Effect of Ganglionic Blocking Compounds on In-vivo Fluid Secretion in the Rat Small Intestine

It is well-known that enteric, secreto-motor nerves mediate cholera toxin-induced fluid secretion in the rat small intestine. This notion is, in part, derived from experiments on anaesthetized animals in which the response to cholera toxin was antagonized by the ganglionic nicotinic receptor antagonist, hexamethonium. In the current study, such anti-secretory action of ganglionic blocking compounds was analysed in an experiment designed to minimize any possible negative effect of general anaesthesia on intestinal secretion. Rats were anaesthetized with ether for 5-10 min, during which time a jejunal loop (10-12 cm) was constructed. The loop was challenged with one of the secretagogues, cholera toxin, prostaglandin E1 (PGE1) or okadaic acid. Saline (control) or either of the ganglionic blockers, hexamethonium and chlorisondamine, was administered intravenously. The rats were killed 5 h (cholera toxin) or 1.5 h (PGE1 and okadaic acid) after challenge, and the amount of fluid accumulated in the loops was determined. Cholera toxin-induced secretion was unchanged by hexamethonium but reduced by approximately 80% by chlorisondamine. The difference in effect between the two blockers might relate to the duration of ganglionic blockade. Chlorisondamine blocked secretion induced by either PGE1 or okadaic acid by approximately 60%. It is suggested that the anti-secretory effect of ganglionic blocking compounds might be a result of blockade of secreto-motor nerves but other mechanisms, for example interference with haemodynamic factors, cannot be ruled out.