Hormonal responses to hemorrhage and their relationship to individual hemorrhagic shock susceptibility

The effect of differences in sympathoadrenomedullary and pituitary-adrenocortical responses of individual animals to 35% hemorrhage on severity of shock induction has been studied in unanesthetized unrestrained rats by measuring plasma concentrations of adrenaline (A), noradrenaline (NA), corticosterone (CS) and adrenocorticotropin (ACTH). The responses of A, CS and ACTH were related to the decrease of blood volume and mean arterial pressure (MAP), whereas plasma NA remained unchanged. Higher susceptibility to blood loss was characterized by more pronounced hemorrhage-induced increase in blood lactate concentration and plasma enzyme activities as well as lethal outcome of hemorrhagic shock. In animals with irreversible hemorrhagic shock, enhanced catecholamine secretion and reduced ACTH release was observed. Furthermore, a revealed direct correlation between A and blood lactate concentration and plasma enzyme activities (aspartate aminotransferase, isocitric dehydrogenase, creatine kinase, lipase and glutathione-S-transferase) may indicate its possible participation in the mechanism of shock induction. In contrast, an inverse relationship of plasma CS to the indicators of shock severity was demonstrated. In conclusion, non-optimal neuroendocrine regulation of cardiovascular adjustments to hemorrhage in shock-prone animals might cause an exaggerated compensatory activation of adrenomedullary catecholamine secretion, which in turn has been shown to exert deleterious vascular and metabolic effects. The mechanisms responsible for reduced ACTH secretion in shock-prone animals remain to be established.