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  • Title: Differential antagonism by epipregnanolone of alphaxalone and pregnanolone potentiation of [3H]flunitrazepam binding suggests more than one class of binding site for steroids at GABAA receptors.
    Author: Prince RJ, Simmonds MA.
    Journal: Neuropharmacology; 1993 Jan; 32(1):59-63. PubMed ID: 8381526.
    Abstract:
    In rat brain membranes, the 3 alpha-hydroxy pregnane steroids, pregnanolone, allopregnanolone, alphaxalone and 5 beta-alphaxalone potentiated 1 nM [3H]flunitrazepam binding at the GABAA receptor, with maximal potentiations of 140-150% of control. The potencies of the 5 alpha isomers were greater than the 5 beta and the presence of an 11-keto group conferred lower potency. The potentiation produced by these steroids was antagonised by the 3 beta-OH isomers epipregnanolone, isopregnanolone and betaxalone (60 microM). The dose-effect curves for pregnanolone and allopregnanolone were shifted to the right, with no reduction in the maximal potentiation. In contrast, the maximal effect of alphaxalone and 5 beta-alphaxalone was reduced with no change in EC50. Alphaxalone (1 microM) caused an increase in the binding of [3H]flunitrazepam in the presence of maximal concentrations of pregnanolone or allopregnanolone. These results suggest multiple sites of action for neurosteroids in the brain.
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