The Effect of Therapeutic Hypothermia on Plasma Levels of Thyroid Hormones During Hemorrhagic Shock in Adult Male Wistar Rats

Background and Aim: Hemorrhagic shock (HS) is one of the most important causes of death. In this study, we investigated the benefits of therapeutic hypothermia (32°C) during HS on blood pressure (BP) and the role of thyroid hormones during HS. Materials and Methods: Twenty-four male Wistar rats were divided into two normothermic hemorrhagic (NH) and hypothermic hemorrhagic (HH) groups (32°C during shock); the animals were then anesthetized, a microcatheter was inserted into the femoral artery, and one into the femoral vein. The arterial samples were centrifuged, and plasma was isolated to measure thyroid hormones later. The microcatheter was fixed to a physiograph to record BP. Animals were exposed to HS for 90 minutes by withdrawing blood from the femoral vein and BP was assessed during HS. Results: The BP of HH animals was significantly higher in most times of HS and at 40 minutes (56.8±4.2 mmHg) in comparison to NH rats (45.4±3.8 mmHg) (P<0.05). In addition, the amount of BP in HH animals at the end of the shock period at 90 minutes (63.8±5.5 mmHg) was significantly (P<0.001) higher in comparison with the NH groups (39±3.2 mmHg). Levels of thyroid hormones T4 and T3 at the end of shock were lower in the HH group compared to the NH group (P<0.001). Conclusion: Therapeutic hypothermia indirectly reduces the level of thyroid hormones and directly reduces the metabolism of non-vital tissues, preserves blood in the central arteries, and increases BP.