Small intestinal permeability in animals and man

Abstract

SUMMARY The permeability ofthe human small intestine has been studied by measuring the clearance from the plasma into the intestinal lumen of substances with molecular weights ranging from 60 to 80 000. A direct relationship has been demonstrated between intestinal loss and plasma concentration and an inverse one between clearance and molecular size.The permeability of the rabbit small intestine has been studied at various levels by measuring the blood-to-lumen clearance of substances of different molecular size ranging from 60 to 40 000. It has been demonstrated that there is a progressive fall in permeability from the duodenum to the terminal ileum for all the substances studied. Part I Small intestinal permeability in manAlthough the prime function of the small intestine is that of absorption and the transfer of substances from the lumen into the body, a continuous flow in the reverse direction is also known to occur. These substances are derived from the plasma by direct permeation through the mucosa, but also pass out into the lumen in secretions from the gallbladder, pancreas, Paneth and goblet cells, or through desquamation of intestinal epithelial cells.In previous experiments with rabbits (Loehry, Axon, Hilton, Hider, and Creamer, 1970) it has been demonstrated that the transfer of substances passing directly from the blood into the lumen is dependent directly upon their concentration in the plasma and inversely upon their molecular size. The aim of the present experiments was to study the blood-to-lumen flow of substances with different molecular size in man. MethodsTwo methods of study were used.

Polytetrafluoroethylene Ingestion as a Way to Increase Food Volume and Hence Satiety Without Increasing Calorie Content

“…Parenteral injections of radiolabeled polyvinylpyrrolidone in humans demonstrated that the permeability cut-off of the human small intestine is MW of 80 000 Da. 24,25 The GI permeability "cut-off" MW was also confirmed using polyethylene glycol (PEG) 26,27 and, even for patients with irritable bowel syndrome, it is below 80 000 Da 28,29 and therefore an order of magnitude below the MW of PTFE which is in the million Das.…”

Physical Determinants of Solute and Water Clearance by the Perfused Dog Jejunum

“…In fact, the jejunum is reported to have the highest perme-stage renal disease. Recognizing that high rates of perfusion provide relatively limited advantages in terms ability to creatinine of any gut segment [23,24,25]. It has been suggested that up to 66% of creatinine pro-of clearing solutes, we have recently described a continent in situ jejunal reservoir for dialysis [1].…”

Intestinal absorption and presystemic disposition of sildenafil citrate in the rabbit: evidence for site-dependent absorptive clearance

“…In addition, the presystemic disposition of the drug was also calculated by measuring the concentration of sildenafil appearing in the plasma during the intestinal perfusion experiment. The rabbit was selected in this study as the model animal because the rabbit GIT physiology is similar to that of the human [10][11][12]. …”