Epidermal growth factor receptor levels in mouse mammary glands in various physiological states

Experiments were undertaken to demonstrate and characterize specific receptors for epidermal growth factor (EGF) in mammary glands of female BALB/c mice in various physiological states. The results of an in vitro desaturation technique are also presented which allow estimation of the total EGF-binding sites per mg membrane protein. Binding of the ligand [125I]iodo-EGF is both time and temperature dependent. Maximum binding to the membrane is achieved after 6 h of incubation with [125I]iodo-EGF at 23 C. Scatchard analysis of equilibrium binding using membrane preparations of mammary glands from virgin mice yields two classes of high affinity receptors with Kd values of 0.8 +/- 0.1 and 5.0 +/- 0.4 X 10(-10) M and receptor concentrations of 10 +/- 1.2 and 23.5 +/- 2 fmol/mg protein, respectively. Membrane preparations of mammary tissues from cycling, gestating, and lactating mice were used to correlate cellular receptor levels to the physiological state of the animal. Beginning at weaning, there is a constant decrease in high affinity receptor level with increasing age, as well as through the early stages of both gestation and lactation. On day 10 of gestation, receptor levels increase, reaching 15.2 +/- 1.6 fmol/mg protein, followed by a decrease to 3.8 +/- 0.9 fmol/mg protein on day 10 of lactation. We conclude that membrane preparations from the mouse mammary gland contain specific high affinity receptors for EGF, and that receptor levels are characteristic of the physiological state.