incorporation data reflects actual DNA synthesis. When normal rat serum was injected, a half-life for SM activity of approximately 3 h was determined. In marked contrast, when serum from hypophysectomized (hypox) rats acutely treated with growth hormone (GH) was used as the source of SM actively, the half-life of the SM actively was short, approximately 8 min. However, when serum from hypox rats chronically treated with GH was injected, the half-life was again long, approximately 4 h. SM activity has been separated from its binding proteins by boiling under acid conditions or chromatography on Sephadex G-50 in 1 N acetic acid. The half-life of this partially purified SM activity was short, in the range of 10-30 min finally, recombination of the partially purified sm activity with the large proteins in normal serum extended in half-life of the sm from 10-03 min to about 2 h. These data indicate that the serum half-life of SM activity is GH dependent and suggest that the serum binding protein, like SM itself, is under GH control.
D000818:Animals; D001681:Biological Assay; D002642:Chick Embryo; D002850:Chromatography, Gel; D046508:Culture Techniques; D004247:DNA / Q000096:biosynthesis; D005347:Fibroblasts / Q000378:metabolism; D005470:Fluorometry; D013006:Growth Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006207:Half-Life; D007016:Hypophysectomy; D007275:Injections, Intravenous; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D013002:Somatomedins / Q000008:administration & dosage / Q000097:blood*; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors
D013002:Somatomedins; D013006:Growth Hormone; D004247:DNA; D013936:Thymidine