DIFFERENT SIGNAL-TRANSDUCTION BY EPIDERMAL GROWTH-FACTOR MAY BE RESPONSIBLE FOR THE DIFFERENCE IN MODULATION OF AMINO-ACID-TRANSPORT BETWEEN FETAL AND ADULT HEPATOCYTES

[1-C-14]-2-aminoisobutyric acid (AIB) uptake and signal transduction p attern after epidermal growth factor (EGF) stimulation were examined i n freshly isolated hepatocytes from 20-day-old fetuses and 3-month-old rats. EGF induced a transient increase of AIB transport after 10 min only in adult animals; the observed unresponsiveness of fetal liver is not dependent on a lack of EGF receptors which are present though to a lesser extent on the plasma membrane in this period. As far as the p roduction of the second messengers, inositol trisphosphate (IP3) and c alcium, is concerned, substantial differences were found: EGF increase d IP3 production in adult hepatocytes, whereas it had no effect in fet al ones. Moreover, the addition of EGF induced a calcium transient in hepatocytes from adult animals, while there was no increase in fetal c ells. The lack of EGF effect on amino acid transport in fetal cells co uld be due to its inability to produce both IP, and calcium transients , suggesting that this transduction pathway is not activated during fe tal life.