title: Ovine placental steroid 17 alpha-hydroxylase/C-17,20-lyase, aromatase and sulphatase in dexamethasone-induced and natural parturition.
abstract: Parturition in the sheep is preceded by an abrupt alteration in placental steroid metabolism causing a shift from progesterone to oestrogen production. This change is believed to be a consequence of the preparatum rise in cortisol in the fetal circulation and involves increases in activities of the enzymes steroid 17 alpha-hydroxylase (cytochrome P-450(17) alpha), steroid C-17,20-lyase, and possibly aromatase and steroid sulphatase. The activity levels have been determined of steroid 17 alpha-hydroxylase, aromatase and steroid sulphatase in placental microsomes in late pregnancy, dexamethasone-induced labour and in natural labour at term. Over the gestational period of 118-140 days, basal levels of placental aromatase were relatively constant (mean value (+/- S.E.M.) of 5.6 +/- 0.5 pmol/min per mg microsomal protein (n = 10]. Pregnenolone and progesterone 17 alpha-hydroxylase activities were undetectable (less than 0.5 pmol/min per mg microsomal protein (n = 7]. In six animals in labour induced with infusion of dexamethasone into the fetus, placental aromatase activity increased to a value of 14.0 +/- 1.0 pmol/min per mg protein; placental pregnenolone 17 alpha-hydroxylase, measured in four of the animals, also increased to 453 +/- 77 pmol/min per mg microsomal protein. In five animals in natural spontaneous labour with vaginal delivery, aromatase activity was 26.7 +/- 5.2 pmol/min per mg microsomal protein and pregnenolone 17 alpha-hydroxylase activity was 141 +/- 14 pmol/min per mg microsomal protein. Steroid sulphatase activity was barely detectable (less than 1.5 pmol/min per mg microsomal protein) during late pregnancy, dexamethasone-induced labour or natural parturition.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Cecil H. and Ida Green Center for Reproductive Biology Sciences, University of Texas Southwestern Medical Center, Dallas 75235-9051.
authors: J I
authors: JI
authors: Mason
authors: J T
authors: JT
authors: France
authors: R R
authors: RR
authors: Magness
authors: B A
authors: BA
authors: Murry
authors: C R
authors: CR
authors: Rosenfeld
mesh_terms: D000446:Aldehyde-Lyases / Q000378:metabolism; D000818:Animals; D001141:Aromatase / Q000378:metabolism; D001192:Arylsulfatases / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003907:Dexamethasone; D005260:Female; D007743:Labor, Obstetric / Q000187:drug effects / Q000378:metabolism*; D008861:Microsomes / Q000201:enzymology; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D012756:Sheep / Q000378:metabolism*; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism*; D043266:Steryl-Sulfatase
chemical_list: D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001141:Aromatase; D013254:Steroid 17-alpha-Hydroxylase; D001192:Arylsulfatases; D043266:Steryl-Sulfatase; D000446:Aldehyde-Lyases