Adrenal response to repeated hemorrhage: Implications for studies of trauma

Endocrine responses to trauma are often inferred from responses seen after a single injury or elective surgery. However, major trauma frequently is followed by emergent surgery, necessitating evaluation of responses to repeated stimuli. We used sequential hemorrhage to study such responses. Splenectomized dogs anesthetized with pentobarbital (25 mg/kg) were hemorrhaged 7.5 ml/kg, 2 days following adrenal vein cannulation. Secretion rates of cortisol and catecholamines were determined in timed adrenal samples by HPLC. The bled volume was reinfused after 1 hour; the procedure was repeated 24 hours later. A significant response in adrenal secretion of cortisol was seen following hemorrhage each day (P<0.001), but the response on day 2 was 40% greater (P<0.05). Secretion rates of epinephrine and of norepinephrine did not change after hemorrhage on day 1 (p>0.20). However, each hormone showed a dramatic response on day 2 increasing to 14 x control levels (P<0.005). There were no differences in any cardiovascular variable during control period or after hemorrhage on the 2 days. The results demonstrate dramatic potentiation of the response to a second insult that persists for at least 24 hours after the first, and suggest that the endocrine response to traumatic injury with emergent surgery cannot be evaluated by studying responses either to isolated insults or to elective surgery.