Typical histological and ultrastructural changes that occur in the pars distalis of the rabbit pituitary after different periods of organ culture are described. The best technique for the maintenance of the maximum proportion of the explant was assessed by comparing cultures grown under different conditions. Explants in air with a medium buffered with N-2-hydroxyethylpiperazine-N 1-2-ethanesulphonic acid (HEPES), not previously used in organ culture, proved more satisfactory than explants in carbogen with bicarbonate-buffered 199, and cultures were maintained for more than 3 weeks.
The survival of cells was assessed on the basis of their cytological integrity; DNA- and RNA-fluorescence with acridine orange was a valuable indicator. Prolactin cells, which were few in uncultured controls, became the most common type of granular cell in long-term cultures.
Cell modifications during culture included the development of a peripheral epithelioid layer and the appearance of numerous microvilli. Microfibrils, coated or smooth vesicles, lytic bodies, desmosomes and intranuclear rods became more common and intranuclear rodlets (fibrous or membranous structures) were identified. Cells often became more electron dense during long-term culture.
Though there was an increase in the number of agranular cells during culture, identifiable granules were retained by many cells throughout culture.