Gastric estrogen increases pituitary estrogen receptor α and prolactin mRNAs during the different pathological conditions of the liver

Age-related alterations of gastric mucosa and estrogen synthesis in rat parietal cells

The stomach has diverse functions other than gastric acid secretion. Multifaceted studies have investigated age-related changes of the gastrointestinal tract. Nevertheless, little is known about estrogen production changes in gastric parietal cells in rats aged over 3 months. We investigated age-related changes in gastric estrogen synthesis and the accompanying changes in liver estrogen receptor from 3 to 24 months. Weights of the body, stomach, and liver increased linearly from 3 to 18 months, then maintained a constant proportion up to 24 months. The gastric mucosa area (in mm²/1 mm muscularis mucosa) showed a constant proportion throughout the rats' life. The population of parietal cells immunostained area with H⁺/K⁺-ATPase decreased gradually with advancing age. Cells that were immunopositive to aromatase antibody were observed at 3-24 months. The expressions of aromatase mRNA and its protein were somewhat lower at 18 and 24 months than at 3 months. The portal venous estradiol concentration at 12 months was 1.5 times higher than that at 3 months, and that at 18 months was a half of that at 3 months. The expression of estrogen receptor mRNA in the liver at 18 and 24 months was about 80% of that at 3 months. Results suggest that the gastric estrogen production declines with aging, and the liver estrogen receptor is also affected accordingly. Simultaneously, the gastric mucosa continues to express aromatase to maintain liver function(s) throughout the animal's life.

Estrogen synthesis in the stomach of Sprague-Dawley rats: comparison to Wistar rats

Aromatase, an estrogen synthase, exists in the gastric parietal cells of Wistar rats. The stomach synthesizes large amounts of estrogens and secretes them into the portal vein. We have been particularly studying gastric estrogen synthesis using Wistar rats. However, estrogen synthesis in the stomach of Sprague-Dawley (SD) rats, which are used as frequently as those of the Wistar strain, has not been clarified. We examined steroid synthesis in the stomach of SD rats using immunohistochemistry, in situ hybridization, Western blotting, real-time PCR, and LC-MS/MS. Aromatase also exists in the stomach of SD rats. Its distribution was not found to be different from that of Wistar rats. Results show that H+/K+-ATPase β-subunit and aromatase colocalized in double immunofluorescence staining. Each steroid synthase downstream from progesterone was present in the gastric mucosa. These results suggest that steroid hormones are synthesized in the parietal cells in the same pathway as Wistar rats. Although mRNA expression of steroid synthases were higher in SD, no significant difference was found in the amount of protein and each steroid hormone level in the portal vein. Although differences between strains might exist in steroid hormone synthesis, results show that SD rats are as useful as Wistar rats for gastric estrogen synthesis experimentation.

Isoform-Dependent Changes in Cytochrome P450-Mediated Drug Metabolism after Portal Vein Ligation in the Rat

BACKGROUND

Surgical removal of complicated liver tumors may be realized in two stages via selective portal vein ligation, inducing the atrophy of portally ligated lobes and the compensatory hypertrophy of nonligated liver lobes. Unlike morphological changes, functional aspects such as hepatic cytochrome P450 (CYP)-mediated drug metabolism remain vaguely understood, despite its critical role in both drug biotransformation and hepatic functional analysis. Our goal was the multilevel characterization of hepatic CYP-mediated drug metabolism after portal vein ligation in the rat.

METHODS

Male Wistar rats (n = 24, 210-230 g) were analyzed either untreated (controls; n = 4) or 24/48/72/168/336 h (n = 4 each) following portal vein ligation affecting approximately 80% of the liver parenchyma. Besides the weights of ligated and nonligated lobes, pentobarbital (30 mg/kg)-induced sleeping time, CYP1A(2), CYP 2B(1/2), CYP2C(6/11/13), CYP3A(1) enzyme activities, and corresponding isoform mRNA expressions, as well as CYP3A1 protein expression were determined by in vivo sleeping test, CYP isoform-selective assays, polymerase chain reaction, and immunohistochemistry, respectively.

RESULTS

Portal vein ligation triggered atrophy in ligated lobes and hypertrophy nonligated lobes. Sleeping time was transiently elevated (p = 0.0451). After an initial rise, CYP1A, CYP2B, and CYP3A enzyme activities dropped until 72 h, followed by a potent increase only in the nonligated lobes, paralleled by an early (24-48 h) transcriptional activation only in nonligated lobes. CYP2C enzyme activities and mRNA levels were bilaterally rapidly decreased, showing a late reconvergence only in nonligated lobes. CYP3A1 immunohistochemistry indicated substantial differences in positivity in the early period.

CONCLUSIONS

Beyond the atrophy-hypertrophy complex, portal vein ligation generated a transient suppression of global and regional drug metabolism, re-established by an adaptive, CYP isoform-dependent transcriptional response of the nonligated lobes.

Expression and localization of aromatase in human gastric mucosa : Immunohistochemical study using biopsy materials

Parietal cells in the gastric mucosa are known not only as cells playing major roles in food digestion but also as cells bearing endocrine function. In addition to their production of gastrin and ghrelin, it has been recently revealed that these cells are also involved in the synthesis and secretion of estrogens with their expression of aromatase in experimental animals. Although aromatase activity has been detected in human gastric cancer cells and related cell lines, much less study has been done to ascertain the expression of the enzymatic activity in normal gastric mucosa. It has not been established which cell type is responsible for estrogen production in human gastric glands consisting of epithelial cells of several types. The aim of this study is to define the expression of aromatase by parietal cells in human gastric glands using immunohistochemical techniques. We retrieved formalin-fixed paraffin embedded materials of gastric biopsies from 16 patients (nine men, seven women). Colocalization of aromatase and H⁺/K⁺-ATPase β-subunit indicated that positive cells are parietal cells, but not chief cells and mucous cells. Furthermore, immunoreactivity of aromatase was detected within gastric glands irrespective of age or sex. These results suggest that human parietal cells synthesize estrogens within gastric mucosa and subsequently secrete them to the portal vein via gastric vein, as they do in rats. These estrogens might influence liver functions in humans. The estrogenic effects related to liver dysfunction might also be attributed to them.

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

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 1900 h), and were sacrificed at every 4-hour interval starting at 0800 h. 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 2400 h than that at 1200 h. The arterial E2 level was also the highest at 2400 h, and showed an apparent circadian rhythm positively correlated with portal venous E2 levels. Conversely, the expression of liver Esr1 peaked at 1200 h and turned to decrement at 2400 h. The population of immunoreactive nuclei with ERα antibody decreased at 2400 h compared with that at 1200 h. 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.

17β-Estradiol in the systemic circulation derives mainly from the parietal cells in cholestatic female rats

PURPOSE

Estrogenic symptoms of liver disease patients including biliary tract disorder with high frequency is observed in clinical cases. However, the origin of 17β-estradiol which is abundant enough to cause symptoms remains uncertain. In male rats, it has been reported that the parietal cells which have an abundance of aromatase-synthesized 17β-estradiol, and a part of 17β-estradiol secreted into the portal vein, may flow into the systemic circulation under a pathophysiological condition of the liver including bile duct ligation (BDL). The aim of this study is to reveal the origin of 17β-estradiol increment in female rats and to investigate the effect of BDL on the ovary during the estrus cycle.

METHODS

Wistar female rats were used, and the common bile duct was ligated twice and transected completely at 7 days before termination. Serum portal venous and arterial 17β-estradiol levels, Cyp19a1 expressions, aromatase protein levels, and estrogen receptor (ER) α levels in the liver were measured during the estrus cycle.

RESULTS

Both arterial and portal venous 17β-estradiol levels increased 2.9 times at proestrus and maintained constant levels during the cycle. The expression of Cyp19a1 and aromatase protein in the stomach maintained constant levels, and significantly decreased during the estrus cycle in the ovary. Hepatic ERα protein and Esr1 expressions decrease by BDL in all stages.

CONCLUSIONS

These results suggest that the increment of serum 17β-estradiol levels in obstructive cholestasis induced by BDL is derived from 17β-estradiol secreted from the parietal cells in females as well as males.

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.

Gastric estradiol-17β (E2) and liver ERα correlate with serum E2 in the cholestatic male rat

Cholestasis is associated with changes in hepatic cholesterol metabolism and serum estrogen levels. Ueyama and colleagues reported that the gastric estradiol-17β (E2) level in the portal vein is several times higher than that in the artery. This study aimed to clarify the relationships between gastric E2, hepatic estrogen receptor (ER) α and cholesterol metabolism in cholestatic male rats induced by bile duct ligation (BDL). After BDL, serum E2 levels in the portal vein and artery were measured by ELISA. The gene expression of gastric estrogen-synthesizing enzymes and various hepatic enzymes for cholesterol metabolism were measured by real-time RT-PCR, and gastric aromatase and hepatic ERα proteins were determined by immunohistochemistry and western blotting. Portal E2 levels increased by 4.9, 5.0, and 3.6 times that of controls at 2 days after BDL (BDL2d), BDL4d, and BDL7d respectively. The change in arterial E2 levels was positively correlated with that in the portal vein. Under these conditions, the expression of hepatic Ers1 (ERα) mRNA and protein was significantly reduced in a negative correlation with serum E2 levels in the portal vein after BDL. The expression of hepatic male-specific cytochrome P450 (CYP) genes Cyp2c55 and Cyp3a2 decreased and female-specific Cyp2c12 increased after BDL. It is postulated that the increase in gastric E2 levels, which occurs after BDL, results in the reduction of hepatic ERα, the elevation of arterial E2 level and leads to cholesterol metabolism becoming sex steroid dependent.

Postnatal development of gastric aromatase and portal venous estradiol-17β levels in male rats

Gastric parietal cells synthesize and secrete estradiol-17β (E₂) into gastric veins joining the portal vein, and a large amount of gastric E₂ first binds to its receptors in the liver. However, the role of the gastric E₂ is not entirely clear during postnatal development. The objective of this study was to reveal the onset of aromatase and other steroid-synthesizing enzymes in the gastric mucosa; to determine the period of rising E₂ levels in the portal vein; and to further understand the relationship between gastric E₂ and liver estrogen receptor α (ERα). The immunoblot bands and the immunohistochemistry of gastric mucosa revealed that aromatase protein began to express itself at 20 days and then increased in the levels of aromatase protein from 20 days onward. Expression of mRNAs for gastric aromatase (Cyp19a1) and other steroid-synthesizing enzymes, 17α-Hydroxylase (Cyp17a1) and 17β-hydroxysteroid dehydrogenase (HSD17b3), also increased similar to the increment of aromatase protein. Portal venous E₂ levels were elevated after 20 days and increased remarkably between 23 and 30 days, similar to gastric aromatase mRNA levels. The E₂ level was approximately three times higher at 40 days than that at 20 days. The liver weight and Esr1 levels began to increase after 20 days and the increment was positively correlated with the change of portal venous E₂ levels. These findings suggest that some changes may occur around 20 days to regulate the gastric E₂ synthesis and secretion.