Association between progesterone binding and cytochrome P-450 content of hepatic microsomes in the rat treated with cobalt-haem

The effect of cobalt protoporphyrin IX (Co-haem) given to male rats in single subcutaneous doses (25-100 mumol/kg body wt.) was studied. Co-haem decreased cytochrome P-450 content and aminopyrine N-demethylase activity, but increased progesterone content and 3H-progesterone binding in a dose-related manner. The effect of a single dose of 50 mumol/kg body wt. was reversible; cytochrome P-450 and progesterone content, and progesterone binding, returned to the normal level 24-40 d after injection but aminopyrine N-demethylase activity was only partially restored. The converse actions of Co-haem on microsomal progesterone and cytochrome P-450 content showed high correlation.