Differential expression of estrogen receptor alpha gene in the ampullae and isthmus regions of the rabbit oviduct during early pregnancy

We characterized the expression pattern of estrogen receptor α (ERα) gene in two regions of the oviduct, ampullae and isthmus, of the rabbit (Oryctolagus cuniculus) during early pregnancy (1–4 days) by RT-PCR and immunohistochemistry. In both regions of the oviduct, ERα mRNA was increased (P < 0.01) in pregnant rabbits as compared with non-pregnant animals (NG). In the ampullae, the greatest amount of ERα mRNA was detected on the third day of pregnancy (1.01 ± 0.02 relative amount), followed by a decrease on Day 4. In the isthmus, an increase in ERα mRNA was observed during the first 4 days of pregnancy, with the greatest amount on Day 3 (1.49 ± 0.3 relative amount). A marked ERα immunostaining was detected in epithelial, stromal and smooth muscle cells of the ampullae on the second and third days of pregnancy as compared with the NG group. In contrast, a significant increase in ERα immunostaining was observed on the first and second days of pregnancy with a reduction on the third and fourth days in the epithelial, stromal and smooth muscle cells of the isthmus. The overall results suggest there is differential expression pattern for the ERα gene in the ampullae and isthmus during early pregnancy of the rabbit, and that these variations are related to specific functions of ERα in the reproductive tract during early pregnancy.