Effect of rat age on blood levels of somatomedin-like growth factors.
Age-related changes in serum levels of somatomedin-like growth factors were measured using a bioassay based on myoblast proliferation in culture. The correspondence of this assay to thymidine incorporation and sulfation factor assays for somatomedins was demonstrated. Comparisons involved individual serum samples from a total of 28 rats at each of three age ranges (young = 2 to 6 month, middle-aged = 12 to 16 month, and old = 24 to 28 month) in five separate experiments. A small (10%) decrease in levels of somatomedin-like activity was observed between young and middle-aged animals, with a greater (20 to 40%) subsequent decrease in old rats. Assays of mixed samples indicated that the age-related decreases in somatomedin-like activity could not be attributed to increases in circulating levels of a dissociable inhibitor of this activity. Paired comparisons of amino acid uptake by isolated omohyoideus muscles from rats of the specified ages suggested that there were no significant age-related changes in response of these muscles to a somatomedin analog.
D000375:Aging; D000818:Animals; D002478:Cells, Cultured; D046508:Culture Techniques; D006131:Growth Inhibitors / Q000494:pharmacology; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D013002:Somatomedins / Q000037:antagonists & inhibitors / Q000097:blood*
D006131:Growth Inhibitors; D013002:Somatomedins