Developmental course of hypertension and regional cerebral blood flow in stroke-prone spontaneously hypertensive rats.

Regional cerebral blood flow (rCBF) was repeatedly measured by the hydrogen clearance method in the frontal cortex of stroke-prone spontaneously hypertensive rats (SHRSP) at the age of 50 days and thereafter. When SHRSP rats developed severe hypertension (over 200 mg Hg at the age of 60 days) rCBF began to decrease abruptly in the frontal cortex--one of the three predilection sites of stroke in these rats. In contrast, such a reduction in rCBF was not noted in either stroke-resistant spontaneously hypertensive rats (SHRSR) which developed moderate hypertension (under 200 mg Hg), or in Wistar-Kyoto rats (WK) with normal blood pressure (under 15 mm Hg). A similar marked reduction of rCBF with severe hypertension (over 200 mm Hg) was also detected in apoplectic gene-free renal infarction hypertensive rats (RHR) experimentally produced from age-matched WK animals. Blood samples were obtained through an implanted femoral artery canula without disturbing the nonanesthetized SHRSP, SHRSR and WK rats. Arterial blood gas analysis (PaCO2, PaO2 and pH) showed no significant differences at the age of 5 months in any of these rats. Chemical cerbrovascular reactivity, that is, an increase in rCBF in response to CO2 inhalation, showed no significant difference among SHRSP rats from the age of 50 days to 5 months. However, it markedly decreased in SHRSP rats at the age of 9 months and thereafter (the average age of male SHRSP rats which develop stroke is 9 months). The present study showed stroke did not occur in antihypertensive agent-treated SHRSP rats. In these SHRSP rats rCBF did not decrease as long as blood pressure was well-controlled.