[Somatomedin inhibition of the growth hormone secretion stimulated by the hypothalamic factor somatocrinin or the synthetic peptide hpGRF].

In the in vitro monolayer pituitary cell culture system somatomedin-C and IGF-I are practically equipotent to inhibit the secretion of growth hormone stimulated by hypothalamic growth hormone releasing factor (GRF) or the synthetic peptide hpGRF-44 (3-200 x 10(-12)M). Highly purified somatomedin-C or IGF-I are active to inhibit the effect of GRF at concentrations of 0.5 to 10 ng/ml(1.0 x 10(-10) M - 1.3 x 10(-9) M) in either short-term (3-4 hrs.) or long-term (24 hrs.) incubation, with no statistical difference between the results obtained in either duration of incubation. IGF-II is less potent than IGF-I as an inhibitor of GRF. The effect of the somatomedins is specific for the secretion of growth hormone and is not duplicated by other growth factors such as epidermal growth factor (EGF) or fibroblast growth factor (FGF).