Foetal bile pigment handling after administration of (14C)haemin

1. Advanced techniques for intra-uterine surgery were used to study haem degradation in foetal sheep prepared in utero with indwelling jugular, carotid and biliary cannulas. [(14)C]haemin was administered I.V. to the foetus, and plasma disappearance, biliary excretion, placental transfer and tissue distribution of radioactivity were measured over a 5-8 hr period.2. 8-30% of the (14)C-label was recovered in foetal bile, about 40% of this as bilirubin and the rest as unidentified [(14)C]haemin derivatives. 4-21% was transferred across the placenta, appearing in maternal bile almost exclusively as [(14)C]bilirubin. Excretion of (14)C-label totalled 18-33%.3. Six adult sheep infused with [(14)C]haemin excreted 19-49% of the dose in the bile over 8 hr, one third as bilirubin.4. The amount of endogenous bilirubin excreted per unit time/unit wt. of foetal liver increased with increasing foetal wt.5. It is concluded that near-term foetal sheep have a maturing mechanism for haem catabolism. Haem is partially excreted in foetal bile as bilirubin. Another fraction is transferred across the placenta, probably after prior conversion to bilirubin. The remainder is converted to un-identifiable end-products. Total excretion is approximately as effective as that in adults.