Levels of serum protease inhibitors during fetal and postnatal development of the pig.

Using electroimmunoassay the levels of the individual protease inhibitors alpha-2-macroglobulin f, alpha-2-macroglobulin s, inter-alpha-trypsin inhibitor, alpha-1-protease inhibitor and alpha-2-antitrypsin were studied in the serum and the amniotic fluid during the fetal and postnatal development of the pig. High concentrations, far above the adult ones, of alpha-2-antitrypsin and especially alpha-1-protease inhibitor, were observed in serum during the fetal period, contrary to the low levels of the alpha-macroglobulins. Thus, the development of these inhibitors in pigs differs markedly from the development in the human fetus. After birth, when the piglet had begun to suckle, the levels of all the inhibitors, except that of alpha-2-macroglobulin s, decreased. This can partly be explained by the dilution of the serum due to the increase in plasma volume and losses via the urine. The sharp increase of alpha-2-macroglobulin s during the first days after birth probably represented an extensive synthesis. All the inhibitors had attained their adult levels at about 35 days after birth. All the protease inhibitors studied, except for alpha-2-macroglobulin s, were found in the amniotic fluid, and reached the maximal levels at about 55-66 days of gestation. These inhibitors appeared to have fetal origin. The physiological significance of the protease inhibitors during fetal and neonatal development of the pig is discussed. it is suggested that the function of these inhibitors might be to protect the cells and tissues from proteolytic attack by the formation of inactive enzyme/inhibitors complexes.