Isotope Labeling article 6 isotope labeling 6 synthesis 6 Pregnenolone 4 carbon 4 cholane derivative 4 pregnenolone 4 radioisotope 4 3beta hydroxycholenic acid 2 Aldehydes 2 Animal 2 Aromatic compounds 2 Carbon Isotopes 2 Carbon Radioisotopes 2 Carboxylic acids 2 Castration 2 Chemistry 2 Chemotherapy 2 Cholanes 2 Cholenes 2 Cholesterol 2 Comparative Study 2 Epididymis 2 Fluorescent Antibody Technique 2 Furans 2 Galactofuranosidases 2 Galactofuranosides 2 Glycoside Hydrolases 2 Hexuronic Acids 2