PORPHYRIN PRODUCTION AND EXCRETION BY LONG-TERM CULTURES OF ADULT-RATHEPATOCYTES AND EFFECT OF LEAD-EXPOSURE

Porphyrin production and excretion and the effects of lead exposure we re studied in long-term cultures of adult rat hepatocytes cultured on a feeder layer of 3T3 cells after addition of 5-aminolevulinic acid, P orphyrin excretion into the culture medium showed an irregular profile during the first 10 days, with a maximum increase of 50% at day 4 and at day 10 a value similar to that of day 1. Thereafter, porphyrin exc retion decreased progressively to 18% of the initial value after 4 wee ks, The cellular porphyrin content, after 7 and 28 days in culture, re ached values 3.8 and 2.4-fold higher than the corresponding day 1 valu e. The exposure to 0.5 and 2.4 mu M Pb2+ for up to 28 days produced a biphasic effect on porphyrin excretion. Firstly, there was a progressi ve decrease up to 81% during the first 6 days of lead exposure and, se condly, this effect was followed by an increase reaching control value s at day 15 and of up to 6.7-fold after 22 days of exposure to 2.4 mu M Pb2+. Similar changes were observed in cellular porphyrin content, T he exposure to 0.5 and 2.4 mu M Pb2+ for 2 and 4 weeks also produced m orphological alterations and release of cytoplasmic enzymes, Our resul ts show that hepatocytes cultured on 3T3 cells produce and excrete por phyrins for 28 days and that exposure for 4 weeks to micromolar lead c oncentrations alters these functions and cell. morphology and produces cytotoxic effects which are better evaluated by monitoring alteration s in porphyrin excretion than by enzyme leakage, They also suggest tha t this culture system is a useful model for assessing the toxic effect s of xenobiotics on the biosynthesis of heme by liver cells.