Sample autoradiographs of TLCs showing 14C-labeled metabolites of progesterone in MCF-7 and MCF-10A cells following an 8-hour incubation with [14C]progesterone (P). The main metabolites identified and quantified for these enzyme activity studies are: (1) 5α-pregnane-3,20-dione, (2) 5α-pregnan-3α-ol-20-one, (3) 5α-pregnan-20α-ol-3-one, (4) 5α-pregnan-3β-ol-20-one, (5) 4-pregnen-3α-ol-20-one (3αHP), (6) 4-pregnen-20α-ol-3-one (20αDHP), (7) 5α-pregnane-3α (β), 20α-diol, (8) 4-pregnene-3α,20α-diol. The extracts were spotted at the origin and the plates were run 2 × in solvent system 1 and 3 × in solvent system 2 in the directions indicated, as described under Methods, and the films were exposed for 8 days. Note greater size/intensity of 5α-pregnane spots (Nos. 1–4, 7) in MCF-7 cells, and greater size/intensity of 4-pregnene spots (No. 5 and 6) in MCF-10A cells.