Gastric 17β-estradiol in portal vein and liver Esr1 make a circadian rhythm in systemic circulation in male rats.

Abstract

The hemodynamics of 17β-estradiol (E2) synthesized and secreted from the stomach has been revealed gradually. This study aimed to clarify the circadian rhythm of E2 synthesis and secretion in the stomach, and the relationship between the expression of hepatic estrogen receptor (ER) α and serum E2 levels in systemic circulation. Wistar male rats were maintained in a room with a 12-h light and 12-h dark cycle (lights on from 0700 to 1900h), and were sacrificed at every 4-hour interval starting at 0800h. The results showed that the expression of gastric Cyp19a1 was higher in nighttime than in daytime, and that the portal venous E2 level was 2.2 times higher at 2400h than that at 1200h. The arterial E2 level was also the highest at 2400h, and showed an apparent circadian rhythm positively correlated with portal venous E2 levels. Conversely, the expression of liver Esr1 peaked at 1200h and turned to decrement at 2400h. The population of immunoreactive nuclei with ERα antibody decreased at 2400h compared with that at 1200h. The regression analysis showed that the liver Esr1 mRNA was negatively correlated to portal venous and arterial E2 levels. It could be concluded that the circadian rhythm of the systemic E2 level depended both on the amounts of gastric E2 in the portal vein and on the Esr1 expression in the liver.