Relationship of Pancreatic Enzyme Secretion to Growth Inhibition in Rats Fed Soybean Trypsin Inhibitor

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Abstract
Rats were fed either heated soybean diets supplemented with soybean trypsin inhibitor (SBTI) or raw soybean diets having equivalent protein and trypsin inhibitor activity for three weeks. During the experiment, growth, intestinal protease activity, food utilization, and nitrogen absorption were determined. The SBTI-supplemented diet depressed growth and reduced food utilization, but with considerably less severity than did the raw soybean diet. Pair feeding, to equalize food intake, indicated that the growth depression produced by the raw soybean resulted largely from a depressed food intake. Food consumption was much less depressed by the SBTI diets. Analyses of the intestinal contents revealed that rats fed SBTI or raw soybean maintained a high level of intestinal protease activity, yet the animals appeared to absorb less nitrogen than the control rats. It was concluded that growth depression produced in the rat by raw soybean results from a combination of restricted food intake and the effects of trypsin inhibitor, which acts, not by inhibiting protein hydrolysis, but by stimulating the pancreas to secrete large quantities of enzyme protein which are ultimately lost to the animal. The effect of this is to create partial deficiencies of the most growth limiting amino acids in the soybean protein.