| Research Abstract |
The endocrine gland, such as an anterior gland consist from the mixed population of different hormone secreting glandular cells. These different glandular cells supposedly differentiated from same stem cell however, the mechanism of cell differentiation in endocrine cells still under discusson. We recently established cell line(MtT/S)from rat plaractinoma. The MtT/S cell line produces only growth hormone(GH)in normal growth medium. The MtT/S cells labeled with bromodeoxyuridine(BrdU)also show staining for GH.Furthermore, mitotic MtT/S cells contain GH immunopositive secretory granules in their cytoplasm. These features indicate that MtT/D cells proliferate as GH-secreting cells. We reported previouly that MtT/S cells transdifferentiate into prolactin cells upon stimulation with insulin or insulin-like growth factor. A requirement of estrogen priming for MtT/S cell transdifferentiation has also been reported. This transdifferentiation is considerably accelerated by addition of EGF, resulting in somatomammotrophs contain both prolactin and GH.In order to reveal the relationship between cell proliferation and cell differentiation, a BrdU labeling experiment was performed. the results indicated that prolactin cells which were induced by stimulation with insulin and EGF showed markedly suppressed BrdU incorporation, indicating that prolactin cells that have transdifferentiated from growth hormone cells are non-proliferate or show only very slow proliferation. In general, prolactin cells are known to be the most active proliferative cells in the pituitary gland. This discrepancy between in vitro and in vivo result is verly important, since it may indicate an unknown mechanism for the regulation of prolacrtin cell proliferation in the anterior pituitary gland. On the other hand these cell differentiation may be controlled by neighboring supportive cells through cell cell communication. The folliculo-stellate cells in the anterior pituitary gland is the most important cand
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