The ultrastructure of the stellate cell in the rabbit pars distalis,

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Abstract
Stellate cells in the rabbit pars distalis have been studied electron microscopically from birth to adulthood. During this period the stellate cells are found in abundance throughout the pars distalis and are the only consistently agranular cells observed in the pars distalis parenchyma. Identifying features of stellate cells are fine cytoplasmic filaments and farreaching cytoplasmic processes. The cytoplasmic processes ramify between adjacent parenchymal cells and are connected to other stellate cells by desmosomes. The stellate cells, linked to one another by desmosomes, thus constitute a meshwork within which the granulated parenchymal cells reside. Processes of stellate cells are also found interposed between the parenchymal basal lamina and the granulated parenchymal cells. The cytoplasmic filaments are distributed throughout the cytoplasm and extend into the fine processes. The filaments do not appear to have any particular orientation to the plasma membrane. Compared to granulated cell types, the cytoplasmic organization of stellate cells is not complex. Mitochondria, smooth and granular endoplasmic reticulum, Golgi membranes, ribosomes, dense bodies and lipid droplets are distributed throughout the cytoplasm, but not in great numbers. Nuclear chromatin is uniformly distributed. A nucleolus may or may not be evident.The ultrastructural features of the stellate cells are in many respects unchanged from birth to adulthood. An exception is in one‐to‐two‐day‐old neonates when in some stellate cells the quantity of cytoplasmic filaments appears increased and there is hyperplasia of the endoplasmic reticulum and Golgi membranes. A similar hyperplasia of these stellate cell organelles can be produced experimentally in adult rabbits by administration of Metopirone.Though the morphological evidence supports a structural or metabolically supportive function for the stellate cell, an additional role as the possible source of adrenocorticotrophic hormone is also discussed.