[A review: classification and ultrastructures of the anterior pituitary cells and their role in function of hormone secretion]

Abstract

Anterior pituitary cells first were classified by their staining behaviour in light microscopic preparations. Later they were classified according to the type of hormone they produce. Although even electron microscopy has been routinized, the functional classification of anterior pituitary cells was not easy. Experimental morphology that was mainly based on observation of the anterior pituitary after extirpation of target endocrine organs was the only method for identifying the probable function of each cell type in the anterior pituitary. The use of antibody against each hormone, that is immunohisto(cyto-)chemistry at light and electron microscopic level, was an epoch-making innovation in the technique for studying endocrine morphology. The technique revealed two or three morphologically different types in each cell group containing the same hormone. These subtypes in cell classification by immuno-electron microscopy are related to the age and sex of the animal. Cell biological research using electron microscopy, especially immunocytochemistry, clarified mechanisms concerning various steps in hormone production, for example, the synthesis of peptide hormones (precursors) in the rough endoplasmic reticulum; transfer to the Golgi apparatus; modification and processing of precursor peptides during the passage through Golgi stacks and the trans-Golgi network that corresponds to GERL; the moving of secretory granules; the mechanism of exocytosis and related membrane events; and the activity of lysosomes related to such endocrine functions as crinophagy and the recycling of membrane constituents retrieved from the cell surface after exocytosis of secretory granules.