Effect of TRH on Phospholipase D Activity in G $H_3$ Cell

Background: G cell are a well characterized and widely used model used for the in vitro study of growth hormone (GH) secretion. Thyrotropin releasing hormone(TRH) binds to receptors belonging to the family of G protein-coupled receptors, and secrets both GH & prolactin. Phopholipase D (PLD) is and enzyme that hydrolyses phosphatidylcholine to yield phosphatidic acid and choline, and plays important roles in celluar proliferation and hormonal secretion. To elucidate the pathway of the action of TRH in G cell, we investigated the activities of PLC and PLD in G cell treated with TRH or phorbor 12-myristate 13-acetate (PMA). Methods: G cells were labeled with []myristate, followed by incubation of with 0.3% ethanol, prior to before the addition of the agonists. The total lipids were extracted from the harvested cells following treatment with the agonists. The PLD activity was assessed by mearsuring [] Phosphatidylethanol from the [] phospholipid using thin layer chromatography. Results: TRH (1 M) stimulated the PLC activity by 44-fold over that the control values. TRH (1 M), mastoparan (5 M), and PMA (500 M) for 30 minutes increased PLD activity by 1.9, 1.5 and 2.2 fold, respectively, in comparison to the controls. The PLD activities after 15, 30, 60, 120 and 240 min treatments of TRH (1 M) were 142%, 170%, 172%, 160% and 115%, respectively.