In vitro Liver Synthesis and Serum Levels of Alpha Fetoprotein and Albumin in the Fetal Pig

Abstract

Serum levels and in vitro synthesis by the liver of alpha fetoprotein (AFP) and albumin in the fetal pig were compared at various stages of gestation. Liver slices and serum were obtained from fetuses from single litters at each of days 25, 30, 45, 55, 85 and 100 of gestation. The in vitro incorporation of [3H]leucine into AFP and albumin by liver slices was determined by immunoprecipitation. Serum samples were also obtained from each fetus in at least 5 litters at each of days 30, 35, 40, 50, 55, 75, 95 and 112. Serum levels of AFP were .apprx. 5 mg/ml during the 1st half of gestation and declined steadily during the 2nd half to less than 2 mg/ml by day 112. The incorporation of [3H]-leucine into AFP by liver slices incubated in vitro represented .apprx. 5% of the total protein synthesis in liver from day 25 fetuses. The fraction of AFP synthesized in vitro declined steadily as fetal age increased reaching 1% of total protein synthesis by day 100. Prior to day 40, serum albumin levels were less than 100 .mu.g/ml but increased rapidly to .apprx. 600 .mu.g/ml by day 55. During the 2nd half of gestation, albumin levels increased gradually to approach 1 mg/ml by day 110. In vitro synthesis of albumin was hardly detectable in liver slices from fetuses of days 25 and 30. At the later times investigated, albumin accounted for 0.1-0.25% of the total in vitro protein synthesis. The observed changes in serum levels of AFP and albumin in the fetal pig are due, at least in part, to changes in the capacity of the liver to synthesize and release these proteins. In litters having a large variation in fetal weight, a strong positive relationship between fetal weight and serum albumin levels was evident. Data collected on 21 litters between 76 and 86 days of gestation indicated a highly significant (P < 0.001) relationship between fetal weight and serum albumin levels when analyzed on a within-litter basis. The possibility of albumin serving as a specific marker of fetal growth rate is discussed.