Potentiation of hemorrhage-evoked catecholamine release by prior blood loss in cats

The effect of prior blood loss on the plasma catecholamine response to acute hemorrhage (H) was assessed in α-chloralose-urethane anesthetized cats. Animals sustained an initial H period of 0 (samples only), 10, or 20% H total blood volume. Ninety minutes after reinfusion of the shed blood, all animals sustained a rapid 20% H. The catecholamine and arterial pressure responses to this second 20% H were assessed every 2 min for 20-min duration. Plasma norepinephrine increased modestly in the 0/20% group (+0.63 ± 0.13 ng/ml) and 10/20% group (+0.66 ± 0.07 ng/ml), whereas the 20/20% group showed a much larger (P < 0.01) mean increase of 3.58 ± 1.16 ng/ml. Plasma epinephrine did not increase after 0/20% (+0.05 ± 0.02 ng/ml), increased slightly after 10/20% H (+0.10 ± 0.05 ng/ml), and demonstrated a large significant increase after 20/20% H (+0.48 ± 0.18 ng/ml). The differential effect of 20% H on catecholamine release, depending on the magnitude of prior blood loss, was not the result of altered mean arterial or pulse pressure responses to H. Correlation analyses revealed that the mean increases in epinephrine and norepinephrine during the post-H sampling period were well correlated in each animal (r = 0.864, P < 0.001). The data indicate that the priming effect of prior blood loss on H evoked catecholamine release: 1) requires an initial loss of 20% of total blood volume; 2) occurs rapidly, as it is seen by 90 min after the initial H period; and 3) affects epinephrine and norepinephrine similarly. We conclude that the immediate past secretory history of the sympathoadrenal system affects its responsiveness to subsequent blood loss.