Effect of GH and insulin on the generation of somatomedin by perfused rat liver.

The release of somatomedin from perfused livers of normal and hypophysectomized (hypox) rats has been studied. Somatomedin was determined by the radioreceptor assay for somatomedin A. The release of somatomedin in the perfusates of normal livers was observed during the initial 30 minutes and maintained during the second and third 30 minutes of recirculation. The addition of insulin at a concentration of 10 mU/ml to the perfusates caused a significant increase in the release of somatomedin in the 1st, 2nd and 3rd 30-minutes recirculatory perfusates. The addition of human growth hormone (25 micrograms/ml) and/or insulin (1 mU/ml) to the perfusates caused a significant increase in somatomedin after 120 minutes of recirculation. Hypox rats released amounts of somatomedin in perfusates similar to those of normal rats. The effect of insulin on the release of somatomedin was greater in hypox rats than that observed in normal rats. The molecular size of the somatomedin released in the perfusate was greater than that of purified somatomedin, suggesting that this somatomedin is bound to carrier proteins.