Factors involved in the intestinal feedback regulation of pancreatic enzyme secretion in the rat.

Further studies on the feedback regulation of pancreatic enzyme secretion by trypsin were conducted in conscious rats, surgically prepared so that pancreatic juice could be collected or returned. Suppression of enzyme secretion by trypsin as well as its stimulation by SBTI occurred only in the upper part of the small intestine, where the hormone CCK is known to be released. Over a limited range, trypsin suppression of pancreatic secretion was proportional to the dose of trypsin. Higher concentrations had no further effect, suggesting "saturation" of the intestine. Trypsin which had its active center blocked by DFP did not suppress enzyme output. These results supported the concept that only trypsin (or chymotrypsin) with an exposed active center suppressed pancreatic enzyme secretion in the rat by somehow suppressing the release of CCK from the intestinal cell. Presumably CCK is released from the intestine following "removal" of trypsin from the intestine either by diverting the juice or by feeding SBTI which binds the enzyme. All of the evidence supported the view that the effect of trypsin or SBTI on pancreatic secretion was mediated at the intestinal level and not in the blood as has been suggested.