Study of The Mechanism of Prolactin Cell Differentiation in The Anterior Pituitary

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Newly established MtT/S-secrete only the rowth hormone(GH). Electron microscopic examination of the MTT/S cells showed a normal somatotroph-like appearance i. e. ., the presence of many growth hormone containing secretory granules, well developed endoplasmic reticulum and Golgi apparatus in their cytoplasm. GRH stimulate GH secretion of MtT/S cell line at the plateau-phase of cell growth. Interestingly, the MTT/S cells in the mitotic phase also contained secretory granules. Furthermore, all of the bromo-deoxyuridine(BrdU)incorporated cells which known an indicator of proliferative cells are growth hormone cells. These characteristics of MTT/S cells are showing this cells proliferate as the GH-cells. No' prolactin(PRL)-cells were observed among MTT/S cells cultured in regular medium, and no PRL in medium and cells was detected with radioimmunoassy and Western blotting analyses, whereas insulin or insulin-like growth factor-1(IGF-1)exerted a marked decrease-in. GH-production and GH-cell … More population. In the medium PRL was detected after a 2-day lag period and a numerous PRecells appeared 5 days after stimulation with insulin or IGF-1. Double immunocytochemistry clearly indicated that no cell contained both PRL and GH. These results show that PRecell transdifferentiated from GH-cells by stimulation with insulin or IGF-1 and this suggests that the MTT/S cell line is an excellent model system showing GHcell/PRecell linea, e. Recent information of the molecular biology indicated that the mammotroph in pituitary cell may-differentiate from somatotroph. However, intra- or extra-cellular mechanism regulating cell differentiation of mammotroph from somatotroph remain unclear. Our newly established MTT/S cell line seems good model for reveal the mechanism pituitary cell differentiation.On the other hand, by the addition of EGF with insulin, the transdifferentiation of GH cells to prolactin is very accelerated and somatomammotroph which have both GH and prolactin were appeared. The existence of somatomammotroph in the pituitary gland is well known however, the meaning of the somatomammotroph in the pituitary gland are unclear. Our result of the appearance of somatomammotroph by the stimulation of insulin and EGF may show somatomammotroph appeared on the process of transdifferentiation of GH-cells to prolactin cells. Less