title: 5-Alpha-dihydroprogesterone formation in human placenta from 5alpha-pregnan-3beta/alpha-ol-20-ones and 5-pregnan-3beta-yl-20-one sulfate.
abstract: 5Alpha-dihydroprogesterone (5alpha-DHP) is the immediate precursor of 5alpha-pregnan-3alpha-ol-20-one, a potent anxiolytic/anesthetic agent in all vertebrate animals tested, including humans. The levels of 5alpha-DHP in the plasma of pregnant women are very high; and during the third trimester of pregnancy, the blood production rate of this steroid may exceed 100 mg/24 h. 5Alpha-DHP in maternal plasma, however, cannot be accounted for totally by the metabolism of maternal plasma progesterone. This study was conducted to evaluate the possibility that 5alpha-DHP is synthesized in placenta from 5alpha-pregnan-3alpha/beta-ol-20-ones delivered to the trophoblast via the fetal umbilical blood. In incubations of placental minces with radiolabelled 5alpha-pregnan-3alpha/beta-ol-20-ones, there is extensive epimerization and the intermediate, 5alpha-DHP, is the major product. In other incubations, 5alpha-pregnan-3beta-ol-20-one-sulfate was hydrolysed and the liberated 5alpha-pregnan-3beta-ol-20-one was converted to 5alpha-DHP by homogenates of placental tissue, but 5alpha-pregnan-3beta-ol-20-one-sulfate was not. The oxidation of 5alpha-pregnan-3alpha/beta-ol-20-ones was concentrated in microsome-enriched preparations of placental tissue and the apparent Kms for 5alpha-pregnan-3alpha-ol-20-one and 5alpha-pregnan-3beta-ol-20-one were 3.6 microM and 78 nM, respectively. The Vmaxs for 5alpha-DHP formation from 5alpha-pregnan-3alpha-ol-20-one and 5alpha-pregnan-3beta-ol-20-one were, respectively, 336 pmol/min/mg protein and 9.7 nmol/min/mg protein. These oxidation reactions were supported by both NAD+ and NADP+. We suggest that progesterone, which enters the umbilical circulation from its site of synthesis in the syncytiotrophoblast, is metabolized in the fetus to 5alpha-pregnan-3alpha/beta-ol-ones and to 5alpha-pregnan-3alpha/beta-yl-20-one sulfates. These metabolites of progesterone, 5alpha-pregnan-3alpha/beta-ol-20-one and 5alpha-pregnan-3beta-yl-20-one sulfate, formed in the fetus, serve as plasma-borne substrates for trophoblast formation of 5alpha-DHP. Because of the hemochorioendothelial nature of human placentation, 5alpha-DHP secreted from the trophoblast will preferentially enter the maternal compartment, thus constituting a maternal plasma progesterone-independent source of 5alpha-DHP.
authors.affiliation: The Cecil H. and Ida Green Center for Reproductive Biology Sciences and the Department of Obstetrics-Gynecology and Biochemistry, The University of Texas Southwestern Medical Center at Dallas, 75235-9051, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Dombroski
authors.forename: M L
authors.initials: ML
authors.lastname: Casey
authors.forename: P C
authors.initials: PC
authors.lastname: MacDonald
mesh_terms: D043582:5-alpha-Dihydroprogesterone; D000777:Anesthetics / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006801:Humans; D007536:Isomerism; D010084:Oxidation-Reduction; D010920:Placenta / Q000737:chemistry / Q000378:metabolism*; D011247:Pregnancy; D011277:Pregnanediones / Q000737:chemistry / Q000378:metabolism*; D011280:Pregnanolone / Q000737:chemistry / Q000378:metabolism*; D013431:Sulfates / Q000737:chemistry
chemical_list: D000777:Anesthetics; D011277:Pregnanediones; D013431:Sulfates; D043582:5-alpha-Dihydroprogesterone; D011280:Pregnanolone