Progesterone receptor isoform expression in response to in utero growth restriction in the fetal guinea pig brain.

Intra-uterine growth restriction (IUGR) is a significant in utero complication that can have profound effects on brain development including reduced myelination and deficits that can continue into adulthood. Progesterone increases oligodendrocyte proliferation and myelin expression, an action that may depend on the expression of progesterone receptor (PR) isoforms A (PRA) and B (PRB). The objective of this study was to determine the effect of IUGR on PR isoform expression in the brain of male and female fetuses and whether effects were associated with a reduction in myelination. We used a guinea pig model that involves selective reduction in maternal perfusion to the placenta at midgestation (35 days, term 70 days). This resulted in a significant reduction in body weight with marked sparing of brain weight. PRA, PRB and myelin basic protein (MBP) expression were measured in the brains of male and female growth-restricted and control fetuses at late gestation. MBP, as a measure of myelination, was found to decrease in association with IUGR in the CA1 hippocampal region with no change observed in the cortical white matter. There was a marked increase in PRA, PRB and total PR expression in the IUGR fetal brain. Control female fetuses demonstrated significantly higher PRA:PRB ratios than males; however, this sex difference was abolished with IUGR. These data suggest the central nervous system effects of clinical use of progesterone augmentation therapy in late pregnancy should be carefully evaluated. The overall upregulation of PR isoforms in association with IUGR suggests increased progesterone action and a possible neuroprotective mechanism.