Neurosteroid metabolism: identification of allopregnanolone and isoallopregnanolone metabolites in rat brain and plasma
(English)Manuscript (preprint) (Other academic)
Metabolism of progesterone produces steroids that by themselves have other functional properties than the hormone. The most prominent metabolite, allopregnanolone (3α-OH-5α-pregnane-20-one), has a strong GABAA receptor agonistic activity. Isoallopregnanolone (3β-OH-5α-pregnane-20-one) is also formed from progesterone; this allopregnanolone epimer can in certain situations function as an antagonist to effects induced by allopregnanolone.
This study was designed to further evaluate the metabolism of allopregnanolone and isoallopregnanolone in the rat. This was done by intravenous injections of either steroid and analyses of selected possible metabolites within the brain as well as in plasma, eight minutes after the injection. Analyses were performed with GC-MS.
It was found that the main metabolites accumulated after the allopregnanolone treatment was the precursor 5α-dihydroprogesterone, followed by isoallopregnanolone. The injected allopregnanolone, as well as the two major metabolites formed, were mainly present in the brain. When isoallopregnanolone was injected, the main metabolites formed were allopregnanolone and 6α-hydroxylated isoallopregnanolone, followed by the precursor 5α-dihydroprogesterone. Interestingly, the metabolites formed after isoallopregnanolone injections were more evenly distributed between the analyzed brain areas and the plasma. After both treatments a high proportion of conjugation (typically around 50%), was in plasma found for both the injected and the produced steroids.
With the high amounts of metabolites found in the brain, there might be a high converting capacity within the brain for these kinds of steroids. This suggests that interchange between the studied epimers is of physiological nature. One may then speculate that the brain uses the conversion between allopregnanolone and isoallopregnanolone to regulate the GABAergic inhibition. If this is the case, a dysregulation of this metabolism might cause symptoms and/or CNS disorders.
IdentifiersURN: urn:nbn:se:umu:diva-27071OAI: oai:DiVA.org:umu-27071DiVA: diva2:276031