Distribution of bilirubin-H³ in the fetal and maternal rat

Abstract

Bilirubin-H3 in maternal or fetal serum was injected in physiologic amounts into the jugular vein of 19- or 21-day-old fetal rats, and distribution of activity in fetal and maternal tissues was measured. Two hours after injection, 93–98% of the activity was recovered in whole fetal homogenates. Activity was not detectable in either maternal serum or liver, indicating less than 2.5% of the total dose was in either tissue. Approximately 1–4% of the total dose appeared in maternal bile. In other experiments, activity in fetal tissues, after correction for trapped serum bilirubin-H3, was: carcass 27%, serum 21%, liver 10%, and intestine 2.5%. Significant activity was detectable in lungs, brain, kidney, and stomach, and traces were noted in heart, placenta, umbilical vessels, and spleen. Based on rate of bilirubin secretion and synthesis in adult rats, fetal synthesis would be 2.5–10 times placental transfer. Results suggest that placental transfer of bilirubin or bilirubin metabolites may not completely explain the low levels of bilirubin found in fetal circulation but indicate that a slow rate of bilirubin production or increased bilirubin storage in fetal tissue are contributing factors.

Transient Familial Neonatal Hyperbilirubinemia*

“…This inhibition is superimposed on a normally occurring delayed development of the hepatic glucuronide conjugating system, particularly glucuronyl transferase activity. The placenta is believed to transfer unconjugated bilirubin from fetus to mother, whose liver conjugates and excretes bilirubin (26,27).…”

Autoradiography with 14C-bilirubin in pregnant normal Wistar rats and Gunn rats with and without phenobarbital or albumin administration

“…Under normal circumstances, unconjugated bilirubin, like other lipid solubile substances, passes from the fetal to the maternal side of the placenta. This has been confirmed by experiments with 8H-bilirubin in rats (Grodsky et al, 1963) and 14C-bilirubin in guinea pigs (Schenker, 1963) and monkeys (Lester et al, 1963). On the other hand, the placenta is impermeable to the water-soluble conjugated bilirubin.…”

Studies in vivo of the effect of unconjugated bilirubin on hepatic phosphorylation and respiration.

“…Only traces of direct-reading bilirubin were found in plasma of bilirubin-infused newborn guinea-pigs. The mean isotope at the end of 60 minutes in plasma and liver, disregarding the small contribution of trapped intrahepatic plasma (Grodsky, Contopoulos, Fanska, and Carbone, 1963) and bile (Barber-Riley, 1963) which, extrapolating from rat data, constitute less than 1 % of injected label, was 23-8 and 21-3 % of injected radioactivity, respectively. Inasmuch as liver, assessed in nine animals, and plasma constitute, respectively, 4-3 and 5-7 % of newborn guinea-pig weight, it appears that the isotope concentration in both compartments was similar on average.…”