5β-Dihydroprogesterone (5β-DHP) is a progesterone receptor agonist and metabolite of progesterone .^1,2It is formed from progesterone by 5β-reductase.²5β-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 but not the GABA_Areceptor antagonist picrotoxin .¹It is a negative modulator of homooligomeric Ρ1 subunit-containing GABA_Areceptors, inhibiting GABA-induced currents inX. laevisoocytes expressing these receptors (IC₅₀= 5.02 µM).³Plasma levels of 5β-DHP decrease at the onset of spontaneous human labor.⁴

1.Putnam, C.D., Brann, D.W., Kolbeck, R.C., et al.Inhibition of uterine contractility by progesterone and progesterone metabolites: Mediation by progesterone and gamma amino butyric acidA receptor systemsBiol. Reprod.45(2)266-272(1991) 2.Bumke-Vogt, C., BÄhr, V., Diederich, S., et al.Expression of the progesterone receptor and progesterone- metabolising enzymes in the female and male human kidneyJ. Endocrinol.175(2)349-364(2002) 3.Morris, K.D., Moorefield, C.N., and Amin, J.Differential modulation of the γ-aminobutyric acid type C receptor by neuroactive steroidsMol. Pharmacol.56(4)752-759(1999) 4.Sheehan, P.M., Rice, G.E., Moses, E.K., et al.5β-dihydroprogesterone and steroid 5β-reductase decrease in association with human parturition at termMol. Hum. Reprod.11(7)495-501(2005)