Evolution of alpha-fetoprotein serum levels throughout life in humans and rats, and during pregnancy in the rat.

Abstract

A radioimmunoassay method (RIA) with specific antisera for human and rat alpha fetoprotein (AFP) was used to study the evolution of AFP levels in humans and rats, respectively, throughout the life span. Sera of 66 rats, aged 3-70 weeks, as well as sera of 201 clinically well children, 192 healthy blood donors, and 16 persons aged 70-98 were assayed. In humans, AFP levels decreased steeply during the 1st year of life, reaching a low basal range by the end of the 2nd year which is maintained throughout adulthood. Rats showed a similar pattern, but concentrations were higher at every stage of life. Puberty occurs in rats while AFP is still decreasing, whereas in humans the adult basal level is stabilized long before puberty. Maternal serum AFP was studied in 29 rats, and the levels were found to begin a sharp increase on the 10th-13th day of gestation. From Day 13-19, a deceleration of AFP increase was observed which led to a decrease between Day 17 and 19. From Day 19-21, AFP levels increased sharply again. A significant correlation was observed on Day 21 of pregnancy between the number of rat fetuses and the maternal AFP level. Hemihysterectomy led to a reduction of AFP level that was grossly proportional to the number of remaining fetuses. The stable level of AFP that persists throughout adult life is attributed to the stability of this protein's synthesis. Conversely, in pregnancy the evolution of serum AFP curve is dependent on the fetal synthesis, maternal and fetal catabolism, and permeability of the placental barrier.