Susceptibility to ischemic insult in hypertensive rats: correlation between degree of ischemia and hypertension.

The Wistar rat, with a blood pressure range of 120-160 mmHg, and two strains of spontaneously hypertensive rats (SHR), stroke-prone (SHRSP, range 210-270 mmHg) and stroke-resistant (SHRSR, range 160-240 mmHg), were used to determine the degree of damage after ischemic insult induced by bilateral carotid artery ligation (BLCL). The survival rate and McGraw Stroke Index correlated well with the degree of hypertension. After BLCL, impairment of cerebral blood flow is abrupt and residual flow is near zero in rats with initial blood pressures greater than 200 mmHg. A markedly deteriorated aerobic metabolism, as measured by the concentrations of ATP, c-AMP and lactate, is seen to precipitate in rats with initial blood pressures greater than 180 mmHg and severe edema occurs if the pressure is more than 160 mmHg. The degree of hypertension that produces high vulnerability to stroke and severe damage to the brain after ischemic insult is indicated as beginning at about 180 mmHg.