SUMMARY 1. Cultures of heart tissue from 13-day chick embryos have been grown for periods of 6 days in a medium of embryo extract and serum and in the presence of varying concentrations of insulin. 2. Doses of 1–3 i.u. insulin/ml. medium greatly stimulate the formation of phospholipids (LP), ribonucleic acid (RNA), deoxyribonucleic acid (DNA) and protein nitrogen (PN). This growth-promoting action of insulin is accompanied by a rise in the RNA : DNA ratio, and in the ratio of RNA to PN in the cells. 3. At doses of 1 × 10−2 i.u./ml. medium insulin increases the formation of LP, RNA and DNA, but there is no growth-promoting action with 1 × 10−4 i.u./ml. Insulins of British and Danish origin act similarly, and the presence of the hyperglycaemic factor associated with insulin (in a specially prepared extract) appears to have no action on the growing explants. 4. With higher concentrations of insulin, enhanced synthesis is accompanied by increased glucose utilization and by a pronounced fall in pyruvate content of the medium. The α-ketoglutaric acid level in the medium is unaffected by these changes. 5. It is concluded that insulin has a direct growth-promoting action on these embryonic cells, and that it stimulates increased energy production and general synthesis through its control over pyruvate metabolism.
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Leslie et al. (1954) studied this question.