Fetal absorption of 3H-leucine injected into the amniotic sacs of pregnants rats.

When injected into the amniotic sacs of fetal rats in late pregnancy, 3H-leucine is rapidly absorbed and incorporated into fetal proteins as determined by liquid scintillation spectrometry. Peak values in the fetal liver and pancreas occur around four hours after injection. Approximately 21% of the radioisotope is retained in the injected fetus at 24 hours. The remainder escapes into the maternal circulation and accounts for a gradual increase in levels in noninjected fetuses from the same litter and for persistently high counts found in maternal serum as late as 24 hours after the injection. Specific activity of the radioisotope in fetal tissues is considerably higher (100- to 200-fold) when 3H-leucine is injected inth the amniotic sac rather than intravenously into the mother. The possible treatment of various fetal disorders by means of intra-amniotic injections is discussed.