The role of the sympathetic nervous system in pressor responses induced by spinal injury

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Abstract
Spinal cord injury consistently evokes a transient 3-4 min rise in systemic pressure, followed by prolonged hypotension. Because the role of sympathetic nervous system in these blood pressure changes is not clear, the pressure responses were studied using systematic ablation of the peripheral sympathetic nervous system. Cats [24] were subjected to bilateral thoracic sympathectomy, adrenalectomy, splanchnicectomy, combinations of the preceding, sham operation or no treatment. Either 3 or 24 h after the ablations, the blood pressure responses were evoked by 400 g-cm contusions of the thoracic cord. Although neither thoracic sympathectomy nor adrenalectomy alone abolished the hypertensive phase, the combination of the 2 procedures did. Both the thoracic sympathetic ganglia and the adrenal glands may participate in the pressor response. Thoracic sympathectomy affected primarily the early part, whereas adrenalectomy diminished the later part of the hypertensive response. This correlates with the function of the former being neurally and the latter being humorally mediated. None of the sympathetic lesions consistently affected the hypotensive phase. Spinal contusion injury produces widespread sympathetic activation, mediating the hypertensive changes.