The role of sympathetic nervous system in the development of neurogenic pulmonary edema in spinal cord-injured rats

Abstract

The pronounced activation of sympathetic nervous system is a necessary prerequisite for the development of neurogenic pulmonary edema (NPE) in rats with balloon compression of spinal cord. In this study we examined whether this is a consequence of rapid activation of spinal pathways leading to sympathetic venoconstriction, blood pressure rise, and reflex bradycardia. We found that NPE development can be prevented by epidural upper thoracic anesthesia or by transection of the upper spinal cord. This indicates an important role of spinal pathways activation. NPE development can also be prevented by moderate blood loss, supporting the role of blood redistribution to pulmonary circulation. In rats developing NPE the catecholamine surge following spinal cord compression involved not only a dramatic increase of circulating norepinephrine but also of epinephrine levels. The pretreatment of rats with α-1 adrenoceptor blocker prazosin, α-2 adrenoceptor blocker yohimbine, or calcium channel blocker nifedipine prevented NPE development, whereas the effect of β-adrenoceptor blockade with propranolol was less convincing. In conclusion, considerable activation of thoracic spinal pathways, followed by marked catecholamine secretion, play a major role in the development of NPE in spinal cord-injured rats. Enhanced α-adrenergic nifedipine-sensitive vasoconstriction is responsible for observed blood pressure changes, subsequent baroreflex bradycardia, and blood volume redistribution, which represent major pathogenetic mechanisms of NPE development.