Permeability of polyethylene glycol in remnant small bowel after massive intestinal resection.

Studies were designed to determine if permeability of adapted (remnant) small bowel mucosa to polyethylene glycol (PEG) was altered after major intestinal resection. Rats underwent 50% small bowel resection with preservation of duodenum and terminal ileum. Sham-operated animals served as controls. Two and four weeks later we cannulated the portal vein and measured mucosal permeability to luminal [3H]PEG and [14C]PEG in isotonic Ringer solution in remnant proximal or distal in situ closed intestinal loops. A lumen-to-portal blood gradient of at least 1000/1 persisted throughout the one-hour experimental period in both resected and sham-operated animals. Thus the adapted remnant intestinal mucosa was highly impermeable to luminal radiotracer PEG. In separate experiments 2 and 4 weeks after 70% small bowel resection or sham operation, in vivo segments of proximal and distal small intestinal were perfused through the lumen for one hour with hypertonic (800 mOsm) mannitol or NaCl solution containing [3H]PEG. There was equal and almost total recovery of [3H]PEG at the end of the experimental period in resected and control animals. The combined data of all experiments indicate that radiotracer PEG may be confidently used as a luminal water phase marker in transport studies of remnant bowel following intestinal resection.

Permeability of adolescent rat intestine to pancreatic ribonuclease.

There are indications that exocrine pancreatic enzymes may undergo an enteric recirculation. Ribonuclease (RNase) is present in considerable quantities in pancreatic exocrine secretions. Therefore we studied the intestinal transport of pancreatic RNase using everted gut sacs from duodenum, midgut, and ileum of young rats. Gut sacs were incubated aerobically at 37 degrees C, 22 degrees C, and 0 degrees C, and anaerobically at 37 degrees C. Measurable amounts of RNase crossed the intestinal barrier, but neither duodenum, midgut nor ileum absorbed RNase preferentially. The experimental data favor simple diffusion of RNase across rat small bowel. However, the amounts of pancreatic RNase absorbed were small. Thus, while our data do not negate the concept of an enteropancreatic recirculation in the rat, only a minor quantity of luminal, pancreatic RNase could recirculate.

In vivo absorption of pancreatic ribonuclease from the small intestine of young and mature rats.

It has been postulated that exocrine pancreatic enzymes may undergo an enteropancreatic recirculation as a mechanism for the conservation of digestive enzymes. Exocrine pancreatic secretions contain considerable amounts of ribonuclease (RNase). Therefore we examined the absorption of RNase from the small bowel of 4-week and 10-week-old rats by measuring concentration changes of the substrate in portal blood after instilling RNase into in vivo, in situ intestinal loops. Unphysiologically high intestinal luminal RNase concentrations were required for sufficient RNase to cross the mucosal barrier and raise portal vein blood RNase levels. A gradient of 1,000:1 existed between intestinal lumen and portal vein blood RNase concentrations in the 4-week-old rats. The gradient was 10 times greater in the mature animals. No significant differences in luminal absorption of RNase from duodenum or ileum were detected. The data indicate that RNase penetrates the intestinal mucosa in vivo but that only small amounts are absorbed. Therefore if an enteropancreatic recirculation of exocrine pancreatic RNase exists in the rat, only negligible quantities of RNase are included in such a recirculation.