Hormone-Induced Synthesis of DNA by Mammary Glandin Vitro

The hormonal requirements for stimulation of DNA synthesis in mouse mammary explants were further studied. Addition of insulin or growth hormone to the synthetic medium augmented the rate at which epithelial cells initiated DNA synthesis, but did not alter the rate of DNA replication. DNA synthesis increased linearly over a wide range of growth hormone concentrations, with a minimal effective concentration of approximately 4 × 10−9m. Although insulin induced larger numbers of epithelial cells to initiate DNA synthesis, its minimal effective concentration was higher, at approximately 4×10−8m (0.1 μg/ml). Experiments with inhibitors of protein synthesis indicated that concurrent protein synthesis is necessary for the initiation of DNA synthesis and for completion of DNA replication in these cells. (Endocrinology 82: 540, 1968)