Editing Steroid (section)

== Catabolism and excretion ==
Steroids are primarily oxidized by [[cytochrome P450|cytochrome P450 oxidase]] enzymes, such as [[CYP3A4]]. These reactions introduce oxygen into the steroid ring, allowing the cholesterol to be broken up by other enzymes into bile acids.<ref name="pmid16872679">{{cite journal | vauthors = Pikuleva IA | title = Cytochrome P450s and cholesterol homeostasis | journal = Pharmacology & Therapeutics | volume = 112 | issue = 3 | pages = 761–73 | date = Dec 2006 | pmid = 16872679 | doi = 10.1016/j.pharmthera.2006.05.014 }}</ref> These acids can then be eliminated by secretion from the [[liver]] in [[bile]].<ref name="pmid16749856">{{cite journal | vauthors = Zollner G, Marschall HU, Wagner M, Trauner M | title = Role of nuclear receptors in the adaptive response to bile acids and cholestasis: pathogenetic and therapeutic considerations | journal = Molecular Pharmaceutics | volume = 3 | issue = 3 | pages = 231–51 | year = 2006 | pmid = 16749856 | doi = 10.1021/mp060010s }}</ref> The expression of the [[oxidase]] gene can be [[Downregulation and upregulation|upregulated]] by the steroid sensor [[PXR]] when there is a high blood concentration of steroids.<ref name="pmid12372848">{{cite journal | vauthors = Kliewer SA, Goodwin B, Willson TM | title = The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism | journal = Endocrine Reviews | volume = 23 | issue = 5 | pages = 687–702 | date = Oct 2002 | pmid = 12372848 | doi = 10.1210/er.2001-0038 | doi-access = free }}</ref> Steroid hormones, lacking the side chain of cholesterol and bile acids, are typically [[Hydroxylation|hydroxylated]] at various ring positions or [[17-ketosteroid|oxidized at the 17 position]], [[Conjugated system|conjugated]] with sulfate or [[glucuronic acid]] and excreted in the urine.<ref name="Steimer-WHO">{{cite web | vauthors = Steimer T | title = Steroid Hormone Metabolism | url = http://www.gfmer.ch/Books/Reproductive_health/Steroid_hormone_metabolism.html | publisher = Geneva Foundation for Medical Education and Research | work = WHO Collaborating Centre in Education and Research in Human Reproduction | access-date = 27 March 2015 | archive-date = 17 February 2015 | archive-url = https://web.archive.org/web/20150217114802/http://www.gfmer.ch/Books/Reproductive_health/Steroid_hormone_metabolism.html | url-status = live }}</ref>