Effects of Heat-Stable Escherichia coli Enterotoxin on Intestinal Alkaline Secretion and Transepithelial Potential Difference in the Rat Intestines in Vivo

Abstract

The effects of the heat-stable enterotoxin of Escherichia coli (ST_a) on intestinal alkaline secretion and transepithelial electric potential difference (PD) were investigated in vivo in denervated segments of rat jejunum, ileum, and proximal colon. ST_a caused a significant increase in alkaline secretion in the jejunum but not in the ileum or colon. The jejunal effect of ST_a may be ascribed to a stimulation of bicarbonate secretion and/or an inhibition of Na⁺/H⁺ exchange. With regard to PD, ST^a caused a marked rise in colonic PD, whereas only a small response was found in the jejunum. No effect on PD was seen in the ileum. Hexamethonium (10mg/kg intravenously) significantly diminished the effects of ST_a on PD, whereas only a small inhibition of the ST_a-induced alkaline secretion was observed. The effect of lidocaine on PD and alkaline secretion was found to be similar to that of hexamethonium. Atiopine had no effect on any of the studied variables. These findings suggest that ST_a exerts, via nerves, a profound influence on the jejunal transport mechanisms responsible for the changes in PD, whereas the influence on alkaline secretion is to a large extent not mediated via enteric nerves. Thus, the extent of enteric nervous control of epithelial function differs for different transport functions. The findings also indicate that the bicarbonate ion is not the anion mainly responsible for the fluid secretion elicited by ST_a.

Key Words:

• Enteric nervous system
• intestinal secretion
• heat-stable Escherichia coli enterotoxin