Change of Vascular Reactivity after Severe Contusive Spinal Cord Injury---Mechanistic Insight into Autonomic Dysreflexia

Background: Acute severe spinal cord injury (SCI) may result in not only quadriplegia or high paraplegia, but also a large fall in mean arterial pressure and heart rate, which is called neurogenic shock. Another life threatening complication during the chronic stage of SCI is autonomic dysreflexia, which is characterized by vasodilatation above the lesion and vasoconstriction below the lesion elicited by innocuous stimuli. It is proposed that the alteration of sympathetic nervous system is the major etiology. However, this idea cannot explain why the neurogenic shock resolved gradually at post-injury 7-10 days, which there was no evidence of any recovery and regeneration of the sympathetic nervous system. That means the exact change of vascular reactivity after SCI is still unknown. Objective: The aim of this study is to investigate the vascular reactivity in both acute and chronic stages of SCI. Materials and Methods: Animals are employed contusive spinal cord injury with NYU impactor under 25 mm-height level. At different recovery time (post-contusive 1 hr, 1, 3, 7, 14, 28 day), we record the blood flow and vascular reactivity of bilateral femoral and carotid arteries by sonogram and organ chamber studies. Then the vessels are harvested for protein analysis and immunohistochemistry for alpha-1 adrenergic receptor. Besides, before the rats are sacrificed, the blood pressures before and after the injection of epinephrine are recorded. Preliminary Data: The blood flow in the injured group is significantly reduced in femoral artery, but increased is the carotid artery in the first week, which exactly reflects the clinical condition. Besides, the alpha-1 adrenergic receptor is more increased in the injured group than the control group. Hypothesis: We propose the recovery of the neurogenic shock and the happen of delay autonomic dysreflexia are related to the alpha-1 adrenergic receptor, which is not only increase in numbers, but also in the sensitivity.