Protein synthesis in the gastrointestinal tissues of the ovine fetus

An isotope dilution procedure employing an 8h continuous infusion of L-[2,3,5,6-3H] tyrosine was used to determine fractional protein synthetic rates in the gastrointestinal tissues of ovine fetuses. The infusions were made into the inferior vena cava of the fetuses at 120-130 days of gestation. Immediately following the termination of the infusion the ewes were sacrificed and fetal tissues were collected, frozen in liquid nitrogen and stored at -20 C. The specific activity of the intracellular free and protein bound amino acid pools was determined from which the fractional synthetic rates (%/day) were calculated. These rates were as follows: reticulo-rumen, 49%; omasum, 10%; abomasum, 14%; proximal duodenum, 93%; and distal colon, 15%. The contribution of duodenum to the whole body protein synthesis was 10.5% while the contribution of the entire GIT (13.9%) was very close to that of liver (14.4%). The specific activity of tyrosine in the amniotic fluid and fetal ruminal fluid averaged 22% and 36% respectively of the specific activity in the plasma. The high turnover of tissue proteins in the fetal gastrointestinal tract as well as the presence of labelled tyrosine in the ruminal fluid indicate the functional importance of gastrointestinal activity in utero preparing the gastrointestinal tract for post-natal life.