1. Male weanling rats were fed casein diets containing 1.25, 2.5, 5.0 and 10 g/kg active or autoclaved proteinase inhibitors (PI) from field bean (Vicia faba L.), and raw- and autoclaved-field-bean meal (FBM) diets. After 7, 14 and 21 d on the diets pancreas weights were measured and pancreas and intestinal trypsin (EC 220.127.116.11) and chymotrypsin (EC 18.104.22.168) assayed.
2. Pancreas weights increased on the raw FBM and active-PI-supplemented diets. Maximum pancreatic hypertrophy measured as the percentage increase above controls was observed after 14 d in rats fed on raw FBM. The same percentage increase in pancreas size compared with appropriate controls was obtained with rats fed casein diets supplemented with 5 g active PI/kg.
3. Pancreas trypsin and chymotrypsin levels decreased with increasing dietary PI level. Similarly, lower pancreas trypsin and chymotrypsin levels were observed in rats given raw FBM.
4. Intestinal trypsin and chymotrypsin increased with increasing dietary PI inclusion level. Although the magnitude of this response decreased with the period of feeding the differences in enzyme levels were still significant even after 21 d.
5. It was concluded that the PI alone in raw-FBM diets could not entirely be responsible for the enlargement of the pancreas and the excess secretion of pancreatic enzymes since in synthetic diets PI levels of five times those in FBM were required to produce responses of similar magnitude.