title: Effect of rat age on serum levels of growth hormone and somatomedins.
abstract: The somatomedins are a family of hormones which appear to mediate many of the anabolic actions of growth hormone; these processes often exhibit an age-associated deterioration in intact animals. We have demonstrated the validity of a radioreceptor assay for the determination of somatomedin levels in rat serum. In this assay, we measure displacement of 125I-labeled Multiplication Stimulating Activity (MSA) from receptors prepared from human placental membranes. Results with this procedure confirm and extend a previous report from this laboratory indicating a significant decrease in somatomedin levels during the latter part of the lifespan. Data are presented to eliminate possible artifactual explanations for the observed age-related changes. Furthermore, we find that the decrease in somatomedin levels can not be a simple result of an age-related decrease in basal levels of growth hormone in serum. We conclude that the decrease with age in circulating levels of the somatomedins is most probably attributable to a decrease in the activity of responsiveness of the tissues (most probably liver) which secrete somatomedins in response to stimulation by growth hormone.
mesh_terms: D000375:Aging; D000818:Animals; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D007335:Insulin-Like Growth Factor II; D008297:Male; D010455:Peptides / Q000378:metabolism; D011869:Radioligand Assay / Q000379:methods; D051381:Rats; D011916:Rats, Inbred F344; D013002:Somatomedins / Q000097:blood*
chemical_list: D010455:Peptides; D013002:Somatomedins; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone