Sympathetic nervous system exclusion following experimental subarachnoid haemorrhage prevents vasospasm in rabbits

The objective of this study was to establish whether the exclusion of the effect of the sympathetic nervous system prevents vasospasm of cerebral arteries after experimental subarachnoid haemorrhage in rabbits.

The effect of sympathetic exclusion on vasospasm was studied in 29 New Zealand rabbits under conditions similar to human subarachnoid haemorrhage: 1. The activity of the sympathetic nervous system was excluded only after subarachnoid haemorrhage. 2. The effect of this exclusion was evaluated on the eighth day after subarachnoid haemorrhage. 3. The single haemorrhage model of experimental subarachnoid haemorrhage was chosen. Four groups of rabbits were investigated. The control group A comprised rabbits without subarachnoid haemorrhage; group B consisted of those with subarachnoid haemorrhage (1 ml autologous blood/kg BW suboccipitally into the cisterna magna); group C included those with subarachnoid haemorrhage and pharmacological sympathetic exclusion by the alpha blocker phenoxybenzamine, and group D was composed of those with subarachnoid haemorrhage and operative sympathetic exclusion by cervical gangliectomy. Changes in the basilar arteries of rabbits were evaluated by computer image analysis, using histologic specimens of vessel walls. A new measuring procedure was developed to assess the intensity of vasospasm; the method has a corrugation coefficient that expresses changes in intimal corrugation.

Comparison of control group A and group B in regard of vessel intima corrugation showed significantly less corrugated intima in group A (P = 0.0042). In comparison with group B, corrugation of the vessel intima in group C was less intense after sympathetic exclusion by phenoxybenzamine following subarachnoid haemorrhage (P = 0.00012). In comparison with group B, a reduced corrugation was also found in group D after sympathetic exclusion by upper cervical gangliectomy following subarachnoid haemorrhage (P = 0.0026).

The results of the study suggest that exclusion of sympathetic nervous system activity in rabbits prevents vasospasm in circumstances similar to subarachnoid haemorrhage in man. Thus, the sympathetic nervous system could play a critical role in the development of vasospasm in subarachnoid haemorrhage.