Subarachnoid haemorrhage-induced sympathoexcitation in rats is reversed bybosentan or sodium nitroprusside

1. The roles played by nitric oxide (NO) and endothelin (ET) in the genesis of sympathetic nervous activation following experimental subarachnoid haem orrhage was investigated using spectral analysis of blood pressure rhythms. 2, Subarachnoid haemorrhage was induced in conscious rats by injecting 0.3 mL homologous blood via a catheter placed along the surface of the brain an d directed towards the circle of Willis, Three hours after the insult and a fter sympathetic activation was evident, animals received either an acute i njection of the ET antagonist bosentan (5 mg/kg, i.v.; n = 7), an infusion of the NO donor sodium nitroprusside (SNP; 18 mug/h; n = 7) or no treatment (II = 7), 3. Three hours following the induction of subarachnoid haemorrhage, the mid -frequency components of systolic blood pressure were markedly elevated, in dicating a pronounced sympathoexcitation, However, blood pressure and heart rate levels remained unchanged at this time. In the absence of treatment, the mid-frequency components of blood pressure remained elevated for a subs equent 2 h, Treatment with a nonhypotensive dose of SNP reversed the sympat hoexcitation within 1 h, Treatment with bosentan was also effective in redu cing the mid-frequency oscillations in blood pressure associated with subar achnoid haemorrhage. 4. Our results indicate that subarachnoid haemorrhage is associated with an acute activation of the sympathetic nervous system. The degree of sympatho excitation can be reversed by the use of either bosentan or SNP.