Changes of gastric aromatase and portal venous 17β-estradiol during the postnatal development and estrus cycle in female rats

Gastric parietal cells synthesize and secrete a large amount of 17β-estradiol into the portal vein. However, there are few studies on the gastric 17β-estradiol during the postnatal development and estrus cycle. The purpose of this study is to clarify the onset and the prepubertal change of gastric 17β-estradiol synthesis; and the effect of gastric 17β-estradiol on the estrus cycle. Wistar female rats aged from 15 to 40 days and 10 weeks were used in the study. The expression of aromatase and estrogen receptor (ER) α mRNAs and proteins was analyzed in the stomach, ovary, and liver by RT-PCR, immunohistochemistry, and Western blotting methods; and 17β-estradiol levels in the artery and portal vein were assayed by the ELISA method. During postnatal development, aromatase protein and aromatase cells in gastric mucosa and portal venous 17β-estradiol levels started increasing after 20 days, and then these subjects reached nearly the same levels as mature female rats at 40 days. In the estrus cycle, the arterial 17β-estradiol level in proestrus was the highest, and the value was 60 % of the portal venous level. Gastric aromatase protein and portal venous 17β-estradiol levels did not change during the estrus cycle. Ovarian ERα levels fluctuated in the same pattern of arterial 17β-estradiol; however, hepatic ERα levels went unchanged. These results showed that gastric aromatase in females expresses earlier than the sexual maturation, and the gastric aromatase protein reaches the same levels as mature rats at 40 days. Furthermore, 17β-estradiol synthesis and secretion in the stomach is not related to those in the ovary.