Investigations of ultrastructure of the adenohypophysis in the domestic pig (Sus scrofa domestica). Part II: "Dark cells" in the pars anterior.

The investigations were done on 34 hypophyses of the pig embryos aged c. 46-79 days of pregnancy. The name "dark cells" was given to one of the type of differentiated cells of the pars anterior which were characterized by intense electron density of the basic cytoplasm. The cells correspond to the "follicular cells" and the "stellate cells" described in many species of adult vertebrates. Probably the dark cells have supporting function, as they originate a system of nets and tubular structures which are the construction of the gland. It seems that the dark cells regulate osmotic pressure of the intercellular fluid, mediate the exchange of substances between the cells and blood vessels, and they take part in the degeneration process of the pars anterior cells of the hypophysis.