Lysosomes in anterior pituitary corticotrophs of the rat. A combined immunocytochemical and enzyme cytochemical study

E600 resistant non-specific esterase activity or acid phosphatase activity were localized in corticotrophic cells identified by postembedding immunocytochemistry (PAP of protein A-immunogold techniques). The lysosomal system of this cell type consists of dense bodies, of a population of small lysosomes mostly situated at the cell periphery in the vicinity of secretory granules as well as of tubular structures. These latter were located either in the central part of the cytoplasm and probably belonged to the Golgi apparatus or at the cell periphery, partly in the extensions. Small lysosomes occurred to be in continuity with enzyme-containing tubules. In a few structures lysosomal enzyme activity and ACTH immunoreactivity overlapped. Some autophagic vacuoles seemed to contain secretory granule matrix. It is suggested that the concept of crinophagy can be extended to the corticotrophs, though the lysosomal system may be involved in the specific function of this cell type by other mechanisms as well.