Estrogen Receptors and the Activity of Nitric Oxide Synthase in the Artery of Female Rats Receiving Hormone Replacement Therapy

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Abstract
Objective: To observe the expression of estrogen receptor and the activity of NOS in the arteries of female rats receiving estrogen replacement therapy. Methods: Seventy-two female rats were randomly divided into four groups: group A: sham-ovariectomy; group B: ovariectomy; group C: ovariectomy with estrogen replacement therapy (benzoate estradiol, 5 μg i.m. once in 2 days); group D: ovariectomy with estrogen and progesterone replacement therapy (benzoate estradiol, 5 μg i.m. once in 2 days and progesterone, 1 mg i.m. once in 2 days). The rats were killed after 2 months. The receptor-binding assay was adopted to measure the estrogen receptors in the arteries of the rats, and the activity of NOS in the arteries was assessed by the hemoglobin reductase method. Results: The ER number and NOS activity in the arteries of the ovariectomized group are less than those in sham-ovariectomy group (p < 0.05). The ER number and NOS activity in the arteries of groups C and D are larger and higher than those in the ovariectomized group (p < 0.05). No significant differences in the ER number and NOS activity were observed between groups C and D. Conclusion: The ER number and NOS activity in the rat artery significantly decrease after ovariectomy, while hormone replacement therapy can significantly increase the artery NOS activity and retain the ER number in the artery of the ovariectomized rats to normal level. The result may contribute to explaining the beneficial effect of estrogen in the prevention of coronary artery diseases in postmenopausal women.

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