On the mode of action of the sympathetic fibres on intestinal fluid transport: evidence for the existence of a glucose-stimulated secretory nervous pathway in the intestinal wall.

The effect of sympathetic nerve stimulation or close i.a. infusion of noradrenaline on net fluid transport was investigated on anesthetized cats. In the presence of glucose in the solution perfusing the intestinal lumen the adrenergic mechanisms increased net fluid absorption in normal intestines. Substituting glucose with mannitol in the perfusate abolished this effect of adrenergic stimulation on the net fluid uptake. Furthermore, the effect of noradrenaline on net fluid transport in normal or choleraic intestines was abolished by tetrodotoxin (TTX), a nerve conductivity blocking agent. This suggests that the sympathetic influence is dependent on intraluminal glucose and that noradrenaline exerts its effect mainly via nerves. TTX significantly increased fluid uptake from normal intestines perfused with an isotonic electrolyte solution containing glucose while a considerably smaller effect was seen in intestinal segments perfused with a solution with mannitol. Based on these findings it is proposed that glucose in some way activates intramural nervous reflex(es) in the intestinal wall. According to this hypothesis the enhancement of fluid transport induced by adrenergic stimuli is explained by an inhibition of the glucose-activated nervous secretion.