Impaired endothelium-dependent vasorelaxation in the basilar arteries of stroke-prone spontaneously hypertensive rats

During high sodium intake, despite similar blood pressure, spontaneously hypertensive rats (SHR) do not share the predisposition to cerebrovascular disease typical for stroke-prone SHR (SHRSP). We have recently provided evidence that in this condition, a reduced endothelium-dependent vasorelaxation is present in the aorta of SHRSP as compared to SHR. The potential relevance of this phenomenon to the susceptibility to stroke in SHRSP is still unclear. To further investigate this aspect, we evaluated the vascular reactivity of the basilar artery in 6 SHRSP and 9 SHR matched for age and sex and maintained for 4 weeks on a Japanese style diet with 1% saline to drink. After sacrifice, basilar arteries were mounted as ring preparation on a myograph. Vasoconstrictive responses were elicited by serotonin (10−7-10−5 M), while endothelium-independent and endothelium-dependent vasorelaxation were assayed by using nitroprusside (10−9-10−5 M) and Substance P (10−10-10−6 M). No differences were found in the vasoconstrictive response to Serotonin (F=0.338, n.s.) and the endothelium-independent vasorelaxation to nitroprusside (F=0.760, n.s.) On the contrary, the endothelium-dependent vasorelaxation to Substance P in SHRSP was significantly reduced as compared to SHR (F=2.614, p<0.05). In conclusion, our results extend the observation of a genetically determined impairment of the endothelium-dependent vasorelaxation in SHRSP to the small resistance vessels of the cerebral circulation and suggest a role for this phenomenon in the susceptibility to stroke in SHRSP.