Proteinase inhibitors in the gastrointestinal tract, pancreas and liver during fetal and postnatal development of the pig.

The occurrence and types of proteinase inhibitors were studied in the digestive system during the fetal and postnatal development of the pig. The protein concentration, the total trypsin-inhibiting capacity and the levels of the individual proteinase inhibitors, alpha 2-macroglobulin f (alpha 2Mf), alpha 2-macroglobulin s (alpha 2Ms), alpha 1-protease inhibitor (alpha 1PI) and alpha 2-antitrypsin (alpha 2AT) quantified by using electroimmunoassay, were assayed in stomach and intestinal contents, in homogenates of the stomach and intestinal mucosa, and in the pancreas and liver. The results showed that during porcine ontogeny high amounts of proteinase inhibitors are present in the digestive system. During the fetal period, the most outstanding characteristic was the high levels of alpha 1PI and alpha 2AT, in contrast to the low levels of the alpha 2-macroglobulins. Furthermore, the trypsin-inhibiting capacity and the levels of alpha 1PI and alpha 2AT showed in most cases a statistically significant decrease during the fetal period (12-36 cm crown-to-rump length). In the neonatal period, 0-96 h after birth, the levels of the individual inhibitors were rather constant, but a significant decrease to low levels of both trypsin inhibition and the individual inhibitors was observed in the adult pig. Trypsin activity was found in approximately half of the pancreas homogenates from the late fetal period and in newborn pigs before they began to suckle. The physiological function of the proteinase inhibitors observed in the digestive system during porcine ontogeny is probably to protect against precocious proteolytic degradation by the formation of inactive enzyme/inhibitor complexes.