Lysosomal enzymes in relation to the isoproterenol-induced secretory cycle in rat parotid gland

Two lysosomal enzymes, cathepsin D and acid phosphatase, were detected in significant amounts in the lysosome-containing subcellular fractions of rat parotid tissue and found to have dissimilar distributions in these fractions. The total levels of these enzymes were measured at various times throughout a complete secretory cycle induced synchronously by fasting rats overnight and administering isoproterenol at time zero. The results showed a 30% increase in cathepsin D activity in the glands by 10 h post-stimulation, and a 20% decrease in acid phosphatase activity 7 h after stimulation. These results suggest that there are cyclic changes in lysosomal enzymes during the secretory cycle of this gland, but that these changes are complex ones and cannot be related to specific cellular processes at this time.