Glicentin (GLIC) and oxyntomodulin (OXM) are released from the ileum and colon during digestion. Both hormones reduce fluid and proton secretion in the stomach. The luminal concentration of sodium and chloride underlying the nutrient absorption, the effect of OXM on electrolyte transport through the small intestine, was assessed in vivo using ligated loops and in vitro using Ussing chambers. In vivo, a zero transport state, estimated by the net water, chloride, and sodium fluxes, was observed when an 80 mM NaCl normoosmolar solution (274 mosm) was administered intraluminally. Active secretion was observed with hyperosmotic challenge (474 mosm). The amplitude of this active secretion increased 2.5- to 3-fold when an electrogenic challenge (NaCl 40 mM) was substituted to the hyperosmotic one. OXM (800 fmol/ml plasma) did not modify the basal transport in the duodenum or in the jejunum (t = 45 min). When active secretion was induced by the hyperosmotic challenge, OXM (200 fmol/ml plasma) had no effect on duodenal or jejunal transport (t = 50 min). When active secretion was induced by an electrogenic challenge, OXM (300 fmol/ml plasma) preferentially reduced the hydromineral transport in jejunum. In vitro, OXM also induced a reduction in the ion transport towards the jejunal lumen (EC50 = 20 pM), the amplitude of which depended upon the integrity of the tetrodotoxin-sensitive neurons. In conclusion, OXM was able to reduce the large secretion induced in rat jejunum in vivo by an electrogenic gradient. In vitro, the antisecretory effect of OXM was partly mediated by the neurons present in the intrajejunal wall.