A scanning electron-microscopic study of "supramarginal cells" in the pituitary cleft of the rat.

Unusual cells lying above the marginal cellular layer of the rat pituitary cleft were studied by SEM and TEM. These cells - from their location termed supramarginal cells - have a characteristically irregular cell body from which arise a number of long and thin branched processes ending among the microvilli and cilia of the marginal cells delimiting the anterior and posterior walls of the cleft. Some supramarginal cells are star-shaped elements with thin extensions, others have a triangular or spindle-shaped body from which emerge long ameboid processes with fibril-like projections. Miniblebs, miniruffles, occasional veils and short microvilli extend over the surface of these elements. Supramarginal cells are very similar to the "Kolmer epiplexus cells" originally found on the choroid plexus or other areas of the third ventricular wall where they are known as "supraependymal cells". Present evidence suggests that supramarginal cells of pituitary cleft might have phagocytic properties and an hematogenous origin as monocytes and, as such, closely resemble Kolmer epiplexus cells of brain ventricles. Others might arise from "folliculo-stellate cells" or closely related marginal cells once they become free into the pituitary cleft. Supramarginal cells are recognized as motile phagocytes acting as scavengers and possibly regulating the extracellular environment of the cleft and associated adenohypophysial tissues.(ABSTRACT TRUNCATED AT 250 WORDS)