Summary. The synthesis of alpha1-fetoprotein (AFP) was measured by radioimmunoassay in tissues and fluids of 19 bovine embryos (14–46 days of gestation) and in tissue cultures of 4 pre-implantation embryos (17–27 days) by incorporation of radioactive methionine. AFP was first detected in Day-14 trophoblasts and secretion of AFP into allantoic fluid occurred by Day 16. Embryonic tissues and fluids in pre-implantation and post-implantation embryos contained levels of AFP that were 550 to 1 500 000 times higher than those found in maternal serum (3·9–298 000 compared with 0·07–0·25 ng/mg protein). High levels of AFP were also found in uterine fluid which suggested significant transfer of this protein from the early post-implantation conceptus. The major sites of AFP synthesis were yolk sac and fetal liver. It is concluded that the synthesis of bovine AFP is not initiated by events associated with implantation.
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