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Objective: Recognizing the important role of eicosanoids in regulatory functions of physiological systems of organisms. Methods: The progression of severe hemorrhagic shock (SHS) in changes of prostaglandins (PGs) I 2 , F 2 a, and thromboxane (TX) A 2 content was studied in the vena cava caudalis of 10 dogs. The SHS was caused by momentary jet hemorrhage from a femoral artery (blood loss volume was 28.2 ±2.7 ml/kg). The mean duration of the animals' lives after the hemorrhage was 298.6+65.9 minutes (min). Results: Instantly, after the hemorrhage, the contents of PG-I2, PG-F 2 , and TX-A 2 increased by 30% (p >.O5) ,2.6% (p >.5), and 96% (p>.001), respectively. After 165.7 ±32.0 min of the hemorrhage, the concentrations of PG-I 2 , PG-F 2 and TX-A 2 exceeded the initial levels by 87.3%, 73.5% and 129.6% (p <.001) respectively. However, after 278.5 ±50.8 min of the hemorrhage, the content of PGI 2 exceeded the initial levels only by 87.4% (p <.001), and then the concentrations of PG-F 2 and TX-A 2 were higher by 95.2% and 153.7% (p <.001) respectively. Conclusions: TX-A 2 and PG-F 2 increases at the first stages of shock progression is one of the mechanisms of protective reaction directed to stop bleeding. However, the growing content of these eicosanoids not only opposed the cytoprotective effects of PG-I 2 action, but promotes severe disorders of coronary circulation. Besides, TX-A 2 and PG-F 2 potentiate the effects of platelet activating factor and leukotrienes, and initiate the processes of lipid peroxidation.

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