Effect of rate of hemorrhage on sympathoadrenal catecholamine release in cats

The effect of rate of blood loss on catecholamine release and cardiovascular compensation to hemorrhage (H) was assessed in α-chloralose-urethane anesthetized cats. Arterial blood was withdrawn at a rapid rate (10% measured blood vol/min) or at a slow rate (2%/min), and responses were compared across three volumes of hemorrhage (10, 20, or 30% of total blood vol). Plasma epinephrine did not increase after 10% H, but increased modestly after rapid (199 ± 25 pg/ml) or slow 20% H (359 ± 92 pg/ml). In contrast, rapid 30% H evoked a significantly (P < 0.01) greater increase in epinephrine than slow 30% H (1,827 ± 274 vs. 630 ± 165 pg/ml). The rate of hemorrhage had no differential effect on hemorrhage-evoked plasma norepinephrine, but a graded increase was seen with increasing volume of hemorrhage. Similarly, hemorrhage-evoked plasma glucose was proportional to the volume of hemorrhage and was not affected by rate of hemorrhage. Volume of hemorrhage was a good indicator of norepinephrine release after rapid or slow rate of hemorrhage, whereas epinephrine release was well correlated with the mean changes in blood pressure during the posthemorrhage sampling period after rapid or slow rate of hemorrhage. The data indicate that hemorrhage-evoked release of epinephrine depends on the rate of blood loss, but only after large (30%) volumes of hemorrhage. Norepinephrine released into the peripheral circulation demonstrates no dependency on rate of hemorrhage, but is well correlated with volume of hemorrhage. It is concluded that reflex activation of the adrenal medulla of the cat after hemorrhage includes neural or humoral control elements that are sensitive to rate as well as to volume of blood loss.