Effects of solution osmolality on absorption of select fluid replacement solutions in human duodenojejunum

These experiments examined relationships between initial osmolality and carbohydrate (CHO) composition of an infused solution and osmolality and water and CHO absorption in a test segment. A triple-lumen tube with a 10-cm mixing segment and a 40-cm test segment was passed into the duodenojejunum. The infusion port was approximately 10 cm beyond the pyloric sphincter. Perfusion solutions were hypotonic (186 mosmol/kg; solution A), isotonic (283 mosmol/kg; solution B), and hypertonic (403 mosmol/kg; solution C). All solutions contained 18 meq Na+ and 3 meq K+. In the mixing segment, osmolality increased 83 mosmol/kg and decreased 90 mosmol/kg for solutions A and C, respectively. Corresponding changes in the test segment were an increase of 60 mosmol/kg and a decrease of 34 mosmol/kg. The osmolality of solution B did not change. In the test segment, mean osmolality and water and total solute fluxes were not significantly different among solutions, but solution C produced 27% greater fluid absorption than did solution A. When net fluid movement from mixing and test segments was determined, solution A produced 17% greater fluid absorption than did solution C. The mean increases in plasma and urine volumes over the 80-min test period were not significantly different. In the test segment, water flux correlated with CHO and Na+ fluxes but not with osmolality. In conclusion, 1) significant differences in solution osmolality were eliminated within the proximal duodenum and 2) perfusing 6% CHO solutions with osmolalities ranging from 186 to 403 mosmol/kg did not produce significant differences in fluid homeostasis (plasma volume) at the end of an 80-min test period.