Transport of 125I-EGF into milk and effect of sialoadenectomy on milk EGF in mice.

Epidermal growth factor (EGF) (urogastrone) is found in high concentrations in mouse and human milk. The origin of milk EGF is unknown. Milk samples were collected from lactating mice 2-6 h after the intravenous administration of a tracer dose of 125I-labeled EGF. The milk contained relatively high levels of radioactivity of which 35-46% was precipitated by trichloroacetic acid-phosphotungstic acid (TCA-PTA) and 26% by a specific antimouse EGF antiserum. Part of the radioactivity in milk was eluted from a Bio-Gel P-10 column at the point at which pure standard 125I-EGF was eluted. These data indicate that the mammary gland of the lactating mouse is capable of sequestering and transporting 125I-EGF into milk. Administration of a thousand-fold excess of unlabeled EGF caused no reduction in TCA-PTA-precipitable radioactivity in milk samples of mice given 125I-EGF. When mice were given 10 micrograms of unlabeled EGF and milk was collected 4 h later, compared with controls the EGF level in milk was doubled. Administration of EGF had no effect on lactose and protein concentrations in the milk, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed no qualitative or quantitative changes in the major milk proteins. Milk collected from lactating mice that were sialoadenectomized 6 mo earlier contained about 50% less EGF compared with controls. After the administration of 125I-EGF high concentrations of radioactivity were also found in the mammary and submandibular glands and in the stomach. In the latter organs, however, 95-96% of the radioactivity was in the acid-soluble fraction.(ABSTRACT TRUNCATED AT 250 WORDS)