Effects of aging and hypertension on cerebral ischemic susceptibility: Evidenced by MR diffusion-perfusion study in rat

Aging is the most significant non-modifiable risk factor and hypertension is the most significant modifiable risk factor for ischemic stroke. We used magnetic resonance imaging (MRI) to investigate the evidence of ischemic susceptibility after aging and hypertension. Four groups of rat were studied: young normotensive Wistar-Kyoto (WKY) rat, aged normotensive WKY rat, young spontaneously hypertensive rat (SHR) and aged SHR. Brain images were acquired at a 3.0T Tim-Trio MRI system. For diffusion-weighted images, apparent diffusion coefficient (ADC) was measured. Relative cerebral blood flow (CBF) was also calculated. Cerebral ischemic susceptibility was examined by using ischemic model of bilateral common carotid artery occlusion. In the MRI study of non-ischemic rat, aged SHR had significantly higher ADC (P< 0.01) and significantly lower CBF (P< 0.01) in the parietal cortex, but aged WKY rat had only significantly lower CBF (P< 0.01) when compared with young WKY rat. The ADC/CBF ratio in the parietal cortex was significantly higher in aged SHR when compared with young WKY rat, young SHR and aged WKY rat (P< 0.01, P< 0.05, P< 0.05, respectively) suggesting a significant diffusion-perfusion disparity in aged SHR. After bilateral common carotid artery occlusion, there was significantly larger damage in the parietal cortex of aged SHR when compared with young WKY rat, young SHR and aged WKY rat (all P< 0.05), but not in the hippocampus and thalamus (P> 0.05). Our study demonstrated a significantly increased ADC value and reduced CBF in the ischemia-vulnerable cortical area. This cerebral diffusion-perfusion disparity is seen mainly in aged rat and can be more evident if associated with hypertension indicating an increased susceptibility of brain tissue to ischemic injury.