Increases in phenolic and nonphenolic ring deiodinase activity due to serum in monolayer liver cell cultures

When monkey hepatocarcinoma cells (NCLP-6E) were treated with 10% of various serum preparations for 24 h at 37 degrees C, nonphenolic ring deiodinase activity increased 2.0- to 2.3-fold. Phenolic ring deiodinase activity also increased 0.9- to 2.1-fold. Dialysis of the sera enhanced the effect on deiodinase activities in some preparations, but reduced activity in other serum preparations. Similarly, a 1.3- to 3.1-fold increase in phenolic ring deiodinase activity was observed in rat hepatoma cells (R-Y121B). In this case, dialysis usually reduced the effect of the sera. It is concluded that both large molecule(s) (undialyzable) and small molecule(s) (dialyzable) in serum contribute to the regulation of phenolic and nonphenolic ring deiodinase activity in NCLP-6E and R-Y121B cells.