EPISODIC HYPERTENSION DUE TO AUTONOMIC DYSREFLEXIA IN ACUTE AND CHRONIC SPINAL CORD-INJURED RATS

Spinal cord injury results in abnormal sympathetic control of the card iovascular system, consisting of exaggerated reflexes with resulting h ypertension and bradycardia that has been termed autonomic dysreflexia . We studied changes in arterial pressure and heart rate caused by col on or urinary bladder distension in unanesthetized acute (7 day) and c hronic (30 day) spinal cord-injured rats to evaluate the time course o f these responses in an animal model of spinal cord injury. In conscio us control rats colon and bladder distension caused brief (2-10 s) pre sser responses of 10 mmHg associated with tachycardia and escape react ions. Colon distension in spinal cord-injured rats increased arterial pressure by 41 +/- 2, 22 +/- 3, and 49 +/- 5 mmHg at 24 h and 7 and 30 days after cord transection, respectively. These responses lasted 30 s-5 min and were accompanied by bradycardia. Distension of the urinary bladder caused similar responses in spinal rats after 24 h and 30 day s of cord transection. We propose that the initial responses may be re lated to loss of descending inhibition of spinal reflexes but that pla stic changes in the spinal cord is one of the mechanisms for the auton omic dysreflexia occurring 1 mo after injury.