Blood pressure responses associated with hemorrhagic shock in anesthetized rats

Blood pressure responses to noradrenaline were studied in anesthetised rats subjected to hypovolemia by a constant pressure--open reservoir technique. Hypovolemia resulted in a decrease of the noradrenaline response, which correlated well to the length of the hypovolemic period and to the arterial perfusion pressure when lower than 60 mmHg. Early after retransfusion of the shed blood the pressure response to noradrenaline continued to decrease and began to recover only after additional 30-60 min. The decline in blood pressure response to noradrenaline during hemorrhagic shock was not significantly altered by adrenalectomy, infusion of various metabolic substrates, such as fat emulsion, Na-pyruvate or ATP-MgCl2, or by protection against respiratory and metabolic acidosis. The results imply that high levels of circulating catecholamines, substrate exhaustion and acidosis may be regarded as secondary factors rather than primary causes of decreased blood pressure response and development of irreversible hemorrhagic shock, and they stress the importance of adequate tissue perfusion in the protection against these disorders.