CONJUGATION OF PARA-NITROPHENOL BY ISOLATED-PERFUSED FETAL SHEEP LIVER

Using our recently described, isolated perfused fetal sheep liver mode l, we have studied the metabolism and disposition of para-nitrophenol (PNP) in intact fetal liver. petal sheep (mean gestational age, 137 +/ - 7 days; range, 127-145 days; n = 8) were delivered under anesthesia near term, and the livers were isolated and perfused rh situ, via the umbilical vein, in an oxygenated 1-liter recirculating system, at pH 7 .40 at 37 degrees C. The perfusate delivery rate was 4.39 +/- 1.46 ml/ g liver/min. Either a 14-mu mol (n = 4), 72-mu mol in = 3), or 14-mu m ol (n = 5) bolus dose of PNP was added to the reservoir. Samples were taken from me reservoir every 5-10 min, and all bile was collected at 15-30-min intervals. Elimination of PNP from perfusate demonstrated Mi chaelis-Menten kinetics, and the calculated pharmacokinetic parameters for PNP elimination were K-M = 13.0 +/- 9.66 mu M, V-max = 32.1 +/- 2 2.4 nmol/min/g liver, and intrinsic clearance = 3.39 +/- 2.54 ml/min/g liver. At the end of the 120-min perfusion period, PNP could be accou nted for entirely as PNP-sulfate (PNP-S) and PNP-glucuronide (PNP-G). The perfusate ratio of PNP-S to PNP-G at 120 min was 2.21 +/- 0.88 at the 14-mu mol dose, 0.86 +/- 0.56 at the 72-mu mol dose, and 0.31 +/- 0.17 at the 144-mu mol dose, because of saturation of sulfate producti on with increasing dose. PNP-S and PNP-G were eliminated into bile in smalt amounts (<3% of dose), and the PNP-S/PNP-G ratio in bile was 1. We conclude that near-term fetal sheep liver can metabolize PNP to PNP -G and PNP-S with efficiencies that may be comparable to those of adul ts, that, as in adults, sulfation is of low capacity, relative to gluc uronidation, and that, unlike adults, fetuses have lime capacity to tr ansport the PNP-G formed in the hepatocytes into bile.