Modulation of 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity in the equine placenta by pregnenolone and progesterone metabolites.
The purpose of this study was to measure 3beta-HSD activity in the equine placenta and to assess the effect of fetal and maternal blood plasma progestagens on 3beta-HSD activity was measured in 8 late gestation (collected by caesarian section at 250 to 320 days) and 7 term (collected by caesarian section at 250 to 320 days) and 7 term (collected at birth) equine placentae using a tritium release assay with [3alpha-3H] pregnenolone as substrate. Mean +/- s.d. Km(app) and Vmax for term placentae were in general higher than for late gestation placentae (0.129 +/- 0.217 micromol/l and 23.85 +/- 9.1 nmol/mg/h respectively vs. 0.016 +/- 0.048 micromol/l and 17.36 +/- 20.9 nmol/mg/h) but there was no statistical difference between them. Inhibition studies were performed on 3 term placentae and 3 late gestation ones. Steroid concentrations used for inhibition studies were close to blood plasma concentrations (0.5 to 2 micromol/l). 3beta-hydroxy compounds (5alpha-pregnene-3beta, 20alpha-diol and 3beta-hydroxy-5alpha-pregnan-20-one) showed noncompetitive or mixed inhibition. Mean Ki(app) of 0.7 micromol/l. Inhibition was competitive with 20alpha-hydroxy-5alpha-pregnan-3-one with a mean Ki(app) of 0.1 micromol/l.
Chavatte
P M
PM
Department of Paediatrics, University of Cambridge, Addenbrooke's Hospital, UK.
Rossdale
P D
PD
Tait
A D
AD
D015096:3-Hydroxysteroid Dehydrogenases / Q000032:analysis / Q000378:metabolism*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D006736:Horses / Q000378:metabolism*; D010920:Placenta / Q000187:drug effects / Q000201:enzymology*; D011247:Pregnancy; D011276:Pregnanediol / Q000097:blood / Q000737:chemistry / Q000494:pharmacology; D011278:Pregnanes / Q000097:blood / Q000737:chemistry / Q000494:pharmacology; D011280:Pregnanolone / Q000097:blood / Q000737:chemistry / Q000494:pharmacology; D011283:Pregnenes / Q000097:blood / Q000737:chemistry / Q000494:pharmacology; D011284:Pregnenolone / Q000097:blood / Q000737:chemistry / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood / Q000737:chemistry / Q000494:pharmacology*
D011278:Pregnanes; D011283:Pregnenes; D011374:Progesterone; D011284:Pregnenolone; D011280:Pregnanolone; D015096:3-Hydroxysteroid Dehydrogenases; D011276:Pregnanediol