Immunocytochemical localization of insulin-immunoreactive cells in the pancreatic ducts of rats treated with trypsin inhibitor

It is well known that soybean trypsin inhibitor exerts trophic effects on the exocrine pancreas, resulting in the hypertrophy of acinar cells. Some evidence also exists for hyperplasia in acinar tissue, the ductal epithelium and islet tissue. Rats maintained for 3 weeks on an oral administration of soybean trypsin inhibitor (200 mg/50 ml drinking water) were compared with untreated animals. Significant changes were noted in treated animals (p<0.01). Trypsin inhibitor-treated rats showed an increase in pancreatic weight (2.33±0.46 g). The volume ratio of acinar, islet and connective tissue as measured by the stereology point-count technique remained the same in both groups. Ductal tissue, however, exhibited an increase in volume ratio, 3.77±4.38% per 2714 μm² area of tissue, in trypsin inhibitor-treated animals. All tissue components showed an increase in the experimental animals: acinar (125%), islet (144%), ductal (325%) and connective tissue (94%). Increased size of acinar cell nuclei, as measured by average cord length, 6.20±0.13 μm, and a decreased nuclear density of acinar cells, 28±4.74 per 150 μm² area of tissue, indicated hypertrophic changes in these cells of the experimental animals. Using immunohistochemical localization and the point-count technique, a significant fraction of the total pancreatic volume in experimental animals was represented by ducts containing immunoreactive cells. The percent of volume ratio, 0.42±0.15% per 2714 μm² area of tissue, was calculated for ducts containing insulin-immunoreactive cells within their epithelium.