Involvement of 5-hydroxytryptamine and prostaglandin E2 in the intestinal secretory action of Escherichia coli heat-stable enterotoxin B

Abstract

The intestinal secretory action of Escherichia coli heat-stable enterotoxin B (STb) is poorly defined. Previous work indicates that STb causes loss of intestinal fluid and electrolytes by a mechanism independent of elevated levels of cyclic nucleotides, the hallmark of other E. coli cytotonic enterotoxins. In the work described in this report, we observed that treatment of ligated rat intestinal loops with purified STb of E. coli resulted in a dose-dependent rise in intestinal secretion concomitant with dose-related increases in levels of serotonin (5-hydroxytryptamine [5-HT]) and prostaglandin E 2 (PGE 2). Treatment of rats with the 5-HT 2 receptor antagonist ketanserin prior to STb challenge resulted in significant (P < 0.05) reduction in intestinal secretion. Blockage of 5-HT 2 receptors with ketanserin also reduced (P < 0.05) the level of PGE 2 observed following STb treatment, indicating that at least a portion of the PGE 2 was formed in response to 5-HT 2 receptor stimulation. In a similar fashion, indomethacin, an inhibitor of cyclooxygenase activity, significantly reduced the level of secretion (P < 0.05) observed following STb treatment yet had no effect on 5-HT levels. Treatment of rats with both ketanserin and indomethacin further reduced STb-mediated secretion to a level not attained by either drug alone. Taken together, our data suggest that secretion due to STb involves both 5-HT and PGE 2 as intestinal secretagogues. Furthermore, PGE 2 formation appears to arise through both 5-HT-dependent and 5-HT-independent pathways.

Interaction of Escherichia coli heat-stable enterotoxin B with rat intestinal epithelial cells and membrane lipids

“…By comparison, STbmediated [Ca P ] i in£ux in cultured cells as well as increases in the short circuit current and potential di¡erence in pig intestinal mucosa are detected within 2 min after exposure to STb [2,17]. Subsequent formation and release of intestinal secretagogs (PGE P and 5-HT) occurs within 20^30 min, which parallels the time range for detecting £uid secretion in the lumen of rats and mice [3,4]. Dissociation of bound IPS I-STb was examined to see if it was as rapid as the association interaction and if the binding process was reversible.…”

“…STb at doses of 91 WM elicits a maximum £uid secretion in mouse and rat intestinal loops, while as little as 5^10 nM of STb causes £uid secretion and PGE P release in pigs [3,4]. STb-mediated [Ca P ] i in£ux and release of arachidonic acid and PGE P occurs at 0.05 WM STb and 50 pmol STb per loop, respectively [3,4]. Thus, at STb concentrations which mediate signal transduction and intestinal secretory responses, the interaction of STb with intestinal epithelial cells is unsaturable and nonspeci¢c.…”

“…The binding isotherms could not be ¢tted by LIGAND if more than one binding site was considered. STb at doses of 91 WM elicits a maximum £uid secretion in mouse and rat intestinal loops, while as little as 5^10 nM of STb causes £uid secretion and PGE P release in pigs [3,4]. STb-mediated [Ca P ] i in£ux and release of arachidonic acid and PGE P occurs at 0.05 WM STb and 50 pmol STb per loop, respectively [3,4].…”

Escherichia coliSTb toxin and colibacillosis: knowing is half the battle

“…This activates the opening of an intestinal ion channel and may also activate protein kinase C and consequently CFTR (Dreyfus et al, 1993;Fujii et al, 1997). The increased calcium levels could regulate the activities of phospholipases A 2 and C and release arachidonic acid from membrane phospholipids leading to the formation of PGE 2 and 5-HT, which mediate H 2 O and electrolytes transport out of the intestinal cells (Hitotsubashi et al, 1992b;Harville & Dreyfus, 1995;Peterson & Whipp, 1995). The quantity of PGE 2 is proportional to the volume of fluid released into the intestinal lumen.…”

Weapons of mass destruction: virulence factors of the global killer EnterotoxigenicEscherichia coli

“…This results in an influx of calcium through a receptordependent ligand-gated calcium channel activating calmodulin-dependent protein kinase II, which opens an intestinal ion channel and may also activate protein kinase C and consequently CFTR (Dreyfus et al, 1993;Sears & Kaper, 1996;Fujii et al, 1997). The increased calcium levels are also thought to regulate phospholipases (A2 and C) that release arachidonic acid from membrane phospholipids, leading to the formation of intestinal secretagogues prostaglandin E2 (PGE 2 ) and 5-hydroxytryptamine (5-HT), which mediate water and electrolyte transport out of intestinal cells (Hitotsubashi et al, 1992;Harville & Dreyfus, 1995;Peterson & Whipp, 1995). PGE 2 and 5-HT are likely to activate the enteric nervous system (Sears & Kaper, 1996;Dubreuil, 1997).…”