The effect of estrogen mediated by NO on cardiovascular responses to cage-switch stress in ovariectomized rats

Abstract

We assessed the hypothesis that chronic estrogen replacement in ovariectomized rats suppresses cardiovascular responses to cage-switch stress by attenuating plasma norepinephrine (NE) release and increasing nitric oxide (NO) production in peripheral vascular bed. Adult ovariectomized rats were randomly assigned placebo-treated (P) or estrogen-treated (E) group and implanted with pellet containing either placebo or 17β-estradiol (1.5 mg/60-day release). After four weeks, to collect blood samples they were catheterized with cannulae into jugular veins. After recovery, rats were exposed to the cage-switch stress for 30 min. Each rat underwent the stress 24h after administration of plain tap water or NG-nitro- L-arginine methyl ester (L-NAME)-supplemented water (250μg/ml in water). Blood samples were collected at rest and at 30 min after the start of the stress. Mean arterial pressure and heart rate responses to cage-switch stress were significantly attenuated in the E group compared with the P group, but the difference disappeared after pretreatment of L-NAME. Stress-induced plasma NO elevation was suppressed after L-NAME in the E group. On the other hand, the surge of plasma NE during the stress was diminished in the E group, but not in the P group. [Jpn J Physiol 54 Suppl:S243 (2004)]