Biochemical changes in rat parotid gland lysosomal enzyme activities after isoprenaline or starvation

Abstract

The content of several lysosomal enzymes was measured in the rat parotid gland when the normal secretory cycle was altered by either reducing or enhancing secretion. The findings support the concept that lysosomes play a role in regulating the gland content of secretory products. The secretory protein, amylase, began to accumulate when secretion was reduced. This was immediately followed by an increase in lysosomal enzymes (cathepsin D and acid phosphatase). Thereafter, amylase activity decreased rapidly followed by a smaller reduction in lysosomal enzymes. When secretion was enhanced by an injection of isoprenaline, amylase was reduced by 95 per cent within two hours; the lysosomal enzymes were decreased by 15–30 per cent. Within 24 h, amylase was restored and increased by 50 per cent whereas the lysosomal enzymes were increased only 10–30 per cent. The activity of acid phosphatase was measured with two different substrates. Activity measured with β-glycerophosphate paralleled that of cathepsin D whereas that measured with p-nitrophenylphosphate did not when secretion was reduced but did when secretion was enhanced. The results support the hypothesis that acid phosphatase activity measured with β-glycerophosphate is lysosomal whereas that measured with p-nitrophenylphosphate may have another cellular location in addition to lysosomes.