An increase in pancreatic enzyme secretion and pancreatic hypertrophy following the ingestion of various trypsin inhibitors are well established phenomena in rats and chicks (1, 2 ) . The diverse origins of the many trypsin inhibitolrs that elicit the pancreatic response-their dissimilarity in molecular weight, heat lability, and other physicochemical properities-suggest that their physiological effect, when fed to animals, must be related to their common property, the ability to inhibit tryptic hydrolysis.No studies, to our knowledge, have been published which have described the pancreatic response to inhibitors of the other major pancreatic proteol y t ic enzyme, chymo tr ypsin. The reason for this lies probably in the fact that, until recently, no "pure" chymotrypsin inhibitor (i.e., one which is devoid of trypsin inhibitor or other enzyme inhibitor activity) suitable for dietary studies was available. With the discovery and isolation by Ryan and Balls ( 3 ) of a chymotrpin inhibitor from potatoes, such a study became feasible. The investigation described below compared the acute exocrine pancreatic response of rats fed a single dose of potato chymotrypsin inhibitor (PCI) to that of rats fed either soy bean trypsin inhibitor (SBTI) or the control diet containing casein.
Materials and Methods.Male, Long-Evans rats weighing 90-1 10 g, were purchased from a local supplier (Simonsen, Gilroy, California) and were maintained ad libitum oa Purina Laboratory Rat Chow. Food was removed from the animals 24 hr before an experiment. In each experiment, the inhibitor or protein to be fed was mixed with 2 g of a basic, 18% casein semipurified diet contain-1 This investigation was supported in part by U S .Public Health Service Grant-in-Aid AM-3046.ing 71% sucrose and no celluflour (4) and with enough water to form a viscous slurry, which was then placed in the animal by stomach tube. The rats were divided into 4 groups: Group I received the basic diet plus 25 mg/100 g of body weight of PCI; group I1 was fed the diet plus 42 mg/100 g of body weight of SBTI; group 111, the control group, was fed the diet plus 50 mg/100 g of body weight of purified casein; group IV was not fed following the 24-hr fast, and was used to establish the fastin,g levels of the enzymes assayed. The quantities of the inhibitors fed in each case were identical in terms of the total amount of enzyme they inhibited (i.e., 25 mg of PCI and 42 mg of SBTI inhibited 42 mg of bovine a-chymotrypsin and 42 mg of bovine trypsin, respectively). The amount of SBTI fed was known from previous experience to be more than adequate to elicit a maximal response from the rat pancreas.Groups I, 11, and I11 were sacrificed by decapitation at 2, 4, 6, and 8 hr after receiving the diets by stomach-tube, and group IV was killed following the 24-hr fast. The pancreas and intestinal contents were immediately removed. The pancreas was dissected free of visible fat and lymph nodes under a dissecting microscope, frozen, and lyophilized. Intestinal contents were collected by dividi...