Interaction of Escherichia coli heat -stable enterotoxin (STa) with its receptor on mammalian intestinal tract

Ahmad Mahmmoud Al-Majali, Purdue University

Abstract

We found that insulin up-regulated the interaction between enterotoxigenic Escherichia coli (ETEC) STa and its receptor suggesting that insulin and other growth factors, which occur at high concentrations in the colostrum, may increase the susceptibility of young subjects to STa-induced diarrhea. We also found that, in 2-day-old mice, STa-receptor density and affinity were higher than in older mice. Results of these studies suggest that the increased susceptibility of human infants and newborn animals to STa-induced diarrhea might be due to the increase in the density and affinity of STa-receptor. We studied the distribution of STa-receptor throughout newborn calf intestinal tract and found that STa-receptor density was higher on enterocytes and brush border membrane vesicles (BBMVs) derived from the ileum than enterocytes and BBMVs prepared from other segments of calf intestine. Additionally, the affinity of the ileum STa-receptors was higher than the affinity of receptors present on the epithelium of other intestinal segments. This study suggests that ileum is the major part of the intestine affected in secretory diarrhea caused by STa-producing ETEC. Challenging newborn calves with diarrheagenic doses of STa resulted in severe profuse watery diarrhea within 2 hours of challenge. Upon necropsy, ileum from STa-challenged calves was markedly engorged with fluids. STa interaction with its receptor was demonstrated, in vivo, using ileal cryostat sections stained with anti-STa and secondary FITC-conjugated antibody. Light and electron microscopic analysis suggested no major ultrastructural changes were caused by STa. Brush border membrane lactase activity was higher in the ileum of STa-challenged calves than in ileum of control calves. A significant increase in the activity of guanylate cyclase in the ileum of STa-challenged newborn calves was observed. Upon analysis of the intestinal contents, we found that Na+ concentration in intestinal contents from the ileum of STa-challenged calves was significantly higher than ileum of control calves. This study supports previous observations on the role of guanylate cyclase in the initiation of STa-induced diarrhea and suggests that the Na+/Cl− coupling may be the major mechanism for ions loss in the diarrheal response that is mostly affected by the ileum in newborn calves.

Degree

Ph.D.

Advisors

Saeed, Purdue University.

Subject Area

Veterinary services

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