Pressor response resulting from experimental contusion injury to the spinal cord

Experimental contusion paraplegic injury to the posterior spinal cord in cats results in a sudden increase of systemic blood pressure to between 200 and 250 mm Hg, and an increase in pulse pressure and a slowing of pulse rate. This initial hypertensive phase lasts approximately 3 to 4 minutes, and then is followed by a hypotensive phase. This pressor response is mediated by the alpha adrenergic receptor sites of the peripheral sympathetic nervous system and can be blocked by intravenous phenoxybenzamine, an alpha adrenergic blocking agent. The hypotensive phase is the result of an overall reduction in alpha adrenergic vascular tone and can be reversed by the infusion of metaraminol or intravenous fluids. The alterations in blood pressure that follow impact injury are most likely related to alterations of peripheral arteriolar resistance and venous return of blood to the heart.