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Raw Soybeans Stimulate Human Pancreatic Proteinase Secretion¹

Halvor Holm, Janne E. Reseland^*, Lill I. Thorsen^*, Audun Flatmark and Lars E. Hanssen^**

Institute for Nutrition Research, University of Oslo, N-0316 Oslo, Norway ^* MATFORSK-Norwegian Food Research Institute, Osloveien 1, N-1430 Aas, Norway Surgical Department B ^** Medical Department, Rikshopitalet, N-0027 Oslo, Norway

Intraduodenal instillation of raw soybeans stimulated pancreatic proteinase secretion in humans. Raw soybeans almost abolished the activity of chymotrypsin and severely reduced (50%) the tryptic activity. Immunoreactive tryptic and chymotryptic material simultaneously appeared in amounts 2 to 4 times basal concentrations. This increase, demonstrated with rocket immunoelectrophoresis, was begun within the first 10 min of soybean instillation. The enhanced secretion also persisted throughout the succeeding saline instillation, and it is suggested that the presence of Kunitz trypsin inhibitor contributed to this postprandial stimulation. An amidase that hydrolyzes low-molecular-weight substrates (i.e., benzoyl-arginine p-nitroanilide) was found in raw soybeans. Its low activity was not assumed to substantially bias standard trypsin assays. The increased proteinase secretion was, as previously published, not preceded by an elevated plasma cholecystokinin concentration. The raw soybeans also caused a nonparallel secretion of amylase and proteinases. Nervous, perhaps cholinergic, regulation mediates the inhibitor-stimulated proteinase secretion in humans. This stimulation yields both a general increase of proteinases and also a specific inhibitor-resistant trypsin. This is consistent with the physiologic need for proenzyme-activation in the presence of inhibitors and for restoration of the proteolytic capacity of the duodenal juice.

KEY WORDS: • cholecystokinin • feedback regulation • humans • trypsin • soybean amidase • soybean proteinase inhibitors

¹ Supported by the Anders Jahres Foundation and the Norwegian Cancer Society.

Manuscript received 8 July 1991. Revision accepted 25 February 1992.