Acute and chronic alterations in blood pressure variability following experimental subarachnoid haemorrhage

This study examined the role of the renin-angiotensin and vasopressin syste ms on systolic blood pressure (SBP) variability following subarachnoid haem orrhage (SAH) in conscious rats. Animals received no treatment, the angiote nsin II AT1 receptor antagonist, losartan, or the vascular vasopressin rece ptor antagonist, AVPX. SAH resulted in a transient sympathetic activation a s estimated from the increase in the mid-frequency oscillations of SBP (3.2 +/- 0.8 mm Hg-2, 3 hours after the injury vs. 1.3 +/- 0.3 mm Hg-2 in contr ol conditions, p < 0.01). On the second and fourth day following SAH, a mar ked elevation in the low-frequency component of SBP was observed (7.1 +/- 1 .0 mm Hg-2 on day 2 vs. 2.6 +/- 0.3 mm Hg-2 in control conditions, p < 0.00 1 and 6.3 +/- 1.1 mm Hg-2 on day 4 vs. 2.6 +/- 0.3 mm Hg-2 in control condi tions, p < 0.01). Pre-treatment with losartan prevented the acute rise in t he mid-frequency oscillations in SBP and partially reduced the low-frequenc y component observed at 2 and 4 days. Administration of AVPX on the second and fourth day following SAH normalised the elevated low-frequency oscillat ions in SBP. This study indicates that the modifications in SBP variability observed in the early and delayed stage after subarachnoid haemorrhage inv olve angiotensin II. Vasopressin seems to be implicated in the delayed deve lopment of low-frequency fluctuations of SBP. (C) 2001 Elsevier Science B.V . All rights reserved.