The human parathyroid chief cell--a model for a polypeptide hormone producing endocrine unit as revealed by various functional and pathological conditions. A thin section and freeze-fracture study.

The ultrastructure of the human parathyroid chief cell has been studied by comparing thin section with freeze-fracture findings in close consideration of functional activity. Assessment of function was based on the careful analysis of normal and pathological conditions of the parathyroids in patients with various entities of hyperparathyroidism including clinical data. In contrast to the atrophic glands contralateral to an actively secreting adenoma, stimulated chief cells especially in cases with acute hyperparathyroidism (hypercalcemic crisis), display several remarkable findings: an enlargement of the nucleus with an increase in pores, an abundant amount of rough endoplasmic reticulum, many mitochondria and conspicuous interdigitations of the plasma membrane and an extensively developed Golgi apparatus with budding of numerous vesicular structures and dense lysosomal bodies as well as secretory granules. The fine structure of these alterations was assumed to reflect different states of function in consideration of clinical and laboratory parameters. The process of extrusion of secretory granules and the retrieval of membrane material by endocytosis was particularly investigated by comparison of images obtained by thin sections and freeze-fracture replicas. Our results demonstrate that the human parathyroid chief cell may serve as an ideal model for the study of a polypeptide hormone synthesizing cell with a well known feedback mechanism expressed by the various pathological conditions in patients with the clinical picture of primary and secondary hyperparathyroidism.