The influence of phenobarbital on the turnover of hepatic microsomal cytochrome b₅ and cytochrome P-450 hemes in the rat

The turnover of ¹⁴C-labeled heme in steady state phenobarbital-induced rats was compared with the turnover of the same hemes in control rats. The half-lives of cytochrome b₅ and cytochrome P-450 hemes in the steady-state induced animals were unchanged (45 and 22 h, respectively). Induction of cytochrome P-450 was found to be caused by an increased rate of synthesis, measured by the rate of δ-amino[4-¹⁴C]levulinate incorporation into heme in the early stages of phenobarbital treatment. When the level of hemoproteins during phenobarbital administration had reached a steady-state induced level, the rate of home destruction was elevated to balance the induced rate of synthesis.