Substrain differences, gender, and age of spontaneously hypertensive rats critically determine infarct size produced by distal middle cerebral artery occlusion.

1. The present work discussed the effects of substrain or genetic differences, gender, and age of the rat on infarct size produced by distal middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats (SHR). 2. In SHR/Kyushu, infarct volume was significantly larger than that of SHR/Izm, while blood pressure levels were essentially the same between the two substrains. Although SHR-SP/Izm had a higher blood pressure than SHR/Kyushu, infarct volumes were the same between SHR/Kyushu and SHR-SP/Izm. These results suggest the presence of blood pressure-independent factors which affect the infarct size after MCAO. 3. Estrogen accounted the large part of greater tolerability against focal brain ischemic injury in female compared with male SHR. 4. We found age-related vulnerability to focal cerebral ischemia in female SHR. This age-related vulnerability in aged female SHR was unrelated to the blood levels of sex hormones such as estrogens and progesterone. 5. Finally, we emphasized the importance of reproducible and least invasive focal ischemia models in stroke research.