Course of epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) in mammary secretions of the goat during end-pregnancy and early lactation

The epidermal growth factor (EGF) plays a crucial role in mammogenesis in m any species. In ruminants, studies are limited, as EGF does not occur in pe ripheral plasma and specific analytical systems do not exist. Therefore a h eterologous radioimmunoassay based on rhEGF was set up to monitor EGF in ma mmary gland secretions from goats during end-pregnancy and early lactation. IGF-I was measured with an established radioimmunoassay. Samples were coll ected from 13 goats for 25 days ante-partum and 25 days post-partum. Mammar y gland secretions were obtained ante-partum by removing a small amount of the udder secretions (control half) or milking (stimulated half). Post-part um normal milk samples were collected. Blood samples were drawn by jugular venipuncture for the same period. EGF was found to occur in different molec ular weight forms in the mammary glands. For routine measurements these pro teins were extracted with acetone and not further separated. IGF-I and EGF concentrations in mammary secretions and similarly IGF-I in blood were high ante-partum and decreased slightly towards birth. IGF-I but not EGF is fou nd in the peripheral plasma. Whereas IGF-I concentrations in blood were qui te constant post-partum, IGF-I and EGF dropped in mammary secretions close to the detection limits. The decrease was more pronounced in the stimulated half than in the control half. The data support a synergistic role for EGF and IGF-I for mammogenesis. Both factors are further influenced by the mil king stimulus and thus the functional state of the udder.