title: Pancreatic bicarbonate response to food-bound hydrogen ion along the gut.
abstract: Recent reports suggest most solid food enters the duodenum as small particles. Our studies showed that small particles of liver were capable of binding hydrogen ions (H+), but there was slow equilibration of H+ between particulate and aqueous phases. We wondered whether titratable acid as H+ bound to meat particles could effectively stimulate pancreatic bicarbonate secretion despite slow diffusion. We studied mongrel dogs with chronic pancreatic fistulas; the intestinal lumen was washed free of endogenous pancreatic enzymes. Pancreatic bicarbonate and protein responses were measured during duodenal perfusion with pH 2 or pH 3 gels that delivered 1, 2, or 4 mEq/15 min of titratable acid (endpoint pH 4.5). Gels consisted of acidified, 0.1-0.7-mm particles of beef liver or bovine serum albumin or lactic acid suspended with 2% starch in 0.15 M NaCl. The liver, bovine serum albumin, and lactate had similar titration curves. At pH 2 or pH 3, liver particles were about as effective as bovine serum albumin in stimulating pancreatic bicarbonate secretion. Likewise, pH 3 liver particles were equipotent with pH 3 lactate on pancreatic bicarbonate secretion when both perfusates were allowed access to the whole intestine. However, when confined to the first 45 cm of proximal intestine, much less H+ was dissipated from the liver versus the lactate; and, correspondingly, there was a much greater decrement in pancreatic bicarbonate secretion from whole gut responses with liver versus lactate. We conclude that titratable acid bound to solid food particles is a potent stimulus of pancreatic bicarbonate secretion despite its slow diffusion. Our studies suggest that H+ slowly diffusing from particles excites pancreatic bicarbonate secretion by triggering H+ receptors along more distal intestine.
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D004285:Dogs; D004386:Duodenum; D005260:Female; D005502:Food; D006851:Hydrochloric Acid / Q000008:administration & dosage / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D008099:Liver; D008297:Male; D010179:Pancreas / Q000378:metabolism*; D010477:Perfusion; D012710:Serum Albumin, Bovine; D012995:Solubility
chemical_list: D001639:Bicarbonates; D012710:Serum Albumin, Bovine; D006851:Hydrochloric Acid