Promotion of Myoblast Proliferation by Hypoxanthine and RNA in Chick Embryo Extract

In the course of our attempt to clarify the growth-promoting activities of chick embryo extract (EE), its heat-stable activity was found to be due to hypoxanthine and its related substances including RNA. When added to a basal culture medium composed of Eagle's MEM, horse serum and Fe-saturated ovotransferrin hypoxanthine or adenine (10 μM) markedly promoted quail myoblast proliferation. The concentration of hypoxanthine in EE was very high (274±34μM) and increased 2-fold during incubation at 37°C, while that in horse serum was very low (<3 μM). Guanine, xanthine and pyrimidines were ineffective. The nucleosides and nucleotides of hypoxanthine and adenine were effective, but the deoxynucleosides strongly inhibited the proliferation of avian myoblasts. Further, RNA was also effective but DNA was not. Hypoxanthine and RNA also promoted rat myoblast proliferation and the deoxynucleosides did not inhibit rat myoblast proliferation. These findings suggest that a supply of raw materials for RNA synthesis is important for optimal proliferation of myoblasts.