Effects of estrogen on bicarbonate secretion of duodenal mucosa

Objective To study the effects of estrogen on bicarbonate secretion of duodenal mucosal, and to observe estrogen receptor (ER) subtypes of estrogen. Methods Sixteen 4-week-old male C57 mice were divided into control group and estrogen group, with eight mice in each group. The mice serum level of estrogen was detected by chemiluminescence. The expression of cystic fibrosis transmembrane conductance regulator (CFTR), solute carrier family 26 (SLC26) A3 and SLC26A6 in the duodenum tissues were determined by real-time polymerase chain reaction (RT-PCR). After SCBN cells treated with estrogen, ERα and ERβ blocking agent, and transfected with silenced ERα and ERβ for 24 and 48 hours, the expression levels of CFTR, SLC26A3 and SLC26A6 mRNA in cells were detected by RT-PCR. The effects of estrogen before and after silenced ERα and ERβ on bicarbonate secretion of SCBN cells were observed by high-speed ion imaging system. T test and rank sum test were used for statistical analysis. Results Compared with that of control group, the serum estrogen level of estrogen group was significantly high ((4 874±942) pmol/L vs. (657±187) pmol/L, t=-11.579, P<0.01). The expression levels of CFTR, SLC26A3 and SLC26A6 mRNAs in duodenum tissues of estrogen group were higher than those of control group (0.856±0.302 vs. 0.452±0.246, 2.910±1.680 vs. 1.120±0.540, 1.272±0.667 vs. 0.319±0.114), and the differences were statistically significant (t=-2.317, -2.483 and -3.721, all P<0.05). Compared with those treated with estrogen for 24 and 48 hours, the levels of CFTR mRNA and SLC26A6 mRNA were lower after the ERβ blocking agent were added into estrogen for 24 and 48 hours (CFTR mRNA: 0.171±0.059 vs. 0.522±0.260 and 0.111±0.014 vs. 0.578±0.297; SLC26A6 mRNA: 0.486±0.289 vs. 1.118±0.571 and 0.492±0.231 vs. 1.551±0.605), and the differences were statistically significant (tCFTRmRNA=2.974 and 2.655, tSLC26A6 mRNA=2.393 and 3.272; all P<0.05). Compared with those of silenced ERα group, the levels of CFTR mRNA, SLC26A3 mRNA and SLC26A6 mRNA were higher after ERα silenced and then added estrogen for 24 and 48 hours (24 h: 5.073±2.270 vs. 1.185±0.494, 1.796±1.168 vs. 0.468±0.108 and 3.085±1.357 vs. 0.706±0.347; 48 h: 5.025±1.998 vs. 1.185±0.494, 1.557±0.653 vs. 0.468±0.108 and 3.290±1.750 vs. 0.706±0.347), and the differences were statistically significant (t24 h=-4.122, -2.773 and -4.162, t48 h=-4.604, -4.034 and -3.250; all P<0.05). Compared with that of silenced ERα group, the bicarbonate secretion increased after ERα silenced and then added estrogen for 24 and 48 hours (0.72±0.17 and 1.15±0.25 vs. 0.35±0.17), and pH also elevated, and the differences were statistically significant (t=-6.516 and -12.387, both P<0.01). Conclusion Estrogen mainly up-regulates the expression of bicarbonate transporter protein in duodenal mucosal epithelial cells through ERβ, and promotes the bicarbonate secretion of duodenal mucosa. Key words: Estrogens; Bicarbonates; Estrogen receptor alpha; Estrogen receptor beta; Cystic fibrosis transmembrane conductance regulator; SLC26A3; SLC26A6