Uptake, transfer and metabolism of prostaglandin E₂ in the isolated perfused human placental cotyledon

(³H) PGE₂ uptake and transfer in the isolated perfused human placental cotyledon was assessed by a ingle pass paired isotope dilution technique utilising (¹⁴C) sucrose as an extracellular marker. Metabolism of (³H) PGE₂ was measured by analysing maternal and fetal effluents from perfused human placental cotyledons after bolus injection of (³H) PGE₂ into ither the maternal or fetal sides. Maximal uptake of (³H) PGE₂ was greater on the maternal (81 +/- 8%) than the fetal sides (42 +/- 12%) and showed saturation with increasing concentrations of PGE₂ only on the fetal side with an apparent Km of 12 +/- 4.9 nmol/l and v_max of 1.5 +/- 0.2 pmol/min/g. Total recoveries of (³H) PGE₂ were 84.6 +/- 11.8 % and 32.6 +/- 6.3 % of the injected dose after injection on the fetal and maternal sides respectively.Transferof (³H) PGE₂ was the same in both directions being 6.4 +/- 1.2 % of the injected dose in the fetal-maternal direction and 5.8 +/- 2.7 % of the injected dose in the maternal-fetal direction. Metabolism was greater on the maternal side (35% of injected (³H) PGE₂) thanthe fetalside(18% of injected (³H) PGE₂) and was principally to the 13,14-dihydro-15-keto-PGE₂ metabolite. Metabolism of (³H) PGE₂ after passage across the placenta was the same in both directions and was of the order of approximately 60%.