title: Relationship of serum somatomedin-like activity and fibroblast proliferative activity with age and growth in the rat.
abstract: An assay for fibroblast proliferative activity (FPA) using human lung fibroblasts, WI-38, was described. The assay was responsive to varying rat serum levels and was not influenced by direct growth hormone (GH) addition. The relationship of serum growth factors to age and body weight was examined in the rat. In study 1, serum was obtained from lean Zucker rats at 3, 5, 7, 9, 11 and 30 wk of age. Six samples were taken at each age and serum samples were analyzed for somatomedin-like activity (Sm) and fibroblast proliferative activity (FPA). Serum Sm was not different at any of the sampling ages. FPA was low at 3 wk, but was higher and constant from 5 wk to 30 wk. In study 2, 73 lean Zucker rats (7 wk of age) were maintained on laboratory chow and water ad libitum for 4 wk, and then serum was obtained by decapitation. The rats were ranked according to each of four different criteria: average daily gain (ADG) for the duration of the study, ADG for the fourth week, total body protein and total body fat. Serum Sm, FPA and insulin concentrations on the top 10 and bottom 10 rats of each ranking were compared. Neither FPA nor insulin was significantly different for any ranking. Serum Sm was significantly higher in the top 10 rats ranked by ADG for the duration of the study. Sm was not significantly different in rats ranked by body weight, total body protein or total body fat. The data suggest that serum somatomedin-like activity (Sm) may be important in the earlier stages of growth in rats.
mesh_terms: D000367:Age Factors; D000375:Aging; D000818:Animals; D001835:Body Weight; D005347:Fibroblasts / Q000201:enzymology*; D006133:Growth Substances / Q000378:metabolism*; D051381:Rats / Q000254:growth & development* / Q000378:metabolism; D013002:Somatomedins / Q000096:biosynthesis / Q000097:blood*
chemical_list: D006133:Growth Substances; D013002:Somatomedins