Effects of previous repeated bleedings on the response of plasma epinephrine and norepinephrine levels of conscious dogs in hemorrhagic shock.

A study was conducted on the effects of repeated hemorrhages and reinfusions on the sympathoadrenal response to subsequent hemorrhagic shock. Conscious dogs with carotid and jugular venous cannulae were subjected to hypovolemia of progressively increasing duration for three days. Plasma catecholamines were measured radioenzymatically. Prehemorrhaged animals subjected to hemorrhage shock on Day 4 demonstrated less increase of catecholamines and earlier return toward normal levels. Nonsurviving animals showed higher catecholamine levels than survivors. After three days of conditioning bleedings, prehemorrhaged animals had lower resting heart rates, but larger increases during shock than control animals. Bleeding volumes and hematocrits were also lower in the prehemorrhaged group. The study demonstrates that, by repeated exposure to hypovolemia, the sympathoadrenal response can be decreased in hemorrhagic shock.