Direct Up-regulation of Estrogen Receptor by Triiodothyronine in Rat Pituitary Tumor MtT/F84

Abstract

To investigate a possible effect of triiodothyronine (T₃) on the regulation of estrogen receptor, estrogen dependent rat pituitary tumor, MtT/F84, was studied in rats which received surgical thyroidectomy (Tx) or were given propylthiouracil (PTU) and were supplemented with T₃. In T₃ loaded rats, the grafted tumor showed high estrogen receptor levels (160-200% of control), whereas low estrogen receptor levels (20-35% of control) were observed in the tumors grown in Tx and PTU treated rats. A single injection of T₃ to Tx rats with MtT/F84 increased the estrogen receptor level in a time dependent manner and reached the maximal level at 6 h. In primary culture of MtT/F84 cells, T₃ increased the specific ³H-estrogen binding to tumor cells in a dose dependent manner (165% of control by 10^-7M T₃) and also in a time dependnet (maximum at 12 h) manner. These data suggest that T₃ directly up-regulates the estrogen receptor level in MtT/F84 cells.