Abstract: | Employing defined media conditions, the insulin sensitivities of mouse mammary gland epithelial cells in primary culture and MCF-7 human mammary epithelial cells were determined. Insulin stimulated the rates of (3H] uridine incorporation into RNA and 3H] leucine incorporation into protein in both primary mouse mammary gland epithelial cell cultures and MCF-7 cell cultures at concentrations approximating the dilution endpoint of the hormone (10-21 M). Insulin stimulated the rate of 3H] thymidine incorporation into DNA in primary mouse mammary gland epithelial cells at the dilution endpoint concentrations. However, MCF-7 cells required insulin concentrations 100-1000-times that necessary in mouse mammary epithelial cultures to elicit an increased rate of 3H] thymidine incorporation into DNA. Evidence is presented which suggests that the increased rates of uptake of 3H- uridine, 3H] thymidine and 3H] leucine into their respective precursor pools is not responsible for the apparent stimulation of RNA, DNA and protein synthesis. |