B F Mitchell1, S Wong. 1. Department of Obstetrics and Gynecology, University of Alberta, Edmonton, Canada.
Abstract
OBJECTIVE: Our purpose was to measure the activity of the reversible enzyme 17 beta,20 alpha-hydroxysteroid dehydrogenase around parturition with estrogen and progestogen substrates. STUDY DESIGN: Classic kinetic studies and explant cultures were used to determine kinetic parameters and net enzyme activities in both oxidative and reductive directions for both sets of substrates. RESULTS: Affinity constant values for estrone, estradiol, and 20 alpha-dihydroprogesterone were 1 to 8 mumol/L. Affinity constant for progesterone was 9 to 25 mumol/L. Maximal velocities for all substrates in the chorion were 20- to 70-fold higher than in amnion and severalfold higher for estrogen substrates compared with the progestins. Around parturition there was a significant change toward net formation of the stronger estrogen (estradiol) and the weaker progestin (20 alpha-dihydroprogesterone), suggesting an increase in the local estrogen/progesterone ratio. CONCLUSION: The enzyme 17 beta,20 alpha-hydroxysteroid dehydrogenase may be an important regulator of the local estrogen/progesterone ratio in fetal membranes around the time of parturition.
OBJECTIVE: Our purpose was to measure the activity of the reversible enzyme 17 beta,20 alpha-hydroxysteroid dehydrogenase around parturition with estrogen and progestogen substrates. STUDY DESIGN: Classic kinetic studies and explant cultures were used to determine kinetic parameters and net enzyme activities in both oxidative and reductive directions for both sets of substrates. RESULTS: Affinity constant values for estrone, estradiol, and 20 alpha-dihydroprogesterone were 1 to 8 mumol/L. Affinity constant for progesterone was 9 to 25 mumol/L. Maximal velocities for all substrates in the chorion were 20- to 70-fold higher than in amnion and severalfold higher for estrogen substrates compared with the progestins. Around parturition there was a significant change toward net formation of the stronger estrogen (estradiol) and the weaker progestin (20 alpha-dihydroprogesterone), suggesting an increase in the local estrogen/progesterone ratio. CONCLUSION: The enzyme 17 beta,20 alpha-hydroxysteroid dehydrogenase may be an important regulator of the local estrogen/progesterone ratio in fetal membranes around the time of parturition.
Authors: M Mazor; R Hershkowitz; F Ghezzi; J Cohen; A Silber; J Levy; J R Leiberman; M Glezerman Journal: Arch Gynecol Obstet Date: 1996 Impact factor: 2.344
Authors: Sunil K Kota; Kotni Gayatri; Sruti Jammula; Siva K Kota; S V S Krishna; Lalit K Meher; Kirtikumar D Modi Journal: Indian J Endocrinol Metab Date: 2013-01