The profile of appearance and disappearance of α-fetoprotein (AFP) in the serum of analbuminemic rats, which have a genetically controlled lack of serum albumin, was studied. During the perinatal stage, AFP was present in the serum of analbuminemic rats, its concentration at birth being 10 mg/ml as in normal rats. In analbuminemic rats, the concentration of serum AFP remained at about 10 mg/ml during the first week after birth and then decreased rapidly during the next 2 weeks, becoming undetectable about 4 weeks after birth. In normal rats, the serum AFP concentration reached a maximum of 11.5 mg/ml at birth and then decreased sharply to an undetectable level within 4 weeks after birth, although a small rebound of AFP concentration was observed about 1 week after birth. AFP synthesis in analbuminemic and normal rats was examined by injecting [3H]leucine i.p. and then measuring the radioactivity incorporated into the acid-insoluble fraction and immunoprecipitable fraction using anti-AFP antiserum. In analbuminemic rats, synthesis of AFP amounted to 7.5% of the total protein synthesis at birth and was maintained at about 7% of the total for the first week after birth and then decreased to 2% at 2 weeks after birth. In normal rats, AFP synthesis also amounted to 7.5% of the total protein synthesis at birth but decreased to about 2% at 2 days after birth and then remained at a low level for about 2 weeks. In both normal and analbuminemic rats, AFP synthesis was undetectable at 4 weeks after birth. These data show that AFP synthesis is shutoff after birth irrespective of the serum albumin concentration during neonatal development.
Supported in part by grants from the Princess Takamatsu Cancer Research Fund, the Ministry of Education, Science and Culture of Japan, and the Japanese Association for the Study of Metabolism and Disease.