Electron microscopic studies on the pars tuberalis of the rat hypophysis.

Abstract

The pars tuberalis of the rat hypophysis was studied with the electron microscope. The pars tuberalis consists of several layers of relatively small epithelial cells lying along the ventral surface of the median eminence. The epithelial cells may be classified into two types. One is the non-granulated cell constituting the major part of the pars tuberalis. These cells show a morphological structure similar to the chromophobes of the pars distalis. Most of them contain relatively large nuclei, a few mitochondria, rough and smooth endoplasmic reticula, and Golgi apparatus. In some places, desmosomes and junctional complexes are observed between the adjacent non-granulated cells. Sometimes, a colloid-like substance fills the intercellular space, into which a great number of microvilli and cilia may project. The other celltype is granulated cells which are large in size and contain a large number of mitochondria, well-developed rough and smooth endoplasmic reticula and Golgi apparatus. The most prominent characteristic of this cell type is the presence of many dark granules, about 150mμ in diameter. These cells resemble the basophils of the pars distalis. The presence of these granulated cells suggests a possible secretory function of the pars tuberalis. In order to clarify the function of the granulated cells, animals were also investigated under several experimental conditions such as adrenalectomy, thyroidectomy and gonadectomy. However, there was no marked morphological change in the fine structure of the pars tuberalis following these experimental conditions.