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Endocrinology, Vol 126, 472-479, Copyright © 1990 by Endocrine Society

ARTICLES

Thyrotropin-releasing hormone inhibits GH4 pituitary cell proliferation by blocking entry into S phase

JS Ramsdell
Department of Anatomy and Cell Biology, Medical University of South Carolina, Charleston 29425.

TRH inhibits the proliferation of GH4 rat pituitary cells. We have characterized TRH inhibition of cell proliferation by four approaches: cell number, [3H]thymidine incorporation per culture, bromodeoxyuridine (BrdUrd) incorporation per cell, and cell cycle distribution. TRH decreases GH4 cell number within 18 h of treatment, and this inhibition is maintained for up to 96 h. TRH inhibits [3H]thymidine incorporation into GH4 cell cultures as early as 12 h, and the inhibition of [3H] thymidine incorporation correlates, after a 6-h lag, with decreased GH4 cell number. TRH inhibition of [3H]thymidine incorporation is concentration dependent and saturable, with half-maximal inhibition (IC50) of 2 nM. TRH inhibition of [3H] thymidine incorporation is receptor number dependent up to 160,000 sites/cell, suggesting no spare receptors for TRH on GH4C1 cells. The precise action of TRH on GH4 cell proliferation was examined by flow cytometry of fluorescein isothiocyanate-anti-BrdUrd- and propidium iodide-DNA stained cells. TRH inhibits the number of cells that incorporate BrdUrd and not the amount of BrdUrd incorporated per cell. Dual analysis indicates that the decreased anti-BrdUrd staining is largely restricted to cells in the early S phase. This action of TRH is prolonged (greater than 32 h) and results in a parallel increase in the number of cells in G2-M and G1. These findings indicate that TRH inhibits GH4 cell proliferation at least in part by inhibiting the number of cells entering the S phase.


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[Abstract] [Full Text] [PDF]


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