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Neurosteroid metabolism: identification of allopregnanolone and isoallopregnanolone metabolites in rat brain and plasma
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology. (Torbjörn Bäckström, UNC)
Institute of Endocrinology, Nároni trída 8, CZ 116 94 Prague, Czech Republic.
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
Umeå University, Faculty of Medicine, Department of Clinical Sciences, Obstetrics and Gynaecology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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. 

URN: urn:nbn:se:umu:diva-27071OAI: diva2:276031
Available from: 2009-11-10 Created: 2009-11-10 Last updated: 2011-04-12Bibliographically approved
In thesis
1. Progesterone metabolites: learning, tolerance, antagonism & metabolism
Open this publication in new window or tab >>Progesterone metabolites: learning, tolerance, antagonism & metabolism
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Progesterone metabolites as allopregnanolone, isoallopregnanolone and tetrahydrodeoxy-corticosterone (THDOC) are increased in the luteal phase of the menstrual cycle, throughout pregnancy and during stress. Allopregnanolone and THDOC are neurosteroids with 3α-hydroxy, 5α-configurations and positive modulating effect on the GABAA receptor. They have similar properties and effect, and share the same binding sites on the GABAA receptor. Isoallopregnanolone has a 3β-hydroxy, 5α-configuration and a diverse effect as a proposed antagonist to both allopregnanolone and THDOC. Neurosteroids are thought to exert their effect predominantly at extrasynaptic GABAA receptors, containing for example α4- or α5-subunits. Such receptors are involved in the tonic response. Different subunits have diverse distribution pattern in the brain and are involved in different functions. The α5-subunit, mainly expressed in the hippocampus, is involved in learning, while α4 is more widespread and involved in e.g. anxiety and anaesthesia.

The aim of the present thesis was to contribute to the knowledge about selected progesterone metabolites and their effects on learning and tolerance development, as well as their metabolism. Also basic characteristics between different α-subunits of the GABAA receptor were evaluated.

The thesis shows that the effect of bicuculline and pentobarbital is not dependent on the α-subunit isoform of the GABAA receptor expressed in oocytes. Acute tolerance developed after allopregnanolone-induced anaesthesia with a decrease at both mRNA and protein levels of the GABAA receptor α4-subunit in the thalamus VPM nucleus. A negative correlation between the α4 mRNA and the increased dose of allopregnanolone needed to maintain the anaesthesia level was also shown. In addition, allopregnanolone induces a learning impairment in the Morris water maze test, when high concentrations of allopregnanolone are present in the brain. This impairment is not possible to reverse by isoallopregnanolone. In α5β3γ2L-transfected HEK-293 cells THDOC induces a baseline shift of its own and also potentiate the GABA-current. Neither of those THDOC effects can be inhibited by isoallopregnanolone. Instead isoallopregnanolone shows an agonistic effect on the THDOC-potentiation of the GABA-response. The main allopregnanolone metabolites identified, 5α-DHP and isoallopregnanolone, as well as allopregnanolone itself are mainly localized to the brain after an i.v. injection. After an isoallopregnanolone injection there is a more even distribution of the given steroid and the metabolites between plasma and brain. There is an epimerisation between isoallopregnanolone and allopregnanolone and vice versa.

In conclusion, the present thesis shows that the α4-subunit in the thalamus VPM nucleus is likely to be involved in the acute tolerance development against allopregnanolone and that allopregnanolone-induced learning impairment is likely to be hippocampus dependent. The lack of antagonistic effect of isoallopregnanolone on the THDOC-induced α5β3γ2L-GABAA response, together with epimerisation of isoallopregnanolone to allopregnanolone, could explain why isoallopregnanolone does not work as an antagonist to the allopregnanolone-induced learning impairment in a hippocampus dependent learning task.

Place, publisher, year, edition, pages
Umeå: Umeå university, 2009. 73 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1306
allopregnanolone, isoallopregnanolone, THDOC, learning, tolerance, antagonism, inhibition, patch clamp, Morris water maze, metabolism, epimerization
National Category
Obstetrics, Gynecology and Reproductive Medicine
Research subject
Obstetrics and Gynaecology
urn:nbn:se:umu:diva-27064 (URN)978-91-7264-888-3 (ISBN)
Public defence
2009-12-05, Sal 914, By 1, 9 tr, NUS, Norrlands Universitetssjukhus, Umeå, 10:00 (English)
Available from: 2009-11-16 Created: 2009-11-09 Last updated: 2010-01-18Bibliographically approved

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Öfverman, CharlotteBäckström, TorbjörnJohansson, Inga-Maj
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