title: The regulation of ovine placental steroid 17 alpha-hydroxylase and aromatase by glucocorticoid.
abstract: Parturition in the pregnant sheep is preceded by an abrupt alteration in placental steroid metabolism causing a shift from progesterone to estrogen production. This change is believed to be a consequence of the prepartum 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. We have investigated the activity levels of aromatase and 17 alpha-hydroxylase in placental microsomes in late pregnancy and dexamethasone-induced labor. Over the gestational period of 118-140 days basal levels of placental aromatase were relatively constant [mean value (+/- SD) of 5.6 +/- 1.6 pmol min-1 mg microsomal protein-1 (n = 10)]. Steroid 17 alpha-hydroxylase activity was undetectable [less than 0.5 pmol min-1 mg microsomal protein-1 (n = 7)]. In six animals in labor induced with infusion of dexamethasone into the fetus, placental aromatase activity had a mean value of 14.0 +/- 2.5 pmol min-1 mg protein-1; placental steroid 17 alpha-hydroxylase, measured in four of the animals, had a mean (+/- SD) activity of 319 +/- 58 pmol min-1 mg microsomal protein-1. Immunoblotting of placental microsomal preparations with specific antibodies to cytochrome P-450(17)alpha and NADPH-cytochrome P-450-reductase indicated that the glucocorticoid-induced activity of 17 alpha-hydroxylase was associated with increased content of cytochrome P-450(17)alpha. Northern blotting with a cDNA probe for cytochrome P-450(17)alpha showed that glucocorticoid increased the levels of mRNA for the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001141:Aromatase / Q000378:metabolism*; D005260:Female; D005938:Glucocorticoids / Q000502:physiology*; D008861:Microsomes / Q000201:enzymology; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D012756:Sheep; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism*
chemical_list: D005938:Glucocorticoids; D013250:Steroid Hydroxylases; D001141:Aromatase; D013254:Steroid 17-alpha-Hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase