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1 Department of Environmental Health, Faculty of Life Science and Human Technology, Nara Women's University, Nara, Nara, Japan
2 Department of Forensic Medicine, Graduate School of Medicine, University of Tokyo, Tokyo, Tokyo, Japan
3 Department of Exercise and Health Science, Faculty of Education, Yamaguchi University, Yamaguchi, Yamaguchi, Japan
* To whom correspondence should be addressed. E-mail: kyoshida{at}m.u-tokyo.ac.jp.
assessed a hypothesis that chronic estrogen replacement in ovariectomized rats has the beneficial effect of suppressing stress-induced cardiovascular responses through
endothelial nitric oxide synthase (eNOS). We employed a radiotelemetry system in order to measure blood pressure and heart rate (HR). Female Wistar rats aged 11 weeks were ovariectomized and implanted with radiotelemetry devices. After 4 weeks, the rats were assigned either to a placebo-treated (P) group (n=6) or a group treated with 17
-estradiol (E) (n=8), subcutaneously implanted with
either placebo- or 17-estradiol (1.5 mg / 60-day release) pellets under anesthesia. These rats underwent either of the two types of stress after 4 weeks of estrogen or placebo treatment. Cage-switch stress and restraint stress rapidly and continuously elevated the mean arterial pressure (MAP) and heart rate both in the P and E groups. However the MAP and HR responses to cage-switch stress, and the MAP but not HR response to restraint stress were attenuated significantly in the E group compared with the P group. A nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester given in drinking water reduced the difference in the pressor response to cage-switch between the E and P groups. Additionally, Western blotting showed that eNOS expression in the mesentery was increased in the E group compared with the P group. Thus, for the first time we showed that mesenteric eNOS over-expression could explain at least partly why chronic estrogen treatment suppressed the enhanced cardiovascular responses to psychological stress in the ovariectomized rat.
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