The role of endogenous thyrotropin releasing hormone (TRH) in maintenance of the blood pressure in awake and unrestrained rats with hemorrhagic hypotension

A pressor effect of TRH in hemorrhagic hypotensive rats was studied. First, TRH (1mg/kg, 2mg/kg, 5mg/kg), its analogue MK771 (0.2mg/kg) and anti-TRH antibody were given intravenously. The change in the mean arterial blood pressure (MAP) was observed. After administration of TRH, MAP rose dose-dependently, and it also rose after administration of MK771. The anti-TRH antibody significantly suppressed the compensatory and reflective increase of MAP following the hemorrhage. This suggested that the endogenous TRH plays an important role in the maintenance of MAP in the hemorrhagic hypotensive state. Next, the same hypotention models were made using adreno-demedullated rats. TRH or anti-TRH antibody was given intravenously. TRH significantly increased MAP, while the anti-TRH antibody suppressed MAP. This indicates that the pressor effect of TRH is not mediated by the adrenal medulla. The endogenous TRH may play its maintenance role of blood pressure via medulla oblongata.

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