Secretory cycle of the pituitary basophils and its morphological evidence.

Abstract

The pituitary basophils of rats were examined electronmicroscopically at various time courses of the following experiments: Acute, subacute and chronic administration or perfusion of TRH and LRH separately or in combination to normal male and ovariectomized female rats as well as thyroidectomy on male rats. The findings showed a sequential, ultrastructural transformation (type I to V) of the basophil which might perform its secretory cycle. The I-type cells represent immature basophils. The II-type cells (correspond to classical TSH-cells) are angular cells in a synthesizing and/or storing phase showing an abundance of secretory granules 100-150nm in diameter. The II/III-type cells come into two categories of cell type, presenting a peripheral vesiculation of the cytoplasm. The III-type cells (correspond to classical LH-cells) are round in shape and possess a number of vesicular structures and secretory granules of about 200nm in diameter throughout the cell body. The III/IV-type cells are characterized by numerous round large cisternae which are filled with fine granulated particles. Secretory granules in these cells are 200-250nm in diameter. The enlarged spherical IV-type cells (correspond to classical FSH-cells) are packed with irregularly expanded endoplasmic reticula. Secretory granules are about 250nm in size. The IV-type cells are presumably at the end stage of granular storage or at the initiation of granular secretion, since there is a transitional cell type (IV/II-type) in which secretory granules are reduced in size (100-150 nm in diameter) and in electron density. Vesicular endoplasmic reticula are infrequently found in the IV/II-type cells, which may be either at the end of the secreting phase or at the subsequent resting phase. The V-type cells appear even in the normal and numerously after repeated or prolonged administrations of TRH or LRH. They may be exhausted basophils. It was not, however, concluded that II-, III-and IVtype cells might correspond to TSH-, LH-and FSH-cells, respectively.Based on a sequential appearance of the cells mentioned above, we propose a hypothesis: The II-type may transform into the III-type, and subsequently into the IV-type which may come back to the II-type.