The pituitary of Aphanius dispar (Rüppell) from hypersaline marshes and freshwater. II. Ultrastructure of the rostral pars distalis.

An ultrastructural study of the rostral pars distalis of the pituitary of Aphanius dispar specimens taken from freshwater or hypersaline marshes revealed significant structural differences which indicate higher activity of the prolactin cells in the hypotonic medium. Prolactin cells from freshwater specimens had larger secretory granules, a higher amount of endoplasmic reticulum, and expanded intercellular spaces with many secretory lakes. These cells contained an unusual cytoplasmic structure, consisting of twisted canals with vesicular lumina, connected to the endoplasmic reticulum of the cell. This structure is about 1-2 micron in diameter. Stellate cells are characterized by extracellular spacing junctions which are particularly noticeable at the confluence of the interstellate cell canaliculi and the pericapillary space.