Intracisternal granules in the adipokinetic cells of locusts are not degraded and apparently function as supplementary stores of secretory material

The intracisternal granules in locust adipokinetic cells appear to represen t accumulations of secretory material within cisternae of the rough endopla smic reticulum, An important question is whether these granules are destine d for degradation or represent stores of (pro)hormones, Two strategies were used to answer this question. First, cytochemistry was applied to elucidat e the properties of intracisternal granules. The endocytic tracers horserad ish peroxidase and wheat-germ agglutinin-conjugated horseradish peroxidase were used to facilitate the identification of endocytic, autophagic, and ly sosomal organelles, which may be involved in the degradation of intracister nal granules. No intracisternal granules could be found within autophagosom es, and granules fused with endocytic and lysosomal organelles were not obs erved, nor could tracer be found within the granules. The lysosomal enzyme acid phosphatase was absent from the granules. Second, biochemical analysis of the content of intracisternal granules revealed that these granules con tain prohormones as well as hormones. Prohormones were present in relativel y higher amounts compared with ordinary secretory granules. Since the intra cisternal granules in locust adipokinetic cells are not degraded and contai n intact (pro)hormones it is concluded that they function as supplementary stores of secretory material.