Okamoto et al. found that a few rats developed higher blood pressure (over 230 mmHg) at 10 weeks old. They selected SHRSP rats that show severe hypertension from young age and M-SHRSP (malignant or precocious SHRSP) rat was established in 1985.
Life expectancy of this strain is a half of SHRSP rat (male: average 90 days, female: average 120 days). This strain develop stroke symptoms earlier than SHRSP rat and the incidence of hypertensive cerebrovascular lesion is over 95%. Small or petechial hemorrhage is frequently observed in the base of the brain.