Separation of Cholera Enterotoxin-Induced Mucus Secretion from Electrolyte Secretion in Rabbit Ileum by Acetazolamide, Colchicine, Cycloheximide, Cytochalasin B and Indomethacin

Abstract

In vivo rabbit ileal loops were prepared and inoculated with purified cholera enterotoxin (CT). After a lag period of about 1 h there was persistent stimulation of water and electrolyte secretion and a transient stimulation of mucus secretion into the luminal fluid. Repeated intraluminal inoculation of prostaglandin E₁ (PGE₁) caused a pattern of water, electrolyte and mucus secretion which was qualitatively the same as that following CT, except that no lag period was observed. Doses of the protein synthesis inhibitor, cycloheximide, the microtubule disrupter, colchicine, and the microfilament disrupter, cytochalasin B, were found that inhibited CT-induced mucus secretion but not water and electrolyte secretion. The carbonic anhydrase inhibitor, acetazolamide, inhibited CT-induced water and electrolyte secretion without inhibiting the mucus secreted over a 5-hour test period. Thus a variety of agents can be used to demonstrate a separation of intestinal water and electrolyte secretion from mucus secretion. The prostaglandin synthesis inhibitor, indomethacin, also inhibited CT-induced water, electrolyte and mucus secretion, but no dose of this agent was found that completely separated the water and electrolyte from the mucus secretion.

Cholera enterotoxin-induced mucus secretion and increase in the mucus blanket of the rabbit ileum in vivo

“…Cholera enterotoxin has been shown to be a potent stimulant of both intestinal mucus secretion (6,7,9,16,19) and mucin synthesis (6, 7), and there is evidence that cholera enterotoxin preferentially stimulates the secretion of the most recently synthesized mucin (6). Previous studies (9,16) and the present study showed that cholera enterotoxininduced mucin secretion into the lumen was short lived, while toxin-induced water and electrolyte secretion was sustained for many hours. The fact that a second exposure to cholera enterotoxin or another secretagogue failed to produce a second mucus secretion response could be explained by one or more of three explanations.…”

“…In the preliminary experiments, mucus secretion was assessed by measuring the apparent viscosity of the luminal fluid after normalizing the fluid volume to loop length. Increased apparent viscosity of the luminal fluid has been shown to correlate with increased nondialyzable hexose concentration in the luminal fluid (16). Figure 1 shows the results of such an experiment in which ileal loops were exposed to a supramaximal concentration of cholera enterotoxin (50 ,ug) for 1 h. Water secretion gradually increased to a maximal level and remained at that level for the duration of the experiment, while mucus secretion into the luminal fluid exhibited a peak value and declined thereafter.…”

“…Again, the increase in mucus secretion was transient, while the increase in water secretion was sustained. When these experiments were repeated with the supramaximal dose of cholera enterotoxin in hour 1 and another known secretagogue, prostaglandin E1 (10-l M), in the luminal fluid during hour 7 (16), no second pulse of mucus secretion was observed and the plateau in water secretion was unaffected. When dibutyryl cAMP and theophylline were substituted for cholera enterotoxin in ileal loops (Table 1), a significant (P < 0.01) net water secretion was observed in hour 1 and this secretion did not significantly change with time.…”

“…Often mucus fragments may be the only formed material visible in such stool. In experimental cholera, the hypersecretion of electrolytes and water into the small intestinal lumen is associated with a hypersecretion of mucus (6,7,9,16,18,19) and goblet cells in the area exposed to cholera enterotoxin are depleted of their content (22). The hypersecretion of water and electrolytes in cholera enterotoxin-treated small intestine is apparently sustained for as long as the mucosal epithelial cell adenylate cyclase is stimulated and tissue cyclic AMP (cAMP) levels are elevated (4, 10, 11), but there is some question as to whether or not the mucus hypersecretion of experimental cholera is cAMP mediated (15, 18Y.…”

The Front Line of Enteric Host Defense against Unwelcome Intrusion of Harmful Microorganisms: Mucins, Antimicrobial Peptides, and Microbiota

“…Both Ca 2ϩ -and cAMP-mediated second messenger cascades acutely regulate mucin secretion from human colonic epithelial cells (44,47,183). Cholera toxin that binds with high affinity to apically localized receptors on mucin-secreting cells (215) is a strong activator of mucin exocytosis (96,214,272,273,284,332). In contrast, Clostridium difficile toxin A is able directly to affect the intestinal epithelial barrier function and down-regulates stimulated mucin exocytosis (48).…”