| Abstract: | The growth-promoting effect of growth hormones and related polypeptides was examined in vitro with a clonogenic assay using human erythroleukemic cells (K562). The erythroleukemia cells were grown in a serum-substituted methylcellulose culture system and colonies counted after 4 days' incubation. Human growth hormone (hGH) was a potent stimulant for K562 cell growth (60% augmentation). The cys(Cam)53-hGH(1-134) fragment of hGH and human chorionic somatomammotropin had less than half the activity of the intact hGH molecule. Bovine growth hormone was inactive in enhancing K562 colony formation. K562 cell proliferation was stimulated by hGH at concentrations as low as 0.1 ng/ml. Insulin stimulated K562 cell proliferation most effectively at a concentration of 1 ng/ml. The K562 culture system may conveniently be employed for determining the in vitro bioactivity of hGH. |
