COMPARISON OF THE EFFECTS OF SECRETAGOGUES ON THE NET MOVEMENT OF ELECTROLYTE AND GLUCOSE-ABSORPTION IN THE PROXIMAL AND MIDDLE SMALL-INTESTINE OF SHEEP

This study was designed to compare the effects of VIP and PGE(2) on gl ucose absorption and net movement of water and electrolytes between th e proximal and middle small intestines of sheep. Intraluminal perfusio n was performed at 1 ml/min with isotonic 10 mM glucose solution adjus ted osmolality by adding NaCl, and the outflow solution was collected every 10 min. After a 30 min control period, VIP (1000 pmol/kg per h, intravenously) or PGE(2) (100 mu M, intraluminally) was infused for 30 min. The basal net movement of water, sodium and potassium did not di ffer significantly between the proximal and the middle small intestine . However, the basal net secretion of bicarbonate in the middle part w as 6.4 times higher than in the proximal part, while inversely, the ab sorption of chloride was 4.9 times higher in the middle part than in t he proximal part. Basal net glucose absorption in the proximal part wa s 1.8 times higher than in the middle part. VIP and PGE(2) reversed th e net absorption of water and sodium to secretion in both loops. VIP a lso stimulated potassium secretion in both loops, while PGE(2) had no effect in either loop. In the proximal loop, VIP only stimulated bicar bonate secretion without changing chloride flux, while PGE(2) markedly stimulated the secretion of both bicarbonate and chloride. In the mid dle loop, both secretagogues did not affect the bicarbonate secretion, but significantly decreased the chloride absorption VIP did not affec t glucose absorption in either loop, while PGE(2) significantly decrea sed it in both loops. In conclusion, the secretory responses of water and electrolytes, except bicarbonate, to VIP and PGE(2) and their acti on on glucose absorption were similar in both the proximal and middle small intestines. Secretory, responses of bicarbonate to VIP and PGE(2 ) were observed only in the proximal part, where the basal secretory l evel was low. This result suggest that the effects of VIP and PGE(2) o n bicarbonate secretion in the small intestine depend on the initial s ecretory activity.