Changes in EGF receptor and its messenger RNA in human placeuta during pregnancy.

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The following facts have been revealed in mice that epidermal growth factor (EGF) has a physiological role in milk secretion and that EGF is physiologically important to maintain pregnancy. It also has been reported that human placenta is very rich in EGF receptor. These findings lead us to study the changes in EGF receptor levels in human placenta to know the physiological importance of EGF in human pregnancy. So far many works have been performed on this theme. However, the results obtained are not consistent. Therefore, we investigated the changes in EGF receptor messenger ribonucleic acid (RNA) levels during pregnancy by Dot and Northern blotting in addition to the conventional binding assay. Also we studied the changes in EGF receptors of isolated trophoblast cells according to the fact that EGF receptor in mainly expressed on the trophoblast cells in human placenta. As a result we obtained the following data.1. although the dissociation constants were not significantly different among the 3 stages (early, middle and late stages of pregnancy), maximal binding sites increased with the progress pregnancy; 0.72(early), 1.02 (middle) and 1.89 pmol/mg protein (late).2. The maximal binding sites in trophoblast cells also increased during pregnancy; 0.82 (early), 1.91 pmol/mg protein (late). This increase was parallel to that in whole placenta.3. The amounts of messenger RNA increased during pregnancy; the ratio was 1:2:2.1 (early:middle:late) and this increase was proportional to that in EGF receptor.These results clearly show the fact that EGF receptor increases during pregnancy and we suggest that EGF may play an important role in feto-placental developments in human pregnancy.