Villus and crypt electrolyte and fluid transport during intestinal secretion

The apical parts of jejunal villi of net-absorbing intestine have been shown to contain sodium chloride concentration gradients which are associated with water absorption (Sjöqvist & Beeuwkes 1989). To determine whether these gradients are different in states of intestinal net secretion, jejunal segments of chloralose-anaesthetized cats were perfused with modified Krebs-Henseleit solutions while secretion was elicited by cholera toxin or vasoactive intestinal polypeptide (VIP). The segments were then rapidly frozen and freeze-dried, and sodium and chloride contents of the lamina propria of single villi were measured by X-ray microanalysis. The apical third of the villus was found to contain a concentration gradient of sodium and chloride when the lumen contained sodium, with no difference between secreting intestine and absorbing control intestine. When the intestine was perfused with hypotonic choline-mannitol solution, no sodium or chloride gradient was found. In this state, treatment of the intestines with secretagogues allowed development of an apical concentration gradient. This demonstrated that the absorptive function of the villus tip was unimpaired during secretion and that secretion from the crypt could supply sufficient electrolyte to allow formation of an apical gradient.