EPIDERMAL GROWTH-FACTOR IN MAMMARY-GLANDS AND MILK FROM RATS - THE INFLUENCE OF INSULIN

Epidermal growth factor (EGF) is one of the major growth-promoting age nts in milk. Using immunohistochemistry we localized EGF in the mammar y glands of lactating rats to the luminal border of the secretory cell s. Following proteolytic pretreatment of the histological sections, th e EGF-immunoreactivity was revealed homogeneously in the cytoplasm of the secretory cells, which might suggest that EGF is present as a prec ursor molecule in the mammary glands. Altered glucose metabolism durin g lactation results in secondary hypoinsulinaemia in the lactating rat . As insulin is also known to affect lactation in several species, we treated normal lactating rats daily with insulin and studied the effec t on the composition of milk. A significant increase in the content of total protein and milk fat was observed after a few days of insulin-t reatment, as compared to a control group [total protein: 50 (36-97) g/ l vs. 42 (35-72) g/1], [milk fat: 35 (22-40)% vs. 29 (23-36)%], [media n (range)]. On day 16 the EGF concentration in milk was significantly increased in insulin-treated rats, as compared to controls [2.66 (1.40 -5.08) nM vs. 1.98 (1.04-3.16) nM]. A similar significant increase was found for the secretion of the cobalamin-binding protein, haptocorrin (HC) 137.7 (15.8-110.4) nM vs. 23.5 (15.5-70.1) nM]. In conclusion, t he highly insulin-sensitive lactating mammary glands were affected by exogenous insulin, since the milk concentrations of EGF, HC, total pro tein and the fat percentage were increased.