Gastrin and gastric secretion

Reconstruction of the gastric cancer microenvironment after neoadjuvant chemotherapy by longitudinal single-cell sequencing

BACKGROUND

Little is known on the tumor microenvironment (TME) response after neoadjuvant chemotherapy (NACT) in gastric cancer on the molecular level.

METHODS

Here, we profiled 33,589 cell transcriptomes in 14 samples from 11 gastric cancer patients (4 pre-treatment samples, 4 post-treatment samples and 3 pre-post pairs) using single-cell RNA sequencing (scRNA-seq) to generate the cell atlas. The ligand-receptor-based intercellular communication networks of the single cells were also characterized before and after NACT.

RESULTS

Compered to pre-treatment samples, CD4+ T cells (P = 0.018) and CD8+ T cells (P = 0.010) of post-treatment samples were significantly decreased, while endothelial cells and fibroblasts were increased (P = 0.034 and P = 0.005, respectively). No significant difference observed with respect to CD4+ Tregs cells, cycling T cells, B cells, plasma cells, macrophages, monocytes, dendritic cells, and mast cells (P > 0.05). In the unsupervised nonnegative matrix factorization (NMF) analysis, we revealed that there were three transcriptional programs (NMF1, NMF2 and NMF3) shared among these samples. Compared to pre-treatment samples, signature score of NMF1 was significantly downregulated after treatment (P = 0.009), while the NMF2 signature was significantly upregulated after treatment (P = 0.013). The downregulated NMF1 and upregulated NMF2 signatures were both associated with improved overall survival outcomes based on The Cancer Genome Atlas (TCGA) database. Additionally, proangiogenic pathways were activated in tumor and endothelial cells after treatment, indicating that NACT triggers vascular remodeling by cancer cells together with stromal cells.

CONCLUSIONS

In conclusion, our study provided transcriptional profiles of TME between pre-treatment and post-treatment for in-depth understanding on the mechanisms of NACT in gastric cancer and empowering the development of potential optimized therapy procedures and novel drugs.

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.

PGE2 mediates the effect of pentagastrin on intestinal adenylate cyclase and Na-K-ATPase activities

The hypothesis that PGE2 mediates the effect of pentagastrin on jejunal Na-K-ATPase and adenylate cyclase activities was tested in rats. Mucosal PGE2 and cAMP contents, Na-K-ATPase and adenylate cyclase activities were determined 45 min after IV pentagastrin (1 microgram/100 g b.w.) administration to pyloric ligated rats. Pentagastrin almost doubled mucosal PGE2 content as compared to that in saline-treated rats: 198 +/- 19 (S.E., N = 11) and 109 +/- 9 (S.E., N = 26) pg/mg tissue, respectively, inhibited mucosal Na-K-ATPase activity: 16.4 +/- 0.7 (S.E., N = 8) as compared to 26.7 +/- 4.0 (S.E., N = 13) mumole/mg protein/h in saline-treated rats, stimulated adenylate cyclase activity by 146% and increased mucosal cAMP content by 80%. Pretreatment with indomethacin (4 mg/kg b.w., s.c./day x 2) prevented the increase in PGE2 content, the stimulation of adenylate cyclase activity and the inhibition of jejunal Na-K-ATPase activity induced by pentagastrin. The results reported thus suggest that the mechanisms whereby pentagastrin affects intestinal water and electrolyte transport are probably mediated by mucosal PGE2 and include inhibition of Na-K-ATPase activity and stimulation of the adenylate cyclase - cAMP system.

Gastrointestinal Function

This chapter discusses the functions of gastrointestinal tract. The principal functions of the gastrointestinal tract are assimilation of nutrients and excretion of the waste products of digestion. Within the gastrointestinal tract, these substances are solubilized and degraded enzymatically to simple molecules, sufficiently small in size and in a form that permits absorption across the mucosal epithelium. The distribution of the different types of secretory cells in the salivary glands varies among species. The mandibular and sublingual glands are mixed salivary glands containing both mucous and serous types of cells, and produce a viscous secretion that contains large amounts of mucus. The cytoplasm of the secretory cells contains numerous zymogen granules that vary in size and number depending on the activity of the gland. These granules contain the precursors of the hydrolytic enzymes responsible for digestion of the major dietary components. The cells of the terminal ducts probably secrete the bicarbonate ion responsible for neutralizing hydrochloric acid that enters the duodenum from the stomach.

The effect of aspirin on the fibrinolytic activity of gastric juice

Fibrinolytic activity in the gastric juice of normal subjects has been studied by a double-blind cross-over technique comparing the effect of placebo and pentagastrin against aspirin and pentagastrin. Aspirin effectively produced a gastritis and pure fibrinolytic activity was detected in the gastric juice, but the number of samples showing pure fibrinolytic activity did not differ between the two groups. In both the placebo and the aspirin groups the presence of a protease active at neutral pH and capable of dissolving fibrin is confirmed. Aspirin is unlikely to cause gastric bleeding by increasing local fibrinolytic activity within the stomach. The model, so constructed, is not sensitive enough to be of value in investigating further the role of gastric fibrinolytic activity in gastric haemorrhage.

Extraction of circulating endogenous gastrin by the gastric fundus

The effect of circulatory transit of the gastric fundus on serum levels of endogenous gastrin measured directly by radioimmunoassay has been studied in 14 dogs. Gastrin was measured in samples obtained simultaneously from the arterial inflow and venous outflow of the gastric fundus. During basal conditions, transit of the gastric fundus resulted in no change in gastrin concentration. During periods of stimulated gastrin release from the antrum, nine of the 14 dogs demonstrated a significant gastric acid secretory response. In these dogs there was a significant arteriovenous difference (approximately 30%) in circulating gastrin values. In the remaining five dogs, which did not demonstrate a significant gastric acid secretory response, there was no arteriovenous difference in circulating gastrin values. It is concluded that the gastric fundus is an important site for the inactivation of stimulated levels of circulating gastrin.