5B-Dihydroprogesterone

5B-Dihydroprogesterone (5B-DHP) is a progesterone receptor agonist and metabolite of progesterone (Item No. 15876).{61565,61566} It is formed from progesterone by 5B-reductase.{61566} 5B-DHP inhibits spontaneous contractions in isolated rat uterus when used at a concentration of 10 µg/ml, an effect that can be blocked by the progesterone receptor antagonist RU486 (mifepristone; Item No. 10006317) but not the GABAA receptor antagonist picrotoxin (Item No. 20771).{61565} It is a negative modulator of homooligomeric ?1 subunit-containing GABAA receptors, inhibiting GABA-induced currents in X. laevis oocytes expressing these receptors (IC50 = 5.02 µM).{61567} Plasma levels of 5B-DHP decrease at the onset of spontaneous human labor.{61568}