Neuroactive pregnanolone isomers during pregnancy

Abstract

The pregnanolone isomers (PI) allopregnanolone (3α-hydroxy-5α- pregnan-20-one), pregnanolone (3α-hydroxy-5β-pregnan-20-one), isopregnanolone (3β-hydroxy-5α-pregnan-20-one), epipregnanolone (3β-hydroxy-5β-pregnan-20-one), progesterone, and estradiol were measured in 138 pregnant women. The sampling was carried out from the first through the 10th month of pregnancy. Gas chromatography-mass spectrometry analysis and RIA were used for the measurement of steroid levels. The ratios of individual PI were similar to those found previously around parturition: about 25:10:7:1 for allopregnanolone, pregnanolone, isopregnanolone, and epipregnanolone, respectively. All the PI showed a significant increase during pregnancy, which was more pronounced in the 3α-steroids. The results indicated changing ratios between 3α-and 3β-PI and between 5α- and 5β-PI throughout pregnancy. The constant allopregnanolone/ isopregnanolone ratio found through pregnancy weakened the hypothesis of the role of isopregnanolone in the onset of parturition. The ratio of estradiol (stimulating uterine activity) to 5α-PI and epipregnanolone exhibited significant changes during pregnancy in favor of estradiol up to the sixth or seventh month, in contrast to the constant estradiol/pregnanolone ratio. A pregnancy-stabilizing role of pregnanolone, counterbalancing the stimulating effect of estradiol on the onset of parturition, was suggested.