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Background: Premenstrual dysphoric disorder (PMDD) affects 3–8% of women in fertile ages. Combined oral contraceptives (OCs) are widely used and some users experience adverse mood effects. The cyclicity of PMDD symptoms coincides with increased endogenous levels of allopregnanolone after ovulation. Allopregnanolone enhances the effect of γ-aminobutyric acid (GABA) on the GABA_A receptor, the principal inhibitory transmitter system in the brain. The sensitivity to other GABA_A receptor agonists than allopregnanolone (i.e. benzodiazepines, alcohol and the 5 β epimer to allopregnanolone, pregnanolone) has been reported to depend on menstrual cycle phase and/or PMDD diagnosis. Isoallopregnanolone, the 3 β epimer to allopregnanolone, has previously been used to verify specific allopregnanolone GABA_A receptor effects. Saccadic eye velocity (SEV) is a sensitive and objective measurement of GABA_A receptor function.

Aims: To study the pharmacological effects, and any effect on gonadotropin release, of intravenous allopregnanolone in healthy women. A second aim was to explore whether allopregnanolone sensitivity differs over the menstrual cycle or during OC use in healthy women, and thirdly in PMDD patients.

Methods: Ten women were challenged with a cumulative dose of intravenous allopregnanolone in the follicular phase of the menstrual cycle. The effect on FSH and LH was compared to women exposed to isoallopregnanolone. A single dose of allopregnanolone was administered once in the follicular phase and once in the luteal phase in another ten healthy women and in ten PMDD patients, and additionally in ten women using OCs. Repeated measurements of SEV, subjectively rated sedation and serum concentrations after allopregnanolone injections were performed in all studies.

Results: Allopregnanolone dose-dependently reduced SEV and increased subjectively rated sedation. Healthy women had a decreased SEV response in the luteal phase compared to the follicular phase. By contrast, PMDD patients had a decreased SEV response and subjectively rated sedation response to allopregnanolone in the follicular phase compared to the luteal phase. There was no difference in the SEV response to allopregnanolone between women using oral contraceptives and healthy naturally cycling women. Allopregnanolone decreased serum levels of FSH and LH whereas isoallopregnanolone did not affect FSH and LH levels.

Conclusion: Intravenous allopregnanolone was safely given and produced a sedative response in terms of SEV and subjectively rated sedation in women. The sensitivity to allopregnanolone was associated with menstrual cycle phase, but in the opposite direction in healthy women compared to PMDD patients. The results suggest mechanisms of physiological tolerance to allopregnanolone across the menstrual cycle in healthy women and support that PMDD patients have a disturbed GABA_A receptor function. In addition, one of our studies suggests that allopregnanolone might be involved in the mechanism behind hypothalamic amenorrhea.