Ultrastructural characterization of human corticotrophs (ACTH cells).

Ultrastructural characterization of human corticotrophs (ACTH cells) was performed by 'superimposition technique', which enabled detailed ultrastructural observation of immunoreactive ACTH cells in adjacent semi-thin light microscopic immunoperoxidase and routine electron microscopic sections. The human corticotrophs were large and round or polygonal and were not stellate. They had scanty rough endoplasmic membranes and were packed with numerous large secretory granules measuring from 250 to 500 nm in diameter. The sizes of secretory granules in 6 human pituitaries were 448 +/- 128, 344 +/- 86, 448 +/- 117, 244 +/- 65, 316 +/- 76, and 340 +/- 93 nm, respectively. The granules were not seen in a single row along the plasma membrane as is the case in the rat. They possessed somewhat irregular outlines with a rarely discernible halo. Different densities of granule matrices were occasionally found. The cells often contained a few large heterogeneous vacuoles. From these findings, the human ACTH cells were recognized to be remarkably different in cell shape and size, properties of secretory granules and cytoplamic inclusions from those of the rat pituitary gland. In respect to secretory granule properties, the human ACTH cells are similar to those of some other mammals (fox, young pig, and lerot). More data is required to elucidate the relationship between human ACTH cell morphology and functional state.