A progesterone metabolite stimulates the release of gonadotropin-releasing hormone from GT1-1 hypothalamic neurons via the gamma-aminobutyric acid type A receptor.
The reduced progesterone metabolite tetrahydroprogesterone (3 alpha-hydroxy-5 alpha-pregnan-20-one; 3 alpha,5 alpha-THP) is a positive modulator of the gamma-aminobutyric acid type A (GABAA) receptor. Experiments performed in vitro with hypothalamic fragments have previously shown that GABA could modulate the release of gonadotropin-releasing hormone (GnRH). Using GT1-1 immortalized GnRH neurons, we investigated the role of GABAA receptor ligands, including 3 alpha,5 alpha-THP, on the release of GnRH. We first characterized the GABAA receptors expressed by these neurons. [3H]Muscimol, but not [3H]flunitrazepam, bound with high affinity to GT1-1 cell membranes (Kd = 10.9 +/- 0.3 nM; Bmax = 979 +/- 12 fmol/mg of protein), and [3H]muscimol binding was enhanced by 3 alpha,5 alpha-THP. mRNAs encoding the alpha 1 and beta 3 subunits of the GABAA receptor were detected by the reverse transcriptase polymerase chain reaction. In agreement with binding data, the benzodiazepine-binding gamma subunit mRNA was absent. GnRH release studies showed a dose-related stimulating action of muscimol. 3 alpha,5 alpha-THP not only modulated muscimol-induced secretion but also stimulated GnRH release when administered alone. Bicuculline and picrotoxin blocked the effects of 3 alpha,5 alpha-THP and muscimol. Finally, we observed that GT1-1 neurons convert progesterone to 3 alpha,5 alpha-THP. We propose that progesterone may increase the release of GnRH by a membrane mechanism, via its reduced metabolite 3 alpha,5 alpha-THP acting at the GABAA receptor.
el-Etr
M
M
Institut National de la Santé et de la Recherche Médicale Unité 33, Lab Hormones, Bicêtre, France.
Akwa
Y
Y
Fiddes
R J
RJ
Robel
P
P
Baulieu
E E
EE
D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology; D001921:Brain / Q000502:physiology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005445:Flunitrazepam / Q000378:metabolism; D015870:Gene Expression; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D009118:Muscimol / Q000378:metabolism / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011280:Pregnanolone / Q000494:pharmacology*; D011374:Progesterone / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000502:physiology*
D014151:Anti-Anxiety Agents; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D009118:Muscimol; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D005445:Flunitrazepam; D011280:Pregnanolone