Cytological Changes of Siperstein's Corticotrophs Following Thyroidectomy

抄録

Anterior pituitaries of male rats were electron-microscopically observed 12hr, 1, 3, 5, 7 and 14 days after thyro-parathyroidectomy in order to investigate the origin and destiny of Siperstein's corticotrophs (S-cells). The formation of a reticular framework by the folliculo-stellate cells may result from the general disaggregation of the solid mass of follicular cells with the pseudolumen into which microvilli project, by losing the junctional complex and pseudolumen. The S-cells, characterized by a row of secretory granules along the cytoplasmic membrane, have properties identical with those of the free agranular folliculo-stellate cells. The star-like shape, numerous ribosomes and polysomes, and elongated narrow rough endoplasmic reticulum, are common characteristics of both cells. Within 12hr to 5 days, the free or reticular folliculo-stellate cells appear in large numbers, and minute secretory granules about 50nm in diameter develop sporadically at their margins. In the course of the 5 days, secretory granules tend to increase in number and grow in size, measuring 100-200nm in diameter. However, the degree of granulation varied considerably from cell to cell during the same interval without complete equilibration with the time course after thyroidectomy. Detection of various transitional cells between folliculo-stellate cells and S-cells suggests that the former may be a stem cell of the latter. Concurrently with hypergranulation, some S-cells hypertrophy and develop a prominent Golgi apparatus, sometimes engulfing a part of the adjacent cell. The other S-cells, however, udergo degranulation associated with excessive vesiculation despite the formation of a circular arrangement of the closed Golgi lamellae. Within 7 days, there are some large vesiculated cells of stellate shape resembling the TX-cells, in which a small number of secretory granules whose diameter was reduced to 50-100nm, remain distributed along the cytoplasmic membrane. Within 14 days, the big TX-cells often appear, being characterized by the deposit of granules in the small cisternae and by the closure of Golgi lamellae which are in the circular arrangement. They are still stellate in shape, being extraordinarily enlarged to an extent 5-6 times that of an acidophil. In addition to the thyroidectomy cells (TX-cells) which are believed to result from the so-called thyrotrophs, the other developmental process of TX-cells in association with the folliculostellate cells was observed in this study. The two kinds of TX-cells are intrinsically different in their fine structures. It is postulated in this study that the folliculostellate cell is a progenitor of the S-cell which is destined to be transformed into the TX-cell, and that the S-cell, for this reason, represents a kind of basophil.