Synthesis, Metabolism, and Pharmacological Activity of 3α-Hydroxy Steroids Which Potentiate GABA-Receptor-Mediated Chloride Ion Uptake in Rat Cerebral Cortical Synaptoneurosomes

Article abstract of DOI:10.1021/jm00168a008

Certain 3α-hydroxy steroids have recently been shown to bind to the γ-aminobutyric acid (GABA) receptor gated chloride ion channel with high affinity and to potentiate the inhibitory effects of GABA when measured both in vitro and in vivo.In the present study, a series of natural and synthetic 3α-hydroxy steroids were tested for their ability to potentiate GABA-receptor-mediated chloride ion (Cl^-) uptake into cerebral cortical synaptoneurosomes.The naturally occurring metabolites 3α-hydroxy-5α-pregnan-20-one (allopregnanolone) and 3α,21-dihydroxy-5α-pregnan-20-one (allotetrahydroDOC) were found to be the most active in augmenting GABA^A-receptor-mediated Cl^- uptake.Pharmacological activity was reduced in the corresponding isomers with the 5β-pregnane configuration and by some, but not all, modifications of the side chain.The ability of these steroids to potentiate muscimol-stimulated Cl^- uptake is lost by acetylation at C₃, introduction of unsaturation at C₉₍₁₁₎, inversion to the 3β-hydroxy isomer, or inversion of configuration at C₁₇.A facile procedure is reported for synthesis of unlabeled and tritium-labeled allopregnolane and allotetrahydro DOC.The 9α,11α,12α-³H-labeled derivatives of allopregnanolone and allotetrahydro DOC were used to identify the distribution and metabolic products af these active steroids.Uptake of the more hydrophobic <³H>allopregnanolone into brain was significantly greater than that of <³H>allotetrahydroDOC.The principal ³H-labeled metabolites recovered from brain were the 3-ketone derivatives of allopregnanolone and allotetrahydroDOC, which are both inactive an GABA-receptor-mediated Cl^- flux.Molecular modeling of active steroids based on quantitative structure-activity relationships provides evidence to support the stereospecificity of the binding interactions and suggests that there may be more than one type of steroid binding site associated with the GABA_A-receptor-mediated chloride ionophore.