Beneficial effect of renin-angiotensin system for maintaining blood pressure control following subarachnoid haemorrhage

Abstract

Subarachnoid haemorrhage is a serious condition often accompanied by delayed cerebral ischaemia. Earlier reports have provided evidence suggesting a role for angiotensin II in the development of cerebral vasospasm following subarachnoid bleeding. We sought to examine the influence of angiotensin II blockade with losartan on blood pressure and survival in animals following experimental subarachnoid haemorrhage, induced in conscious rats by injecting homologous blood via a catheter placed along the surface of the brain. We combined measurements of plasma renin activity with blood pressure recording in order to examine renin-angiotensin system activation following experimental subarachnoid haemorrhage. Following subarachnoid injury an approximately three-fold increase in plasma renin activity occurred (3.4 +/- 1.0 vs. 10.1 +/- 1.8 ng angiotensin I produced/ml/h, p < 0.01). In animals treated with losartan (20 mg/kg) prior to the induction of subarachnoid haemorrhage blood pressure fell dramatically following the cerebral injury (124 +/- 5 vs. 94 +/- 7 mmHg, p < 0.001), whereas blood pressure remained unchanged in control animals. Survival was markedly reduced in those animals treated with losartan. Given the pronounced decrease in blood pressure and impaired survival following subarachnoid haemorrhage in animals treated with losartan, it would appear that the acute activation of the renin-angiotensin system following this insult is in fact a desirable, compensatory response.