Somatomedins: A New Look at Old Questions
The somatomedins were originally recognized as GH dependent serum factors which mediated GH action on cartilage in-vitro, while the source of these serum factors was at first unknown, the liver was widely suspected. McConaghey and Sledge1 in 1970 reported that rat livers released somatomedins bioactivity during perfusion and the release was increased by GH. This finding has been confirmed with more specific assay methods and extended to studies of isolated hepatocytes2. Modern molecular biological probes have confirmed GH regulation of IGF-I gene expression in rat and mouse liver. The role of the liver as the major source of serum IGF-II is less well established in man because most of the studies of IGF-II gene expression have been done in rats and mice. In this species, IGF-II m RNA drops to a very low level in all tissues except choroid plexus and meninges3. The fact that IGF-II is not elevated in acromegaly and only decreases to about 50% of normal in hypopituitary patients is indicative of reduced GH dependence.
KeywordsChoroid Plexus Longitudinal Bone Growth Fibrosarcoma Cell Line Hypopituitary Patient IGFI Action
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