Synergistic stimulation of Swiss mouse 3T3 fibroblasts by epidermal growth factor and other factors in human mammary secretions

: The concentration of epidermal growth factor (EGF) in human mammary secretions was about 50 nmol/l for several weeks prepartum. It then fell to about 13 nmol/l within 4 days after parturition, in parallel with the decrease in protein concentration which is associated with the onset of lactation. In contrast, the concentration of EGF in urine samples from the same donors remained constant throughout this period. All the immunoreactive EGF in mammary secretions competed at the EGF receptors on Swiss mouse 3T3 fibroblasts. The stimulation of these cells by samples of mammary secretions was, however, much greater than that induced by EGF alone, indicating the presence of other factors which synergize with EGF. Gel filtration of mammary secretions revealed two major peaks of mitogenic activity, corresponding to EGF and a factor of higher molecular weight. The latter could synergize with added EGF, insulin or bombesin, and thus falls into a different functional class from any of these factors.