Interaction between Bovine Casein and V. Cholerae Enterotoxin in the Rabbit Ileal Loop

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Abstract
Summary: Secretory IgA from human breast milk neutralizes cholera enterotoxin in the rabbit ileal loop system. No similar protection by purified bovine milk proteins could be demonstrated; however, one bovine milk protein, casein, had a deleterious effect on intestine exposed to very small quantities of enterotoxin. Highly purified cholera toxin (10 or 100 ng) was incubated with bovine protein solutions for 60 min at 37°C. One-milliliter aliquots were then injected into prepared rabbit intestine loops. The animals were sacrificed at 18 h and the intestinal loop contents were aspirated, and a volume to length of loop ratio (V/L) was determined. The activity of 100 ng of toxin was not enhanced by the majority of bovine milk proteins, but bovine casein caused a 14-40% increase in the fluid production (V/L of casein + toxin versus toxin, 1.05 versus 0.92 and 1.82 versus 1.30). All of the bovine proteins but casein inhibited the action of low dose enterotoxin. Bovinec asein caused a 78-90% increase in fluid production by loops exposed to a suboptimal toxin dose (10 ng) (V/L of casein + toxin versus toxin, 1.12 versus 0.63 and 0.95 versus 0.50). Virtually all of this enhancement of enterotoxin fluid response resided in the purified alpha-casein fraction.

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