Angiotensin receptor antagonists delay nitric oxide-deficient stroke in stroke-prone rats

We investigated whether chronic deficiency of nitric oxide (NO) in stroke-prone spontaneously hypertensive rats (SHRSP) precipitates stroke and whether exogenous nitrates and other pharmacological agents can prevent stroke. Groups of five-week-old male SHRSP rats chronically received saline, L-nitro-arginine methyl ester (L-NAME) in saline, L-NAME along with pharmacological agents (L-arginine, isosorbide dinitrate, enalapril maleate and L-158,809; angiotensin receptor antagonist; 5,7-dimethyl-2-ethyl-3(-)[[2'-(1H-tetrazol-5-yl)biphenyl-4-yl]meth yl]-imidazo[4,5-b]pyridine) in saline to drink. The development of visible neurological deficits following various treatments was considered as an occurrence of stroke. Within hours following onset of stroke, the rats were anesthetized, catheterized and attached to a Cardiomax blood pressure recorder. SHRSP treated with L-NAME (10+/-2 mg/day) developed stroke in 11+/-2 days while no neurological deficit was seen in animals receiving saline till the end of the study period (35 days). Blockade of the renin-angiotensin system with enalapril or L-158,809 significantly delayed the onset of stroke (19+/-2 and 20+/-2 days, respectively), but caused only slight reductions in mean arterial blood pressure. These results suggest that chronic inhibition of NO synthase in SHRSP is associated with the development of stroke and such stroke appears to be renin-angiotensin system-dependent.