Metabolism of progesterone and estradiol by microsomes and purified cytochrome P-450 RLM3 and RLM5.

The metabolism of progesterone and estradiol by cytochrome P-450 RLM3 and RLM5 and by male rat liver microsomes was compared. Products formed were identified by thin layer chromatography and by gas chromatography-mass spectrometry. Eleven metabolites were detected from progesterone metabolism. Three proved to be reduction products formed only by the microsomes and seven metabolites were identified. Those identified were 5 alpha-pregnane-3,20-dione, 3 beta-hydroxy-5 alpha-pregnane-20-one, 2 alpha-hydroxyprogesterone, 6 beta-hydroxyprogesterone, 6 alpha-hydroxyprogesterone, 15-hydroxyprogesterone, and 16 alpha-hydroxyprogesterone. RLM3 formed 6 beta- and 16 alpha-hydroxyprogesterone as major products and 6 alpha- and 15-hydroxyprogesterone as minor ones. RLM5, however, formed 2 alpha-hydroxy- and 16 alpha-hydroxyprogesterone as major products, and 6 beta-hydroxyprogesterone as a minor product. RLM5 and microsomes did not produce detectable levels of 15-hydroxyprogesterone. Two very polar metabolites were produced from progesterone by both RLM3 and RLM5 but were not seen with microsomes and were not identified. Four metabolites were formed from estradiol. One, 15-hydroxyestradiol, was formed only by RLM3. No other product was formed by this enzyme at appreciable rates. RLM5 and microsomes also formed estrone, estriol, and 2-hydroxyestradiol, but the first of these was a very minor product. This study clearly shows a stereospecificity and positional specificity in metabolism of steroid hormones by cytochrome P-450 isozymes of the untreated rat.