Research for SHR by Young Scientists—Mini‐review

Abstract

Nitric Oxide in Cerebral Blood Flow and Metabolism. Takanori Noguchi,1 Katsumi Ikeda,2 Yasuto Sasaki,3 Junichiro Yamamoto,3 Junji Seki,4 Kazuo Yamagata,5 Yasuo Nara,5 Shigeyoshi Itohara,1 and Yukio Yamori.6 1Laboratory for Behavioral Genetics, Brain Science Institute, The Institute of Physical and Chemical Research (RIKEN), Saitama, Japan. 2Department of Food Science and Nutrition, School of Human and Environmental Sciences, Mukogawa Women's University, Nishinomiya, Japan. 3Faculty of Nutrition, Kobe Gakuin University, Kobe, Japan. 4Department of Biomedical Engineering, National Cardiovascular Center Research Institute, Osaka, Japan. 5Graduate School of Integrated Science and Art, University of East Asia, Yamaguchi, Japan. 6WHO Collaborating Center Research for Cardiovascular Diseases, Kyoto, Japan.Cerebral ischemia and reperfusion induced apoptosis in hippocampal neurons in stroke‐prone spontaneously hypertensive rats (SHRSP) but not in Wistar‐Kyoto rats (WKY). The purpose of our study is to examine the dynamic changes in the levels of cerebral pial arterioles hemodynamics, hippocampal NO production/release and cerebral blood flow (CBF) and mRNA expressions following ischemia and reperfusion in SHRSP.Mean red blood cell velocities were decreased by ischemia, moreover, the reduction of mean red cell velocities in male rats were significantly larger than female rats in all strains. Arterioles in SHRSP appeared to be less numerous and markedly smaller in diameter than those of age matched WKY and SHR. The concentrations of plasma nitrite/nitrate were decreased significantly (p < 0.05) in male rats compared with female rats.The production of NO in cerebral ischemia and reperfusion in the rat hippocampus was investigated using an in vivo microdialysis system and automatically injected into the on‐line HPLC‐NO detector system in male SHRSP and WKY. Regional CBF was measured as follows: a probe with a diameter of 0.5 mm was attached to the surface of the parietal cortex and cortical blood flow in the parietal lobe was measured continuously using laser Doppler flowmetry (ALF 21; Advance Co. Ltd, Tokyo, Japan). Moreover, monitored CBF was measured with a laser Doppler perfusion imaging system (LDPI; Lisca Inc, Sweden). After anesthesia, consecutive measurements were obtained after scanning the same region of cerebral cortex with the LDPI. The basal level of NO production in the hippocampus of SHRSP (15.8±1.1 pmol/20 µL dialysate) was significantly higher than that in WKY (19.3±0.6 pmol/20 µL dialysate; p < 0.05). NO production during ischemia was significantly decreased in both strains below that of sham operation (p < 0.05), and that the decrease in NO production in SHRSP was significantly greater than that of WKY (p < 0.05). After reperfusion, NO production was increased to the basal level and maintained at slightly higher basal level for 2 hr. The production of NO in SHRSP was lower than WKY until 30 min after reperfusion. The changes in CBF measured by LDF and LDPI were similar to the changes in NO production in cerebral ischemia and 30 min after reperfusion. There were no observed increases in CBF in SHRSP after reperfusion, however, the maximum production of hippocampal NO was significantly greater than in WKY and sham operation group. The reductions in hippocampal NO production and CBF in SHRSP were significantly larger than those in WKY, suggesting that NO production was dependent on CBF in cerebral ischemia and reperfusion. However, CBF independent NO production in SHRSP was observed at 50–100 min after reperfusion. Therefore, we suggest that these alterations in increasing NO production might be related to apoptosis in neurons after cerebral ischemia and reperfusion.To examine the mechanism of apoptosis by ischemia and reperfusion in SHRSP, neuronal and inducible nitric oxide synthase (eNOS and iNOS), Bcl‐2, Bcl‐xs, cytochrome oxidase (Cyt‐O), thioredoxin‐1 (TRX‐1) and thioredoxin‐2 (TRX‐2) mRNA were assessed in the hippocampus of SHRSP and WKY. There were no significant differences in nNOS, iNOS, Bcl‐2, Bcl‐xs and Cyt‐O mRNA expression between SHRSP and WKY in sham operation, however, neuronal and inducible NOS, Bcl‐xs and Cyt‐O mRNA expression in SHRSP were significantly increased after cerebral ischemia and reperfusion (p < 0.05). Neuronal and inducible NOS mRNA expressions were increased in SHRSP after ischemia and reperfusion. These alterations of NOS mRNA expression might be related to the severer apoptosis in hippocampal neurons reported previously in SHRSP.