Mortality and histological findings of the brain during and after cerebral ischemia in male and female spontaneously hypertensive rats.

Mortality and pathological changes of the brain during and after cerebral ischemia induced by bilateral carotid artery occlusion (BCO) were studied in male and female spontaneously hypertensive rats (SHR). Systolic arterial blood pressure at rest was significantly higher in male SHR (228 +/- 13 mm Hg, mean +/- S.E.M.) than female (192 +/- 12) (P less than 0.05). The average survival time during permanent occlusion was 11 +/- 6 h (mean +/- S.D.) in male SHR and 17 +/- 7 in female (P less than 0.005), though the cumulative mortality during 24-h ischemia was not different between male (88%) and female SHR (84%). Severe ischemic changes of nerve cells in the brain, especially in the cortex and hippocampus, were observed in 50% of male SHR at 3-h ischemia, while only 15% was observed in female SHR even after 7-h ischemia. After the temporary ischemia followed by reperfusion for 24 h, the mortality was varied between male and female SHR; 0, 31 and 100% after 1-, 3- and 5-h ischemia, respectively, in male SHR and 0% after 1- to 3-h ischemia and 33% after 5- to 7-h ischemia, respectively, in female. Ischemic changes of the brain tissue, such as acidophilic cytoplasm, nuclear degeneration and intercellular edema, were more frequent and severe in male SHR than female after recirculation following 3- or 5-h ischemia. It is concluded that the mortality and post-ischemic viability seem to be determined by the duration of ischemia and also by the degree of the neuronal damage, and female SHR is more tolerated for ischemic insult in comparison to male SHR.