Thyroid hormonal axis regulates protein C anticoagulation pathway in rats

Effects of the hormones of the hypothalamic-pituitary-thyroid axis on some basic parameters of the activity of protein C anticoagulation pathway in rats are studied. Thyrotropin-releasing hormone (0.06 mg/kg body mass), thyrotropin (1 IU/kg), triiodothyronine (T3) (0.08 mg/kg), thyroxine (T4) (0.08 mg/kg), administered subcutaneously for three consecutive days on four different groups of rats increased significantly activated protein C, free protein S and protein S activity, and reduced the soluble endothelial protein C receptor. Protein C antigen and total protein S were significantly elevated only by thyrotropin-releasing hormone and thyroid-stimulating hormone, but they were not affected by T3 and T4 treatment. The data indicate the hypothalamic-pituitary-thyroid axis is involved in the regulation of the protein C anticoagulation pathway in rats by activation of this system, suggesting a tendency of hypocoagulability.