Abstract
Ornithine decarboxylase (ODC) activity is markedly stimulated in fetal rat primary hepatocyte cultures by the addition of fresh growth medium and in hepatoma-derived cell cultures 2-6 hr following the addition of fresh serum-containing or serum-free medium. The three hepatoma-derived continuous cell lines studied were: H-4-II-E (rat), Hepa-1 (mouse), and HTC (rat "minimal deviation" hepatoma). When ice-cold fresh medium is added and the cultures are then incubated at 37°, ODC induction is greater than when fresh medium, prewarmed to 37°, is added. ODC induction is less in confluent cultures than in logarithmically growing cultures, and less in frozen postmitochondrial supernatant fractions than in freshly prepared fractions. No relationship is apparent between ODC induction and total cellular content of either cyclic AMP or cyclic GMP. Whereas 3-isobutyl-1-methylxanthine stimulates cyclic AMP levels, this inhibitor of phosphodiesterase does not enhance ODC activity. These results do not support the hypothesis that stimulation of monooxygenase and ODC activities by various inducers of P-450 is mediated by the increased amount of cyclic AMP. ODC induction is never found to be greater in 3-methylcholanthrene-treated cultures than in control cultures. "Basal" ODC activities in nonstimulated liver- or hepatoma-derived cells in culture are 2-25 times greater than those in liver of the nonstimulated adult intact animal. Therefore, a difference in ODC induction between 3-methylcholanthrene-treated and control cultures (a) may be obscured by the already elevated ODC activity, (b) may not be a necessary prerequisite for the induction of aryl hydrocarbon hydroxylase to occur, or (c) may be necessary if the starting ODC activity is very low but unnecessary if the starting ODC activity is already high. These data point out the difficulties in using cell culture to study the relationship between drug-metabolizing enzyme induction and ODC induction.
ACKNOWLEDGMENTS We thank Dr. Takami Oka for valuable discussions concerning the manuscript. The expert technical secretarial assistance of Ms. Kitty Kunkle is greatly appreciated.
- Copyright © 1981 by The American Society for Pharmacology and Experimental Therapeutics
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