Quantitative distribution of brush cells in the rat gastrointestinal tract: brush cell population coincides with NaHCO3 secretion.

The function of brush cells is obscure, but recent cytochemical studies indicate that rat bile duct brush cells secrete NaHCO(3). The aim of this study was to determine the quantitative distribution of brush cells at 16 sites of the rat gastrointestinal tract and to investigate the role of NaHCO(3) secretion at these sites. Specimens of 16 sites of the gastrointestinal tracts of three female Long-Evans rats were fixed in a periodate-lysine-paraformaldehyde solution. Frozen sections were stained with the anti-cytokeratin 18 antibody, a selective marker for brush cells. The numbers of brush cells were counted from photographs. The percentages of brush cells in the epithelium at the 16 sites were gastric groove, 32.3%; corpus adjacent to the gastric groove, 2.5%; corpus, 0.4%; antrum, 0.4%; duodenum adjacent to the pyloric ring, 2.3%; proximal duodenum, 0%; duodenum facing the bile duct orifice, 0%; distal duodenum, 0.2%; proximal jejunum, 0.1%; transitional site between the jejunum and the ileum, 0.1%; distal ileum, Peyer's patch dome, 1.5%; and the villi, 0.4%; caecum, 2.1%; proximal colon, 0.2%; middle colon, 0.1%; distal colon, 0.1%; and rectum, 0.1%. We concluded that the population of brush cells is high in the gastric groove, the duodenum adjacent to the pyloric ring, and the caecum, where NaHCO(3) is postulated to neutralize gastric HCL or organic acids produced by enteric bacteria. The brush cell population is low in the duodenum and jejunum, which receive bile and pancreatic juice.