{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,20]],"date-time":"2026-07-20T14:20:33Z","timestamp":1784557233323,"version":"3.55.0"},"reference-count":62,"publisher":"Bioscientifica","issue":"1","content-domain":{"domain":["joe.bioscientifica.com"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2018,7]]},"abstract":"<jats:p>\n                    <jats:italic>In vivo<\/jats:italic>\n                    and\n                    <jats:italic>in vitro<\/jats:italic>\n                    evidence indicates that the bioactive, 5\u03b1-reduced progesterone metabolite, 5\u03b1-dihydroprogesterone (DHP) is synthesized in the placenta, supporting equine pregnancy, but its appearance in early pregnancy argues for other sites of synthesis also. It remains unknown if DHP circulates at relevant concentrations in cyclic mares and, if so, does synthesis involve the non-pregnant uterus? Jugular blood was drawn daily from cyclic mares (\n                    <jats:italic>n<\/jats:italic>\n                    \u2009=\u20095). Additionally, ovariectomized mares (OVX) and geldings were administered progesterone (300\u2009mg) intramuscularly. Blood was drawn before and after treatment. Incubations of whole equine blood and hepatic microsomes with progesterone were also investigated for evidence of DHP synthesis. Sample analysis for progesterone, DHP and other steroids employed validated liquid chromatography\u2013tandem mass spectrometry methods. Progesterone and DHP appeared a day (d) after ovulation in cyclic mares, was increased significantly by d3, peaking from d5 to 10 and decreased from d13 to 17. DHP was 55.5\u2009\u00b1\u20093.2% of progesterone concentrations throughout the cycle and was highly correlated with it. DHP was detected immediately after progesterone administration to OVX mares and geldings, maintaining a relatively constant ratio with progesterone (47.2\u2009\u00b1\u20092.9 and 51.2\u2009\u00b1\u20092.7%, respectively). DHP was barely detectable in whole blood and hepatic microsome incubations. We conclude that DHP is a physiologically relevant progestogen in cyclic, non-pregnant mares, likely stimulating the uterus, and that it is synthesized peripherally from luteal progesterone but not in the liver or blood. The presence of DHP in pregnant perissodactyla as well as proboscidean species suggests horses may be a valuable model for reproductive endocrinology in other exotic taxa.\n                  <\/jats:p>","DOI":"10.1530\/joe-18-0215","type":"journal-article","created":{"date-parts":[[2018,5,31]],"date-time":"2018-05-31T11:15:29Z","timestamp":1527765329000},"page":"25-32","update-policy":"https:\/\/doi.org\/10.1530\/crossmarkpolicy-5","source":"Crossref","is-referenced-by-count":7,"title":["5\u03b1-dihydroprogesterone concentrations and synthesis in non-pregnant mares"],"prefix":"10.1530","volume":"238","author":[{"given":"A J","family":"Conley","sequence":"first","affiliation":[{"name":"1Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"E L","family":"Scholtz","sequence":"additional","affiliation":[{"name":"1Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"E L","family":"Legacki","sequence":"additional","affiliation":[{"name":"1Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"C J","family":"Corbin","sequence":"additional","affiliation":[{"name":"1Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"H K","family":"Knych","sequence":"additional","affiliation":[{"name":"2Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"G D","family":"Dujovne","sequence":"additional","affiliation":[{"name":"1Department of Population Health & Reproduction, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B A","family":"Ball","sequence":"additional","affiliation":[{"name":"3Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington Kentucky, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"B C","family":"Moeller","sequence":"additional","affiliation":[{"name":"2Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California, USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"S D","family":"Stanley","sequence":"additional","affiliation":[{"name":"2Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis, California, 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the corpus luteum of the African elephant (Loxodonta africana)","volume":"102","year":"1994","journal-title":"Journal of Reproduction and Fertility"},{"key":"ref291","doi-asserted-by":"crossref","first-page":"94","DOI":"10.1016\/0039-128X(95)00199-Z","article-title":"Steroid transformations in pregnant mares: metabolism of exogenous progestins and unusual metabolic activity in vivo and in vitro","volume":"61","year":"1996","journal-title":"Steroids"},{"key":"ref481","doi-asserted-by":"crossref","first-page":"421","DOI":"10.1530\/REP-15-0547","article-title":"The dynamic steroid landscape of equine pregnancy mapped by mass spectrometry","volume":"151","year":"2016b","journal-title":"Reproduction"},{"key":"ref01","doi-asserted-by":"crossref","first-page":"551","DOI":"10.1016\/S0093-691X(01)00425-3","article-title":"Expression of 3beta-hydroxysteroid dehydrogenase, cytochrome p450 17alpha-hydroxylase\/17,20-lyase and cytochrome p450 aromatase enzymes in corpora lutea of diestrous and 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