Human and Clinical Nutrition Raw Soybeans Stimulate Human Pancreatic Proteinase Secretion1 HALVOR HOLM, JANNE E. RESELAND, * LILL I. THORSEN, * AUDUN FLATMARKr 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, and 1Surgical Department B and **Medical Department, Rikshopitalet, N-0027 Oslo, Norway ABSTRACT 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 ma terial 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 se cretion 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 protein- ases. Nervous, perhaps cholinergic, regulation mediates the inhibitor-stimulated proteinase secretion in humans. This stimulation yields both a general increase of pro- teinases 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. J. Nutr. 122: 1407-1416, 1992. INDEXINGKEYWORDS: •cholecystokinin •feedback regulation •humans •trypsin •soybean amidase •soybean proteinase inhibitors The feedback regulation of pancreatic secretion in humans has been debated (Adler et al. 1989, Owyang et al. 1986a). In rats, the animal most frequently used as a model, a feedback regulation seems well docu mented on the basis of certain levels of free trypsin in the duodenum and plasma cholecystokinin (CCK).2 Reduction of tryptic (and chymotryptic) activity by proteinase inhibitors, or by diversion of pancreatic juice, causes a prompt increase in plasma CCK that in turn stimulates pancreatic enzyme secretion (Fushi et al. 1989, Liddle et al. 1984, Miyasaka and Green 1984). Continued CCK stimulation causes hyper- thropy and hyperplasia, resulting in nodules and later in neoplastic changes in the rat pancreas (Liener et al. 1985). In a recent study (Holm et al. 1988a) raw soybeans, a soybean protein isolate or bovine serum albumin were continuously instilled into human duodena on different days while intermittent samples of blood and duodenal juice were collected. Only when bovine serum albumin was instilled was a significant in crease in plasma CCK found. Parallel to this increase in CCK, increases in trypsin (EC 3.4.21.4) chymotrypsin (EC 3.4.21.1) and amylase (EC 3.2.1.1) activities were also found. The CCK concentrations during soybean protein isolate and raw soybean instil lations were almost identical to the basal CCK levels. A considerably larger increase in proteinase activities was seen during the soybean protein isolate instilla tion, whereas the raw soybeans caused a substantial inhibition of proteolytic activity. Although the tryptic and the chymotryptic activities varied consid erably, no significant difference could be seen in the amylase activity when any of the three test proteins was instilled. In two similar instillation experiments with proteinase inhibitors, a general stimulation 'Supported by the Anders Jahres Foundation and the Norwegian Cancer Society. Abbreviations used: BAPNA, Mx-DL-arginine p-nitroanilide; BTEE, Mx-benzoyl-L-tyrosine ethyl ester,- CCK, cholecystokinin; ODn, optical density at n nm; S-2677, Af-t-butyloxycarbonyl-L- glutamyl-(ot-O-benzyl)-glycyl-arginine-p-nitroanilide-HCl; SBTI, Kunitz soybean trypsin inhibitor,- TTBS, tris-tween buffered saline. 0022-3166/92 $3.00 ©1992 American Institute of Nutrition. Received 8 luly 1991. Accepted 25 February 1992. 1407 by guest on June 6, 2015 jn.nutrition.org Downloaded from