Subcellular redistribution of lysosomal enzymes during caerulein-induced pancreatitis

The subcellular distribution of the lysosomal enzymes cathepsin B and D in the pancreas was evaluated in rats infused with saline (control) or a maximal (0.25 μg·kg^-1·h^-1) or a supramaximally stimulating dose (5 μg·kg^-1·h^-1) of the secretagogue caerulein. The latter results in acute edematous pancreatitis, inhibition of digestive enzyme secretion, and the localization of digestive zymogens in organelles whose fragility has been increased by caerulein infusion [A. Saluja et al. Am. J. Physiol. 249 (Gastrointest. Liver Physiol. 12): G702-G710, 1985]. Samples from control animals were found to have 29.9 ± 1.8% of the cathepsin B activity in the pellet centrifuged at 1,300 g for 15 min (containing primarily zymogen granules) and 54.7 ± 2.5% in the pellet centrifuged at 12,000 g for 12 min (containing primarily lysosomes and mitochondria). After supramaximal stimulation with caerulein for 3.5 h the pellet centrifuged at 1,300 g for 15 min had 55.1 ± 2.5%, and the pellet centrifuged at 12,000 g for 12 min had 30.6 ± 2.0% of cathepsin B activity. This redistribution was time dependent, noted within 1 h of starting caerulein infusion, and maximal after 2.5 h of infusion. Electron microscopic immunolabeling studies revealed localization of cathepsin D in discrete organelles that, in the samples from animals infused with a supramaximally stimulating dose of caerulein, were larger, more abundant, and more concentrated in the pellet centrifuged at 1,300 g for 15 min than in the controls. During infusion with supramaximal doses of caerulein, the cathepsin B-containing organelles were found to become progressively more fragile. These observations, using biochemical and immunolabeling techniques and isolated fractions, confirm and extend, at the quantitative level, the results of morphological studies in intact cells previously reported [O. Watanabe et al. Am. J. Physiol. 246 (Gastrointest. Liver Physiol. 9) G457-G467, 1984]. Taken together, these studies suggest that intravacuolar zymogen activation by lysosomal enzymes may be an important event in secretagogue-induced pancreatitis.