Life Stage and Secretory Cycle of Anterior Pituitary Basophils

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Thyrotrophs, LH-and FSH-gonadotrophs have long been universally believed to be the three independent types of basophils responsible for production of corresponding hormones. In our preparations of normal rat pituitaries stained with aldehyde thionin-PAS-orange G, however, cell type distinction among these three kinds of basophils based on the staining property was found to be almost impossible, because of the intermediate forms frequently encountered, suggesting possible transformation of basophils among these types. The LH-gonadotroph may be, in our opinion, one of the intermediate forms between thyrotrophs and FSH-gonadotrophs. The same enlarged polygonal thyrotrophlike cell was studied by optical and electron microscopy on the adjacent two slices. Their intracellular thioniophilic site corresponds with accumulation of granules on the electron microscopic level. Electron density of these granules varied from low to high in each cell, sometimes giving the picture of haloed granules. Polygonal lean basophils with a row of granules with the diameter of 100-150mμ along the plasmamembrane were identified as the immature basophils, but not as the thyrotrophs. The same ovoid LH-gonadotrophlike cell was examined by optical and electron microscopy on the adjacent two slices. According to characteristics of their fine structure, they may be nothing but the young FSH-gonadotroph-like cells with scanty round vesicles and imperfect Golgi-ring. When chromophobes dissociated and collected with negligible contamination with granulated cells were cultured in the media added with a small amount of TRH or LH-RH, some of them were converted into FSH-gonadotroph-like cells. “Cell conversion” is thought to take place similarly from chromophobes to the terminal FSH-gonadotroph-like cells via either thyrotroph-like or LH-gonadotroph-like cells, regardless of the kind and dose of used RH. Based on these findings, the entire life stage of basophils originating from chromophobes was demonstrated in a system in vitro along with hormone bioassays of explants and media. Such “cell-metamorphosis” may follow the order of immature basophil (Type I) →thyrotroph-like cells (Type II) →LH-gonadotroph-like cells (Type III) →FSH-gonadotroph-like cells (TypeIV) →degenerating cells. The course of life stage of cultured chromophobes was as long as 30 or 50 days with the remarkable variation due to the dose of the added hormones. Continuous, stepwise intravenous injections of TRH for 7 hr occasionally gave rise to some castration-like effect on the basophils in rats. In systems not only in vitro but also in vivo, the life stage of the cells originating from chromophobes might progress chronically along the basophil-axis. When chromophobes in vivo transform into the thyrotroph-like cells, they could start to operate repeatedly their own short term secretory cycles. The fine structures of various types of basophils involved in a secretory cycle were demonstrated in the normal rats and those injected with TRH and LH-RH. FSH-gonadotroph-like cells filled with the expanded round vesicles tend to rapidly multiply within 5min after an injection of TRH or LH-RH; LH-gonadotrophlike and thyrotroph-like cells, containing the numerous granules associated with haloed granules and closed ER, become the predominant component of basophils of the glands within 10 (TRH) or 30min (LH-RH); optical and electron microscopic changes of three kinds of basophils return to the prestimulated status within 60 (TRH) and 180min (LH-RH). Two possibilities are discussed concerning the secretory cycle: One deals with only one secretory cycle common to the all types of basophils, and the other with three separated secretory cycles with regard to the thyrotroph, LH-and FSH-gonadotroph respectively.
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Life Stage and Secretory Cycle of Anterior Pituitary Basophils

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