Growth stimulating activity in bovine pituitary extract specific for a rat mammary carcinoma cell line

We report the isolation of a bovine pituitary growth factor (MGF) for a rat mammary carcinoma cell line, 64-24, which was isolated from a highly hormone-dependent mammary tumor. The MGF has been partially purified by a series of Diaflo ultrafiltration membrane sievings, isoelectric focusing and Sephadex columns. The MGF has a molecular weight of approximately 1,000 to 2,000 daltons and has a U.V. absorption spectrum typical for a polypeptide. Its isoelectric point is approximately pH 3.8-4.0. The factor is heat stable. The growth stimulating activity of the MGF does not stimulate other rat cell lines (22-1, RMG or HTC lines) but is specific for the 64-24 mammary tumor cell line. The MGF is not among previously reported pituitary hormones or growth factors.