ScienceDaily (Dec. 21, 2011) — Sensitivity to allopregnanolone, a hormone that occurs naturally in the body after ovulation and during pregnancy, changes during the course of the menstrual cycle and is different in women with severe pre-menstrual syndrome (PMS) compared with women without PMS complaints.

This has been shown by Erika Timby in her doctoral dissertation recently defended at Umeå University, Sweden.

Women without mood changes prior to menstruation are more sensitive to allopregnanolone immediately after menstruation and less sensitive before. On the other hand, sensitivity to allopregnanolone in women who suffer from severe PMS with pronounced mood shifts ahead of every period is the opposite: these women are more sensitive before than after. This may mean that they have less ability to adapt to hormonal variations prior to menstruation.

It is unclear what causes this, however, but it may be that these individuals have an altered function in one of the brain's signal substance system, the so-called GABA system. The researchers indirectly measure the effect on the GABA system with the help of a special method that monitors the speed of eye movements when the subject follows a moving point of light.

In the studies women were given the endogenous substance allopregnanolone in doses that elevated the allopregnanolone in the blood to levels normally seen during pregnancy. A fatiguing effect was recorded in the form of slower eye movement and increased feeling of tiredness.

"We have studied few women, but this is one of the first studies to examine the effects of this particular metabolite from the corpus luteus hormone in humans. Greater knowledge of the underlying mechanisms of pronounced PMS can ultimately provide clues for new methods of treatment," says Erika Timby, a specialist physician at the Women's Clinic, Norrlands University Hospital in Umeå and a doctoral candidate at the Department of Clinical Science, Unit for Obstetrics and Gynecology, Umeå University.

Dissertation: Allopregnanolone effects in women. Clinical studies in relation to the menstrual cycle, premenstrual dysphoric disorder and oral contraceptive use.